Estimating cardiac output from blood pressure and heart rate: the liljestrand & zander formula

Cardiac output (CO) is an important indicator of cardiovascular function. Several invasive and non-invasive methods have been developed and validated to assess CO in the clinical setting. These are often computationally complex or proprietarily-restricted, and thus, not feasible in ambulatory investigations and the laboratory research setting. Simple mathematical transforms have been proposed to estimate CO from pulse pressure (PP = mean systolic blood pressure (SBP) minus mean diastolic blood pressure (DBP)), and mean heart rate (HR). Recently we evaluated one such simple technique [CO=(PPxHR)x.002], and found moderate correlation between the CO estimate and Modelflow-derived CO. Here we aimed to evaluate a more sophisticated formula, proposed in 1940 by Liljestrand and Zander. CO was estimated (COEST) dividing PP by the sum of SBP and DBP and multiplying the product by HR. This index was correlated with the Modelflow (3 element Windkessel) -derived CO. Baseline beat-to-beat blood pressure data from 67 young (mean age = 19.94± 2.8), healthy men (n = 30) and women (n = 37) was available for analysis. Overall, the correlation of COEST and CO was moderate (r = .42, p <.0001) and stronger in men (r = .66, p < .0001) compared to women (r = .36, p < .05). These results suggest that at least in some situations the Liljestrand and Zander method may provide an adequate measure of CO when other methods are not available.