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Is there a threshold duration of vascular occlusion for hindlimb reactive hyperemia?

Department of Exercise Science, The University of Iowa, Iowa City, Iowa

Submitted 15 April 2005 ; accepted in final form 21 May 2005

Relatively brief changes in perfusion pressure and flow through arterioles occur in a number of conditions, such as in the flying environment and during such common everyday activities such as bending forward at the waist. Also, brief periods of negative vertical acceleration (G_z) stress, which reduces perfusion in the lower body, has been shown to impair the regulation of arterial pressure during subsequent positive G_z stress. To examine the contribution that reactive hyperemia makes in these settings, studies on the hindlimb circulation of anesthetized rats (n = 8) were carried out by imposing graded duration vascular occlusion (1, 2, 4, 10, and 30 s) to test the hypothesis that there is a threshold duration of reduction in perfusion that must be exceeded for reactive hyperemia to be triggered. Vascular conductance responses to 1 s of terminal aortic occlusion were no different before and after myogenic responses were blocked with nifedipine, indicating that 1 s of occlusion failed to elicit reactive hyperemia. Two seconds of occlusion elicited a small but significant elevation in hindlimb vascular conductance. The magnitude of the reactive hyperemia was graded in direct relation to the duration of occlusion for the 2-, 4-, and 10-s periods of occlusion and appeared to be approaching a plateau for the 30-s occlusion. Thus there is a threshold duration of terminal aortic occlusion (2 s) required to elicit reactive hyperemia in the hindlimbs of anesthetized rats, and the reactive hyperemia that results possesses a threat to the regulation of arterial pressure.

rat; blood flow; blood pressure regulation

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				D. D. Sheriff, I.-H. Nadland, and K. Toska Hemodynamic consequences of rapid changes in posture in humans J Appl Physiol, August 1, 2007; 103(2): 452 - 458. [Abstract] [Full Text] [PDF]