Circulation during intermittent lung ventilation in the garter snake Thamnophis

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Abstract
Systemic and pulmonary arterial and ventricular blood pressures have been recorded in both lightly anaesthetized and unanaesthetized, unrestrained garter snakes of the genus Thamnophis. Systemic blood pressure was 65/44 cmH2O compared with only 52/21 cmH2O in the pulmonary circulation. Peak systolic pressures throughout the ventricle were identical and were the same as systemic systolic pressures. Reduction of pulmonary arterial blood pressure arose solely from an impedance to blood flow located in a narrow region of the pulmonary ventricular outflow tract. Atropine greatly reduced this impedance. No changes in the blood pressure relationships within the central arterial circulation were observed during intermittent, voluntary lung ventilation. It is concluded that the ventricle of the snake Thamnophis functions as a single pump which perfuses both the pulmonary and systemic circulations, with pulmonary and systemic arterial pressure differences arising from the impedance characteristics of the ventricular outflow tracts.

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