Measurement of cardiac output by the thermodilution method in conscious spontaneously hypertensive rats

The usefulness of the thermodilution method for measuring cardiac output (CO) was evaluated in awake rats by comparison with electromagnetic flowmetry. CO was measured in 3- and 6-month-old conscious spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). The correlation co-efficient between CO obtained by the two methods was 0.66 (p less than 0.01). Although CO values obtained by the thermodilution technique tended to be overestimated in comparison with those determined by electromagnetic flowmetry, this method was shown to be useful for measuring CO in unanesthetized rats because of its technical simplicity. Left ventricular mass (LVM) and the ratio of CO to LVM were significantly greater in SHR than in WKY at both ages and CO/LVM increased with increasing age in SHR. The ratio of heart work (HW) to body weight (HW/BW) was increased only in 3-month-old SHR compared with WKY and there was no difference in HW/LVM in 3- and 6-month-old SHR compared with age-matched WKY. The present results suggest that the development of cardiac hypertrophy in SHR is an adaptation to the increased HW due to high afterload.