Near-infrared spectroscopy determined brain and muscle oxygenation during exercise with normal and resistive breathing

To elevate effects of carbon dioxide (CO2) retention by way of an increased respiratory load during submaximal exercise (150 W), the concentration cha nges of oxy- (Delta HbO(2)) and deoxy-haemoglobin (Delta Hb) of active musc les and the brain were determined by near-infrared spectroscopy (NIRS) in e ight healthy males. During exercise, pulmonary ventilation increased to 33 (28-40) L min(-1) (median with range) with no effect of a moderate breathin g resistance (reduction of the pneumotach diameter from 30 to 14 and 10 mm) . The end-tidal CO2 pressure (PETCO2) increased from 45 (42-48) to 48 (46-5 8) mmHg with a reduction of only 1% in the arterial haemoglobin O-2 saturat ion (SaO2) During control exercise (normal breathing resistance), muscle an d brain Delta HbO(2) were not different from the resting levels. and only t he leg muscle Delta Hb increased 14 (-2-10) muM, (P < 0.05). Moderate resis tive breathing increased <Delta>HbO(2) of the intercostal and vastus latera lis muscles to 6 +/- (-5-14) and 1 (-7-9) muM(P < 0.05), respectively, whil e muscle <Delta>Hb was not affected. Cerebral Delta HbO(2) and Delta Hb bec ame elevated to 6 (1-15) and 1 (-1-6) muM by resistive breathing (P < 0.05) . Resistive breathing caused an increased concentration of oxygenated haemo globin in active muscles and in the brain. The results indicate that CO2 in fluences blood flow to active skeletal muscle although its effect appears t o be smaller than for the brain.