A minimally invasive monitoring system of cardiac output using aortic flow velocity and peripheral arterial pressure profile

摘要

BACKGROUND:: In managing patients with unstable hemodynamics, monitoring cardiac output (CO) can provide critical diagnostic data. However, conventional CO measurements are invasive, intermittent, and/or inaccurate. The purpose of this study was to validate our newly developed CO monitoring system. METHODS:: This system automatically determines peak velocity of the ascending aortic flow using continuous-wave Doppler transthoracic echocardiography and estimates cardiac ejection time and aortic cross-sectional area using the pulse contour of the radial arterial pressure. These parameters are continuously processed to estimate CO (COest). In 10 anesthetized closed-chest dogs instrumented with an aortic flowprobe to measure reference CO (COref), hemodynamic conditions were varied over wide ranges by infusing cardiovascular drugs or by random atrial pacing. Under each condition, COref and COest were determined. Absolute changes of COref (ΔCOref) and COest (ΔCOest), and relative changes of COref (%ΔCOref) and COest (%ΔCOest) from the corresponding baseline values were determined in each animal. We calibrated COest against COref to obtain proportionally scaled COest (COest). RESULTS:: A total of 1335 datasets of COref and COest were obtained, in which COref ranged from 0.17 to 5.34 L/min. Bland-Altman analysis between COref and COest indicated that the limits of agreement (the bias ± 1.96 × SD of the difference) and the percentage error (1.96 × [SD of the difference]/[mean CO] × 100) were from -1.01 to 1.13 L/min (95% confidence interval, -1.76 to 1.88 L/min) and 43%, respectively. The agreement between COref and COest was improved, with limits of agreement from -0.53 to 0.49 L/min (95% confidence interval, -0.62 to 0.59 L/min) and the percentage error of 20%. Polar plot analysis between ΔCOref and ΔCOest indicated that mean ± 1.96 × SD of polar angle was -2 ± 22 . Four quadrant plot analysis indicated that %ΔCOest correlated tightly with %ΔCOref (R = 0.93). The %ΔCOest and %ΔCOref changed in the same direction in 95% of the datasets. Reliability of this system was well preserved under conditions of random atrial pacing and also in a continuous manner. CONCLUSION:: Over a wide range of hemodynamic conditions, irrespective of cardiac beat irregularity, this system may allow minimally invasive monitoring of CO with a good trending ability. The present results warrant further research and development of this system for future clinical application.