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The effects of acute and chronic systemic hypoxia on muscle oxygen supply and oxygen consumption in the rat
Author(s) -
Marshall Janice M.,
Davies William R.
Publication year - 1999
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1111/j.1469-445x.1999.tb00072.x
Subject(s) - hypoxia (environmental) , oxygen , consumption (sociology) , medicine , cardiology , chemistry , organic chemistry , social science , sociology
SUMMARY The aims of the present study were to evaluate how acute systemic hypoxia affects O 2 delivery to skeletal muscle and muscle O 2 consumption ( V̇ O2 ) of the rat and to establish how these relationships are altered by chronic systemic hypoxia. Thus, the effects of breathing different concentrations of O 2 (air, 12% and 8% O 2 ) upon oxygen delivery and V̇ O2 were studied in hindlimb muscles of control, normoxic (N) rats and of rats that had been made chronically hypoxic in a chamber at 12% O 2 for 3–4 weeks (CH) rats. Under anaesthesia, arterial blood pressure, femoral blood flow (FBF), arterial O 2 content ( C a,O2 ) and venous O 2 content in the efflux from hindlimb were measured. In N rats, changing the inspirate from air to 12 % and 8 % O 2 for 5 min each, reduced C a,O2 from 20 ± 0.3 ml (100 ml) −1 in air to 13 ± 1.0 ml (100 ml) −1 in 8 % O 2 . FBF did not change significantly (1.7 ± 0.1 ml min −1 in air) so that O 2 delivery to hindlimb muscles fell from 0.28 ± 0.07 to 0.16 ± 0.02 ml min −1 in 8 % O 2 . Nevertheless, the V̇ O2 of hindlimb muscles was well maintained: 0.06 ± 0.02 ml min −1 in air and 0.08 ± 0.02 ml min −1 in 8 % O 2 . In CH rats breathing 12% O 2 , C a,O2 (23 ± 10 ml (100 ml) −1 ) was comparable to that of N rats breathing air, due to an increase in haematocrit, as were FBF (1.6 ± 0.2 ml min −1 ) and O 2 delivery (0.39 ± 0.05 ml min −1 ). However, V̇ O2 was 2–5‐fold greater in CH rats (0.16 ± 0.03 ml min −1 ). As in N rats, FBF was well maintained at 1.7 ± 0.2 and 1.6 ± 0.2 ml min −1 in 8 % O 2 and air, respectively. Further, V̇ O2 was also well maintained, at 0.17 ± 0.02 and 0.12 ± 0.02 ml min −1 in 8% O 2 and air, respectively. These results suggest that, contrary to previous reports, muscle V̇ O2 of the rat is independent of O 2 delivery over a wide range of O 2 delivery values. They also suggest that muscle V̇ O2 of CH rats is similarly independent of O 2 delivery. The novel finding that muscle V̇ O2 has a greater absolute value in CH rats can, we propose, be explained by an increase in V̇ O2 of the vasculature rather than of the skeletal muscle fibres and reflects increased biosynthetic activity of the vessel walls and/or vascular remodelling.