Reflex respiratory and peripheral vascular responses to stimulation of the isolated perfused aortic arch chemoreceptors of the dog

Self Cite

122

SUMMARY1. In the anaesthetized dog the carotid sinuses and aortic arch were isolated from the circulation and separately perfused with blood by a method which enabled the mean pressure, pulse pressure and pulse frequency to be varied independently in each vasosensory area. The systemic circulation was perfused at constant blood flow by means of a pump and the systemic venous blood was oxygenated by an extracorporeal isolated pump-perfused donor lung preparation.2. When the vasosensory areas were perfused at non-pulsatile pressures within the normal physiological range of mean pressures, the reflex reduction in systemic vascular resistance produced by a given rise in mean carotid sinus pressure was significantly greater than that resulting from the same rise of aortic arch pressure.3. On the other hand, when the vasosensory areas were perfused at normal pulsatile pressures andwithin the normal physiological range ofmean pressures, there was no difference in the size ofthe reflex vascular responses elicited by the same rise in mean pressure in the carotid sinuses and in the aortic arch.4. Whereas the vasomotor responses elicited reflexly by changes in mean carotid sinus pressure are modified by alterations in pulse pressure, those evoked by the aortic arch baroreceptors through changes of mean pressure are onlyweakly affected by modifications in pulse pressure. Evidence for this was obtained from single stepwise changes of mean pressure in each vasosensory area during pulsatile and non-pulsatile perfusion, and from curves relating the mean pressure in the carotid sinuses or aortic arch and systemic arterial perfusion pressure.5. The vasomotor response elicited by combined stimulation of the 9-2 J. E. ANGELL JAMES AND M. DE B. DALY carotid sinus and aortic arch baroreceptors was greater than either response resulting from their separate stimulation.6. When the mean perfusion pressures in the two vasosensory areas are changed together, the curve relating mean pressure to systemic arterial pressure during pulsatile perfusion of the areas is considerably flatter than that for non-pulsatile perfusion.7. Increasing the pulse pressure in the carotid sinuses or aortic arch caused a decrease in systemic vascular resistance, the response elicited from the carotid sinuses being the larger.8. Altering the phase angle between the pulse pressure waves in the carotid sinuses and aortic arch had no effect on systemic vascular resistance.9. In both vasosensory areas, increasing the pulse frequency caused a reduction in systemic vascular resistance.

Section: Introductionmentioning

confidence: 77%

“…The frequency of the pulsations was varied by altering the gear ratio between the motor and pump. The aortic arch was isolated from the circulation as described by Daly et al (1965).…”

Section: Methodsmentioning

confidence: 99%

Section: Carotid Sinusesmentioning

confidence: 99%

See 1 more Smart Citation

Comparison of the reflex vasomotor responses to separate and combined stimulation of the carotid sinus and aortic arch baroreceptors by pulsatile and non‐pulsatile pressures in the dog

James¹,

Daly²

1970

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122

“…Full details of the two types of preparation used in this study have been described elsewhere (Daly, Hazzledine & Howe, 1965;, and therefore only the essential points of the techniques will be given here.…”

Section: Methodsmentioning

confidence: 99%

The reflex effects of alterations in lung volume on systemic vascular resistance in the dog

Daly¹,

Hazzledine²,

Ungar³

1967

Self Cite

117

SUMMARY1. The reflex effects of alterations in lung volume on systemic vascular resistance have been studied in anaesthetized dogs under conditions in which the systemic circulation was perfused at constant blood flow. The pressures in the isolated perfused carotid sinuses and aortic arch, and the arterial blood Po2 and Pco2 were maintained constant.2. A maintained inflation of the lungs produced by injection of air into the trachea caused a fall in systemic arterial perfusion pressure, indicating vasodilatation. The size of the systemic vasodilator response varied directly with the pressure and volume of gas used to inflate the lungs. A similar effect was observed when the tidal volume of lungs ventilated by an intermittent positive pressure was increased.3. Collapse of the lungs by creating a pneumothorax in closed-chest spontaneously breathing animals evoked a systemic vasoconstrictor response which was reversed when the lungs were re-expanded.4. These vasodilator responses were abolished by dividing the pulmonary branches of the thoracic vagosympathetic nerves. Evidence is presented that the afferent fibres run in the cervical vagosympathetic nerves and through the stellate ganglia.5. The responses were unaffected by atropine, but were abolished by hexamethonium, guanethidine and by bretylium tosylate, indicating that they are mediated via the sympathetic nervous system. 6. Evidence is presented that the lungs are a constant course of afferent impulses inhibiting the 'vasomotor centre', and that the lung inflationsystemic vasodilator reflex is a potential mechanism operating in eupnoeic breathing. M. DE BURGH DALY AND OTHERS

“…Stimulation of the carotid bodies causes slowing of the heart (Bernthal, Greene & Revzin, 1951;Daly & Scott, 1958;Downing, Remensnyder & Mitchell, 1962;MacLeod & Scott, 1964;Scott, 1966a, b) and systemic vasoconstriction (Bernthal, 1938;Daly & Scott, 1962;Daly & Ungar, 1966), whereas excitation of the aortic bodies elicits bradyeardia or tachycardia (Comroe & Mortimer, 1964) and vasoconstriction (Daly, Hazzledine & Howe, 1965;Daly & Ungar, 1966).…”

Section: Introductionmentioning

confidence: 99%

Cardiovascular responses in apnoeic asphyxia: role of arterial chemoreceptors and the modification of their effects by a pulmonary vagal inflation reflex

James¹,

Daly²

1969

Self Cite

134

SUMMARY1. In the spontaneously breathing anaesthetized dog, the systemic circulation was perfused at constant blood flow; there was no pulmonary blood flow and the systemic arterial blood Po. and PCO, were controlled independently by an extracorporeal isolated pump-perfused donor lung preparation. The carotid and aortic bodies were separately perfused at constant pressure with blood of the same composition as perfused the systemic circulation.2. Apnoeic asphyxia, produced by stopping the recipient animal's lung movements and, at the same time, making the blood perfusing the systemic circulation and the arterial chemoreceptors hypoxic and hypercapnic by reducing the ventilation of the isolated perfused donor lungs, caused an increase in systemic vascular resistance.3. While the systemic arterial blood was still hypoxic and hypercapnic, withdrawal of the carotid and aortic body 'drive' resulted in a striking reduction in systemic vascular resistance. Re-establishing the chemoreceptor 'drive' immediately increased the vascular resistance again.4. Apnoeic asphyxia carried out while the carotid and aortic bodies were continuously perfused with oxygenated blood of normal Pco, had little or no effect on systemic vascular resistance. 5. The systemic vasoconstrictor response produced by apnoeic asphyxia was reduced or abolished by re-establishing the recipient animal's lung movements, and this effect occurred in the absence of changes in the composition of the blood perfusing the systemic circulation and arterial chemoreceptors. This abolition of the vasoconstriction was due to a pulmonary reflex.6. Apnoeic asphyxia slowed the rate of the beating atria due to excita-