Sea-level Residents Research Articles

Effect of repeated normobaric hypoxia exposures during sleep on acute mountain sickness, exercise performance, and sleep during exposure to terrestrial altitude

There is an expectation that repeated daily exposures to normobaric hypoxia (NH) will induce ventilatory acclimatization and lessen acute mountain sickness (AMS) and the exercise performance decrement during subsequent hypobaric hypoxia (HH) exposure. However, this notion has not been tested objectively. Healthy, unacclimatized sea-level (SL) residents slept for 7.5 h each night for 7 consecutive nights in hypoxia rooms under NH [n = 14, 24 ± 5 (SD) yr] or "sham" (n = 9, 25 ± 6 yr) conditions. The ambient percent O(2) for the NH group was progressively reduced by 0.3% [150 m equivalent (equiv)] each night from 16.2% (2,200 m equiv) on night 1 to 14.4% (3,100 m equiv) on night 7, while that for the ventilatory- and exercise-matched sham group remained at 20.9%. Beginning at 25 h after sham or NH treatment, all subjects ascended and lived for 5 days at HH (4,300 m). End-tidal Pco(2), O(2) saturation (Sa(O(2))), AMS, and heart rate were measured repeatedly during daytime rest, sleep, or exercise (11.3-km treadmill time trial). From pre- to posttreatment at SL, resting end-tidal Pco(2) decreased (P < 0.01) for the NH (from 39 ± 3 to 35 ± 3 mmHg), but not for the sham (from 39 ± 2 to 38 ± 3 mmHg), group. Throughout HH, only sleep Sa(O(2)) was higher (80 ± 1 vs. 76 ± 1%, P < 0.05) and only AMS upon awakening was lower (0.34 ± 0.12 vs. 0.83 ± 0.14, P < 0.02) in the NH than the sham group; no other between-group rest, sleep, or exercise differences were observed at HH. These results indicate that the ventilatory acclimatization induced by NH sleep was primarily expressed during HH sleep. Under HH conditions, the higher sleep Sa(O(2)) may have contributed to a lessening of AMS upon awakening but had no impact on AMS or exercise performance for the remainder of each day.

Prolonged high-altitude residence impacts verbal working memory: an fMRI study

Oxygen is critical to normal brain functioning and development. In high altitude where the oxygen concentration and pressure are very low, human cognitive capability such as working memory has been found to be jeopardized. Such effect might persist with long-term high-altitude residence. The current study investigated the verbal working memory of 28 high-altitude residents with blood level oxygen dependent (BOLD) functional magnetic resonance imaging (fMRI), in contrast with that of the 30 sea level residents. All of the subjects were healthy college students, matched on their age, gender ratio and social-economic status; they also did not show any difference on their hemoglobin level. The high-altitude subjects showed longer reaction time and decreased response accuracy in behavioral performance. Both groups showed activation in the typical regions associated with the 2-back verbal working memory task, and the behavioral performance of both groups showed significant correlations with the BOLD signal change amplitude and Granger causality values (as a measure of the interregional effective connectivity) between these regions. With group comparison statistics, the high-altitude subjects showed decreased activation at the inferior and middle frontal gyrus, the middle occipital and the lingual gyrus, the pyramis of vermis, as well as the thalamus. In conclusion, the current study revealed impairment in verbal working memory among high-altitude residents, which might be associated with the impact of prolonged chronic hypoxia exposure on the brain functionality.

Hematological and Physiological Adaptations Following 46 Weeks of Moderate Altitude Residence

