title: Density-dependent reduction of nitric oxide diffusing capacity after pneumonectomy.
abstract: Airway lengthening after pneumonectomy (PNX) may increase diffusive resistance to gas mixing (1/D(G)); the effect is accentuated by increasing acinar gas density but is difficult to detect from lung CO-diffusing capacity (Dl(CO)). Because lung NO-diffusing capacity (Dl(NO)) is three- to fivefold that of Dl(CO), whereas 1/D(G) for NO and CO are similar, we hypothesized that a density-dependent fractional reduction would be greater for Dl(NO) than for Dl(CO). We measured Dl(NO) and Dl(CO) at two tidal volumes (Vt) and with three background gases [helium (He), nitrogen (N(2)), and sulfur hexafluoride (SF(6))] in immature dogs 3 and 9 mo after right PNX (5 and 11 mo of age). At maturity (11 mo), background gas density had no effect on Dl(NO), Dl(CO), or Dl(NO)-to-Dl(CO) ratio in sham controls. In PNX animals, Dl(NO) declined 25-50% in SF(6) relative to He and N(2), and Dl(NO)/Dl(CO) declined approximately 50% in SF(6) relative to He at a Vt of 15 ml/kg, consistent with a significant 1/D(G). At 5 mo of age, Dl(NO)/Dl(CO) declined 25-45% in SF(6) relative to He and N(2) in both groups, but Dl(CO) increased paradoxically in SF(6) relative to N(2) or He by 20-60%. Findings suggest that SF(6), besides increasing 1/D(G), may redistribute ventilation and/or enhance acinar penetration of the convective front.
authors.affiliation: Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9034, USA.
authors.forename: Connie C W
authors.initials: CC
authors.lastname: Hsia
authors.forename: Xiao
authors.initials: X
authors.lastname: Yan
authors.forename: D Merrill
authors.initials: DM
authors.lastname: Dane
authors.forename: Robert L
authors.initials: RL
authors.lastname: Johnson
mesh_terms: D000375:Aging / Q000502:physiology; D000818:Animals; D001835:Body Weight / Q000502:physiology; D002248:Carbon Monoxide / Q000378:metabolism; D004285:Dogs; D006371:Helium; D006454:Hemoglobins / Q000378:metabolism; D008168:Lung / Q000254:growth & development; D008176:Lung Volume Measurements; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D011013:Pneumonectomy; D011653:Pulmonary Diffusing Capacity / Q000502:physiology*; D013459:Sulfur Hexafluoride; D013990:Tidal Volume / Q000502:physiology
chemical_list: D006454:Hemoglobins; D006371:Helium; D009569:Nitric Oxide; D002248:Carbon Monoxide; D013459:Sulfur Hexafluoride