In vivo human brachial artery elastic mechanics: effects of smooth muscle relaxation.
BACKGROUND
The effects of smooth muscle relaxation on arterial wall mechanics are controversial. We used a new, in vivo, noninvasive technique to measure brachial artery wall mechanics under baseline conditions and following smooth muscle relaxation with nitroglycerin (NTG).


RESULTS
Eight healthy, normal subjects (6 male, 2 female; age 30+/-3.1 years) participated in the study. The nondominant brachial artery was imaged through a water-filled blood pressure cuff using an external ultrasound wall-tracking system at baseline and following 0.4 mg sublingual NTG. Simultaneous radial artery pressure waveforms were recorded by tonometry. Transmural pressure (TP) was reduced by increasing water pressure in the cuff. Brachial artery area, unstressed area, compliance, stress, strain, incremental elastic modulus (Einc), and pulse wave velocity (PWV) were measured over a TP range from 0 to 100 mm Hg. Baseline area versus TP curves generated 30 minutes apart were not significantly different. NTG significantly shifted area versus TP (P<0.0001) and compliance versus TP (P<0.001) curves upward, whereas the Einc versus TP (P<0.05) and PWV versus TP (P<0. 01) curves were shifted downward. NTG also significantly shifted stress versus strain (P<0.01) and Einc versus strain (P<0.01) curves to the right.


CONCLUSIONS
We conclude that brachial artery elastic mechanics can be reproducibly measured over a wide range of TP and smooth muscle tone using a new noninvasive ultrasound technique. Smooth muscle relaxation with NTG increases isobaric compliance and decreases isobaric Einc and PWV in the human brachial artery.
Cardiovascular Division, Department of Medicine, and the Graduate Program in Biophysical Sciences and Medical Physics, Department of Radiology, University of Minnesota, Minneapolis, USA. bankx001@tc.umn.edu
A J
AJ
Bank
D R
DR
Kaiser
S
S
Rajala
A
A
Cheng
D000328:Adult; D001794:Blood Pressure; D001916:Brachial Artery / Q000000981:diagnostic imaging / Q000502:physiology*; D004548:Elasticity; D005260:Female; D006801:Humans; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D005996:Nitroglycerin / Q000494:pharmacology; D011673:Pulsatile Flow; D012016:Reference Values; D015203:Reproducibility of Results; D014463:Ultrasonography
D005996:Nitroglycerin