title: Effects of ambient pressure on pulmonary nitric oxide.
abstract: Airway nitric oxide (NO) has been proposed to play a role in the development of high-altitude pulmonary edema. We undertook a study of the effects of acute changes of ambient pressure on exhaled and alveolar NO in the range 0.5-4 atmospheres absolute (ATA, 379-3,040 mmHg) in eight healthy subjects breathing normoxic nitrogen-oxygen mixtures. On the basis of previous work with inhalation of low-density helium-oxygen gas, we expected facilitated backdiffusion and lowered exhaled NO at 0.5 ATA and the opposite at 4 ATA. Instead, the exhaled NO partial pressure (Pe(NO)) did not differ between pressures and averaged 1.21 ± 0.16 (SE) mPa across pressures. As a consequence, exhaled NO fractions varied inversely with pressure. Alveolar estimates of the NO partial pressure differed between pressures and averaged 88 (P = 0.04) and 176 (P = 0.009) percent of control (1 ATA) at 0.5 and 4 ATA, respectively. The airway contribution to exhaled NO was reduced to 79% of control (P = 0.009) at 4 ATA. Our finding of the same Pe(NO) at 0.5 and 1 ATA is at variance with previous findings of a reduced Pe(NO) with inhalation of low-density gas at normal pressure, and this discrepancy may be due to the much longer durations of low-density gas breathing in the present study compared with previous studies with helium-oxygen breathing. The present data are compatible with the notion of an enhanced convective backtransport of NO, compensating for attenuated backdiffusion of NO with increasing pressure. An alternative interpretation is a pressure-induced suppression of NO formation in the airways.
authors.affiliation: Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden. tryggve.hemmingsson@karolinska.se
authors.forename: Tryggve E
authors.initials: TE
authors.lastname: Hemmingsson
authors.forename: Dag
authors.initials: D
authors.lastname: Linnarsson
authors.forename: Claes
authors.initials: C
authors.lastname: Frostell
authors.forename: Alain
authors.initials: A
authors.lastname: Van Muylem
authors.forename: Yannick
authors.initials: Y
authors.lastname: Kerckx
authors.forename: Lars E
authors.initials: LE
authors.lastname: Gustafsson
mesh_terms: D000328:Adult; D000531:Altitude; D001274:Atmospheric Pressure; D006801:Humans; D008168:Lung / Q000502:physiology*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D010313:Partial Pressure; D011654:Pulmonary Edema / Q000209:etiology* / Q000378:metabolism; D055815:Young Adult
chemical_list: D009569:Nitric Oxide