Although acclimatization to moderate altitude (MA) is thought to be unnecessary or to require minimal adaptation, retrospective data from the U.S. Air Force Academy (USAFA), a military college located at 2210 m, suggested otherwise. To further examine the utility of USAFA as a model for MA acclimatization, a longitudinal experimental design was prospectively utilized to determine the magnitude and time course of selected hematological and performance parameters following 46 weeks at this unique MA setting. Incoming USAFA male freshmen (n=55) were divided into experimental groups based on prior residence at sea level (SL) or MA. Hematological and performance parameters were repeatedly assessed during their entire first year at MA. Hematological data consisted of a complete blood count (CBC) with reticulocyte parameters, as well as determination of serum levels of ferritin, erythropoietin, and soluble transferrin receptor (sTfR). Performance testing included aerobic (1.5-mile run) and physical (push-ups, sit-ups, pull-ups, and standing long jump) fitness tests, maximal aerobic capacity, and running economy. Significant (p<0.05; main effect) hematological differences between SL and MA subjects were observed for the majority of the study. MA subjects had a significantly higher hemoglobin concentration ([Hb], +5.5%), hematocrit (+2.8%), and serum ferritin (+59.0%) and significantly lower sTfR (-11.4%) values than their SL peers. Although both serum ferritin and sTfR demonstrated a significant altitude group x time interaction, [Hb] and hematocrit did not. A significant main effect of altitude without interaction was also observed for performance parameters, with SL subjects having a significantly lower Vo2peak (-5.9%), slower 1.5- mile run time (+5.4%), poorer running economy (+6.6%), and lower composite physical fitness test score (-13.9%) than MA subjects. These results suggest that complete acclimatization to 2210 m by former SL residents may require lengthy physiological adaptations, as both hematological and physical performance differences persisted between groups. Further research at this uniquely well controlled MA setting is warranted.

Structural Modifications of the Brain in Acclimatization to High-Altitude

Adaptive changes in respiratory and cardiovascular responses at high altitude (HA) have been well clarified. However, the central mechanisms underlying HA acclimatization remain unclear. Using voxel-based morphometry (VBM) and diffusion tensor imaging (DTI) with fractional anisotropy (FA) calculation, we investigated 28 Han immigrant residents (17–22 yr) born and raised at HA of 2616–4200 m in Qinghai-Tibetan Plateau for at least 17 years and who currently attended college at sea-level (SL). Their family migrated from SL to HA 2–3 generations ago and has resided at HA ever since. Control subjects were matched SL residents. HA residents (vs. SL) showed decreased grey matter volume in the bilateral anterior insula, right anterior cingulate cortex, bilateral prefrontal cortex, left precentral cortex, and right lingual cortex. HA residents (vs. SL) had significantly higher FA mainly in the bilateral anterior limb of internal capsule, bilateral superior and inferior longitudinal fasciculus, corpus callosum, bilateral superior corona radiata, bilateral anterior external capsule, right posterior cingulum, and right corticospinal tract. Higher FA values in those regions were associated with decreased or unchanged radial diffusivity coinciding with no change of longitudinal diffusivity in HA vs. SL group. Conversely, HA residents had lower FA in the left optic radiation and left superior longitudinal fasciculus. Our data demonstrates that HA acclimatization is associated with brain structural modifications, including the loss of regional cortical grey matter accompanied by changes in the white matter, which may underlie the physiological adaptation of residents at HA.

Altitude-related Differences in Running Economy Among Sea Level Residents During 46 Weeks at Moderate Altitude

Altitude-related Differences in Running Economy Among Sea Level Residents During 46 Weeks at Moderate Altitude

Hematological Acclimatization and De-acclimatization of Former Sea Level Residents Exposed Chronically (46wks) to Moderate Altitude

Rapid loss in total hemoglobin mass (THM) as a result of neocytolysis has been documented in astronauts as well as high altitude mountain climbers upon return to lower altitudes. Whether similar hematological changes occur when moderate altitude (MA) residents return to sea level (SL) is unknown. PURPOSE: As part of a larger study examining physiological/hematological adaptations to MA, a subset of cadets' change in THM was assessed following 3 wks at SL after acclimatizing to the U.S. Air Force Academy (USAFA, 2210 m). METHODS: 58 freshman cadets' (18.3 + 0.4 yr; 8 MA, 50 SL (33 males, 17 females)) THM was assessed within the first 72 hrs of in-processing USAFA utilizing the optimized CO re-breathing protocol, and every 4 to 7 wks thereafter, to include just prior to departure from USAFA for a 3 wk winter break and immediately upon return to USAFA. Using a double-blind protocol, subjects were randomly assigned to either a placebo group (cornstarch) or a low-dose iron supplement group (100 mg ferrous sulfate), with doses to be taken daily throughout the study. RESULTS: SL cadets' THM increased significantly (p < 0.01) over time with the iron cohort peaking at wk 15 (+73.7 ± 39.4g, +10.4%), the placebo cohort peaking at wk 28 (+68.6 ± 9.4g, +9.4%); there was no significant (p = 0.31) change among the MA cadets. However, significant (p < 0.05) loss of THM was observed upon return to SL during the 3 wk winter break:Table: No caption provided.CONCLUSIONS: A significant 40+% loss of THM gained during MA adaptation occurred among subjects who returned to SL for 3 wks, suggesting the occurrence of neocytolysis. This research funded by a HQ AF/SGRS grant. Disclaimer: Views expressed are those of the authors and do not reflect the official policy or position of the USAF, the DoD, or the US Government.

