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POINT-COUNTERPOINT COMMENTS

Evidence of venous suction, but from where?

University of Wisconsin
John Rankin Laboratory of Pulmonary Medicine
Madison, Wisconsin
e-mail: jordanmiller{at}wisc.edu

This letter is in response to the Point-Counterpoint series "The muscle pump is/is not an important determinant of muscle blood flow during exercise" that appeared in the July issue (vol. 99: 371–375, 2005; doi:10.1152/japplphysiol.00381; http://jap.physiology.org/content/vol99/issue1).

Letter to Editor: As noted by Dr. Sheriff, radiographic studies showing rapid intramuscular venous filling after brief calf contraction (1) along with reports of negative deep venous pressures (2) have popularized the idea that muscular contraction can widen the intramuscular arteriovenous pressure gradient and elicit an increase in muscle blood flow. However, in the original articles the investigators emphasize that the rapid filling of the deep veins occurs predominantly as a result of the emptying of the superficial venous vasculature (1, 2). Although there is undoubtedly a contribution of arterial inflow to the refilling of the intramuscular veins, a "vascular waterfall" may exist in the intramuscular arterioles (3), which may prevent a lowering of venous pressure from contributing to the "effective" transarteriolar pressure gradient. That these vessels may not completely collapse during or after a submaximal muscular contraction does not exclude the presence of a vascular waterfall, as all that is required is an increase in transarteriolar resistance that is inversely proportional to the intramuscular arteriovenous pressure gradient.

Perhaps altering blood viscosity to manipulate the transarteriolar pressure decrement (and thus dynamic changes in blood flow) during exercise could provide some insight into the contribution of changes in venous pressure to muscle perfusion during exercise. Although such an approach would not be without challenges to overcome, it could avoid some of the limitations that have precluded the widespread acceptance of the impressive experiments from Clifford's group by the "muscle pump proponents," and it could provide a much needed novel approach to the assessing of the potential contribution of "venous suctioning" to exercise hyperemia.

REFERENCES

1. Almen T and Nylander G. Serial phlebography of the normal lower leg during muscular contraction and relaxation. Acta Radiol 57: 264–272, 1962.[ISI][Medline]
2. Arnoldi CC. On the conditions for the venous return from the lower leg in healthy subjects and in patients with chronic venous insufficiency. Angiology 17: 153–171, 1966.[Free Full Text]
3. Shrier I and Magder S. Maximal vasodilation does not eliminate the vascular waterfall in the canine hindlimb. J Appl Physiol 79: 1531–1539, 1995.[Abstract/Free Full Text]

This Article Full Text (PDF) Free Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Miller, J. D. Search for Related Content PubMed PubMed Citation Articles by Miller, J. D.