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Department of Anesthesiology, Academic Medical Centre, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands; and Nepal International Clinic, Naxaul, Kathmandu, Nepal
The purpose of this study was twofold:
1) to determine whether at high
altitude cerebral blood flow (CBF) as assessed during CO2 inhalation and during
hyperventilation in subjects with acute mountain sickness (AMS) was
different from that in subjects without AMS and
2) to compare the CBF as assessed
under similar conditions in Sherpas at high altitude and in subjects at
sea level. Resting control values of blood flow velocity in the
middle cerebral artery (VMCA), pulse
oxygen saturation (SaO2), and
transcutaneous PCO2 were measured at
4,243 m in 43 subjects without AMS, 17 subjects with AMS, 20 Sherpas,
and 13 subjects at sea level. Responses of
CO2 inhalation and
hyperventilation on
VMCA,
SaO2, and transcutaneous PCO2 were measured, and the cerebral
vasomotor reactivity (VMR =
VMCA/PCO2)
was calculated as the fractional change of
VMCA per Torr
change of PCO2, yielding a
hypercapnic VMR and a hypocapnic VMR. AMS subjects showed
a significantly higher resting control
VMCA than did
no-AMS subjects (74 ± 22 and 56 ± 14 cm/s, respectively;
P < 0.001), and
SaO2 was significantly lower (80 ± 8 and 88 ± 3%, respectively; P < 0.001). Resting control VMCA values in
the sea-level group (60 ± 15 cm/s), in the no-AMS group, and in
Sherpas (59 ± 13 cm/s) were not different. Hypercapnic VMR values
in AMS subjects were 4.0 ± 4.4, in no-AMS subjects were 5.5 ± 4.3, in Sherpas were 5.6 ± 4.1, and in sea-level subjects were 5.6 ± 2.5 (not significant). Hypocapnic VMR values were significantly higher in AMS subjects (5.9 ± 1.5) compared with no-AMS subjects (4.8 ± 1.4; P < 0.005) but were
not significantly different between Sherpas (3.8 ± 1.1) and the
sea-level group (2.8 ± 0.7). We conclude that AMS subjects have
greater cerebral hemodynamic responses to hyperventilation, higher
VMCA
resting control values, and lower SaO2 compared with no-AMS
subjects. Sherpas showed a cerebral hemodynamic pattern
similar to that of normal subjects at sea level.
mountain sickness; Sherpa; transcranial Doppler; transcutaneous carbon dioxide
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