Biomedical subjects

J R Sutton

Publications and source records attributed to J R Sutton.

At least 37 records · Page 2Linked to original sources

PubMed1996

Fluid and electrolyte hormonal responses to exercise and acute plasma volume expansion.

To investigate the effect of acute graded increases in plasma volume (PV) on fluid and regulatory hormone levels, eight untrained men (peak aerobic power 45.2 +/- 2.2 ml.kg-1.min-1) performed prolonged cycle exercise (46 +/- 4% maximal aerobic power on three occasions, namely, with no PV expansion (Con) and after 14% (Low) and 21% (High) expansions, respectively. The exercise plasma levels of aldosterone (Aldo), arginine vasopressin (AVP), and atrial natriuretic peptide (ANP) were all altered by acute PV increases. A pronounced blunting (P < 0.05) of the Aldo response during exercise was observed, the magnitude of which was directly related to the amount of hypervolemia (Con < Low < High). At 120 min of exercise, Aldo concentrations were 660 +/- 71, 490 +/- 85, and 365 +/- 78 pg/ml for Con, Low, and High conditions, respectively. In contrast, the lower AVP and the higher ANP observed during exercise appeared to be due to the effect of PV expansion on resting concentrations. Because osmolality did not vary among conditions, the results indicate that PV represents an important primary stimulus in the response of Aldo to exercise. The lower exercise blood concentrations of both epinephrine and norepinephrine observed with PV expansion would suggest that a lower sympathetic drive may be implicated at least in the lower Aldo responses.

Adult↗

PubMed1995

Measurement of sarcoplasmic reticulum function in mammalian skeletal muscle: technical aspects.

Two recently developed methods for measuring the maximal rate of Ca2+ uptake and Ca2+ ATPase activity (EC 3.1.6.38) in vitro use muscle homogenate rather than isolated sarcoplasmic reticulum (SR). In this study we investigated technical aspects of these assays, including specificity and variability of the assays, the effect of different freezing treatments on maximal Ca2+ uptake and Ca2+ ATPase activity of human and rat muscle homogenate, stability of the homogenate, and the modification of the Ca2+ uptake assay to measure Ag(+)-induced Ca2+ release. Addition of cyclopiazonic acid (20 microM) blocked Ca2+ uptake, demonstrating specificity of the assay. Using frozen muscle homogenate, the inter- and intraassay variation for both assays was less than 9%. Whereas homogenates were stable to freezing for both Ca2+ uptake and Ca2+ ATPase activity, there was a significant (P < 0.05) decrease in activity when muscle was freeze-dried or quickly frozen in small pieces. After 1 h on ice, rat muscle homogenate Ca2+ uptake and Ca2+ ATPase activity had decreased by 6.0% (ns) and 3.6% (P < 0.05), respectively; after 3 h, activity had decreased by 15.3 and 14.7%, respectively (P < 0.01). The Ca2+ uptake assay was modified to allow measurement of Ag(+)-induced Ca2+ release. Following homogenate addition, after the SR vesicles were loaded with Ca2+ and [Ca2+] had declined to a plateau, AgNO3 (141 microM) was added, initiating release of Ca2+ into the assay solution. Addition of dithiothreitol (4 mM) blocked the Ag(+)-induced Ca2+ release, demonstrating specificity of the assay.

Animals↗

PubMed1995

Relationships between muscle membrane lipids, fiber type, and enzyme activities in sedentary and exercised rats.