Hydration effects on vascular fluid dynamics during acute exposure to 3,048 m

Vascular fluid dynamics [plasma volume (PV) and total circulating protein (TCP)] during acute (8‐h) high‐altitude (ALT) exposure are poorly described and the impact of hypohydration (HYPO) on these responses has not been reported. Seven men (25 ± 7 yr; 44.1 ± 4.9 ml/kg/min V02peak completed 4 experimental trials in a counterbalanced design. Subjects were sea level (SL) residents who had completed 4 days of heat acclimation prior to the trials. Trials were: a) SL‐Euhydrated (SL‐EUH); b) SL‐HYPO; c) ALT‐EUH; and d) ALT‐HYPO. The day before each trial, subjects completed a standardized exercise‐heat stress bout either with (EUH) or without (HYPO, −4% body mass) fluid replacement. Subjects maintained hydration status overnight and the following morning entered a hypobaric chamber (27°C) and rapidly ascended to either 150 m or 3,048 m (O2 saturation = 89 ± 3 %). During each 8 h trial, subjects were sedentary except for completing a standardized submaximal exercise bout (60 min) between 1–2.5 h of exposure. Plasma osmolality was not altered by ALT but was increased (291 ± 5 to 300 ± 6 mosmol/kg) by HYPO. PV was not altered by ALT (3.37 ± 320 L) but was reduced (320 ± 120 ml, 9.5%, p&lt;0.01) by HYPO. TCP (268 ± 30 g) was not altered by ALT or HYPO. These data indicate that vascular fluid dynamics are not altered during the initial 8h of exposure to 3,048 m regardless of hydration status.Not reflecting official views of the Army or DoD.

Altitude Threshold for Sleep Disturbances During Exposure to Acute Hypobaric Hypoxia

To determine the altitude threshold for sleep disturbances during exposure to hypobaric hypoxia, 43 sea‐level (SL) residents (mean±SD, 22±4 yr) completed a one night sleep assessment at SL and during exposure to one of six levels of hypobaric hyoxia (2000 m (N=4), 3000 m (N=5), 3500 m (N=8), 4000 m (N=9), 4300 m (N=12), or 4500 m (N=5)). Each wore a pulse oximeter to measure arterial oxygen saturation (SaO2) and desaturation events (# of &gt; 6% drops in SaO2 for ≥ 8 sec) and a wrist motion detector to estimate sleep quality (awakenings/hr) and quantity (% sleep). Mean sleep SaO2 (%) decreased (P&lt;0.05) from SL (96±1) to 2000 m (92±1), 3000 m (89±2), 3500 m (83±4), 4000 m (73±4), 4300 m (72±4) and 4500 m (71±4). Desaturation events/hr did not increase from SL (0±1) at 2000 m (1±12), 3000 m (12±34) or 3500 m (5±4) but increased (P&lt;0.05) at 4000 m (34±48), 4300 m (56±50) and 4500 m (117±17). Awakenings/hr did not increase from SL (1±1) at 2000 m (1±2), 3000 m (2±2) m, or 3500 m (2±2) but increased (P&lt;0.05) at 4000 m (3±1), 4300 m (6±4) and 4500 m (5±3). The % sleep did not decrease from SL (95±6) at 2000 m (95±21), 3000 m (87±21) and 3500 m (88±22) but decreased (P&lt;0.05) at 4000 m (72±20), 4300 m (54±28) and 4500 m (63±25). These results suggest that although mean sleep SaO2 decreases at moderate altitudes, the threshold for significant sleep disturbances does not occur until 4000 m. Authors′ views; not official U.S. Army or DoD policy.

