Am. J. Respir. Crit. Care Med., Vol 152, No. 5, 11 1995, 1633-1640.
Effect of varying inspired oxygen concentration on diaphragm glutathione metabolism during loaded breathing
GS Supinski, D Nethery, R Ciufo, J Renston and A DiMarco
Department of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.
Recent studies have suggested that loaded breathing elicits alterations in
diaphragmatic glutathione levels that may be mediated by free radicals and
may also be linked to the development of diaphragm fatigue. While
free-radical generation in a number of pathophysiologic conditions is known
to be a function of ambient oxygen concentrations, the effect of varying
inspired oxygen concentration on the diaphragmatic response to loaded
breathing (i.e., on diaphragm fatigue and glutathione levels) has not been
studied. In this study, we compared the effect of loaded breathing,
continued until respiratory arrest in decerebrate rats breathing room air
(RA), with the effect of the same load on animals breathing 100% oxygen
(O2). After arrest, the animals' diaphragms were excised, force generation
was assessed in vitro, and diaphragmatic levels of reduced glutathione
(GSH) and oxidized glutathione (GSSG) were determined. Similar measurements
were made on unloaded control animals. We found both similarities and
differences in the response to loading in O2- and RA-breathing animals.
O2-breathing loaded animals had a greater load endurance, lower blood
pressure at the end of loading, higher carbon dioxide levels, and greater
high-frequency fatigue at the conclusion of loaded trials than did
RA-breathing animals. The degree of low-frequency fatigue was similar,
however, in the O2- and RA-breathing loaded groups (i.e, twitch force
averaged 7.9 +/- 0.6, 8.4 +/- 0.5, 3.8 +/- 0.9, and 4.5 +/- 0.8 N/cm2,
respectively, in the RA/unloaded, O2/unloaded, RA/loaded, and O2/loaded
groups, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)
