Cardiac compliance and dimensions in carbon monoxide-induced cardiomegaly

Adult male rats inhaled 500 ppm CO continuously for 38 to 47 days to produce significant cardiomegaly. In a first experiment in which heart wall stiffness was examined, haematocrit rose 45.1% and the ratio of the sum of right ventricle (RV) and left ventricle (LV) to body weight (mg X g-1) increased from 2.69 to 3.34. Compliance (ml X mmHg-1) of CO LV's and RV's studied from 0 to 25 mmHg intraluminal pressure, was generally greater than that of LV's and RV's from controls at the same pressure. These differences were greater for RV's. There was no difference between control RV's and LV's at the same distending pressure. The differences between treated and control groups disappeared when compliance was normalised per g heart weight. In a second experiment in which heart dimensions were examined, haematocrit ratio increased 48.6% and 2V (RV + LV) to body weight ratio (mg X g-1) increased from 2.77 to 3.45. Atrial weight was also greater. LV apex to base length increased 6.4% and LV outside diameter increased 7.3. No significant differences in LV, RV or interventricular septum (S) thickness resulted from CO exposure, as measured at three sites in each, in four cross-sections of the heart between the apex and base. In general, LV wall was slightly thicker than S, while RV was about 35% that of LV. The findings suggest that chronic carboxyhaemoglobinaemia produces largely eccentric cardiomegaly, and that there is no intrinsic change in wall stiffness.