Patients with Asthma, COPD or other diseases of the lung are often assessed using spirometry. A key parameter is FEV1 (the volume of air that can be forcibly blown out in one second, after full inspiration) and a range of spirometers, varying in complexity from simple peak flow monitors for the home to digital point of care diagnostic machines, have been developed over the years.However, the relationship between inspiratory and expiratory flow is not as obvious as one might think. Patients may struggle more when exhaling than when inhaling for instance.

When trying to match a patient up to a specific inhalation therapy, it is useful to know something about their inspiratory flow capacity. Clement Clarke's excellent In-Check DIAL is used to check the peak inspiratory flow rates that patients can achieve with a range of simulated device resistances so that the care-provider can try to match the patient up with a suitable device.

With such an array of inhalation devices already available and more in development, each with its own bespoke principle of operation, we thought it might be interesting to delve a little bit deeper and look at not just the peak value but the entire inspiratory profile so we designed and built our own wireless digital device.



At the heart of our device is a tiny pressure sensor which monitors the mouthpiece pressure. The resistance of the device is set by varying the diameter of an orifice in the inlet channel. With a known resistance and a pressure reading every few milliseconds we were able to calculate and display the flow rate as it varied throughout the inspiratory maneuver. With a little bit of maths we were also able to plot the inhaled volume and even the air power in watts. From these data all sorts of further parameters can be examined. for example the time to peak inspiratory flow may be a vital characteristic; there is a stark difference between how the dose from a peeled blister is released when compared to a capsule for instance.

The device itself is beautifully simple to use. Once fitted with a disposable mouthpiece with a resistance matched to a particular device resistance, a membrane switch is activated and an LED illuminates denoting it is ready to use. The device can be configured to check that some threshold parameters have been achieved providing feedback in real-time via LEDs whilst also saving the data for later analysis.

Surprising insights

We brought the device to DDL to let the 'experts' have a go and the results were pretty interesting. Click here to find out why.


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