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Sublingual nitroglycerin delays arterial wave reflections despite increased aortic "stiffness" in patients with
J Soma1, B A Angelsen, D Techn
1Department of Medicine, Section of Cardiology, University Hospital of Trondheim, Norway. johannes.soma@medisin.ntnu.no
Insights
Sublingual nitroglycerin delays arterial wave reflections and increases aortic impedance in hypertensive patients. This suggests peripheral arterial dilation counteracts some hemodynamic effects.
Area of Science:
- Cardiovascular Physiology
- Pharmacology
Background:
- Nitroglycerin's venodilating effects are known to benefit heart conditions.
- Its impact on arterial pulsatile hemodynamics in hypertension requires further definition.
Purpose of the Study:
- To investigate the effects of sublingual nitroglycerin on arterial hemodynamics in patients with sustained hypertension.
Main Methods:
- Doppler echocardiography and subclavian artery pulse tracing were used.
- Aortic characteristic impedance and wave reflection were calculated.
- Windkessel models estimated arterial bed parameters.
Main Results:
- Nitroglycerin delayed arterial wave reflections by 17% and increased aortic characteristic impedance by 20%.
- Mean arterial pressure decreased 7%, but pulse pressure remained unchanged.
- Stroke volume, aortic flow acceleration time, and cardiac output decreased.
Conclusions:
- Sublingual nitroglycerin dilates peripheral arteries in hypertensive individuals, delaying reflected pressure waves.
- Reflex sympathetic activation may offset some effects of reduced mean arterial pressure on aortic stiffness.
Abstract:
Venodilatation with consequent reduction in left ventricular filling and end-diastolic wall stress is an important mechanism for the beneficial effects of nitroglycerin in ischemic heart disease and in left ventricular failure. The effects of sublingual nitroglycerin on arterial pulsatile hemodynamics are less well defined. Doppler echocardiography and the calibrated subclavian artery pulse tracing were used to assess hemodynamics in subjects with sustained arterial hypertension (n = 25) before and 5 to 10 minutes after sublingual deposition of 0.5 mg glyceryl trinitrate. Aortic characteristic impedance was calculated by averaging the modulus of the input impedance (ratio of pressure to flow) at high frequencies and by calculating the ratio of pressure and flow increments during upstroke. The pressure wave was split into forward and backward components, and the reflection coefficient (the ratio of backward to forward pressures) was calculated. Parameters of the arterial bed were estimated by using 2- and 3-element Windkessel models. Nitroglycerin delayed the return of arterial wave reflections by 17% (P =.02) and increased aortic characteristic impedance by 20% (P =. 01), but it did not influence total arterial compliance. Mean arterial pressure decreased 7% (P =.0001), but pulse pressure did not change. Stroke volume and the acceleration time of aortic root flow decreased by 13% (P =.0001) and 8% (P =.01), respectively. Cardiac output decreased 7% (P =.01), despite an increase in heart rate of 10% (P =.0001). Peripheral resistance tended to decrease (4%, P =.06). Thus, in subjects with sustained hypertension, sublingual nitroglycerin dilates peripheral, predominantly muscular arteries with a subsequent delayed return of reflected pressure waves. Reflex activation of the sympathetic nervous system with consequent increased acceleration of left ventricular ejection seems to counteract the effect of reduced mean arterial pressure (distending pressure) with respect to the "stiffness" of the aorta.