IntroductionPatients with COPD commonly exhibit pursed-lip breathing during exercise, a strategy that, by increasing intrinsic positive end-expiratory pressure, may optimise lung mechanics and exercise tolerance. A similar role for laryngeal narrowing in modulating exercise airways resistance and the respiratory cycle volume–time course is postulated, yet remains unstudied in COPD. The aim of this study was to assess the characteristics of laryngeal narrowing and its role in exercise intolerance and dynamic hyperinflation in COPD.MethodsWe studied 19 patients (n=8 mild–moderate; n=11 severe COPD) and healthy age and sex matched controls (n=11). Baseline physiological characteristics and clinical status were assessed prior to an incremental maximal cardiopulmonary exercise test with continuous laryngoscopy. Laryngeal narrowing measures were calculated at the glottic and supra-glottic aperture at rest and peak exercise.ResultsAt rest, expiratory laryngeal narrowing was pronounced at the glottic level in patients and related to FEV1 in the whole cohort (r=−0.71, p<0.001) and patients alone (r=−0.53, p=0.018). During exercise, glottic narrowing was inversely related to peak ventilation in all subjects (r=−0.55, p=0.0015) and patients (r=−0.71, p<0.001) and peak exercise tidal volume (r=−0.58, p=0.0062 and r=−0.55, p=0.0076, respectively). Exercise glottic narrowing was also inversely related to peak oxygen uptake (% predicted) in all subjects (r=−0.65, p<0.001) and patients considered alone (r=−0.58, p=0.014). Exercise inspiratory duty cycle was related to exercise glottic narrowing for all subjects (r=−0.69, p<0.001) and patients (r=−0.62, p<0.001).ConclusionsDynamic laryngeal narrowing during expiration is prevalent in patients with COPD and is related to disease severity, respiratory duty cycle and exercise capacity.

No abstract

IntroductionPatients with idiopathic persistent exertional dyspnoea are often labelled as having a breathing pattern disorder (BPD). There are no agreed objective diagnostic measures for BPD, which complicates its characterisation and response to therapy. Approximate entropy (ApEn) is a measure of unpredictability, based on chaos theorem, which quantifies the degree of irregularity in time-series data.ObjectivesTo measure ApEn of ventilatory variables during a cardiopulmonary exercise test (CPET) in patients referred with unexplained dyspnoea. We hypothesised that ApEn of tidal volume and breathing frequency would be greater (i.e. more irregular) in patients with BPD than healthy controls.MethodsWe studied 20 adults (14 female) with unexplained dyspnoea referred for CPET and diagnosed with BPD (by a senior respiratory physiotherapist blinded to ApEn data) and 15 age- gender- and BMI-matched healthy controls. Underlying cardiorespiratory disease was excluded using various investigations (e.g. imaging and echocardiography) prior to referral, in addition to tests performed on the day of CPET; namely pulmonary function and blood gas analysis. ApEn of various ventilatory parameters including tidal volume, breathing frequency and minute ventilation was calculated at rest and during a cycle-ergometer CPET.ResultsBPD patients had greater dyspnoea (modified BORG) at rest (1.4 ± 1.2 vs 0.2 ± 0.6; P < 0.01) and lower peak oxygen uptake (VO2) (P < 0.01; Table 1). Peak exercise respiratory exchange ratio was similar between groups (1.14 ± 0.17 vs 1.13 ± 0.08, P = 0.84) as were nadir values for ventilatory equivalent for CO2 (28.5 ± 5.2 vs 25.5 ± 3.6, P = 0.07) and end-exercise arterial PCO2 (4.21 ± 0.68 vs 4.1 ± 0.67, P = 0.68). ApEn was significantly greater in the BPD cohort for the duration of the test (Table 1); however differences were not apparent at rest. There was no relationship between ApEn and baseline symptom scores.Abstract S49 Table 1Participant characteristics and exercise responsesBPD (N = 20)Healthy Controls (N = 15)Age (years)49 (14)50 (18)BMI (kg/m2)26.0 (5.0)24.5 (3.7)FEV1 (% predicted)107 (18)95 (18)*FEV1/FVC0.78 (0.06)0.75 (0.12)VO2/kg Peak (ml/min/kg)20.7 (7.1)37.9 (14.9)**VO2 Peak (% Predicted)79.8 (17.5)124.8 (27.3)**ApEn Tidal Volume 1.31 (0.23)1.04 (0.28)**ApEn Breathing Frequency1.42 (0.22)1.24 (0.24)*ApEn Minute Ventilation1.01 (0.29)0.64 (0.22)**ConclusionMeasurement of ventilatory ApEn in patients referred with unexplained dyspnoea quantified irregularity of breathing pattern and was significantly greater (more irregular) in BPD than controls. These differences were not apparent from resting phase analysis. Quantifying increased dys-regulation in exercise hyperpnoea using ApEn can be applied to ventilatory variables collected during standard CPET, and thus could aid in diagnosis and evaluating treatment response in BPD. Further work should explore how ventilatiory ApEn relates to perception of symptoms.