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Breathing Machine

Simulating human breathing

Do you need to simulate human breathing? We have the solution – The Warwick Technology Digital Breathing Machine. Easily integratable into whatever test rig you may already have, the machine can reproduce anything the human lungs can produce. A precision electric actuator can move air to recreate inhalation and exhalation as precisely as required. Simply describe what waveform is required in terms of flowrate over time and the machine will recreate it, accurately and on demand. Need a tweak? The waveform can be instantly adjusted and changed as required.

Used for industrial hygiene testing, academic research, design evaluation, production testing – it has a wide range of applications and users. Click on the website to find out more : http://warwicktech.co.uk

The Digital Breathign Machine annotated

For infomation on recording and reproducing live subject human breathing using the machine, see the following post(s) on our website.

Masks

Is it time to upgrade your face mask?

An update to our previous post: Should I wear a face covering?

By now, many of us have built up a small collection of reusable face masks that we have on rotation. But with the new variant spreading quickly and reports from overseas about higher-grade medical masks being required in some public places, it is time to take stock of what you’re using to cover your face.

Growing concerns about the faster-spreading COVID-19 variants have prompted France to ban certain homemade masks from being worn in public in favour of higher-grade ones, while Germany and Austria now require ‘filtering face piece’ (FFP) masks to be worn on public transport and in shops.

There is no such change here yet, though a BSI Flex Standard is in development which would set a minimum limit on filtration efficiency (i.e. how well the mask blocks particles from escaping).

The advice until now has largely been that for the public, reusable face coverings are a more practical, economical and environmental option than higher-grade medical masks, which are needed by healthcare professionals and are often single-use, and require specialist fitting to be effective.

For now, this advice still stands, though the World Health Organisation (WHO) does advise if you are older or vulnerable to consider wearing a disposable surgical mask in some circumstances.

But if your reusable masks are looking a bit tired and worn, don’t fit well, or only have one or two layers, it’s time to upgrade your personal protective arsenal.

There are big differences between how effective different face coverings are. As a general rule, more layers are better, though you’ll also want to be able to breathe comfortably.

What is an FFP mask and do you need one?

FFP masks are designed to protect the wearer from breathing particles in, as well as filtering exhalations. These masks must comply with British Standard EN149:2001 and be CE marked. FFP masks should be moulded to the face, to create a seal where no air can slip out. They are labelled one, two or three, according to filtration efficiency.

FFP2 and FFP3 masks filter above 94% and 99% of bacteria respectively, so these are the ones being referred to. FFP2 respirators are roughly the equivalent of N95 masks in the US or KN95 respirators in China.

However, they aren’t very practical for everyday use by the public on a global scale, for cost, environment and supply reasons.

They’re mostly single use, so the impact on the environment is significant, and keeping up a regular supply of these will take a toll on your finances too. If there’s a sudden rush to buy these masks, we could be facing similar concerns about lack of PPE for frontline staff as was seen last spring.

The other caution is that these masks really need to be fitted properly to do the job – otherwise air will just escape around the edges (particularly if you have any facial hair).

Reusable masks can have highly effective filtration

The French ban on homemade face coverings applies to ‘fabric masks with lesser filtering qualities’ of around 70%.

The worst offenders are the single-layer stretchy masks.

The face coverings that were rated highest for filtration are able to block more than 99% of bacterial particles penetrating the mask material.

It should be noted that coronavirus particles can be much smaller (as little as 0.1 micrometre in diameter), but measuring bacterial filtration efficiency is the standard test for products of this type and gives an idea of how well face coverings provide a barrier for particles generally, using bacteria as a proxy.

Upgrading your face covering

There are several options for improving how effective your face covering is:

New mask, more layers – opt for a mask with either two layers and a filter pocket or three layers. Make sure it fits your face snugly. If you have a larger or smaller face, look for a mask that has several size options or adjustable straps for a closer fit.

Additional layers – if you have an unused filter pocket, you can either buy some disposable filters, or try using kitchen roll or coffee filters, both of which add another layer of filtration to your mask.

