RESPONSES OF INTERNAL MAMMARY ARTERY GRAFT FLOW TO NITROPRUSSIDE - A DUPLEX-DOPPLER STUDY IN HYPERTENSIVE HEARTS

Objective To assess the response of internal mammary artery (IMA) flow of hypertensive hearts to nitroprusside infusion. Methods Fifteen pat ients were studied with a high-frequency duplex Doppler probe from the supraclavicolar approach. All the patients had undergone coronary art ery bypass surgery with an IMA graft into the left anterior descending artery. The investigated patients were normotensives (controls, n = 5 ) and hypertensive with a normal (group 1, n = 5) or a hypertrophic (g roup 2, n = 5) left ventricle. Values of the left ventricular mass ind ex were 102 +/- 11 g/m(2) in controls, 115 +/- 18 g/m(2) in group 1 an d 153 +/- 8 g/m(2) in group 2. The IMA flow volume was studied at base line and continuously during nitroprusside infusion. The arterial bloo d pressure was measured each minute by a cuff sphygmomanometer. In eac h patient we considered the peak flow volume (percentage increment fro m baseline) and the flow volume at the end point (the lowest tolerated diastolic blood pressure). Results Nitroprusside infusion induced a c omparable flow-volume increment in controls (38 +/- 27%) and in group 1 (24 +/- 11%). Conversely, the flow-volume increment was trivial in g roup 2 (6 +/- 6%). At the end point, the flow volume was similar to th e baseline value in controls (with diastolic blood pressure 67 +/- 9 m mHg) and in group 1 (diastolic blood pressure 61 +/- 4 mmHg), whereas the flow volume declined significantly from baseline (by 23%) in group 2 at a perfusion pressure of 79 +/- 9 mmHg. Conclusion Hypertensive p atients with a normal left ventricular mass exhibit a coronary Row beh aviour similar to that of normotensives in response to a nitroprusside infusion. Conversely, hypertrophic hypertensives show a blunted nitro prusside-induced coronary vasodilator response and are much more vulne rable to coronary flow reductions in the face of hypotension. This dyn amic assessment of flow patterns can be obtained non-invasively by dup lex Doppler monitoring of IMA graft flow.