Effects of CO2 exposure on distribution of various forms of iron and copper in guinea-pig tissues.

The effects on iron and copper distribution and metabolism of exposure to high levels of CO2 were studied in the guinea-pig. Mature, male animals were placed in an atmosphere of 15% CO2, 21% O2 (balance N2), and sacrificed from 1 h to 1 week thereafter. Total iron and copper concentrations of blood, liver, spleen and bone, as well as concentrations of heme and ferritin iron, were measured together with blood hematocrit, reticulocytes, plasma hemoglobin, plasma ceruloplasmin and copper concentrations. The results show clearly that rapid and sustained red cell damage or hemolysis ensued several h from the start of CO2 treatment. This resulted in loss of iron and copper from the blood, an influx of both elements into liver, spleen and bone, and a rise in plasma ceruloplasmin. Influx of iron into liver and spleen caused an accumulation of ferritin, the main site for iron storage in cells. Following the effect on red cells, there was an accumulation of heme iron, and a decreased hematocrit, best explained by a depressed activity of the reticuloendothelial and erythropoietic systems. A period of adaptation succeeded these events, in which all blood parameters and most tissue values returned to normal, despite the continuing presence of high CO2. The only changes not reversed were the elevations in liver, spleen and bone iron stores. These remained high, with a net accumulation of greater than 2 mg iron, or 3-4 times more than originally present. The results indicate that at least in the guinea-pig, high CO2 exposure results in red cell damage and other events leading to an accumulation of additional iron in the body; also, that iron accumulated as ferritin and hemosiderin in liver and spleen may not be readily available to restore blood hemoglobin concentrations on an acute basis.

Phasic changes in bone CO2 fractions, calcium, and phosphorus during chronic hypercapnia.

The bone CO2 buffering system and bone calcium and phosphorus were studied in guinea pigs exposed to 1% CO2 for periods up to 8 wk and killed at weekly intervals together with control animals of the same age. Measurements were made of arterial CO2 tension, pH, standard bicarbonate, and bone Ca and P. Heat-stabile bone CO2 (carbonate) was determined as dry bone CO2 and heat-labile bone CO2 (bicarbonate) as delta wet-dry bone CO2. During the first 3-4 wk of exposure to 1% CO2, a systemic acidosis was found as indicated in a lowered pH, increased arterial CO2 tension, and decreased standard bicarbonate. The acidosis subsided during the last 4 wk of exposure. Phasic changes in bone bicarbonate were observed as shown in immediate rise lasting for 2 wk followed by a 2-wk decline and second rise after 6 and 8 wk. Bone carbonate exhibited the opposite change during the first 4 wk and thereafter remained stable at an elevated level. Bone Ca and P fell in association with increasing bone bicarbonate and rose with increasing bone carbonate.

Bone CO2-titration curves in acute hypercapnia obtained with a modified titration technique.

Bone CO2-titration curves were obtained in mature rats weighing 500-600 g. Animals were exposed for one hour to 1, 3, 5, 10, or 15% CO2 in air. Measurements of bone CO2, were made using a modified titrimetric analysis on fresh and oven-dried samples of paired rat femurs. A manometric method was used for comparison. Arterial blood samples were obtained for measurements of partial pressure of CO2 in arterial blood (PaCO2). Within the range of environmental CO2 concentrations studied, a linear relationship was observed between the PaCO2 and the increment in fresh bone CO2 content. This relationship is defined by the equation: delta fresh bone CO2 (mmol/kg) = 61.8 +/- 0.68 PaCO2. The CO2 increment was confined to a heat-labile, presumably soluble pool comprising 10.5% of the total bone CO2 content. No change in the water content of the bone was observed as a result of acute CO2 exposure. The results of this study demonstrate the rapid in vivo CO2 uptake of bone in response to exposure to increased CO2 levels.

CO2-induced kidney calcification.

