Baroreflex response and vasodilating drugs in essential hypertension

Blood pressure, heart rate, and arterial diameter of the brachial artery were studied in patients with sustained essential hypertension before and after administration of three vasodilating drugs: dihydralazine, diltiazem, and dinitrate isosorbide (ISDN). The diameter of the brachial artery was measured using a pulsed Doppler device, enabling the angle between the ultrasound beam and the vessel axis to be evaluated with a precision inferior to 2 percent. The three drugs had similar effects in decreasing the blood pressure and the forearm vascular resistance. Dihydralazine reduced the arterial diameter (p less than 0.001) and increased heart rate. Diltiazem and ISDN increased markedly the arterial diameter (p less than 0.001) but did not change heart rate. Dihydralazine decreased the tangential tension of the arterial wall, while diltiazem and ISDN did not. The study provided evidence that, with vasodilating drugs, the changes in the caliber of peripheral large arteries, which are a determinant of wall arterial tension, can influence the baroreflex-mediated tachycardia caused by use of the drugs.