Effects of Positive End-Expiratory Pressure Breathing on Exercise-Induced Asthma*

Abstract

Five volunteers, all with a history of childhood asthma that had persisted, though at a reduced severity and incidence, through their teens to the present, performed six treadmill runs on separate days for 6 min at 80% of VO₂ max followed by 20 min of recovery. Two trials were completed under each of the following conditions: normal, positive end-expiratory pressure breathing (PEEP) during the work, and PEEP post-excercise. For each trial, forced vital capacity maneuvers (FVC) were completed twice at rest, at the 3rd and 6th min of exercise, and every 5 min during the 20-min recovery. No significant effects of PEEP on resting pulmonary function values was found nor was P_ET CO₂ altered for rest, exercise, or recovery for PEEP vs normal trials. For the normal exercise tests, post-exercise broncho-constriction was shown by at 30% to 50% decrease in FEV_1.0, 30% to 40% drop in PEF, and a 45% to 65% decrease in maximal flow at 50% VC (MEF₅₀), comparing post-exercise values to rest. PEEP during and PEEP post conditions significantly (P < 0.01) decreased the severity of exercise-induced asthma (EIA) as PEFR and FEV_1.0 values remained within 20% of rest levels and MEF₅₀ within 30%. Since Pet CO₂ was not altered by the PEEP conditions, the airway response cannot be mediated through CO₂ effect. It is known that PEEP does reduce air trapping, but since PEEP during work had a lasting effect into recovery this indicates that some additional mechanism may be involved.

PEEP - EIA - asthma - EIB