Insulin resistance in skeletal muscle is associated with 1) relative increases in the proportion of glycolytic and fast-twitch muscle fibers and decreases in the proportion of more oxidative fibers and 2) a higher proportion of the saturated fatty acids in membrane structural lipids. Exercise is known to improve insulin action. The aims of the current studies were 1) to investigate the relationship between muscle fiber type and membrane fatty acid composition and 2) to determine how voluntary exercise might influence both variables. In sedentary Wistar rats in experiment 1, increased amounts of unsaturated fatty acids were found in the more oxidative insulin-sensitive red quadriceps and soleus muscles, whereas reduced levels of polyunsaturated fatty acids were found in primarily glycolytic white quadriceps muscles. In experiment 2, voluntary running-wheel exercise by adult female rats over 45 days resulted in reduced proportions of type IIb fibers (P = 0.01) and increased proportions of type IIa/IIx fibers (P = 0.03) in extensor digitorum longus muscle. The magnitude of these changes was related to the distance run (r = -0.73, P = 0.04; r = 0.79, P = 0.02, respectively). Exercise significantly increased oxidative capacity, as assessed by the proportion of intensely NADH-stained fibers (P = 0.0004) and citrate synthase (P = 0.003) and hexokinase (P = 0.04) activities. Citrate synthase activity was also increased by exercise in soleus muscle, where, as expected, no fiber type changes were detected. No significant differences in the fatty acid profile of soleus and extensor digitorum longus were found between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Heat exhaustion in The Sun-Herald City to Surf fun run.

OBJECTIVE: To investigate the relationship between motivational factors and physical and biological causes of heat exhaustion in fun run entrants. DESIGN AND SETTING: Case-control study, The Sun-Herald City to Surf fun runs in Sydney in 1991 and 1992. PARTICIPANTS: There were 63,732 race entrants who completed the run and received a finishing time; 79 runners with heat exhaustion and 310 age, sex and performance matched controls were enrolled in the study. MAIN OUTCOME MEASURE: A diagnosis of heat exhaustion was made if a runner collapsed and, when first receiving medical care, had a rectal temperature of 38 degrees C or higher. RESULTS: Two readily identifiable groups of runners were at high risk of heat exhaustion--accomplished non-élite (preferred) runners and runners of good ability (Group A). The attack rate was highest among accomplished non-élite runners, but a combination of a relatively high rate and the large number of entrants in Group A runners accounted for most cases. Four major risk factors for heat exhaustion were identified: motivation to exceed previous performance targets; failure to drink fluids during the run; failure of trained runners to acclimatise for the race by training in the warmer parts of the day; and previous history of heat exhaustion. CONCLUSION: Information from this investigation will enable more effective targeting of educational prevention programs in The Sun-Herald City to Surf fun run and provide baseline data for monitoring the effectiveness of these programs to modify high risk behaviour by participants.

Adolescent↗

PubMed1994

Effect of chronic acetazolamide administration on gas exchange and acid-base control after maximal exercise.

The interaction between systems regulating acid-base balance (i.e., CO2, strong ions, week acids) was studied in six subjects for 10 min after 30 s of maximal isokinetic cycling during control conditions (CON) and after 3 days of chronic acetazolamide (ChACZ) administration (500 mg/8 h po) to inhibit carbonic anhydrase (CA). Gas exchange was measured; arterial and venous forearm blood was sampled for acid-base variables. Muscle power output was similar in ChACZ and CON, but peak O2 intake was lower in ChACZ; peak CO2 output was also lower in ChACZ (2,207 +/- 220 ml/min) than in CON (3,238 +/- 87 ml/min). Arterial PCO2 was lower at rest, and its fall after exercise was delayed in ChACZ. In ChACZ there was a higher arterial [Na+] and lower arterial [lactate-] ([La-]) accompanied by lower arterial [K+] and higher arterial [Cl-] during the first part of recovery, resulting in a higher arterial plasma strong ion difference (sigma [cations] - sigma [anions]). Venoarterial (v-a) differences across the forearm showed a similar uptake of Na+, K+, Cl-, and La- in ChACZ and CON. Arterial [H+] was higher and [HCO3-] was lower in ChACZ. Compared with CON, v-a [H+] was similar and v-a [HCO3-] was lower in ChACZ. Chronic CA inhibition impaired the efflux of CO2 from inactive muscle and its excretion by the lungs and also influenced the equilibration of strong ions.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetazolamide↗

PubMed1994

Sympathetic and parasympathetic indicators of heart rate control at altitude studied by spectral analysis.

