Circulatory pressure-volume relationship and cardiac output in DOCA-salt rats

We studied the total vascular pressure-volume relationship and cardiac output (CO) in conscious rats receiving DOCA-salt or sham treatment. The mean circulatory filling pressure (MCFP) was measured by briefly inflation an indwelling balloon in the right atrium, and the MCFP-blood volume (BV) relationship over +/- 10% of BV was determined by rapid blood infusion or withdrawal. CO was measured in separate experiments using Fick's principle. Arterial pressure-volume relationship was also determined in additional experiments on anesthetized rats. Compared with sham rats, the mean arterial pressure was unchanged at 1 week, increased at 2 weeks, and increased further thereafter in the DOCA-salt rats. The BV was unchanged at 1 week, expanded at 2 weeks, unchanged at 5 weeks, and contracted at 8 weeks. There were no significant changes in MCFP, total vascular compliance (the inverse of the slope), nor unstressed volume (extrapolated volume axis intercept) at 2, 5, and 8 weeks. Total vascular capacity, assessed as BV at MCFP of 7.6 mm Hg, increased at 2 weeks, was unchanged at 5 weeks, and decreased at 8 weeks. Arterial compliance decreased at 5 and 8 weeks. CO remained unaltered at 1, 2, 5, and 8 weeks. These results suggest that the altered total vascular capacity may serve to maintain a normal CO against a rising afterload in the conscious DOCA-salt hypertensive rats, and that the decreased total vascular capacity may be a secondary hemodynamic feature with progression of hypertension.