Field Monitoring Of Neuroendocrine And Cardiovascular Alterations During A Himalayan Expedition To High Altitude

Diminished oxygen availability attendant to high altitude (HA) ascent challenges metabolic homeostasis resulting in altered neuroendocrine and cardiovascular control. Identifying field methods that are sensitive to such changes would improve monitoring of the acclimatization process. PURPOSE: To characterize changes in self-collected urinary neurotransmitters (NTs) and heart rate variability (HRV) with ascent to HA. METHODS: Eleven medical professionals (6 males, 5 females, BMI = 22.4 ± 2.3 kg/m2, age = 29 ± 14 yr) underwent a 21-day expedition to remote regions of the Greater Himalayan Range. The expedition began at ≤ ~2,000 m (PRE) followed by 6 days at moderate altitude (MA; ~2,400-2,800 m) and 3 days at HA (~3,600-4400 m). Daily 60-s, post-waking HRV measures were self-recorded supine and standing using the Elite HRV smartphone application for analysis of R-R intervals (RR) and the root mean square of successive differences (RMSSD). Concentrations of 21 NTs from dried urine samples were determined via liquid chromatography-mass spectrometry. Differences were assessed by linear mixed models fitted using restricted maximum likelihood with Greenhouse-Geisser correction and Tukey post-hoc testing. RESULTS: Progressive exposure to higher elevations had a main effect on supine and standing RR, as well as inhibitory (e.g., tryptophan, serotonin, taurine) and excitatory (e.g., glutamine, histidine, histamine, tyrosine, tyramine, and normetanephrine) NTs (all p < 0.05). There was no main effect on RMSSD. While no differences in RR or NTs were evident from PRE to MA, further ascent from MA to HA reduced supine RR (-65 ± 38 ms, p = 0.02), standing RR (-64 ± 43 ms, p < 0.01), tryptophan (-48 ± 28%, p = 0.03), serotonin (-23 ± 28%, p = 0.04), taurine (-80 ± 21%, p < 0.01), glutamine (-66 ± 29%, p = 0.02), histidine (-72 ± 23%, p < 0.01), histamine (-48 ± 37%, p = 0.02), tyrosine (-61 ± 31%, p = 0.01), and tyramine (-63 ± 38%, p = 0.01), while normetanephrine increased (+113 ± 72%, p = 0.01). CONCLUSION: In our modest sample of medical professionals, self-collected urinary and heart rate measures were sensitive to alterations in neuroendocrine signaling and cardiovascular control with ascent to HA; however, ultra-short HRV profiles may not be sensitive enough to detect changes in RMSSD.