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At least 127 records · Page 7Linked to original sources
PubMed1997

Right ventricular collagen type III and IV gene expression increases during early phases of endurance training in hypobaric hypoxic condition.

The objective of this study was to examine the effects of prolonged exposure to hypobaric hypoxic condition, physical training and their combination on collagen type I, III and IV gene expression in the ventricles and atria of rat heart. Male rats were assigned to four groups: normobaric sedentary (NS) and trained (NT), and hypobaric sedentary (HS) and trained (HT). Exposure to and treadmill running training in hypobaric condition were carried out in a hypobaric chamber (770-740 mbar, 2250-2550 m). Experimental periods were 10, 21 and 56 days; the groups of 91 days served as recovery groups from experimental settings of 56 days. Exposure to hypobaric condition as such and in combination with endurance training for 10 days increased right ventricular weight-to-body weight ratio (RV/BW) by 26% (p < 0.001) and 23% (p < 0.01), respectively, when compared to 10NS. RV/BW was significantly increased also in 21HT and 56HT. Left ventricular weight-to-body weight ratio was 13% (p < 0.01) and 14% (p < 0.01) higher in 21HT and 56HT, respectively, than in the respective NS. Right ventricular collagen type III mRNA level was 33% (p = 0.065) and 38% (p < 0.01) higher in 10HT than in 10NS and 10NT, respectively. Right ventricular collagen type IV mRNA level was 29% (p < 0.001) higher in 10HT than in 10NS. Relatively slight left ventricular hypertrophy was not associated with significant changes in collagen mRNA levels. Decreased left ventricular subepicardial prolyl 4-hydroxylase activity in 10HS and 10HT suggests transient corresponding decrease in the rate of collagen synthesis. This study shows that combination of endurance training and moderate hypobaric hypoxic condition leads to increased right ventricular collagen type III and IV gene expression associated with right ventricular hypertrophy.

Animals↗
PubMed1992

Peak oxygen uptake during arm stroke under a hypobaric hypoxic condition.

The purpose of this study was to examine the limiting factor for swimming by measuring peak oxygen uptake (peak VO2) during front crawl (C) and arm stroke (A) under a hypobaric hypoxic condition. Seven-trained swimmers (age; 19-21 yrs, 100 m free style event; 57.2 +/- 2.5 secs) were measured twice under a normal (N) (751 mmHg) and a hypobaric hypoxic (H) (602 mmHg) condition in a chamber where atmospheric pressure was regulated. Water flow rate started at 0.80 m.sec-1 and was increased by 0.05 m.sec-1 every 2 min up to 1.00 m.sec-1. Subsequently, flow rate was increased by 0.05 m.sec-1 every minute until exhaustion. VO2 was measured with an automatic analyzer. The peak heart rate under N was not significantly different from that under H in both C (N; 190 +/- 9, H; 184 +/- 6 beats.min-1) and A (N; 180 +/- 6, H; 181 +/- 6 beats.min-1). Peak VO2 values during A (N; 3.42 +/- 0.27, H; 3.08 +/- 0.19 l.min-1) were significantly lower by 15-20% than those during C (N; 4.18 +/- 0.18, H; 3.65 +/- 0.11 l.min-1) for both N and H (p less than 0.01). Peak VO2 values under H were significantly lower than those under N during both C and A (p less than 0.01). There was no significant difference in the magnitude of decrease in peak VO2 between C (12.0 +/- 3.4%) and A (9.8 +/- 3.8%) under H. This ratio of decrease agrees with previous investigations that studied centrally limited exercise, such as running and cycling, under similar levels of hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

A ventilation capacity test for the Eustachian tube using a soundproof pressure chamber.

Using a soundproof pressure chamber, we performed Békésy air conduction audiometry at 1000 Hz under the following pressure conditions: 1) from atmospheric pressure (AP) to 200 mmH2O below AP, 2) AP to 200 mmH2O above AP, 3) AP to 700 mmH2O below AP, and 4) AP to 700 mmH2O above AP. In conditions 1) and 2), the patient was instructed not to swallow until the pressure change was complete, then to swallow once every 15 seconds. The number of swallows required for hearing to return to the baseline level was counted. In conditions 3) and 4), the patient was told to swallow as many times as possible both before and after completion of the pressure change; maximum hearing level and the time needed for return to the baseline level were measured. Although all except one of the seven patients with suspected tubal dysfunction showed normal results with catheter insufflation and tympanometry, six of the seven showed abnormality and one reported the disappearance of ear stuffiness after the ventilation capacity test. We concluded that this test is useful not only for the diagnosis of tubal dysfunction but also as a possible therapy for aiding adaptation to changing environmental pressure.

