Peak flowmeter resistance decreases peak expiratory flow in subjects with COPD

Previous studies have shown that the added resistance of a mini-Wright peak expiratory flow (PEF) meter reduced PEF by similar to 8% in normal subject s because of gas compression reducing thoracic gas volume at PEF and thus d riving elastic recoil pressure. We undertook a body plethysmographic study in 15 patients with chronic obstructive pulmonary disease (COPD), age 65.9 +/- 6.3 yr (mean +/- SD, range 53-75 yr), to examine whether their recorded PEF was also limited by the added resistance of a PEF meter. The PEF meter increased alveolar pressure at PEF (Ppeak) from 3.7 +/- 1.4 to 4.7 +/- 1.5 kPa (P = 0.01), and PEF was reduced from 3.6 +/- 1.3 l/s to 3.2 +/- 0.9 l/ s (P = 0.01). The influence of flow limitation on PEF and Ppeak was evaluat ed by a simple four-parameter model based on the wave-speed concept. We con clude that added external resistance in patients with COPD reduced PEF by t he same mechanisms as in healthy subjects. Furthermore, the much lower Ppea k in COPD patients is a consequence of more severe flow limitation than in healthy subjects and not of deficient muscle strength.