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Biomedical subjects

J O Owe

Publications and source records attributed to J O Owe.

10 recordsLinked to original sources
PubMed1999

Cerebral artery blood velocity in normal subjects during acute decreases in barometric pressure.

To investigate the effect of acute changes in barometric pressure on regional cerebral perfusion we studied the middle cerebral artery (MCA) blood velocity in five healthy male volunteers by means of a low-pressure chamber. The MCA blood velocity, arterial blood and respiratory gases were measured at the barometric pressures of 1, 0.8, 0.65, and 0.5 atmospheres. The observed blood velocity (Vo) showed no systematic changes. Decreases in barometric pressure induced hypoxia and hypocapnia. When normalizing the MCA blood velocity (Vn) to a standard P(CO2) (5.3 kPa), thereby correcting for the hypoxic induced hypocapnia, we obtained an inverse relationship between cerebral artery blood velocity and arterial blood oxygen content (CaO2). The oxygen supply to the brain, estimated as the product of Vo and CaO2, decreased with lowering of the barometric pressure. However, the product of Vn and CaO2 remained constant. This suggests the existence of a regulatory mechanism attempting to maintain a constant oxygen supply to the brain during acute changes in CaO2, if the hyperventilation induced decrease in PCO2 can be omitted. In the artificial situation of a low pressure chamber, our findings are quite similar to those obtained at sea level. This indicates that the underlying mechanisms of control of cerebral blood flow do not change during acute exposure to altitude.

Acute Disease↗
PubMed1998

[Medical problems among airline passengers].

Worldwide, there are more than one billion air travelers each year. Flying in a modern jet airliner is a safe, efficient and relatively comfortable mode of transport, although a few susceptible passengers may be adversely affected by environmental and physiological stresses like pressure change, reduced level of oxygen, dry air, immobility due to cramped seating, noise, vibration and turbulence, in addition to stressful airports. This article describes these factors and their medical implications and includes some practical medical advice to travellers. Reported inflight illness and injuries in two major Scandinavian airlines 1993-97 are presented.

Aerospace Medicine↗
PubMed1998

Effects of hypobaric hypoxia on postural control.

BACKGROUND: While the effects of accelerative forces on the vestibular system have been thoroughly investigated, the effects of hypobaric conditions on the postural system have attracted less attention. The purpose of the study was to investigate if postural control is affected by hypobaric hypoxia. HYPOTHESIS: Moderate hypobaric hypoxia may reduce postural control. METHODS: Subjective and multiple objective measurements of postural control with open and closed eyes were made in 16 military aircrew standing on a static balance platform before, during, and after exposure to an altitude chamber training profile with a maximum altitude of 25,000 ft. RESULTS: No subjective dizziness and no clinical unsteadiness were noted. However, significant changes in body sway were found at the balance platform during hypobaric exposure at 18,000, 14,000 and 8000 ft compared with the baseline registrations. The relative increase in sway movements was greater in the eyes open condition compared with the eyes closed condition, and significant for movements in the anteroposterior plane but not in the lateral plane. Most sway parameters returned to pre-exposure values on return to ground level. CONCLUSIONS: Acute hypobaric hypoxia, corresponding to the tested altitudes, influenced postural control primarily in the anteroposterior plane with eyes open. This is in agreement with other studies showing that vision is the first of the special senses to be altered by lack of oxygen.

Adult↗
PubMed1991

Baroreflex responsiveness during hypobaric hypoxia.

Baroreflex responses to graded neck suction during held expiration were studied in five healthy females at sea level and at a simulated altitude of 4,572 m (15,000 ft), with and without oxygen administration. An apparent resetting of the baroreflex was observed during hypobaric hypoxia, but this effect was abolished by oxygen administration. Held expiration alone induced a pulse prolongation in all experimental conditions, however this bradycardiac response was smaller during hypobaric hypoxia than during the two normoxic conditions. When the bradycardic responses of held expiration were subtracted, the baroreflex responses to neck suction were equal in all experimental situations. Similarly, the baroreflex was unaffected by hypobaric hypoxia when the R-R interval prolongations were expressed in percentage of the R-R intervals immediately prior to the neck suction. These data indicate that reduced ambient pressure per se has no influence on the carotid baroreflex control of heart rate.

Adult↗
PubMed1989

Arterial PCO2 and pH in man during 3 days' exposure to 2.8 kPa CO2 in the inspired gas.

