Maximum cerebral blood flow velocities (CBFV) and cerebral oxygen delivery (COD) by hemisphere and altitude
| CBFV | COD | |||||
|---|---|---|---|---|---|---|
| Sea level (130 m) | Moderate altitude (1300 m) (Kathmandu) | High altitude (3500 m) (Namche Bazaar) | Cerebral oxygen delivery | |||
| Mean (SD) Velocity (cm/sec) | Mean (SD) % Change from low altitude | Mean (SD) % Change from low altitude | Mean (SD) % Change from moderate altitude | Mean (SD) % Change in from low to high altitude | ||
| MCA* (n=9) | Left | 69.1 (12.5) | 35.2 (33.4)1 | 29.2 (42.3)2 | 4.2 (19.3) | 18.7 (44.0) |
| Right | 84.0 (8.4) | 7.2 (11.4) | 9.9 (12.0) | 3.0 (10.9) | 1.9 (7.5) | |
| ACA* (n=7) | Left | 45.3 (13.2) | 43.4 (53.4) | 65.2 (69.0)2 | 28.3 (42.7) | 47.8 (60.4) |
| Right | 51.1 (22.4) | 94.1 (159.7) | 109.1 (179.2)2 | 13.5 (34.4) | 41.6 (68.7) | |
| PCA*$ (n=7) | Left | 37.4 (11.2) | 40.5 (71.0) | 49.9 (75.0) | 15.1 (35.4) | 34.9 (65.6) |
| Right | 38.7 (6.2) | 21.1 (43.9) | 17.5 (33.5) | 6.4 (29.4) | 12.6 (25.7) | |
| BA* (n=9) | 53.2 (12.6) | 4.5 (16.4) | 9.5 (21.8) | 4.9 (14.0) | −1.3 (19.0) | |
Percentage change in COD was calculated using the following formula: ((AltSPo2×AltCBFV)−(SeaSpo2×SeaCBFV))/(SeaSpo2×SeaCBFV) where: AltSpo2 is the SpO2 value at altitude; AltCBFV is the CBFV at altitude; SeaSpO2 is the SpO2 at sea level; and sea CBFV is the CBFV at sea level, and haemoglobin is assumed to be constant.
There were significant effects of hemisphere, F(1,8)=10.66, p=0.011, η2=0.57 and of altitude, F(2,7)=5.08, p=0.043, η2=0.59 on maximum MCA velocities, and a significant interaction, F (2,7)=5.33, p=0.039, η2=0.60. Inspection of table 3 reveals that CBFV in the MCA significantly increased at moderate and high altitude, compared with sea level, to a greater degree in the left than in the right hemisphere.
Although inspection of table 3 shows that CBFV appeared to increase within the ACA, both left and right, this just failed to reach significance despite a large effect, F(2,5)=5.28, p=0.059, η2=0.68, likely due to the small N, a finding confirmed by posthoc, pairwise comparisons which revealed significant increases in ACA CBFV in both hemispheres from low to high altitude. There were no significant effects of hemisphere or altitude on PCA, and no effect of altitude in the BA, all F<2.3.
Data are presented as mean or geometric mean (SD), velocities are reported as cm/s; 1=significant between groups difference between low and moderate altitude; 2=between low and high altitude.
$PCA values were transformed for the analysis using the natural logarithm; however, the mean (SD) values are provided for ease of interpretation.
*Middle cerebral artery (MCA), anterior cerebral artery (ACA), posterior cerebral artery (PCA), basilar artery (BA).