Comparison of several pulse-pressure techniques for monitoring stroke volume

Values of stroke volume calculated from five different formulas utilising parameters derived from the aortic-pressure pulse waveform were compared with stroke-volume values calculated from the thoracic electrical-impedance waveform, which was recorded simultaneously with the aortic-pressure waveform. A total of 195 beats from three closed-chest anaesthetised dogs were compared. During the recording of the impedance and blood-pressure waveforms, the cardiac output was measured by dye and saline dilution. The mean of stroke-volume values from the impedance method was 39% greater than the mean ‘stroke volume’ calculated by dividing the dye cardiac-output value by the mean heartrate measured during the recording of the dye-dilution curve. The correlation between impedance and dye cardiac-output values was 0·879. The correlation of dye ‘stroke volume’ with values calculated by all four formulas was about 0·89. Individual stroke volumes could be markedly affected by variations in the beat-by-beat values of the total systemic resistance.