Category: 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.

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.

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

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

How to simulate the human breathing pattern more accurately.

Humans don’t breathe in standard ways. They are not a pure sine wave, in and out evenly. The inhale may be rapid and then a long slow exhale. Older style breathing simulators cannot achieve this variation, being mechanically driven pistons. With a computer controlled drive system, the wave form can be any shape required. It can be repeated endlessly, on demand.

If true human breathing simulation is required, then recording an human’s actual breathing pattern is required. The machine can then reproduce that recording as required. Again, with a computer controlled, infinitely flexible drive system this can be reproduced on demand.