CHAPTER 32

                     Anthropometric Changes and Fluid Shifts

     WILLIAM E. THORNTON, G. WYCKLIFFE HOFFLER, AND JOHN A. RUMMEL

MAN’S BODY, both as a species and as an individual, has been shaped by continuous exposure to gravity and a large portion of it is dedicated to more or less continuously opposing gravitational forces. One could confidently predict that placing the human body in weightlessness would produce changes in size, shape, and composition. Many of these changes and their effects were described by astronauts from the earliest days of space flight, for example: puffy faces, stuffy noses, engorged head veins, low back discomfort, and the "bird legs" of space.

The anthropometric studies in American space programs prior to Skylab were:

Preflight and postflight leg volume measurements on the later Apollo flights.

Stereophotogrammetry of the crew preflight and postflight on Apollo 16.

On Skylab only leg volume measurements, and stereophotogrammetry preflight and postflight, and maximum calf girths in-flight were originally scheduled.

In an effort to obtain the most comprehensive and coherent picture of changes under weightlessness, we initiated a set of measurements on Skylab 2 and at every opportunity, added additional studies. All pertinent information from ancillary sources, even news photographs were gleaned and collated.

On Skylab 2, the initial anthropometric studies were scheduled in conjunction with the muscle study described in chapter 31. A single set of facial photographs was made in-flight. Additional measurements were made on Skylab 3, with photographs and truncal and limb girth measurements in-flight.

Prior to Skylab 4, a few of us felt there was considerable evidence for large and rapid fluid shifts, so a series of in-flight volume and center of mass measurements and infrared photographs were scheduled to be conducted as early as possible in the Skylab 4 mission.

A number of changes were properly documented for the first time, most important of which were the fluid shifts. The following description of Skylab anthropometrics will address work done on Skylab 4 primarily.

Procedure

The series of direct anthropometric measurements shown in figure 32-1 were made preflight and postflight on all missions, and in-flight on the Skylab 4 mission. Leg and arm girth measurements were made every 3 centimeters by means of a calibrated tape jig attached to the limb to insure accurate location. As part of their experimental protocol, Drs. G.W. Hoffler and R.L. Johnson made such leg measurements preflight and postflight on Apollo and Skylab and, to avoid repetition, data from these measurements were shared on Skylab. We extended their technique of measurement to include the arms on all Skylab missions preflight and postflight. The in-flight limb measurements on Skylab 4 were made with an unattached single tape and a calibrated longitudinal tape.

For general documentation, a series of pre-flight, in-flight, and postflight front, side, and back photographs were made with the crewmen in standard anatomical position. To note postural changes, an in-flight series of photographs were made with the crewman completely relaxed and free floating. An infrared sensitive color film was used in an attempt to document the superficial venous blood distribution.

The infrared film had poor resolution and at the last minute, 35 mm was substituted for 70 mm film further reducing resolution. Quality of the in-flight anatomical and postural photographs suffered. However, a good deal of vascular detail could be determined that would not have been available on ordinary film.

As a simple way to indicate fluid shifts, center of mass and center of gravity (CG) measurements were made (fig. 32-2). A teeter board was used for these measurements on Earth.

In-flight it was possible to obtain center of mass directly by tying a cord around the subject and then pulling the cord at right angles to the subject. If the cord was anywhere off the center of mass the subject would tilt. The crew claimed this scheme was accurate to a few millimeters.

Observations and Data

Figure 32-3 shows typical changes of the preflight and in-flight front view and the preflight, in-flight, and postflight side view; these tracings of the Skylab 4 Scientist Pilot are typical of the changes seen. Relaxed postural changes varied somewhat throughout the flight and from individual to individual. The posture in figure 32-3 is the characteristic posture of weightlessness.

The spinal column was flexed with loss of the thoracolumbar curve but with retention of the cervical curvature, such that the head is thrust forward. Both upper and lower limbs have moved toward a quadruped position. Postflight, there was surprisingly little change from preflight posture.

Figure 32-4 are plots showing the effects of gravitational unloading on truncal size. The Pilot of Skylab 4 had the largest changes with gain of some 2 inches in height and loss of 4 inches in abdominal girth. Chest girth was also initially reduced in both inspiration and expiration, but trended toward "normal" in-flight. Postflight, which is poorly shown in these figures, there was a more or less rapid trend toward preflight values. It seems that most of the increase in height was caused by expansion of the intervertebral discs which were unloaded. This stretched the torso and probably aided in reduction of abdominal girth. Abdominal viscera may be considered semiliquid, and when their weight was removed the normal tone of abdominal muscles moved them in and upward. Changes in chest girth are not so easily explained, but if the spinal column moved upward without a similar anterior elevation of the sternum, then the rib (costovertebral) angles is increased, effectively reducing thoracic girth. Changes noted in the Commander were virtually the same as those noted in the Scientist Pilot.

