Heart rate variability and stroke volume variability to detect central hypovolemia in spontaneously breathing, young, healthy volunteers

Variability in cardiac stroke volume (SVV) is used in clinical practice for diagnosis of hypovolemia, but currently limited to patients on mechanical ventilation. We investigated if SVV and heart rate variability (HRV) could detect central hypovolemia in spontaneously breathing humans. Ten subjects underwent simulated central hypovolemia by lower body negative pressure (LBNP). Heart rate, respiratory frequency and mean arterial blood pressure were measured. Stroke volume (SV) was estimated by ModelFlow (Finometer). Respiratory SVV was calculated by: 1) SVV%=(SVmax-SVmin)/SVmean during one respiratory cycle, 2) SVIntegral from the power spectra (Fourier transform) at 0.15-0.4 Hz and 3) SVV_norm=√(SVIntegral/SVmean). HRV was calculated by the same methods. SVV and HRV were reduced by all three methods during LBNP compared to during baseline. HRV% ≤ 11% and SVIntegral ≤ 12 ml² were best to detect central hypovolemia. We conclude preliminarily that HRV% and SVIntegral detect central hypovolemia and are good candidates for further clinical testing.