Estimation of Cardiac Output in Insect Hearts Paced at Different Rates

Insects have been often used as experimental animal models because of their considerable genetic homology with humans, short lifespan and low-cost maintenance. This study aims to estimate hemodynamic parameters (both systolic and the cardiac output) in response to increase in heart rate in the perfused in situ cardiac tube of the mealworm beetle Tenebrio molitor using a software developed in our laboratory, in which the heart is modeled as a prolate spheroid. A negative relationship between rate and the systolic parameters (e.g., stroke volume and ejection fraction) was observed, but the cardiac output was not statistically affected by heart rate. Considering that the end-diastolic volume was not significantly changed by rate, the negative staircase cannot be attributed mostly to the heterometric (Frank-Starling) regulation of cardiac systolic force.