CARDIOVASCULAR Monitoring non-invasive cardiac output and stroke volume during experimental human hypovolaemia and resuscitation

Key points † Controlled application of lower body negative pressure simulated hypovolaemia and resuscitation in human subjects. † Thoracic electrical bioimpedance, and arterial blood pressure (ABP) analysis by the Long Time Interval method, were the most discriminatory measurements. † The Modelflow method of ABP analysis effectively tracked hypovolaemia, but underestimated resuscitation. † Pulse pressure tracked hypovolemia and resuscitation, but underestimated changes in stroke volume. Background. Multiple methods for non-invasive measurement of cardiac output (CO) and stroke volume (SV) exist. Their comparative capabilities are not clearly established. Methods. Healthy human subjects (n1⁄421) underwent central hypovolaemia through progressive lower body negative pressure (LBNP) until the onset of presyncope, followed by termination of LBNP, to simulate complete resuscitation. Measurement methods were electrical bioimpedance (EBI) of the thorax and three measurements of CO and SV derived from the arterial blood pressure (ABP) waveform: the Modelflow (MF) method, the long-time interval (LTI) method, and pulse pressure (PP). We computed areas under receiver-operating characteristic curves (ROC AUCs) for the investigational metrics, to determine how well they discriminated between every combination of LBNP levels.