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

Abstract

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. To determine in adults aged 18-60 years if PEF measured sitting differs from that measured standing. Crossover design with alternating position of initial measurement in people attending primary care clinics in Barbados. 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 <i>t</i>-test. 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. PEF measurements are reduced when performed sitting compared to standing. The difference is small and unlikely to alter clinical management in most cases.