Effect of chest wall vibration timing on peak expiratory ﬂow and inspiratory pressure in a mechanically ventilated lung model

Shannon, H.; Stiger, R.; Gregson, R.K.; Stocks, J.; Main, E.

doi:10.1016/j.physio.2010.02.007

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Volume 96, Issue 4 , Pages 344-349, December 2010

Effect of chest wall vibration timing on peak expiratory ﬂow and inspiratory pressure in a mechanically ventilated lung model

H. Shannon
- Portex Unit: Respiratory Physiology and Physiotherapy, UCL Institute of Child Health, London, UK
- Great Ormond Street Hospital for Children NHS Trust, London, UK
- Correspondence: Portex Unit: Respiratory Physiology and Physiotherapy, UCL Institute of Child Health, 30 Guilford Street, London WC1N 1EH, UK. Tel.: +44 0 207 242 9789x2689; fax: +44 0 207 829 8634.
R. Stiger
- Portex Unit: Respiratory Physiology and Physiotherapy, UCL Institute of Child Health, London, UK
- University Hospitals of North Staffordshire NHS Trust, Stoke on Trent, UK
R.K. Gregson
- Portex Unit: Respiratory Physiology and Physiotherapy, UCL Institute of Child Health, London, UK
- Great Ormond Street Hospital for Children NHS Trust, London, UK
- University of Southampton with Southampton University Hospitals NHS Trust, Southampton, UK
J. Stocks
- Portex Unit: Respiratory Physiology and Physiotherapy, UCL Institute of Child Health, London, UK
E. Main
- Portex Unit: Respiratory Physiology and Physiotherapy, UCL Institute of Child Health, London, UK

published online 22 April 2010.

Abstract

Objective

To investigate the effects of chest wall vibration timing on air flow and pressure in a ventilated lung model.

Design

Laboratory-based bench study.

Participants

Thirty physiotherapists with experience in intensive care.

Intervention

Physiotherapists applied three sets of eight chest wall vibrations to an intubated, mechanically ventilated mannequin. Vibrations were applied at the start of expiration (optimal), mid to late inspiration (early) and early to mid expiration (late). Air flow, peak pressure and volume were measured continuously. Forces applied during vibrations were recorded using a force-sensing mat, placed under the physiotherapists’ hands.

Results

During optimal and early vibrations, peak expiratory flow increased significantly compared with baseline ventilation [mean difference for optimal vibrations 8.8l/minute, 95% confidence interval (CI) 6.0 to 11.6; mean difference for early vibrations 7.0l/minute, 95% CI 4.3 to 9.9]. Late vibrations did not enhance expiratory flow. Peak inspiratory pressure was significantly higher during early vibrations compared with baseline values (mean difference 5.6cmH₂O, 95% CI 2.9 to 8.2). Peak inspiratory pressure generated during early vibrations was, on average, 8.4cmH₂O greater than with optimal timing.

Conclusion

The safety and effectiveness of respiratory physiotherapy treatments are likely to be influenced by the timing of vibrations within the breath cycle. Early vibrations generate potentially dangerous peak inspiratory pressures. Late vibrations, although not harmful, are not effective at increasing peak expiratory flow. This is an important consideration when training physiotherapists and evaluating outcomes of treatments in intensive care.

Keywords: Physiotherapy (techniques), Respiration, Artificial and critical care, Vibration