Biomedical subjects

A Cymerman

Publications and source records attributed to A Cymerman.

At least 109 records · Page 6Linked to original sources

PubMed1987

Operation Everest II: man at extreme altitude.

Rapid ascent to high altitude may cause serious problems for climbers, skiers, and aviators. In contrast, gradual ascent enables humans to function where the unacclimatized cannot. To examine changes in the O2 transport system that produce acclimatization, eight men were taken in a decompression chamber (without other stresses experienced on high mountains) to a simulated altitude of 8,840 m (29,028 ft, ambient PO2 = 43 Torr) in 40 days. Maximal O2 uptake fell to 1.2 l/min, and arterial PO2 and PCO2 were 30 and 11 Torr, respectively, with arterial pH of 7.56. Many sophisticated studies were done: Swan-Ganz catheterization and inert gas diffusion studies at three altitudes showed that normal cardiac function persisted, pulmonary vascular resistance increased and at extreme altitude was not lowered by O2, and pulmonary ventilation-perfusion mismatch increased, though variably. This appears to be an important factor limiting performance at extreme altitude. This paper presents the background, general approach, and a summary of major observations reported in detail in other papers.

Acclimatization↗

PubMed1987

Operation Everest II: pulmonary gas exchange during a simulated ascent of Mt. Everest.

Eight normal subjects were decompressed to barometric pressure (PB) = 240 Torr over 40 days. The ventilation-perfusion (VA/Q) distribution was estimated at rest and during exercise [up to 80-90% maximal O2 uptake (VO2 max)] by the multiple inert gas elimination technique at sea level and PB = 428, 347, 282, and 240 Torr. The dispersion of the blood flow distribution increased by 64% from rest to 281 W, at both sea level and at PB = 428 Torr (heaviest exercise 215 W). At PB = 347 Torr, the increase was 79% (rest to 159 W); at PB = 282 Torr, the increase was 112% (108 W); and at PB = 240 Torr, the increase was 9% (60 W). There was no significant correlation between the dispersion and cardiac output, ventilation, or pulmonary arterial wedge pressure, but there was a correlation between the dispersion and mean pulmonary arterial pressure (r = 0.49, P = 0.02). When abnormal, the VA/Q pattern generally had perfusion in lung units of zero or near zero VA/Q combined with units of normal VA/Q. Alveolar-end-capillary diffusion limitation of O2 uptake (VO2) was observed at VO2 greater than 3 l/min at sea level, greater than 1-2 l/min VO2 at PB = 428 and 347 Torr, and at higher altitudes, at VO2 less than or equal to 1 l/min. These results show variable but increasing VA/Q mismatch with long-term exposure to both altitude and exercise. The VA/Q pattern and relationship to pulmonary arterial pressure are both compatible with alveolar interstitial edema as the primary cause of inequality.

Acclimatization↗

PubMed1987

An environmentally-controlled extended-use small animal hypobaric chamber.

An environmentally-controlled extended-use small animal hypobaric chamber has been designed to study small laboratory animals at low barometric pressures for long periods of exposure. The rectangular chamber (91.4 X 71.1 X 50.8 cm) is constructed of aluminum plate and acrylic resin with a volume of 3.3 X 10(5) cm3. A computer/data acquisition control unit provides for controlling and collecting data on pressure, temperature, and relative humidity (RH) for sustained operations. Altitude simulation is achieved using a two-stage, air-cooled vacuum pump with a displacement of 30 cm3 X min-1. The pressure within the chamber is controlled by an incremental throttling valve in the vacuum line. Temperature (0-100 degrees C) is accomplished by using a remote-controlled constant temperature circulating bath. RH (20-80%) is regulated by pre-conditioning the ventilation purge air prior to entering the chamber. Acceptable levels of oxygen and carbon dioxide gases are maintained by purging with sufficient volumes of fresh air.

Animals↗

PubMed1987

Effect of dexamethasone on symptoms of acute mountain sickness at Pikes Peak, Colorado (4,300 m).

