Validation of a Noninvasive Assessment of Pulmonary Gas Exchange During Exercise in Hypoxia

Abstract

Pulmonary gas exchange efficiency, determined by the alveolar-to-arterial Po2 difference (A-aDo2), progressively worsens during exercise at sea-level; this response is further elevated during exercise in hypoxia. Traditionally, pulmonary gas exchange efficiency is assessed through measurements of ventilation and end-tidal gases paired with direct arterial blood gas (ABG) sampling. Because these measures have a number of caveats, particularly invasive blood sampling, the development of new approaches for the noninvasive assessment of pulmonary gas exchange is needed. Is a noninvasive method of assessing pulmonary gas exchange valid during rest and exercise in acute hypoxia? Twenty-five healthy participants (10 female) completed a staged maximal exercise test on a cycle ergometer in a hypoxic chamber (Fio2= 0.11). Simultaneous ABGs via a radial arterial catheter and noninvasive gas-exchange measurements (AGM100) were obtained in 2-minute intervals. Noninvasive gas exchange, termed the O2 deficit, was calculated from the difference between the end-tidal and the calculated Pao2 (via pulse oximetry and corrected for the Bohr effect by using the end-tidal Pco2). Noninvasive O2 deficit was compared with the traditional alveolar to arterial oxygen difference (A-aDo2), using the traditional Riley analysis. Under conditions of rest at room air, hypoxic rest, and hypoxic exercise, strong correlations between the calculated gPao2 and directly measured Pao2 (R2= 0.97; P< .001; mean bias= 1.70mmHg) were observed. At hypoxic rest and exercise, strong relationships between the estimated and directly measured Pao2 (R2= 0.68; P< .001; mean bias= 1.01mmHg) and O2 deficit with the traditional A-aDo2 (R2= 0.70; P< .001; mean bias= 5.24mmHg) remained. Our findings support the use of a noninvasive measure of gas exchange during acute hypoxic exercise in heathy humans. Further studies are required to determine whether this approach can be used clinically as a tool during normoxic exercise in patients with preexisting impairments in gas exchange efficiency.