Hypoxia decreases exhaled nitric oxide in mountaineers susceptible to high-altitude pulmonary edema.
An exaggerated hypoxic pulmonary vasoconstriction is essential for development of high-altitude pulmonary edema (HAPE). We hypothesized that susceptibility to HAPE may be related to decreased production of nitric oxide (NO), an endogenous modulator of pulmonary vascular resistance, and that a decrease in exhaled NO could be detected during hypoxic exposure. Therefore, we investigated respiratory tract NO excretion by chemiluminescence and pulmonary artery systolic pressure (Ppa,s) by echocardiography in nine HAPE-susceptible mountaineers and nine HAPE-resistant control subjects during normoxia and acute hypoxia (fraction of inspired oxygen [FI(O2)] = 0.12). The subjects performed oral breathing. Nasally excreted NO was separated from respiratory gas by suction via a nasal mask. In HAPE-susceptible subjects, NO excretion in expired gas significantly decreased (p < 0.05) during hypoxia of 2 h in comparison with normoxia (28 +/- 4 versus 21 +/- 2 nl/min, mean +/- SEM). In contrast, the NO excretion rate of control subjects remained unchanged (31 +/- 6 versus 33 +/- 6 nl/ min, NS). Nasal NO excretion did not differ significantly between groups during normoxia (HAPE-susceptible group, 183 +/- 16 nl/ min; control subjects, 297 +/- 55 nl/min, NS) and was not influenced by hypoxia. The changes in Ppa,s with hypoxia correlated with the percent changes in lower respiratory tract NO excretion (R = -0.49, p = 0.04). Our data provide the first evidence of decreased pulmonary NO production in HAPE-susceptible subjects during acute hypoxia that may contribute among other factors to their enhanced hypoxic pulmonary vascular response.
Busch
T
T
Department of Anesthesiology and Intensive Care Medicine, Charité, Campus Virchow-Klinikum, Humboldt-University, Berlin, Germany.
Bärtsch
P
P
Pappert
D
D
Grünig
E
E
Hildebrandt
W
W
Elser
H
H
Falke
K J
KJ
Swenson
E R
ER
D000328:Adult; D000532:Altitude Sickness / Q000503:physiopathology*; D001944:Breath Tests; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008168:Lung / Q000098:blood supply; D008297:Male; D008875:Middle Aged; D009569:Nitric Oxide / Q000502:physiology*; D011654:Pulmonary Edema / Q000503:physiopathology*; D011659:Pulmonary Gas Exchange / Q000502:physiology; D014661:Vasoconstriction / Q000502:physiology
D009569:Nitric Oxide