• We revised our design from the Venturi design, and we now need to decide whether to build a Lilly or Fleisch type spirometer. Both are currently used in commercial models. We are examining the pros and cons of each design and hope to have a basic prototype of each built by the end of the week. Feedback on the design features and construction is welcome as always. Find out more about these spirometer designs here:

Fleisch – http://spirxpert.com/technical2.htm

Lilly – http://spirxpert.com/technical3.htm

• After much consideration, we have decided to pursue Adobe AIR as the platform for our software. We believe that AIR will provide the smoothest path to a highly-functional graphic interface that is capable of displaying all of the data we want. However, AIR does have its disadvantages, including a large RAM requirement and no direct access to USB devices. We are examining the use of the Merapi Project software to acquire our data through a Java application (allowing USB access), but would be interested to hear other alternatives.  Here is our rationale for choosing Adobe AIR over Microsoft Silverlight, Processing, and Java:

Design matrix for software decision

• We are currently working on correlating input voltages with the output of the ZMD 31014. This process will allow us to correlate the data we see on the screen with the differential pressure recorded by the sensor. Our current setup has been giving unexpected data, but we hope to resolve the problems soon.

Info we need

We want to make our product as functional as possible for our customers, so we want to know as much as we can about the operating environment for our spirometer. Information about the following topics would be greatly appreciated!

• What types of cleaning solutions are available or commonly used in your clinics? Ethanol, Cidex, other?
• How much RAM do your computers generally have?
  • We plan on creating a graphically intensive program to show video and animation and are concerned about the capabilities of the users’ computers.
• Do patients tidal breathe through your spirometer prior to forced exhalation or do they place the spirometer to their lips after their max inhalation?
  • If you have used both types of procedures, which do you prefer? Why?
  • We would prefer NOT to have patients tidal breathe through our spirometer to reduce the risk of cross-contamination.
  • Also, we want training videos to portray the use of our spirometer accurately and ensure that it is consistent with most commercial spirometer procedures.

Thanks for your help! Please send any comments or suggestions to  openspirometry@gmail.com, or leave a comment on this post.

There are numerous benefits to using a signal conditioner, including the ability to control the amplification of the sensor using software instead of physical op-amps, minimizing the components on and the size of our circuit board. The signal conditioners can also be calibrated to allow correction for sensor offset and temperature effects. Finally, the signal conditioner incorporates an A/D converter, allowing the output signal to be transmitted in the digital formats of either I2C or SPI. The 31014 signal conditioner produced by ZMD is specially designed for resistive bridge sensors, such as our differential pressure sensor.

The BME design team met with Eric Hoffman and Isaac Wiedmann of ZMD to learn how to connect the 31014 to our existing pressure sensor and how to use the various features of the chip. Isaac also demonstrated a personal project of his that uses a differential pressure sensor to calculate the velocity of a fluid flow through a tube. In his design, a flexible plastic tube has a small constriction where the second pressure is measured, causing a larger differential pressure between the inputs. The team connected this portion of his project to their pressure sensor and expired through the tube. The ZMD software collected the output, and the data was graphed on an Excel worksheet.

Flow-time figure

We’ll add technical details to the long neglected hardware section of the wiki soon. Many thanks to David H, Eric, and Isaac.

In the meantime, we’re turning our focus to the construction of the spirometer body. Once manufactured, we will attach sensor circuitry and correlate the signal output with known air flow rates. After correlation, the spirometer will be able to measure air flows through the tube in units of L/s. The team will then create software that will use this data to calculate air flow vs. volume graphs and important measurements such as FEV1 and FVC.

The team will be giving a poster presentation on May 1st in the UW-Madison Engineering Centers Building from 12-2PM. Please come say hello and check out their prototype; you’ll also be able to check out all the other great student design projects underway this semester.

- J Glynn

Pressure sensor setup

They’ve started preparing for their upcoming mid-semester presentation on the project which will take place Friday afternoon. I hope to post some of the details of the presentation soon afterwards.