Exercise Performance of Sea-Level Residents at 4300 m After 6 Days at 2200 m

Partial acclimatization resulting from staging at moderate altitude reduces acute mountain sickness during rapid exposure to higher altitudes (e.g., 4300 m). Whether staging also benefits endurance performance has not yet been scientifically evaluated. Determine the effectiveness of staging at 2200 m on time trial (TT) performance of unacclimatized sea-level residents (SLR) during rapid exposure to 4300 m. There were 10 healthy men (mean +/- SE: 21 +/- 1 yrs) who performed 720 kJ cycle TT at SL and following -2 h of exposure to 4300 m (459 Torr) before (ALT-1) and after (ALT-2) living for 6 d at 2200 m (601 Torr). Hemoglobin concentration ([Hb]), hematocrit (Hct), arterial oxygen saturation (SaO2), ratings of perceived exertion (RPE), and heart rate (HR) were measured before and during exercise. Compared to SL (73 +/- 6 min), TT performance was impaired (P < 0.01) by 38.1 +/- 6 min at ALT-1, but only by 18.7 +/- 3 min at ALT-2. The 44 +/- 8% TT improvement at 4300 m was directly correlated with increases in exercise SaO2 (R = 0.88, P < 0.03), but not to changes in [Hb] or Hct. In addition, RPE was lower (13 +/- 1 vs.16 +/- 1, P < 0.01) and HR remained at approximately 148 +/- 5 bpm despite performing the TT at a higher power output during ALT-2 than ALT-1 (120 +/- 7 vs.100 +/- 10 W, P < 0.01). Partial acclimatization resulting from staging attenuated the impairment in TT performance of SLR rapidly exposed to 4300 m. The close association between improved TT performance and changes in exercise SaO2, compared to a lack of association with changes in [Hb] or Hct, suggest ventilatory acclimatization may have been the major factor contributing to the performance improvement.

Normobaric Hypoxia Exposure During Sleep Produces Sleep-Specific Ventilatory Acclimatization At High Altitude

Sea-level (SL) residents have used repeated exposures to normobaric hypoxia (NH) during sleep to induce ventilatory acclimatization prior to rapid ascent to high altitude (HA). However, few reports have verified whether ventilatory acclimatization resulting from sleeping in NH is retained during subsequent HA exposure. PURPOSE: To determine if ventilatory acclimatization induced during NH is present during HA exposure. METHODS: Two groups of SL residents having similar resting end-tidal partial pressure of CO2 (PetCO2), peak oxygen uptake (∼47 ml/kg/min), and age (∼24 yr) slept for ∼6.5 hrs/night for 7 consecutive nights in portable rooms under blinded NH (n=14) or sham (n=8) conditions. Ambient % O2 for the NH group was progressively reduced by ∼0.30% O2 each night from ∼16.2% O2 (2200 m equivalent) on the 1st night to ∼14.4% O2 (3050 m) on the 7th night. The sham group remained at ≥20.5% O2 (150 m). Within 25 hrs of treatment end, all were exposed to HA (Pikes Peak, CO; 4300 m). At SL before and within 1 hr after treatment end, and in the first 24 hrs of HA, resting arterial oxygen saturation (SaO2) and PetCO2, and steady-state exercise and sleep SaO2 were measured. RESULTS: (Mean±SE) Over 7 nights during sleep, NH SaO2 decreased (p<0.05) from 92±1 to 88±1%, but sham SaO2 remained at 96±1%. From before to after treatment, SL resting PetCO2 decreased (p<0.001) for the NH group (39.1±0.8 to 34.9±0.7 mmHg) but not for the sham group (39.1±0.7 vs 38.3±1.0 mmHg). Within the first 5 hrs of HA, there were no between-group differences (NH vs sham) in resting PetCO2 (33.5±0.7 vs 33.1±1.0 mmHg), SaO2 (83±2 vs 83±1%) or exercise SaO2 (74±1 vs 73±2%). First night sleep SaO2 in HA was higher (p=0.031) for NH than for sham (78±1.3 vs 73±1.5%). CONCLUSION: These results indicate that ventilatory acclimatization induced by sleeping in NH is present at HA during sleep but not during the awake state. Thus, sleeping in NH at SL may not induce functionally useful ventilatory acclimatization for subsequent rapid ascent to high altitude. Funding: US Army MRMC ATO IV.MD.2006.01. Authors‘ views; not official U.S. Army or DoD policy.

