Continuous measurement of cardiac output with the use of stochastic system identification techniques

Abstract

The limitations of developing a technique to measure cardiac output continuously are given. Logical explanations are provided for the economic, technical, and physiologic benefits of a stochastic system identification technique for measuring cardiac output. Heat is supplied by a catheter-mounted filament driven according to a pseudorandom binary sequence. Volumetric fluid flow is derived by a cross-correlation algorithm written in the C language. In vitro validation is performed with water in a flow bench. The computed flow (y) compared with the in-line-measured flow (x) yields the linear regression y = 1.024x - 0.157 (r = 0.99). The average coefficient of variation is less than 2% over a volumetric fluid flow range of 2 to 10 L/min.

Continuous versus intermittent thermodilution cardiac output measurement during orthotopic liver transplantation

“…Possible reasons for the discrepancy are the averaging algorithm of continuous cardiac output measurement and the influence of baseline drift in pulmonary artery temperature indicated by specific and rapid changes in temperature difference, which run in parallel with the marked changes in bias after caval clamping and after reperfusion. Due to the signal processing algorithm, the displayed continuous cardiac output represents the mean of the measurements of the last 3-6 min [10]. If cardiac output decreases or increases suddenly, as occurs after caval clamping and reperfusion of the graft [1][2][3][18][19][20][21], continuous cardiac output measurements initiated within 6 min may reflect mixed data from before and after the event.…”

“…This incorporates a thermal filament located between 14 and 25 cm from the catheter tip. The filament is usually positioned in the right ventricle and transfers a safe level of heat [14] by generating a pseudorandom binary on-off sequence [10]. The filament input sequence and power and the distal thermistor response are cross-correlated and a modified StewartHamilton equation is used to determine cardiac output fully automatically (Vigilance, Baxter Healthcare Corp.).…”

“…Using the same catheter and equipment, it was possible to obtain intermittent cardiac output measurements by means of standard procedures and algorithms [9,10]. Intermittent cardiac output measurements were performed at end-expiration by manually injecting 10-ml boluses of cold saline solution through a closed delivery system (CO-Set, Baxter Healthcare Corp.).…”

“…The measurements are based on the thermodilution technique and in contrast to standard intermittent thermodilution cardiac output measurement, heat instead of cold is transferred to the blood using a thermal filament mounted on a pulmonary artery catheter. Continuous thermodilution cardiac output is computed automatically by the accompanying equipment without any need for calibration [10]. Under stable conditions, a good correlation and high levels of accuracy and precision have been found between continuous and intermittent cardiac output measurement [4,5,[7][8][9].…”

Cardiac output measurement in critically ill patients: comparison of continuous and conventional thermodilution techniques

“…The temperature alter-CAN J ANAESTH 1995 / 42: i ! /pp972- 6 ation is detected downstream in the pulmonary artery and cross-correlated with the input sequence to produce a thermodilution wash-out curve. Cardiac output is computed from a conservation of heat equation using the area under the curve.…”