title: Airway and lung tissue mechanics in asthma. Effects of albuterol.
abstract: We examined the partitioning of total lung resistance (RL) into airway resistance (Raw) and tissue resistance (Rti) in patients with mild to moderate asthma (baseline FEV1, 54 to 91% of predicted) before and after albuterol inhalation. An optimal ventilator waveform was used to measure RL and lung elastance (EL) in 21 asthmatics from approximately 0.1 to 8 Hz during tidal excursions. Analysis of the RL and EL provided separate estimates of airway and lung tissue properties. Eleven subjects, classified as Type A asthmatics, displayed slightly elevated RL but normal EL. Their data were well described with a model consisting of homogeneous airways leading to viscoelastic tissues before and after albuterol. The other 10 subjects, classified as Type B asthmatics, demonstrated highly elevated RL and an EL that became highly elevated at frequencies above 2 Hz. These subjects required the inclusion of an airway wall compliance in the model prealbuterol but not postalbuterol. This suggests that the Type B subjects were experiencing pronounced constriction in the periphery of the lung, resulting in shunting of flow into the airway walls. Spirometric data were consistent with higher constriction in Type B subjects. Both groups demonstrated significant (p < 0.05) decreases in Raw and tissue damping after albuterol, but tissue elastance decreased only in the Type B group. The percent contributions of Raw and Rti to RL were similar in both groups and did not change after albuterol. We conclude that in asthma, Raw comprises the majority (> 70%) of RL at breathing frequencies. The relative contributions of Raw and Rti to RL appear to be independent of the degree of smooth muscle constriction.
authors.affiliation: Department of Biomedical Engineering, Boston University; and Pulmonary Division, Brigham and Women's Hospital, Boston, Massachusetts, USA.
authors.forename: D W
authors.initials: DW
authors.lastname: Kaczka
authors.forename: E P
authors.initials: EP
authors.lastname: Ingenito
authors.forename: E
authors.initials: E
authors.lastname: Israel
authors.forename: K R
authors.initials: KR
authors.lastname: Lutchen
mesh_terms: D000280:Administration, Inhalation; D000293:Adolescent; D000328:Adult; D000403:Airway Resistance / Q000187:drug effects / Q000502:physiology*; D000420:Albuterol / Q000008:administration & dosage / Q000627:therapeutic use*; D001249:Asthma / Q000188:drug therapy* / Q000503:physiopathology*; D001993:Bronchodilator Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D006801:Humans; D008170:Lung Compliance / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D015656:Respiratory Mechanics / Q000187:drug effects; D013147:Spirometry
chemical_list: D001993:Bronchodilator Agents; D000420:Albuterol