Добірка наукової літератури з теми "Oxygen-conserving reflexes"

The trigemino-cardiac reflex (TCR) represents the most powerful of the autonomous reflexes and is a subphenomenon in the group of the so-called “oxygen-conserving reflexes”. Within seconds after the initiation of such a reflex, there is a powerful and differentiated activation of the sympathetic system with subsequent elevation in regional cerebral blood flow (CBF), with no changes in the cerebral metabolic rate of oxygen (CMRO2) or in the cerebral metabolic rate of glucose (CMRglc). Such an increase in regional CBF without a change of CMRO2or CMRglcprovides the brain with oxygen rapidly and efficiently. Features of the reflex have been discovered during skull base surgery, mediating reflex protection projects via currently undefined pathways from the rostral ventrolateral medulla oblongata to the upper brainstem and/or thalamus, which finally engage a small population of neurons in the cortex. This cortical center appears to be dedicated to transduce a neuronal signal reflexively into cerebral vasodilatation and synchronization of electrocortical activity; a fact that seems to be unique among autonomous reflexes. Sympathetic excitation is mediated by cortical-spinal projection to spinal preganglionic sympathetic neurons, whereas bradycardia is mediated via projections to cardiovagal motor medullary neurons. The integrated reflex response serves to redistribute blood from viscera to the brain in response to a challenge to cerebral metabolism, but seems also to initiate a preconditioning mechanism. Previous studies showed a great variability in the human TCR response, in special to external stimuli and individual factors. The TCR gives, therefore, not only new insights into novel therapeutic options for a range of disorders characterized by neuronal death, but also into the cortical and molecular organization of the brain.

AbstractTrigeminocardiac reflex (TCR) is a well-established neurogenic reflex although its exact mechanism and clinical significance remain unclear. This reflex may be incited by stimulation of the trigeminal nerve anywhere along its course starting from the peripheral distribution to the central nucleus. It usually manifests as bradycardia, asystole, hypotension, apnoea and gastric hypermotility; though other clinical manifestation such as tachycardia and hypertension may also occur. Diving reflex (DR) shares many similarities with TCR in both clinical manifestation and mechanism of action and is often considered as a modified or subtype of TCR. DR is an important physiological adaptation to withstand hypoxia during apnoea in many animal species including humans and thus belongs to a group of oxygen-conserving reflexes. Although TCR is a physiological reflex having protective function, an exaggerated response may have fatal consequences. Surgeries or stimulation involving head, neck and face region (area supplied by trigeminal nerve) are particularly prone to provoke this reflex. Vigilant and continuous monitoring for early identification of warning signs and communication with surgeon to interrupt the stimulus immediately is enough to cease the reflex in most of the cases. However, failure to identify and treat in time may have deleterious consequences and thus TCR has gained much attention and awareness in recent years. Over the last two decades, our knowledge on TCR has expanded but we still remain far from complete elucidation of pathophysiology, mechanism and clinical significance of this unique ‘brain and heart connection’ called TCR.

AbstractCratonic eclogite is the product of oceanic crust subduction into the subcontinental lithospheric mantle, and it also is a fertile diamond source rock. In contrast to matrix minerals in magma-borne xenoliths, inclusions in diamond are shielded from external fluids, retaining more pristine information on the state of the eclogite source at the time of encapsulation. Vanadium is a multi-valent element and a widely used elemental redox proxy. Here, we show that that xenolithic garnet has lower average V abundances than garnet inclusions. This partly reflects crystal-chemical controls, whereby higher average temperatures recorded by inclusions, accompanied by enhanced Na2O and TiO2 partitioning into garnet, facilitate V incorporation at the expense of clinopyroxene. Unexpectedly, although diamond formation is strongly linked to metasomatism and xenoliths remained open systems, V concentrations are similar for bulk eclogites reconstructed from inclusions and from xenoliths. This suggests an oxygen-conserving mechanism for eclogitic diamond formation, and implies that eclogite is an efficient system to buffer fO2 over aeons of lithospheric mantle modification by subduction-derived and other fluids.