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

Background: Pulmonary gas exchange efficiency, determined by the alveolar-to-arterial Po difference (A-aDo), 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.

Research Question: Is a noninvasive method of assessing pulmonary gas exchange valid during rest and exercise in acute hypoxia?

Study Design And Methods: Twenty-five healthy participants (10 female) completed a staged maximal exercise test on a cycle ergometer in a hypoxic chamber (Fio = 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 O deficit, was calculated from the difference between the end-tidal and the calculated Pao (via pulse oximetry and corrected for the Bohr effect by using the end-tidal Pco). Noninvasive O deficit was compared with the traditional alveolar to arterial oxygen difference (A-aDo), using the traditional Riley analysis.

Results: Under conditions of rest at room air, hypoxic rest, and hypoxic exercise, strong correlations between the calculated gPao and directly measured Pao (R = 0.97; P < .001; mean bias = 1.70 mm Hg) were observed. At hypoxic rest and exercise, strong relationships between the estimated and directly measured Pao (R = 0.68; P < .001; mean bias = 1.01 mm Hg) and O deficit with the traditional A-aDo (R = 0.70; P < .001; mean bias = 5.24 mm Hg) remained.

Interpretations: 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.