Effects of sublingual nitroglycerin on working conditions of the heart and arterial system: analysis using wave intensity

Abstract

The effects of nitroglycerin (NTG) on the vascular system are well known. However, the effects of NTG on the heart are still obscure, because these effects are modified by those on the vascular system, and vice versa. Therefore, to evaluate the hemodynamic effects of NTG, it is important to understand the interaction between the heart and the vascular system. Wave intensity (WI) is a new hemodynamic index that provides information about working conditions of the heart interacting with the arterial system. The purpose of this study was to evaluate the interactive effects of NTG on the cardiovascular system in normal subjects using wave intensity. We simultaneously measured carotid arterial blood flow velocity and diameter change using a specially designed ultrasonic system, and calculated the WI and the stiffness parameter β. Measurements were made in 13 normal subjects (9 men and 4 women, aged 47 ± 10 years) in the supine position before and after sublingual NTG. The maximum value of WI (W 1) and the mid-systolic expansion wave (X) increased (W 1 from 9.1 ± 4.3 to 12.3 ± 5.5 × 10(3) mmHg m/s(3), P < 0.001; X from 105 ± 185 to 345 ± 370 mmHg m/s(3), P < 0.05). β increased (from 10.5 ± 3.8 to 14.1 ± 3.8, P < 0.001). The pressure contours changed considerably. NTG increased W 1 and the mid-systolic expansion wave, which suggests enhanced cardiac power during the initial ejection and mid-systolic unloading. These results are new findings about the effects of NTG that can be added to the widely known late systolic unloading and preload reduction. NTG also increased arterial stiffness, which reduces the Windkessel function. By using an echo-Doppler system, WI can be obtained noninvasively. WI has the clinical potential to provide quantitative and detailed information about working conditions of the heart interacting with the arterial system.