Review of roentgenographic bone demineralization studies of the Gemini space flights

Abstract

Several factors may have been conducive to misinterpretation of bone mineral changes in some of the Gemini astronauts which were reported previously by this laboratory. Evaluations of roentgenograms of a standard bone phantom made at the same times and on the same Xray units indicate that the reported mass losses among the Gemini 4 and 5 astronauts were 7% too high. This error is attributed to a 4% inherent absorption difference between the 2 calibration wedges used prior to launch and after recovery, and 3% of the error is attributable to variations in Xray beam qualities among the 3 Xray units used in the experiment. The corrected density losses during the Gemini 4 flight are 2.9 and 3.8% for the command pilot and pilot, respectively, instead of the 7.8 and 10.3% values originally reported. Similarly, the corrected density losses during Gemini 5 were 9.2 and 2.5% instead of the originally reported losses of 15.1 and 8.9% for the command pilot and pilot, respectively. Computed calcium losses necessary to yield the wedge equivalency changes originally reported in Gemini 4 and Gemini 5 would have had to be considerably greater than 600 mg/day, while in the Gemini 7 flight in which Xray exposure conditions were more accurately controlled, a mean daily loss of skeletal calcium of 65 mg. would be required which is explainable under current knowledge of calcium mobility. The modified data indicate that the observed changes in bone density pre and post flight were close to the overall experimental error that it is questionable whether any changes occurred at all. However, skeletal calcium losses which would concur with Xray density changes of the observed magnitudes (63 to 350 mg. of calcium per day) would not be physiologically impossible.