There was considerable evidence of large and rapid shifts in fluid from the lower to upper body prior to Skylab 4. Indeed, no subject has been discussed more in space physiology; nevertheless, virtually no one was willing to accept it. Such large and rapid shifts seemed to be contradicted by the relatively small gains in postflight leg volume which obviously contained tissue increases. Single in-flight midcalf girth measurements on Skylab 2 and 3 were also misleading for they indicated much smaller and slower changes consistent with a predominant component of muscle atrophy.

To prove the point, collection had to be scheduled during activation, the busiest portion, of an already overscheduled mission. The changes recorded in these data became a tribute to the flight crews and management team and again illustrated the outstanding characteristic of manned space flight, the flexibility to optimize returns from an experiment or a mission. Leg and arm volumes were calculated by measuring the girth of each 3-centimeter segment and treating all the segments as a tapered cylinder, then summing these volumes.

Mission day 3 was the earliest possible that these measurements could be scheduled, although it is a measurement which should have started within hours of orbital insertion; even then, only two crewmen performed these measurements on mission day 3. Figure 32-5 shows that there is a rapid loss in leg volume; the curves on these plots are only estimates, and I suspect the shift was essentially over by the first day. Remember these are changes in one leg only and on mission day 8 total change was approximately 2 liters and 13 percent of total leg volume for each crewman.

Note that on recovery the majority of the increase in leg volume was complete by the time of first measurement on the day of recovery; or within a matter of hours after reexposure to one-g.

I agree with Dr. Michael Whittle (ch. 22) that the slower postflight trends show tissue replacement. Surprisingly, the arms showed no evidence of fluid shift and the changes seen were small and probably related to metabolism.

Where did this fluid go? There was no weight loss in two of the three crewmen compatible with loss of this amount of fluid.

Center of mass measurements were scheduled on this flight primarily to follow the time course of fluid shifts, since only minutes were required for the measurement. Unfortunately, schedules were changed such that the points of real interest were over before the first measurement could be made. Figure 32-6 is a plot of the center of mass, the upper curve shows the center of mass changes and the complication by the increase in height, shown in the lower curve. Center of mass shifted cephalad more than could be accounted for by the height increase which is another small confirmation of fluid shift.

The astronauts have long reported objective and subjective descriptions of puffy facies, head fullness, and other symptoms of increased fluid in the head.

Finally, there are the photographs. While these do not allow quantitation, they provided powerful evidence for increased fluid in the head and neck region.

Figure 32-7, a photograph of the Pilot on Skylab 2, was the first taken for this purpose. Although it is slightly distorted it still demonstrates the puffy facies—note the thickened eyelids. This in-flight photograph was made near the end of the mission and demonstrates that this type of edema and venous congestion still remained.

Next, figure 32-8 is a picture of the Commander of Skylab 3 with the preflight view on the right-hand side; again the in-flight photograph was made near the end of the mission. Although angle and lighting differ, I believe the difference in facies is apparent.

Finally, we have the assessment of the infrared photographs. Original plans were to machine analyze the superficial venous pattern, but the quality was too variable, therefore, only a qualitative assessment was made. However, several features were obvious. From the first through the last mission the following was observed in all in-flight photographs of the crewmen:

          Only superficial veins were visualized.

     Foot and lower leg veins were not distended as they are in standing position under one-g.

The veins were not completely empty for the dorsal arcade of the foot and digital branches were easily seen with the infrared film.

Calf veins were not distended but were still visible.

          Several superior branches in the anterior thigh were moderately full.

Little difference could be seen between preflight and in-flight patterns of the trunk and upper arms. Hand and forearm veins were well filled and distended in-flight. This was surprising since superficial arm veins, like those of the leg have increasing amounts of wall muscle as they become more distal.

Jugular veins were always completely full and distended as were veins of temple and forehead.

Postflight, there was a prompt reversion to preflight pattern, however, foot and lower leg filling appeared to be less in the early recovery period.

Changes in mass have already been discussed and are obviously related to the changes seen here.

It was not possible to document body composition changes with specific gravity and other measurements. Observation of all crews, and especially those on Skylab 2 and 3, left the impression that loss of fat had occurred, except for the Commander of Skylab 4. Radioisotopic studies by Drs. P.C. Johnson and C.S. Leach confirmed an increased loss of fat by all crewmen except the Commander of Skylab 4.

Discussion

What is the importance of the changes observed under weightlessness? The major changes are shown in table 32-I.

Change in height is as much a conversation piece as anything else. One crewman, for example, is shorter than his wife and was elated to find in-flight that he was finally taller. Postflight there was an undershoot, and he came home to her on the third day postflight shorter than ever. Such changes provide new data points for those studying the human skeleton and, hopefully, will add to the knowledge of it.

In future flight, allowances may have to be made in custom fitted gear. For example, small height increases greatly increase the difficulty of donning pressure suits; these difficulties are reported in the Task and Work Performance studies in chapter 16.

Reduction in waist girth with cephalad shift of abdominal viscera probably alters maximum lung volumes but to no great extent. Vital capacity is reduced by lying down in one-g and the effects are somewhat analagous. Apparently it did alter some internal relationships for at least one crewman felt that running and jumping on the treadmill produced unpleasant jouncing of gastric contents. One could speculate on the effects that such shifts would have on pathological processes of the bowel e.g., hiatus hernia or a perforation. It is hardly necessary to comment on the changes in chest girth which were small.

