Effect of hypoxia on psychomotor performance during graded exercise.

We evaluated the combined effects of reduced O2 (12%) and graded ergometer exercise (10, 70, and 140 W) on the performance of a psychomotor task. Six men participated in two test sessions each. Each session began with the baseline data (air) and finished with exposure data (12% or 21%, random, unidentified). The gas mixtures were air (control condition) and 12% O2-balance N2 (12% O2 condition). The psychomotor task score was degraded during the 140 W work rate of the 12% O2 condition (p less than 0.05). Reductions of the SaO2 (p less than 0.05) at each work rate proved that hypoxia existed during exercise in the 12% O2 condition. The arterial blood gases indicated that respiratory alkalosis was mixed with metabolic acidosis during the hypoxic exercise. The results differ from previously reported findings of an arousal effect of exercise on psychomotor performance and the decrement of task performance at work rates less than or equal to 50 W. We conclude that hypoxia degraded the performance of the psychomotor task during graded exercise.

Symptomatology during hypoxic exposure to flame-retardant chamber atmospheres.

Hypoxia was studied in 12 men during 63-h exposures to 17 and 13% O2, with the subjects serving as their own controls by repeating the measurements in 21% O2. All test atmospheres were contaminated with 0.9% CO2 to simulate the condition of living aboard submarines. The mean SaO2's were 97-98% in all conditions of 21% O2, 96% in 17% O2 (n.s.), and 92% in 13% O2 (P less than 0.05). The blood concentrations of 2,3-diphosphoglycerate were elevated in 13 and 17% O2 (P less than 0.05). Seventeen percent O2 did not cause significant symptoms of environmental stress; however, 13% O2 caused symptoms of acute mountain sickness in 5 of 12 men. In the last 7 h of exposure to 17% O2, reduction of the barometric pressure to 576 Torr reduced the ambient PO2 to 98 Torr (similar to the PO2 of 13% O2 at normobaric pressure). This induced symptoms of acute mountain sickness in 3 of 11 men. All symptomatology and physiologic changes were reversed during recovery in 21% O2. Monitoring devices indicated the presence of volatile organic contaminants at a mean concentration of 6.1 ppm in the chamber atmosphere. Combustion tests in the occupied chamber showed that flame propagation was retarded by lowering the O2 concentration from 21 to 13-17%. We conclude that men can live comfortably in a normobaric, flame-retardant atmosphere consisting of 17% O2-0.9% CO2-6.1 ppm volatile organic compounds-balance N2.

Submarine atmospheres.

Nuclear submariners live and work in an atmosphere composed of approximately 80% naturally occurring nitrogen, 19% oxygen (manufactured aboard ship), and a complex mixture of inorganic and organic contaminants. The concentrations of contaminants exist as a balance between the rates of production from human and operational activities and the rate of removal by engineering systems. The biological effects of inorganic gases, particularly carbon dioxide, have been extensively studied. Investigators are now attempting to define the composition and concentration of volatile organic compounds that accumulate during 90-day submergences. Medical studies have not conclusively shown that crewmembers incur adverse health effects from continuous exposures to the sealed atmospheres of nuclear submarines.

Carbohydrate metabolism in U.S. Navy submarine personnel.

One- and two-hour postprandial glucose and insulin values were measured in 58 submariners with 5 or more FBM patrols and in 58 non-submariners. An interrelationship between serum glucose and insulin for classifying defects in carbohydrate metabolism indicated that 55% of the submariners and 45% of the non-submariners exhibited some type of defect. Exercise appears to play an important role in the maintenance of normal carbohydrate metabolism in these subjects. Non-submariners reported engaging in significantly more exercise than did submariners. Negative correlation between exercise vs. 1 and 2-h glucose and 2-h insulin was significant for all subjects. An inverse relationship was observed between amount of exercise and the severity of carbohydrate metabolic defects in submariners and non-submariners as well as in normal weight and obese individuals. No statistical differences were found between the submariner and non-submariner groups with respect to age, % body fat, fatness (normal or obese), glycosylated hemoglobin, or family history of diabetes.

Blood volume responses in partially dehydrated subjects working in the cold.

The effects of high-salt diets, cold, and heavy exercise have been examined in 33 Marine Corps volunteers living and working in a cold chamber. Temperatures varied from -29 degrees C during working hours to -4 degrees C, simulating partly warmed shelters, at night. Dehydrated operational rations were eaten and fluid intakes were controlled. When quantities of water were consumed at or above the amounts determined in previous studies in this series to prevent symptoms of cold-induced dehydration with these diets, ie., 2.5-3.0 L/d with diets containing 24 g of NaCl/d or about 2.0 L/d with 8 g NaCl/d, blood volumes increased 5-10%, primarily as a result of plasma volume expansion. This finding apparently confirms the results of earlier workers who have noted plasma volume increases in subjects undergoing vigorous exercise training. In subjects receiving 0.5 L/d or more below recommended quantities of water, intravascular volume increases developed slowly and quite erratically during 5 d of exercise. Intravascular volume increases responded within 1-2 d when fluid levels became appropriate for either high- or low-salt intakes. Besides confirming recommendations concerning water needed with dehydrated diets under conditions of the experiment, the observation of intravascular fluid volume increases during exercise training--despite limiting fluid intakes--raises the question of whether there are any physiological advantages from this adaptive mechanism.

Relationship of personality factors and some social habits to cardiovascular risk in submariners.

