Biphasic cuirass ventilation
Biphasic cuirass ventilation (BCV) is a method of ventilation which requires the patient to wear an upper body shell or cuirass, so named after the body armor worn by medieval soldiers. The ventilation is biphasic because the cuirass is attached to a pump which actively controls both the inspiratory and expiratory phases of the respiratory cycle. This method is a modern improvement of 'Negative Pressure Ventilation' (NPV), which could only control inspiratory breathing, relying on passive recoil for exhalation. Biphasic Cuirass Ventilation's Secretion Clearance modality has also been termed 'External Chest Wall Oscillation' (ECWO), 'High Frequency Chest Wall Oscillation' (HFCWO), and 'External High Frequency Oscillation' (EHFO). BCV may be considered a refinement of the iron lung ventilator. Biphasic cuirass ventilation was developed by the late Dr Zamir Hayek, a pioneer in the field of assisted ventilation. Some of Dr Hayek's previous inventions include the Hayek Oscillator, an early form of the technology.
As the ventilation provided by the cuirass is biphasic, it is possible to achieve both large breaths (tidal volumes) and a high respiratory rate (from 6 to 1200 breaths per minute). The biphasic function allows control over the I:E ratio, which is the ratio between the time allowed for inspiration (pumping air out of the cuirass and creating a negative pressure around the chest) and expiration (pumping air into the cuirass and creating an increase in pressure around the chest.) Most other types of ventilation depend on the passive recoil of the patient's chest, which limits the respiratory rate.
BCV has been successfully used on patients with:
- Acute respiratory failure
- Chronic obstructive pulmonary disease (COPD)
- Neuromuscular (e.g., SMA, Duchennes, etc.)
- Head and spinal injuries
- Problems with weaning from positive pressure ventilation (PPV)
- Ventilation during anesthesia in ear, nose, and throat (ENT) procedures
- Cystic fibrosis (CF), and those who require physiotherapy
- AIDS related lung disease
- Ventilation post-operation (e.g., post-coronary bypass, Fontan, Fallot, post-pneumonectomy)
- Ondine's curse
BCV is non-invasive and therefore avoids some of the problems associated with invasive ventilation such as infection and barotrauma. Unlike intermittent positive pressure ventilation (IPPV), BCV is active in both the inspiratory and expiratory phases (biphasic). This allows greater control over the tidal volumes and respiratory rate. BCV may also help to maintain and redevelop the respiratory muscles which may weaken with respiratory failure and mechanical ventilation, this allows patients to be weaned from a ventilator. BCV also does not impair cardiac function, as IPPV does. BCV is often used as an aid in patients with poor cardiac output.
Unlike conventional negative pressure ventilation, biphasic cuirass ventilation is able to quickly reduce any harmful buildup of CO2 using its active expiratory phase. Many published papers and case studies now show how effective BCV is at reducing CO2 buildup. It has also now been shown that the most effective ventilation frequency to reduce CO2 when using BCV is 60 cycles per minute. The oscillations caused by BCV assist in the removal of secretions which are a symptom of many respiratory diseases. Lastly, because BCV does not require the patient to be intubated or to have a tracheostomy, patients can have BCV at home.
BCV has limited effect on patients who suffer from extreme obesity. BCV requires patients to maintain their own patent airway (patients with Obstructive Sleep Apnea may require additional assistance from positive pressure ventilation to open the airway). BCV should not be used on open wounds or burn victims.
See also 
- "The future of respiratory technology". Medivent International. Retrieved 2008-07-15. "The RTX Respirator has frequencies ranging from 6 to 1200 cycles per minute, allowing it to also ventilate at high frequency"
- Lockhat D., Langleben D. and Zidulka A. (1992). "Hemodynamic differences between continual positive and two types of negative pressure ventilation.". American Review of Respiratory Disease 148: 677–80.
- Broomhead C. J., Dilkes M. G. and Monks P.S. (1995). "Use of the Hayek oscillator in a case of failed fibreoptic intubation". British Journal of Anaesthesia 74 (6): 720–1. doi:10.1093/bja/74.6.720. PMID 7640134.
- Dilkes M.G., McNeill J.M., Hill A.C., Monks P.S., McKelvie P. and Hollamby R.G. (1993). "Use of the Hayek oscillator in a case of failed fibreoptic intubation". Annals of Otology, Rhinology and Laryngology 102: 455–8.
- Penny D., Hayek Z. and Redington A. (1991). "The Effects of Positive and Negative Extrathoracic Pressure Ventilation on Pulmonary Blood Flow after Total Cavolpulmonary Shunt Procedure". International Journal of Cardiology 30 (1): 128–30. doi:10.1016/0167-5273(91)90137-E. PMID 1991664.
- Shekerdemian L.S., Bush A., Lincoln C., Shore D.F., Petros A.J. and Redington A.N. (1997). "Cardiopulmonary interactions in healthy children and children after simple cardiac surgery: the effects of positive and negative pressure ventilation". Heart 78 (6): 587–93. PMC 1892328. PMID 9470877.