Acoustic Impedance Tests↗
PubMed1975

Pituitary-thyroid function of rats in hypobaric oxygen-inert gas environments.

Rats (200-260 g) were exposed in sealed, recycling chambers continuously for 2-30 days to gas mixtures designed to maintain the same alveolar PO2 in the presence or absence of inert gas. Mixtures with inert gas (N2, He, or Ne) were at ground level; those without inert gas (100 percent O2) were in an altitude chamber. The O2 categories were: I-100 percent O2 at 747 torr; II-74 percent O2 + 26 percent inert and 566 torr 100 percent O2; III-47 percent O2 + 53 percent inert and 381 torr 100 percent O2; IV-21 percent O2 + 79 percent inert and 197 torr 100 percent O2. One of the two room-air controls was "restricted-fed" to the level of the lowest intake group. Measurements included body, pituitary, and thyroid weight, food and water intake, plasma volume and hematocrit, pituitary and plasma TSH, and plasma PBI. Severe depression in all variables and over 50 percent mortality was seen in I by day 4. All variables were depressed in II, but there was no mortality to 20 days. Pituitary-thyroid function appeared to be particularly sensitive to depression by hyperoxia, with plasma TSH levels reduced between 42 and 60 percent in II and III. No effect was attributable to the inert gas, whether it was N2, He, or Ne, nor was any specific effect traceable to the presence or absence of inert gas.

Animals↗
PubMed2000

The psychometric and cardiac effects of dimenhydrinate in the hyperbaric environment.

STUDY OBJECTIVES: To examine the psychometric and cardiac effects of dimenhydrinate at 1 and 3 atmospheres (atm) of pressure (0 and 66 feet of sea water, respectively), and to make recommendations about the drug's safety in the diving environment. DESIGN: Double-blind, placebo-controlled, crossover study SETTING: Monoplace hyperbaric chamber of a university hospital. SUBJECTS: Thirty active divers (mean age 38 yrs). INTERVENTIONS: A bank of seven tests was used to assess cognitive function during four different dive combinations: placebo-1 atm, placebo-3 atm, dimenhydrinate-1 atm, and dimenhydrinate-3 atm. MEASUREMENTS AND MAIN RESULTS: Heart rate and cardiac rhythm were recorded during all dives. Repeated-measures multivariate analysis of variance was used to analyze the effects of dimenhydrinate, depth, and drug-depth interaction. Dimenhydrinate resulted in a significant decrease in scores of mental flexibility (trail-making, part B, p<0.05) but had no effect on scores in the six other psychometric tests (p>0.05). It had no effect on mean heart rate (p>0.05), although frequent unifocal ventricular ectopic beats occurred in two subjects after ingestion of the drug. Depth resulted in a significant decrease in verbal memory test scores (p=0.001) and mean heart rate (p<0.001). CONCLUSION: Dimenhydrinate adversely affects mental flexibility. This effect, when added to the adverse effect of depth on memory, may contribute to the dangers of diving.

Aged↗
PubMed1975

Effects of long-term exposures to 100% oxygen at selected simulated altitudes on the pulmonary surfactant in mice.

