S13 Effect of portable non-invasive ventilation on thoracoabdominal volume regulation in recovery from intermittent exercise in patients with COPD

Background We previously identified that 8/24 COPD patients did not improve dynamic hyperinflation (DH) (DH non-responders) with the application of portable non-invasive ventilation (pNIV; Inspiratory/Expiratory Positive Airway Pressure: 18/8 cmH2O) compared to the pursed lip breathing (PLB) technique during recovery from intermittent exercise (Chynkiamis et al 2020). In the present study we employed Optoelectronic Plethysmography during acute application of pNIV and PLB in recovery from exercise to examine potential differences in the pattern of thoracoabdominal volume regulation between DH responders and DH non-responders.

Methods 14 COPD patients (FEV1: 55±21%predicted) performed 2 intermittent cycling trials (consisting of 5 bouts for 2 minutes at 80% of peak work rate interspersed with 2 minutes of recovery) using PLB or pNIV during recovery on a balanced order sequence.

Results Patients exhibited two different patterns of response to exercise-induced DH during pNIV compared to PLB application: those who recruited expiratory abdominal muscles, thereby compensating end-expiratory rib cage hyperinflation (DH responders: n=7) and those who did not recruit expiratory abdominal muscles to compensate rib cage hyperinflation (DH non-responders: n=7). In DH responders, pNIV application compared to PLB in the 1st minute of recovery decreased total end-expiratory thoracoabdominal volume by 364±114 ml (p=0.019), secondary to greater reduction in end-expiratory abdominal volume by 338±171 ml (p=0.047). In contrast, in DH non-responders, pNIV application compared to PLB increased end-expiratory thoracoabdominal volume by 379±76 ml (p=0.004), secondary to increased end-expiratory rib cage volume by 348±44 ml (p=0.001) with no change in end-expiratory abdominal volume (31±81 ml; p=0.720). Lung function measures were not different between responders and non-responders. However, DH responders had greater BMI (32.8±6.8) compared to DH non-responders (23.6±4.9) (p=0.019).

Conclusions Reports that the respiratory muscles of patients with high BMI might have a mechanical advantage compared to patients with normal BMI (O’Donnell & Ciavaglia, 2014) may partly explain the difference between responders and non-responders. Moreover, pNIV used in the present study provided high extrinsic positive end-expiratory pressure (PEEPe), matching more effectively the higher intrinsic positive end-expiratory pressure, reported in patients with high BMI (O’Donnell & Ciavaglia, 2014). However, PEEPe was likely excessive for the DH non-responders, thereby worsening DH.