Read more at the Which magazine website

Breathing Machine

Recording human breathing for reproduction (part 2)

Manipulating recorded human breathing for reproduction

When recording human breathing for accurate simulation requires consideration of gaseous exchange. The strict volumes of inspiration and expiration may not match. This is a problem for any breathing machine that tries to accurately replicate human breathing. With no way to create this small imbalance between inhalation and exhalation, the piston extremes of reciprocation gradually move along the cylinder until and end wall is reached and the movement is restricted.

To solve this issue with the Digital Breathing machine, a software solution is applied to the recorded waveform trace. This calculates the start and end points of the trace and allows it to be tilted to ensure the piston does not ‘creep’ to beyond the limits of the piston stroke. This applies a very small correction to each data point. The overall effect is to make the trace fully reproduceable while minimising the error by spreading it incrementally across the recording.

An image of the correction can be seen below:

Conversion of human breathing traces

The top graph shows a sample human breathing recording. The graph below shows the movement required from the piston to reproduce that flow pattern. In blue is the trace required to reproduce it exactly. As can be seen this will gradually move to outside the operable limits of the cylinder. The yellow trace is the manipulated output, allowing the full reproduction of the waveform trace.

Back to part 1.

Breathing Machine

Recording human breathing for reproduction (part 1)

Recording human breathing for reproduction (part 1)

Reproducing human breathing accurately can be required for a number of reasons in laboratory conditions. This requires a recording method that allows the free movement of airflow while recording that movement. One type of device capable of this is the “screen pneumotachograph”. This uses a small low back pressure screen through which the airflow is passed, back and forth. This produces a small back pressure across the screen, which can be measured with a differential pressure gauge or manometer.

A screen pneumotachograph diagram
A screen pneumotachograph

The two halves of the device can be separated and the screen removed for cleaning between test subjects (particularly important at this time). The differential pressure transducer provides a calibrated output that can be read by a computer data acquisition system.

With the Warwick Technology Digital Breathing Machine such a device can be supplied as an option. It takes the form of a screen pneumotachograph coupled with a rack mounting digital differential pressure unit. These are paired together with a UKAS calibration certificate.  The pressure unit can provide signals back through the data acquisition system built in to the machine. Recording and manipulation software is provided with the option.

Part 2

Breathing Machine

Principles of operation of a breathing simulator

Principles of operation of a breathing simulator

A basic overview of a breathing simulator is as follows:

The machine is, at its simplest, a piston moving within a cylinder or a bellows expanding and contracting. This forces air back and forth in the same way as the human lungs do. It requires a reciprocating motion from the piston or bellows face, usually provided by a rotating motor. Some kind of mechanical linkage is used to change the rotary motion of the motor into the reciprocation of the piston or bellows. In order to change the movement of the piston, this linkage must be altered. This requires the machine to be stopped and disassembled or otherwise adjusted mechanically.

The latest generation of breathing simulators (such as the Warwick Technology Digital Breathing Machine) use an electric actuator to provide the reciprocating motion. This uses a stepper motor through a recirculating ball screw to create the linear action. The stepper motor is controlled from a computer, enabling any movement to be performed, and changes to that motion can occur instantaneously. A simple breathing machine can only create sine waves of output flow. An actuator controlled simulator can produce anything required.

Sine wave reproduction graphic
Simple sine wave reproduction
Sneeze simulation reproduction graphic
Simulation of a sneeze – a non-sinusoidal output

The conversion of flow rate required to movement of the piston is all handled by the computer control software. Using a solid piston and cylinder rather than a bellows means there is a rigid conversion of movement of the piston to the movement of the air.

The Warwick Technology Digital Breathing Machine
The Warwick Technology Digital Breathing Machine

Masks

Efficacy of Face Shields Against Cough Aerosol Droplets from…

Efficacy of Face Shields Against Cough Aerosol Droplets from a Cough Simulator

This is a very interesting study undertaken a few years ago into the efficacy of face shields as protection against coughing. This used one of our machines to simulate the inhaling human. We are now looking to develop the existing machines ability to produce the coughing airflow. It could then effectively perform both parts of this test arrangement. The same arrangement could of course be set up to test other forms of face covering – masks etc.

Face mask efficacy test set up diagram

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4734356/

Masks

Mask effectiveness

A video showing researchers in Japan testing masks using the real coronavirus:

Don’t try this at home, folks…