Peak flow meters, both mechanical and electronic, have been available to asthma patients for years. A number of inexpensive spirometers that meet ATS-ERS standards are now available for little as $500. Although these spirometers are primarily intended for a doctor’s office and not intended for self-monitoring by asthmatics, a number of even less expensive spirometers intended for personal use have recently appeared on the market.

Additionally, in the last couple of years there have been at least four different university engineering projects to develop a low-cost spirometer, with a goal of costing substantially less than $100 and are intended for self-monitoring or for use in third world countries. Although these could be considered to be demonstration projects, several have the potential to become viable products.

Durability, ease of cleaning and accuracy are the primary goals a low-cost spirometer must meet. Three of the four spirometer projects have developed a simple pneumotachometer based on differential pressure across a tube narrowing or screen that are not only inexpensive, but relatively easy to clean. The other project developed an oscillating fluidic sensor that uses a microphone pickup.

Although the projects have reported that their devices meet ATS-ERS standards for accuracy, I will take this with a grain of salt. In each case accuracy was measured against a calibrated flow rate or a 3-liter calibration syringe. None of the projects have actually compared spirometry results using their device on one or more individuals against spirometry results from standard PFT Lab equipment.

It is also not clear to me whether any consideration to BTPS correction of the measured results is being made. The published technical details on these projects are limited, but I have seen no mention of ambient temperature measurement. Since there are significant differences in air temperature, humidity and viscosity between inhaled and exhaled air this raises further questions about accuracy claims. Of further concern each project seems to be relying on the characteristics of the device itself to maintain accuracy (but since a calibration syringe costs several hundred dollars this appears to be deliberate and in keeping with the design goal of low cost).

One very important aspect of these university projects is the use of smartphones. This keeps cost down because signal processing and analysis is done by software on the smartphone and results then have the potential to be sent automatically either to a doctor’s office or to a central database. Smartphones have a tremendous ability to act as a unifying factor in the process of collecting and transmitting personal health information. 

Although I have doubts about using any of these devices in a Pulmonary Function lab, are they accurate enough for self-monitoring by asthmatics and other pulmonary patients? Maybe they are. Portable peak flow meters have been shown to be inaccurate for decades but that doesn’t seem to have prevented their widespread use. For peak flow meters, physicians have stressed that patients need to utilize a peak flow diary and learn for themselves where their danger levels are.

Strictly speaking, precision, the ability to repeatedly produce the same results, is more important than accuracy. Since changes in FEV1 over time are critical when monitoring asthma what’s going to matter with a low cost personal spirometer is whether or not it can produce results that are reproducibly stable over long periods of time. This, unfortunately, is exactly what low-cost personal spirometers have not yet demonstrated. This is not to say they can’t, just that it hasn’t been shown.

Personal spirometers also haven’t been around long enough to demonstrate durability. The sensing element it self may be durable and easy to clean but the electronic components may not be. Still, when produced in sufficient quantity they may be inexpensive enough to be considered semi-disposable.

Good quality spirometry requires more than just an accurate spirometer. The fun part and the hard part of being a pulmonary function technician is getting patients to perform tests correctly More than one of the university projects recognized that patients need coaching and developed software that would lead a patient through testing. They have also developed software that recognizes cough, glottal closure and early termination of exhalation.

A variety of medical instruments and applications have been developed for smartphones. Many of these are intended for third-world nations where cell phones are common, but medical care and expertise are not. Medical costs in the United States continue to skyrocket however, and personal medical monitoring devices that work with smartphones may be a way to control costs by reducing office visits and hospitalizations. Many clinics already have contracts with HMO’s and other insurers that pay them to keep patients out of the hospital. For this reason alone I would suggest that personal spirometers will need to be embraced, not avoided.

Although presently they may make sense for motivated patients that want to be more involved in their own care, for the time being I would have to say that personal spirometers are not quite ready for prime time. Broader adoption will have to wait until the manufacturers of personal spirometers, oximeters, blood pressure monitors, glucose monitors, thermometers and other personal health care monitoring devices (yes, bathroom scales should be included too) adopt a common smartphone (bluetooth?) interface. As importantly, doctor’s offices, clinics and hospitals will need software to manage this personal health information.

In the long run routine the use of personal spirometers will probably reduce the amount of spirometry performed in hospital clinics and doctor’s offices. This is not because routine spirometry will not continue to be performed during office and clinic visits. Spirometry will still likely be necessary in order to verify a patient’s personal spirometer results but there will likely be fewer patient visits and more managing patient care remotely.

Pulmonary labs should involve themselves in teaching and validating personal spirometer use by their patients. Pulmonary function labs that depend on clinic spirometry for a significant part of their workload should consider placing more reliance of tests that cannot be performed remotely (lung volumes, diffusing capacity, HAST, CPET) although this will require the cooperation of ordering physicians.

University Projects:

Low-cost Spirometer

Winner of NBIB 2012 Undergraduate Biomedical Engineering competition in the Technology to Aid Underserved Populations and Individuals with Disabilities category.

Abigail Cohen, Andrew Brimer, Olga Neyman, Braden Eliason, Charles Wu.

Washington University in St. Louis

Fluidic flow sensor

Telespiro

First prize from the Institute of Electrical and Electronics Engineers (IEEE), 2013Engineering Conference on Point of Care Healthcare Technologies in Bangalore, India.

Will Carspecken

Oxford University/Harvard Medical School

Android smartphone 

Mobilespiro

Top Demo Prize First International Workshop on Mobile Systems, Applications and Services for Healthcare.

Third place in the Microsoft Imagine Cup 2011 World Finals

Part of the Scalable Health Initiative at Rice University

Siddhartha Gupta, Peter Chang, Nonso Anyigbo, Ashutosh Sabharwal

Rice University

Pneumotachometer

Android smartphone via bluetooth, remote database

Low-cost Spirometer

David Van Sickle, Jeremy Glynn, Jeremy Schaefer, Andrew Bremer, Andrew Dias

University of Wisconsin at Madison

Fleisch or venturi Pneumotachograph

Project since discontinued, looking for students to continue. 

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