What physiological changes accompany this adaptation and how long do they persist after the individual returns to sea level? To investigate these questions David E. Smucker of Wheaton, Ill., recently undertook for a high school science project to convert a 30-gallon steel drum into a chamber for simulating environments between sea level and 30,000 feet. At simulated altitudes of up to 15,000 feet automatic controls maintain the chamber at any desired air pressure, temperature, relative humidity and concentration of oxygen and carbon dioxide. At higher simulated altitudes the apparatus is controlled manually. A removable disk of clear plastic provides an opening at one end of the chamber for admitting experimental animals.

Although the chamber is suitable for the investigation of a broad range of questions related to the effects of high - altitude on small animals, Smucker s experiments were confined to the measurement of changes in the weight and blood of albino rats maintained for a few weeks at a simulated altitude of 10,000 feet. Smucker writes: "There appear to be two schools of thought about the effect of exposing an organism to high altitude. One group holds that organisms exposed to high altitude are strengthened by the experience. They argue, for example, that airplane pilots or astronauts who have become acclimatized to extreme altitudes have a better chance of survival if they later find themselves in thin air. The other group believes that exposure to high altitude is damaging, both physically and mentally. My experiment was not designed to assess an issue of this sophistication, but the results appear to support the latter opinion. I shall describe first the apparatus and then the experiment.

"The drum that serves as my chamber is made of 19-gauge galvanized steel [see illustration below]. One end was removed and fitted with anairtight sealing ring. A hole nine inches in diameter was cut in the other end and fitted with a 13-inch cover of clear plastic 1/4 inch thick. This window and its gasket are held in place by a circle of eight equally spaced bolts soldered to the end of the drum. Electrically insulated lead-ins are installed in the surrounding steel on the end of the drum for connecting various accessories. The outer surface of the chamber is insulated by a two-inch layer of fiber glass or rock wool held in place by forms made of plywood. The insulation helps to maintain uniform temperature in the chamber and to prevent condensation.

"Air pressure in the chamber is measured by a homemade barometer consisting of a U-shaped glass tube closed at one end and partly filled with mercury. The general controls include lights inside the chamber, switches, an automatic time switch and motors that operate the compressors. The compressors, controls and a reservoir that is part of the heating system are mounted on a separate base to isolate the chamber from vibration.

"The temperature of the chamber is controlled by circulating water of the appropriate temperature from a five-gallon reservoir through a radiator equipped with a small fan. For maintaining temperatures above that of the room a thermostat inside the chamber controls a 660-watt electrical heating unit in the reservoir. Both the radiator fan and the circulating pump can also be controlled manually. For cooling the chamber below room temperature the heating unit is replaced by a container of ice; the extent to which the temperature falls is controlled by switching the circulating pump on and off.

"The radiator was improvised from a refrigerator condenser by cutting the unit into two sections and fitting the openings with copper tubing that serves for hose connections. The fan was placed between the two sections, and the assembly was enclosed in an open-end jacket of sheet metal [see Figure 4]. The reservoir was made from a five-gallon drum of 24-gauge steel, the centrifugal pump from 1/16-inch sheet brass. The pump is driven by a motor removed from a record player.

"Air pressure in the chamber is reduced by a refrigerator compressor modified to operate as a vacuum pump [see "The Amateur Scientist," March, 1960]. For manual control the pump is switched on and off when necessary. A valve between the pump and the chamber controls the pumping rate

"At simulated altitudes of up to 15,000 feet the pressure can be controlled automatically by a sensitive pressure switch that operates the vacuum pump through a relay salvaged from an automatic record player. The pressure switch is a modified General Electric Type J-1 that employs a bellows for sensing pressure differences. Low pressure is applied to the inside of the bellows, high pressure to the outside. The switch closes when the pressure inside the bellows differs from that on the outside by an amount equivalent to a column of mercury eight millimeters high.

"The pressure inside the chamber at an altitude equivalent to that of the atmosphere at 10,000 feet differs from the pressure at sea level by approximately 23 centimeters of mercury. To adapt the switch to this higher pressure I added a helical compression spring that acts against one side of the bellows to oppose the pressure exerted by the atmosphere [see Figure 5]. The opposite end of the spring is seated against a screw for adjusting the pressure exerted by the spring against the bellows. By altering the setting of the screw the switch can be regulated to operate at any chamber pressure through the range from 400 to 760 millimeters of mercury, equivalent to altitudes ranging from sea level to 15,000 feet.

"The concentration of carbon dioxide in the chamber is controlled by circulating a portion of the air inside the chamber through sodium hydroxide. Similarly, the concentration of water vapor is controlled by circulating the same portion of air through calcium chloride. The filtering unit that contains these chemicals consists of a 24-inch length of l 1/2-inch, thin-walled electrical conduit plugged at the ends by rubber stoppers perforated for hose connections. Air entering the top of the filter passes through the chemicals and returns from the bottom to the environmental chamber.

