Fig. 3.— a) Plot of the difference between mouth whistle pressure (Pmo,W) and gastric whistle pressure (Pga,W) against the mean of Pmo,W and Pga,W in 12 healthy subjects. The bias and limits of agreement were -26 cmH2O and -83–31 cmH2O, respectively. b) Plot of the difference between Pmo,W and oesophageal whistle pressure (Poes,W) against the mean of Pmo,W and Poes,W in 12 healthy subjects. The bias and limits of agreement were 9 cmH2O and -17–35 cmH2O, respectively. c) Plot of the difference between Pmo,W and maximum expiratory pressure (PE,max) against the mean of Pmo,W and PE,max in 10 amyotrophic lateral sclerosis (ALS) patients. The bias and limits of agreement were 7 cmH2O and -15–29 cmH2O, respectively. d) Plot of the difference between Pmo,W and Pga,W against the mean of Pmo,W and Pga,W in 10 ALS patients. The bias and limits of agreement were -5 cmH2O and -19–9 cmH2O, respectively. e) Plot of the difference between Pmo,W and Poes,W against the mean of Pmo,W and Poes,W in 10 ALS patients. The bias and limits of agreement were 3 cmH2O and -10–16 cmH2O, respectively.