But, as Walsh explains, so-called periodic breathing is a phenomenon found exclusively in newborns. In older children and
adults, the pneumogram is used to look for respiratory disturbances such as upper airway obstruction. “And to do that, we need to add more channels,” Walsh says. An airflow channel is needed as well as pulse oximetry. That is when the test becomes known as an oxi-pneumogram, often referred to as a “four-channel recording or oxicardiorespirogram.”
The test is widely employed to diagnose obstructive sleep apnea (OSA). “In older patients we look for sleep-disordered breathing–not sleep disorders, which are neurological–but respiratory disorders that occur at night while the patient is asleep,” Walsh explains. “The four-channel recording includes no EEG or other information about whether the patient is asleep or in what stage of sleep he or she may be. But the characteristic respiratory abnormalities of OSA are simply not found except during sleep,” Walsh says.
In the four-channel recording, airflow is measured by thermistry, that is, by placing a temperature sensor on the upper lip to record the inflow of cool, room temperature air and the outflow of warm, expired air. The technique is indirect, as Walsh points out, and may not be useful if a fan is blowing across the patient’s face or if the room temperature is extremely hot. But it serves well in most instances.
In an older child or adult, Walsh also likes to record body position and tracheal noise. This is the so-called snore channel,
although Walsh prefers the term tracheal noise. “The microphone is taped to the throat close to the trachea. By looking at the tracing, I can’t tell if the patient is talking or snoring–although we assume it is snoring if the patient is reportedly asleep,” Walsh says.
Whatever equipment the practitioner chooses should provide full disclosure raw data. This means the printout contains a complete record of the test session, without censoring or excerpting portions of the recording. “The printout should be indistinguishable from a polysomnogram tracing of those same channels, so when you look at it, you should be looking at waveforms that duplicate the bottom portion of a polysomnogram,” Walsh says.
The four to six channels of an oxipneumogram make up a level III device. According to Walsh, the American Sleep Disorders Association defines four levels of diagnostic devices. While level IV devices are considered screening tools–for example, a pulse oximeter is a level IV device–devices at levels III and above are considered diagnostic. A polysomnogram recorded in a sleep disorders center is considered a level I device. At level III, the four-channel recording is also diagnostic, albeit with a narrower scope. “Most sleep doctors cavalierly refer to four- and six-channel devices as screening devices, but they are not,” Walsh says.
They are, however, controversial. According to Walsh, some respiratory care practitioners involved in sleep testing believe that the diagnostic capability of the oxipneumogram is too limited. The procedure can diagnose only obstructive sleep apnea and central apnea. What if the client is suffering from another disorder? “If the client tells me that he snores–snores loudly–is excessively sleepy during the day, and his spouse reports that he has breathing pauses during the night, I say, if it looks like a duck, walks like a duck, and quacks like a duck…,” Walsh replies. On the other hand, if there is no snoring, or the client is experiencing heartburn, or the spouse is complaining about being kicked during the night, perhaps the client is not sufferng from OSA and should have a full sleep study in a laboratory. Walsh uses an accepted battery of screening questions to identify clients with a high probability of OSA and a low probability of other disorders. Only after they pass the screening does he consider them candidates for a home oxipneumogram.
What if an unattended, four-channel study identifies something other than OSA? “Every program doing these kinds of studies needs to have a close relationship with a sleep laboratory,” Walsh says. “Maybe the client doesn’t have obstructive sleep apnea–you’ve ruled that out–but what if you see another type of disturbance on the tracing? That needs to be followed up.”
Some RCPs also question the practice of conducting unattended studies at home. What if the leads come off? Then the procedure will have to be repeated and this will be inconvenient and unfair to the patient. “My answer to this is simply that the leads don’t come off as frequently as the critics claim,” Walsh says. With his approach, a therapist goes to the home on the test night, makes sure that all the equipment is securely in place, and instructs the patient and family until they are sure they know what to do.
Even before he is willing to schedule an unattended study, however, Walsh screens the client carefully over the phone. Is the prospective patient competent? Coherent? Compliant? “They have to meet what we call the 3 C’s, or we won’t study them at home; we’ll refer them for testing in a lab,” Walsh says. Language difficulties are common, as the hospital is situated in a highly multicultural part of the city. Although Walsh employs a Spanish-speaking therapist to serve the many Spanish-speaking members of the community, he often needs interpreters to communicate with clients who speak Russian, Korean, “and about 12 other languages.”
He also tries to find out whether the client is willing to comply with the procedure. “A lot of people do the study under duress from their spouse. You can bet they won’t be compliant.” He asks potential clients if they wake up in the night. If so, are they oriented. “If someone tells me that they wake up sitting on the side of the bed and for a moment they don’t know where they are, I’ll tell them that we need to test them in a lab. Otherwise, they may drag or pull off the equipment before they realize it,” Walsh says.
But for clients who are good candidates, he believes that the home study has many advantages. Done correctly, it yields data equal to or of better quality than a lab study. It is more comfortable than sleeping in the lab. It is less costly for both the provider and the payor. And for the referring physician, it is quick. “When the doctor calls me, I can have this test done and have an interpreted report in his hands in 24 to 48 hours. I challenge full sleep disorder centers to match that performance,” Walsh says.