A single combined thermal/pressure sensor using polyvinylidene fluoride (PVDF) film is as effective in measuring sleep-disordered breathing events during polysomnography (PSG) as are separate thermal and pressure sensors, according to a new study.
The study by Meir Kryger, Todd Eiken, and Li Qin, published in the journal Sleep and Breathing, involved 60 patients at two different sleep labs. The patients wore a third PVDF airflow sensor in addition to the traditional thermal sensor and pressure sensor. Apnea and hypopnea events were scored by the sleep lab technologists using American Academy of Sleep Medicine (AASM) guidelines with the thermal sensor for apnea and the pressure sensor for hypopnea (scorer 1). The digital PSG data were also forwarded to an outside RPSGT for scoring of respiratory events detected in the PVDF airflow channels (scorer 2). The indices used to calculate apnea severity obtained with the combined PVDF thermal and pressure sensor were equivalent to those obtained using AASM-recommended sensors.
Regarding the clinical implications for these results, the authors posit that there are several key advantages to using a single PVDF sensor for PSGs. “It eliminates patient discomfort from having to wear two sensors, and eliminates the nasal pressure cannula, which, when it becomes dislodged, will not record anything,” says Eiken, a RPSGT who is chief clinical officer at Mays & Associates. “The nasal cannula itself causes a degree of nasal resistance with the cannula inserted into the nose. The nasal pressure transducer creates a waveform that is non-linear to actual airflow, which results in an exaggeration in the number of apnea events. Only one airflow channel is required within the PSG montage instead of two, which makes scoring easier. The elimination of pressure transducers in future home sleep test design may result in smaller devices and less costly devices.”
However, PVDF sensors are not currently approved by the AASM to replace the two separate sensors. PVDF sensors have been in existence for just over 10 years and did not have enough peer-reviewed research for the AASM scoring task force to review prior to making its scoring manual recommendations in 2007, Eiken says. “It is possible that dual airflow sensor requirements may not have even been established if the PVDF airflow timing were just a few years earlier,” Eiken says.
So, at present, use of PVDF sensors in place of two separate thermal and pressure sensors is limited. “An assumption is that as long as the AASM does not recognize and publish any information in its standards regarding PVDF airflow, or the use of a single airflow sensor for both apnea and hypopnea detection, people are hesitant to make that change,” Eiken says. “However, many sleep centers use PVDF airflow sensors in place of the thermistor sensor that is recommended by the AASM. They recognize the sensitivity of the material. It is used extensively in pediatric PSG as the overall tidal volume being generated by infants is less than adults and the PVDF sensors are able to detect and display the reduced airflow.”