About 10 years ago, my medical director came into my office and asked me to try out a home monitoring device to screen for sleep apnea.

It was a large vest that adjusted across your chest with a giant Velcro strap. It had a pocket where you placed the recorder and monitored heart rate and SpO₂via a pulse oximeter and a thermistor for oro-nasal airflow. Additionally, a snore sensor taped onto your neck monitored snoring. As this was a "one-size-fits-all" device, there was quite a lot of Velcro material that did not fit snugly around my 170 pound frame.

The next morning, I returned the device to the physician and we downloaded the software and took a look at my study. The results showed data were abruptly lost at 2:30 a.m. When the doctor asked why the test stopped at that time, I replied, "That was the part of the night when I rolled over and I got stuck."

"You got stuck?" he inquired.

"Yeah," I replied. "I rolled over and Velcroed myself to my flannel sheets. I couldn't move so I had to rip the thing off and slide out through the bottom."

The sleep field has come a long way since then. We have improved the availability to acquire more data and do so in a more precise and accurate manner. We have replaced Piezo-crystal bands with RIP belts or thoracic EMG leads to get chest wall excursions recorded. We have augmented the PTAF with the oral thermistor to better capture nasal and oral flow. And we have added additional leads to better capture delta wave activity from their point of origin from the brain.

With these improved methods and advances in technology, we finally have the tools to take obstructive sleep apnea testing out of the lab and into the home.

Choosing a device

Devices in the home market available for sleep testing are divided into four groups depending on how many channels of information they obtain and which parameters they measure. Depending on your budget and needs, you can have as many as seven or more channels (Type II) or as few as three (Type IV). While some Type IV devices operate with less than three channels, the American Academy of Sleep Medicine guidelines requires three channels at a minimum. The more channels that you can run in the home environment, the closer you are to obtaining a full range of sleep data.

When evaluating for purchase, cost is always a factor, but durability of the equipment in the home setting has to be a primary focus. Amplifiers and recording equipment are notoriously sensitive by their nature and a "heavy duty" home device needs to be able to withstand and sustain accuracy through multiple tests and possible abuse by the patient.

Also of concern is the potential of "missing" events and yielding a false negative test. In one study, a 19 percent failure rate was identified utilizing SpO₂ tonometry, and actigraphy.¹With an unattended interface, you still need to reduce artifact and movement data as much as possible.

Another dimension

Cardio-pulmonary coupling (CPC) technology can add another dimension to home sleep testing. CPC works under the premise that ECG obtained via a modified lead II placement will pick up the respiratory patterns and the associated bradycardia/tachycardia events associated with the apnea/arousal response. By linking the respiratory and cardiac data together in an algorithm, you combine both signals to measure the coupling between respiration and heart variations.

By plotting out those relationships, you can get some fairly accurate assessments of the breathing patterns at night and the types of events causing them. The limiting variable is the heart rate. It must remain constant without a lot of ectopy as that will artificially skew the interpretation.

Patients with a known arrhythmia, like atrial fibrillation, may not be able to utilize the device, but it holds great promise for many as a self-administered tool in the near future. Much like a glucose meter on the shelf at your local pharmacy, it may soon be possible to pick up a device like this and bring it to your local physician for follow-up.

Take up the challenge

Whichever technology is utilized in the home testing environment, the data needs to be acquired and interpreted in a standard fashion that can be replicated in the lab to remove doubt as to the validity of the information obtained.

Home systems are not foolproof, but they can be used reliably when they are administered by a trained sleep technologist and interpreted by a physician. The advancement of more simplified devices where patients do not have a nest of wires to apply will elevate the field to a higher level and demonstrate the commitment to care.

In the current health care climate, this adaptive behavior also will show our proactive approach to helping contain costs as well as using advances in the field to ultimately stimulate more volume into the labs and most importantly, give treatment and hope to the millions of people who suffer from OSA.

As leaders in the field of sleep medicine, we want to stay at the head of the pack. Let's take up the challenge to utilize the tools we have to reach the masses in a responsible and reliable manner.

Reference

1. Penzel T, Kesper K, Pinnow I, Becker HF, Vogelmeier C. Peripheral arterial tonometry, oximetry and actigraphy for ambulatory recording of sleep apnea. Physiol Meas. 2004;25(4):1025-36.

Stephen Tarnoczy, BS, RRT, RPSGT, is a respiratory care instructor at Apollo College in Las Vegas.