SUMMARY Cardiac output, plasma volume and regional hemodynamic factors involved in blood pressure regulation were investigated in hypertensive patients refractory to the combined treatment with diuretics, propranolol and hydralazine. The patients were compared to hypertensive patients, matched for sex, age, weight, glomerular filtration rate and initial untreated blood pressure, responding adequately to the corresponding therapy. Cardiac output was determined with the dye-dilution technique (indocyanine green) and plasma volume with Evans Blue. Blood flow and vascular resistance at rest and at maximal vasodilatation in a skin (hand) and a muscle (calf) vascular bed were determined using venous occlusion plethysmography and intra-arterial and auscultatory blood pressure recordings, respectively. Maximal vasodilatation was obtained by direct and indirect heating, arterial occlusion and hand muscle work (hand), or by arterial occlusion and muscle work (calf).
The refractory patients had increased total peripheral resistance in comparison with the responders, while cardiac output and plasma volume did not differ between the groups. This suggests that increased peripheral resistance is the important factor for sustained blood pressure elevation during the influence of the actual therapy. Furthermore, compared with the controls, the refractory patients had increased vascular resistance at maximal dilatation. This indicates a vascular abnormality in this group. Since the dilatation procedure abolishes smooth muscle tone in the resistance vessels almost completely, the vascular abnormality is interpreted as a structural change most likely, an adaptive thickening of the vessel wall associated with hypertension. The results indicate that this abnormality is more pronounced in the patients refractory to treatment.