title: The prone position results in smaller ventilation defects during bronchoconstriction in asthma.
abstract: The effect of body posture on regional ventilation during bronchoconstriction is unknown. In five subjects with asthma, we measured spirometry, low-frequency (0.15-Hz) lung elastance, and resistance and regional ventilation by intravenous (13)NN-saline positron emission tomography before and after nebulized methacholine. The subjects were imaged prone on 1 day and supine on another, but on both days the methacholine was delivered while prone. From the residual (13)NN after washout, ventilation defective areas were defined, and their location, volume, ventilation, and fractional gas content relative to the rest of the lung were calculated. Independent of posture, all subjects developed ventilation defective areas. Although ventilation within these areas was similarly reduced in both postures, their volume was smaller in prone than supine (25 vs. 41%, P < 0.05). The geometric center of the ventilation defective areas was gravitationally dependent relative to that of the lung in both postures. Mean lung fractional gas content was greater in the prone position before methacholine and did not increase as much as in the supine position after methacholine. In the prone position at baseline, areas that became ventilation defects had lower gas content than the rest of the lung. In both positions at baseline, there was a gradient of gas content in the vertical direction. In asthma, the size and location of ventilation defects is affected by body position and likely affected by small differences in lung expansion during bronchoconstriction.
authors.affiliation: Department of Medicine, Pulmonary and Critical Care Unit, Bulfinch 148, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA. rharris@partners.org
authors.forename: R Scott
authors.initials: RS
authors.lastname: Harris
authors.forename: Tilo
authors.initials: T
authors.lastname: Winkler
authors.forename: Guido
authors.initials: G
authors.lastname: Musch
authors.forename: Marcos F
authors.initials: MF
authors.lastname: Vidal Melo
authors.forename: Tobias
authors.initials: T
authors.lastname: Schroeder
authors.forename: Nora
authors.initials: N
authors.lastname: Tgavalekos
authors.forename: José G
authors.initials: JG
authors.lastname: Venegas
mesh_terms: D000328:Adult; D001249:Asthma / Q000150:complications / Q000473:pathology* / Q000503:physiopathology*; D016084:Bronchoconstriction / Q000502:physiology*; D005260:Female; D006801:Humans; D008168:Lung / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D008297:Male; D016210:Methacholine Chloride; D009590:Nitrogen Radioisotopes; D016684:Prone Position / Q000502:physiology; D011659:Pulmonary Gas Exchange; D012123:Pulmonary Ventilation / Q000187:drug effects / Q000502:physiology*; D015656:Respiratory Mechanics / Q000502:physiology*; D013147:Spirometry; D055815:Young Adult
chemical_list: D009590:Nitrogen Radioisotopes; D016210:Methacholine Chloride