Submitted on January 31, 2008
Accepted on August 22, 2008
PULMONARY GAS EXCHANGE RESPONSE TO EXERCISE- AND MANNITOL- INDUCED BRONCHOCONSTRICTION IN MILD ASTHMA
Phillip Anthony Munoz1, Federico P. Gomez1, Hernan A. Manrique1, Josep Roca1, Joan Albert Barbera1, Iven Young2, Sandra D Anderson2, and Roberto Rodriguez-Roisin1*
1 Servei de Pneumologia, Hospital Clinic, Barcelona, Spain; IDIBAPS and CibeRes, Universitat de Barcelona, Barcelona, Spain
2 Department of Respiratory Medicine, Royal Prince Alfred Hospital, Camperdown, New South Wales, Australia
* To whom correspondence should be addressed. E-mail: rororo{at}clinic.ub.es.
Both exercise (EIB) and mannitol challenges were performed in asthmatic patients to assess and compare their pulmonary gas exchange responses for an equivalent degree of bronchoconstriction. In 11 subjects with EIB (27±4[SD]yrs; FEV1, 86±8% predicted) ventilation-perfusion (VA/Q) distributions (using multiple inert gas elimination technique) were measured 5, 15 and 45 min after cycling exercise (FEV1 fall, 35±12%) and after mannitol (33±10%), one week apart. Five min after EIB, minute ventilation (VE, by 123±60%), cardiac output (QT, by 48±29%) and oxygen uptake (VO2, by 54±25%) increased whereas PaO2 (by 14±11mmHg) decreased due to moderate VA/Q imbalance, assessed by increases in dispersions of pulmonary blood flow (Log SDQ, by 0.53±0.16) and alveolar ventilation (Log SDV, by 0.28±0.15) (dimensionless) (p<0.01 each). In contrast, for an equivalent degree of bronchoconstriction and minor increases in VE, QT and VO2, mannitol decreased PaO2 more intensely (by 24±9 mmHg) despite fewer disturbances in Log SDQ (by 0.27±0.12). Notwithstanding, mannitol-induced increase in Log SDV at 5 min (by 0.35±0.15) was similar to that observed during EIB, as was the slow recovery in Log SDV and high VA/Q ratio areas, at variance with the faster recovery of Log SDQ and low VA/Q ratio areas. In asthmatics, EIB provokes more VA/Q imbalance but less hypoxemia than mannitol, primarily due to post-exercise increases in VE and QT benefiting PaO2. VA/Q inequalities during both challenges most likely reflect uneven airway narrowing and blood flow redistribution generating distinctive VA/Q patterns, including the development of areas with low and high VA/Q ratios.
