Case study: How accurate low flow pumps help automate diabetes control device
The Profil Institut für Stoffwechselforschung GmbH [institute for metabolic research] is using Watson-Marlow OEM pump technology in a medical device designed to automatically measure and control blood sugar levels in patients suffering from diabetes.
Each of Profil’s ClampArt glucose clamp devices use three Watson-Marlow 400ST/RX pumps. A total of 28 ClampArt devices have already been completed and have been used routinely in clinical practice for more than eight years, resulting in several hundred thousand operating hours without a single pump failure.
Profil is a contract research institute (CRO) that specialises in performing clinical trials on new diabetes medication. One of its core areas is the study of glucose clamps – complex procedures that determine the properties of newly developed insulin preparations.
After administering the blood sugar-lowering medication to a patient, a small amount of blood is continually taken over a period of up to 48 hours to analyse the blood sugar level minute-by-minute. Until recently, such tests had to be conducted manually, making them labour intensive and subject to problems such as inaccuracies and human error.
ClampArt is Profil’s automated glucose clamp solution. After entering a target blood sugar level, known as the clamp level, ClampArt can control and maintain this level by administering glucose automatically. Bedsides measuring glucose concentrations, the method of pumping such small amounts of fluid, both precisely and at very low flow rates, was one of the main engineering challenges to overcome.
Selection dilemma
“The selection of a suitable pump was a big factor in the development of ClampArt,” says Dr Tim Heise, lead scientist and co-founder of Profil. “Initially we experimented with several different pumps that proved unsuitable. The main problem was that glucose clamps operate with very low flow rates of only 7.5 ml/h and consequently with tube diameters of only 0.4 mm.”
None of the pumps tested originally by Profil could provide the precision needed at such low flow rates. Furthermore, the tubes could not withstand the constant, high contact pressure. That is, until the institute made an enquiry with Watson-Marlow.
Watson-Marlow recommended using its 400 series OEM pumps, which have been designed for flow rates of just 0.2 µl/min up to 2 l/min. When combined with a wide selection of pumpheads and control units, pump solutions can be configured to suit specific customer requirements.
Trio of pumps
In ClampArt, a total of three Watson-Marlow 400ST/RX pumps are deployed. The first supplies the body with a sodium chloride and heparin mixture to prevent the blood from clotting, while the second ‘sensor’ pump continually takes a small amount of blood from the patient. This is pumped into a mixing chamber, where it is mixed by the third pump with a haemolysis buffer and transported to the measuring unit so that glucose concentration can be measured.
The solution involved minor customisation as the small tube diameter of 0.4 mm meant the gap between the pumphead rollers and the track was too big. As a result, Watson-Marlow increased the roller sizes in the pumphead, making the gap the ideal size for the tubes used. This solved the problem of high contact pressure and offered longer tube life.
Successful outcome
“Watson-Marlow gave us expert advice during the development process,” confirms Dr Heise. “We are very satisfied with our specially designed pump model because it supplies the low flow rates we require with the highest degree of precision.”
As glucose clamps can last up to 48 hours, the pumps must work reliably. Test patients usually remain at Profil overnight, so the pumps need to operate as quietly as possible. The pumps can also be programmed and controlled individually by means of a separate control line, while in terms of safety they operate at only 12-60V and stop automatically whenever the cover is lifted. This made it easier to obtain CE certification for ClampArt.
“After several years of research and development we have created, with ClampArt, an analysis instrument that has been used successfully in our clinics since 2012. As far as we know, there are no rival products with comparable performance in either Europe or the USA,” concludes Dr Heise.