The first device to be deployed will be the external respiratory aid. A simplified picture of this device is illustrated in Figure 1.

In the long run, we hope also to be able to incorporate the device within a complete prosthetic lung that will employ no electrical or mechanical parts. A schematic of such a device is illustrated in Figure 2

The Haemair respiratory aid and prosthetic lung.

The unique feature of the Haemair approach is that it is aimed at conscious mobile patients. To this end, we match oxygen and carbon dioxide mass transfer rates to the respiratory demand of the patient. Furthermore, we employ a flow of natural air to provide oxygen and remove carbon dioxide.

There are three main variants of our device. The simplest to employ consists of a mass exchanger, as illustrated in figure 3. It takes deoxygenated blood, extracted from a main vein, removes carbon dioxide, replaces it with oxygen, and returns the oxygenated blood to the body. The second variant places the mass exchanger within the body to eliminate the hazard of taking a significant blood flow outside the body. The final version is a prosthetic lung, as illustrated in figure 2.

In all three variants, mass transfer is controlled so that performance mimics that of natural lungs. In this way, the natural respiratory control mechanism controls heart rate etc, and control is fully integrated with the natural respiratory system.

The external device will be deployed first. It is easily reversible and major parts are available for maintenance. The easy reversibility is important in treating emergency and acute cases for which the device might be needed for no more than hours or weeks. Once we have established that long maintenance-free operation is possible, we can move on to the intermediate device. The clinical procedure to “plumb” the device into the blood circulation system is more complex and maintenance is more difficult. However, the engineering is simpler. The only significant external item required is a small air pump, or fan. This device is more suited to patients who will need it for months – for example, as a bridge to transplant. It should enable patients to leave hospital and continue treatment at home. The final variant, a prosthetic lung, serves as an alternative to a lung transplant. This variant is illustrated in figure 3. It cannot be deployed until we have extensive favourable experience with the reversible devices. However, it offers hope to those currently excluded from transplant waiting lists – for example, most terminal emphysema sufferers.