The effect of sympathetic stimulation on proximal brachial artery mechanics in humans--differential behaviour within the length of the brachial artery?
OBJECTIVE
The mechanical properties of arteries play a major role in the regulation of blood pressure and cardiac performance. The effect of sympathetic stimulation on the mechanical properties of the proximal brachial artery was analysed in 18 healthy volunteers, nine young (25 +/- 2 years) and nine elderly (69 +/- 2 years).


METHODS
A non-invasive ultrasonic echo-tracking system for measurement of systolic/diastolic variation of the proximal brachial artery diameter in combination with intra-arterial pressure measurements was used to determine wall mechanics. The pressure-diameter (P-D) relationship, distensibility coefficient (DC), compliance coefficient (CC) and stiffness(beta) were obtained at rest and during sympathetic stimulation induced by lower body negative pressure (LBNP).


RESULTS
The peripheral vascular resistance increased by 100 and 72%, respectively in the young and elderly during LBNP (P < 0.001). Simultaneously, the mechanical properties of the proximal brachial artery remained unaltered, as estimated from both P-D relationship and stiffness in young (beta-index rest: 5.2 +/- 0.9, LBNP: 5.5 +/- 1.3, NS) as well as elderly (beta-index rest: 13.6 +/- 4.6, LBNP: 16.1 +/- 4.7, NS).


CONCLUSIONS
LBNP-induced sympathetic activation does not change proximal brachial artery mechanics, in contrast to earlier reports on the muscular distal brachial artery. This may imply that the transition between elastic and muscular artery behaviour is within the length of the brachial artery, where the site of transition from elastic to muscular wall structure needs to be specified in future studies.
Department of Medicine and Care, University of Linköping, Linköping, Sweden.
N
N
Bjarnegård
A
A
Rydén Ahlgren
B
B
Sonesson
T
T
Länne
D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology; D001696:Biomechanical Phenomena; D001794:Blood Pressure; D001916:Brachial Artery / Q000033:anatomy & histology / Q000502:physiology*; D005260:Female; D005542:Forearm / Q000098:blood supply; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D010812:Physical Stimulation; D012039:Regional Blood Flow; D013564:Sympathetic Nervous System / Q000502:physiology*; D014655:Vascular Resistance / Q000502:physiology