The adaptive responses of the cardiovascular system to altitude appear to be dominated by increased sympathetic neural activity. We investigated the combined roles of the sympathetic and parasympathetic nervous systems (SNS and PNS, respectively) in the early (days 4-5) and subsequent (days 11-12) phases of acclimatization on Pike's Peak, CO (4,300 m), by spectral analysis of heart rate variability. Male subjects were randomly assigned to groups receiving oral propranolol (240 mg/day; n = 6) or a matched placebo (n = 3). On ascent to altitude, the high-frequency, fractal, and total spectral powers were reduced in the placebo group during days 4-5 and 11-12. At altitude during days 4-5, all three placebo group subjects increased SNS and decreased PNS activities compared with at sea level, and during days 11-12 SNS decreased and PNS increased compared with days 4-5. Relative to the placebo group, propranolol caused lengthening of the R-R interval; increases in high-frequency power, total spectral power, and the PNS indicator; and a decrease in the SNS indicator. Total spectral power tended to decrease at altitude, but there were no effects of altitude on PNS and SNS indicators in the propranolol group. The data from the placebo and propranolol groups suggest that both the PNS and SNS are involved in the elevated heart rate during the early phase of altitude acclimatization. Changes in heart rate variability during days 11-12 at altitude must be considered in light of the possible reductions in sympathetic receptor number noted in previous studies.

Acclimatization↗

PubMed1993

Operation Everest II: an indication of deterministic chaos in human heart rate variability at simulated extreme altitude.

It has been shown that fluctuation of human heartbeat intervals (heart rate variability, HRV) reflects variations in autonomic nervous system activity. We studied HRV at simulated altitudes of over 6000 m from Holter electrocardiograms recorded during the Operation Everest II study (Houston et al. 1987). Stationary, approximately 30-min segments of HRV data from six subjects at sea level and over 6000 m were supplied to (1) spectral analysis to evaluate sympathetic and parasympathetic nervous system (SNS, PNS) activity, (2) the analysis of Poincaré section of the phase space trajectory reconstructed on a delayed coordinate system to evaluate whether there was fluctuation with deterministic dynamics, (3) the estimation of the correlation dimension to evaluate a static property of putative attractors, and (4) the analysis of nonlinear predictability of HRV time series which could reflect a dynamic property of the attractor. Unlike HRV at sea level, the recordings at over 6000 m showed a strong periodicity (period of about 20 s) with small cycle-to-cycle perturbation. When this perturbation was expressed on a Poincaré section, it seemed to be likely that the perturbation itself obeyed a deterministic law. The correlation dimensions of these recordings showed low dimensional values (3.5 +/- 0.4, mean +/- SD), whereas those of the isospectral surrogates showed significantly (P < 0.05) higher values (5.3 +/- 0.5) with embedding dimensions of 5.6 +/- 0.9.(ABSTRACT TRUNCATED AT 250 WORDS)

Altitude↗

PubMed1993

Minimal hypoxic pulmonary hypertension in normal Tibetans at 3,658 m.

Elevated pulmonary arterial pressure in high-altitude residents may be a maladaptive response to chronic hypoxia. If so, well-adapted populations would be expected to have pulmonary arterial pressures that are similar to sea-level values. Five normal male 22-yr-old lifelong residents of > or = 3,600 m who were of Tibetan descent were studied in Lhasa (3,658 m) at rest and during near-maximal upright ergometer exercise. We found that resting mean pulmonary arterial pressure [15 +/- 1 (SE) mmHg] and pulmonary vascular resistance (1.8 +/- 0.2 Wood units) were within sea-level norms and were little changed while subjects breathed a hypoxic gas mixture [arterial O2 pressure (PaO2) = 36 +/- 2 Torr]. Near-maximal exercise [87 +/- 13% maximal O2 uptake (VO2max)] increased cardiac output more than threefold to values of 18.3 +/- 1.2 l/min but did not elevate pulmonary vascular resistance. Breathing 100% O2 during near-maximal exercise did not reduce pulmonary arterial pressure or vascular resistance. We concluded that this small sample of healthy Tibetans with lifelong residence > or = 3,658 m had resting pulmonary arterial pressures that were normal by sea-level standards and exhibited minimal hypoxic pulmonary vasoconstriction, both at rest and during exercise. These findings are consistent with remarkable cardiac performance and high-altitude adaptation.

