Pulmonary hemodynamics responses to hypoxia and/or CO2 inhalation during moderate exercise in humans

  • Stéphane Doutreleau
  • Irina Enache
  • Cristina Pistea
  • Bernard Geny
  • Anne CharlouxEmail author
Integrative Physiology
Part of the following topical collections:
  1. Integrative Physiology


In this study, we hypothesized that adding CO2 to an inhaled hypoxic gas mixture will limit the rise of pulmonary artery pressure (PAP) induced by a moderate exercise. Eight 20-year-old males performed four constant-load exercise tests on cycle at 40% of maximal oxygen consumption in four conditions: ambient air, normobaric hypoxia (12.5% O2), inhaled CO2 (4.5% CO2), and combination of hypoxia and inhaled CO2. Doppler echocardiography was used to measure systolic (s)PAP, cardiac output (CO). Total pulmonary resistance (TPR) was calculated. Arterialized blood pH was 7.40 at exercise in ambient and hypoxia conditions, whereas CO2 inhalation and combined conditions showed acidosis. sPAP increases from rest in ambient air to exercise ranged as follows: ambient + 110%, CO2 inhalation + 135%, combined + 184%, hypoxia + 217% (p < 0.001). CO was higher when inhaling O2-poor gas mixtures with or without CO2 (~ 17 L min−1) than in the other conditions (~ 14 L min−1, p < 0.001). Exercise induced a significant decrease in TPR in the four conditions (p < 0.05) but less marked in hypoxia (− 19% of the resting value in ambient air) than in ambient (− 33%) and in both CO2 inhalation and combined condition (− 29%). We conclude that (1) acute CO2 inhalation did not significantly modify pulmonary hemodynamics during moderate exercise. (2) CO2 adjunction to hypoxic gas mixture did not modify CO, despite a higher CaO2 in combined condition than in hypoxia. (3) TPR was lower in combined than in hypoxia condition, limiting sPAP increase in combined condition.


Exercise Hypoxia CO2 inhalation Pulmonary artery pressure Human Cardiac output 


CaO2 (or CO2)

Arterial oxygen (or carbon dioxide) content


Cardiac output


Tricuspid valve maximal gradient


Fraction of inspired oxygen or carbon dioxide


Hypoxic pulmonary vasoconstriction


Nitric oxide


Alveolar pressure in oxygen


Arterial pressure in oxygen


Mixed venous blood pressure in oxygen


Pulmonary artery pressure






End-tidal partial pressure in carbon dioxide


Pulmonary vascular resistance


Respiratory exchange ratio


Right atrial pressure


Right ventricle


Total pulmonary resistance


Tricuspid regurgitation velocity


Carbon dioxide output


Minute ventilation


Oxygen consumption


Maximal oxygen consumption



An ADIRAL (Association d’Aide aux Traitements à Domicile) research grant (2012 N1) supported the purchase of the AltiTrainer, SMTEC, Nyon, Switzerland.

Compliance with ethical standards

The study was approved by the Ethical Committee (Comité de Protection des Personnes “EST IV”, HUS No. 5546, NCT 01898858) of the University Hospitals of Strasbourg and conformed to the standards set by the Declaration of Helsinki.

Conflict of interest

The authors declare that they have no conflict of interest.


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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Service de Physiologie et d’Explorations Fonctionnelles, Pôle de Pathologie Thoracique, Hôpitaux Universitaires de Strasbourg, Equipe d’Accueil 3072, Fédération de Médecine Translationnelle de StrasbourgUniversité de StrasbourgStrasbourgFrance
  2. 2.Service de Physiologie et d’Explorations Fonctionnelles, Nouvel Hôpital CivilHôpitaux Universitaires de StrasbourgStrasbourg CedexFrance

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