Respiratory physiology & neurobiology
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Dyspnea, or the uncomfortable awareness of respiratory distress, is a common symptom experienced by most people at some point during their lifetime. It is commonly encountered in individuals with pulmonary disease, such as chronic obstructive pulmonary disease (COPD), but can also be seen in healthy individuals after strenuous exercise, at altitude or in response to psychological stress. Dyspnea is a multifactorial sensation involving the brainstem, cortex, and limbic system, as well as mechanoreceptors, irritant receptors and chemoreceptors. ⋯ They stimulate the respiratory control system in response to hypoxia and/or hypercapnia, and the resultant increase respiratory motor output can be consciously perceived as unpleasant. They also can induce the sensation of dyspnea through an as yet undetermined mechanism-potentially via direct ascending connections to the limbic system and cortex. The goal of this article is to briefly review how changes in blood gases reach conscious awareness and how chemoreceptors are involved in dyspnea.
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Respir Physiol Neurobiol · May 2009
Editorial ReviewPathophysiology of dyspnea evaluated by breath-holding test: studies of furosemide treatment.
Breath-holding is one of the most powerful methods to induce the dyspneic sensation, and the breath-holding test gives us much information on the onset and endurance of dyspnea. In conscious subjects, immediately after the start of breath-holding at functional residual capacity (FRC), there is a certain period of no particular respiratory sensation lasting for 20-30s, which is designated "no respiratory sensation period". This period is terminated by the onset of dyspnea and followed by a progressive increase in the intensity of dyspnea until the breaking point of breath-holding. ⋯ Alleviation of dyspnea with inhaled furosemide in conscious subjects is also consistent with the result of animal studies in which inhaled furosemide suppresses the escape behavior in the lightly anesthetized condition. The purpose of this article is to emphasize the usefulness of breath-holding test as a tool for evaluation of dyspnea. Furthermore, the possible mechanisms of alleviation of dyspnea with inhaled furosemide are highlighted.
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Respir Physiol Neurobiol · Apr 2009
Physiological response to increasing levels of neurally adjusted ventilatory assist (NAVA).
This study evaluated the response to increasing levels of neurally adjusted ventilatory assist (NAVA), a mode converting electrical activity of the diaphragm (EAdi) into pressure, regulated by a proportionality constant called the NAVA level. Fourteen rabbits were studied during baseline, resistive loading and ramp increases of the NAVA level. EAdi, airway (Paw) and esophageal pressure (Pes), Pes pressure time product (PTPes), breathing pattern, and blood gases were measured. ⋯ At this breakpoint, Pes, PTPes, EAdi, and P(a)(CO)(2) were similar to baseline. Further increase of the NAVA level reduced Pes, PTPes and EAdi without changes in ventilation. In conclusion, observing the trend in Paw during a ramp increase of the NAVA level allows determination of a level where the inspiratory effort matches unloaded conditions.
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Respir Physiol Neurobiol · Mar 2009
Clinical TrialThe compensatory responses to upper airway obstruction in normal subjects under propofol anesthesia.
Upper airway obstruction during sleep can trigger compensatory neuromuscular responses and/or prolong inspiration in order to maintain adequate minute ventilation. The aim of this study was to investigate the strength of these compensatory responses during upper airway obstruction during propofol anesthesia. We assessed respiratory timing and upper airway responses to decreases in nasal pressure in nine propofol anesthetized normal subjects under condition of decreased (passive) and increased (active) neuromuscular activity. ⋯ Compared to the passive condition, PCRIT decreased significantly (5.3 +/- 3.8 cm H2O, p < 0.05) and RUS increased (7.4 cm H2O ml-1 s, p < 0.05) in the active condition. The IDC increased progressively and comparably as decreased in both the passive and active conditions (p < 0.05). These findings imply that distinct compensatory mechanisms govern the modulation of respiratory pattern and pharyngeal patency during periods of airway obstruction under propofol anesthesia.
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Respir Physiol Neurobiol · Mar 2009
Regional lung blood flow and ventilation in upright humans studied with quantitative SPECT.
We used quantitative Single Photon Emission Computed Tomography (SPECT) to study the effect of the upright posture on regional lung blood flow and ventilation. Nine (upright) plus seven (prone and supine) healthy volunteers were studied awake, breathing spontaneously. Regional blood flow and ventilation were marked in sitting upright, supine and prone postures using (113m)In-labeled macroaggregates and inhaled Technegas ((99m)Tc); both remain fixed in the lung after administration. ⋯ In comparison with horizontal postures, both blood flow and ventilation were greater in caudal regions when upright. The redistribution was greater for blood flow than for ventilation, resulting in decreasing ventilation-to-perfusion ratios down the lung when upright. We conclude that gravity redistributes regional blood flow and ventilation in the upright posture, while the influence is much less in the supine and prone postures.