Regional vascular capacitance in rabbit one-kidney, one clip hypertension

One-kidney Goldblatt hypertensive rabbits (New Zealand White) were studied after durations of renal artery clipping that varied from 6 to 17 days. Measurements included arterial pressure (ABP), iliac venous pressure (IVP), left atrial pressure (LAP), cardiac output (CO) (by thermodilution), blood volume (BV), cardiopulmonary volume (CPV), and hindleg thermodilution volume (HLV). These were determined at steady-state as well as during acute blood volume expansion. In sham-clipped animals, ABP was 74 +/- 1 mm Hg. This increased to 92 +/- 3 mm Hg by 6 to 9 days post-clipping, to 96 +/- 3 mm Hg by 10 to 13 days, to 89 +/- 4 mm Hg by 14 to 17 days. CO remained near 150 ml/min . kg until Day 13 and fell to 127 +/- 8 ml/min . kg at 14 to 17 days because of a fall in heart rate. Blood volume and stroke volume did not change significantly from 62 +/- 1 ml/kg and 0.60 +/- 0.04 ml/kg, respectively. The development of hypertension was due entirely to changes in peripheral resistance. CPV was 8.5 ml/kg initially and increased significantly as hypertension developed. HLV did not change significantly from about 10 ml/kg. During acute blood volume expansion, hypertensive animals showed smaller transient increases in CO than did sham-clipped normotensives, but the associated blood pressure rise was greater. This reduced vasodilator capacity was accompanied by reduced distensibility of the cardiopulmonary bed. In sham-clipped animals, the cardiopulmonary pressure/volume slope was between 0.05 and 0.07 mm Hg per ml/kg. This increased to 0.44 mm Hg per ml/kg by 14--17 days of clipping. The corresponding value for the hindleg region did not change significantly from 0.2 mm Hg per ml/kg. Cardiac output and stroke volume were directly correlated with cardiopulmonary volume. The slope of this correlation decreased significantly during hypertension. The data suggest that decreased cardiopulmonary compliance in hypertension minimizes transient changes in cardiac output. This is especially important for arterial blood pressure control in view of the impaired vasodilator capacity of the hypertensive circulation.