Effect of nitroglycerin on aortic impedance, diameter, and pulse-wave velocity.

Abstract

The effects of an intravenous infusion of 1 |xg/kg/min nitroglycerin were studied on systemic arterial properties in nine acutely instrumented dogs. Aortic impedance and pulse-wave velocity were calculated from measured pressure and flow signals collected during random ventricular pacing. Central aortic diameter was simultaneously determined with ultrasonic dimension crystals. Mean blood pressure was maintained constant to avoid the confounding effects of passive, pressure-induced changes in vascular properties. Nitroglycerin both reduced the amplitude of peripheral vascular reflections and delayed the return of these reflections to the aortic root. This reflection delay was manifested as a consistent leftward shift in both impedance modulus and phase. The magnitude of this reflection delay could not be entirely accounted for on the basis of the measured changes in average pulse-wave velocity along the aorta. ; 2) increased arterial compliance, as determined by both the rate of aortic diastolic pressure decay and pressure-diameter relations in peripheral arteries 6 ; and 3) decreased magnitude of arterial pulse-wave reflections. -3This study used an acute canine preparation to further define the effects of nitroglycerin on systemic arterial properties. We measured the effects of intravenous nitroglycerin on aortic impedance, diameter, and pulse-wave velocity (PWV). The use of spectral analysis techniques, in conjunction with random cardiac pacing, allowed us to determine the impedance spectrum with a frequency resolution as small as 0.1 Hz. Our results indicate that nitroglycerin has significant effects on both the magnitude and timing of peripheral vascular reflections. Materials and Methods In Vivo MethodsNine mongrel dogs (body weight 17-23 kg) were anesthetized with a combination of pentobarbital and fentanyl (initial dose: 12 mg/kg pentobarbital and 50 u.g/kg fentanyl; subsequent infusion: 1.1 mg/kg/hr and 15 u,g/kg/hr, respectively). Instrumentation in all dogs included a nonconstricting ultrasonic flow probe (model T-101, Transonic Systems, Ithaca, New York) in the ascending aorta, a Millar pressure catheter (Houston, Texas) in the ascending aorta, inserted through the right common carotid artery, and a central venous pressure catheter passed through the femoral vein. The Millar catheter was positioned at the same level as the aortic flow probe by palpating the catheter tip within the aorta. Additional instrumentation in seven dogs included a second Millar catheter in the femoral artery, inserted and attached with a nonocclusive purse-string suture, and a pair of ultrasonic crystals on the aortic arch (5-HHz crystals connected to a sonomicrometer; model 401, Schuessler, Cardiff by the Sea, California). These ultrasonic crystals, used to measure aortic diameter, were attached to opposing sides of the aortic adventitia with either fine sutures (tied to a flexible woven backing sheet) and/or a small amount of cyanoacrylate glue.7 Permanent atrioventricular block was produced in all dogs by injection of 40% ...

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

“…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. 25 -30 We have observed similar effects with nitroglycerin on the contour of the aortic 25 -31 and the carotid 27 arterial pressure wave, with the drug causing marked reduction in the amplitude of the late systolic pressure peak.…”

Assessment of aortic stiffness by local and regional methods

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