Academic literature on the topic 'Slow component amplitude'

Amplitude and habituation of event-related potentials are abnormal in migraine. We investigated 43 migraine and 41 healthy families to evaluate the influences of age, sex and familial contribution on the variance of amplitude and habituation of the contingent negative variation (CNV). Analysis of individual differences in relation to the CNV habituation was performed. The study demonstrated that habituation of the early CNV component characterizes migraine considerably better than the CNV amplitudes. Habituation, however, is strongly influenced by age. Migraine adults and children generally showed reduced habituation. Surprisingly, more than 30% of the healthy adults demonstrated a marked loss of habituation. The reduced CNV habituation represented a high sensitivity but low specificity to migraine, especially in children. CNV amplitude and habituation parameters revealed a considerable familial contribution associated with migraine. No familial influence on either morphology or habituation of the CNV in healthy families or between healthy members of migraine families was observed. The low specificity and familial transmission of CNV parameters in members of migraine families suggest that increased amplitudes and reduced habituation of CNV do not constitute a primary risk factor for migraine, but rather represent a predisposition. Genetic components probably affect variation of the CNV amplitude and habituation.

AbstractWe study geostrophic adjustment in rotating barotropic fluid when the angular speed of rotation $\boldsymbol{\Omega}$ does not coincide in direction with the acceleration due to gravity; the traditional and hydrostatic approximations are not used. Linear adjustment results in a tendency of any localized initial state towards a geostrophically balanced steady columnar motion with columns parallel to $\boldsymbol{\Omega}$. Nonlinear adjustment is examined for small Rossby numbers Ro and aspect ratio $H/L$ ($H$ and $L$ are the layer depth and the horizontal scale of motion), using multiple-time-scale perturbation theory. It is shown that an arbitrary perturbation is split in a unique way into slow and fast components evolving with characteristic time scales $(\mathit{Ro}f)^{-1}$ and $f^{-1}$, respectively, where $f $ is the Coriolis parameter. The slow component does not depend on depth and is close to geostrophic balance. On times $O(1/f\, \mathit{Ro})$ the slow component is not influenced by the fast one and is described by the two-dimensional fluid dynamics equation for the geostrophic streamfunction. The fast component consists of long gyroscopic waves and is a packet of inertial oscillations modulated by an amplitude depending on coordinates and slow time. On times $O(1/f\, \mathit{Ro})$ the fast component conserves its energy, but it is coupled to the slow component: its amplitude obeys an equation with coefficients depending on the geostrophic streamfunction. Under the traditional approximation, the inertial oscillations are trapped by the quasi-geostrophic component; ‘non-traditional’ terms in the amplitude equation provide a meridional dispersion of the packet on times $O(1/f\, \mathit{Ro})$, and, therefore, an effective radiation of energy from the initial perturbation domain. Another important effect of the non-traditional terms is that on longer times $O(1/f\, \mathit{Ro}^{2})$ a transfer of energy between the fast and the slow components becomes possible.

1. Postsynaptic potentials were recorded in lumbar motoneurons of the frog in response to electrical activation of dorsal roots. After chemical synaptic transmission was blocked by replacing Ca2+ with Mg2+ in the superfusion medium, it was confirmed that the remaining electrical excitatory postsynaptic potentials (EEPSPs) recorded in motoneurons consisted of potential changes-produced by electrical coupling between the motoneurons and the stimulated axons. The EEPSPs could then be used as an assay to study the reliability of spike propagation into presynaptic terminals. 2. EEPSPs typically consisted of three components. The first was a small positive deflection (prespike or presynaptic volley) that could also be recorded extracellularly. The second component was a spikelike fast positive component and the third was a slow positive component that followed the second but had a distinct maximum and a slow decay. The amplitude of the fast component did not correlate with that of either the prespike or the slow component. 3. 4-Aminopyridine (0.1 mM), which widens action potentials by blocking K+ channels, increased the amplitude and width of EEPSPs. Heptanol (1-4 mM), which is known to be a blocker of electrical coupling, could block EEPSPs. 4. The amplitudes of EEPSPs evoked by dorsal root stimulation were compared at different temperatures (7.5-19.5 degrees C). A slight decrease of the amplitude of the fast component with increasing temperature (Q10 = 0.8) was within limits predicted by resistance-capacitance filtering of the presynaptic spike at the different temperatures, suggesting that the temperature does not affect propagation of the spike in this synapse. 5. The amplitude of the fast component of EEPSPs evoked by single-pulse and paired-pulse stimulation did not fluctuate more than the baseline noise in 37 experiments in which the SD of baseline noise was < 100 microV. We conclude that electrical synaptic transmission does not fluctuate intermittently in this system, and that branch points conduct or fail to conduct for periods of time longer than the longest period in the analyzed experiments.

The contingent negative variation (CNV) amplitudes of 16 subjects with migraine without aura were studied during pain-free intervals and during attacks and the results were compared with those of 22 healthy subjects. In 32 trials the CNV amplitudes were calculated for (a) “total interval”, (b) “early CNV component”, (c) “late CNV component”, and (d) habituation. There was a significantly higher total CNV amplitude in migraine subjects during pain-free intervals compared to that of the healthy subjects and migraine patients during an attack. Healthy subjects as well as subjects studied during the attack showed a significant habituation whereas migraine subjects studied during pain-free intervals did not. This suggests that the higher CNV amplitude in migraine patients studied between pain-free attacks may be due in part to impaired habituation.