Normobaric hypoxia exposure during sleep does not improve time‐trial performance in hypobaric hypoxia

This study determined if sleeping in normobaric hypoxia (NH) induces sufficient acclimatization to improve time‐trial (TT) performance in hypobaric hypoxia (HH). Two groups of sea‐level (SL) residents having similar peak oxygen uptakes (~47 ml/kg/min), ages (~24 yr), and weights (~75 kg) slept for ~6.5 hrs/night for 7 consecutive nights in portable rooms under blinded NH (n=14) or SL (n=8) conditions. Ambient % O2 for the NH group was progressively reduced by ~0.30% O2 each night from ~16.2% O2 (2200 m equivalent) on the 1st night to ~14.4% O2 (3050 m) on the 7th night. The SL group remained at =20.5% O2 (150 m). Within 25 hrs of treatment end, all were exposed to HH (Pikes Peak, CO; 4300 m). At SL before treatment and in the first 5 hrs of HH, an all‐out, 7‐mile treadmill TT was performed. Volunteers freely adjusted speed but grade was fixed at 3%. Heart rate (HR) and oxygen saturation (SaO2) were recorded every 5 min. For both groups, TT duration increased (P&lt;0.01) while HR and SaO2 decreased (P&lt;0.02) from SL to HH. There were no between‐group differences at SL or HH for TT duration (SL: 75±4 vs 73±4 min; HH: 103±6 vs 106±6 min), HR (SL: 165±2 vs 168±5 b/min; HH: 154±1 vs 150±3 b/min) or SaO2 (SL: 95±1 vs 96±1; HH: 74±1 vs 73±2). These results indicate that sleeping 7 nights in NH did not induce sufficient acclimatization to improve TT performance in HH. Funding: US Army MRMC ATO IV.MD.2006.01. Authors' views; not official U.S. Army or DoD policy.

Intermittent Hypoxic Exposure Does Not Improve Sleep at 4300 m

The purpose of this study was to determine in sea-level residents if 6 to 7 consecutive days of normobaric intermittent hypoxic exposure (IHE) (hypoxia room: 2-h ambient PO2=90 mmHg sedentary and 1-h ambient PO2=110 mmHg exercising at 80+/-5% of maximum heart rate) improved sleep quality (awakenings per hour) and quantity at altitude (4300 m). We hypothesized that IHE would improve sleep arterial oxygen saturation (SaO2) levels and decrease desaturation events, thereby contributing to improvements in sleep quality and quantity during subsequent exposure to high altitude. Ten sea-level residents (mean+/-SE: 22+/-1 yr, 179+/-2 cm, 79+/-3 kg) were assigned to an IHE group and six to a SHAM group (20+/-0.5 yr, 180+/-3 cm, 77+/-4 kg). Sleep quantity, SaO2, and heart rate (HR) were monitored at sea level and during high altitude (i.e., 4300 m in a hypobaric chamber) before pretest (PRE-T) and 60 h after posttest (POST-T) for the last IHE or SHAM treatment. Over the 6 to 7 days of IHE, resting SaO2 increased from 75+/-1% to 81+/-3% in the IHE group, while the SHAM group remained at 98+/-1%. From PRE-T to POST-T at 4300-m exposure, both the IHE and SHAM groups had significantly higher sleep SaO2, fewer desaturation events per hour, and an increase in the percentage of time asleep while sleeping (sleep percent). The IHE group, but not the SHAM group, had significantly lower sleep HR and a trend to more awakenings during the POST-T 4300-m exposure. These results indicate that although IHE treatment induced significant ventilatory acclimatization, relative to the SHAM group, IHE did not further improve sleep SaO2 quality and quantity following rapid ascent to 4300 m. Rather, it is likely that the acquired ventilatory acclimatization was lost in the 60 h between the last IHE session and the POST-T altitude exposure.