The purpose of this investigation was to evaluate the effects on pulmonary surfactant in mice after long-duration exposure to 100% oxygen at various partial pressures equivalent to 842 mb (632) mmHg) or less. Six-month-old female CBA mice, weighing 25-35 g, were exposed to the pure oxygen environment. The effect on pulmonary surfactant was evaluated in two groups of 16 experimental animals and compared with control groups which were maintained in a similar environmentally controlled chamber at sea level conditions. Group I was exposed to pure oxygen at 842 mb (632 mmHg), a level known to be toxic and lethal. Group II was initially exposed for 60 d to pure oxygen at 420 mb (315 mmHg), a level not expected to be lethal, and the oxygen partial pressure gradually increased in steps over a 150-d period until an oxygen partial pressure at 842 mb (632 mmHg) was reached. In Group I, 12 out of 16 mice died of respiratory distress within 7 d. One died on the 10th day and three survived to complete 15 d of exposure but were euthanized because of severe despiratory distress. Mice in Group II which were exposed to pregressively increasing oxygen partial pressures survived. Pulmonary surfactant was obtained by saline lavage of the lungs. Chloroform/methanol extracted samples from oxygen-exposed mice in Group I displayed lower surfactant activity than Group II or controls. In fact, surfactant activity of mice dying in respiratory distress after 7 d was markedly lower than that of all other animals. Mice in Group II exhibited significantly lower(p less than 0.05) surfactant activity than controls, X = 34.71 and 38.58 respectively. This lower surfactant activity was consistent for Group II throughout the 150-d exposure except at the 90-d and 150-d exposures. The findings of this investigation support preceding studies which contend that the lung is the most vulnerable target for oxygen toxicity at altitude. It appears that an adaptive process involving both quantitative and qualitative changes in the pulmonary surfactant enabled animals in Group II to survive the progressively increasing ocygen partial pressures in an environment where survival would not normally be possible.

Animals↗
PubMed1984

Hyperbaric diuresis at a thermoneutral 31 ATA He-O2 environment.

The basic pattern of body water exchange was studied in four Japanese male divers during exposure to a thermoneutral 31 ATA (He-O2) environment for 3 d (Seadragon V). The hyperbaric chamber temperature was raised from 25 degrees C +/- 0.5 degrees C at 1 ATA (air) predive to 31.5 degrees C +/- 0.3 degrees C at 31 ATA. Both rectal and mean skin temperatures were measured every hour (including during sleep) and were maintained at the same level at both pressures. The exposure to 31 ATA induced an increase in the daily urine flow and a corresponding reduction in the insensible (and evaporative) water loss without changing the total daily water output. However, the daily fluid intake decreased by 600 ml at 31 ATA, and hence the divers developed a state of negative fluid balance, as reflected by a reduction in body weight and an increase in hematocrit. All changes in the pattern of body water exchange observed at 31 ATA were gradually reversed during subsequent decompression. As observed in a previous dive to 31 ATA (Seadragon IV) in which there was a subtle cold stress (as indicated by the 1 degree C reduction in mean skin temperature at 31 ATA), the increase in daily urine flow at pressure was almost entirely due to the increase in overnight urine flow. However, the hyperbaric nocturia observed in the present dive was a water diuresis in nature whereas that in the previous dive was an osmotic diuresis. These results indicate that the hyperbaric diuresis at 31 ATA is due to an increase in overnight urine flow and that the hyperbaric nocturia is not in any way related to the subtle cold stress attendant in many hyperbaric environments.

Adult↗
PubMed2003

Hyperbaric oxygen therapy in acute ischemic stroke: results of the Hyperbaric Oxygen in Acute Ischemic Stroke Trial Pilot Study.

BACKGROUND AND PURPOSE: Hyperbaric oxygen therapy (HBO) has promise as a treatment for acute stroke. This study was conducted to evaluate the efficacy, safety, and feasibility of using HBO in acute ischemic stroke. METHODS: We conducted a randomized, prospective, double-blind, sham-controlled pilot study of 33 patients presenting with acute ischemic stroke who did not receive thrombolytics over a 24-month period. Patients were randomized to treatment for 60 minutes in a monoplace hyperbaric chamber pressurized with 100% O2 to 2.5-atm absolute (ATA) in the HBO group or 1.14 ATA in the sham group. Primary outcomes measured included percentage of patients with improvement at 24 hours (National Institutes of Health Stroke Scale [NIHSS]) and 90 days (NIHSS, Barthel Index, modified Rankin Scale, Glasgow Outcome Scale). Secondary measurements included complications of treatment and mortality at 90 days. RESULTS: Baseline demographics were similar in both groups. There were no differences between the groups at 24 hours (P=0.44). At 3 months, however, a larger percentage of the sham patients had a good outcome defined by their stroke scores compared with the HBO group (NIHSS, 80% versus 31.3%; P=0.04; Barthel Index, 81.8% versus 50%; P=0.12; modified Rankin Scale, 81.8% versus 31.3%; P=0.02; Glasgow Outcome Scale, 90.9% versus 37.5%; P=0.01) with loss of statistical significance in a intent-to-treat analysis. CONCLUSIONS: Although our HBO protocol appears feasible and safe, it does not appear to be beneficial and may be harmful in patients with acute ischemic stroke.

