• mechanical insufflation
• scoliosis
• cough flow physiology

We read with interest the recent paper by Sivasothy et al on the effect of manually assisted cough and mechanical insufflation on cough flows.¹ The authors reported that mechanical insufflation at pressures of 20 cm H₂O did not significantly increase peak cough flows and volumes for patients with neuromuscular disease (NMD) and scoliosis of more than 70°. In previous studies in which patients with NMD, including those with scoliosis, air stacked consecutively delivered volumes to the maximum volumes and pressures (often over 60 cm H₂O) that they could hold with a closed glottis, cough flows were always greatly increased.² It is true that few of these patients had scoliosis exceeding 30° since the patients systematically undergo spinal instrumentation to prevent severe scoliosis. Nevertheless, we wish to suggest that it is likely that the cough flows did not appear to increase significantly in the patients with scoliosis because inadequate pressures were used and the number of patients was too small to reach levels of statistical significance. Indeed, it has been shown in animal models³ and it is widely felt by patients using mechanical insufflation-exsufflation that pressures of 35–40 cm H₂O are the minimum required to be effective.⁴