Adult↗

PubMed1993

Autonomic regulation of heart rate response to exercise in Tibetan and Han residents of Lhasa (3,658 m).

To test the hypothesis that native high-altitude residents have less beta-sympathetic and more parasympathetic tone than newcomers, we compared the effects of beta-sympathetic and parasympathetic blockade in 10 Tibetan and 9 Han acclimatized male residents of Lhasa, Tibet Autonomous Region, China (elevation 3,658 m). Each subject was studied during cycle ergometer exercise at 70, 132, and 191 W after placebo (normal saline), beta-sympathetic (propranolol, 0.2 mg/kg iv), or parasympathetic (atropine, 0.04 mg/kg iv) blockade in random order on different days. At rest, the fall in resting heart rate with propranolol and the rise with atropine were equal in Tibetan and Han subjects. During exercise, the fall in heart rate with propranolol relative to placebo values was greater in the Han than in the Tibetan group, whereas the rise in heart rate with atropine was greater in the Tibetans. Propranolol or atropine administration did not change minute ventilation per unit O2 consumption in either group. At the highest level of exercise on the placebo day, the Tibetans achieved a higher work load and level of O2 consumption than the Han subjects. Propranolol or atropine reduced O2 consumption and work load similarly in the two groups at the highest exercise level. The results supported our hypothesis that native Tibetan residents of high altitude exhibit more para-sympathetic and less beta-sympathetic tone during exercise. Neither relatively greater parasympathetic nor less sympathetic activation appeared implicated in the greater exercise capacity of Tibetans compared with that of acclimatized newcomer residents of high altitude.

Adult↗

PubMed1992

Oxygen transport and cardiovascular function at extreme altitude: lessons from Operation Everest II.

Operation Everest II was designed to examine the physiological responses to gradual decompression simulating an ascent of Mt Everest (8,848 m) to an inspired PO2 of 43 mmHg. The principal studies conducted were cardiovascular, respiratory, muscular-skeletal and metabolic responses to exercise. Eight healthy males aged 21-31 years began the "ascent" and six successfully reached the "summit", where their resting arterial blood gases were PO2 = 30 mmHg and PCO2 = 11 mmHg, pH = 7.56. Their maximal oxygen uptake decreased from 3.98 +/- 0.2 L/min at sea level to 1.17 +/- 0.08 L/min at PIO2 43 mmHg. The principal factors responsible for oxygen transport from the atmosphere to tissues were (1) Alveolar ventilation--a four fold increase. (2) Diffusion from the alveolus to end capillary blood--unchanged. (3) Cardiac function (assessed by hemodynamics, echocardiography and electrocardiography)--normal--although maximum cardiac output and heart rate were reduced. (4) Oxygen extraction--maximal with PvO2 14.8 +/- 1 mmHg. With increasing altitude maximal blood and muscle lactate progressively declined although at any submaximal intensity blood and muscle lactate was higher at higher altitudes.

Adult↗

PubMed1992

Are Tibetans better adapted?

Evidence is reviewed from our recent (1987-1991) investigations which demonstrate better high-altitude adaptation among Tibetans than in acclimatized newcomers or other lifelong high-altitude residents. Characteristics of oxygen transport contributing to the Tibetans' remarkable exercise performance are described.

Acclimatization↗

PubMed1992

Effect of acetazolamide on gas exchange and acid-base control after maximal exercise.