Relationship between autonomic nervous system function and acute mountain sickness

Objective To elucidate the role of the autonomic nervous system (ANS) in acute mountain sickness (AMS) during the initial phase at acute high-altitude exposure. Methods Ninety-nine healthy sea-level residents rapidly ascended to Tibet plateau (3 675 m altitude) by airplane from Chengdu plain (560 m altitude). ANS function was tested in plain and day 2–4 in Tibet by heart rate variability (HRV), cold pressor test (CPT). AMS was evaluated by clinic symptomatic scores. All subjects were divided into non-AMS group (57, scores ≤ 4) and AMS group (42, scores > 4). Results Compared with non-AMS group, AMS group had higher standard deviation of normal to normal intervals (SDNN), root mean square of delta RR (rMSSD), low-frequency (LF) power, and normalized low-frequency (LFnu) power in plain ( P < 0.05). After arrival at 3 675 m altitude, AMS group had greater reduction in percentage of delta RR > 50 ms(PNN 50), rMSSD ( P < 0.01) and SDNN, LF, total power (TP) ( P < 0.05). Although no significant differences in the increase of SP and DP during CPT were found between 2 groups in plain, the SP increase during CPT of AMS group was less than non-AMS group ( P < 0.05) at 3 675 m altitude. AMS symptomatic scores was not only positively correlated with SDNN, rMSSD, LF/HF in plain ( P < 0.05), but also negatively correlated with HFnu in plain ( P < 0.05). Conclusion During the initial high altitude exposure, ANS modulation is generally blunted, but the relatively predominant sympathetic control is enhanced, and this characteristic change of ANS function is positively correlated with the development of AMS.

Angiotensin-Converting Enzyme Genotype and Arterial Oxygen Saturation at High Altitude in Peruvian Quechua

The I-allele of the angiotensin-converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism has been associated with performance benefits at high altitude (HA). In n = 142 young males and females of largely Quechua origins in Peru, we evaluated 3 specific hypotheses with regard to the HA benefits of the I-allele: (1) the I-allele is associated with higher arterial oxygen saturation (Sa(O(2))) at HA, (2) the I-allele effect depends on the acclimatization state of the subjects, and (3) the putative I-allele effect on Sa(O(2)) is mediated by the isocapnic hypoxic ventilatory response (HVR, l/min(1)/% Sa(O(2))(1)). The subject participants comprised two different study groups including BLA subjects (born at low altitude) who were lifelong sea-level residents transiently exposed to hypobaric hypoxia (<24 h) and BHA subjects (born at HA) who were lifelong residents of HA. To control for the possibility of population stratification, Native American ancestry proportion (NAAP) was estimated as a covariate for each individual using a panel of 70 ancestry-informative molecular markers (AIMS). At HA, resting and exercise Sa(O(2)) was strongly associated with the ACE genotype, p = 0.008 with approximately 4% of the total variance in Sa(O(2)) attributed to ACE genotype. Moreover, I/I individuals maintained approximately 2.3 percentage point higher Sa(O(2)) compared to I/D and D/D. This I-allele effect was evident in both BLA and BHA groups, suggesting that acclimatization state has little influence on the phenotypic expression of the ACE gene. Finally, ACE genotype was not associated with the isocapnic HVR, although HVR had a strong independent effect on Sa(O(2)) (p = 0.001). This suggests that the I-allele effect on Sa(O(2)) is not mediated by the peripheral control of breathing, but rather by some other central cardiopulmonary effect of the ACE gene on the renin-angiotensin-aldosterone system (RAAS).

Living For Six Days At 2200 M Improves Prolonged Time-Trial Performance Of Sea-Level Residents Exposed To 4300 M.