In a previous controlled study, dexamethasone (DEX) was shown to prevent acute mountain sickness (AMS) during exposure to simulated high altitude. To determine the effect of DEX during actual altitude exposure, 16 young men were treated with either DEX (4 mg every 6 h) or placebo for 48 h prior to and 48 h after being rapidly transported from sea level to the summit of Pikes Peak, CO (4,300 m). Symptoms of AMS were evaluated twice daily at Pikes Peak using the Environmental Symptoms Questionnaire and a clinical assessment. During treatment the mean symptom scores were higher for subjects taking placebo in 18 out of 20 comparisons. On an individual basis, 60% of the subjects receiving placebo met the criteria for being "sick" compared to 31% of subjects receiving DEX. Beginning 24 h after cessation of treatment, DEX subjects experienced a progressive increase in symptom scores which lasted through the end of the altitude sojourn (day 6). The results indicate that DEX is an effective prophylactic treatment for AMS in an actual mountain environment, but that AMS symptoms can occur if the drug is stopped abruptly.

Acute Disease↗

PubMed1987

Operation Everest II: Altitude decompression sickness during repeated altitude exposure.

The incidence of altitude decompression sickness (ADS) was studied in 23 altitude scientists during repeated altitude exposure to 15,000-29,000 ft (4572-8839 m) in a decompression chamber. Prior to each altitude exposure, a 30-60-mm pre-breathing period with 100% oxygen took place. Ascent was made to an altitude at a rate of 2000 ft X min-1. The altitudes studied ranged from 15,000-29,000 ft (4572-8839 m). Symptoms reported appear consistent with previous reports. Incidence of ADS at 26,000-29,000 ft (7925-8839 m) was 29.7%, during 274 chamber flights and 1264.6 h of altitude time. Incidence appeared related to frequency of exposure, severity of altitude, and physical activity. Incidence was not related to age, duration of exposure, or body index (weight/height 2). This high incidence of ADS reported in this study is similar to that reported by NASA.

Adult↗

PubMed1987

Respiratory response and muscle function during isometric handgrip exercise at high altitude.

The purpose of this investigation was to determine if the hyperventilatory response to fatiguing isometric exercise at sea level could predict resting ventilation and acute mountain sickness (AMS) at 4300 m altitude. Exercise consisted of four successive endurance handgrips held to complete fatigue at 40% of maximum isometric handgrip strength (MHS). There was no relationship between the magnitude or pattern of exercise-induced hyperventilation at sea level and the severity of AMS later at altitude. Sea level hyperventilatory response was not predictive of resting ventilation at altitude. Altitude exposure progressively increased both the incidence and magnitude of the hyperventilatory response to exercise and prolonged it for 60-90 s into the recovery period, providing support for the "central command" theory of ventilatory control during isometric exercise. MHS was significantly increased at altitude--by 11% on day 2 and 16% on day 6. Endurance times to fatigue were reduced, but not always significantly so. A follow-up study involving more practice at sea level demonstrated MHS to be significantly increased throughout an entire 18-d stay at 4300 m and for 3, but not 5, days after descent. Significant changes in endurance could not be demonstrated. Neither AMS nor changes in body weight or circulating norepinephrine levels can account for the temporal pattern of increased grip strength, but the respiratory alkalosis occurring at altitude appears to be a likely mechanism.

Adult↗

PubMed1986

The effect of naproxen on acute mountain sickness and vascular responses to hypoxia.

The role of prostaglandins in the pathogenesis of acute mountain sickness and two hypoxia-induced vascular responses was evaluated using the cyclooxygenase inhibitor naproxen. Eleven men spent 24 hours at sea level, followed by 34 hours of decompression to 428 mm Hg while receiving naproxen (N), 250 mg twice daily or placebo (P) in a double-blind crossover trial. Serum naproxen levels measured by high pressure liquid chromatography were not changed by hypoxia. The severity of acute mountain sickness (AMS) by the Environmental Symptom Questionnaire scores and observer assessment were unaffected by drug treatment. Retinal artery diameter measured from projected fundus photographs was increased after 27 hours at altitude (11.4 +/- .5 mm) vs. sea level (9.4 +/- .5 mm, p less than 0.05) during both trials. Upright mean arterial pressure fell after 6 hours at altitude (79 +/- 3 mm Hg during N and P vs. 92 +/- 3 at sea level, p less than 0.01). Minute ventilation, end expiratory alveolar PO2 and PCO2 did not differ between drug trials. This study suggests vasodilating prostaglandins do not have a major role in the genesis of AMS, hypoxia-induced retinal vasodilatation, or postural blood pressure responses in man.

Acute Disease↗

PubMed1986

Propranolol does not impair exercise oxygen uptake in normal men at high altitude.