Light microscopic examination of kidney tissue of guinea pigs exposed to 1.5% CO2, 21% O2, and balance N2 for periods as long as 42 days and of rats exposed to the same CO2 concentrations for up to 91 days showed that the incidence of focal kidney calcification increased with length of exposure. Calcification occurred primarily in the tubules of the renal cortex. Another group of guinea pigs were exposed to 1% CO2, 21% O2, and the balance N2 for periods up to six weeks and were later killed at regular intervals, together with control animals of the same litter. In the exposed animals, arterial PCO2 was elevated by 3-4 mmHg and hydrogen ions by about 4 nmol/liter. The standard bicarbonate level was lowered by 1-1.5 mmol, indicating a lack of renal reabsorption of bicarbonate (HCO3), which in turn placed greater stress on the bone buffer system and apparently caused bone calcium and phosphorus mobilization. Bone calcium and phosphorus levels exhibited a cyclic decrease, which resulted in cyclic hypercalcemia and hyperphosphatemia, after one week and six weeks of exposure to 1% CO2. Kidney calcium content increased significantly after two weeks of exposure (27%) and remained at this elevated level during subsequent exposures between the third and sixth weeks. These findings indicate that once the kidney calcification process has started, kidney mineralization is independent of fluctuations in the blood calcium level. A rise in plasma phosphate level that occurred after one day of exposure could have been a precipitating factor in the calcification process. The small but consistent increases in ionized calcium during a 4-week exposure to 1% CO2 may have stimulated the parathyroid, causing an increased blood calcium level that was independent of the two calcium tides in the blood associated with marked bone calcium loss.

Effect of intermittent exposure to 3% CO2 on respiration, acid-base balance, and calcium-phosphorus metabolism.

One subject was exposed for six days to increasing levels of CO2, rising at a constant rate from 0.03 to 3.0% CO2 within a 15-h period followed by 9 h of air breathing. To assess acid-base parameters, arterialized capillary blood was taken from a finger twice daily (at 8 a.m. and 11 p.m.) at times corresponding to the beginning and end of the intermittent exposure to CO2. Venous blood samples were obtained on alternate days at the same times. Urine specimens were collected twice daily. The subject was on a liquid diet. Resting respiratory minute volume (VE), oxygen consumption (VO2), carbon dioxide excretion (VCO2), alveolar carbon dioxide and oxygen tension (PACO2) and PAO2) were measured twice daily. PACO2 and PAO2 were also determined at the end of breath-holding twice daily; CO2 tolerance tests and lung function tests were also carried out. In contrast to the effects of chronic exposure to 3% CO2, the CO2 tolerance tests showed an increased sensitivity (increase of slope) and breath-holding PACO2 did not change, indicating that acclimatization to CO2 did not develop. The ventilatory response to CO2 was not sufficient to prevent CO2 accumulation in the body; this accumulation was eliminated during the nightly air-breathing periods on the fourth and fifth days, indicated by higher values of PaCO2 and PACO2. The known renal response to hypercapnia, consisting of an increased excretion of titratable acidity, ammonia, and hydrogen ion excretion, occurred but was interrupted after the first day and was triggered again on the fourth and fith days when accumulated CO2 was released from body CO2 stores. The second renal response was associated with a marked calcium excretion, which suggests that bone CO2 stores were involved.

Proliferation of pneumocyte II cells in prolonged exposure to 1% CO2.

Guinea pigs were exposed to 1% CO2 in a mixture of 21% O2, balance N2 and were killed at weekly intervals, together with control animals housed in the same type of environmental chamber and exposed to normal ambient CO2. The exposed animals showed a persistent elevation of PaCO2, averaging about 4 mmHg, and a small decrease in pH (-0.04 units). During the whole exposure period standard bicarbonate remained 1-1.5 mEq below control levels, indicating a failure of the kidney to increase bicarbonate reabsorption. Electron microscopic studies after 4 and 6 weeks of exposure to 1% CO2 showed ultrastructural changes of the lungs, consisting of marked increases in the size and number of pneumocyte II cells that were still present two weeks and to a lesser extent four weeks after recovery. Changes in the pneumocyte II cell were postulated to be compensatory reactions to impairing CO2 effects on the alveolar lining cell (Type I cell).

Effect of prolonged exposure to 0.5% CO2 on kidney calcification and ultrastructure of lungs.

Guinea pigs were exposed for up to 8 weeks to 0.5% CO2, 21% O2, and balance N2. Control groups of the same age were kept simultaneously in environmental chambers on air. A slight increase in PaCO2 and decrease in pH were observed at various periods of exposure to 0.5% CO2. After eight weeks of exposure, an increased kidney calcification, indicated by increased kidney calcium content, was found. Plasma calcium was significantly elevated at this point, apparently because of the release of calcium from bone. After 8 weeks of recovery on air that followed 8 weeks of exposure to 0.5% CO2, values had returned to control levels. No significant ultrastructural changes were found in the lungs after 4, 6, and 8 weeks of exposure to 0.5% CO2.

Analysis of health data from 10 years of Polaris submarine patrols.

