Received March 23, 2007
Revised April 18, 2007
Accepted after revision May 29, 2007
Cardiovascular Control [210]
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Role of vascular bed compliance in vasomotor control in skeletal muscle
Mair Zamir 1,
Ruma Goswami 1,
Deborah Salzer 1,
J Kevin Shoemaker 1*
1 The University of Western Ontario
* To whom correspondence should be addressed. E-mail: kshoemak{at}uwo.ca.
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Abstract |
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The current view of neurogenic vasomotor control in skeletal muscle is based largely on changes in vascular bed resistance. The purpose of this study was to determine to what extent vascular bed compliance may also play a role in this regulation. For this purpose, pressure (Millar and Finometer) and flow (Doppler ultrasound) waveforms were measured simultaneously in the brachial artery of seven healthy individuals under physiological manouvers which were expected to produce non-neurogenic changes in resistance (wrist cuff occlusion; n = 5) or compliance (arm elevation; n=6) of the forearm vascular bed. In addition, neurogenic changes were assessed during lower body negative pressure (LBNP) and a cold pressor test (CPT) (n=7). Vascular resistance (R) was calculated from the average flow and pressure values. A lumped Windkessel model was used to obtain vascular bed compliance (C) from these concurrently measured waveforms. Mechanical effects on R were examined by wrist occlusion (n = 6) and on C by elevating the arm relative to the heart (n = 5) in order to modify myogenic tone. Compared with baseline (3.81 ± 1.59 ml/min/mmHg) wrist occlusion increased R (65 ± 75%; P<0.05) with minimal change in C (-15 ± 16%; n.s.). Compared with the arm in neutral position (0.0075 ± 0.003 mL/mmHg) elevation of arm above heart level produced a 86 ± 41% increase in C (P<0.05) with little change in R (-5 ± 11%). Neurogenic contributions were tested using lower body negative pressure (LBNP) and the cold pressor test (CPT). LBNP induced a 29 ± 24 % increase in R and a 26 ± 12% decrease in C (both P<0.05). The CPT induced no consistent change in R but a 22 ± 7% reduction in C (P<0.05). It was concluded that vascular bed compliance is an important variable which should be considered along with vascular bed resistance in the mechanics of vasomotor regulation in skeletal muscle.
Key Words:
Skeletal muscle, Vascular blood flow, Vasoconstriction
