Changes in pulmonary gas exchange during resistive loading that do not cause a sense of shortness of breath

It is known that hypoxic hypometabolism occurs as a result of reduced delivery of oxygen to tissues. We have shown earlier that this response may be observed during latent hypoxia, when blood oxygen saturation ( Sp O 2 ) is reduced to 95%. There is a hypothesis that the body can prevent a disturbance of the balance between oxygen delivery and consumption by developing a protective response to reduce oxygen demand. To test the hypothesis, a study was carried out under normal oxygenation conditions, in which a weak additional resistance of 0.4 cm H 2 O L −1 s was used as a trigger. The study sample comprised 14 healthy subjects of both sexes. Gas exchange parameters under normal and combined resistive loading conditions were studied. It was found that the respiratory rate was reduced by 8%, and the tidal volume was increased by 12%. At the same time, oxygen consumption and carbon dioxide production were significantly decreased by 9 and 10%, respectively. These findings suggest that a decrease in the rates of oxygen consumption and carbon dioxide production is a nonspecific protective response to prevent the disturbance of the balance between oxygen delivery and consumption.