Key result
Varanid lizards show much shorter ventricular diastole than mammals at ~46% of cycle length.
Why the study?
The cardiac filling dynamics and venous return mechanisms in varanid lizards, characterized by a shorter ventricular diastole than mammals, were not well understood.
No immediate implications for human diastolic assessment; leaves open translational value of atrial-dominant filling in comparative models.
The duration of ventricular diastole relative to the cardiac cycle length is much shorter (46%) in varanids than in mammals (>70%). 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. 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. 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.
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Johansen et al. (1984) studied Healthy physiology (varanid lizards). Varanid lizards physiology vs. Mammals was evaluated on Duration of ventricular diastole relative to cardiac cycle length. The duration of ventricular diastole relative to cardiac cycle length is much shorter in varanid lizards (46%) than in mammals (>70%), with atrial contraction acting as the primary filling agent.
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