The changes in leg blood flow during and after mild or severe acute hypoxaemia in healthy humans

The present study examines the leg blood flow changes in resting healthy humans during and after a 10-min period of mild (PaO2=5.60 kPa) or severe hypoxaemia (PaO2=4.53 kPa) induced by breathing hypoxic gas mixtures. A Colour Duplex Scan system allowed to measure the cross-sectional area (CSA) and mean blood flow (Q) in a femoral artery (FA) and a femoral vein (FV) and also in an artery supplying leg muscles (medial gastrocnemius artery, MGA). During the mild as well as the severe hypoxaemia and their recovery periods, no significant variations of Q and CSA occurred in FA and FV. During the mild hypoxaemia and the first 10 min of the recovery period, Q and CSA of MGA increased (maximal changes: +84 and +20%, respectively). By contrast, a marked Q decrease and a reduced CSA were measured in MGA during the severe hypoxaemia (-67 and -60%, respectively). This reduced muscle blood flow was followed by a vasodilatation (CSA increase = +30%), which began 10 min after the hypoxaemia ended and persisted for a further 10-min period. This study shows that the time course of muscle blood flow changes in response to acute hypoxaemia depends on the PaO2 level. Reverse effects were measured during the mild or the severe hypoxaemia, whereas a post-hypoxaemic vasodilatation occurred in all circumstances.