VO2 max, the maximum volume of oxygen consumed by the body during exercise, is a measure of an individual's cardiovascular function. It indicates one's maximal capacity to do aerobic work, and is commonly measured in units of milliliter per kilogram of body weight per minute. Dividing the oxygen volume by body weight accounts for differences in body size. LSAH comparisons show values similar to those observed for the general population, whereas the astronauts have almost 20% higher VO2 max value than the corresponding comparison groups. These higher VO2 max levels may be a reflection of the higher fitness level of astronauts as compared to the comparison participants. However, both groups show about the same rate of decline in VO2 max with aging.
Pulmonary function was assessed through two measurements, FEV1 and FVC. FEV1. stands for forced expiratory volume 1, the volume of air that is forcefully exhaled in one second, in liters (L). FVC, or forced vital capacity, is the volume of air that can be maximally forcefully exhaled, in liters, so that FEV1 is actually a subset of FVC. Values of 3.0 L and 4.0 L are considered average FEV1 and FVC levels in the general population.
For FEV1, male astronauts younger than 35 years of age show a higher level than the corresponding comparison group. This advantage was virtually gone by the next age group, as both male astronauts and comparisons show almost identical FEV1 values for ages 35-64 years. Only in the oldest age group did male astronauts have higher FEV1 levels than the comparisons again. Female astronauts younger than 35 years of age have a lower mean FEV1 value than the female comparisons. However, their FEV1 values decline less steeply with age as compared to those of the comparisons, so that female astronauts of the 40-59 years age group show a slightly higher value of FEV as compared to female comparisons in the same age group.
Similar aging trends are also observed for the astronauts and comparisons for their FVC values, though the decline rates for all male participants are less steep as compared to their decline of FEV1 values with age. Male astronauts show higher FVC volumes than male comparisons in the younger age groups, but this advantage evens out in the ages between 40 and 60 years, before reappearing in the oldest age groups.
Female comparisons show a decline in FVC volumes as they age. However, the FVC values for female astronauts hold steady across the age groups instead of showing the expected aging trend, which may be a function of the small sample size or retention of better physical fitness of this participant group.
In general, higher values of cardiopulmonary function obtained for the astronauts are expected. The somewhat unusual trends shown by female astronauts may result from the small sample size of the group. These current observations suggest that cardiopulmonary function in both groups is affected by age in the same ways; further observations will continue, and will be shared with study participants.
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