S49 Ventilatory irregularity quantified by approximate entropy identifies disordered breathing in patients with unexplained dyspnoea: Abstract S49 Table 1

Abstract

during awake CPAP titration to quantify the effect of chest inflation on the load of the respiratory system. Patients and methods Obese patients (body-mass-index, BMI >30) with confirmed obstructive sleep apnoea (OSA) were studied and NRD (sEMG para) and the surface EMG of the external oblique (sEMG abd) were recorded and normalised to baseline activity (awake, supine). The apnoea-hypopnoea index (AHI) and 95 th percentile of CPAP were determined in sleep studies. The patients were then studied whilst awake and breathing on CPAP (4-20 cmH 2 O, increments of 2 cmH 2 O/3 mins), with the modified Borg score (mBorg) recorded. Results 15 patients (age 48 ± 10 years, 12 male, BMI 38.9 ± 5.8) suffering with moderate-severe OSA (AHI 32.2 ± 21.1/h, 95 th percentile nocturnal CPAP 14.1 ± 3.8 cmH 2 O) were studied. Awake, sEMG para declined by 15.1 ± 1.5% from base-line when CPAP was applied, with the nadir at a CPAP of 10.6 ± 3.4 cmH 2 O (p = 0.026). Further increase in CPAP levels led to a rise in sEMG para and breathlessness (mBorg at lowest sEMG para 0.9 ± 0.8 points, at CPAP of 20 cmH 2 O 2.7 ± 2.7 points, p = 0.02). Conclusion The respiratory system is maximally offloaded with subtherapeutic CPAP levels in OSA. Levels of NRD observed at effective CPAP levels are associated with breathlessness which can impact on CPAP compliance. Introduction Patients with idiopathic persistent exertional dysp-noea 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 unpredict-ability, based on chaos theorem, which quantifies the degree of irregularity in time-series data. Objectives To 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. Methods We 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 cardiores-piratory 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. Results BPD 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 (VO 2) (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