The contribution of respiratory muscle work to the development of the O2consumption (V˙o 2) slow component is a point of controversy because it has been shown that the increased ventilation in hypoxia is not associated with a concomitant increase inV˙o 2 slow component. The first purpose of this study was thus to test the hypothesis of a direct relationship between respiratory muscle work andV˙o 2 slow component by manipulating inspiratory resistance. Because the conditions for aV˙o 2 slow component specific to respiratory muscle can be reached during intense exercise, the second purpose was to determine whether respiratory muscles behave like limb muscles during heavy exercise. Ten trained subjects performed two 8-min constant-load heavy cycling exercises with and without a threshold valve in random order. V˙o 2 was measured breath by breath by using a fast gas exchange analyzer, and the V˙o 2 response was modeled after removal of the cardiodynamic phase by using two monoexponential functions. As anticipated, when total work was slightly increased with loaded inspiratory resistance, slight increases in baseV˙o 2, the primary phase amplitude, and peak V˙o 2 were noted (14.2%, P < 0.01; 3.5%, P > 0.05; and 8.3%, P < 0.01, respectively). The bootstrap method revealed small coefficients of variation for the model parameter, including the slow-component amplitude and delay (15 and 19%, respectively), indicating an accurate determination for this critical parameter. The amplitude of the V˙o 2 slow component displayed a 27% increase from 8.1 ± 3.6 to 10.3 ± 3.4 ml · min−1 · kg−1( P < 0.01) with the addition of inspiratory resistance. Taken together, this increase and the lack of any differences in minute volume and ventilatory parameters between the two experimental conditions suggest the occurrence of aV˙o 2 slow component specific to the respiratory muscles in loaded condition.

It is presently unclear how the fast and slow components of pulmonary oxygen uptake (V˙o 2) kinetics would be altered by body posture during heavy exercise [i.e., above the lactate threshold (LT)]. Nine subjects performed transitions from unloaded cycling to work rates representing moderate (below the estimated LT) and heavy exercise (V˙o 2 equal to 50% of the difference between LT and peakV˙o 2) under conditions of upright and supine positions. During moderate exercise, the steady-state increase in V˙o 2was similar in the two positions, butV˙o 2 kinetics were slower in the supine position. During heavy exercise, the rate of adjustment ofV˙o 2 to the 6-min value was also slower in the supine position but was characterized by a significant reduction in the amplitude of the fast component ofV˙o 2, without a significant slowing of the phase 2 time constant. However, the amplitude of the slow component was significantly increased, such that the end-exerciseV˙o 2 was the same in the two positions. The changes inV˙o 2 kinetics for the supine vs. upright position were paralleled by a blunted response of heart rate at 2 min into exercise during supine compared with upright heavy exercise. Thus the supine position was associated with not only a greater amplitude of the slow component forV˙o 2 but also, concomitantly, with a reduced amplitude of the fast component; this latter effect may be due, at least in part, to an attenuated early rise in heart rate in the supine position.

Slow waves (slow wavesICC) were recorded from myenteric interstitial cells of Cajal (ICC-MY) in situ in the rabbit small intestine, and their properties were compared with those of mouse small intestine. Rabbit slow wavesICC consisted of an upstroke depolarization followed by a distinct plateau component. Ni2+ and nominally Ca2+-free solutions reduced the rate-of-rise and amplitude of the upstroke depolarization. Replacement of Ca2+ with Sr2+ enhanced the upstroke component but decreased the plateau component of rabbit slow wavesICC. In contrast, replacing Ca2+ with Sr2+ decreased both components of mouse slow wavesICC. The plateau component of rabbit slow wavesICC was inhibited in low-extracellular-Cl−-concentration (low-[Cl−]o) solutions and by 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS), an inhibitor of Cl− channels, cyclopiazonic acid (CPA), an inhibitor of internal Ca2+ pumps, or bumetanide, an inhibitor of Na+-K+-2Cl− cotransporter (NKCC1). Bumetanide also inhibited the plateau component of mouse slow wavesICC. NKCC1-like immunoreactivity was observed mainly in ICC-MY in the rabbit small intestine. Membrane depolarization with a high-K+ solution reduced the upstroke component of rabbit slow wavesICC. In cells depolarized with elevated external K+, DIDS, CPA, and bumetanide blocked slow wavesICC. These results suggest that the upstroke component of rabbit slow wavesICC is partially mediated by voltage-dependent Ca2+ influx, whereas the plateau component is dependent on Ca2+-activated Cl− efflux. NKCC1 is likely to be responsible for Cl− accumulation in ICC-MY. The results also suggest that the mechanism of the upstroke component differs in rabbit and mouse slow wavesICC in the small intestine.