"The inner wall of the tube is lined along its upper seven inches with plastic screening made by rolling a strip of screening seven inches wide and 20 inches long into a cylinder. This arrangement permits air not only to flow into the end of the column of sodium hydroxide but also to pass down the inner wall of the pipe and through the side of the chemical. When the screening is not used, water vapor causes a crust to form over the top of the chemical; within 14 hours the crust blocks the flow of air. A short plug of fiber glass at the bottom of the tube prevents chemical dust from entering the environmental chamber.

"A separate compressor is used for circulating air through the filter. The motor that powers this compressor is controlled by a timer salvaged from an old stoker. The timing unit can be set for operating the filter once or twice an hour for intervals of up to 15 minutes.

"Relative humidity can be increased any desired amount by bubbling a portion of the air through a flask of water. The plumbing connected to this flask is fitted with a bypass valve for regulating the flow of air and hence the relative humidity. A standby compressor-and-valve system allows any of the three compressors to be substituted quickly for either of the other two. In addition all three compressors can be operated in unison as vacuum pumps for lowering the pressure quickly. When they are thus connected, an altitude equivalent to 30,000 feet can be simulated in 2 1/2 minutes.

"Electric power is wired into the chamber through airtight, insulated fittings of two types. One consists of a conductor sealed into glass tubing that in turn is sealed inside copper tubing. The copper tubing is soldered into holes in the chamber. Fittings of the second type were made from 1/2- and 3/4-inch pipe couplings. These were machined at one end, fitted into holes in the end of the chamber and soldered in place. Holes that make a close fit with rubber-insulated wire were then drilled axially through a pair of pipe plugs that fit the couplings. One plug of each pair is screwed into the inner end of its coupling. The wire is then threaded through the other plug, placed through the coupling and threaded through the first plug. The space between the plugs is packed with modeling clay and the second plug is screwed in place. When tightened, the assembly makes a good seal.

"The experiment, which took 96 days, was made in order to learn the effect an exposure to an altitude of 10,000 feet would have on albino rats in the absence of all other variables. Throughout that period the chamber operated automatically with no mechanical difficulty for 850 hours and consumed 81 kilowatt-hours of power. During the first 32 days the rats were studied under normal conditions. Then they were exposed to high altitude for 32 days; finally they were kept under observation for an additional 32 days to study any aftereffects that might result from the exposure.

"Six rats from the same litter- Sprague-Dawley male albinos 28 days old-were selected for the experiment. The animals were fed a balanced diet and given tap water. They were weighed each day at 5:30 A.M. (This was the only time at which I would have access to the rats every day of the three-month period.) At the end of the first 32-day period the two rats of lowest weight were eliminated from the experiment.

"Two of the remaining animals were days, was made in order to learn the effect an exposure to an altitude of 10,000 feet would have on albino rats in the absence of all other variables. Throughout that period the chamber operated automatically with no mechanical difficulty for 850 hours and consumed 81 kilowatt-hours of power. During the first 32 days the rats were studied under normal conditions. Then they were exposed to high altitude for 32 days; finally they were kept under observation for an additional 32 days to study any aftereffects that might result from the exposure.

"Six rats from the same litter- Sprague-Dawley male albinos 28 days old-were selected for the experiment. The animals were fed a balanced diet and given tap water. They were weighed each day at 5:30 A.M. (This was the only time at which I would have access to the rats every day of the three-month period.) At the end of the first 32-day period the two rats of lowest weight were eliminated from the experiment.

"Two of the remaining animals were used as controls, the other two as experimental animals. In the first phase of exposure the heaviest rat was placed in the chamber and the next in weight was reserved as a control. The third-heaviest was also placed in the chamber and the lightest was reserved as a control. After 16 days of exposure the roles of the rats of intermediate weight, as recorded at the beginning of the exposure period, were reversed: the second-heaviest rat was placed in the chamber and the third-heaviest was removed from the chamber and used as a control. The heaviest animal was exposed to simulated high altitude for the full 32-day period and the lightest was never exposed.

"All rats were weighed daily and a count of the red blood cells was made every other day; cell counts were made on one pair of rats one day and on the other pair the next day. During the final post-exposure period I continued to weigh the rats daily, but I took the red-cell count only once a week. The experimental and control animals were kept in identical cages. The location of food and water was the same for all animals and the cages were cleaned daily.

"The temperature of the air for both experimental and control animals was maintained within 1 1/2 degrees of 73 degrees Fahrenheit; the relative humidity was kept below 20 percent. Carbon dioxide in the chamber was carefully maintained at the same concentration as that of the room air because this gas controls respiration and hence the functioning of the entire body. To replace the oxygen consumed by the animals fresh air was continuously added to the chamber by means of a needle valve. This controlled leak did not alter the simulated altitude because the automatic switch maintained the chamber at constant pressure. All cages received identical amounts of artificial light.

