Apnoea and postural equilibrium: at which lung volume?

Introduction: In healthy subjects, quiet breathing induces specific centre of pressure (CP) oscillations (Caron, O. et al. j neulet 2004; 366:6-9). The aim of this study was to assess if apnoea-induced improved control of balance, is dependent on lung volume. Methods: 26 healthy subjects (10F; 32.9±13y.o.; BMI: 23,7±2,6 kg.m-2) were studied in seating position, during natural breath (NB) and apnoeas at functional residual capacity (FRC), total lung capacity (TLC) and residual volume (RV). CP displacement was recorded with force plate [AMTI] synchronized to optoelectronic system [Vicon] measuring ventilation (41 markers on the trunk). CP Antero-Posterior (AP) range frequency analysis was computed with Fourier transform sampled at 0.02Hz. The apnoeas were compared to NB with a non-parametrical test (Wilcoxon) at the RF±0.1Hz (11 comparison points). Results: Mean breathing frequency (BF) was 15.2±4.2/min. FRC apnoea significantly reduced CP AP range compared to NB; while FRC and TLC apnoeas increased it (Figure 1). Figure 1: CP AP range frequency spectrum centred on BF (*p Conclusion: Apnoea postural stabilization strategy depends on lung volume. It is optimal at FRC with significant decrease of AP range compared to NB; while perturbations appear at higher or lower volumes. Postural disabilities in some chronic respiratory diseases may be partly related to abnormal lung volume relaxation.