Regional pulmonary perfusion, inflation, and ventilation defects in bronchoconstricted patients with asthma.
BACKGROUND
Bronchoconstriction in asthma leads to heterogeneous ventilation and the formation of large and contiguous ventilation defects in the lungs. However, the regional adaptations of pulmonary perfusion (Q) to such ventilation defects have not been well studied.


METHODS
We used positron emission tomography to assess the intrapulmonary kinetics of intravenously infused tracer nitrogen-13 ((13)NN), and measured the regional distributions of ventilation and perfusion in 11 patients with mild asthma. For each subject, the regional washout kinetics of (13)NN before and during methacholine-induced bronchoconstriction were analyzed. Two regions of interest (ROIs) were defined: one over a spatially contiguous area of high tracer retention (TR) during bronchoconstriction and a second one covering an area of similar size, showing minimal tracer retention (NR).


RESULTS
Both ROIs demonstrated heterogeneous washout kinetics, which could be described by a two-compartment model with fast and slow washout rates. We found a systematic reduction in regional Q to the TR ROI during bronchoconstriction and a variable and nonsignificant change in relative Q for NR regions. The reduction in regional Q was associated with an increase in regional gas content of the TR ROI, but its magnitude was greater than that anticipated solely by the change in regional lung inflation.


CONCLUSIONS
During methacholine-induced bronchoconstriction, perfusion to ventilation defects are systematically reduced by a relative increase in regional pulmonary vascular resistance.
Harris
R Scott
RS
Department of Medicine (Pulmonary and Critical Care Unit and General Medicine Unit), Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA. rharris@partners.org
Winkler
Tilo
T
Tgavalekos
Nora
N
Musch
Guido
G
Melo
Marcos F Vidal
MF
Schroeder
Tobias
T
Chang
Yuchiao
Y
Venegas
José G
JG
D000328:Adult; D001249:Asthma / Q000378:metabolism / Q000503:physiopathology*; D016084:Bronchoconstriction / Q000502:physiology*; D016085:Bronchoconstrictor Agents / Q000008:administration & dosage; D005260:Female; D006801:Humans; D008297:Male; D016210:Methacholine Chloride / Q000008:administration & dosage; D009590:Nitrogen Radioisotopes / Q000493:pharmacokinetics*; D049268:Positron-Emission Tomography; D011652:Pulmonary Circulation / Q000502:physiology; D012123:Pulmonary Ventilation / Q000502:physiology*; D014692:Ventilation-Perfusion Ratio / Q000502:physiology
D016085:Bronchoconstrictor Agents; D009590:Nitrogen Radioisotopes; D016210:Methacholine Chloride