"The experimental animals were exposed for 23 hours daily and were returned to the normal pressure of Wheaton, III. (altitude 705 feet), during the remaining hour when the cages were cleaned and supplied with fresh food and water. The filtering chemicals were also renewed during this hour, the rats were weighed and the blood-cell counts were made. The controls were serviced identically during the following hour.

"When a red-cell count was made, the animal was wrapped in a bath towel with its tail protruding. The tail was placed in warm water for five minutes, after which the tip was nicked slightly. The animals ignored the nick and evidently experienced little, if any, pain. A small specimen of blood was then removed with a pipette and promptly diluted to one part in 200 with Ringer's solution: a mixture of S.6 grams of sodium chloride, .3 gram of potassium chloride and .33 gram of calcium chloride in one liter of purified water. After the blood was removed the tail was dipped momentarily in alcohol to disinfect it and then in cold water to arrest the bleeding. Warming the tail before taking the specimen may have increased the red-cell count but it should not have affected the relative results because the procedure was carried out routinely on both controls and experimental animals.

"The diluted blood was placed on a hemacytometer and the count was then made with the aid of a microscope. The number of cells per cubic millimeter was computed by taking into account the area on the hemacytometer occupied by red cells and the dilution of the blood. To ensure that the counts would be accurate I practiced the technique under the supervision of an experienced technician before I did the experiment. Incidentally, no cell counts were made during the 32-day interval prior to the exposure of the animals to high altitude because they were young and the loss of blood, however slight, might have influenced the results.

"In general, the experiment proceeded without incident, but one event is worth mentioning because it taught me the importance of maintaining sterile conditions. On the second day of the exposure interval I found mixed among the blood cells protozoa that could not be identified with any organism known to infect rats. After wasting a lot of time examining the animals I checked the Ringer's solution and found that it was swarming with the intruders! Somehow the solution had been contaminated. Data were taken and tabulated every day of the experiment except Christmas Day and three days of the post-exposure period when I was sick. These days are indicated by gaps in the graphs of the results [see illustration below].

"The four animals are identified in the graphs by the letters A, B, C and D. The dotted portion of a curve indicates the interval during which the animal was exposed to high altitude. The larger graph depicts changes in weight; the smaller graph, the results of the red-cell count. During the base, or pre-exposure, interval six animals were housed three to a cage: A, B and C in one cage and, in another, D plus the two lightest rats that were subsequently eliminated. During the 14th day of this period varnish remover was used for refinishing some woodwork in the room where the cages were kept. Evidently the fumes were toxic because all the animals lost weight. During the 19th day the water was removed from the cage of A, B and C to learn if these animals would react alike. All lost weight. During the 30th day A, B and C again lost weight for some reason I could not ascertain. Something may have contaminated the water.

"The first red-cell count was taken on the 31st day, just before A and B were exposed to high altitude. Both exposed rats lost weight during the next four days. They became inactive and ate and drank very little. After a week in the chamber they began to adapt to the thin air. Their appetite and vigor returned and they almost regained their normal rate of growth. Their red-cell count increased from less than nine million cells per cubic millimeter to more than 16 million cells in the first seven days. The red-cell count of the controls also increased as expected because red-cell concentration increases as rats age. C's count, however, appeared to increase at a rate somewhat above normal for its age.

"On the 50th day B and C were switched: B was returned to normal pressure and C was exposed to high altitude. The result is dramatically apparent on the graph. C's reaction to exposure paralleled that of A and B. After being returned to low altitude B gained weight rapidly and its red-cell count dropped to normal and then below normal. Later it rose to normal. After the 64th day A and C were returned to normal pressure. Their weight increased rapidly. A's red count paralleled that of B, except that it required more time to return to normal, whereas that of C increased instead of decreasing after the animal was returned to normal pressure. It then returned to normal and dipped below. The cell count taken on the 63rd day was just under 18 million cells per cubic millimeter. The experiment was terminated at the end of the 96th day, but the animals were kept for observation of any possible aftereffects of the experience. None has been evident.

"Only 65 percent of the oxygen at sea level is available to animals at an altitude of 10,000 feet. This condition appears to induce lethargy for a time and leads to loss of weight until the rats adjust to the thin air in about a week. This adjustment is accompanied by an impressive increase in the concentration of red cells that transport oxygen to the tissues. The subsequent growth of A and B, which were exposed to the chamber when they were much younger than C, has been more retarded than C's. This difference is most evident in A, the animal that was exposed longest. One unavoidable experimental condition-the daily interruption of one hour I when the animals were returned to normal pressure while measurements were made and the cages were serviced -may have influenced the results. The effect of this daily interruption is not known.

Bibliography

PHYSICS AND MEDICINE OF THE ATMOSPHERE AND SPACE. Edited by Otis O. Benson, Jr., and Hubertus Strughold. John Wiley & Sons, Inc., 1960.

THE SCIENTIFIC AMERICAN BOOK OF PROJECTS FOR THE AMATEUR SCIENTIST. C. L. Stong. Simon and Schuster, 1960.

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