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Hypoxia and CO alter O2 extraction but not peripheral diffusing capacity during maximal aerobic exercise

European Journal of Applied Physiology volume 114, pages 837–845 (2014)Cite this article

Abstract

Purpose

To determine if and how hypoxia combined with elevated carboxyhaemoglobin fraction (F HbCO) affects peripheral diffusing capacity and O2 extraction in animals exercising at their maximal aerobic capacity (\( \dot{V}{\text{O}}_{ 2\hbox{max} } \)).

Methods

Six goats ran on a treadmill at speeds eliciting \( \dot{V}{\text{O}}_{ 2\hbox{max} } \) while breathing inspired O2 fractions (F IO2) of 0.21 or 0.12 with F HbCO 0.02 or 0.30. We measured O2 consumption and arterial and mixed-venous blood variables to assess how hypoxia and elevated F HbCO individually, and in combination, alter O2 transport and utilisation.

Results

Peripheral diffusing capacity did not differ among the four gas combinations (P = 0.867), whereas O2 extraction fraction increased with hypoxia [0.920 ± 0.018 (SD)] and decreased with elevated F HbCO (0.792 ± 0.038) compared to control (0.897 ± 0.032). Oxygen extraction increases with hypoxia due to the sigmoid relationship between O2 saturation (SO2) and O2 partial pressures (PO2) affecting low (hypoxia) and high (normoxia) PO2 differently. Oxygen extraction decreases with elevated F HbCO because elevated F HbCO increases haemoglobin (Hb) affinity for O2 and raises SO2, especially at very low (mixed-venous) PO2. Pulmonary gas exchange was impaired only with combined hypoxia and elevated F HbCO due to hypoxia decreasing alveolar PO2 and O2 flux coupled with elevated F HbCO increasing Hb affinity for O2 and decreasing the rate of PO2 increase for a given rise in SO2.

Conclusion

This study quantifies the mechanisms by which O2 delivery and peripheral diffusion interact to limit \( \dot{V}{\text{O}}_{ 2\hbox{max} } \) when O2 delivery is reduced due to breathing hypoxic gas with elevated F HbCO.

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Abbreviations

AaDO2 :

Ideal alveolar–arterial O2 partial pressure difference

C aO2 :

Arterial O2 concentration

D ′T O2 :

Index of peripheral diffusing capacity (\( \dot{V}{\text{O}}_{ 2\hbox{max} } \)/mixed-venous PO2)

D TO2 :

Peripheral diffusing capacity (\( \dot{V}{\text{O}}_{ 2\hbox{max} } \)/mean-capillary PO2)

F HbCO :

Carboxyhemoglobin fraction

F IO2 :

Inspired O2 fraction

Hb:

Haemoglobin

Hbavail :

Hb available to bind O2 (not CO-bound nor methaemoglobin)

OEC:

O2 equilibrium curve

PO2 :

O2 partial pressure

SO2 :

O2 saturation

\( \dot{V}{\text{O}}_{ 2\hbox{max} } \) :

Maximal aerobic capacity

XX/YY:

Percentages of O2 (XX) in inspired gas and HbCO (YY) in blood

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Acknowledgments

We thank John Pascoe, Joan Rowe, Spenser Perloff, Pamela Etchegoyen, Joel Figueroa, Halley Olveria, Jason Eng, Elizabeth Thome and Jaclyn Gosliga for invaluable surgical and technical assistance throughout the studies. We thank Charles Stebbins and Edward Schelegle for comments on the manuscript. This work was sponsored by the U.S. Army Medical Research and Materiel Command under sub-contracts W81XWH-06-C-0051 and W81XWH-11-D-0011 with L-3 Communications/Jaycor. The opinions or assertions contained herein are private views of the authors, and are not to be construed as official or as reflecting views of the Department of the Army or the Department of Defense. Cleared for public release 20 May 2013.

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None.

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  1. School of Veterinary Medicine, Department of Surgical and Radiological Sciences, University of California, One Shields Avenue, Davis, CA, 95616, USA

    George H. Crocker & James H. Jones

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  1. George H. Crocker
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  2. James H. Jones
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Correspondence to James H. Jones.

Additional information

Communicated by David C. Poole.

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Crocker, G.H., Jones, J.H. Hypoxia and CO alter O2 extraction but not peripheral diffusing capacity during maximal aerobic exercise. Eur J Appl Physiol 114, 837–845 (2014). https://doi.org/10.1007/s00421-013-2799-0

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Keywords

  • Goat
  • Carbon monoxide
  • Oxygen transport
  • Aerobic capacity