Table 5.

Functional residual capacity (FRC) values in the upright seated position and FRC change from reclined to upright

		Patients	Controls	p Value for difference between patient and control groups
	N	21*	30
FRC seated (litres)	Median (IQR)	2.84 (2.30 to 3.15)	2.92 (2.54 to 3.84)	0.31†
FRC seated (% predicted)	Median (IQR)	84.0 (73.0 to 104.0)	99. 5 (86.5 to 112.3)	0.02†
	N	15*	30
FRC change from reclined to upright (litres)	Median difference (IQR)	0.21 (0.1 to 0.37)	0.235 (–0.08 to 0.43)	0.88†
p Value for difference between paired (reclined and upright) values for each group		<0.01‡	<0.01‡

*Of the 21 patients with upright FRC measurements, 6 did not have reclined FRC measurements, as they did not tolerate reclining for a prolonged period wearing the facemask; so there are 15 patients with paired upright and reclined measurements.

†p Value calculated using Mann-Whitney U test.

‡p Value calculated using Wilcoxon matched pairs test.