Cardiac output estimated from an arterial blood pressure waveform by the “long‐time interval” algorithm is a superior predictor of lower‐body negative pressure level

Abstract

We evaluated how several algorithms for cardiac output (CO) estimation from the arterial blood pressure waveform (ABP) predict lower body negative pressure levels in healthy human subjects. In the past century, over a dozen techniques have been developed to estimate CO, a cardinal cardiovascular parameter, from an ABP. A source of error is the superposition of antegrade ABP components (which drive flow forwards) with retrograde components (which retard flow). The "Long-time Interval (LTI)" algorithm has been recently proposed, which avoids this potential error. The LTI algorithm may have utility in detecting and quantifying circulatory abnormalities. Healthy human subjects were subjected to lower body negative pressure (LBNP) in five minute steps which increased from baseline to a maximum of -70 mmHg (or until the subjects became symptomatic). Non-invasive peripheral ABP was recorded using a Finometer. We applied three CO estimators to the recorded ABP data: the LTI method; the pulse-pressure / heart rate product; and the mean arterial pressure. Only the LTI method could predict LBNP changes. By avoiding the confounding effects of retrograde reflected waves in the ABP, the LTI method may provide superior non-invasive circulatory monitoring.