At 2700 and 3700 m, the activity of the autonomic nervous system measured by heart rate variability was decreased in untrained office workers. The sympathetic nervous system was dominant to the parasympathetic at 3700 m. These alterations in the autonomic nervous system might play some role in physical fitness at high altitudes.

Purpose: In this study we examined whether normocapnia maintained by hyperventilation after lower limb tourniquet deflation prevents an increase in cerebral blood flow velocity. Methods: Thirteen patients, undergoing elective orthopedic surgery, requiring a pneumatic tourniquet around the lower extremity, were divided into two groups. In group I, ventilation was controlled at tidal volume of I 0 mL'kg -i and respiratory rate of eight per minute after tourniquet release. In group 2, ventilation was controlled to maintain PETCO 2 between 30 and 35 mml-lg after tourniquet release. Arterial blood pressure, heart rate, peak and mean middle cerebral artery (MCA) flow velocity, and arterial blood gas were measured every minute for ten minutes after tourniquet release. The MCA blood flow velocity was measured using Transcranial Doppler ultrasonography (TCD). l~.~ults: In group I, the maximum peak MCA flow velocity was 53 -+ 6 cm'sec -t (50 96 +_ 6% increase compared with pre-release value), and achieved 3 _ 0.4 min after tourniquet release. In group 2, there was no increase either in mean or peak MCA velocity after tourniquet release. Concision: Normocapnia maintained by hyperventilation after tourniquet deflation prevents an increase in cerebral blood flow velocity.Objectis : VErifier si la normocapnie maintenue par.l'hyperventilation aprEs le d~gonflage d'un garrot autour du membre inf&ieur emp&he I'augmentation de la vitesse du flux sanguin c&6bral. MEthodr : Treize patients, admis pour une chirurgie orthop~dique n&essitant un garrot pneumatique autour du membre inf&ieur, ont Et~ r~partis en deux groupes. AprEs le rel~chement du garrot, on note que : clans le Groupe I, la ventilation Etait maintenue au volume courant de I 0 ml'kg -~ et la fr~quence respiratoire ~ huit par minute ; dans le Groupe 2, la ventilation ~tait contr61& pour maintenir la PE,CO2.entre 30 et 35 mmHg ; la tension art&ielle, la fr~quence cardiaque, la vitesse moyenne et maximale du flux de I'artEre c&~brale moyenne (ACM) et les gaz du sang art&iel Etaient mesur6s ~ chaque minute pendant dix minutes. La vitesse du flux de rACM a ~t~ mesurEe par &hographie-Doppler transcr~nienne (DTC). P.~.sLdtats : Dans le Groupe I, la vitesse maximale du flux de rACM a ~t6 de 53 _+ 6 cm.sec-' (50 % _ 6 % d'augmentation en comparaison des valeurs pr&6dant la lib&ation du garrot), eta ~t~ atteinte 3 _+ 0,4 min apr& le garrot. Dans le Groupe 2, il n'y a pas eu d'augmentation de la vitesse moyenne ou maximale du flux de I'ACM aprEs le garrot. Conclusion : ~ normocapnie maintenue par rhyperventilation apr& le d~gonflage du garrot peut emp&her une augmentation de la vitesse du flux sanguin c6r~bral.

The CAVI is independent of BP and reproducible regardless of the induction of anesthesia and is significantly higher in patients with CAD. The CAVI might be able to predict atherosclerosis and coronary artery stenosis in patients undergoing cardiovascular surgery.

The pathophysiology of altitude-related disorders in untrained trekkers has not been clarified. In the present study, the effects of workload on cardiovascular parameters and regional cerebral oxygenation were studied in untrained trekkers at altitudes of 2700 m and 3700 m above sea level. We studied 6 males and 4 females at each altitude, and their average ages were 31.3+/-7.1 y at 2700 m and 31.2+/-6.8 y at 3700 m, respectively. The resting values of heart rate and mean blood pressure were not significantly different at 2700 m and 3700 m than at sea level. However, increases in these values after exercise were more prominent at high altitudes (heart rate increase = 51.6% at 2700 m and 70.4% at 3700 m; mean blood pressure increase: 19.0% at 2700 m and 17.2% at 3700 m). In addition, post-exercise blood lactate concentration was significantly higher at 3700 m than at sea level or at 2700 m (i.e., 7.6 mM at 3700 m, 3.8 mM at 2700 m, and 4.17 mM at 0 m, respectively). Exercise induced an acute reduction in the arterial oxygen saturation value (SpO2) at 2700 m and 3700 m (i.e., 11.2% reduction at 2700 m and 9.4% at 3700 m), whereas no changes were observed at sea level. The resting values of regional oxygen saturation (rSO2)--measured by a near infra-red spectrophotometer at sea level, 2700 m, and 3700 m-were nearly identical. Exercise at sea level did not reduce this value. In contrast, we observed a decrease in rSO2 after subjects exercised at 2700 m and 3700 m (i.e., 26.9% at 2700 m and 48.1% at 3700 m, respectively). The rSO2 measured 2 min and 3 min after exercise at 3700 m was significantly higher than the preexercise value. From these observations, we concluded that alterations in cardiovascular parameters were apparent only after an exercise load occurred at approximately 3000 m altitude. Acute reduction in cerebral regional oxygen saturation might be a primary cause of headache and acute mountain sickness among unacclimatized trekkers.

No abstract