Baroreceptor and chemoreceptor influences on heart rate during the respiratory cycle in the dog.

Abstract

SUMMARY1. Brief stimuli were delivered to the carotid chemoreceptors or baroreceptors in dogs anaesthetized with pentobarbitone or chloralose. Chemoreceptor stimulation was achieved by rapid retrograde injections of 0-2-05 ml. warmed, CO2-equilibrated saline through a cannula in the external carotid artery. Baroreceptor stimulation was achieved by forceful retrograde injection of 2-5 ml. air-equilibrated saline, or of freshly drawn arterial blood, into the external carotid artery after first clamping the common carotid artery.2. Brief baroreceptor stimuli had no noticeable effect on breathing. Brief chemoreceptor stimuli had no effect on breathing in some dogs, but in many produced a reflex increase in the depth of inspiration when delivered during inspiration. In these same dogs, brief chemoreceptor stimuli delivered in expiration either prolonged the expiratory pause or evoked an active expiratory effort.3. Prompt decreases in heart rate were elicited by brief sudden chemoreceptor or baroreceptor stimuli when these were delivered during the expiratory phase of respiration. The stimuli did not modify the control heart rate pattern when delivered during inspiration. If the carotid sinus nerve or the vagus nerves were cut the responses were abolished. 4. Brief chemoreceptor or baroreceptor stimuli remained effective in evoking prompt decreases in heart rate during periods of apnoea in the end-inspiratory position (Hering-Breuer inflation reflex). In periods of apnoea after prolonged artificial hyperventilation the stimuli were sometimes ineffective at first, but were always effective late in the period of apnoea, again producing prompt cardiac slowing.5. After denervation of the lungs, brief baroreceptor and chemoreceptor stimuli continued to evoke prompt falls in heart rate when given during B. T. HAYMET AND D. I. McCLOSKEY expiration. When delivered during inspiration the same stimuli were either ineffective, or less effective.

Mild hypovolemic stress alters autonomic modulation of heart rate.

“…Respiratory modulation of HR may result from a number of mechanisms, which include 1) direct coupling between respiratory activity and efferent cardiac vagal activity in the brain stem 28 ; 2) central respiratory modulation of arterial baroreceptor reflex sensitivity 5) mechanical modulation of ventricular preload and afterload, resulting in arterial pressure changes and subsequent arterial baroreceptor reflex modulation of HR 32 ; and 6) central respiratory modulation of peripheral or central chemoreceptors, or both. 33 Because a decrease in central venous volume decreases atrial size, deactivates cardiopulmonary baroreceptors, possibly changes their sensitivity, and decreases ventricular preload, eventually decreasing arterial pressure, changes in any of the first five mechanisms listed above might explain our findings of decreased respiratory-related vagal modulation to mild central hypovolemia.…”

Inspiratory inhibition of vagal responses to baroreceptor and chemoreceptor stimuli in the dog.

“…05 ml) of carbondioxide-equilibrated saline into the carotid sinus. These small volumes did not change carotid sinus pressure, and have been shown previously not to affect baroreceptor nerve endings (Haymet & McCloskey, 1975).…”

“…One cannula was used for recordings of pressure within the carotid sinus. Through the other cannula selective baroreceptor stimuli were delivered by sudden retrograde injections of 2-5 ml air-equilibrated saline, after first clamping the common carotid artery caudal to the carotid sinus (Haymet & McCloskey, 1975). Selective chemoreceptor stimuli were given by injections (approx.…”

“…Pulses of pressure of 50-200 ms duration delivered into the carotid sinus selectively stimulate afferent baroreceptor fibres in the carotid sinus nerve for the duration of the pressure pulse (Haymet & McCloskey, 1975). The cardiac vagal responses to such stimuli are bursts of activity which outlast the stimulus pulses (Fig.…”

Increase in the timing coincidence of a respiration event induced by listening repeatedly to the same music track

“…The link between respiration and music is important, because there is a strong correlation between respiration and heart rate [8][9][10][11], and also between respiration and emotion [12][13][14][15][16]. Revealing the relationship between music and respiration will give us the key to develop the new musical device, which will utilize respiration information in presenting music.…”