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POINT-COUNTERPOINT COMMENTS

Chronic hypoxia-induced pulmonary hypertension does/does not lead to loss of pulmonary vasculature

Virgen Milagrosa University Foundation
San Carlos City, Pang, Philippines
e-mail: johnberg{at}hawaii.edu

The following letter is in response to Point:Counterpoint: "Chronic hypoxia-induced pulmonary hypertension does/does not lead to loss of pulmonary vasculature" that appears in this issue.

To the Editor: In their initial statement supporting the hypothesized loss of precapillary arteries in chronic hypoxia Rabinovitch, Chesler, and Molthen (6) provide evidence derived from perfusion studies using contrast dyes and other markers. In reply, McLoughlin and McMurtry (5) introduce the problem of artifactual measurements resulting from hypoxic pulmonary vasoconstriction (HPV) of pulmonary arteries. I believe that clarification of how HPV may cause the proposed loss of vessels to occur may contribute to the debate. One way this could happen is through uneven HPV where flow in some vascular channels may become entirely blocked and downstream vessels would appear to be lost through a lack of perfusion. Hultgren (4) initially introduced the concept of uneven HPV in pulmonary arteries to explain the observed patchy distribution of high-altitude pulmonary edema in humans. Anatomically, pulmonary arteries in the adult human lung have a highly variable distribution of smooth muscle (2) consistent with the observed variability of HPV response between individuals. Studies by Dawson et al. (1), using the double-indicator dilution method, showed that hypoxia causes more than a doubling of transit times for infused indicator agents in dog lungs, suggesting that flow rates through parallel channels become more variable with hypoxia. More recently, Hopkins et al. (3), using functional magnetic resonance imaging techniques, provide additional evidence for uneven HPV. It is therefore likely that at least some of the data presented in defense of vessel loss as a cause of pulmonary hypertension may be the result of uneven HPV and artifactual inclusion of HPV-blocked vessels.

REFERENCES

1. Dawson CA, Bronikowski TA, Linehan JH, Hakim TS. Influence of pulmonary vasoconstriction on lung water and perfusion heterogeneity. J Appl Physiol 54: 654–660, 1983.[Abstract/Free Full Text]
2. deMello D, Reid LM. Arteries and veins. In: The Lung: Scientific Foundations, edited by Crystal RG and West JB. New York: Raven, 1991, p. 767–777.
3. Hopkins SR, Garg J, Bolar DS, Balouch J, Levin DL. Pulmonary blood flow heterogeneity during hypoxia and high-altitude pulmonary edema. Am J Respir Crit Care Med 171: 83–87, 2005.[Abstract/Free Full Text]
4. Hultgren HN. High altitude pulmonary edema. In: Biomedicine of High Terrestrial Altitude, edited by Hegnauer AH. New York: Springer-Verlag, 1969, p. 131–141.
5. McLoughlin P, McMurtry I. Counterpoint: Chronic hypoxia-induced pulmonary hypertension does not lead to loss of pulmonary vasculature. J Appl Physiol; doi:10.1152/japplphysiol.00274a.2007.
6. Rabinovitch M, Chesler N, Molthen RC. Point: Chronic hypoxia-induced pulmonary hypertension does lead to loss of pulmonary vasculature. J Appl Physiol; doi:10.1152/japplphysiol.00274.2007.

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 Web of Science 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 Berg, J. T. Search for Related Content PubMed PubMed Citation Articles by Berg, J. T.