Correlational and contingency analytical techniques were used to investigate the relationship between subtest scores on the Minnesota Multiphasic Personality Inventory (MMPI) and coronary heart disease (CHD) risk factors in 1000 submariners. Groups of personality traits, both enhancing and protecting against risk of heart disease, were identified in these subjects. Personality trait patterns tending to be least associated with cardiovascular risk are tentatively identified by the three MMPI scales: psychasthenia, schizophrenia, and social introversion. On the other hand, the scales most strongly related to CHD risk in the submariner sample were denial of symptoms as measured by the K-scale, hypochondriasis, and hysteria. While the inherent inaccuracy in the prediction of CHD risk in young healty individuals limits generalization from these findings, the potential utility of the MMPI to assist in risk detection is indicated. Comparisons of cigarette smoking, coffee drinking, and alcohol consumption with personality characteristics identified by the MMPI yielded trait clusters associated with each addictive habit. Cigarette smoking and alcohol consumption tended to correlate with traits positively associated with CHD risk. The correlations between those addictive habits and MMPI subtest scores were most significant for the F-scale, which measures inordinate tendencies to exaggerated emotional symptoms, and for the psychopathic deviate and hypomania scales. Significant negative correlations were found between the amount of coffee consumed and those personality traits negatively associated wit CHD risk. These negative relationships were most significant for the MMPI scales schizophrenia and psychasthenia. Though the relationships were not necessarily construed to be causal, the contrasting modes through which these drug-associated habits appeared to relate to cardiovascular risk lend some support to the assumption that individuals with various specific sets of personality characteristics tend to incorporate these additive behaviors into their behavior repertoire in very different ways.

Biochemical and hematologic profiles of 1000 submariners.

Control biochemical and hematologic data were gathered for 1017 healthy submariners who ranged in age from 19.5 to 43.5 years. Means, standard deviation, and frequency distribution are presented for 24 whole blood and serum variables and, where appropriate, for 11 urinary variables. After statistical separation of the effects of aging and length of submarine service, it has been determined that the following correlations were significant in this sample: neutrophil and leucocyte levels, serum cholesterol, and both fasting and postprandial glucose correlated positively with age; serum alkaline phosphatase levels and age correlated negatively. Age-corrected positive correlations were demonstrable between length of submarine service and both serum cholesterol content and alkaline phosphatase activity; after a loading test, glucose levels showed a negative relationship to length of submarine service. Split-sample correlation analyses verified these significant correlations, with the exception of the apparent rise in alkaline phosphatase activity with increasing length of submarine duty.

Cardiovascular risk factors in submariners.

A sizeable group of biochemical, hematologic and physiologic variables that significantly affect the prognosis for diseases of aging, especially for coronary heart disease (CHD), were studied in 1017 submariners. Skinfold thickness in these subjects was determined to be higher than in most other groups of men of similar age; the total level of body fat was within the range of high normality. Serum cholesterol levels, cigarette smoking, relative weight, and blood pressure appeared to be the factors most directly responsible for the extent of cardiovascular risk in this group of submariners. Though submariners as a group do not apparently have appreciably higher levels of CHD risk than other American men, there was a significant tendency for total risk to increase with length of submarine service as well as with age. A similar age-independent increase in serum cholesterol correlating with length of submarine service was reported earlier. Split-sample analyses support the reliability of the age-corrected correlations of CHD risk with time of submarine service. Although no attempt was made to prove a direct relationship between alcohol consumption or coffee drinking and cardiovascular risk, there were strong correlations noted. These factors, combined with serum cholesterol levels, cigarette smoking, and relative weight, deserve consideration as potentially modifiable CHD risks.

Hematologic changes after two exposures to 6.7 ATA air at three-day intervals.

Hematologic parameters were studied in human subjects exposed to various diving regimens. A series of exposures in a dry chamber to a simulated depth of 188 ft of seawater gauge (fswg), 6.7 ATA, utilizing compressed air, were carried out according to standard Navy diving tables. The subjects were serially followed for a control period prior to diving and subsequently for up to 1 wk. Little significant change occurred except for alterations in some platelet factors. In another series of experiments, the single excursion was followed by a second dive to 188 fswg 3 days later, again with appropriate hematologic monitoring. A pronounced eosinopenia and increased clotting times were observed soon after reaching the surface. Platelet depletion associated with increased clumping and elevated megathrombocyte levels persisted long after the second excursion. A latent hemodilution also developed 3--5 after the second dive. These findings clearly demonstrate that repeated hyperbaric exposures produce additive effects and further suggest that no diving procedure is completely innocuous.

Biochemistry and hematology at decompression sickness: a case report.

A 24-year-old hospital corpsman, a volunteer in a series of dry chamber air dives to a simulated pressure equivalent to 188 FSWG (57.3 MSWG), developed left knee pain shortly after standard decompression. A tentative diagnosis of decompression sickness was made and recompression therapy was initiated with alleviation of pain occurring at 60 FSWG (18.3 MSWG). A U.S. Navy Treatment Table "5 (oxygen breathing) regimen was then selected and completed uneventfully. The subject had been undergoing biomedical evaluation for several days prior to diving; thus, a clinically diagnosed case of dysbarism with subsequent treatment was available for study. This individual was then monitored for a 10-d period. The acute phase of decompression sickness was characterized by a marked shortening of clotting time and a thrombocytopenia with accompanying increased platelet aggregates. The recovery phase was categorized by a variety of hematological and bio-chemical changes. Hemodilution, an elevated megathrombocyte index, and a tendency toward eosinopenia were evident for most of the 10-d observation period. Other persistent alterations detected during this period included a relative hyperglycemia, depressed urine Na+/K+, and increased ketosteroid excretion. These observations indicate that abatement of pain after treatment of dysbarism can be followed by the onset of a variety of biochemical and hematological changes. Moreover, complete recovery may require upwards of 10 d.