Medical reports from 885 Fleet Ballistic Missile (FBM) submarine patrols (7,650,000 man-days) were analyzed. The data were categorized and compared with data obtained by medical personnel from surface fleet personnel (1,215,918 man-days) during a continuous 7--8 months' deployment of surface vessels in 1973. Surface fleet personnel had a higher illness rate in the categories of respiratory, traumatic, gastrointestinal, dermal, infections, and miscellaneous illness, and a lower rate in genitourinary, systemic (including mononucleosis), cranial, and neuropsychiatric illness compared to submarine personnel. Because of improved atmosphere control, a sharp decline in the level of submarine contaminants occurred between 1965--67. Reports from the 1968--73 period showed a decrease in: 1) respiratory; 2) ear, nose, and throat; 3) gastrointestinal; 4) cardiovascular; 5) urologic; and 6) general medical illness categories; the number of general surgery, orthopedics, dental, and eye illness cases was not affected. Neurologic and psychiatric disease showed the only increases in incidence for this period. The overall decrease in illness can be attributed mainly to the fall in the incidence of respiratory disease, known to be affected by reduced air pollution, and the decline in gastrointestinal illness. This decline occurred in a period during which the incidence of both classes of illness went up in the general population, according to the Health Interview Survey published by DHEW. The improvement of atmosphere control in submarines caused a substantial reduction in contaminants (a decline in tobacco smoking also occurred in this period), which led to a decrease in incidence of illness, particularly respiratory disease. No direct causal relationship between reduction in air pollution and reduction in the incidence of disease could be proven within the framework of this study, however.

Calcium, magnesium, and phosphorus metabolism, and parathyroid-calcitonin function during prolonged exposure to elevated CO2 concentrations on submarines.

Studies of calcium and phosphorus metabolism and acid-base balance were carried out on three Fleet Ballistic Missile (FBM) submarines during prolonged exposure to elevated concentrations of CO2. The average CO2 concentration in the submarine atmosphere during patrols ranged from 0.85% to 1% CO2. In the three studies, in which 9--15 subjects participated, the urinary excretion of calcium and phosphate fell during the first three weeks to a level commensurate with a decrease in plasma calcium and increase in phosphorus. In the fourth week of one patrol, a marked increase was found in urinary calcium excretion, associated with a rise in blood PCO2 and bicarbonate. Urinary calcium excretion decreased again during the 5th to 8th week, with a secondary decrease in blood pH and plasma calcium. During the third patrol, the time course of acid-base changes corresponded well with that found during the second patrol. There was a trend toward an increase in plasma calcium between the fourth and fifth week commensurate with the transient rise in pH and bicarbonate. Plasma parathyroid and calcitonin hormone activities were measured in two patrols and no significant changes were found. Hydroxyproline excretion decreased in the three-week study and remained unchanged in the second patrol, which lasted 57 days. It is suggested that during prolonged exposure to low levels of CO2 (up to 1% CO2), calcium metabolism is controlled by the uptake and release of CO2 in the bones. The resulting phases in bone buffering, rather than renal regulation, determine acid-base balance.

Effect of 18-h watch schedules on circadian cycles of physiological functions during submarine patrols.

Circadian rhythms of body temperatures, pulse rate, and respiration rate were measured in 11 subjects every 4 h during certain periods on two submarine patrols. Data on systolic and diastolic blood pressure were also obtained on five crew members during the first period. All the subjects of the first patrol were on an 18-h watch schedule (6 h on, 12 h off). During the second patrol, three subjects were on an 18-h watch schedule and three were on a 24-h watch schedule. Cosinor analysis for positive (P less than 0.05) detection of rhythm demonstrated that all subjects on the 18-h watch schedule developed 18-h cycles of body temperature, pulse rate, respiration rate, and systolic and diastolic blood pressure, which were then superimposed on the persisting 24-h cycles of the same function. The three subjects on a 24-h watch schedule did not show the 18-h cycles. Moreover, additional 12-, 36-, and 48-h cycles (harmonics and subharmonics of 24-h cycles) were found in all subjects on both patrols, attesting to the disintegration of circadian cycles under these conditions. Average sleep time tended to decrease toward the end of the patrol.

Carboxyhemoglobin levels during a submarine patrol.

One of the major contaminants from tobacco smoking aboard a nuclear submarine is carbon monoxide (CO). While this gas is controlled to 15 parts per million or lower by catalytic burners, there still remains a residual low level in the atmosphere. This study has shown that, on one submarine, the average ambient concentration was 7 ppm, which produced an average carboxyhemoglobin level in 15 nonsmokers of 2.1%, 1.7%, and 1.7% at the start, middle, and end of a 40-d patrol. Because submariners are generally healthy and young, it is concluded that CO exposures at these ambient levels do not constitute a major risk factor to the physiological well-being of these submariners, nor are they expected to cause any decrement in performance.

