Pulmonary function testing
An average of 15 minutes was taken to perform reliable supine spirometry after performing sitting spirometry. In the neuromuscular group, the mean sitting FEV1% and sitting FVC% were 78% (SD ±21.9) and 75% (SD±20.5) respectively as shown in Table 3. The percentage difference in ΔFVC between sitting and supine in these NMD children was 9%.
Children breathing spontaneously had an FEV1% of 83% (SD±21.9) and an FVC% of 78% (SD±20.5) and a mean drop in FVC% in the supine position of 7% (SD±17.9). Children on nocturnal NIV had baseline sitting FEV1% and FVC% values of 72%(SD±17.9) and 70%(SD±24.5), respectively, with a mean drop of 12% in the supine position to an FVC% of 58(SD±18.8). Healthy controls had a baseline sitting lung function of FEV1 % and FVC% of 95% (SD±5.2) and 98% (SD±4.8), respectively, with a mean drop of 4% in ΔFVC in the supine position, (p<0.001 compared to children with NMD) (Table 3).
Amongst the 11 children who could not do spirometry, 3 children had cognitive delay and were unable to perform acceptable and reproducible spirometry in the sitting position. Another three children were excluded because they did not have acceptable or repeatable spirometry. Five children had severe restrictive lung disease (FVC<40%) and were able to perform sitting spirometry but were excluded because of poor spirometry technique in the supine position.