It has not been firmly established how respiration adapts to long-term CO2 exposure in man. We have therefore exposed five healthy human subjects to 2.8 kPa CO2 in the inspired gas for about 70 h in a chamber with controlled atmospheric conditions at ambient pressure PCO2 and pH were determined in arterial or arterialized venous blood drawn before, during and after the exposure. One subject was studied twice. We found that PaCO2 increased acutely and then increased further within the 5- to 24-h period of exposure to 2.8 kPa CO2. No consistent change was observed during the following 2 days. At the end of exposure the PaCO2 was 0.5 kPa above the pre-exposure level. When the breathing gas was switched back to room air, PaCO2 promptly returned to pre-exposure values. The secondary rise in PaCO2 within the first day would correspond to a decrease in alveolar ventilation of about 10% assuming constant production and elimination of CO2. Arterial pH remained slightly below the pre-exposure level during the entire exposure period. A slight renal compensation resulting in an increase in base excess of about 1 mmol l-1 may have occurred in the middle part of the exposure period. We conclude that a significant, but moderate, respiratory adaptation takes place during the first day of exposure to an increased inspired load of CO2.

Acid-Base Equilibrium↗
PubMed1987

Lack of bubble formation in hypobarically decompressed cells.

Suspensions of human erythrocytes or of unicellular microorganisms (Tetrahymena pyriformis, Euglena gracilis, Escherichia coli, and Microcyclus aquaticus) were equilibrated with nitrogen gas pressures up to 200 atm and rapidly decompressed to hypobaric pressures below the vapor point of water. The intracellular environments proved to be very tolerant to the gas supersaturations induced. None or only a few cells were damaged in each case, and bubbles were never observed intracellularly after decompression. In view of such extreme tolerances, it is doubtful that bubbles originate intracellularly during decompression of multicellular organisms, in which bubbles occur with far lower gas supersaturations, unless the tolerances are greatly affected by extensive mechanical deformations of the cells or by the presence of internalized particles with bubble-promoting properties.

Animals↗
PubMed1985

Analyses of maximum cardiopulmonary performance during exposure to acute hypoxia at simulated altitude--sea level to 5000 meters (760-404 mm Hg).

The maximum cardiopulmonary performance of seven healthy male subjects was studied repeatedly in graded hypoxia at ambient pressures ranging from 760 to 404 mm Hg (sea level to 5000 m of simulated altitude). Using this approach it has been possible to not only establish a reproducible value for VO2max, but to determine an equation which may be used to predict the VO2 at altitude for healthy, unacclimatized males exercising to exhaustion. Moreover, we have attempted to explain the limits to pulmonary ventilation at decreasing levels of PO2 by comparing a given VO2max (STPD) to the corresponding VEmax (BTPS), showing that any further increase in the latter is impossible when a certain level of altitude has been reached. Finally, our series of experiments indicates that the HRmax falls at altitude. Although statistically significant, this decrement is not conspicuous. Thus, when used with the VO2max to calculate the number of ml of O2 consumed per beat of the heart, the "oxygen pulse" turns out to be more sensitive to the fall in VO2max at altitude than to the corresponding decrease in the HRmax.

Adult↗
PubMed1984

Modification of the 'dividing bradycardia' by hypoxia or exercise.

The oxygen-conserving efficiency of the physiological adjustments to diving depends on two factors: (1) the rate of onset of reflex action, and (2) the extent to which circulating blood is withdrawn from the organs which are not irreparably damaged by transient hypoxia. We report a study in which either hypoxia or exercise has been imposed as an additional stress on human subjects performing apneic face immersion in order to determine any early changes in the reflex rate of onset and/or the final level of cardiovascular adjustment. It is concluded that the rate of onset of the diving reflex varies with the stresses imposed whereas the final level of adjustment does not.

Adult↗
PubMed1984

Central nervous reactions to a 6.5-hour altitude exposure at 3048 meters.

In this study of CNS reactions to mild hypoxia, 7 subjects were decompressed to the equivalence of 3048 m altitude breathing air, for 6.5 h. On reaching 3048 m, and for every second h thereafter, a battery of neuropsychological tests were administered. In addition, blood and performance measures were sampled and a symptom check list was administered. The performance tests indicated significant effects of hypoxia. In contrast to earlier studies on grade of hypoxia and performance, no relationship between impaired performance and duration of exposure to hypoxia was found. Repeated testing throughout exposure indicated stable individual reactions. Endocrine variables did not support the hypothesis that activation or 'stress' caused the impairment observed. In addition to impaired neuropsychological test performance and impaired task performance, the subjects reported headache, weakness and some dizziness. Comparisons between different tests confirmed previous results showing that mild hypoxia yields varying degrees of impairment on different cognitive functions.

Adult↗