Does peak expiratory flow measured sitting differ from that measured standing? A cross-over study in primary care in Barbados

BACKGROUND: Several authorities recommend measuring peak expiratory flow (PEF) standing. Limited evidence suggests that PEF obtained sitting is similar in magnitude but there are no studies in African populations. AIM: To determine in adults aged 18–60 years if PEF measured sitting differs from that measured standing. DESIGN & SETTING: Crossover design with alternating position of initial measurement in people attending primary care clinics in Barbados. METHOD: Quota sampling by age, sex, and clinic of adults aged 18–60 years was done and an interviewer-administered questionnaire was completed. PEF sitting and standing was measured with an European Union (EU) scale Mini-Wright® meter. The highest of three readings in each position was used and the difference in means tested for significance using the paired sample t-test. RESULTS: Characteristics of the 199 participants were 44% male; 96.5% of African descent; mean age 37 years (standard deviation [SD] 12.8); 22% with an asthma diagnosis; 23% tobacco users; and 22% marijuana users. Mean PEF standing was 438.4 versus 429.7 lmin(–1) sitting, mean difference 8.7 (95% confidence interval [CI] = 3.6 to 13.8). For men, mean PEF standing was 518.7 versus 506.3 lmin(–1) sitting, mean difference 12.4 (95% CI = 3.3 to 21.5). For women, mean PEF was 374.7 standing versus 368.9 lmin(–1) sitting, mean difference 5.8 (95% CI = 0.11 to 11.5). A Bland-Altman plot accounting for trend and a Lin’s correlation coefficient of 0.935 demonstrated good agreement between standing and sitting PEF. CONCLUSION: PEF measurements are reduced when performed sitting compared to standing. The difference is small and unlikely to alter clinical management in most cases.