Resting limb muscle perfusion during inspiratory muscle loading in hypoxia and normoxia.

INTRODUCTION: Fatiguing of respiratory muscles reduces peripheral muscle perfusion. Further, acute hypoxia enhances respiratory muscle fatigue. This study investigated the effects of inspiratory muscle loading (IML) on resting locomotor muscle perfusion in hypoxia compared to normoxia.

METHODS: Ten subjects completed two study days of fatiguing IML (blinded, randomized) in normobaric hypoxia (targeted oxygen saturation 80%) and normoxia, respectively. Contrast-enhanced ultrasound (CEUS) of the gastrocnemius muscle and popliteal doppler ultrasonography were used to monitor muscle perfusion. Based on CEUS and monitored cardiac output, perfusion surrogate parameters (CLPaer and CLPap ) were established.

RESULTS: Muscle perfusion declines early during IML in normoxia (CLPaer : -54±25%, p<0.01; CLPap : -58±32%, p<0.01) and hypoxia (CLPaer : -43±23%, p<0.01; CLPap : -41±20%, p<0.01). Hypoxia compared to normoxia increased cardiac output before (+23±19%, p<0.01 ANOVA) and during (+22±20%, p<0.01 ANOVA) IML, while local muscle perfusion during IML remained unchanged (CLPaer : p=0.41 ANOVA; CLPap : p=0.29 ANOVA).

CONCLUSION: Acute hypoxia compared to normoxia does not affect locomotor muscle perfusion during fatiguing IML.