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  • This episode of Real Engineering is brought to you by Brilliant, a problem solving website

  • that teaches you to think like an engineer.

  • This subject needs no introduction. The entire world is talking about the same thing. Covid-19

  • has turned the world upside down in just a couple of weeks, and the human race is scrambling

  • to adapt to this new pandemic.

  • Covid-19 is racing through populations. For many the symptoms are mild, for others the

  • virus debilitates them. Their lungs' ability to transfer carbon dioxide and oxygen in and

  • out of the blood begins to fall. Each breath becomes more laboured, until eventually they

  • become too exhausted to breathe on their own. [1]

  • The patients that are presenting to hospitals with these symptoms need medical intervention

  • before they suffocate. Unfortunately we do not have a cure. The best medical treatment

  • currently is to simply assist their lung function with mechanical ventilation. But, hospitals

  • are experiencing such huge influxes of patients that they do not have enough ventilators to

  • cope.

  • This has led to a call out to any and all capable of manufacturing ventilators to join

  • the fight against this common enemy.

  • Medtronic, a company I have worked for in the past, has it's primary ventilator manufacturing

  • facility based in my hometown of Galway. [2]Here they produce this ventilator. The Puritan

  • Bennett 980 Mechanical Ventilator. A top of the line high performance ventilator that

  • would give doctors a huge leg up in combating the viral pneumonia that patients are experiencing,

  • but it's a complicated bit of machinery.

  • They currently produce 225 units a week and are pulling employees from the stent manufacturing

  • facility I worked at, to help boost production to 500 a week.

  • This however won't come even close to fulfilling the demand that is yet to peak. There is this

  • impending doom looming over us that soon hospitals in countries like the US will experience what

  • Italy has already experienced. An overwhelming flood of patients.

  • So many enthusiastic engineers who want to help out are volunteering their expertise

  • to develop a low cost ventilator that any manufacturing facility could adapt to build.

  • Every single design I have come across centres around one key bit of technology. A BVM, or

  • bag valve mask. BVM are plastic bags that a clinical care practitioner can manually

  • deflate with their hands. It's what a first responder would use if a patient wasn't

  • breathing, instead of giving mouth to mouth resuscitation. It's a cheap and easy way

  • to force air into the lungs. All these designs are basically just robotic arms that can squeeze

  • this bag at a set frequency endlessly.

  • They of course could be manufactured quickly and in great numbers, but ventilators aren't

  • just air pumps that force air into a patient's lungs.

  • One of the primary problems facing doctors currently is managing a side effect of mechanical

  • ventilation, barotrauma. [3]

  • To understand this we first need to understand how the lungs operate under normal conditions,

  • so let's have a quick biomechanics class on breathing with our sister channel Real

  • Science.

  • Two muscle groups typically act to control breathing. [4] The diaphragm, which is a large

  • muscle which separates the abdomen from the chest, and the intercostal muscles which are

  • the muscles which reside between the bones of your rib cage.

  • When you breathe in your diaphragm contracts, which causes it to move toward the abdominal

  • cavity, while the external intercostal muscles between the ribs also contract which lifts

  • the rib cage outwards. Both of these actions increase the volume of the thoracic cavity,

  • the cavity that your lungs reside in. The increase in volume causes a corresponding

  • decrease in pressure, which allows air outside the body at atmospheric pressure to fill the

  • lungs and equalise the pressure.

  • The key thing to note here is that negative pressure drives inhalation. The lungs don't

  • inflate like a balloon. They expand and equalize with atmospheric pressure. On exhalation the

  • process reverses with a small spike above atmospheric pressure to push the air out again.

  • Mechanical ventilation cannot work like this. It has to force air into the lungs from the

  • outside and essentially blow the lungs up like a balloon. If this is not tightly controlled

  • the air pressure could work against the diaphragm and the intercostal muscles and end up increasing

  • the pressure in the alveoli above their typical max pressure.

  • The alveoli are tiny thin air sacs in the lung that are in contact with blood vessels

  • to allow oxygen and carbon dioxide to diffuse between the blood and the lungs. To do this

  • they have to be extremely thin and because of that they are very delicate pieces of tissue.

  • Over expanding them will lead to inflammation at best or rupture at worst. This is what

  • barotrauma is. [5]

  • To make this worse, those suffering from acute respiratory distress syndrome, like those

  • affected by Covid-19, are more at risk of suffering from this side effect of mechanical

  • ventilation [6], as the alveoli that are filled with fluid prevent air from entering them,

  • causing the pressure to elevate even higher in the functioning alveoli. The last thing

  • we want to do is damage the healthy tissue of a patient suffering from damaged lung tissue.

  • That is the opposite of helping.

  • To avoid this doctors need to carefully choose their settings on a ventilator. The primary

  • guidance for this is to limit the volume and pressure of air entering the lungs. [7]

  • So, any low cost ventilator will need a method to control these settings. Designs like this

  • one, which can only vary it's volume output, as far as I can tell, by connecting the push

  • rod closer to the centre of rotation of the cam. There is no variable control here. This

  • device would likely do more harm than good. The designer's heart is ofcourse in the right

  • place, but if a YouTuber can spend a day reading a ventilator design book, so can they.

  • However, my patience goes to zero for massive multi-million dollar companies like Virgin

  • Orbit, who present these designs as their own. Who clearly have done zero research into

  • what is needed from a ventilator and just built something as quickly as possible to

  • get some positive PR for their company. Look, they even had time to put a big sign behind

  • them for the video.