It is well established that the magnitude of the initial impairment in prolonged time-trial (TT) performance that occurs when sea-level residents (SLR) ascend rapidly to high altitude (e.g., 4300 m) is attenuated with acclimatization to the same elevation. Whether adaptations acquired from living temporarily at a moderate altitude ("staging") just prior to the high altitude exposure will also benefit TT performance is less certain. PURPOSE: To determine the effectiveness of staging at 2200 m on TT performance of SLR during subsequent exposure to 4300 m. METHODS: Ten healthy men (mean ± SE: 21 ± 1 yrs) were tested on a cycle ergometer during steady-state exercise (SSE) and then during a 720 kJ maximum effort TT at SL, and again beginning within 3 hrs of exposure to 4300 m (459 Torr) before (preSTG) and after (postSTG) staging for 6 d at 2200 m (601 Torr). SSE during preSTG and postSTG was performed for 20 min at low (73 ± 5 W) and moderate (116 ± 8 W) power outputs to assess adaptation. During the TT, the men freely adjusted power output. Arterial oxygen saturation (SaO2), heart rate (HR), and ratings of perceived exertion (RPE) were measured every 5 min during all exercise. RESULTS: At 4300m, from preSTG to postSTG, SaO2 increased during low SSE (75 ± 2 to 77 ± 1%) while HR (148 ± 5 to 140 ± 5 b/min) and RPE (12 ± 1 to 9 ± 1) decreased during moderate SSE (all P<0.01). TT duration increased (P<0.01) from 73 ± 6 min at SL to 111 ± 6 min at preSTG and to 92 ± 7 min at postSTG, and was 17 ± 6% (19 ± 6 min) faster postSTG than preSTG (P<0.01). Despite performing the TT at a higher power output postSTG than preSTG (120 ± 7 vs 100 ± 10 W, P<0.01), RPE was lower (13 ± 1 vs 16 ± 1, P<0.01) and SaO2 tended to be higher (76 ± 1 vs 74 ± 1%, P=0.15). TT performance of all 10 men improved preSTG to postSTG (range: 2 to 56 min) with the extent of each individual's improvement being directly related to their increase in SaO2 during SSE and the TT (R = 0.88, P<0.03). CONCLUSIONS: The impairment in prolonged TT performance of SLR rapidly exposed to 4300 m was attenuated after living for 6 days at a moderate altitude of 2200 m. The close association between improved TT performance and higher exercise SaO2 suggest the major contributing factor was increased ventilation. Funding provided by US Army Medical Research and Materiel Command ATO IV.MD.2006.01. Authors' views; not official U.S. Army or DoD policy.

Effects of Staging at 2200 m on Eye-Hand Speed and Accuracy of Sea-Level Residents Exposed to 4300 m

Effects of Staging at 2200 m on Eye-Hand Speed and Accuracy of Sea-Level Residents Exposed to 4300 m

Residents at High Altitude Show a Lower Glucose Profile Than Sea-Level Residents Throughout 12-Hour Blood Continuous Monitoring

It is known that residents at high altitude (HA) have a lower basal glycemia than residents at sea level (SL). However, whether such a difference is maintained throughout the full day remains unknown. We compared 12-h blood glucose profiles from 10 healthy males native residents at HA (3250 m) and 8 male residents at SL. Glucose profile at HA was lower throughout the glucose monitoring than that at SL (mean profile: 50.6 +/- 3.7 and 73.4 +/- 4.0 mg/dL, respectively; p < 0.001). Basal and postprandial insulin and triacylglycerol values were similar in both groups. In conclusion, HA natives resident have a lower blood glucose profile than SL residents throughout 12-h continuous monitoring.

