Cardiothoracic impedance does not reflect beat‐to‐beat changes in cardiac stroke volume during mild lower body negative pressure (707.1)

Abstract

Background: Variability in cardiac stroke volume (SVV) has been proposed as a clinical tool to assess the magnitude of acute hemorrhage. We investigated how three non‐invasive methods represent the beat‐to‐beat changes of cardiac stroke volume (SV).Methods: Ten healthy subjects underwent mild simulated hemorrhage through lower body negative pressure (LBNP) at ‐30 mmHg after a five minutes resting period at baseline. SV beat‐to‐beat was estimated simultaneously by three non‐invasive methods: Ultrasound Doppler (SV_usd), finger arterial blood pressure curve (SV_bpc) and cardiothoracic impedance (SV_imp). SVV was calculated at respiratory frequency between 0.15 and 0.40 Hz from spectral analysis. The median and 95% confidence intervals (CI) were calculated by Hodges‐Lehman’s estimates from epochs of 120 seconds at baseline and at ‐30 mmHg of LBNP. Statistical differences were calculated by Wilcoxon matched‐pairs signed rank test.Results: SVV_usd and SVV_bpc decreased at ‐30 mmHg LBNP to 32% (18%, 47%) and 32% (21%, 43%) of baseline variability. In contrast, SVV_imp was unchanged at ‐30 mmHg (88% (42%, 182%), p=0.82) relative to baseline.Conclusion: Cardiac stroke volume estimated by Ultrasound Doppler and finger arterial blood pressure curve reflect the same variations beat‐to‐beat during simulated hemorrhage. Cardiothoracic impedance does not reflect beat‐to‐beat changes in SV.Grant Funding Source: The Research Council of Norway