A method for continuous on-line monitoring of systemic vascular resistance (COMS) after open heart procedures

A new method for continuous on-line measurement (COMS) of systemic vascular resistance (SVR) utilizing simple computer analysis of the peripheral arterial waveform is presented. The fundamental equation of this method is: (Formula: see text) where SVR is systemic vascular resistance, dP/dt is the peak dP/dt of the peripheral arterial waveform, and P' is the pressure at the time of peak dP/dt. F and a are calibration constants determined by taking simultaneous measurements by an independent method (thermodilution) before (low SVR) and immediately after (high SVR) aortocoronary bypass operations. In 22 patients 255 COMS of SVR readings were recorded simultaneously with thermodilution cardiac output measurements. Patients were exposed to situations such as temperature changes, volume load, blood loss, and the effect of drugs such as various catecholamines, nitroglycerin, and nitroprusside. Linear regression analysis was performed to compare the SVR calculated from thermodilution with the COMS-SVR measurements. SVR values ranged from 450 to 4400 dynes/sec/-5 and correlation between COMS and thermodilution was r = 0.98. Correlation coefficients of individual patients ranged from r = 0.9 to r = 0.986. We found COMS SVR measurements accurate, reliable, and extremely helpful in the management of hemodynamically unstable patients.