Effect of Increased Respiratory Muscle Activation on Blood Flow to Inactive and Active Limb Muscles

Abstract

It is unclear whether blood flow to inactive and active limb muscles are altered when the respiratory muscle activation is increased during submaximal exercise. PURPOSE: The purpose of this study was to clarify the effect of increasing inspiratory muscle work on blood flow to inactive and active limbs. METHODS: Healthy young men (n=7, 20±2 yrs) performed two mild bilateral dynamic knee-extension and -flexion exercises for 10 min. The trials consisted of spontaneous breathing for 5 min followed by voluntary hyperventilation either with or without inspiratory resistance for 5 min (40% of maximal inspiratory mouth pressure, inspiratory duty cycle of 50% and a breathing frequency of 40 breaths/min). Mean arterial blood pressure (MAP) was monitored using finger photoplethysmography. Blood flow to the brachial artery (inactive limb) and in femoral artery (active limb) were recorded using Doppler ultrasound. RESULTS: MAP during exercise was higher (P<0.05) with inspiratory resistance (121±6 mmHg) than without resistance (98±6 mmHg). Brachial artery blood flow increased during exercise without inspiratory resistance (127±38 ml/min) as compared with resting level, while it decreased with inspiratory resistance (69±31 ml/min). Femoral artery blood flow increased at the onset of exercise and was maintained throughout exercise without inspiratory resistance (2426±573 ml/min) and was unchanged when inspiratory resistance was added (2517±663 ml/min) (P>0.05). CONCLUSIONS: These results suggest that sympathetic control of blood redistribution to active limbs is promoted, partly, by respiratory muscle-induced metaboreflex.