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Journal of Experimental Biology 113,389-399 (1984)
Published by Company of Biologists 1984

Venous Return and Cardiac Filling in Varanid Lizards

KJELL JOHANSEN ¹ and WARREN W. BURGGREN ²

¹ Department of Zoophysiology, University of Aarhus, DK-8000 Aarhus C, Denmark
² Department of Zoology, University of Massachusetts, Amherst, MA 01003, U.S.A.

1. The duration of ventricular diastole relative to the cardiac cycle length is much shorter (46%) in varanids than in mammals (>70%).

2. Atrial systolic pressures were high (15-20 cmH₂O), and atrial contraction was apparent in pressure waveforms from the ventricular cavum arteriosum and cavum pulmonale. Atrial contraction coincides with the short period of ventricular diastole and represents the filling agent for the ventricular cava.

3. Increased central venous flow coincides with ventricular contraction, which by reducing the intrapericardial pressure will promote the expansion and filling of the atria and central veins, implying a suctional element of cardiac filling.

4. Inspiration during spontaneous breathing will reduce central venous pressure, steepen the pressure gradient towards the heart and aid flow towards central veins. There is a positive correlation between the systolic level of central venous pressure and cardiac cycle duration.

Key words: Cardiac filling, venous return, reptiles

Accepted on May 11, 1984

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