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Reflex responses from the main pulmonary artery and bifurcation in anaesthetised dogs

McMahon, N.C., Drinkhill, M.J., Myers, D.S. and Hainsworth, R. (2000) Reflex responses from the main pulmonary artery and bifurcation in anaesthetised dogs. Experimental Physiology, 85 (4). pp. 411-420. ISSN 0958-0670

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Abstract

This study was undertaken to determine the reflex cardiovascular and respiratory responses to discrete stimulation of pulmonary arterial baroreceptors using a preparation in which secondary modulation of responses from other reflexes was prevented. Dogs were anaesthetised with [alpha]-chloralose, artificially ventilated, the chests widely opened and a cardiopulmonary bypass established. The main pulmonary arterial trunk, bifurcation and extrapulmonary arteries as far as the first lobar arteries on each side were vascularly isolated and perfused through the left pulmonary artery and drained via the right artery through a Starling resistance which controlled pulmonary arterial pressure. Pressures distending systemic baroreceptors and reflexogenic regions in the heart were controlled.

Reflex vascular responses were assessed from changes in perfusion pressures to a vascularly isolated hind limb and to the remainder of the subdiaphragmatic systemic circulation, both of which were perfused at constant flows. Respiratory responses were assessed from recordings of efferent phrenic nerve activity. Increases in pulmonary arterial pressure consistently evoked increases in both perfusion pressures and in phrenic nerve activity. Both vascular and respiratory responses were obtained when pulmonary arterial pressure was increased to above about 30 mmHg. Responses increased at higher levels of pulmonary arterial pressures. In 13 dogs increases in pulmonary arterial pressure to 45 mmHg increased systemic perfusion pressure by 24 ± 7 mmHg (mean ± S.E.M.) from 162 ± 11 mmHg. Setting carotid sinus pressure at different levels did not influence the vascular response to changes in pulmonary arterial pressure. The presence of a negative intrathoracic pressure of -20 mmHg resulted in larger vascular responses being obtained at lower levels of pulmonary arterial pressure. This indicates that the reflex may be more effective in the intact closed-chest animal. These results demonstrate that stimulation of pulmonary arterial baroreceptors evokes a pressor reflex and augments respiratory drive. This reflex is likely to be elicited in circumstances where pulmonary arterial pressure increases and the negative excursions of intrathoracic pressure become greater. They are likely, therefore, to be involved in the cardio-respiratory response to exercise as well as in pathological states such as pulmonary hypertension or restrictive or obstructive lung disease.

Item Type: Article
Copyright, Publisher and Additional Information: © Cambridge University Press
Academic Units: The University of Leeds > Faculty of Medicine and Health (Leeds) > Leeds Institute of Genetics, Health and Therapeutics (LIGHT) > Academic Unit of Cardiovascular Medicine (Leeds)
The University of Leeds > Faculty of Medicine and Health (Leeds) > School of Medicine (Leeds) > Leeds Institute of Genetics, Health and Therapeutics (LIGHT) > Academic Unit of Cardiovascular Medicine (Leeds)
Depositing User: Repository Assistant
Date Deposited: 25 May 2006
Last Modified: 08 Feb 2013 17:02
Published Version: http://dx.doi.org/10.1017/S095806700001945X
Status: Published
Publisher: Cambridge University Press
Refereed: Yes
Identification Number: 10.1017/S095806700001945X
URI: http://eprints.whiterose.ac.uk/id/eprint/1233

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