COTTER, P.A.*; EVERSON, J.J.; RODNICK, K.J.: What comes in must go out:Ventricular blood flow patterns in the Rainbow Trout

Hemodynamic parameters in fish are often measured using invasive techniques, limiting the use of repeated measure experimental designs. We used high-resolution (10 MHz) echocardiography, and doppler analysis of sagittal images to determine ventricular filling (diastolic) and emptying (systolic) patterns in 3 body-size categories (400-500g, 600-800g, >1kg, n = 2/category) in hatchery-reared, anesthetized, Rainbow Trout (Oncorhynchus mykiss) at 14oC. Doppler analysis allows determination of both velocity (cm/s) and duration of blood flow (s) through atrioventricular and ventriculobulbar valves. Subtracting end-systolic from end-diastolic volume yielded stroke volume. We calculated flow (ml/s) through valves using stroke volume and diastolic/systolic time. Duration of ventricular systole (mean = 0.41s, SD = 0.07) was independent of body mass and approximately 2x that of diastole in all individuals. Flow (range = 0.9 – 4.2 ml/s) and blood velocity (range = 67.7 – 120 cm/s) of ventricular systole were approximately 50% that observed in diastole. In summary, despite size-dependent changes in stroke volume (range = 0.27 – 1.47 ml), the duration of systole and diastole, and heart rate remain relatively constant, suggesting compensatory mechanisms are involved in increasing cardiac output with increasing ventricle size. Electrocardiographic (ECG) data collected concurrently with echocardiographic/doppler imaging will help decipher the relative contribution of both atrial contraction and ventricular relaxation in cardiac blood flow patterns in the growing trout heart.