Vascular compliance after nitroprusside in hypertension

The effect of sodium nitroprusside (NP) infusion on systemic arterial compliance in hypertensive subjects was assessed using pulse-contour analysis (PCA). Seven male patients aged 41 to 71 years (mean age 59 years) were studied after 30 minutes rest in the supine position and during continuous NP infusion. Proximal arterial compliance, C1, and distal arterial compliance, C2, were determined by analyzing the diastolic portion of a brachial artery pressure pulse and cardiac output (CO). During NP infusion, mean arterial pressure (MAP) decreased by 19% (p < 0.02), heart rate (HR) increased by 11% (p < 0.02), and CO decreased by 12%. Systemic vascular resistance (SVR) tended to decrease (6%), but this response was somewhat variable. Both C1 and C2 exhibited a significant increase, with C1 rising by 17% (p<0.10) and C2 rising by 326% (p<0.02). These data indicate that NP may be exerting its pressure-lowering effects both by dilating arterial vessels and by making them more compliant. Furthermore, it appears that both C1 and C2 are more sensitive indicators of changes in vascular functional state than SVR.