Although G-protein-coupled (metabotropic) receptors are known to modulate the production of motor patterns, evidence from the escape swim central pattern generator (CPG) of the nudibranch mollusk, Tritonia diomedea, suggests that they might also participate in the generation of the motor pattern itself. The dorsal swim interneurons (DSIs), identified serotonergic neurons intrinsic to the Tritonia swim CPG, evoke dual component synaptic potentials onto other CPG neurons and premotor interneurons. Both the fast and slow components were previously shown to be due to serotonin (5-HT) acting at distinct postsynaptic receptors. We find that blocking or facilitating metabotropic receptors in a postsynaptic premotor interneuron differentially affects the fast and slow synaptic responses to DSI stimulation. Blocking G-protein activation by iontophoretically injecting the GDP-analogue guanosine 5′- O-(2-thiodiphosphate) (GDP-β-S) did not significantly affect the DSI-evoked fast excitatory postsynaptic potential (EPSP) but decreased the amplitude of the slow component more than 50%. Injection of the GTP analogues guanosine 5′- O-(3-thiotriphosphate) (GTP-γ-S) and 5′-guanylyl-imidodiphosphate, to prolong G-protein activation, had mixed effects on the fast component but increased the amplitude and duration of the slow component of the DSI-evoked response and, with repeated DSI stimulation, led to a persistent depolarization. These results indicate that the fast component of the biphasic synaptic potential evoked by a serotonergic CPG neuron onto premotor interneurons is mediated by ionotropic receptors (5-HT-gated ion channels), whereas the slow component is mediated by G-protein-coupled receptors. A similar synaptic activation of metabotropic receptors might also be found within the CPG itself, where it could exert a direct influence onto motor pattern generation.

The primary aim of this thesis was to develop a better understanding of the physiology and perceptual responses associated with the performance of continuous (CE) and intermittent exercise (IE) in patients with moderate chronic obstructive pulmonary disease (COPD). A secondary aim was to examine factors that could potentially limit exercise tolerance in COPD patients, particularly in relation to the dynamics of the cardiovascular system and muscle metabolism. The results of the four studies conducted to achieve these aims are presented in this thesis. In Study 1, the physiological, metabolic and perceptual responses to an acute bout of IE and CE were examined in 10 individuals with moderate COPD. Each subject completed an incremental exercise test to exhaustion on a cycle ergometer. Subjects then performed IE (1 min exercise: 1 min rest ratio) and CE tests at 70% of peak power in random order on separate days. Gas exchange, heart rate, plasma lactate concentration, ratings of breathlessness, inspiratory capacity and the total amount of work completed were measured during each exercise test. Subjects were able to complete a significantly greater amount of work during IE (71 ± 32 kJ) compared with CE (31 ± 24 kJ). Intermittent exercise was associated with significantly lower values for oxygen uptake, expired ventilation and plasma lactate concentration when compared with CE. Subjects also reported a significantly lower rating of breathlessness during IE compared to CE. The degree of dynamic lung hyperinflation (change in end-expiratory lung volume) was lower during IE (0.23 ± 0.07 L) than during CE (0.52 ± 0.13 L). The results suggest that IE may be superior to CE as a mode of training for patients with COPD. The greater amount of total work performed and the lower measured physiological responses attained with intermittent exercise could potentially allow greater training adaptations to be achieved in individuals with more limited lung function. The purpose of Study 2 was to compare the adaptations to 8 wk of supervised intermittent and continuous cycle ergometry training, performed at the same relative intensity and matched for total work completed, in patients with COPD. Nineteen subjects with moderate COPD were stratified according to age, gender, and pulmonary function, and then randomly assigned to either an IE (1 min exercise: 1 min rest ratio) or CE training group. Subjects trained 3 d per week for 8 wk and completed 30 min of exercise. Initial training intensity, i.e., the power output applied during the CE bouts and during the exercise interval of the IE bouts, was determined as 50% of the peak power output achieved during incremental exercise and was increased by 5% each week after 2 wk of training. The total amount of work performed was not significantly different (P=0.74) between the CE (750 ± 90 kJ) and IE (707 ± 92 kJ) groups. The subjects who performed IE (N=9) experienced significantly lower levels of perceived breathlessness and lower limb fatigue during the exercise-training bouts than the group who performed CE (N=10). However, exercise capacity (peak oxygen uptake) and exercise tolerance (peak power output and 6-min walk distance) improved to a similar extent in both training groups. During submaximal constant-load exercise, the improved (faster) phase II oxygen uptake kinetic response with training was independent of exercise mode. Furthermore, training-induced reductions in submaximal exercise heart rate, carbon dioxide output, expired ventilation and blood lactate concentrations were not different between the two training modes. Exercise training also resulted in an equivalent reduction for both training modes in the degree of dynamic hyperinflation observed during incremental exercise. Thus, when total work performed and relative intensity were the same for both training modes, 8 wk of CE or IE training resulted in similar functional improvements and physiological adaptations in patients with moderate COPD. Study 3 examined the relationship between exercise capacity (peak oxygen uptake) and lower limb vasodilatory capacity in 9 patients with moderate COPD and 9 healthy age-matched control subjects. While peak oxygen uptake was significantly lower in the COPD patients (15.8 ± 3.5 mL·min-1·kg-1) compared to the control subjects (25.2 ± 3.5 mL·kg-1·min-1), there were no significant differences between groups in peak calf blood flow or peak calf conductance measured 7 s post-ischemia. Peak oxygen uptake was significantly correlated with peak calf blood flow and peak conductance in the control group, whereas there was no significant relationship found between these variables in the COPD group. However, the rate of decay in blood flow following ischemia was significantly slower (p less than 0.05) for the COPD group (-0.036 ± 0.005 mL·100 mL-1·min-1·s-1) when compared to the control group (-0.048 ± 0.015 mL·100 mL-1·min-1·s-1). The results of this study suggest that the lower peak exercise capacity in patients with moderate COPD is not related to a loss in leg vasodilatory capacity. Study 4 examined the dynamics of oxygen uptake kinetics during high-intensity constant-load cycling performed at 70% of the peak power attained during an incremental exercise test in 7 patients with moderate COPD and 7 healthy age-matched controls. The time constant of the primary component (phase II) of oxygen uptake was significantly slower in the COPD patients (82 ± 8 s) when compared to healthy control subjects (44 ± 4 s). Moreover, the oxygen cost per unit increment in power output for the primary component and the overall response were significantly higher in patients with COPD than in healthy control subjects. A slow component was observed in 5 of the 7 patients with COPD (49 ± 11 mL·min-1), whereas all of the control subjects demonstrated a slow component of oxygen uptake (213 ± 35 mL·min-1). The slow component comprised a significantly greater proportion of the total oxygen uptake response in the healthy control group (18 ± 2%) than in the COPD group (10 ± 2%). In the COPD patients, the slow component amplitude was significantly correlated with the decrease in inspiratory capacity (r = -0.88, P less than 0.05; N=5), indicating that the magnitude of the slow component was larger in individuals who experienced a greater degree of dynamic hyperinflation. This study demonstrated that most patients with moderate COPD are able to exercise at intensities high enough to elicit a slow component of oxygen uptake during constant-load exercise. The significant correlation observed between the slow component amplitude and the degree of dynamic hyperinflation suggests that the work of breathing may contribute to the slow component in patients with COPD.

