Effects of acute hypoxia on cerebral and muscle oxygenation during incremental exercise.
To determine if fatigue at maximal aerobic power output was associated with a critical decrease in cerebral oxygenation, 13 male cyclists performed incremental maximal exercise tests (25 W/min ramp) under normoxic (Norm: 21% Fi(O2)) and acute hypoxic (Hypox: 12% Fi(O2)) conditions. Near-infrared spectroscopy (NIRS) was used to monitor concentration (microM) changes of oxy- and deoxyhemoglobin (Delta[O2Hb], Delta[HHb]) in the left vastus lateralis muscle and frontal cerebral cortex. Changes in total Hb were calculated (Delta[THb] = Delta[O2Hb] + Delta[HHb]) and used as an index of change in regional blood volume. Repeated-measures ANOVA were performed across treatments and work rates (alpha = 0.05). During Norm, cerebral oxygenation rose between 25 and 75% peak power output {Power(peak); increased (inc) Delta[O2Hb], inc. Delta[HHb], inc. Delta[THb]}, but fell from 75 to 100% Power(peak) {decreased (dec) Delta[O2Hb], inc. Delta[HHb], no change Delta[THb]}. In contrast, during Hypox, cerebral oxygenation dropped progressively across all work rates (dec. Delta[O2Hb], inc. Delta[HHb]), whereas Delta[THb] again rose up to 75% Power(peak) and remained constant thereafter. Changes in cerebral oxygenation during Hypox were larger than Norm. In muscle, oxygenation decreased progressively throughout exercise in both Norm and Hypox (dec. Delta[O2Hb], inc. Delta [HHb], inc. Delta[THb]), although Delta[O2Hb] was unchanged between 75 and 100% Power peak. Changes in muscle oxygenation were also greater in Hypox compared with Norm. On the basis of these findings, it is unlikely that changes in cerebral oxygenation limit incremental exercise performance in normoxia, yet it is possible that such changes play a more pivotal role in hypoxia.
Subudhi
Andrew W
AW
Department of Biology, University of Colorado Altitude Research Center, Denver Health Science Center and Colorado Springs Campuses, Colorado 80918, USA. asubudhi@uccs.edu
Dimmen
Andrew C
AC
Roach
Robert C
RC
D000064:Acclimatization; D000208:Acute Disease; D000328:Adult; D000531:Altitude; D001810:Blood Volume; D002540:Cerebral Cortex / Q000098:blood supply / Q000378:metabolism* / Q000503:physiopathology; D002560:Cerebrovascular Circulation; D018592:Cross-Over Studies; D015444:Exercise; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D000860:Hypoxia / Q000097:blood / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue; D010100:Oxygen / Q000097:blood / Q000378:metabolism*; D010101:Oxygen Consumption; D010108:Oxyhemoglobins / Q000378:metabolism; D010807:Physical Endurance; D012123:Pulmonary Ventilation; D052097:Quadriceps Muscle / Q000098:blood supply / Q000378:metabolism* / Q000503:physiopathology; D015203:Reproducibility of Results; D016037:Single-Blind Method; D019265:Spectroscopy, Near-Infrared
D006454:Hemoglobins; D010108:Oxyhemoglobins; C100003:deoxyhemoglobin; D010100:Oxygen