Effect of glyceryl trinitrate on peripheral arteries alters left ventricular hydraulic load in man

Abstract

Effects of sublingual glyceryl trinitrate (GTN) were studied in ten patients without heart failure during diagnostic cardiac catheterisation following angiography. GTN caused substantial reduction in peak left ventricular and aortic pressure (19 mmHg) with lesser reduction in mean aortic pressure (9 mmHg) and no change in diastolic aortic pressure. Reduction in stroke volume (by 15%), associated with fall in left ventricular end diastolic pressure (by 4 mmHg) was insufficient to explain the marked (17 mmHg - 34%) reduction in pulse pressure. Decrease in pulse pressure was associated with loss of the late systolic peak on both the aortic and left ventricular pressure wave. This peak is caused by pulse wave reflection. GTN caused no change in peripheral resistance or in indices of aortic compliance (characteristic impedance, total arterial compliance) but was associated with reduction in fluctuations of both modulus and phase of aortic impedance. All these changes in pressure waves and in impedance spectra are explicable on the basis of decreased peripheral wave reflection. This can be attributed to the known vasodilatory effect of GTN on the peripheral arteries. Simulation of arterial vasodilatation in a multi-branched model of the systemic arterial system confirmed this interpretation. Dilatation of peripheral arteries explains in part the beneficial effects of GTN in adult man.

Assessment of aortic stiffness by local and regional methods

“…Both effects would contribute to reducing the propagative properties of arterial wave velocities in the aorta. 37,38 In our model, the AoStiff index is a variable integrating two components: the local resistance of the aorta to the flow (that is, the turbulences and the mean shear stress) and the distensibility of the aortic wall, which could vary independently. With GTN administration, both components may counterbalance each other, leading to an apparently unchanged AoStiff.…”

Arterial dilation and reduced wave reflection. Benefit of dilevalol in hypertension.

“…Vasoconstriction has little effect on wave reflection from the peripheral vascular bed, probably because wave reflection is already high under control circumstances as a result of high resting arteriolar tone, whereas vasodilation causes profound reduction in wave reflection. Effects of vasodilation on ascending aortic pressure wave contour have been studied by Takazawa, 22 Yaginuma et al, 25 and Fitchett et al 29 All have shown marked reduction in the amplitude of the late systolic pressure peak in the ascending aorta of human adults with nitroglycerin. Yaginuma et al 25 and Fitchett et al 29 have measured ascending aortic impedance as well and have confirmed that this change in pressure was attributable to reduction of wave reflection from peripheral sites.…”

“…Effects of vasodilation on ascending aortic pressure wave contour have been studied by Takazawa, 22 Yaginuma et al, 25 and Fitchett et al 29 All have shown marked reduction in the amplitude of the late systolic pressure peak in the ascending aorta of human adults with nitroglycerin. Yaginuma et al 25 and Fitchett et al 29 have measured ascending aortic impedance as well and have confirmed that this change in pressure was attributable to reduction of wave reflection from peripheral sites. This has recently been confirmed in dogs by Latson et al 30 Because the effect of nitroglycerin was seen without reduction in peripheral resistance, all investigators attributed this phenomenon to dilation of small conduit arteries.…”

Editorial Commentary

“…3,13 For example, nitroglycerin administration produces marked changes in the pressure pulse waveshape, which can be dissociated from a change in total peripheral resistance or the pulse transit time measured by aortic pulse wave velocity. 14,15 The effects are explained by changes in the mechanical properties of peripheral muscular arteries that result in improved impedance matching and attenuation of wave reflection in response to nitroglycerin. Direct ultrasonic techniques employed to assess local wall properties of peripheral muscular arteries indicate that arterial compliance (a property that depends on arterial geometry and intrinsic vessel wall properties) improves consistently, whereas distensibility (an intrinsic property of the arterial wall materials) does not necessarily change in response to nitroglycerin administration.…”