To investigate the interactions between the systems that contribute to acid-base homeostasis after severe exercise, we studied the effects of carbonic anhydrase inhibition on exchange of strong ions and CO2 in six subjects after 30 s of maximal isokinetic cycling exercise. Each subject exercised on two randomly assigned occasions, a control (CON) condition and 30 min after intravenous injection of 1,000 mg acetazolamide (ACZ) to inhibit blood carbonic anhydrase activity. Leg muscle power output was similar in the two conditions; peak O2 uptake (VO2) after exercise was lower in ACZ (2,119 +/- 274 ml/min) than in CON (2,687 +/- 113, P less than 0.05); peak CO2 production (VCO2) was also lower (2,197 +/- 241 in ACZ vs. 3,237 +/- 87 in CON, P less than 0.05) and was accompanied by an increase in the recovery half-time from 1.7 min in CON to 2.3 min in ACZ. Whereas end-tidal PCO2 was lower in ACZ than in CON, arterial PCO2 (PaCO2) was higher, and a large negative end-tidal-to-arterial difference (less than or equal to 20 Torr) was present in ACZ on recovery. In ACZ, postexercise increases in arterial plasma [Na+] and [K+] were greater but [La-] was lower. Arteriovenous differences across the forearm showed a greater uptake of La- and Cl- in CON than in ACZ. Carbonic anhydrase inhibition with ACZ, in addition to impairing equilibration of the CO2 system to the acid-base challenge of exercise, was accompanied by changes in equilibration of strong inorganic ions. A lowered plasma [La-] was not accompanied by greater uptake of La- by inactive muscle.

Acetazolamide↗

PubMed1992

Physiological effects of tapering in highly trained athletes.

This study examined some of the physiological and performance effects of three different tapers in highly trained athletes. After 8 wk of training, nine male middle-distance runners were randomly assigned to one of three different 7-day tapers: a high-intensity low-volume taper (HIT), a low-intensity moderate-volume taper (LIT), or a rest-only taper (ROT). After the first taper, subjects resumed training for 4 wk and performed a second taper and then resumed training for 4 wk and completed the remaining taper, so that each subject underwent all three tapers. Performance was measured before and after each taper by a treadmill run to fatigue at a velocity equivalent each subject's best 1,500-m time. Voluntary isometric strength and evoked contractile properties of the quadriceps were measured before and after each taper, as were muscle glycogen concentration and citrate synthase activity (from needle biopsies) and total blood and red cell volume by 125I and 51Cr tagging. Maximal O2 consumption was unaffected by all three tapers, but running time to fatigue increased significantly after HIT (+22%). It was unaffected by LIT (+6%) and ROT (-3%) procedure. Citrate synthase activity increased significantly with HIT and decreased significantly with ROT. Muscle glycogen concentration increased significantly after ROT and HIT, and strength increased after all three tapers. Total blood volume increased significantly after HIT and decreased after ROT.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Increased energy intake minimizes weight loss in men at high altitude.

The hypothesis that high-altitude weight loss can be prevented by increasing energy intake to meet energy requirement was tested in seven men, 23.7 +/- 4.3 (SD) yr, taken to 4,300 m for 21 days. Energy intake required to maintain body weight at sea level was found to be 3,118 +/- 300 kcal/day, as confirmed by nitrogen balance. Basal metabolic rate (BMR), determined by indirect calorimetry, increased 27% on day 2 at altitude and then decreased and reached a plateau at 17% above the sea level BMR by day 10. Energy expended during strenuous activities was 37% lower at altitude than at sea level. Fecal excretion of energy, nitrogen, total fiber, and total volatile fatty acids was not significantly affected by altitude. Energy intake at altitude was adjusted after 1 wk, on the basis of the increased BMR, to 3,452 +/- 452 kcal/day. Mean nitrogen balance at altitude was negative (-0.25 +/- 0.71 g/day) before energy intake was adjusted but rose significantly thereafter (0.20 +/- 0.71 and 0.44 +/- 0.66 g/day during weeks 2 and 3). Mean body weight decreased 2.1 +/- 1.0 kg over the 3 wk of the study, but the rate of weight loss was significantly diminished after the increase in energy intake (201 +/- 75 vs. 72 +/- 48 g/day). Individual regression lines drawn through 7-day segments of body weight showed that in four of seven subjects the slopes of body weight were not significantly different from zero after the 2nd wk. Thus weight loss ceased in four of seven men in whom increased BMR at altitude was compensated with increased energy intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Muscle accounts for glucose disposal but not blood lactate appearance during exercise after acclimatization to 4,300 m.

