Limitations to the Efficiency of Pulmonary Gas Exchange During Exercise in Man

  • M. D. Hammond
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 227)


The human lung must function over a wide range of metabolic demands and environmental conditions. It is not rare for oxygen consumption (\(\rm\dot{v}\)O2) to vary from 3-5 ml · kg · min−1 at rest to as much as 70 ml · kg · min−1 during exercise only moments later, or for inspired PO2 (PIO2) to range from 150 Torr (sea level) to 80 Torr (equivalent altitude 4500 meters) or less over a period of hours, to days. The ability to function in these different circumstances comes with a small price: although the lung is remarkably efficient at rest at sea level, it becomes less so at higher \(\rm\dot{v}\)O2 (Asmussen and Nielsen, 1960), particularly at high altitude. For example, in healthy resting subjects the ideal alveolar-arterial PO2 difference (A-aDO2) is normally only 5-10 Torr, but it may increase to 25 Torr or more during neavy exercise (Dempsey et al., 1984). While this increased gradient has relatively little effect on arterial O2 content at sea level, it can lead to substantial additional arterial desaturation at altitude, where subjects are operating on the steep descending slope of the oxyhemoglobin dissociation curve.


Diffusion Limitation Pulmonary Capillary Wedge Pressure Normobaric Hypoxia Simulated Altitude Oxyhemoglobin Dissociation Curve 
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Copyright information

© Plenum Press, New York 1988

Authors and Affiliations

  • M. D. Hammond
    • 1
  1. 1.Division of Pulmonary and Critical Medicine Department of Internal MedicineUniversity of South Florida, College of Medicine James A. Haley Veterans HospitalTampaUSA

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