Manual hyperinflation (MHI) is used by physiotherapists as a treatment technique in intubated patients. This study investigated the effect of three different MHI techniques using a Mapleson-C circuit configuration with a CIG Medishield valve on volume delivered (Vt), peak inspiratory (PIFR) and expiratory flow rates (PEFR), and peak airway pressure (PAP) in a test lung model. The protocols differed in the degree of valve closure and inclusion of an inspiratory pause. For protocols 1, 2 and 3 the measures were Vt-1.33 (0.21), 2.74 (0.13), 3.55 (0.12) litres; PAP-14.30 (0.82), 24.00 (0.47), 30.20 (0.92) cmH2O and PIFR-1.13 (0.05), 1.51 (0.15), 1.32 (0.09) l/s respectively. All pair comparisons were statistically significant except for PEFR (l/s), which was significantly lower for protocol 1 [1.62 (0.06)], compared to protocols 2 [2.01 (0.25)] and 3 [2.10 (0.19)] but not between protocols 2 and 3. Circuit and technique choice should be considered in relation to the specific therapeutic aim of treatment.