Evaluation of a simple estimation method for the derivation of cardiac output from arterial blood pressure and heart rate.

Cardiac Output (CO) is an important hemodynamic index of blood flow from and to the heart. Numerous estimation methods have been developed and validated for obtaining CO in clinical applications; however, the invasive nature of these may preclude their utility in less controlled settings. Additionally, several of the available non-invasive applications feature algorithms which are computationally complex or proprietarily-restricted and may not be feasible in all research contexts, such as ambulatory investigations. Among the many simple mathematical transforms purported to estimate CO, a common approach has been to multiply the stroke volume (SV) by the heart rate (HR), where stroke volume is obtained by multiplying the pulse pressure (PP) by a constant value (k). Contemporary interpretations have identified k = 2 as the ideal multiplier; however there is some controversy regarding the origin of this factor as well as the reliability of the resulting estimate. In the present study we evaluated this simple technique using baseline beat-to-beat blood pressure data from 67 young (mean age = 20.04 ± 2.8 years), healthy men (n = 30) and women (n = 37). Using Modelflow-derived CO as a reference, estimated CO (COest) was calculated from the mean Systolic and Diastolic blood pressures and the heart rate. Overall, the correlation between CO & COest was moderate (r = .60, p <.001). This association was stronger in men (r = .70, p <.001) compared to women (r = .54, p <.001). Bland-Altman analysis confirmed this pattern as 97% of cases for men fell within the limits of agreement. Overall, our results indicate that under resting conditions this derivation is comparable to the Modelflow estimate and seemingly more consistent in men compared to women.