Decreased maximal O2 uptake (VO2max) and stimulation of the sympathetic nervous system have been previously shown to occur at high altitude. We hypothesized that tachycardia mediated by beta-adrenergic stimulation acted to defend VO2max at high altitude. Propranolol treatment beginning before high-altitude (4,300 m) ascent reduced heart rate during maximal and submaximal exercise in six healthy men treated with propranolol (80 mg three times daily) compared with five healthy subjects receiving placebo (lactose). Compared with sea-level values, the VO2max fell on day 2 at high altitude, but the magnitude of fall was similar in the placebo and propranolol treatment groups (26 +/- 6 vs. 32 +/- 5%, P = NS) and VO2max remained similar at high altitude in both groups once treatment was discontinued. During 30 min of submaximal (80% of VO2max) exercise, propranolol-treated subjects maintained O2 uptake levels that were as large as those in placebo subjects. The maintenance of maximal or submaximal levels of O2 uptake in propranolol-treated subjects at 4,300 m could not be attributed to increased minute ventilation, arterial O2 saturation, or hemoglobin concentration. Rather, it appeared that propranolol-treated subjects maintained O2 uptake by transporting a greater proportion of the O2 uptake with each heartbeat. Thus, contrary to our hypothesis, beta-adrenergic blockade did not impair maximal or submaximal O2 uptake at high altitude due perhaps to compensatory mechanisms acting to maintain stroke volume and cardiac output.

Adult↗

PubMed1986

Effect of spironolactone on acute mountain sickness.

This study examined the effectiveness of spironolactone as a prophylactic agent for the prevention of acute mountain sickness (AMS). Spironolactone, 25 mg PO QID, or placebo was administered to nine subjects in a double-blind, placebo-controlled, crossover design. Medication was given for 48 h prior to and during a 46-h exposure to 427 mm Hg (4570 m) in a hypobaric chamber. Six subjects demonstrated prevention of either the cerebral or respiratory symptoms of AMS during at least one segment of the altitude sojourn.

Acute Disease↗

PubMed1986

The effect of spironolactone on the cardiocirculatory responses to upright tilt at sea level and at simulated high altitude.

The objective of this study was to determine if spironolactone (S) alters the cardiocirculatory responses to upright tilt at sea level (SL;50 m) and during 44 h of simulated altitude (HA;4,600 m). In a double-blind, crossover-designed study, 9 male subjects (age range: 18-25 years) received 25 mg orally, four times per day of either S or an identically-appearing placebo (P) 2 d prior to and during HA. The crossover was separated by 2 weeks. Heart rate, stroke volume, cardiac output, calf blood flow, total peripheral resistance and systemic blood pressure were obtained during supine rest and after 10 min of 60 degrees head-up tilt using an impedance monitor and an electro-sphygmomanometer. The 24-h determinations of urinary volume, sodium and potassium as well as venous plasma values for sodium, potassium and chloride were obtained daily. There were no statistically significant differences between P and S treatment periods for: caloric, electrolytes or fluid ingestion; urinary volume or electrolytes; plasma electrolytes; or any of the cardiocirculatory parameters measured in the supine or upright position at SL or during HA. It was concluded that S did not induce a significant diuresis or significantly alter vascular responsiveness to negatively effect the normal cardiocirculatory responses to upright tilt at sea level or simulated high altitude.

Adult↗

PubMed1985

The influence of cardiorespiratory fitness on the decrement in maximal aerobic power at high altitude.

There are conflicting reports in the literature which imply that the decrement in maximal aerobic power experienced by a sea-level (SL) resident sojourning at high altitude (HA) is either smaller or larger for the more aerobically "fit" person. In the present study, data collected during several investigations conducted at an altitude of 4300 m were analyzed to determine if the level of aerobic fitness influenced the decrement in maximal oxygen uptake (VO2max) at HA. The VO2max of 51 male SL residents was measured at an altitude of 50 m and again at 4300 m. The subjects' ages, heights, and weights (mean +/- SE) were 22 +/- 1 yr, 177 +/- 7 cm and 78 +/- 2 kg, respectively. The subjects' VO2max ranged from 36 to 60 ml X kg -1 X min -1 (mean +/- SE = 48 +/- 1) and the individual values were normally distributed within this range. Likewise, the decrement in VO2max at HA was normally distributed from 3 ml X kg-1 X min-1 (9% VO2max at SL) to 29 ml X kg-1 X min-1 (54% VO2max at SL), and averaged 13 +/- 1 ml X kg-1 X min-1 (27 +/- 1% VO2max at SL). The linear correlation coefficient between aerobic fitness and the magnitude of the decrement in VO2max at HA expressed in absolute terms was r = 0.56, or expressed as % VO2max at SL was r = 0.30; both were statistically significant (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1985

A software package for administering and monitoring the Environmental Symptoms Questionnaire (ESQ-III).