In-flight postural changes are listed in table 32-II. These postural changes have two significant considerations. Human engineering should allow for the most efficient work positions in the future. For example, a chair designed for use in one-g to support the weight of legs and torso, is not shaped to provide good passive support in weightlessness. The body has to be forced into such a position by use of a tight waist restraint. Secondly, these changes under weightlessness should be of interest to those making theoretical studies of postural mechanisms and the like and provide them with new data points.

Fluid shifts are of more importance. Although tissue fluid and blood shifts are so closely interrelated as to be difficult to separate, I feel something is gained by treating them separately. Blood shifts occur rapidly; they begin seconds after change in forces but their long-term effects may last months.

Standing upright under one-g, veins and arteries below the heart have increasing hydrostatic pressure as the veins descend toward the feet where the force may be 80 to 100 mm Hg. Shortly above the heart, the venous pressure becomes zero and the vessels are virtually empty and at least partially collapsed. Under weightlessness, without this superimposed hydrostatic pressure, venous pressure, except for negligible flow pressures, are the same throughout the body. Volumes are now shifted only in response to the compliances, the tension if you will, of the various areas of the venous systems. The result is that we have essentially central venous or right atrial pressure throughout the entire venous system. Veins such as head and neck which are normally empty, fill until their back pressure is equal to that of the pressure in, for example, a foot vein, which develops the same pressure at a much smaller volume. When a subject changes from a standing to a lying position under one-g, a nominal 700 milliliters of blood leaves the legs and probably a comparable volume is shifted centrally. Most of this blood volume moves to that undefined "central volume" and produces a small increase in pressure with a probable effect of increasing cardiac output.

A second result of the fluid shift produced results that were easier to document. Certain body sensors detect this as an abnormally large volume and cause plasma to be reduced thus leaving high hemoglobin and hematocrits in the circulating blood (ch. 26). An as yet unknown sensor is activated to detect and reduce over a matter of weeks red blood cell production such that red cell mass becomes appropriate to the new volume. Such readjustment to altered volumes are also seen under one-g; for example, individuals with leg varicosities have increased blood volumes. I think that the reduced loss of red cell mass in the Skylab 4 Commander is further evidence of reduced leg venous volume. Table 32.-III illustrates this.

On return to one-g, a reverse process ensues. After the first day repeated blood tests show an anemia which is slowly replaced by an increasing red cell mass. These changes are delineated in table 32-IV.

Tissue fluid shifts are larger in volume than blood shifts but somewhat slower acting. When standing under one-g there is a hydrostatic column of up to 80 to 100 mm Hg pressure on arteries, veins, and capillaries in the foot. This pressure is opposed by tissue pressures and after a period of extravasation they equalize. Under weightlessness, the reverse occurs with resorbtion of fluid by the tissues until transmural pressures are again balanced. In the upper body areas and particularly the head, we have the opposite effect from increased transmural pressure which produces edema. These processes are simultaneous. Tissue fluid shifts are delineated in table 32-V.

Whether this shift of fluid produces an increase in intravascular volume or not depends upon how rapidly fluid is regained from some areas and lost to others. It is at least theoretically possible that fluid is lost more rapidly than it is gained, with a reduction of intravascular volume. I do not think this happens and expect there may be a very slight expansion of intravascular volume which, coupled with the blood from leg veins, may result in a small fluid loss via the Gauer-Henry scheme (increased atrial pressure and diuresis), or some other mechanism. However, remember that tissue fluid shifts occur under one-g without undue diuresis. Legs are smaller in the morning and eyes are puffy, and a shave lasts longer if made an hour or so after arising.

Fluid shifts should be investigated as a possible participant in the vestibular upsets (ch. 11) that have occurred. Time course and other aspects of these vestibular upsets are suggestive and I have no hard evidence for or against this.

Summary

In summary we have documented for the first time anthropometric changes and the correct magnitude and time course of fluid shifts under weightlessness that have implications for future human factors engineering and that explain some medical phenomena. More importantly these data provide a fundamental point of departure for future research.

Bedrest studies for example have not properly considered such fluid shifts. We now have better criteria for evaluating the fidelity of weightless analogs such as bedrest and water immersion.

Most importantly we again find the human body capable of making stable adaptation to two widely differing environments in an amazingly short time. In the course of these experiments, I think data has been offered to justify the title "Earth man—Space man."

Acknowledgments

Any listing of individuals here is bound to omit several who made contributions. Above all the Skylab 4 crew is to be commended for gathering the data with surprising accuracy under trying conditions which included virtually no training for the tasks. The work could not have been implemented without the support of Dick Johnston, Bill Schneider, Kenneth Kleinknecht, and others in Skylab management. Jack Ord greatly influenced the direction of this and my other experiments by our previous collaboration during the Manned Orbiting Laboratory project.

 

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