Teardown: UCL-Ventura CPAP breathing aid

Covid-19 has launched many global engineering groups on projects that aim to reduce the impact of the pandemic. Among those that target healthcare, one of the most successful has been the UCL-Ventura, a continuous positive airway pressure (CPAP) non-invasive breathing aid for hospital patients. At the time of writing, more than 1,100 units had been manufactured and delivered to 46 hospitals across the UK, and deliveries continue.

The Ventura project combines elements that show how this kind of device is best realised in an emergency. Those include skill clustering, product selection, rapid prototyping, data management and – particularly important for a medical device – close alignment with the needs of regulators.

The project was primarily a collaboration between the Mechanical Engineering department and the Institute of Healthcare Engineering at University College London (UCL), University College London Hospitals (UCLH) and Mercedes-AMG High Performance Powertrains. Other partners include Oxford Optronix, which provides oxygen monitors for the CPAP device, and Mashoom, an online data management software suite developed by UCL alumni.

The involvement of Mashoom illustrates the importance of connections. Within UCL itself, the natural links between its medical and engineering sides are strengthened by having a dedicated body for healthcare engineering. Beyond that, UCL’s engineering teams have established connections to Formula 1 (and Mercedes specifically) both personally and through projects such as F1 in Schools. This initiative, where leading teams support UK education, has its central London base at MechSpace, UCL’s recently opened engineering facility in Kings Cross where specification and prototyping of the Ventura took place.

Leveraging the social and physical infrastructure, Ventura’s collaborators were able to move very quickly. The first step on the engineering side was taken at a meeting between UCL’s Professor Tim Baker and two long-standing Mercedes contacts, Andy Cowell and Ben Hodgkinson, on 18 March. Baker outlined that he had been alerted to the need for CPAP aids by colleagues from UCLH.

The first prototype was then delivered just 100 hours later, and clinical trials of the CPAP began at UCLH and sister hospitals on 27 March. On 31 March, the NHS placed the first order for the devices and Mercedes began production on repurposed capacity at its site in Brixworth, Northamptonshire.

Design and specification were thus concentrated at a single site and conducted on a rapid prototyping basis before moving into volume manufacture. The MechSpace work generated 3D models and detailed manufacturing drawings (for this kind of device with its safety demands, traditional techniques rather than baseline 3D printing were seen as necessary).

This data was passed on for manufacturing within Mercedes’ in-house product lifecycle management and precision engineering capabilities, chiefly tailored – appropriately for translation to a medical device –to the extremely tight tolerances demanded in elite motorsport.

The choice of device, though, was also very important. Baker’s medical colleagues, consultant intensivists Professor Mervyn Singer and Dr Dave Brealey, prompted the group to look at the Respironics WhisperFlow, a CPAP already in wide use across the NHS. This had value on multiple levels.

First, the choice meant that Ventura would be largely an exercise in reverse engineering – a global healthcare crisis is hardly a good time to start reinventing the wheel.

Second, while much of the media coverage had focused on ventilators – an invasive form of care that requires sedation – evidence from other countries suggested CPAP could help many Covid-19 patients who needed hospital treatment, often avoiding the need for more extreme measures. Moreover, CPAP devices are simpler to manufacture than ventilators.

A CPAP system pushes a mixture of air and oxygen into the patient’s nose and mask at a continuous rate via a medical mask. A CPAP thus uses positive pressure based on the Venturi effect to keep airways open. Mechanical valves allow medical staff to adjust the pressure level and the air/oxygen mix as appropriate. However unlike a ventilator, a CPAP has no autonomous moving parts.

Third, because the Ventura is based on the WhisperFlow, it has already effectively undergone regulatory approval. The issues facing the UK Medical and Healthcare Products Regulatory Agency were therefore more to do with ensuring that they were signing off on something that met an existing template rather than an entirely new design.

This regulatory issue is one that is arguably being overlooked in the sometimes impatient coverage of how Covid-19 projects are (or are not) coming to fruition, as professor of healthcare engineering Rebecca Shipley, another of the project's lead collaborators and vice dean for health in UCL's Engineering Sciences faculty, explains.

"The MHRA has been under a lot of pressure. It has to make sure that all submissions meet the tightest medical specifications - that's still its job even in an emergency- but it only has so many people qualified to review them. You can't just add people to do something that specialised overnight, and if you submit something new that makes their job even bigger," she says.

"Because you want to get these things into hospitals as quickly as possible, you need to take an approach that simplifies review and approval."

The Ventura design is now available to qualified groups worldwide under an open-source licence (appropriate because this really is the antithesis of a DIY project), and has already gone through a series of revisions and refinements.

To date, 1,800 teams from 105 countries have taken licences and 20 have manufactured their own prototypes to test. Groups that believe they may also qualify can find out more at https://covid19research.uclb.com/

The Ventura team are now looking at areas such as PPE for this type of rapid engineering. 

To license full schematics for the UCL-Ventura CPAP and produce their own units, potential users must apply for an open-source licence.

Key components: UCL-Ventura CPAP

Valve assembly

1. Knob

2. Grub screw

3. Snap ring

4. Valve needle large washer

5. Valve needle small washer

6. Body

7. Valve needle

8. O ring (3x)<''>Exploded view

9. Outlet flow insert

10. Cross drilling bung

11. O ring (3x)

12. Air inlet cover

13. Oxygen adjustment valve assembly

14. Flow adjustment valve assembly

15. On-off valve assembly

16. Oxygen inlet

17. Hypodermic bung assembly

18. Silencer