Is Normobaric Hypoxia Effective For Sustaining Previously Acquired Altitude Acclimatization-induced Improvements In Mood State?

Abstract

PURPOSE: Mood state has been shown to improve with high altitude (HA) acclimatization to 4300 m. The purpose of this study was to determine if these acclimatization effects on mood state persist during reintroduction to 4300 m altitude (RA) after 12 days at sea level (SL) and whether or not normobaric hypoxia (NH) treatment is an effective countermeasure to prevent de-acclimatization. METHODS: Seventeen SL residents (age= 22 ± 6 yr, weight= 75.2 ± 13.3 kg; mean ± SD) completed in the following order: 1) 4 days of baseline SL testing; 2) 12 days of HA acclimatization at 4300 m; 3) 12 days at SL post-HA acclimatization where each received either NH (n=9, FiO2=0.122) or Sham treatment (n=8; FiO2=0.207); and 4) 24-hour reintroduction to 4300 m altitude (RA) in a hypobaric chamber (460 Torr). Mood state was assessed using the Automated Neuropsychological Assessment Metrics Mood Scale (ANAM-MS), which includes the measurement of 7 mood dimensions: vigor, restlessness, depression, anger, fatigue, anxiety and happiness. The test was administered in the afternoon (~2-3pm) on 5 occasions at SL, once after 2h at HA (HA1), 20h at HA (HA2), 11 days at HA exposure (HA11), and following 4 h of RA (RA4). RESULTS: As there were no group differences between NH and Sham mood test scores at any of the time points, data were combined. Fatigue increased (P<0.05) from SL (0.44 ± 0.58) to HA1 (1.16 ± 1.17) and HA2 (1.93 ± 1.26) and then decreased (P<0.05) from HA2 to HA11 (0.67 ± 0.78) and remained low at RA4 (0.58 ± 0.72). Vigor decreased (P<0.05) from SL (2.80 ± 1.42) to HA1 (1.54 ± 1.19) and HA2 (1.33 ± 1.31), and then remained unchanged (P>0.05) from HA2 to HA11 (1.46 ± 1.58), and this effect persisted at RA4 (1.33 ± 1.05). Anxiety increased (P<0.05) from SL (0.17 ± 0.31) to HA1 (0.49 ± 0.97), decreased (P<0.05) from HA1 to HA2 (0.07 ± 0.17), remained unchanged from HA2 to HA11 (0.19 ± 0.60), and remained low at RA4 (0.14 ± 0.30). All other mood states remained unchanged from SL to HA and then RA. CONCLUSION: These results suggest that HA-induced improvements in mood state are retained during RA after 12 days at SL whether or not NH treatment is utilized. Authors’ view not official US Army or DOD policy. Funding USAMRDC.