Regulation of intracellular pH in lungs and other tissues during hypercapnia.

Using a 14C-labeled DMO, 36Cl and 3H method, we have determined the in vivo buffering capacity of lung, kidney, heart, skeletal muscle, and extracellular fluid (ECF) of guinea pigs during hypercapnia (FICO2 = 0.15). After 1 days' exposureto 15% CO2, both the relative CO2 buffer values (delta HCO3/deltapH) and the "%pH regulation" were lung greater than kidney greater than heart greater than ECF greater than skeletal muscle. For lung tissue the intracellular pH was significantly decreased only during acute (8 h) hypercapnia and had completely returned to control values after 7 days with arterial PCO2 congruent to 122 Torr. Kidney and cardiac muscle also showed ca. 100% regulation of pH at 7 days, whereas skeletal muscle and ECF showed only 80 and 70% pH regulation, respectively. The results are discussed with respect to the important (and pH-dependent) metabolic functions of the lung and kidney.

Human tecg changes during prolonged hyperbaric exposures breathing N2-O2 mixtures.

In an effort to determine whether hyperbaric exposures while breathing N2-O2 mixtures have an effect on cardiac depolarization and repolarization, electrocardiograms of 10 divers participating in four N2-O2 saturation dives were analyzed. In all cases, a decline in heart rate was observed upon compression to saturation depth (20-30%); a slow adaptation and return of heart rate toward normal was observed in those dives where the depth and environmental parameters remained constant. twhenever excursion dives were performed, the heart rate responded by decreasing on deeper excursions and increasing on upward excursions. Hyperbaric bradycardia disappeared after 8 days at pressure during the saturation dives at 50 and 60 feet seawater gauge (fswg), but was still present at this time at 200 fswg. The magnitude of the hyperbaric bradycardia produced by excursion dives following saturation at depth was influenced by the state of adaptation of heart rate. Decompression was uniformly accompanied by a rapid increase in heart rate resulting in a significant elevation in the postdive period. Alterations in myocardial repolarization as evidenced by Q-T interval, ST, and T wave changes were observed. Development of slight right ventricular conduction delay compatible with right ventricular strain was noted in four of the divers during the two deepest dives to 100 and 198 fswg. During the latter dive, progressive decrease in P wave amplitudes and eventual loss of P waves resulting in an apparent nodal rhythm was observed in one diver. Multiple premature ventricular contractions occurred in another diver. These observations, along with the reports by other authors, suggest that the different variables associated with the hyperbaric environment--gas density, pressure, inert gas--have a definite effect on the pacemaker activity of the heart and myocardial depolarization and repolarization.

Threshold temperatures for shivering in acute and chronic hypercapnia.

Threshold temperatures for shivering in acute and chronic hypercapnia were determined in guinea pigs by measuring the time course of cervical cord temperature, skin temperature, oxygen consumption (Vo2), and electrical muscle activity during cold exposure (15 degrees C). Prior to acute exposure to CO2, the shivering threshold was determined in each animal during control conditions breathing air. With increasing CO2 concentrations (5,7.5, and 15% CO2) the shivering thresholds fell to lower temperatures, decreasing by approximately 40 degrees C at 15% CO2. The shift of the shivering threshold to lower values found during acute exposure to 15% CO2 was reversed after chronic exposure to 15% CO2 for 3 days, which marks the time of metabolic adaptation to CO2.

Effect of chronic hypercapnia on body temperature regulation.

Guinea pigs and rats exposed to 15% CO2 for 7 days showed a parallel time course of changes in pH, body temperature (TB), and oxygen consumption (VO2). Between 1 and 6 h of exposure the maximal drop in actual pH occurred in guinea pigs simultaneously with the maximal fall in TB and VO2. During the subsequent period pH TB, VO2 rose again. Skin blood content (heat loss) also exhibited a biphasic pH-dependent time course. Animals showing no partial compensation of respiratory acidosis during 3 days exposure also failed in raising their TB back to normal in this time. The behavior of TB was found to be a good indicator of the acid-base status and adaptive potential of the animals to hypercapnia. Similar results were obtained in rats. Thermo-regulatory processes in the hypothalamus were affected during exposure to 15% CO2. Both guinea pigs and rats showed a decrease in norepinephrine content of the hypothalamus during the first part of exposure reaching a maximal fall at the end of 24 h. The serotonin content increased slightly during this period. During prolonged exposure to 3% CO2 for 7 days, TB showed a transient rise, and VO2 was slightly elevated.