The effect of hypoxia on capillary flow direction in the isolated perfused rat heart
Cicutti, N.; Rakusan, K.
Canadian Journal of Cardiology 10(3): 367-373
1994
ISSN/ISBN: 0828-282X PMID: 8162534 Document Number: 429471
OBJECTIVE: To characterize regional capillary flow direction in the isolated perfused heart subjected to acute hypoxia. DESIGN: A technique incorporating sequential infusion of differently colored 10 mu-m microspheres into hearts of adult male Sprague-Dawley rats was employed in two series of experiments. In series A, a control group (n = 10) received three infusions of colored microspheres (each distinctly colored) in sequence during normoxic perfusion. A 'hypoxic' group (n = 12) received the initial two infusions under identical conditions, with the third infusion under conditions of experimental hypoxia. Hearts in series B (n = 5) received two differently colored infusions, the initial under normoxic conditions and the second during hypoxia. Subsequent histological examination of 40 mu-m sections obtained from mid-myocardial (MID) and subendocardial (SUB-E) regions of the heart revealed flow vectors based on the sequence of colors trapped within neighboring capillaries. RESULTS: Series A - A prevalence in concurrent flow was observed among neighboring capillaries, with significantly lower percentages in SUB-E than in MID (P lt 0.01). A higher percentage of countercurrent flow was revealed subsequent to the hypoxic intervention than during the earlier normoxic period, as well as in comparison with normally perfused controls (P lt 0.01). Flow vector observations from series B depicted lower proportions of concurrent flow compared with the two-colour normoxic interval in 'hypoxic' hearts from series A (P lt 0.05). CONCLUSION: Reversals in capillary flow direction, suggested by the reorientation of final injected microspheres relative to the positions of earlier injected microspheres, were interpreted as a response to sustain myocyte oxygenation due to severe reductions in arterial oxygen tension.