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At least 1,297 records · Page 72Linked to original sources
PubMed1978

Blood flow and relative tissue PO2 of brain and muscle: role of carotid chemoreceptors.

The effects of inspiration of low O2 and/or high CO2 gas mixtures on relative tissue PO2 and perfusion of brain and muscle were studied in 60 pentobarbital-anesthetized spontaneously respiring rats. These animals were studied in intact condition, after administration of phenoxybenzamine hydrochloride, 2 mg/kg, or after bilateral denervation of their carotid bodies. In the intact rats, the relative tissue PO2 ratio of biceps brachii to cerebral white matter always decreased after exposure to the above gas mixtures. This indicated a better maintenance of O2 supply to demand in the brain than in muscle. After either carotid denervation or alpha adrenergic blockade, this change in the ratio was no longer significant. Further, cerebral blood flow responses to these gas mixtures were attenuated (avg + 5.3%) compared to previous work in intact rats. It is concluded that the brain is best protected against hypoxia and/or hypercapnia when the carotid chemoreflex is intact.

Animals↗
PubMed1979

Decreased exercise hyperpnea in patients with bilateral carotid chemoreceptor resection.

Exercise hyperpnea was compared in 5 asthmatics 25 yr after bilateral carotid body resection (BR), 4 others 19 yr after unilateral resection (UR), and 12 controls (C) matched for age and pulmonary flow limitation. In the BR group, ventilation rose less with exercise, mostly because BR experienced less tachypnea. End-tidal PCO2 rose 5.8 +/- 3.2 (P less than 0.05) to 46 Torr at 50 W. In UR and C the same load did not increase PETCO2 significantly (+2.1 and +1.4 Torr, respectively). Arterial-end-tidal PCO2 differences before and 15--45 s postexercise were insignificant in all three groups. Heart rate and blood pressure rose equally in the three groups, suggesting that the ventilatory effects were not secondary to blood flow differences and disclosing no evidence of baroreceptor denervation during glomectomy.

Adult↗
PubMed1982

Role of the carotid chemoreceptors in regulation of inspiratory onset.

We studied the effect of intermittent tidal breaths of CO2-enriched air (3-9% CO2) on the duration of expiratory time (TE) in five trained dogs, before and after (3 dogs) bilateral surgical denervation of the carotid bodies (CBD). During studies the dogs lay quietly, either awake or in nonrapid-eye-movement sleep, and breathed through a cuffed endotracheal tube inserted via a chronic tracheostomy. Studies were conducted during bilateral blockade of the cervical vagus nerves (VB), achieved by circulating cold alcohol through radiators placed around exteriorized vagal skin loops. Prior to CBD, single breaths of CO2 significantly shortened TE and thus advanced the onset of the subsequent inspiration. Further, the decrease in TE induced by the CO2 stimulus was in direct proportion to the inspired CO2 concentration. Thus 3% CO2 shortened TE by 1.82 +/- 0.93 (SD) s, and 9% CO2 by 3.44 +/- 1.53 s. Changes in TE occurred in the absence of associated changes in either tidal volume or inspiratory time. After CBD, test breaths of CO2 failed to shorten TE during VB. We conclude that the carotid bodies have the ability to mediate changes in the timing of inspiratory onset in response to a transient CO2 stimulus.

Animals↗
PubMed1987

Role of carotid chemoreceptors and pulmonary vagal afferents during helium-oxygen breathing in ponies.

Our purpose was to assess compensatory breathing responses to airway resistance unloading in ponies. We hypothesized that the carotid bodies and hilar nerve afferents, respectively, sense chemical and mechanical changes caused by unloading, hence carotid body-denervated (CBD) and hilar nerve-denervated ponies (HND) might demonstrate greater ventilatory responses when decreasing resistance. At rest and during treadmill exercise, resistance was transiently reduced approximately 40% in five normal, seven CBD, and five HND ponies by breathing gas of 79% He-21% O2 (He-O2). In all groups at rest, He-O2 breathing did not consistently change ventilation (VE), breathing frequency (f), tidal volume (VT), or arterial PCO2 (PaCO2) from room air-breathing levels. During treadmill exercise at 1.8 mph-5% grade in normal and HND ponies, He-O2 breathing did not change PaCO2 but at moderate (6 mph-5% grade), and heavy (8 mph-8% grade) work loads, absolute PaCO2 tended to decrease by 1 min of resistance unloading. delta PaCO2 calculated as room air minus He-O2 breathing levels at 1 min demonstrated significant changes in PaCO2 during exercise resistance unloading (P less than 0.05). No difference between normal and HND ponies was found in exercise delta PaCO2 responses (P greater than 0.10); however, in CBD ponies, the delta PaCO2 during unloading was greater at any given work load (P less than 0.05), suggesting finer regulation of PaCO2 in ponies with intact carotid bodies. During heavy exercise VE and f increased during He-O2 breathing in all three groups of ponies (P less than 0.05), although there were no significant differences between groups (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1992

Peripheral chemoreceptor modulation of the pulmonary vasculature in the cat.

The present study was undertaken to determine whether stimulation of the carotid and aortic bodies (cb and ab) could affect the pulmonary vasculature. Our hypothesis was that each promoted vasodilation and thus could modulate the pulmonary vasoconstrictor response to hypoxia. The experimental design of the first set of experiments took advantage of the facts that 1) the ab, but not the cb, increases its neural output in response to CO, whereas both respond to a decreased arterial PO2 (hypoxic hypoxia, HH) and 2) the aortic nerves in cats are easily transected. Hence, both cb and ab sent neural activity to the brain stem when the intact cat was exposed to 10% O2 in N2. Only the ab sent information during CO hypoxia (COH intact). Only the cb did so during HH in the cat in which the aortic nerves had been transected, removing the aortic body (HH abr); neither ab nor cb did so during COH abr. Fifteen anesthetized paralyzed artificially ventilated cats were fit with catheters in the femoral artery and vein, right and left atria, left ventricle, and pulmonary artery and with an aortic flow probe. In the HH intact and HH abr conditions, there was a significant rise in cardiac output, whereas pulmonary arterial pressure (Ppa) rose initially but then leveled off while cardiac output continued to rise. During the 15-min exposure to HH, pulmonary vascular resistance [PVR = (Ppa - Pla)/cardiac output, where Pla is left atrial pressure] rose initially and then decreased significantly at 2-3 min. In response to COH, PVR showed only a significant decrease. In the second set of experiments, seven cats were instrumented as above and had loops placed in the common carotid arteries for selectively perfusing the cbs. In response to a brief infusion of venous blood mixed with 0.3-0.5 micrograms NaCN, which selectively stimulated only the cb, aortic flow remained relatively constant while heart rate and Ppa - alveolar pressure difference decreased significantly; so also did PVR. These data are consistent with the hypothesis that stimulation of the ab and cb singly or together can provoke a significant pulmonary vasodilation in the anesthetized paralyzed artificially ventilated cat.

Animals↗