Testing differential pressure sensors

Early on I learned some interesting details about each of their backgrounds and interests and have been wanting to introduce them.

Jeremy G grew up in a little town north of Minocqua (the true Northwoods of Wisconsin) surrounded by trees and lakes and, in his words, “not much else.” He studied abroad in Ireland last semester and spends time here on outdoor activities, especially cross-country skiing in the winter.

Jeremy S is a junior from Waterford, WI, interested in bioinstrumentation and medical imaging, who also gets outdoors as he can to hunt and fish.

Andrew D is a junior BME major in the bioinstrumentation track, who’s made it his goal before graduation to finish a Mickey’s scrambler in one sitting.

Andrew Bremer is a junior studying BME at UW-Madison. Outside of school he is an officer in the UW chapter of the Biomedical Engineering Society and also works as a campus tour guide. Born and raised in Madison, he is a true Madisonian – he enjoys Badger sporting events, Babcock ice cream, (the World’s Largest) Bratfest, cheese, Concerts on the Square, hanging out on the Memorial Union Terrace, and all other things that make Madison unique!

Thanks to each of them for their enthusiasm and hard work so far this semester.

Commercial disposable mouthpieces > $1 each

One of the most fun and challenging parts of this project is trying to build creative solutions to problems that are inefficiently solved today by commercial markets – in other words, solutions rooted in a different ethic that presume an abundance of funds.

In the case of the spirometer, nowhere is this more apparent than with the mouthpieces that commercial spirometer companies manufacture to accompany their machines. The majority, if not all, manufacturers sell disposable mouthpieces to minimize the potential of nosocomial contamination. With good reason. We know from studies of SARS, for example, that respiratory equipment can be a vehicle for infection. And some respiratory physicians, like my friend Raj Singh, a chest physician at Apollo Hospital in Chennai and GINA Executive Committee member, have argued that we don’t know enough about how devices used in respiratory practice – spirometers, peak flow meters – might spread disease.

The disposable mouthpiece is obviously a smart way to tackle that, but in many cases companies charge more than a dollar per mouthpiece. 

Yesterday our group spent a while sharing ideas about what kind of mouthpiece we should aim for – disposable or reusable – and ways to get us quickly to a workable solution.

Initially, a reusable mouthpiece that could be easily decontaminated seemed like a good option; after all, you don’t have to invest in manufacturing and distributing mouthpieces. We moved on to thinking about how you would disinfect a reusable mouthpiece and what kind of design would guarantee that cleaning is done (and done thoroughly) after use.

We quickly realized that just as a disposable solution presumes an affordable and available supply of mouthpieces, so does a reusable mouthpiece require a supply of disinfectant material, and of course, the intention to disinfect. We know that in many cases, clinicians in low and lower-middle income settings reuse equipment designed to be disposed of, and that, no matter how misguided, there are lots of practical reasons for this (see Mark Nichter and M. Lakshman’s article for a great ethnographic look at the behavior of providers in India around the reuse of  injection paraphernalia).

So yesterday we came up with two main directions, each with a couple of variations, that we could go:

Develop a permanent mouthpiece:

• And a cheap and easy way to disinfect it, or
• A simple and widely available disposable barrier (balloon, condom, plastic bag)

OR

Develop a disposable mouthpiece, that: 

• Can be made from locally available materials (soda bottles, toilet paper rolls) 
• Could be manufactured by local people as a cottage industry
• Deteriorates after use to limit repeat usage

In the end, we opted to go forward with the latter option: Try to develop a very cheap disposable sleeve, made from a material with a limited lifespan. We also decided to try to alert providers and patients to the importance of ensuring that a new sleeve was used by each patient by adding this point to the audiovisual materials we’re developing to guide patients and physicians through the test.

Today we start looking into the cost and type of materials that might work. We’d love feedback on the decision or suggestions about materials we should investigate.