Acute Disease↗
PubMed1977

Dyspnea in divers at 49.5 ATA: mechanical, not chemical in origin.

Pulmonary function was studied in six divers living in a hyperbaric chamber at a pressure nearly fifty times normal (49.5 atmospheres absolute (ATA), equivalent to 488 m or 1600 ft seawater (fsw)). As expected, ventilatory function was reduced. At 49.5 ATA, maximum voluntary ventilation (MVV) was 45% less than the control value. Instantaneous rates of gas flow during forced expiration were similarly reduced, especially those flow rates measured high in the lung volume. These reductions occurred despite an apparent increase in functional residual capacity (FRC) and the use of transpulmonary pressures considerably greater than those exerted during the same maneuvers at normal (sea-level) pressure. During underwater work at 49.5 ATA, the divers rapidly became exhausted at moderate levels of oxygen consumption (1.9 liters/min), showing severe dyspnea and impending syncope. These symptoms were not due to retention of carbon dioxide, nor to hemodynamic or metabolic causes. Thus, dense gas breathing, like asthma, exemplifies a state in which severe dyspnea may occur with normal or low arterial carbon dioxide and normal oxygen transport. The physiological adjustments the divers employed were similar to those seen in acute asthma, imposing an elastic load in addition to the flow-resistive work of breathing a gas mixture eight times as dense as air. Although men can do moderate work under conditions similar to those of this experiment, they will have only a limited physiological reserve available to meet the possibilities of emergencies or respiratory infections.

Adult↗
PubMed2000

The psychometric and cardiac effects of pseudoephedrine in the hyperbaric environment.

STUDY OBJECTIVES: To examine the psychometric and cardiac effects of pseudoephedrine at 1 and 3 atmospheres (atm) of pressure (0 and 66 feet of sea water, respectively), and to make recommendations about the agent's safety in the diving environment. DESIGN: Double-blind, placebo-controlled, crossover study. SETTING: Monoplace hyperbaric chamber of a university hospital. SUBJECTS: Thirty active divers (mean age 38 yrs). INTERVENTION: A bank of seven tests was used to assess cognitive function during four different simulated dive combinations: placebo-1 atm, placebo3 atm, pseudoephedrine-1 atm, and pseudoephedrine-3 atm. MEASUREMENTS AND MAIN RESULTS: Heart rate and cardiac rhythm were recorded during all dives. Repeated-measures analysis of variance was used to analyze the effects of pseudoephedrine, depth, and drug-depth interaction. No significant, independent effects of pseudoephedrine were seen on any of the seven psychometric test scores (p>0.05), although the drug tended to increase anxiety scores (p=0.092). Depth resulted in a significant increase in anxiety scores (p=0.021) and a significant decrease in verbal fluency test scores (p=0.041); it had no significant effects on the other five psychometric tests (p>0.05). Pseudoephedrine caused a significant increase (p=0.036) in mean heart rate, and depth caused a significant decrease (p=0.013). Neither pseudoephedrine nor depth affected cardiac rhythm. CONCLUSION: Pseudoephedrine does not cause significant alterations in psychometric performance at 3 atm of pressure that might increase the risk of diving. Depth causes significant adverse effects on anxiety levels and semantic memory at 3 atm. Pseudoephedrine and depth have significant but opposite effects on heart rate; although, these effects are unlikely to be clinically significant during diving. It is unlikely that pseudoephedrine adds significant risk to the diver.

Adult↗
PubMed2006

Substrate utilization during prolonged exercise with ingestion of (13)C-glucose in acute hypobaric hypoxia (4,300 m).

