WAVE-SPEED-DETERMINED FLOW LIMITATION AT PEAK FLOW IN NORMAL AND ASTHMATIC SUBJECTS

The purpose of this study was to examine whether peak expiratory flow is determined by the wave-speed flow-limiting mechanism. We examined 1 7 healthy subjects and 11 subjects with stable asthma, the latter trea ted with inhaled bronchodilators and corticosteroids. We used an esoph ageal balloon and a Pitot-static probe positioned at five locations be tween the right lower lobe and midtrachea to obtain dynamic area-trans mural pressure (A-Ptm) curves as described (O. F. Pedersen, B. Thiesse n, and S. Lyager. J. Appl. Physiol. 52: 357-369, 1982). From these cur ves we obtained cross-sectional area (A) and airway compliance (Caw = dA/dPtm) at PEF, calculated flow at wave speed [(V) over dot ws = A[A/ (Cawrho)(0.5)], where rho is density] and speed index is (SI = (V) ov er dot/(V) over dot ws). In 13 of 15 healthy and in 4 of 10 asthmatic subjects, who could produce satisfactory curves, SI at PEF was >0.9 at one or more measured positions. Alveolar pressure continued to increa se after PEF was achieved, suggesting flow Limitation somewhere in the airway in all of these subjects. We conclude that wave speed is reach ed in central airways at PEF in most subjects, but it cannot be exclud ed that wave speed is also reached in more peripheral airways.