Md. Daly et Jfx. Jones, RESPIRATORY MODULATION OF CAROTID AND AORTIC BODY REFLEX LEFT-VENTRICULAR INOTROPIC RESPONSES IN THE CAT, Journal of physiology, 509(3), 1998, pp. 895-907
1. The reflex changes in the inotropic state of the left ventricle, me
asured as the dP/dt(max) (maximum rate of change of pressure), occurri
ng in response to selective stimulation of the carotid and aortic body
chemoreceptors by sodium cyanide, were studied in the cat anaesthetiz
ed with a mixture of chloralose and urethane. 2. The animals were arti
ficially ventilated with an open pneumothorax. The beast rate and mean
arterial blood pressure were maintained constant. 3. With on-going ce
ntral respiratory activity, stimulation of the carotid bodies caused a
n increase in respiratory movements. Variable changes in left ventricu
lar dP/dt(max) occurred, the predominant response being an increase. T
he mean change was 8.3+/-2.9% from a control value of 6850 +/- 450 mmH
g s(-1). Stimulation of the aortic bodies resulted in a smaller increa
se in respiration or no effect, but a significant increase occurred in
left ventricular dP/dt(max) of 19.6 +/- 2.9% from a control value of
6136 +/- 228 mmHg s(-1). No significant changes in left ventricular en
d-diastolic pressure occurred in response to stimulation of either gro
up of chemoreceptors. 4. Tests of chemoreceptor stimulations were repe
ated during temporary suppression of the secondary respiratory mechani
sms: the central respiratory drive was suppressed reflexly by electric
al stimulation of the central cut ends of both superior laryngeal nerv
es and lung stretch afferent activity was minimized by stopping artifi
cial respiration. Carotid body stimulation again evoked variable respo
nses, the predominant now being a reduction in left ventricular dP/dt(
max) of 3.1% from a control value of 5720 +/- 320 mmHg s(-1), which wa
s significantly different to that occurring during on-going spontaneou
s respiration. Aortic body stimulation caused an increase in left vent
ricular dP/dt(max) similar to the response during on-going spontaneous
respiration. 5. The positive inotropic responses were mediated via th
e sympathetic nervous system, as indicated by their abolition as a res
ult of intravenous injections of the P-adrenoceptor blocking agent, pr
opranolol. 6. It is concluded that the carotid bodies exert a small va
riable effect on left ventricular dP/dt(max), the predominant positive
inotropic response being due to the concomitant neurogenic effects of
the increase in respiration. In contrast, the positive inotropic resp
onse to excitation of the aortic chemoreceptors is not respiratory mod
ulated.