Biological variation of resting measures of ventilation and gas exchange in a large healthy cohort

Purpose: Resting measures of ventilation and gas exchange are impacted by a variety of physiological stressors, such as those resulting from a research intervention or an extreme environment. However, the biological variation of these parameters, an important statistical consideration for identifying a meaningful physiological change, has not been quantified.

Methods: We performed a retrospective analysis of 21 studies completed by the U.S. Army Research Institute of Environmental Medicine (USARIEM) from 1985 to present, totaling 411 healthy volunteers. First, we determined the intraindividual, interindividual, and analytic coefficients of variation (CV_I, CV_G, and CV_A, respectively) and subsequently the index of individuality and heterogeneity (II and IH, respectively). Second, when deemed appropriate via these outcomes, we defined the accompanying static and dynamic thresholds, beyond which a significant deviation from normal is indicated.

Results: End-tidal partial pressure of oxygen (P_ETO₂) and the respiratory exchange ratio (RER) approached the II threshold required to be considered useful in the static assessment of physiological deviations from normal. P_ETO₂ and peripheral oxygen saturation (SpO₂) approached the IH threshold required to be considered useful in the dynamic assessment of physiological deviations from normal.

Conclusions: This analysis identifies RER and P_ETO₂ as parameters that might be most useful when aiming to identify a meaningful ventilatory change following a research intervention or stressor. Alternatively, other parameters of ventilation and gas exchange, such as P_ETCO₂ and V_E, may be less useful for observing an anticipated physiological change.