Automatic static pV curves measurement (RM software)

Objective

To develop software capable of managing the ventilator to perform standard pV curve measurement and to test it on a lung model.

Methods

Adult Star (Infrasonics, Inc) ventilator was used for our study. The RM software was created in Visual Basic for Win 95, using software orders from the manufacturer. It is based on occlusion method for pV curve measurements as described by Levy et al., Baseline ventilation is interrupted just for one test breath. Flow and pressures are measured from built in single screen Silverman pneumotachometer and proximal pressure transducer. Data are automatically collected in Microsoft Excel file. Our lung model was lung simulator SMS (Sandland manufacturing service Ltd., Harlow-Essex-England).

Protocol

We tested the RM software in four different settings: combination of two compliances (20 and 50 ml/cmH₂O) each with resistances 5 and 20 cmH₂O/l/s. Five pV curves were done for each setting. Ten tidal volumes were applied (100, 200, 300 ...1000 ml) to get one pV curve.

Results

Regression analysis was performed for each pV curve. Mechanical properties of our lung model implies the use of non-linear regression: Vt = A × p × sin (B × p+C) +D, where A, B, C, D are the regression parameters, however for mathematical simplicity we used linear regression Vt = A × p +B. The correlation coefficient and A, B parameters were pooled from each settings measurement and mean ± SD were calculated:

Our results showed little variability for each setting. Resistance didn't affect the measurement of compliance as was expected.

Conclusion

RM software for PC is reliable on repetitive measurements and precise enough to measure static pV curves in a lung model with tidal volumes exceeding 150 ml. Further validation with independent pneumotachometer and pressure transducer is necessary. Thereafter RM software probably can be used in clinical settings.

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