Physiological responses to acute hypoxia and indictors of acute mountain sickness in males

Currently, acute hypoxia and the underlying mechanisms of acute mountain sickness (AMS) have not been characterized. Here, we investigated the responses of the cardiopulmonary system and cerebral blood flow (CBF) to acute hypoxia and the related compensatory factors for AMS. A total of 123 healthy young male subjects were recruited in Chengdu (500 m) and arrived in Lhasa (3700 m) by plane. Demographic information was recorded within 24 h after their arrival. Physiological parameters and AMS symptoms were measured at resting conditions. The incidence of AMS was 58.5% (72/123) after acute exposure to 3700 m. The AMS group had significant increases in cardiac output (CO), heart rate (HR), epinephrine, norepinephrine and lower oxygen saturation (SaO(2)) and significant differences in electrocardiographic parameters and tricuspid regurgitation pressure compared with the non-AMS group (all P-values < 0.05). Combining indicators including HR >= 85/min, MCAv (Middle cerebral artery flow velocity) >= 66 cm/s, SaO(2) <= 88% and tricuspid regurgitation (TR) pressure >= 25 mmHg can contribute to AMS diagnosis, with a positive predictive value and specificity of 97.87% and 98.04%, respectively. HR (>= 85/min), MCAv (>= 66 cm/s), SaO(2) (<= 88%) and TR pressure (>= 25 mmHg) are the key compensatory factors for DO2 (oxygen delivery) and may play a key role in the physiological responses involved in the acclimatization to acute hypoxia. These factors may be related to the mechanism of AMS development and can be used as objective indicators for AMS diagnosis.