Although it is true that the Hayek RTX Respirator uses a cuirass, it would not be accurate to describe the method of ventilation it uses as negative pressure, as the old cuirass ventilators were categorized.
Negative pressure ventilators - While the tank (iron lung) negative pressure ventilators (NPV) provided complete ventilation in some patients with normal lungs (polio, neuromuscular etc.), cuirass NPV per definition could only augment ventilation and could not provide complete ventilation. The reason for this was that whilst the inspiratory phase was active, the passive expiratory phase required time to recoil limiting frequency to most often no more than 30 cycles per minute. As the tidal volume by the cuirass is also limited, minute ventilation (tidal volume x frequency) was low and unable to provide complete ventilation. Furthermore NPV is known to aggrevate heart failure. For these reasons positive pressure replaced it as the preferred method of ventilation.
The Hayek RTX's method of ventilation is Biphasic Cuirass Ventilation (BCV) and works by controlling both the inspiratory and expiratory phases of the respiratory cycle. The Hayek RTX has frequencies ranging from 6 to 1200 cycles per minute, allowing it to also ventilate at high frequency.
As it is Biphasic it is possible to achieve both higher tidal volumes (the sum of the negative inspiratory tidal volume and positive expiratory tidal volume) as well as higher frequencies. Both of these allow for a much higher minute ventilation to be created thus it is often able to provide complete ventilation with normal and sick lungs. The Hayek RTX has managed to overcome many of the drawbacks of negative pressure ventilation. Furthermore, unlike the old negative pressure machines BCV has been shown in clinical studies, to increase cardiac output.
A further advantage in the Hayek RTX is its patented cuirass and seal system, which combines flexibility, strength and softness to provide more effective and comfortable ventilation to the patient than other cuirass predecessors which on the whole were much more rigid.