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Control of Ventilation
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The carotid and aortic bodies are composed of type 1 or glomus cells and type 2 or sustentacular cells. The glomus cells contain large amounts of dopamine and nerve endings, whereas the type 2 cells resemble glia with a supporting function. Stimulation of the peripheral chemoreceptors blocks the potassium currents and causes membrane depolarization. The voltage-gated Ca++ channels open, and the influx of Ca++ provokes exocytosis of neurotransmitters, which stimulate the nerve endings to produce an action potential. The peripheral chemoreceptors are stimulated by low oxygen tension, not low oxygen content, of the blood. Conditions with low blood oxygen content, but relatively normal oxygen tension (anaemia, carboxyhaemoglobin), do not stimulate ventilation via the peripheral chemoreceptors. A high can cause a smaller but quicker response resulting in mild hyperventilation.
Reflex Regulation of Skeletal Muscle Blood Flow
Published in Irving H. Zucker, Joseph P. Gilmore, Reflex Control of the Circulation, 2020
Steven Loyal Britton, Patricia J. Metting
While it is unequivocal that the peripheral chemoreflexes can reflexly influence cardiovascular variables including skeletal muscle blood flow, it appears unlikely that they play a dominant role in the cardiovascular adjustments to exercise in healthy subjects. Data from Musch et al. (1986) demonstrate that blood gases do not change enough or in the appropriate direction during exercise to activate the peripheral chemoreceptors. During mild dynamic exercise (35% of VO2 max), PaCO2 decreased 5.2 mmHg, pHa increased 0.029 units, and PaO2 increased 5.9 mmHg. At a moderate exercise level (64% VO2 max) the blood gas values changed little from those at the mild level of exercise; only with exercise at VO2 max was there a modest, but significant decline in pHa (to 7.378) that was produced metabolically. Nevertheless, the peripheral chemoreceptors may be significant in limiting muscle blood flow during exercise in subjects with compromised cardiovascular or pulmonary function.
The respiratory system
Published in Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella, Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella
Chemoreceptors provide the most important input to the medullary respiratory center in terms of regulating ventilation to meet the metabolic requirements of the body. Chemoreceptors are sensitive to changes in PO2, PCO2 and pH. There are two types of chemoreceptors: Peripheral chemoreceptorsCentral chemoreceptors
Physiological and oxidative stress responses to intermittent hypoxia training in Sprague Dawley rats
Published in Experimental Lung Research, 2020
Megha A. Nimje, Himadri Patir, Rajesh Kumar Tirpude, Prasanna K. Reddy, Bhuvnesh Kumar
These changes can be attributed to the fact that at normoxic condition (21% FiO2); heart rate is modulated beat to beat mainly by arterial baroreceptors.38 However, during exposure to hypoxia, peripheral chemoreceptors act as regulators of autonomic activity and reset baroreflex control of heart rate and sympathetic activity, allowing higher levels of heart rate, blood pressure and sympathetic drive.39 The reduction in SpO2 level followed by hyperventilation and tachycardia during IHT in the present investigation may be due to the reason that hypoxia reduces the partial pressure of arterial oxygen leading to decreased arterial oxygen saturation (SpO2), which further stimulate peripheral chemoreceptors to hyperventilate in order to restore arterial oxygen levels as observed by.40 Breathing pattern and the activity of the chemoreceptors influence the modulation of heart rate during exposure to hypoxia.41 This results in cardiovascular system adjustments to deliver more blood to tissues to compensate for reduced oxygen delivery.42 In our study, rats exposed to hypoxia showed hyperventilation which further modulated the heart rate to beat faster in other to increase the cardiac output resulting in efficient tissue oxygenation.
Association between heart rate variability and haemodynamic response to exercise in chronic heart failure
Published in Scandinavian Cardiovascular Journal, 2019
Aaron Koshy, Nduka C. Okwose, David Nunan, Anet Toms, David A. Brodie, Patrick Doherty, Petar Seferovic, Arsen Ristic, Lazar Velicki, Nenad Filipovic, Dejana Popovic, Jane Skinner, Kristian Bailey, Guy A. MacGowan, Djordje G. Jakovljevic
Chronic heart failure manifests an overactivation of the sympathetic system and parasympathetic withdrawal. This derangement in heart rate variability is further associated with excessive levels of circulating catecholamines [25]. It is expected that sympathetic drive may improve cardiac contractility and response to exercise resulting in higher values of cardiac output, stroke volume, heart rate, blood pressure and cardiac power output. Our results confirm the trend of positive relationship between HRV and exercise heamodynamics. This association may partially be explained by the role of peripheral chemoreceptors [26]. In heart failure, chemoreceptor sensitivity is increased in response to sympathetic overactivity and is associated with improved exercise capacity and measures of heart rate variability as previously documented [26,27].
Congenital central hypoventilation syndrome: diagnosis and management
Published in Expert Review of Respiratory Medicine, 2018
Melissa A. Maloney, Sheila S. Kun, Thomas G. Keens, Iris A. Perez
While individuals with CCHS lack ventilatory responses to gradual hypercapnia and hypoxia in rebreathing challenges [7], other aspects of ventilatory control appear intact. In order to test peripheral chemoreceptor function in CCHS patients, Gozal et al. [31] tested awake ventilatory responses to abrupt hypoxia, hyperoxia, and hypercapnia. In this study, CCHS patients demonstrated a ventilatory response similar to that of control subjects, suggesting that peripheral chemoreceptor function is at least partially intact [31]. This pattern is consistent with observations in healthy controls, who also demonstrate a more robust ventilatory response to abrupt hypoxia and hypercapnia than to gradual hypoxia and hypercapnia [32]. CCHS patients are also able to increase minute ventilation and tidal volume in response to exercise, although not to the same degree as normal subjects [33]. Passive lower extremity movement in both awake and sleep states leads to increased alveolar ventilation [34,35]. This finding demonstrates that CCHS patients have intact mechanoreceptor function and the pathway by which mechanoreceptors stimulate breathing remains intact.