The primary aim of this thesis was to develop a better understanding of the physiology and perceptual responses associated with the performance of continuous (CE) and intermittent exercise (IE) in patients with moderate chronic obstructive pulmonary disease (COPD). A secondary aim was to examine factors that could potentially limit exercise tolerance in COPD patients, particularly in relation to the dynamics of the cardiovascular system and muscle metabolism. The results of the four studies conducted to achieve these aims are presented in this thesis. In Study 1, the physiological, metabolic and perceptual responses to an acute bout of IE and CE were examined in 10 individuals with moderate COPD. Each subject completed an incremental exercise test to exhaustion on a cycle ergometer. Subjects then performed IE (1 min exercise: 1 min rest ratio) and CE tests at 70% of peak power in random order on separate days. Gas exchange, heart rate, plasma lactate concentration, ratings of breathlessness, inspiratory capacity and the total amount of work completed were measured during each exercise test. Subjects were able to complete a significantly greater amount of work during IE (71 ± 32 kJ) compared with CE (31 ± 24 kJ). Intermittent exercise was associated with significantly lower values for oxygen uptake, expired ventilation and plasma lactate concentration when compared with CE. Subjects also reported a significantly lower rating of breathlessness during IE compared to CE. The degree of dynamic lung hyperinflation (change in end-expiratory lung volume) was lower during IE (0.23 ± 0.07 L) than during CE (0.52 ± 0.13 L). The results suggest that IE may be superior to CE as a mode of training for patients with COPD. The greater amount of total work performed and the lower measured physiological responses attained with intermittent exercise could potentially allow greater training adaptations to be achieved in individuals with more limited lung function. The purpose of Study 2 was to compare the adaptations to 8 wk of supervised intermittent and continuous cycle ergometry training, performed at the same relative intensity and matched for total work completed, in patients with COPD. Nineteen subjects with moderate COPD were stratified according to age, gender, and pulmonary function, and then randomly assigned to either an IE (1 min exercise: 1 min rest ratio) or CE training group. Subjects trained 3 d per week for 8 wk and completed 30 min of exercise. Initial training intensity, i.e., the power output applied during the CE bouts and during the exercise interval of the IE bouts, was determined as 50% of the peak power output achieved during incremental exercise and was increased by 5% each week after 2 wk of training. The total amount of work performed was not significantly different (P=0.74) between the CE (750 ± 90 kJ) and IE (707 ± 92 kJ) groups. The subjects who performed IE (N=9) experienced significantly lower levels of perceived breathlessness and lower limb fatigue during the exercise-training bouts than the group who performed CE (N=10). However, exercise capacity (peak oxygen uptake) and exercise tolerance (peak power output and 6-min walk distance) improved to a similar extent in both training groups. During submaximal constant-load exercise, the improved (faster) phase II oxygen uptake kinetic response with training was independent of exercise mode. Furthermore, training-induced reductions in submaximal exercise heart rate, carbon dioxide output, expired ventilation and blood lactate concentrations were not different between the two training modes. Exercise training also resulted in an equivalent reduction for both training modes in the degree of dynamic hyperinflation observed during incremental exercise. Thus, when total work performed and relative intensity were the same for both training modes, 8 wk of CE or IE training resulted in similar functional improvements and physiological adaptations in patients with moderate COPD. Study 3 examined the relationship between exercise capacity (peak oxygen uptake) and lower limb vasodilatory capacity in 9 patients with moderate COPD and 9 healthy age-matched control subjects. While peak oxygen uptake was significantly lower in the COPD patients (15.8 ± 3.5 mL·min-1·kg-1) compared to the control subjects (25.2 ± 3.5 mL·kg-1·min-1), there were no significant differences between groups in peak calf blood flow or peak calf conductance measured 7 s post-ischemia. Peak oxygen uptake was significantly correlated with peak calf blood flow and peak conductance in the control group, whereas there was no significant relationship found between these variables in the COPD group. However, the rate of decay in blood flow following ischemia was significantly slower (p less than 0.05) for the COPD group (-0.036 ± 0.005 mL·100 mL-1·min-1·s-1) when compared to the control group (-0.048 ± 0.015 mL·100 mL-1·min-1·s-1). The results of this study suggest that the lower peak exercise capacity in patients with moderate COPD is not related to a loss in leg vasodilatory capacity. Study 4 examined the dynamics of oxygen uptake kinetics during high-intensity constant-load cycling performed at 70% of the peak power attained during an incremental exercise test in 7 patients with moderate COPD and 7 healthy age-matched controls. The time constant of the primary component (phase II) of oxygen uptake was significantly slower in the COPD patients (82 ± 8 s) when compared to healthy control subjects (44 ± 4 s). Moreover, the oxygen cost per unit increment in power output for the primary component and the overall response were significantly higher in patients with COPD than in healthy control subjects. A slow component was observed in 5 of the 7 patients with COPD (49 ± 11 mL·min-1), whereas all of the control subjects demonstrated a slow component of oxygen uptake (213 ± 35 mL·min-1). The slow component comprised a significantly greater proportion of the total oxygen uptake response in the healthy control group (18 ± 2%) than in the COPD group (10 ± 2%). In the COPD patients, the slow component amplitude was significantly correlated with the decrease in inspiratory capacity (r = -0.88, P less than 0.05; N=5), indicating that the magnitude of the slow component was larger in individuals who experienced a greater degree of dynamic hyperinflation. This study demonstrated that most patients with moderate COPD are able to exercise at intensities high enough to elicit a slow component of oxygen uptake during constant-load exercise. The significant correlation observed between the slow component amplitude and the degree of dynamic hyperinflation suggests that the work of breathing may contribute to the slow component in patients with COPD.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Physiotherapy and Exercise Science
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In Chapters 1 and 4, we briefly summarized the symptoms of parkinsonism. Parkinsonism implies movement problems that are typical of Parkinson’s disease. They remain treatment issues during the lifetime of people with Parkinson’s disease, even if dementia develops. Similarly, parkinsonism also typically occurs in DLB, although to variable degrees. In these disorders parkinsonism primarily reflects low brain dopamine levels and improves with dopamine replacement therapy, often markedly. Parkinsonism occurs when a region of the brain called the basal ganglia ceases to work properly (see Figure 4.2 in Chapter 4). As discussed in Chapter 4, the substantia nigra is a crucial regulator of basal ganglia activity, which is mediated by dopamine release in the striatum. The substantia nigra degenerates in these Lewy disorders and, as a result, brain dopamine declines. With a decline in dopamine, movement slows. Bradykinesia is the medical term for such slowness. This manifests as not only slowed movement but also less movement and smaller than normal movements. Unconscious automatic movements, such as blinking or arm swing, diminish. A unique tremor of the hands (sometimes legs) often develops when these limbs are in a relaxed position (rest tremor). For unknown reasons, the brain is not affected symmetrically, hence, neither is the body. Typically, one side of the body is much more impaired than the other. The extent to which these symptoms develop differs from person to person and includes various combinations of the following components. The slowness may be apparent on one or both sides of the body. For example, one leg may lag behind when walking. The overall appearance is characterized by moving much slower than expected for one’s age. The person feels as if they are moving in molasses—everything slows down. Many of our daily activities involve repeated small movements, such as writing or brushing teeth. In the Lewy conditions of DLB and PDD, the size (amplitude) of repetitive movements diminishes, impairing the activity. This is exemplified by the small handwriting of someone with parkinsonism, termed micrographia. Clinicians assess repetitive motor function by asking the patient to repetitively tap the thumb and index finger.

