Operation Everest II: oxygen transport during exercise at extreme simulated altitude.

A decrease in maximal O2 uptake has been demonstrated with increasing altitude. However, direct measurements of individual links in the O2 transport chain at extreme altitude have not been obtained previously. In this study we examined eight healthy males, aged 21-31 yr, at rest and during steady-state exercise at sea level and the following inspired O2 pressures (PIO2): 80, 63, 49, and 43 Torr, during a 40-day simulated ascent of Mt.

Hemodynamic and sympathoadrenal responses to altitude in humans: effect of dexamethasone.

Altitude exposure alters hemodynamics and sympathoadrenal function and elicits acute mountain sickness (AMS). Since dexamethasone prevents AMS and influences responsiveness to catecholamines, we studied hemodynamic and sympathoadrenal responses to 4,570 m simulated altitude in 8 subjects treated with dexamethasone or placebo. Mean pulse rates were less at altitude with dexamethasone (96.

Maximal cardiorespiratory responses to one- and two-legged cycling during acute and long-term exposure to 4300 meters altitude.

During exposure to altitudes greater than about 2200 m, maximal oxygen uptake (VO2max) is immediately diminished in proportion to the reduction in the partial pressure of oxygen in the inspired air. If the exposure lasts longer than a couple of days, an increase in arterial oxygen content (CaO2), due to a hemoconcentration and an increase in arterial oxygen saturation, occurs. However, there is also a reduction in maximal cardiac output (Qmax) at altitude which offsets the increase in CaO2 and, therefore, VO2max does not improve.

Responses of plasma human atrial natriuretic factor to high intensity submaximal exercise in the heat.

No data exists regarding responses of human atrial natriuretic factor (ANF) to exercise in the heat. The purpose of this study was to examine the responses of plasma ANF to high intensity submaximal (71% +/- 0.9 VO2max) exercise in the heat over an eight day acclimation period.

Propranolol blocks metabolic rate increase but not ventilatory acclimatization to 4300 m.

Previously, we found resting metabolic rate increased at high altitude but the mechanism and consequences of this increase were unclear. We sought to test the role of beta-sympathetic activation for increasing metabolic rate and the contribution of an increase in metabolic rate to raising total ventilation at altitude. Following baseline studies at sea level, two groups of six healthy male subjects received either placebo or propranolol (80 mg/8 h) for 3 days prior to ascent to Pikes Peak (4300 m) where treatment was continued for 15 days.

Effects of arterial ligation and embolization on pulmonary vascular pressure distribution.

The effects of embolization on the longitudinal distribution of pulmonary vascular pressures with respect to vascular compliance were determined by the vascular inflow and outflow occlusion technique in isolated blood-perfused pig lungs treated with papaverine to prevent vasomotor responses. Embolization with microspheres having mean diameters of 75, 200, and 550 microns and with barrier beads (2 X 3 X 3.5 mm) significantly increased the pressure gradient across the relatively compliant middle region (delta Pm) without increasing the gradients across the relatively noncompliant regions on the arterial (delta Pa) or venous (delta Pv) ends of the vasculature.

Oxygen transport during exercise at extreme altitude: Operation Everest II.

Eight male volunteers had rest and exercise measurement to determine the mechanisms of oxygen transport during a 40-day chamber decompression simulating high-altitude exposure equivalent to the summit of Mt Everest. Five subjects completing the study decreased their maximum oxygen uptake by 72%. During maximal or near-maximal exercise, arterial PCO2 fell as low as 8 mm Hg, defending the alveolar PO2 and confirming marked hyperventilation.

Operation Everest II: preservation of cardiac function at extreme altitude.

Hypoxia at high altitude could depress cardiac function and decrease exercise capacity. If so, impaired cardiac function should occur with the extreme, chronic hypoxemia of the 40-day simulated climb of Mt. Everest (8,840 m, barometric pressure of 240 Torr, inspiratory O2 pressure of 43 Torr).

Operation Everest II: elevated high-altitude pulmonary resistance unresponsive to oxygen.

High altitude increases pulmonary arterial pressure (PAP), but no measurements have been made in humans above 4,500 m. Eight male athletic volunteers were decompressed in a hypobaric chamber for 40 days to a barometric pressure (PB) of 240 Torr, equivalent to the summit of Mt. Everest.

