Effect of hematocrit on cerebral blood flow with induced polycythemia

J. Massik, Y. L. Tang, M. L. Hudak, R. C. Koehler, R. J. Traystman, M. D. Jones

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43 Scopus citations


Cerebral blood flow (CBF) is lowered during polycythemia. Whether this fall is due to an increase in red blood cell concentration (Hct) or to an increase in arterial O2 content (Ca(O2)) is controversial. We examined the independent effects of Hct and Ca(O2) on CBF as Hct was raised from 30 to 55% in anesthetized 1- to 7-day-old sheep. CBF was measured by the radiolabeled microsphere technique before and after isovolemic exchange transfusion with either oxyhemoglobin-containing erythrocytes (in 5 control animals) or with methemoglobin-containing erythrocytes (in 9 experimental animals). Following exchange transfusion in the control animals, Hct rose (30 ± 1 vs. 55 ± 1%, mean ± SE), Ca(O2) increased (15.1 ± 0.8 vs. 26.7 ± 0.9 vol%), and CBF fell (66 ± 9 vs. 35 ± 5 ml·min-1·100 g-1). Because the fall in CBF was proportionate to the rise in Ca(O2), cerebral O2 transport (CBF x Ca(O2)) was unchanged. Following exchange transfusion in the experimental animals, Hct rose (32 ± 1 vs. 55 ± 1%) but Ca(O2) did not change. Nevertheless, CBF still fell (73 ± 4 vs. 48 ± 2 ml·min-1·100 g-1) and, as a result, cerebral O2 transport also fell. The latter cannot be attributed to a fall in cerebral O2 uptake, as cerebral O2 uptake was unaffected during each of these conditions. Comparison of the two groups of animals showed that ~60% of the fall in CBF may be attributed to the increase in red cell concentration alone. It is probable that this effect is due largely to changes in blood viscosity.

Original languageEnglish (US)
Pages (from-to)1090-1096
Number of pages7
JournalJournal of applied physiology
Issue number3
StatePublished - 1987
Externally publishedYes

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)


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