Estimation of shear and flow rates in pial arterioles during somatosensory stimulation.
We tested the hypothesis that a shear stress-dependent mechanism is involved in the dilation of pial arterioles during somatosensory stimulation. In alpha-chloralose-anesthetized rats implanted with cranial windows, we simultaneously measured the diameter and flow velocity of pial arterioles with video and dual-slit methods. Stimulation (0.2-0.3 V, 5 Hz, 0.5 ms pulses for 20 s) of the contralateral sciatic nerve evoked consistent dilator responses in pial arterioles (36 +/- 1 micron diam) without affecting blood pressure. The dilator responses consisted of an initial transient peak dilation of 30 +/- 3%, followed by a sustained dilation of 13 +/- 1% (n = 11). Mean velocity increased by 16.4 +/- 5.7% at 5 s after stimulus onset. Wall shear rate and volume flow were calculated from diameter and velocity data by assuming a parabolic flow profile. There was no significant change in wall shear rate, whereas flow rate increased significantly during sciatic nerve stimulation. The present findings suggest that a flow (shear stress)-mediated mechanism does not play an important role in the dilator response of pial arterioles to sciatic nerve stimulation.
Ngai
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AC
Department of Neurological Surgery, University of Washington School of Medicine, Seattle 98104, USA.
Winn
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HR
D000818:Animals; D001160:Arterioles / Q000502:physiology; D002560:Cerebrovascular Circulation; D004558:Electric Stimulation; D004912:Erythrocytes / Q000502:physiology; D018056:Hemorheology; D006935:Hypercapnia / Q000503:physiopathology; D008297:Male; D010841:Pia Mater / Q000098:blood supply*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve / Q000502:physiology; D013003:Somatosensory Cortex / Q000502:physiology*; D013314:Stress, Mechanical