Effects of moderate alcohol consumption and hypobaric hypoxia: implications for passengers’ sleep, oxygen saturation and heart rate on long-haul flights

Kurzfassung

The study was performed at the Institute of Aerospace Medicine of the German Aerospace Center in Cologne. Participants stayed in the sleep laboratory for 12 nights and days. Forty-eight participants in the age between 18 and 40 years were included and randomly assigned to two groups stratified by age, gender, and BMI. The Control Group slept two experimental nights (00:00 a.m. – 04:00 a.m.) under conditions of normobaric normoxia in the sleep lab (n = 23; 53 m altitude), whereas the InFlight Group spent two experimental nights (00:00 a.m. – 04:00 a.m.) in a simulated crew-rest compartment in the altitude chamber (n = 17; 753 hPa corresponding to 2438 m above sea level, hypobaric condition). In addition, realistic noise as inside a plane (70 dB(A), recorded during a flight from Cologne to Kairo) was generated. The order of nights was counterbalanced and two eight-hour recovery nights (11:00 p.m. – 07:00 a.m.) were scheduled between conditions. During the experimental nights polysomnography, SpO₂, and heart rate were recorded. The stay in a hypobaric environment is known to decrease oxygen saturation and increase heart rate. Alcohol, which is often consumed on-board, has similar effects, but hypobaric hypoxia-induced changes are usually more pronounced. Our study was the first, to investigate the combined impact of hypobaric hypoxia and alcohol during sleep. The combined exposure to alcohol and hypobaric condition decreased SpO₂ and increased heart rate to a median (25th/75th percentile) of 85.32% (82.86/85.93) and 87.73 bpm (85.89/93.86) during sleep compared to 88.07% (86.49/88.49) and 72.90 bpm (70.59/78.17) in the non-alcohol hypobaric condition, to 94.97% (94.59/95.33) and 76.97 bpm (65.17/79.52) in the alcohol and 95.88% (95.72/96.36) and 63.74 bpm (55.55/70.98) in the non-alcohol condition of the sleep lab group (all p<0.0001), respectively. Under the combined exposure SpO₂ was 201.18 min (188.08/214.42) below the clinical hypoxia threshold of 90% SpO₂ compared to 173.28 min (133.03/199.03) in the hypobaric condition, and to 0 min (0/0) in both sleep lab conditions. Deep sleep (N3) was reduced to 46.50 min (39.00/57.00) under the combined exposure compared to both sleep lab conditions (alcohol: 84.00 min (62.25/92.75); non-alcohol: 67.50 min (58.50/87.75); both p<0.003). Young and healthy individuals experienced prolonged and clinically relevant desaturations (SpO₂ < 90%) and heart rate accelerations during sleep indicating that the combination of alcohol and inflight hypobaric hypoxia challenged the cardio-vascular system. Effects on oxygen saturation and heart rate were supra-additive. Our results showed that the on-board consumption of alcohol is an underestimated health risk that could be easily be avoided. Practitioners, passengers and crew should be informed about the potential risks, and public awareness of this topic should be raised through patient charities, public campaigns and airlines’ written health advice.