The relationship between pleural effusion, neural respiratory drive and breathlessness - preliminary results from the SINE study

The mechanisms of breathlessness in pleural effusion are poorly understood with no data on neural respiratory drive (NRD) in this condition. The SINE (ISRCTN36677860) pilot physiology study aimed to evaluate the relationship between pleural effusion and NRD. Patients with a unilateral pleural effusion were recruited, 2017-20. Surface intercostal space parasternal EMG (EMGpara) was measured during resting breathing, normalised to maximal inspiratory efforts (EMGpara%max) before and after thoracentesis using an 8French catheter. Eight patients were enrolled. Mean (SD) age 61 (21.8) years, 5 female, 7 right sided, 5 malignant. Complete fluid evacuation achieved in all patients with mean volume drained 1735 (694.5) ml. Mean pleural pressure baseline vs post drainage was 9.9 (5.9) vs -4.1 (8) cmH20. EMGpara reduced from 11.3 (27) µV to 7.2 (2.3) µV (mean difference -4.06µV; 95%CI -7.7 to -0.4, p=0.034). EMGpara%max reduced from 25.4 (15.2) % to 16.7 (10.5) % (mean difference -8.8%; 95%CI -17.8 to 0.3, p=0.056). Neural respiratory drive index (NRDI - product of EMGpara%max and respiratory rate) fell from 610.9 (448.5) to 349.8 (255) (mean difference -261; 95%CI -539.4 to 17.3, p=0.062). Dyspnoea improved with change in 100mm visual analogue score immediately post drainage (-19.6mm; 95% -40.3 to 1.0, p=0.060) and 24hours later (-28.4mm; 95%CI -48.4 to -3.3, p=0.012). ΔEMGpara%max and ΔVASpost-drainage were strongly positively correlated, r=0.817, p=0.025. Pleural effusions are associated with increased NRD which falls following thoracentesis and correlates strongly with an improvement in breathlessness.