GXT Responses in Altitude-Acclimatized Cyclists during Sea-Level Simulation

This study examined the effects of gender on graded exercise stress test (GXT) response in moderate-altitude (MA)-acclimatized cyclists during sea-level (SL) simulation. It was hypothesized that alterations in arterial saturation would relate to changes in VO2peak. Twenty competitive cyclists (12 males, 8 females) who were residents of MA locations underwent two randomized bicycle GXTs: one under local normoxic hypobaria, and the other under simulated SL conditions. Under the SL condition, the cyclists demonstrated a significant increase (2-3%) in absolute and relative VO2peak, improved (4%) economy at lactate threshold (LT), and time-adjusted peak power (7%); the range of improvement between individuals varied from -6% to +25%. Simulated SL also resulted in a greater arterial saturation (S(a)O2) at rest and VO2peak, and significantly less desaturation (4 vs 8%) from rest to VO2peak. The individual variability in the change (Delta) in VO2peak was not significantly correlated to SL S(a)O2 or any other S(a)O2 variable analyzed, regardless of whether we examined each gender individually or combined. Significant correlations were found between Delta-peak power and Delta-economy as well as Delta-VO2peak and Delta-GXT time. These correlations as well as degree of improvement varied by gender. These data suggest that chronic residence at MA may attenuate the occurrence of exercise-induced arterial hypoxemia and eliminate the relationship between S(a)O2 and Delta-VO2peak that has been reported among SL residents acutely exposed to altitude. Additionally, the improvements that occur in predictors of aerobic performance when MA residents are exposed acutely to SL conditions have a large degree of individual variability, and the mechanism(s) for improvement may vary by gender.

Physical Fitness and Hematological Changes During Acclimatization to Moderate Altitude: A Retrospective Study

While high altitude adaptations have been studied extensively, limited research has examined moderate altitude (MA: 1500 to 3000 m) adaptations and their time course, despite the fact that millions of people sojourn to or reside at MA. We retrospectively examined long-term MA acclimatization by analyzing recurring physical fitness test results and hematological data among 2147 college-age male cadets previously residing at either sea level (SL) or MA and currently attending the U.S. Air Force Academy (USAFA), a unique, regimented, and well-controlled military university located at 2210 m. Significant (p < 0.01) differences were found in aerobic and anaerobic fitness test scores between former SL and MA subjects, with MA subjects scoring 27 points (8%) higher during a 1.5-mile aerobic fitness run and 18 points (6%) higher than SL subjects in the anaerobic fitness test for 2 yr. These differences may be partly explained by the hematological differences observed. Hemoglobin concentration ([Hb]) was significantly (p < 0.001) higher (6.3%; approximately 1 g/dL) in MA subjects prior to arrival at USAFA and acutely, but the difference between altitude conditions was gone at the next retrospective blood draw (+17 months). After 2.5 yr at USAFA, former SL residents had significantly (p < 0.001) higher [Hb] by +10%, or 1.5 g/dL versus prearrival values. This study suggests that significant hematological acclimatization occurs with MA exposure and requires greater than 7 months to reach stability. The altitude-induced erythropoiesis may explain in part the improvements in aerobic performance, but altitude-related anaerobic differences still remain after hematological acclimatization.

Autonomic regulation during orthostatic stress in highlanders: comparison with sea‐level residents

This report is a comparison of orthostatic tolerance and autonomic function in three groups of high-altitude dwellers: Andeans with and without chronic mountain sickness (CMS) and healthy Ethiopians. Results are compared with those from healthy sea-level residents. The aim was to determine whether different high-altitude populations adapted differently to the prevailing hypobaric hypoxia. Orthostatic tolerance was assessed using a test involving head-up tilt (HUT) and graded lower body suction. This was performed at the subjects' resident altitude. Blood pressure (Portapres) and R-R interval (ECG) were recorded during the test, and spectral and cross-spectral analyses of heart period and systolic blood pressure time series were performed using data obtained both while supine and during HUT. The transfer function gain in the low-frequency range (LF, approximately 0.1 Hz) at the point of maximal coherence was used as a measure of cardiac baroreflex sensitivity (BRS). As previously reported, Peruvians displayed an unusually good orthostatic tolerance, while Ethiopians showed an orthostatic tolerance comparable to that of healthy sea-level residents. There were no significant differences between groups in the supine values of the spectral analysis results. Head-up tilt induced the expected changes in Ethiopians (an increase in the LF components and a decrease in the respiratory components) but not in Andeans. Cross-spectral analysis showed abnormal results from all groups of high-altitude dwellers. These results indicate that Ethiopians, but not Peruvians, behave similarly to sea-level residents in terms of orthostatic tolerance and autonomic responses to orthostatic stress, as assessed from spectral analyses, and this indicates good adaptation to their environment. However, in all the high-altitude groups the results of cross-spectral analysis were atypical, suggesting some degree of impairment in baroreflex function.