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.

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.

Shallow habitat air dives I and II: human hematologic responses to compressed air saturation diving.

Two subjects each were exposed to pressure equivalents of 50 (SHAD I) and 60 (SHAD II) feet of sea water gauge (FSWG) for 30 and 28 d, respectively. Red blood cell (RBC) count, hemoglobin (Hb) content, and reticulocyte count of venous blood from divers were measured before, during, and after these exposures. RBC count of the divers decreased a maximum of 7.1% in the 50-ft dive and 10.7% in the 60-ft dive compared to surface control values. Hb content fell 7.7% and 11.1% in the 50- and 60-ft dives, respectively, when compared to nondiving subjects. Reticulocyte counts tended to increase late in the pressurization phase and during the recovery. The total month-long responses of Hgb in SHAD I, and RBC, Hgb, and reticulocyte count in SHAD II were significantly altered when compared to those of the surface control subjects. The changes in these factors were directly attributable to the month-long exposure to the total hyperbaric environment. The threshold for hematological effects of chronic exposure to compressed air would seem to lie between 50 and 60 FSWG.

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.