The latest version of the Environmental Symptoms Questionnaire (ESQ-III) contains 67 symptoms designed to allow researchers to evaluate a broad range of environmental stresses. We have developed an interactive computer software package that administers and monitors the ESQ-III. This package, written in a format maximizing clarity, provides consistency of administration from one test or day to another, checks for response inconsistencies, maintains subject motivation, provides feedback to the subject and allows an investigator to quickly inspect raw and computed results. Further, because there is no interaction between investigators and subjects, no experimenter bias can be introduced. This package can be adapted to almost any computer system having a CRT and at least one disc drive.

Aerospace Medicine↗

PubMed1985

Anthropometric changes at high altitude.

Eight white males (18-25 yr) were evaluated before, during and after 18-d residence on the summit of Pikes Peak, CO (4300 m; high altitude, HA) to describe the anthropometric changes associated with weight loss and to test the accuracy of a number of previously published prediction equations in assessing any alteration of the relative fat-to-lean tissue ratio during exposure to HA. Body weight (BW), 10 circumference (C), and 7 skinfold (SF) measurements were obtained preprandial at sea level (SL) and on days 2,4,6,9,12,16, and 18 at HA. Body density was estimated by hydrostatic weighing (HW) pre- and post-HA. BW differed from SL (p less than 0.01) after day 9 at HA. HW indicated that the pre- to post-HA weight loss was partitioned into a 2.06 kg loss in fat-free body mass (p less than 0.001) and an insignificant increase in fat wt (0.58 kg). Percent body fat (BF) increased from 16.6 to 17.7 (p less than 0.02). After day 9 of HA, the sum of SF and C measurements increased (p less than 0.02) and decreased (p less than 0.05) from SL, respectively. The largest changes occurred in the chest and scapula SF and in the C of the hip, neck, calf, and two abdominal sites. The alterations in triceps, waist, and total SF were related to the increase in fat weight and BF (r greater than 0.71).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1985

Hemodynamic responses to upright tilt at sea level and high altitude.

Hemodynamic responses to upright tilt were studied in eight young men at sea level (SL); after 1 h at 4,300 m simulated altitude (SA); and at 18 h, 66 h and 114 h during residence at 4,300 m (HA). Heart rate (HR), stroke volume (SV), cardiac output (CO), calf blood flow (CBF), blood pressure (BP) and total peripheral resistance (TPR) were obtained during supine rest and after 13 min of 60 degrees head-up tilt using an impedance monitor and electrosphygmomanometer. SL to HA changes in blood volume (BV) were calculated from hematocrit and hemoglobin values. Plasma norepinephrine (Nor) was measured at SL and after 18 h and 66 h of HA. Supine HR, TPR and BP were increased while SV, CO and CBF were reduced SL to HA (p less than 0.05). HR and BP in the upright position were increased SL to HA (p less than 0.05). The responses to tilt (delta supine to upright) were unaltered SL vs SA. With prolonged exposure, SV, CO, TPR and CBF responses to tilt were reduced (p less than 0.05). The reduced responses to tilt at HA were associated with a 10% decline in BV (p less than 0.01) and a 40% increase in Nor (p less than 0.05). It was concluded that the reduction in SV during tilt at SL and SA was compensated for by increases in HR and TPR in order to maintain BP. After 18 h HA, BP in the upright position was maintained only by an increase in HR.

Adult↗

PubMed1983

Procedures for the measurement of acute mountain sickness.

Although acute mountain sickness (AMS) has been studied for well over a century, a standard measure or index of the degree of illness for use in experimental research does not exist. This paper outlines a definition and procedures for an operational measurement of AMS using the Environmental Symptoms Questionnaire (ESQ). After 58 men completed over 650 ESQs during a stay of 1-3 weeks atop Pike's Peak (4300 m), factor analysis produced nine distinct symptom groups, with two factors representing AMS. The first factor contains symptoms indicative of cerebral hypoxia and is labeled AMS-C. The second reflects respiratory distress and is called AMS-R. Signal detection theory was used to establish a criterion score value for each factor. Standard deviation values were used to derive indices of sickness severity. Discussion is given to the possible relationships between the two types of AMS and the more serious conditions of cerebral and pulmonary edema.

