title: Pulmonary capillary reserve and exercise capacity at high altitude in healthy humans.
abstract: OBJECTIVE
  We determined whether well-acclimatized humans have a reserve to recruit pulmonary capillaries in response to exercise at high altitude.
  
  
  METHODS
  At sea level, lung diffusing capacity for carbon monoxide (DLCO), alveolar-capillary membrane conductance (DmCO), and pulmonary capillary blood volume (V c) were measured at rest before maximal oxygen consumption ([Formula: see text]) was determined in seven adults. Then, DLCO, DmCO and V c were measured pre- and post-exhaustive incremental exercise at 5150 m after ~40 days of acclimatization.
  
  
  RESULTS
  Immediately after exercise at high altitude, there was an increase in group mean DmCO (14 ± 10%, P = 0.040) with no pre- to post-exercise change in group mean DLCO (46.9 ± 5.8 vs. 50.6 ± 9.6 ml/min/mmHg, P = 0.213) or V c (151 ± 28 vs. 158 ± 37 ml, P = 0.693). There was, however, a ~20% increase in DLCO from pre- to post-exercise at high altitude (51.2 ± 0.2 vs. 61.1 ± 0.2 ml/min/mmHg) with a concomitant increase in DmCO (123 ± 2 vs. 156 ± 4 ml/min/mmHg) and V c (157 ± 3 vs. 180 ± 8 ml) in 2 of the 7 participants. There was a significant positive relationship between the decrease in [Formula: see text] from sea level to high altitude and the change in DLCO and lung diffusing capacity for nitric oxide (DLNO) from rest to end-exercise at high altitude.
  
  
  CONCLUSIONS
  These data suggest that recruitment of the pulmonary capillaries in response to exercise at high altitude is limited in most well-acclimatized humans but that any such a reserve may be associated with better exercise capacity.
authors.affiliation: Division of Cardiovascular Diseases, Department of Internal Medicine, Mayo Clinic, Rochester, USA. b.taylor@exeter.ac.uk.|School of Sport and Health Science, College of Life and Environmental Sciences, University of Exeter, St. Luke's Campus, Heavitree Road, EX1 2LU, Exeter, UK. b.taylor@exeter.ac.uk.
authors.forename: Bryan J
authors.initials: BJ
authors.lastname: Taylor
authors.affiliation: Division of Cardiovascular Diseases, Department of Internal Medicine, Mayo Clinic, Rochester, USA.
authors.forename: Kirsten E
authors.initials: KE
authors.lastname: Coffman
authors.affiliation: Division of Cardiovascular Diseases, Department of Internal Medicine, Mayo Clinic, Rochester, USA.|Division of Aerospace Medicine, Mayo Clinic, Rochester, USA.
authors.forename: Douglas T
authors.initials: DT
authors.lastname: Summerfield
authors.affiliation: Division of Cardiovascular Diseases, Department of Internal Medicine, Mayo Clinic, Rochester, USA.
authors.forename: Amine N
authors.initials: AN
authors.lastname: Issa
authors.affiliation: Division of Cardiovascular Diseases, Department of Internal Medicine, Mayo Clinic, Rochester, USA.|School of Kinesiology, University of Minnesota, Minneapolis, USA.
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Kasak
authors.affiliation: Division of Cardiovascular Diseases, Department of Internal Medicine, Mayo Clinic, Rochester, USA.
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Johnson
mesh_terms: D000328:Adult; D000531:Altitude; D001810:Blood Volume; D002196:Capillaries / Q000502:physiology*; D015444:Exercise; D005260:Female; D006801:Humans; D008168:Lung / Q000098:blood supply*; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D011652:Pulmonary Circulation; D011659:Pulmonary Gas Exchange
keywords: Lung diffusing capacity; Maximal oxygen consumption; Pulmonary artery systolic pressure; Sea level