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

Chest. 2020 Oct;158(4):1644-1650. doi: 10.1016/j.chest.2020.04.017. Epub 2020 Apr 25.


Background: 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.

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 (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.

Results: 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 = 1.70 mm Hg) were observed. At hypoxic rest and exercise, strong relationships between the estimated and directly measured Pao2 (R2 = 0.68; P < .001; mean bias = 1.01 mm Hg) and O2 deficit with the traditional A-aDo2 (R2 = 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.

Keywords: exercise; hypoxia; noninvasive; pulmonary gas exchange; validation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Validation Study

MeSH terms

  • Adult
  • Exercise / physiology*
  • Female
  • Humans
  • Hypoxia / physiopathology*
  • Male
  • Pulmonary Gas Exchange / physiology*
  • Respiratory Function Tests / methods*
  • Young Adult