Reflex vascular responses from aortic arch, carotid sinus and coronary baroreceptors in the anaesthetized dog

Abstract

SUMMARYIn chloralose-anaesthetized dogs, pressures applied to coronary, carotid and aortic baroreceptors were changed independently and the resulting reflex vascular responses were determined. Increases in pressure to each group of baroreceptors resulted in reflex vasodilatation; the maximal responses to distension of carotid and coronary baroreceptors were significantly larger than those to aortic receptors, but not different from each other. Increases in pressure in all three regions induced maximal responses at similar times from the onset of the pressure stimulus. However, the time for recovery of vascular resistance following a decrease in baroreceptor pressure differed. Vasoconstriction following a period of coronary hypertension occurred slowly, requiring 70 s for 90 % of the response to develop. This was significantly longer than the corresponding times for carotid and aortic receptors (about 28 s). The rate of vasoconstriction in response to coronary baroreceptor unloading was influenced by the period for which the pressure stimulus was applied and vasoconstriction was even slower when the pressure stimulus had been maintained for 8 min. The mechanism responsible for delaying the vasoconstriction following a period of coronary hypertension is not known, but this effect may have important implications for the control of arterial blood pressure.

Absence of Reflex Vascular Responses from the Intrapulmonary Circulation in Anaesthetised Dogs

“…Responses to left lung inflation which were similar to those previously reported were also demonstrated (Daly et al 1986). We also showed that the systemic and hind limb vasculatures were responsive to carotid baroreceptor stimulation, again giving responses quantitatively similar to those previously reported (Challenger et al 1987;McMahon et al 1996). Furthermore, in two animals, increasing intrapulmonary vascular pressures reduced efferent phrenic nerve discharge by over 50%.…”

“…Pressure was increased from the controllevelfor2minandthenitwasloweredbacktothecontrol level for a further 2 min before the next increase in intrapulmonary pressure. Pressure perfusing the aortic arch and coronary baroreceptors (McMahon et al 1996) was maintained constant throughout the tests at 98 mmHg and that to the carotid baroreceptors was maintained at near 60 mmHg. Ventilatory rate and stroke volume were unchanged once the cardiopulmonary bypass was established.…”

Carotid Baroreceptor Reflexes in Humans During Orthostatic Stress

“…However, against this opinion are the findings from controlled animal preparations that discrete decreases in distension to any of the low pressure areas within the thorax do not increase vascular resistance. Atrial receptors have little or no effect on vascular resistance (Linden & Kappagoda,1982), and unloading of pulmonary vascular receptors would be expected, if anything, to result in vasodilatation (Ledsome & Kan, 1977;McMahon et al 1996). Changes in ventricular distension have very little effect and only when grossly distended (Wright et al 2000).…”

“…Changes in ventricular distension have very little effect and only when grossly distended (Wright et al 2000). In fact the only vascular receptors within the intrathoracic region that appear capable of inducing large vascular responses are the coronary arterial receptors and these seem to function as high pressure arterial baroreceptors (McMahon et al 1996). Even the evidence from transplanted patients has been questioned, as other studies undertaken after patients had had longer to recover from the transplant surgery indicated that arterial baroreceptors were much more important than 'cardiopulmonary receptors' in cardiovascular control (Jacobsen et al 1993).…”

Absence of reflex vascular responses from the intrapulmonary circulation in anaesthetised dogs

“…Pressures to baroreceptors in the carotid sinuses, aortic arch and coronary arteries (McMahon et al 1996) were also held constant, and bypassing the heart would have controlled pressures to cardiac receptors (Hainsworth, 1991). Ventilation and blood gas composition were also carefully controlled.…”