  • As far as I can tell, the earliest design that proposed using these BVM was from an

  • MIT student project in 2010. This paper has been online that entire time and if people

  • are truly copying it, they are leaving out some clever design ideas that make it more

  • functional. [8]

  • Their design included a spirometer, which measures the air flow rate out of the BVM,

  • by integrating this value they can calculate the volume of air delivered.

  • This then feeds into a controller which can vary how tightly the BVM was squeezed to change

  • the volume of air delivered. This gave the device a nice range of tidal volumes ranging

  • from 200 milliliters to 750.

  • This is a better design, and may be useful in a do or die situation. But, it is not perfect.

  • The breaths per minute controller is simply set on a time based frequency, ranging from

  • 5 to 30 breaths per minute.

  • This is called a mandatory breath. It's entirely determined by the machine. You will

  • take a breath whether you like it or not. This would obviously be uncomfortable and

  • requires the patient to be heavily sedated to the point of paralysis, but it can also

  • exacerbate barotrauma if the patient's diaphragm and intercostal muscles are resisting the

  • inhalation.

  • High performance ventilators can work like this, but they typically don't. Their breath

  • sequences are normally triggered by the patient. They are still able to breathe. They just

  • need help because they are exhausting themselves with the effort. In order to do this the machine

  • needs some way of triggering the breath cycle and ending it too, based on observations of

  • the patient. This can be done in a number of ways.

  • It can be pressure triggered, where a sensor detects a drop in airway pressure indicating

  • the thoracic cavity is expanding. It can be flow triggered, where a sensor detects airflow

  • into the lungs, or it can be triggered by a sensor detecting electrical activity of

  • the diaphragm, indicating that the diaphragm is contracting to expand the thoracic cavity.

  • This also requires very fast microprocessors to detect and react to the triggers.

  • I have seen no low cost ventilators incorporating this vital component of ventilator design.

  • And it truly is a vital component.

  • A very difficult part of the ventilation process is weaning people off it again. A ventilator

  • which requires someone to be sedated to the point of paralysis makes it very difficult

  • to get them breathing naturally on their own again.

  • There are a multitude of other design considerations to be made with ventilators.

  • I studied biomedical engineering, and there is a heavy emphasis on medical subjects like

  • surgical practice”, many of which are taught by doctors, not engineers. The first

  • thing those doctors taught us is to start your design by speaking to the end user, the

  • doctors. I spoke with Rohin Francis, a doctor who runs the fantastic Midlife Crisis channel,

  • to get a better understanding of some of the other things we engineers need to remember

  • when designing these machines.

  • Thanks Brian. As you've already heard, COVID-19 patients frequently develop an acute respiratory

  • distress-like syndrome, or ARDS, which not only fills the alveoli with fluid, making

  • gas exchange harder, but also increases the likelihood of the alveoli collapsing shut

  • at the end of every breath out. This is because diseased areas of the lung don't produce

  • surfactant normally. Pulmonary surfactant is a clever substance produced by alveolar

  • cells which coats their inner surface and one of its key jobs is keeping these tiny

  • sacs open when the lungs are deflated, which is what happens in healthy lungs. But in ARDS,

  • when you breathe out, those alveoli collapse shut and sometimes whole sections of the lung

  • collapse, called atelectasis. Trying to force them open with every breath requires more

  • pressure and hugely increases the risk of barotrauma.

  • So, we use positive end-expiratory pressure or PEEP, to try to prevent this. I usually

  • explain this by saying imagine you've got your head out of the window of a fast-moving

  • car with your mouth open, don't do this by the way, in addition to all the insects,

  • you also have a constant air pressure exerted on your airway, making it ever so slightly

  • harder to breathe out. That's PEEP. PEEP is a constant positive pressure that prevents

  • those alveoli collapsing at the end of each breath and also helps open up - or recruit

  • - collapsed areas of the lung.

  • In COVID-19 we are seeing patients requiring very high levels and tight control of PEEP

  • to maintain their oxygen levels and protect the lungs and this is something that a basic

  • bag-squeezing vent cannot really achieve. From the mechanisms I've seen so far, I'd

  • be concerned about the possibility of baro and/or volu-trauma.

  • Most of these patients are on a ventilator for a few weeks at the moment. A basic bag-squeezer

  • might be adequate for the first day or so when a patient is deeply sedated, but simply

  • won't work as you try to ease off the sedatives. Additionally, your upper airways warm and

  • humidify air entering the lungs, but they are taken out of the equation by the endotracheal

  • tube which goes directly into the lower airways. Without the warming and humidifying features

  • of modern ventilators, lung tissue will get rapidly damaged.

  • This isn't even a ventilator, it's an anesthetic machine. Because the ventilators

  • I was going to film with are in use right now, and even this big thing can only provide

  • very basic ventilation.

  • And while we do need more ventilators, what's even more valuable are the intensive care

  • nurses and respiratory therapists to work them, but they take significantly longer to

  • produce.

  • So, as you can probably tell, there is a lot more to ventilation than just pumping air

  • into a patient. Tight regulation of Pressure, volume, , oxygen percentage control and humidification

  • would all require more complicated mechanics than these simply BVM pumps. Designing a ventilator

  • fit for purpose with cheap and easy to manufacture components is a difficult job, but I'm positive

  • a viable product will come to light soon. Especially as this is not a new problem. Poorer

  • countries have been struggling