Higher animals have four basic tissue types: epithelial tissue, connective tissue, nervous tissue, and muscle. Of these, nerve and muscle are grouped together as ‘excitable cells’ because the cell membrane has the ability to vary membrane ion conductance and membrane voltage so as to transmit meaningful signals within and between cells. Within excitable cells information is transmitted using either an amplitude-modulated (AM) code using slow, electrotonic potentials, or a frequency-modulated (FM) code when signalling is by action potentials. Much of the signalling between excitable cells occurs at chemical synapses where a chemical neurotransmitter is released from presynaptic cells and then interacts with postsynaptic membrane receptors. Clinical symptoms can arise when the release of chemical neurotransmitters is disturbed, or when availability of postsynaptic receptors is altered. Thus, a reduction in dopamine release from basal ganglia substantia nigra cells is found in Parkinson’s disease, while myasthenia gravis results from loss of nicotinic acetylcholine receptors at the neuromuscular junction of skeletal muscle. Sometimes transmission from cell to cell is not by chemical neurotransmitter but by electrical synapses, where gap-junctions provide direct electrical connectivity. Transmission between cardiac muscle cells occurs in this way. Some cardiac arrhythmias, such as Wolff –Parkinson–White syndrome, are a consequence of an abnormal path of electrical conduction between cardiac muscle fibres. Sensory cells on and within the body pass information via afferent pathways from the peripheral nervous system into the central nervous system (CNS). CNS processes and sensory information are integrated to produce outputs from the CNS. These outputs pass by various efferent routes to the effector organs: skeletal muscle, cardiac muscle, smooth muscle, and glands. It is through these effectors that the CNS is able to exert control over the body and to interact with the environment. Alterations of function anywhere in the afferent, integrative, or efferent aspects of the system, as well as defects in the effectors themselves, are likely to lead to significant clinical symptoms and signs. The efferent outflow from the CNS has two major components. One, the somatic nervous system, innervates only skeletal muscle. The other is the autonomic nervous system (ANS), which innervates cardiac muscle, smooth muscle, and the glands of the viscera and skin.

