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[i]Apollo 15 will remain an anomaly in the Apollo Program. Preflight and inflight activities went well. The lunar surface operations were characterized by heavy work schedules and some sleep difficulties. The crewmen worked to a point of near exhaustion on some occasions, and the Commander pulled a shoulder muscle while operating the lunar surface drill. The pain from the muscle injury interfered with his sleep on the lunar surface and during the return flight to Earth, and persisted for several weeks. At the conclusion of Apollo 15's lunar surface activities, a very tired crew departed the moon to rendezvous with the Command Module.
The schedule of the labors after the link-up was also heavy, and the Command Module Pilot had to rely on his already fatigued companions to transfer equipment from the Lunar Module to the Command Module, a task he himself had been slated to perform. Once transfer operations were complete, difficulty was experienced in sealing the hatch between the two vehicles. This problem necessitated two additional lunar orbits and additional labors before the tunnel connecting the vehicles was successfully sealed and the LM could be jettisoned.
After Lunar Module jettison, the crew was engaged in a space suit integrity check when a bigeminal rhythm appeared on the console monitoring Astronaut Irwin's electrocardiogram. Paper copies of the trace were called for to establish that the irregularity was not artifactual. The bigeminal arrhythmia lasted for 10 to 20 beats, and was followed by a series of premature ventricular and atrial beats, interspersed with normal ones. One other crewman had exhibited some arrhythmias, but they were far less serious than those with which Astronaut Irwin was afflicted. The crew had transmitted no messages indicating a problem. [b]In fact, Astronaut Irwin reported later that he had experienced a feeling of a brief loss of contact as though he had momentarily gone to sleep. In retrospect, this episode could have been a momentary loss of consciousness at the precise time the arrhythmia was noted.[/b] After the arrhythmias were noted, continuous electrocardiographic recordings were obtained for all three crewmen while they slept.
It took the Apollo 15 crew three to four weeks after the flight to return to preflight normal levels of exercise and cardiovascular orthostatic tolerance. This was the longest recovery period seen in our space program and was uncomfortably reminiscent of the findings of the eighteen-day Soviet Soyuz 9 mission. This Soviet mission had been marked by a prolonged recovery wherein cardiovascular, vestibular, and musculoskeletal difficulties were experienced by the crewmen. While it would have been, ideally, preferable to shield the two astronauts from public attention, it  was judged in the best interest of the space program to provide information about their conditions.
There is a reasonable basis for suspecting that the Apollo 15 crew was launched with a potassium deficit. They had engaged in very rigorous training for lunar surface tasks prior to this space mission in intense summer heat. The crew drank considerable amounts of an electrolyte solution during this training, which tended to leach potassium from the system. These factors, coupled with inflight diets that were not particularly high in potassium, are believed to have contributed to negative potassium balances.
Apollo 16 and 17 crewmen were free of any cardiac difficulties during their missions. This may have been in part due to the institution of a program involving dietary potassium supplements and revised work/rest schedules to preclude a negative potassium balance. Such a negative balance can contribute to cardiac irritability and can predispose to arrhythmias. The crews of both missions were also free of any clinical illness during flight. Again, the meticulously conducted Flight Crew Health Stabilization Program seemed to be effective. All crewmen took sleeping medications to ensure sufficient rest to complete busy lunar surface schedules. Both the Apollo 16 and 17 missions were unqualified successes from an operational and a medical standpoint.[/i]
[i]One of the Apollo 15 crewmen experienced a single run of bigeminal cardiac rhythm (22 coupled beats) as he lay in his couch observing Lunar Module tunnel leak rates. This was the fir-t significant arrhythmia observed during any American space flight. Another Apollo 15 crewman exhibited a few supraventricular premature contractions resulting in coupled beats but not a sustained bigeminal rhythm. It was at first conjectured that a dietary deficiency of potassium might have been a contributory factor. Subsequent careful analysis of the dietary intake and mission simulation studies with potassium restriction failed to substantiate this hypothesis. The etiology remains obscure. Fatigue following strenuous lunar surface activity most certainly was a factor. Other contributory factors are speculative and are likely to remain so. It should be noted that the crewman with the sustained bigeminal episode subsequently sustained a myocardial infarction in April 1973, some 21 months after his flight of July 1971. Thus, coronary atherosclerosis was very likely a factor in this case.[/i]
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