We hypothesized that the increased blood glucose disappearance (Rd) observed during exercise and after acclimatization to high altitude (4,300 m) could be attributed to net glucose uptake (G) by the legs and that the increased arterial lactate concentration and rate of appearance (Ra) on arrival at altitude and subsequent decrease with acclimatization were caused by changes in net muscle lactate release (L). To evaluate these hypotheses, seven healthy males [23 +/- 2 (SE) yr, 72.2 +/- 1.6 kg], on a controlled diet were studied in the postabsorptive condition at sea level, on acute exposure to 4,300 m, and after 3 wk of acclimatization to 4,300 m. Subjects received a primed-continuous infusion of [6,6-D2]glucose (Brooks et al., J. Appl. Physiol. 70: 919-927, 1991) and [3-13C]lactate (Brooks et al., J. Appl. Physiol. 71:333-341, 1991) and rested for a minimum of 90 min, followed immediately by 45 min of exercise at 101 +/- 3 W, which elicited 51.1 +/- 1% of the sea level peak O2 uptake (65 +/- 2% of both acute altitude and acclimatization peak O2 uptake). Glucose and lactate arteriovenous differences across the legs and arms and leg blood flow were measured. Leg G increased during exercise compared with rest, at altitude compared with sea level, and after acclimatization. Leg G accounted for 27-36% of Rd at rest and essentially all glucose Rd during exercise. A shunting of the blood glucose flux to active muscle during exercise at altitude is indicated. With acute altitude exposure, at 5 min of exercise L was elevated compared with sea level or after acclimatization, but from 15 to 45 min of exercise the pattern and magnitude of L from the legs varied and followed neither the pattern nor the magnitude of responses in arterial lactate concentration or Ra. Leg L accounted for 6-65% of lactate Ra at rest and 17-63% during exercise, but the percent Ra from L was not affected by altitude. Tracer-measured lactate extraction by legs accounted for 10-25% of lactate Rd at rest and 31-83% during exercise. Arms released lactate under all conditions except during exercise with acute exposure to high altitude, when the arms consumed lactate. Both active and inactive muscle beds demonstrated simultaneous lactate extraction and release. We conclude that active skeletal muscle is the predominant site of glucose disposal during exercise and at high altitude but not the sole source of blood lactate during exercise at sea level or high altitude.

Acclimatization↗

PubMed1992

Operation Everest II: metabolic and hormonal responses to incremental exercise to exhaustion.

The reasons for the reduced exercise capacities observed at high altitudes are not completely known. Substrate availability or accumulations of lactate and ammonium could have significant roles. As part of Operation Everest II, peak oxygen uptakes were determined in five normal male volunteers with use of progressively increasing cycling work loads at ambient barometric pressures of 760, 380, and 282 Torr. Decrements from sea level (SL) to 380 and 282 Torr occurred in peak power output (19 and 47%), time to exhaustion (19 and 48%), and oxygen uptake (41 and 61%), respectively. Arterial saturations after exhaustive exercise were decreased to 63% at 380 Torr and 39% at 282 Torr. At 380 and 282 Torr, postexercise plasma concentrations of glucose and free fatty acids were not increased, whereas plasma glycerol concentrations were decreased relative to SL (145 +/- 24 microM at 380 Torr and 77 +/- 10 microM at 282 Torr vs. 213 +/- 24 microM at SL). Preexercise plasma insulin concentrations were elevated at both 380 and 282 Torr (87 +/- 16 pM at 380 Torr and 85 +/- 18 pM at 282 Torr vs. 41 +/- 30 pM at SL). In general, postexercise concentrations of plasma catecholamines were decreased at altitude compared with SL. Preexercise lactate and ammonium concentrations were not different at any simulated altitude. From these data neither substrate availability nor metabolic product accumulation limited exercise capacity at extreme simulated altitude.