In this chapter, the anatomical, functional, and in vivo myoelectrical characteristics of the normal stomach are reviewed. The anatomical regions of the stomach are shown in Figure 3.1. Major areas are the fundus, the body (corpus), antrum, and pyloroduodenal area. Extrinsic innervation of the stomach is provided by the vagus nerve and splanchnic nerves. The pacemaker region is shown on the greater curvature of the stomach between the fundus and the corpus. From the pacemaker region, spontaneous electrical depolarization and repolarization occurs and generates the myoelectrical waves that are termed the gastric pacesetter potentials, or slow waves. The prominent muscle layers of the stomach are the circular and the longitudinal muscle layers (see Fig. 3.1, middle). The oblique muscle layer is included in the muscularis. Between these smooth muscle layers lie the neurons of the myenteric plexus, the gastric components of the enteric nervous system. Afferent neurons, interneurons, and postganglionic parasympathetic neurons all have synaptic interactions in the myenteric plexus. Intrinsic neurons and extrinsic excitatory and inhibitory neurons from the vagus nerve and splanchnic nerves, intraluminal contents, and hormones modulate contraction and relaxation of the smooth muscle in the different regions of the stomach. Important anatomical and functional relationships exist among the circular smooth muscle layer, the myenteric neurons, and the interstitial cells of Cajal (ICCs) (see Fig. 3.1, bottom). The ICCs are the pacemaker cells, the cells that spontaneously depolarize and repolarize and set the myoelectrical rhythmicity of the stomach and other areas of the gastrointestinal tract. The interstitial cells are electrically coupled with the circular muscle cells. Low-amplitude rhythmic circular contractions occur at the pacemaker rhythm. Rhythmicity and contractility of the circular muscle layer are modulated by ongoing activity excitatory and inhibitory of myenteric neurons that synapse with the interstitial cells. The interstitial cells have a variety of other receptors. Electrocontractile activities of the gastric smooth muscle are modified by neuronal and hormonal inputs appropriate for fasting and specific postprandial conditions. Control of rhythmicity may be modulated by a variety of stimuli that affect the interstitial cells and is a focus of intense investigation.

A study was conducted on the features of the formation of slow brain potentials preceding the performance of a given movement and similar activity that occurs during an imaginary move-ment (without a motor component).The study used a modified technique for registering the "readiness potential" (RP) using a sound stimulus as a starting signal for making a real move-ment (compression of the expander) and an imaginary movement. A slow negative potential (SNP) was recorded, which, in terms of amplitude-time parameters and spatial representation, corresponds to the classical RP and is considered as an electrographic equivalent of the motor program formation process. The physiological similarity/difference of the SNP potentials rec-orded during a real and imaginary movement was evaluated.

Gas foil bearing (GFB) technology has reached great maturity as per engineered design and construction and its system integration into rotating machinery. Empirical research has gone beyond showing a few instances of acceptable mechanical performance, to demonstrate GFB multiple-cycle repeatable performance in spite of persistent large amplitude sub synchronous whirl motions. A GFB is a forgiving mechanical element whose engineered resilient underspring structure contains and ameliorates large rotor excursions. Analyses, however, fail to distinguish the hardening stiffness from the FB underspring structure, which under conditions of large force excitations due to imbalance, produces a complex rotordynamic behavior, rich in sub harmonic motions when operating at super critical speeds. This paper extends an earlier analysis of a rigid rotor-GFB system that dispenses with the gas film component to predict the effect of shaft rotation acceleration/deceleration on rotor amplitudes of motion and whirl frequency content. For operation above the system critical speed and as the rotor accelerates, large amplitude whirl motions appear with a main subsynchronous frequency tracking rotor speed, first at 50% speed and later bifurcating into at 33% whirl frequency. Rotor imbalance awakens and exacerbates the system nonlinear response. Slow rotor accelerations result in responses with more abundant subsynchronous whirl patterns, increased amplitudes of whirl, and accompanied by a pronounced mechanical hysteresis when the rotor decelerates. Large rotor imbalances produce both jump phenomenon and a stronger hysteresis during slow acceleration and deceleration cases. Material damping (dry friction) in the FB aids to reduce and delay the nonlinear response, eventually eliminating the multiple frequency behavior. The results bring to attention rotordynamic issues during start up and shut down events that can result from an inadequate FB technology or an unacceptable rotor imbalance grade condition.

Abstract Present capabilities of the NASA CARES/Life code include probabilistic life prediction of ceramic components subjected to fast fracture, slow crack growth (stress corrosion), and cyclic fatigue failure modes. Currently, this code has the capability to compute the time-dependent reliability of ceramic structures subjected to simple time-dependent loading. For example, in slow crack growth (SCG) type failure conditions CARES/Life can handle the cases of sustained and linearly increasing time-dependent loads, while for cyclic fatigue applications various types of repetitive constant amplitude loads can be accounted for. In real applications applied loads are rarely that simple, but rather vary with time in more complex ways such as, for example, engine start up, shut down, and dynamic and vibrational loads. In addition, when a given component is subjected to transient environmental and or thermal conditions, the material properties also vary with time. The objective of this paper is to demonstrate a methodology capable of predicting the time-dependent reliability of components subjected to transient thermomechanical loads that takes into account the change in material response with time. In this paper, the dominant delayed failure mechanism is assumed to be SCG. This methodology has been coded into CARES/Life, which has also been modified to have the capability of interfacing with commercially available FEA codes executed for transient load histories. An example involving a ceramic exhaust valve subjected to combustion cycle loads is presented to demonstrate the viability of this methodology and the CARES/Life program.

