Analysis of physiological responses to +Gx loads during space flights (SFs) 8-12 days in duration was carried out in ten non-professional crew members of the International Space Station (ISS), many of whom were accepted to participate in SFs while having partial health deficiency. The results were compared to the data on ten apparently healthy crew members of the Mir Orbital Station (OS) who participated in SFs of a similar duration. The age (29-60 years) of the subjects from the ISS crew was older than the age (31-49 years) of the subjects from the Mir OS crew. Objective data showed that subjects from the ISS crew had significantly higher levels of sinus tachycardia and tachypnea during settling into orbit and re-entry than subjects from the Mir OS crew. In some cases, extrasystolic arrhythmias were recorded in subjects from the ISS crew during the pre-launch period. The arrhythmias persisted during the ascent to orbit, and usually became more considerable during the descent to Earth. During the descent to Earth, the subjects from the ISS crew demonstrated, in general, a higher rate of heart rhythm disorders, which were characterized by more pronounced polymorphism and a greater severity. Particularly significant changes in electrocardiograms (ECGs) were observed in two subjects from the ISS crew aged 60 years. These disorders were sporadic in all the cosmonauts. The results of the study show that individual characteristics of cardiac rhythm regulation observed before the start may lead to marked changes in ECG during +Gx loads during the descent from the orbit to Earth. This should be taken into account in preparing individual medical programs for non-professional members of ISS crews in order to minimize health risks. The study has also demonstrated the necessity for stricter criteria of selection for ISS missions for older candidates with partial health deficiency. © 2011 Pleiades Publishing, Ltd.