Acute Disease↗

PubMed1982

Sparing effect of chronic high-altitude exposure on muscle glycogen utilization.

Substrate utilization during heavy [approximately 85% maximum O2 consumption (VO2max)] bicycle exercise was examined in eight low-altitude residents at sea level (SL) and after acute (2 h) and chronic (18 days) high-altitude (HA) exposure at 4,300 m. Mean VO2max was approximately 27% lower at acute HA than at SL and did not change significantly with continued HA exposure. Biopsies from the vastus lateralis muscle and venous blood samples were obtained before and after 30 min of exercise, whereas determinations of the respiratory exchange ratio (R) were made at 10-min intervals during each of the submaximal bouts. Resting levels of serum-free fatty acids at acute and chronic HA were, respectively, two and three times higher than SL but were unchanged with exercise. Exercise did not alter resting serum glycerol levels at SL or during acute HA, but during chronic HA resting glycerol levels were increased 11-fold. Although mean blood lactate concentrations following exercise at SL and acute HA were not significantly different, postexercise lactate concentrations were 87% lower after chronic HA. During exercise at SL and acute HA, muscle glycogen utilization and R were not different. At chronic HA, muscle glycogen utilization and R were 41 and 15% lower, respectively. These data suggest that after chronic HA exposure, increased mobilization and use of free fatty acids during exercise resulted in sparing of muscle glycogen.

Adaptation, Physiological↗

PubMed1982

Differentiated ratings of perceived exertion are influenced by high altitude exposure.

Differentiated ratings of perceived exertion (RPE) were obtained from eight low-altitude residents during cycle exercise at sea level (SL) and after acute (less than 2 h) and chronic (18 d) exposure to high altitude (4,300 m; HA). Mean VO2max was 27% lower with acute HA exposure. Subjects cycled for 30 min at an exercise intensity requiring 85% of VO2max. Respiratory exchange measurements and differentiated RPE were obtained at minutes 5, 15 and 25 of exercise, and pre- and post-exercise blood samples were collected. Differentiated RPE included a local muscular rating, a central or cardiopulmonary ratings, and an overall rating. Despite reduced absolute exercise intensity during acute HA exercise, local RPE were unchanged from SL values. Chronic HA exercise, however, was associated with a significant reduction in local RPE. Blood lactate accumulation during SL exercise was not significantly greater than central ratings, while neither differed significantly from the overall ratings. None of the differentiated ratings differed significantly during acute and chronic HA exercise; central RPE were highest of the ratings during chronic HA exercise. The ventilatory equivalent for oxygen during HA exercise (both acute and chronic) was significantly higher than at SL. This apparent rearrangement in the relative order of magnitude of these three differentiated ratings suggests an alteration in the relationship between perceptual cues sensed as effort.

Adult↗

PubMed1981

Components of alveolar-arterial O2 gradient during rest and exercise at sea level and high altitude.

To determine the effects of exercise and high altitude on the contributions of shunt, ventilation-perfusion (V/Q) nonhomogeneity, and diffusion limitation to the alveolar-arterial O2 gradient (AaDo2), we measured pulmonary exchange of O2, CO2, and six inert gases (SF6, ethane, cyclopropane, halothane, diethyl ether, and acetone) during rest and exercise in unanesthetized dogs at sea level and after acute exposure to an altitude of 6,096 m in a hypobaric chamber. Shunt and dead-space fractions, calculated from inert gas measurements, did not change. High altitude decreased the inert gas partial pressure gradients between mixed alveolar gas and mixed end-capillary blood, indicating that V/Q relationships became more homogeneous. Exercise had no effect on these gradients. At sea level, AaDo2 was mainly due to V/Q nonhomogeneity, with a small portion due to shunt. At high altitude, the contribution of shunt became negligible and that of V/Q nonhomogeneity diminished. These improvements were partially offset, however, by a gradient due to diffusion limitation. Exercise had no effect on AaDo2 or any of its components. At high altitude, estimated pulmonary O2 diffusing capacity averaged 20.8 ml.min-1 at rest and 35.3 ml-min-1.Torr-1 during exercise.

Altitude↗