Total vascular pressure-volume relationship in conscious rats with chronic heart failure

To define the changes in the venous circulation in chronic left ventricular (LV) failure, we measured the mean circulatory filling pressure (MCFP), blood volume, and effective vascular compliance in conscious rats with heart failure, 3 wk after coronary ligation. Rats with myocardial infarction and LV end-diastolic pressure (EDP) > 15 mmHg were considered to have chronic heart failure. Rats with chronic heart failure (n = 11) showed an increase (P < 0.001) in LV EDP to 24 ± 2 mmHg compared with 6 ± 1 mmHg in sham-operated (n = 9) and 7 ± 1 mmHg in normal (n = 6) rats. In the rats with chronic heart failure the MCFP was increased to 9.9 ± 0.2 mmHg (P < 0.001) compared with 7.6 ± 0.2 mmHg in the sham-operated and 7.7 ± 0.2 mmHg in the normal rats. Effective vascular compliance was determined from MCFP-blood volume curves. In rats with chronic heart failure, the effective vascular compliance was decreased to 2.40 ± 0.08 ml · mmHg^-1 · kg^-1 from 3.34 ± 0.16 in sham-operated rats and 3.35 ± 0.22 ml · mmHg^-1 · kg^-1 in normal rats. The blood volume and the unstressed vascular volume of the rats with chronic heart failure were not statistically different from the sham-operated rats. These results suggest that venous capacitance is decreased in chronic heart failure, due to a decrease in effective vascular compliance with no significant change in unstressed vascular volume. Hexamethonium chloride did not alter the effective vascular compliance of the rats with heart failure. The etiology of these changes remains to be determined, although cardiovascular reflexes inhibited with ganglionic blockade did not appear to play an important role.