Cardiac stroke volume variability measured non-invasively by three methods for detection of central hypovolemia in healthy humans

Hypovolemia decreases preload and cardiac stroke volume. Cardiac stroke volume (SV) and its variability (cardiac stroke volume variability, SVV) have been proposed as clinical tools for detection of acute hemorrhage. We compared three non-invasive SV measurements and investigated if respiration-induced fluctuations in SV may detect mild and moderate hypovolemia in spontaneously breathing humans. Ten healthy subjects underwent experimental central hypovolemia induced by lower body negative pressure to -60 mmHg or onset of presyncopal symptoms. SV beat-to-beat was estimated simultaneously by ultrasound Doppler, finger arterial blood pressure curve and impedance cardiography. SVV was calculated by spectral analysis between 0.15 and 0.40 Hz. Relative changes in SV did not show significant differences between the methods. The SVV measured by ultrasound Doppler and arterial blood pressure curve decreased at -30 mmHg to 32 % (ultrasound Doppler: 95 % CI 18-47, arterial blood pressure curve: 95 % CI 21-43) and at maximal simulated hypovolemia to 23 % (ultrasound Doppler: 95 % CI 14-81) and 21 % (arterial blood pressure curve: 95 % CI 9-33) of baseline variability. The variability in cardiac stroke volume from the impedance cardiography did not change significantly during the simulated hypovolemia, to 88 and 76 % of baseline variability. Cardiac stroke volume estimated by ultrasound Doppler and by arterial blood pressure curve showed parallel variations beat-to-beat during simulated hemorrhage, whereas impedance cardiography did not appear to track beat-to-beat changes in cardiac stroke volume. The variability in cardiac stroke volume was decreased during mild and moderate hypovolemia and could be used for early detection of hypovolemia.