The influence of varying oxygen tensions in inspired gas on133Xenon muscle clearance and fatigue levels during sustained and dynamic conctractions

Abstract

Isometric and isotonic endurance levels of both elbow flexors and knee extensors were tested during inspired gas mixtures of ca. 10%, 21% or 100% oxygen in nitrogen. The four work loads were set a 25, 50, 60 and 70% of maximal volitional isometric strength (IS). The isotonic exercise routine was carried out using weight lifting techniques of 20 repetitions per min from 75° to 105° of elbow flexion and knee extension respectively. Prior to, during, and after the endurance experiments¹³³Xe clearance was monitored by light weight scintillation counters. A depot of 0.1 to 0.2 ml of isotonic saline containing 50 to 150 μCi of the isotope was used as an intramuscular tracer. The exercise clearance values varied inversely to the test load during isometric exercise. Isotonic exercise for both elbow flexors and knee extensors showed increasing clearance values up to 60% IS. Above this level a decrease in total clearance was recorded. Oxygen tension had no statistical effect on the clearance values. However, the relatively large scatter of the¹³³Xe clearance method, and an inhomogenous perfusion of skeletal muscle may have masked any anticipated effect of the various O₂ tensions. Variations due to the raised intramuscular pressure appeared to be much more dominant than the hypothezised variation due to the 3 set oxygen tensions.