Tissue and Arterial Oxygen Saturation During Exercise of Varying Intensity in Asthmatic Subjects

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PURPOSE: Previous research suggests that respiratory and limb muscles compete for blood flow during heavy exercise in normal subjects (Harms et al., J Appl. Physiol. 82:1573–83, 1997). Our aim was to characterize the effects of exercise of varying intensity upon limb and respiratory muscle oxygen saturation during exercise in individuals with asthma, where inspiratory muscle work may be elevated as a consequence of hyperinflation. METHODS: Fourteen asthmatic subjects to undertake 3 separate exercise tests. Peak power (PP) output was determined during a continuous incremental ramp test on a cycle ergometer. On a separate occasion, graded submaximal exercise was undertaken at 20, 30, 40, and 50% of PP (3 min stages). The final test was at 70% of PP to the limit of tolerance (Tlim). Near-infrared spectroscopy (NIRS) recorded local tissue oxygenation continuously; the optodes were placed on the vastus lateralis (VL) of the subjects left leg, and at the 6th intercostals (IC). Mean NIRS values were determined for the last min of each stage in the submaximal test, for each min of the Tlim test during the 1st 5 min and at Tlim isoendpoint. Arterial O2 saturation (SaO2) was measured each minute by ear oximetry. RESULTS: During the submaximal test, there was no significant (p>0.05) decline in SaO2 or change in deoxy-hemoglobin (deoxy-Hb) in the VL or IC, but there was a significant increase (p<0.05) in total hemoglobin content (THC) and oxy-hemoglobin (HbO) at the end of the 50% PP stage in the VL. During the Tlim test there was a significant decrease (p<0.05) in SaO2 at all time points. There was a significant increase (p<0.05) in THC at the VL at the endpoint of the Tlim test, but no significant differences (P<0.05) were found for HbO. Deoxy-Hb was higher at min 3, 4, 5 and the isoend in the VL and the IC in the Tlim test. There was no significant change (p>0.05) in THC at the IC, but a significant decrease in HbO. CONCLUSION: These data confirm that during submaximal exercise there is an increase in blood flow to the active VL with no change in blood flow to the IC. During the high intensity exercise of the Tlim test, oxygen extraction increased in the VL and IC.