Vasomotion enhanced by normovolemic hemodilution in rat diaphragmatic microcirculation.
OBJECTIVE
Since vasomotion--the rhythmic contraction and dilatation of arterioles--is frequently observed during homeostatic challenge, it has been assumed that vasomotion may cause the vulnerable portions of tissue to become intermittently oxygenated rather than permanently anoxic. This study used laser-Doppler flowmetry to investigate the effect of normovolemic hemodilution on the incidence, frequency and relative amplitude of vasomotion in rat diaphragm microcirculation.


METHODS
Blood was substituted normovolemically with equal volumes of a 6% solution of dextran 70 (molecular weight 70,000). Infrared light (wavelength 780 nm) was delivered to and detected from diaphragm tissue area approximately 1 mm in diameter and 0.5 mm in depth. The light scattered by a moving red blood cell results in a Doppler frequency shift. Vasomotion was analyzed with Fourier transformation and autoregressive modeling.


RESULTS
Following hemodilution, systemic hematocrit showed a stepwise decrease of 4 hemodilution levels (80%, 60%, 51%, and 43% of baseline values). Vasomotion was found in 13/20 (65%) at baseline, and 20/20 (100%) at the 43% level (p < 0.05 from baseline). The median fundamental frequencies during the control state and at the 4 corresponding incremental hemodilution levels were 3.29 cycles per minute (cpm), 3.30 cpm, 3.14 cpm, 3.26 cpm, and 3.42 cpm (p < 0.05 from baseline). The median relative amplitudes at baseline and 4 hemodilution stages were 31.7%, 38.5%, 40.0% (p < 0.05 from baseline), 40.7% (p < 0.05 from baseline), and 41.6% (p < 0.05 from baseline).


CONCLUSIONS
This study found that an acute reduction of systemic hematocrit greatly increased the activity of vasomotion in the diaphragm microvascular bed of rats, suggesting vasomotion could be a protective mechanism against tissue hypoxia.
Lee
Cheng-Hung
CH
Department of Internal Medicine, College of Medicine, National Cheng Kung University, Tainan, Taiwan.
Chang
Han-Yu
HY
Chen
Chang-Wen
CW
Hsiue
Tzuen-Ren
TR
D000818:Animals; D001160:Arterioles / Q000502:physiology*; D003964:Diaphragm / Q000098:blood supply*; D006400:Hematocrit; D006438:Hemodilution; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow; D014661:Vasoconstriction; D014664:Vasodilation