Central cardiovascular responses to submersion asphyxia in the duck

Abstract

Pressure recordings from the central systemic veins, the aorta, the left ventricle, as well as intratracheal pressure, have been obtained during simulated dives of domestic ducks. Upon submersion a conspicuous bradycardia gradually developed. The systemic arterial pressure did not change significantly during the profound bradycardia. There was a distinct increase in the central venous pressure and in the diastolic pressure of the left ventricle. The pressure increase surpassed a concomitant intratracheal pressure rise. The circulation time from the right atrium to the base of the aorta was prolonged four to five times during profound bradycardia. The data suggest that the stroke volume remains unchanged or decreases in spite of an increased filling pressure. The increased transit time through the lungs is suggestive of an increased resistance to flow in the pulmonary bed. The data also indicate an increased resistance to outflow from the larger systemic arteries. It is suggested that a marked change in the activity of the autonomic innervation to the myocardium takes place during submersion.