The Naval Postgraduate School has added wave making capability to the existing small tow tank that resides on campus. A new collaborative research effort between the Systems Engineering and Mechanical and Aerospace Engineering Departments is underway that utilizes this new capability. The aim of this new effort is to understand and predict the unsteady hydrodynamic loads experienced by a submerged vehicle operating near the surface. The tow tank was originally built around 1970 but only had the capability of testing models at slow speed in calm water. Even with this limited capability, a number of interesting studies were conducted in the facility including measuring the drag on a towed hydropower turbine and examining the forces due to collisions between floating ice equivalent objects and a composite plate. The new wave making capability in the tow tank is provided by a vertical plunging wedge that was modeled off of the sediment tank wavemaker at the United States Naval Academy. The wedge rides on a pair of vertical rails with the oscillation amplitude and frequency controlled by a linear actuator and electric motor. A variable angle wave absorbing beach is planned for the opposite end of the tank. An additional component of this modernization effort is the creation of a numeric tow tank, using ANSYS CFX, which can simulate the wave dynamics in the tank. This allows complementary numerical and experimental components of future research efforts. The current experimental effort involves characterizing the performance of the wavemaker and quantifying the wave environment throughout the tank. The wedge to wave amplitude transfer function has been determined over the relevant amplitude and frequency space. The uniformity of a wave crest has also been examined. For the numeric tow tank work, the wedge motion has been duplicated and the simulated wave elevation and propagation down the tank are being compared to experimentally measured results.

This paper is focused on the optimization of mistuned blades assembling rearrangement under the forced response. First, in order to avoid the greatly increase of the calculation greatly by the whole circle bladed-disk finite element model, a reduced-order model is developed based on the component mode synthesis. CPU+GPU heterogeneous architecture parallel computation is used to accelerate modal analysis of the disk and blade sectors substructures. Second, a modified ant colony algorithm is applied to the combinatorial optimization to find the optimal rearrangement pattern of bladed-disk assembly. Different from classical algorithm, the individual mistuned information is used to construct heuristic function based on intentional mistuning pattern, which can avoid slow convergence of ant colony algorithm and increase the search speed efficiently. At last, a high-fidelity 3D FEM model with 43 mistuned blades is used to demonstrate the capabilities of the techniques in reducing the maximum displacement resonance response of the bladed-disk system. The numerical simulation showed that this program based on the reduced-order model proposed in this article gained 4.3 speedup compared with ANSYS full model under the scale of 500k nodes. The displacement response amplitude of the blades decreased by 32% with 60 steps (1200 times FEM calculation) by the new optimization method. The physical mechanism of reducing the bladed-disk response is explained by comparing the optimized and worst arrangement patterns. The results clearly demonstrate that the optimized rearrangement pattern of mistuned blades is able to reduce the response amplitude of the forced vibration significantly, and the algorithm proposed in this article is practical and effective.

Abstract Fatigue analyzes are performed to ensure that no damage leading to failure will occur in a component. In ASME III NB-3222.4(e), a method is provided for analyzing a component’s resistance against cyclic loads. In ASME NB-3228.5 or alternatively NB-3653.6 (c) a simplified elastic-plastic method is given to take plasticity into account. According to NB-3228.4 (c), fatigue evaluation is allowed with plastic analysis where the stress amplitude is determined from the numerically maximum principal total strain range. This report examines the fatigue life, using a continuum mechanics approach, of a pipe penetration that is subjected to a rapid cooling down followed by a slow heating up. Simplified elastic-plastic analysis and plastic analysis are performed. The analysis also takes into account the FEN-factor according to the method given NUREG/CR6909. The fatigue life is also determined by a fracture mechanics approach using a R6 based fracture assessment and crack growth analysis. The results show a large difference in fatigue life depending on the method used. For the plastic analyzes it is of great importance to the result in which direction the evaluation is made. For the present case the maximum principal total strain range is obtained in the radial direction. The stresses in this direction are small. A crack tangentially to this direction lacks physical significance to a pipe geometry and cannot lead to failure. In this case it is recommended that evaluation is made for the strain range in the axial direction for pipe geometries instead of the maximum principal total strain range.

