Table 1.
Metabolic, respiratory, and cerebral blood flow velocity responses to incremental exercise
| Variable | Normoxia |
Hypoxia | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Rest | Wmax |
Rest | Wmax | |||||||
| 25% | 50% | 75% | 100%† | 25% | 50% | 75% | 100%† | |||
| Power, W | 0±0 | 110±15 | 177±27 | 240±40 | 305±52 | 0±0 | 99±9 | 151±19 | 203±28 | 256±38* |
| HR, beats/min | 73±13 | 121±11 | 142±12 | 162±12 | 178±10 | 82±20 | 130±16 | 146±15 | 161±11 | 172±10* |
| O2 saturation, % | 96±2 | 94±2 | 93±2 | 92±2 | 90±3 | 85±4* | 76±4 | 73±5 | 71±6 | 70±7* |
| O2 uptake, l/min | 0.41±0.10 | 1.69±0.29 | 2.24±0.43 | 2.89±0.57 | 3.49±0.76 | 0.45±0.23 | 1.54±0.31 | 2.04±0.47 | 2.35±0.42 | 2.74±0.60* |
| CO2 output, l/min | 0.37±0.10 | 1.53±0.23 | 2.26±0.35 | 3.28±0.53 | 4.49±0.78 | 0.39±0.17 | 1.38±0.31 | 1.91±0.33 | 2.61±0.47 | 3.31±0.71* |
| Minute ventilation, l/min btps | 15.7±5.1 | 48.8±8.2 | 68.6±11.6 | 101.5±20.6 | 159.6±32.6 | 18.6±8.2 | 53.5±11.9 | 73.9±15.7 | 105.9±21.6 | 151.1±32.9 |
| f, breaths/min | 14±5 | 24±4 | 28±6 | 37±8 | 56±11 | 16±6 | 25±6 | 31±8 | 41±9 | 57±14 |
| Vt, liters | 1.1±0.4 | 2.0±0.4 | 2.4±0.5 | 2.6±0.5 | 2.7±0.4 | 1.1±0.4 | 2.0±0.5 | 2.3±0.6 | 2.5±0.6 | 2.5±0.7 |
| Minute ventilation/O2 uptake | 38.1±8.0 | 28.9±2.7 | 30.7±3.9 | 35.0±5.2 | 46.0±8.2 | 43.3±12.3* | 34.8±4.3 | 37.0±6.6 | 45.1±6.2 | 56.0±9.9* |
| Minute ventilation/CO2 output | 41.5±5.0 | 31.7±2.7 | 30.1±3.1 | 30.6±4.0 | 35.3±5.4 | 48.2±10.5* | 39.0±4.9 | 38.9±5.2 | 40.9±5.3 | 46.0±6.1* |
| End-tidal Po2, Torr | 75.8±10.4 | 74.2±8.2 | 77.4±7.1 | 82.9±6.7 | 91.7±6.5 | 47.6±7.2* | 46.7±4.2 | 49.6±4.7 | 54.7±4.6 | 60.0±5.2* |
| End-tidal Pco2, Torr | 33.8±4.5 | 37.5±4.6 | 38.1±4.5 | 36.2±5.3 | 28.7±5.4 | 29.0±4.9* | 30.9±4.3 | 30.3±4.8 | 27.8±4.2 | 23.3±4.1* |
| MCA Vmean, cm/s | ||||||||||
| Left | 53.8±10.0 | 62.0±12.6 | 68.0±15.1 | 70.3±16.0 | 65.1±14.6 | 56.6±11.4 | 68.9±16.2 | 75.4±14.8 | 75.2±15.3 | 70.4±14.7* |
| Right | 56.2±10.2 | 65.9±11.3 | 72.0±14.0 | 74.4±16.0 | 69.9±15.5 | 60.0±11.4 | 74.0±10.5 | 79.3±12.9 | 79.3±14.6 | 76.7±14.4* |
| MCA Vmean, %change | ||||||||||
| Left | 0±0 | 15.4±13.1 | 26.0±16.1 | 31.0±20.1 | 21.2±21.4 | 0±0 | 25.9±21.1 | 33.5±24.7 | 35.1±24.3 | 26.9±21.0 |
| Right | 0±0 | 18.2±12.0 | 28.9±13.6 | 32.7±17.2 | 24.8±18.3 | 0±0 | 25.9±21.1 | 34.8±25.0 | 34.2±22.0 | 30.4±24.9 |
| Mean BP, %change | 0±0 | 16.1±8.9 | 25.6±8.9 | 32.2±10.0 | 38.1±12.8 | 0±0 | 16.1±9.4 | 22.9±9.7 | 30.4±12.8 | 36.8±17.2 |
Values are means ± SD (n = 23). HR, heart rate; f, respiratory rate; MCA Vmean, middle cerebral artery mean blood flow velocity; BP, blood pressure. O2 saturation in the middle finger was measured by pulse oximetry. Repeated-measures ANOVA (2 trials × 5 work rates) were performed on each variable. Post hoc paired t-tests were performed on rest and 100% maximal work rate (Wmax) values only.
*
P < 0.05 vs. normoxia.
†
All 100% Wmax values were different from rest (P < 0.05).