Figure 3 : Univariate regression modelling estimates of pressure for each length of tubing for flow rates up to 20 L/min.

Solid lines and data points are experimental measures. Dotted lines are linear regression modelling for each experimental length of tubing. Recommended therapeutic PEP range of 10 cm H₂O to 20 cm H₂0 and physiological flow rate range is shown. PEP, positive expiratory pressure; cm H₂0, centimetres of water pressure; L/min, litres per minute; mm, millimetres; cm, centimetres.