GAS-COMPRESSION IN LUNGS DECREASES PEAK EXPIRATORY FLOW DEPENDING ON RESISTANCE OF PEAK FLOWMETER

It has recently been shown (O. F. Pedersen T. R. Rasmussen, O. Omland, T. Sigsgaard, P. H. Quanjer, and M. R. Miller. fur. Respir. J. 9: 828 -833, 1996) that the added resistance of a mini-Wright peak flowmeter decreases peak expiratory flow (PEF) by similar to 8% compared with PE F measured by a pneumotachograph. To explore the reason for this, 10 h ealthy men (mean age 43 yr, range 33-58 yr) were examined in a body pl ethysmograph with facilities to measure mouth flow vs. expired volume as well as the change in thoracic gas volume (Vb) and alveolar pressur e (PA). The subjects performed forced vital capacity maneuvers through orifices of different sizes and also a mini-Wright peak flowmeter. PE F with the meter and other added resistances were achieved when flow r eached the perimeter of the flow-Vb curves. The mini-Wright PEF meter decreased PEF from 11.4 +/- 1.5 to 10.3 +/- 1.4 (SD) Vs (P < 0.001), P A increased from 6.7 +/- 1.9 to 9.3 +/- 2.7 kPa (P < 0.001), an increa se equal to the pressure drop across the meter, and caused Vb at PEF t o decrease by 0.24 +/- 0.09 liter (P < 0.001). We conclude that PEF ob tained with an added resistance Like a mini-Wright PEF meter is a wave -speed-determined maximal flow, but the added resistance causes gas co mpression because of increased PA at PEF. Therefore, Vb at PEF and, ac cordingly, PEF decrease.