title: Ventilation heterogeneity measured by multiple breath inert gas testing is not affected by inspired oxygen concentration in healthy humans.
abstract: Multiple breath washout (MBW) and oxygen-enhanced MRI techniques use acute exposure to 100% oxygen to measure ventilation heterogeneity. Implicit is the assumption that breathing 100% oxygen does not induce changes in ventilation heterogeneity; however, this is untested. We hypothesized that ventilation heterogeneity decreases with increasing inspired oxygen concentration in healthy subjects. We performed MBW in 8 healthy subjects (4 women, 4 men; age = 43 ± 15 yr) with normal pulmonary function (FEV1= 98 ± 6% predicted) using 10% argon as a tracer gas and oxygen concentrations of 12.5%, 21%, or 90%. MBW was performed in accordance with ERS-ATS guidelines. Subjects initially inspired air followed by a wash-in of test gas. Tests were performed in balanced order in triplicate. Gas concentrations were measured at the mouth, and argon signals rescaled to mimic a N2washout, and analyzed to determine the distribution of specific ventilation (SV). Heterogeneity was characterized by the width of a log-Gaussian fit of the SV distribution and from Sacinand Scondindexes derived from the phase III slope. There were no significant differences in the ventilation heterogeneity due to altered inspired oxygen: histogram width (hypoxia 0.57 ± 0.11, normoxia 0.60 ± 0.08, hyperoxia 0.59 ± 0.09,P= 0.51), Scond(hypoxia 0.014 ± 0.011, normoxia 0.012 ± 0.015, hyperoxia 0.010 ± 0.011,P= 0.34), or Sacin(hypoxia 0.11 ± 0.04, normoxia 0.10 ± 0.03, hyperoxia 0.12 ± 0.03,P= 0.23). Functional residual capacity was increased in hypoxia (P= 0.04) and dead space increased in hyperoxia (P= 0.0001) compared with the other conditions. The acute use of 100% oxygen in MBW or MRI is unlikely to affect ventilation heterogeneity.NEW & NOTEWORTHYHyperoxia is used to measure the distribution of ventilation in imaging and MBW but may alter the underlying ventilation distribution. We used MBW to evaluate the effect of inspired oxygen concentration on the ventilation distribution using 10% argon as a tracer. Short-duration exposure to hypoxia (12.5% oxygen) and hyperoxia (90% oxygen) during MBW had no significant effect on ventilation heterogeneity, suggesting that hyperoxia can be used to assess the ventilation distribution.
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, California; and shopkins@ucsd.edu.|Department of Radiology, University of California, San Diego, La Jolla, California.
authors.forename: Susan R
authors.initials: SR
authors.lastname: Hopkins
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, California; and.
authors.forename: Ann R
authors.initials: AR
authors.lastname: Elliott
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, California; and.|Department of Radiology, University of California, San Diego, La Jolla, California.
authors.forename: G Kim
authors.initials: GK
authors.lastname: Prisk
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, California; and.
authors.forename: Chantal
authors.initials: C
authors.lastname: Darquenne
mesh_terms: D000328:Adult; D001944:Breath Tests / Q000379:methods; D005260:Female; D005652:Functional Residual Capacity / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000378:metabolism / Q000503:physiopathology; D008168:Lung; D008297:Male; D008875:Middle Aged; D005741:Noble Gases / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D012119:Respiration; D012129:Respiratory Function Tests / Q000379:methods; D013990:Tidal Volume / Q000502:physiology; D014691:Ventilation / Q000379:methods; D055815:Young Adult
chemical_list: D005741:Noble Gases; D010100:Oxygen
keywords: hyperoxia; multiple breath washout; oxygen enhanced imaging; ventilation heterogeneity