The thermodilution technique in on‐line computation of the left ventricular volumes on anaesthetized dogs

Abstract

The thermal dilution technique and its suitability for automatic computation of left ventricular volumes were evaluated on 28 anaesthetized dogs. The end-diastolic volume (EDV) was computed from ventricular washout curves in two ways, first utilizing the ratio between the indicator amount and its peak concentration (first ejection method); and secondly the ratio between stroke volume and ejection fraction with the latter obtained by subtracting the residual fraction from 1.0. The residual fraction was determined as the mean of ratios between successive steps of four ventricular ejections on the downslope of the curve (downslope method). The linear correlation coefficient between the EDV determinations (n = 366) was 0.926, and slope y = 1.14 X + 0.5 ml with 4.6 ml as standard error of estimate. The first ejection method gave on average 15% higher EDV values than the downslope method. When heart rate was increased by pacing from 88 to 240/min, both methods showed a reduction of the EDV, but the downslope method to a greater degree. When afterload was increased but heart rate decreased by phenylephrine, the first ejection method but not the downslope method indicated an increase in EDV. Otherwise, when pronounced tachy- or bradycardia were avoided, ventricular volumes yielded by the two methods were comparable. Indicator injection did not substantially affect ventricular pressure dynamics. The first ejection method seems to be a simple means for repeated measurements of EDV even in the case of diseased hearts.

Mean outflow resistance as a marker of left ventricular afterload

“…Consequently, enddiastolic volume was obtained by dividing stroke volume by ejection fraction. The volumes were computed as the mean obtained from three successive aortic thermal dilution curves (8).…”

Effects on dogs of surface-induced hypothermia and rewarming on the right heart function and pulmonary circulation

“…The onset of mechanical systole of the ventricle was de®ned as the onset of the rise in systolic ventricular pressure. The onset of the rise in systolic pressure was determined according to an algorithm described by Jensch et al (1976) and further developed by Kettunen (1985). The algorithm was based on the computation of the slopes of the ventricular pressure curve.…”

“…If a given RR-interval was more than 20% shorter than the average RR-interval, the beat was regarded as premature and was excluded from the analysis as was the following beat. Cardiac output, left ventricular volumes and ejection fraction were computed as a mean obtained from three successive thermal dilution curves from the pulmonary artery by the method described by Ganz and Swan (1974) and modi®ed further by Kettunen (1985Kettunen ( , 1986. The stroke volume was obtained by dividing the cardiac output by the heart rate.…”