Adult↗

PubMed1992

Altitude acclimatization and energy metabolic adaptations in skeletal muscle during exercise.

To determine whether the working muscle is able to sustain ATP homeostasis during a hypoxic insult and the mechanisms associated with energy metabolic adaptations during the acclimatization process, seven male subjects [23 +/- 2 (SE) yr, 72.2 +/- 1.6 kg] were given a prolonged exercise challenge (45 min) at sea level (SL), within 4 h after ascent to an altitude of 4,300 m (acute hypoxia, AH), and after 3 wk of sustained residence at 4,300 m (chronic hypoxia, CH). The prolonged cycle test conducted at the same absolute intensity and representing 51 +/- 1% of SL maximal aerobic power (VO2 max) and between 64 +/- 2 (AH) and 66 +/- 1% (CH) at altitude was performed without a reduction in ATP concentration in the working vastus lateralis regardless of condition. Compared with rest, exercise performed during AH resulted in a greater increase (P < 0.05) in muscle lactate concentration (5.11 +/- 0.68 to 22.3 +/- 6.1 mmol/kg dry wt) than exercise performed either at SL (5.88 +/- 0.85 to 11.5 +/- 3.1) or CH (5.99 +/- 0.88 to 12.4 +/- 2.1). These differences in lactate concentration have been shown to reflect differences in arterial lactate concentration and glycolysis (Brooks et al. J. Appl. Physiol. 71: 333-341, 1991). The reduction in glycolysis at least between AH and CH appears to be accompanied by a tighter metabolic control. During CH, free ADP was lower and the ATP-to-free ADP ratio was increased (P < 0.05) compared with AH.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗

PubMed1992

Operation Everest II: arterial oxygen saturation and sleep at extreme simulated altitude.

Frequent sleep disturbances and desaturation during sleep are common at high altitude, but few data are available from the highest altitudes at which humans are known to sleep. Because sleep fragmentation at low altitude may impair mental function and oxygen deprivation produces lasting central nervous system abnormalities, a better understanding of the severity of sleep disturbances and oxygen desaturation at extreme altitudes is important. The purpose of this study was to determine the severity of sleep disturbance and the extent of arterial oxygen desaturation at extreme simulated altitude. Out of eight healthy male subject volunteers who started, five aged 27.2 +/- 1.5 yr completed the study during 6 weeks of progressive hypobaric hypoxia in a decompression chamber. The men were studied at barometric pressures of 760, 429, 347, 282 mm Hg and following return to 760 mm Hg. All demonstrated frequent nighttime awakenings (37.2 awakenings per subject per night at 282 mm Hg, decreasing significantly to 14.8 on return to sea level, p less than 0.05). Total sleep time decreased from 337 +/- 30 min at 760 mm Hg to 167 +/- 44 min at 282 mm Hg (p less than 0.01). Rapid eye movement (REM) sleep decreased from 17.9% +/- 6.0% of sleep time at sea level to 4.0% +/- 3.3% at 282 mm Hg (p less than 0.01). Sleep continuity as reflected by brief arousals increased from 22 +/- 6 arousals per hour of sleep at sea level to 161 +/- 66 arousals per hour at 282 mm Hg (p less than 0.01). All subjects showed arterial oxygen desaturation proportional to the altitude. The average oxygen saturation (SaO2) was 79% +/- 3% at 429 mm Hg, 66% +/- 6% at 347 mm Hg, and 52% +/- 2% at 282 mm Hg. Sleep stage had only a minimal effect on SaO2 at any altitude. SaO2 was negatively correlated with brief sleep arousals, r = -0.72, p less than 0.01. All subjects demonstrated periodic breathing with apneas throughout much of the night at 347 and 282 mm Hg. These data indicate that sleep quality progressively worsens as SaO2 decreases despite lack of progressive changes in sleep stages at altitude. This study extends previous information on the severity of desaturation during sleep, and suggests that improvements in oxygenation might prove beneficial in restoring consolidated sleep, possibly even improving daytime performance.

Adult↗