Energy substrate oxidation was measured using indirect respiratory calorimetry combined with tracer technique in five healthy young male subjects, during a 80-min exercise period on ergocycle with ingestion of 140 g of (13)C-labelled glucose, in normoxia and acute hypobaric hypoxia (445 mmHg or 4,300 m), at the same relative [77% V(.-)((O)(2)(max))] and absolute workload (161+/-8 W, corresponding to 77 and 54% V(.-)((O)(2)(max)) in hypoxia and normoxia). The oxidation rate of exogenous glucose was not significantly different in the three experimental situations: 21.4+/-2.9, 20.2+/-1.2 and 17.2+/-0.6 g over the last 40 min of exercise at approximately 77 and approximately 54% V(.-)((O)(2)(max)) in normoxia and in hypoxia, respectively, providing 12.5+/-1.5, 16.8+/-1.1 and 14.9+/-1.1% of the energy yield, although ingestion of glucose during exercise resulted in a higher plasma glucose concentration in hypoxia than normoxia. The contribution of carbohydrate (CHO) oxidation to the energy yield was significantly higher in hypoxia (92.0+/-2.1%) than in normoxia for both a given absolute (75.3+/-5.2%) and relative workload (78.1+/-1.8%). This greater reliance on CHO oxidation in hypoxia was entirely due to the significantly larger contribution of endogenous glucose oxidation to the energy yield: 75.9+/-1.7% versus 66.6+/-3.3 and 55.2+/-3.7% in normoxia at the same relative and absolute workload.

Adult↗
PubMed2001

Thermal stability of the human body under hyperbaric environmental conditions: a theoretical study.

I report here a theoretical study of the dependence on ambient pressure of heat and mass (water vapour) rate transfer processes between the human body and its gaseous surroundings, for monocomponent gases (N2, O2, He) and/or diatomic gas mixtures (He-O2, N2-O2). Heat and water vapour rate transport are described by the following rate transfer parameters: the convective heat transfer coefficient (hc), the evaporative heat transfer coefficient (he) and the Lewis relationship (LR). It is shown that the thermal stability of the human body under hyperbaric conditions is proportional to the evaporative resistance. It is also shown that in a He atmosphere the change in the thermal state caused by a heat load of 1 W x m(-2) at sea level is equivalent to the effect of a heat flow of 0.186 W x m(-2) at 30 atmospheres absolute. This indicates that the thermal state of the body is more prone to instability at increasing ambient pressures.

Atmosphere Exposure Chambers↗
PubMedDate not supplied

Tyrosine administration prevents hypoxia-induced decrements in learning and memory.

Exposure to hypobaric hypoxia rapidly produces decrements in learning and memory. Tyrosine, a neurotransmitter precursor, has beneficial behavioral effects when administered to animals and humans exposed to various acute stressors. To determine whether tyrosine would protect rats from the adverse effects of hypobaric hypoxia on spatial reference and working memory, it was administered to 27 male Fischer 344 rats tested in the Morris water maze. Rats were tested starting at 2 and 6 h of an 8 h exposure to a simulated altitude of 5950 m (19,500 ft) or sea level. Tyrosine or placebo was administered 1/2 h prior to each testing session (400 mg/kg, IP). Altitude exposure significantly increased working memory escape latency; treatment with tyrosine reversed this decrement. There was no effect of altitude or tyrosine on reference memory. There were also no treatment-related differences in performance when animals were tested the next day at sea level. The beneficial effects of tyrosine on working memory performance may be due to a direct effect of tyrosine on memory, alleviation of a hypoxia-induced retardation of learning, or to other central or peripheral effects of this dietary catecholamine precursor.

Altitude↗
PubMed1991

European EVA decompression sickness risks.

For the first manned flight of Hermes there will be a capability of performing EVA. The European EVA Space Suit will be an anthropomorphic system with an internal pressure of 500 hPa of pure oxygen. The pressure reduction from the Hermes cabin pressure of 1013 hPa will induce a risk for Decompression Sickness (DCS) for the EVA crewmember if no adequate protective procedures are implemented. Specific decompression procedures have to be developed. From a critical review of the literature and by using knowledge gained from research conducted in the past in the fields of diving and aerospace medicine safe protective procedures are proposed for the European EVA scenario. An R factor of 1.2 and a tissue half-time (t1/2) of 360 minutes in a single-tissue model have been identified as appropriate operational values. On the basis of an acceptable risk level of approximately 1%, oxygen prebreathing times are proposed for (a) direct pressure reduction from 1013 hPa to a suit pressure of 500 hPa, and (b) staged decompression using a 700 hPa intermediate stage in the spacecraft cabin. In addition, factors which influence individual susceptibility to DCS are identified. Recommendations are also given in the areas of crew selection and medical monitoring requirements together with therapeutic measures that can be implemented in the Hermes scenario. A method for demonstration of the validity of proposed risks and procedures is proposed.

Aerospace Medicine↗