Reflex inotropic responses of the heart from lung inflation in anaesthetized dogs

In anaesthetized dogs a tracheal divider was inserted to allow inflation of one lung with various pressures. Left ventricular inotropic responses were assessed by measuring the maximum rate of change of left ventricular pressure (dP/dt max) using a preparation in which aortic pressure, carotid sinus pressure and heart rate were held constant.Heart responses to lung inflation were variable. In five dogs there was a consistent tachycardia, in three bradycardia and in six there was no change. In the dogs in which heart rate increased, inflation of one lung with pressures between 0.5 and 2.0 kPa (5 and 20 cm H₂O) resulted in no significant change in dP/dt max. In the remaining dogs there was a decrease in dP/dt max which was more pronounced at the higher inflation pressures. The negative inotropic response was shown to be a reflex with afferent nerve endings in the lung and with the efferent pathway in the sympathetic nerves.