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 hu mans during and after a 10-min period of mild (PaO2 = 5.60 kPa) or severe h ypoxaemia (PaO2 = 4.53 kPa) induced by breathing hypoxic gas mixtures. A Co lour Duplex Scan system allowed to measure the cross-sectional area (CSA) a nd mean blood flow ((Q)) over dot in a femoral artery (FA) and a femoral ve in (FV) and also in an artery supplying leg muscles (medial gastrocnemius a rtery, MGA). During the mild as well as the severe hypoxaemia and their rec overy periods, no significant variations of (Q) over dot and CSA occurred i n FA and FV. During the mild hypoxaemia and the first 10 min of the recover y period, (Q) over dot and CSA of MGA increased (maximal changes: +84 and 20%, respectively). By contrast, a marked (Q) over dot decrease and a reduc ed CSA were measured in MGA during the severe hypoxaemia (-67 and -60%, res pectively). This reduced muscle blood flow was followed by a vasodilatation (CSA increase = +30%), which began 10 min after the hypoxaemia ended and p ersisted 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 th e PaO2 level. Reverse effects were measured during the mild or the severe h ypoxaemia, whereas a post-hypoxaenic vasodilatation occurred in all circums tances.