Adaptation of a mouse Doppler echocardiograph system for assessing cardiac function and thermal performance in a juvenile salmonid

Abstract

Measures of cardiac performance are pertinent to the study of thermal physiology and exercise in teleosts, particularly as they pertain to migration success. Increased heart rate, stroke volume and cardiac output have previously been linked to improved swimming performance and increased upper thermal tolerance in anadromous salmonids. To assess thermal performance in fishes, it has become commonplace to measure the response of maximum heart rate to warming using electrocardiograms. However, electrocardiograms do not provide insight into the hemodynamic characteristics of heart function that can impact whole-animal performance. Doppler echocardiography is a popular tool used to examine live animal processes, including real-time cardiac function. This method allows for nonsurgical measurements of blood flow velocity through the heart and has been used to detect abnormalities in cardiovascular function, particularly in mammals. Here, we show how a mouse Doppler echocardiograph system can be adapted for use in a juvenile salmonid over a range of temperatures and timeframes. Using this compact, noninvasive system, we measured maximum heart rate, atrioventricular (AV) blood flow velocity, the early flow-atrial flow ratio and stroke distance in juvenile Atlantic salmon (Salmo salar) during acute warming. Using histologically determined measures of AV valve area, we show how stroke distance measurements obtained with this system can be used to calculate ventricular inflow volume and approximate cardiac output. Further, we show how this Doppler system can be used to determine cardiorespiratory thresholds for thermal performance, which are increasingly being used to predict the consequences that warming water temperatures will have on migratory fishes.

Cardiac hemodynamics and ventricular stiffness of sea-run cherry salmon (Oncorhynchus masou masou) differ critically from those of landlocked masu salmon

“…In comparison, the lower heart rate cherry salmon had longer ventricular diastole, and the event of ventricular filling of blood occurred before atrial contraction began; however, no biphasic inflow waveform was observed in masu salmon, even though the time duration from ventricular ejection to the onset of atrioventricular inflow increased. However, since juvenile Atlantic salmon of 15 g body weight showed biphasic waveforms [95], it is possible that our data of pulsed-wave Doppler echocardiography are O. masou -specific. Elastic reaction forces, muscle contraction, and differences in chamber size between the atria and ventricles have been considered as candidates for the driving forces of ventricular filling, but they have not been sufficiently understood yet [96, 97].…”

Proteomic analysis of temperature-dependent developmental plasticity within the ventricle of juvenile Atlantic salmon (Salmo salar)

“…We determined cardiorespiratory thresholds for thermal performance in the two developmental treatments by measuring the response of pharmacologically stimulated maximum heart rate ( f Hmax ) to acute warming using noninvasive Doppler echocardiography in anaesthetized juveniles, according to Muir et al (2021b) . In these thermal performance trials, temperature was increased at a rate of 10°C h −1 until the onset of cardiac arrythmias, starting from the fish's respective rearing temperatures (11°C for +0-fish and 15°C for +4-fish; Muir et al, 2021a ).…”

Cardiac hemodynamics and ventricular stiffness of sea-run cherry salmon (Oncorhynchus masou masou) differ critically from those of landlocked masu salmon

“…No biphasic inflow waveform was observed, in masu salmon, even though the time duration from ventricular ejection to the onset of atrioventricular inflow increased. Further, since juvenile Atlantic salmon of 15 g body weight showed biphasic waveforms [87], it is possible that our data derived from pulsed-wave Doppler echocardiography are species specific. Elastic reaction forces, muscle contraction, and differences in chamber size between the atria and ventricles have been considered as candidates for the driving forces of ventricular filling, but are not yet sufficiently understood [88,89].…”