Cardiac output and muscle blood flow during rest-associated apneas of elephant seals

In order to evaluate hemodynamics and blood flow during rest-associated apnea in young elephant seals (Mirounga angustirostris), cardiac outputs (CO, thermodilution), heart rates (HR), and muscle blood flow (MBF, laser Doppler flowmetry) were measured. Mean apneic COs and HRs of three seals were 46% and 39% less than eupneic values, respectively (2.1 ± 0.3 vs. 4.0 ± 0.1 mL kg− 1 s− 1, and 54 ± 6 vs. 89 ± 14 beats min− 1). The mean apneic stroke volume (SV) was not significantly different from the eupneic value (2.3 ± 0.2 vs. 2.7 ± 0.5 mL kg− 1). Mean apneic MBF of three seals was 51% of the eupneic value. The decline in MBF during apnea was gradual, and variable in both rate and magnitude. In contrast to values previously documented in seals during forced submersions (FS), CO and SV during rest-associated apneas were maintained at levels characteristic of previously published values in similarly-sized terrestrial mammals at rest. Apneic COs of such magnitude and incomplete muscle ischemia during the apnea suggest that (1) most organs are not ischemic during rest-associated apneas, (2) the blood O2 depletion rate is greater during rest-associated apneas than during FS, and (3) the blood O2 store is not completely isolated from muscle during rest-associated apneas.