Welds have been inspected by radiography for years, but this technology has major drawbacks: low detection rates for critical planar defects (i.e. cracks and lack of fusion), subjective interpretation, no vertical sizing capability, significant safety hazards, licensing issues, plant closures, and is generally slow. For decades, the main alternative was manual ultrasonics, which is also slow, subjective and normally has little hardcopy record. New technology and techniques are now available for improved weld inspections, specifically phased array technology and diffraction techniques. Phased arrays are essentially the industrial version of medical ultrasound, but require a very different approach. In contrast to medical activities, industrial applications typically require a correctly angled beam, with large quantities of data, on variable component geometry, and the ability to save and image defects. All this capability is now packaged in a portable unit, which can be used for rapid and reliable weld inspections. Specifically, the OmniScan MX can now perform a single linear scan of the weld, while the instrumentation performs multiple scans at different angles simultaneously. In addition, phased arrays can perform unique scans, like S-scans (sectorial scans), record and display all data in “top, side, end” views or similar, and perform multi-mode scans. Phased arrays permit electronic rastering in many different modes, which saves considerable inspection time; for example, some estimates show that phased arrays are five or more times quicker than manual scanning. Besides being portable and requiring just a single operator, portable phased arrays are now economically competitive with other weld inspection techniques — and generally provide a much better inspection. The “new” techniques consist of forward and backward diffraction for sizing defects. In reality, both these techniques have been around for years, but new technology has made them more practical. Forward diffraction (TOFD or Time-Of-Flight Diffraction) is now well established, and has been demonstrated for many applications. For most weld inspections, TOFD just requires a single linear pass, with two transducers (or arrays) on either side of the weld. TOFD provides good sizing and defect detection in the midwall, though it has dead zones at the two surfaces. Generally, sizing with TOFD is significantly better than with amplitude techniques, but is limited to defects ∼3 mm and up. TOFD also has the great advantage that it is highly independent of defect orientation, unlike pulse echo techniques. Even better, phased arrays can perform both pulse echo and TOFD simultaneously during a single linear scan, so giving essentially a “complete” weld inspection. Another diffraction sizing technique which has received relatively little attention until recently is “tip back diffraction”. This approach uses the low amplitude signals reflected back from crack tips to size defects. Back diffraction has the great advantages that it is intuitive, and can size defects as small as ∼1 mm, which is generally better than TOFD. However, tip back diffraction has the major disadvantage that it is sometimes difficult to correctly distinguish the crack tips from other signals, and signal-to-noise ratio is usually poor. These two limitations are largely overcome by phased arrays; first, the imaging allows correct determination of the crack tip, and second, new piezo-composite arrays with focusing and filtering give significantly improved signal amplitudes. S-scan imaging can be performed with off-the-shelf phased array equipment. Some of the more advanced phased array techniques include: 2D and 1.5D arrays for improved beam shaping and focusing; curved arrays, also for better sizing; special TRL-PA (Transmit-Receive Longitudinal Wave-Phased Array) probes for austenitic steels; additional beams for special inspections. Examples of these inspections on welds will be given. Overall, a combination of phased arrays with TOFD or back diffraction allows the operator to perform cost-effective inspections with high reliability, repeatability, good defect sizing and full data storage.

Fatigue of Niobium stabilized austenitic stainless steel (X6CrNiNb1810 mod) was studied using specimens extracted from a solution annealed and quenched primary piping material sample. This paper reports and discusses results of non-standard experiments to complement previously published test data. The NPP primary piping components spend long times in operation temperature between fatigue cycles originating from thermal transients. This was roughly simulated by fatigue tests periodically interrupted for intermediate annealing in elevated temperature. Fatigue endurance was notably increased when low strain amplitudes were used. The life extension is explained by the cyclic stress strain response. Hardening followed by slow cyclic softening was consistently observed after annealing. It is generally assumed that cumulative accumulation of fatigue damage occurs at a wide range of loading amplitudes. We performed two level and spectrum straining tests combining amplitudes above and below the (Nf &gt; 107) endurance limit. The endurance limit seems to be effective also in variable amplitude loading. In terms of modified Miner rule, even “negative damage” was obtained in two level tests below and above the constant amplitude endurance limit. This behavior is linked to prominent secondary hardening of the steel.

Relaxation and quenching of excited states of Br2 in CC14 is studied by time-resolved photothermal grating combined with near-IR fluorescence. A slow rise in diffraction transient signals from photothermal gratings, due to nonradiative relaxation of excited states, is observed for Br2 in CC14. Near-IR fluorescence measurement reveals that there are two decay components; the fast component has a lifetime about 6 ns, and the slower component has a lifetime around 20 ns, depending on Br2 concentration and oxygen content in the sample. The slower component is assigned to the decay of A' state. From the amplitudes of thermal grating, the quantum yield of the A' state formation is estimated to be 0.33+0.03. Stern-Volmer plot of the measured decay rate of A' state, including results obtained from both near-IR fluorescence and photothermal grating measurement, suggests that quenching of A' state proceeds initially at diffusion-limited rate at low concentration and reduces to nondiffusion-limited at higher concentration. Possible mechanisms for the observed decrease of quenching rate as concentration increases are also discussed.

As turbine inlet temperatures are pushed ever higher in an attempt to improve efficiency and power, it has become critical to cool component surfaces. One surface that is particularly difficult to treat because of the complex flow field that surrounds it is the nozzle guide vane endwall. Past studies have indicated that leakage bypass flow emerging from the combustor-turbine junction may be effectively harnessed for cooling purposes. When combined with endwall film-coolant injection, component service life may be significantly extended. This paper presents results from a computational study investigating a three-dimensional slot geometry at the combustor-turbine interface. The downstream edge of the slot was scalloped using a simple periodic function intended to enhance thermal benefit to the endwall by manipulating coolant distribution. Effects of varying the slot geometry amplitude and phase were investigated along with the slot nominal width and upstream distance from the vane. Initial results indicate dramatic effects can be realized depending upon the scalloping used.