Altitude acclimatization attenuates plasma ammonia accumulation during submaximal exercise.

This study examined the effects of acclimatization to 4,300 m altitude on changes in plasma ammonia concentrations with 30 min of submaximal [75% maximal O2 uptake (VO2max)] cycle exercise. Human test subjects were divided into a sedentary (n = 6) and active group (n = 5). Maximal uptake (VO2max) was determined at sea level and at high altitude (HA; 4,300 m) after acute (t less than 24 h) and chronic (t = 13 days) exposure.

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.

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.

Local sweating and cutaneous blood flow during exercise in hypobaric environments.

The effect of acute hypobaric hypoxia on local sweating and cutaneous blood flow was studied in four men and four women (follicular phase of menstrual cycle), who exercised at 60% of their altitude-specific peak aerobic power for 35 min at barometric pressures (PB) of 770 Torr (sea level), 552 Torr (2,596 m), and 428 Torr (4,575 m) at an ambient temperature of 30 degrees C. We measured esophageal temperature (Tes), mean skin temperature (Tsk, 8 sites), and local sweating (ms) from dew-point sensors attached to the skin at the chest, arm, and thigh. Skin blood flow (SkBF) of the forearm was measured once each minute by venous occlusion plethysmography.

Effects of atropine on thermoregulatory responses to exercise in different environments.

The thermoregulatory effects of atropine (2 mg im) were examined in six heat-acclimated subjects during exercise in three environments, which provided different evaporative capacities, but similar heat stress as indicated by the wet bulb, globe temperature index (WBGT). Subjects walked in environments of Ta = 42.3 degrees C, Tdp = 14.

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).

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.

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.

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.

Nitrendipine attenuates the pulmonary vascular remodeling and right ventricular hypertrophy caused by intermittent hypoxia in rats.

We designed experiments to determine whether intermittent hypoxia would produce significant pathologic and physiologic changes in rats and whether pretreatment with a calcium channel blocker, nitrendipine, would reduce the pulmonary vascular remodeling and right ventricular hypertrophy caused by intermittent hypoxia. Intermittent exposure to hypobaric hypoxia (0.5 atmospheres) 10 h a day for 30 days increased the hematocrit (65 +/- 1 versus 42 +/- 1%, mean +/- SEM), right ventricular systolic pressure (33 +/- 1 versus 20 +/- 1 mmHg), and right ventricular weight adjusted for body weight (RV/BW) (126 +/- 6 versus 60 +/- 2 mg/100 g) in male Sprague-Dawley rats.

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.

Nature and distribution of vascular resistance in hypoxic pig lungs.

We used the vascular occlusion technique in pig lungs isolated in situ to describe the effects of hypoxia on the distribution of vascular resistance and to determine whether the resistive elements defined by this technique behaved as ohmic or Starling resistors during changes in flow at constant outflow pressure, changes in outflow pressure at constant flow, and reversal of flow. During normoxia, the largest pressure gradient occurred across the middle compliant region of the vasculature (delta Pm). The major effect of hypoxia was to increase delta Pm and the gradient across the relatively noncompliant arterial region (delta Pa).

Medical Complaints After a Marathon Run in Cool Weather.

In brief: Little information is available about medical complaints after marathons held in cool weather. To obtain such information medical records were maintained on every runner requesting medical attention after the Bostonfest Marathon on Oct 30, 1983. One hundred sixty-four (11.

Effects of imidazole and indomethacin on fluid balance in isolated sheep lungs.

We determined the effects of extracorporeal perfusion with a constant flow (75 ml . min-1 . kg-1) of autologous blood on hemodynamics and fluid balance in sheep lungs isolated in situ.

Efficacy and safety of naloxone in septic shock.

We evaluated the effectiveness and safety of iv naloxone in 12 septic patients who remained hypotensive despite volume replacement, appropriate antibiotics, and vasopressor therapy. Only four patients responded positively to naloxone, by increases in mean arterial pressure of between 10 to 15 mm Hg that lasted for 15 to 60 min. These patients could not be distinguished from the others on the basis of underlying illness, laboratory or physical findings, length of preceding hypotension, or glucocorticoid therapy.