Effect on Physical Position of Peak Inspiratory Flow in Stable COPD: An Observational Study.

Background:We examined the effect of physical position on peak inspiratory flow (PIF) in patients with chronic obstructive pulmonary disease (COPD) using dry powder inhalers (DPIs) with low medium (R2) and/or high (R5) internal resistance. Methods:This prospective study in stable, ambulatory patients with spirometry-confirmed COPD evaluated the effect of three physical positions on maximal PIF achieved. Participants had PIF of 30-90 L/min (R5) or 60-90 L/min (R2 DPIs) using the In-Check™ DIAL. PIF was measured in triplicate randomly in three positions that patients might be in while using their inhaler (standing, sitting, and semi-upright [supine position with head of bed at 45°, neck flexed forward]) against prescribed DPI resistance (R2/R5/both). Correlations between PIF and percent decline in PIF between positions and differences in participant characteristics with >10% vs. ≤10% PIF decline standing to semi-upright were calculated. Results:Seventy-six participants (mean age, 65.2 years) had positional measurements; 59% reported seated DPI use at home. Mean (standard deviation) PIF standing, sitting, and semi-upright was 80.7 (13.4), 77.8 (14.3), and 74.0 (14.5) L/min, respectively, for R2 and 51.1 (9.52), 48.6 (9.84), and 45.8 (7.69) L/min, respectively, for R5 DPIs. PIF semi-upright was significantly lower than sitting and standing (R2; P < 0.0001) and standing (R5; P = 0.002). Approximately half had >10% decline in PIF from standing to semi-upright. Patient characteristics exceeding the 0.10 absolute standardized difference threshold with the decline in PIF for both the R2 and R5 DPIs were waist-to-hip ratio, modified Medical Research Council dyspnea score, and post-bronchodilator % predicted forced vital capacity and PIF by spirometry. Conclusions:PIF was significantly affected by physical position regardless of DPI resistance. PIF was highest when standing and lowest when semi-upright. We recommend patients with COPD stand while using an R2 or R5 DPI. Where unfeasible, the position should be sitting rather than semi-upright. Trial registration: ClinicalTrials.gov identifier NCT04168775; Trial registration date: November 19, 2019.