An on-line computer system for monitoring respiratory and cardiac functions of patients

A computer-based noninvasive and continuous patient monitoring system for breath-by-breath assessment of cardiorespiratory functions was developed. Transthoracic impedance changes caused by respiratory and cardiac activities were measured with separate impedance plethysmographs of different frequencies. A mini-computer system calculated on-line eight respiratory parameters (VT, f, VE, PETO2, PETCO2, VO2, VCO2, and R) in cooperation with expired gas analysis data from a mass-spectrometer, and three cardiac parameters (SV, HR and Q). These parameters were displayed simultaneously at the end of each breath. In order to improve the signal-to-noise ratio of the impedance cardiogram to a level allowing computer determination, an ensemble averaging technique was utilized. The computer-derived cardiorespiratory parameters obtained during voluntary hyperventilation and a passive tilt demonstrated reasonable changes.