Patients with suspected obstructive sleep apnea (OSA) may no longer have to spend an expensive and uncomfortable night at a sleep center to monitor their sleep-disordered breathing. Researchers at the Philadelphia VA Medical Center have shown that patients fare just as well using portable home monitors to detect OSA, according to a study presented at the recent American Thoracic Society (ATS) annual meeting in New Orleans.
"There is a large interest right now in the cardiovascular consequences of OSA," lead author Sam Kuna, MD, chief of the pulmonary, critical care and sleep section at the Philadelphia VA, told Cardiovascular Business News. "There is a number of cross-sectional and longitudinal studies regarding the link between sleep apnea and cardiovascular events, and several observational studies that report treatment of sleep apnea patients with continuous positive airway pressure (CPAP) reduces that risk compared to a controlled population."
The link between sleep apnea and cardiac disorders has been the intermittent oxygen desaturation associated with the shallow breathing during sleep, Kuna said. "This is felt to be the mediator of the increase in sympathetic drive and other factors that lead to the cardiac problems."
The National Institutes of Health recently issued a request for applications to develop further evidence of the link between OSA and cardiovascular disease, looking at the effect of CPAP treatment on intermediate markers (high blood pressure, pro-inflammatory biomarkers and increased sympathetic activity) of cardiovascular risk. "That pilot study is to prepare for a larger clinical trial looking at effective CPAP treatment in the U.S.," Kuna said. "To date, several small studies have shown that intervention with CPAP leads to a reduction in these cardiovascular surrogate markers.
" Kuna's own study presented at ATS was an effort to validate what he and colleagues had already experienced. "It was our clinical impression that there was no difference between the two approaches in-laboratory and at-home sleep testing and we were very gratified the study supported those findings."
In the study, Kuna et al randomized nearly 300 patients to undergo either standard in-lab sleep-testing or at-home testing. Of the 223 patients who started CPAP treatment after evaluation, 185 completed three months of follow up.
Researchers found that those who had undergone at-home testing showed improvements after three months of CPAP treatment similar to those who had undergone in-lab diagnosis.
"Proponents of in-laboratory testing argue that patients performing in-lab testing might have better outcomes than those performing home testing. For example, during in-lab testing, the patient spends a greater amount of time with a technologist who is able to educate the patient about OSA and CPAP and help the patient overcome any barriers to diagnosis and treatment that might arise during testing," Kuna said. "But our results did not find a difference between home and in-lab testing in terms of clinical outcomes. The two management pathways appear to be equivalent in terms of patients' functional outcomes and ability to use CPAP treatment."
Kuna's group used a type 3 home monitor (Embletta, Embla Systems). There are four types of systems in use:
- Type 1 is the standard in-lab monitor. It generally measures these functions: brain (EEG), heart rhythm (EKG), eye movement, muscle activity, respiratory airflow and pulse oximetry (oxygen desaturation).
- Type 2 has similar functions to the standard lab monitor, but is for home use.
- Type 3 just measures respiratory signals and excludes the EEG that would allow the determination of whether the patient is awake or asleep.
- Type 4 is even more reduced in its recording. It has one or more channels, usually including pulse oximetry.
Medicare reimburses for home monitor use (total Medicare reimbursement in the Philadelphia area is about $250), but requires the type 4 monitor to have at least three channels. At the Philadelphia VA, a respiratory therapist instructs patients how to use the home monitors. Patients apply the sensors before going to sleep and mail the devices back to the VA the next morning. Models exist that allow the transfer of data into a computer via a USB port to then be sent to the hospital via email.
Kuna chose a type 3 monitor for the study because he wanted the monitor to be able to detect whether the sleep apnea was due to obstructive phenomenon or was central apnea, a type caused by the brain signaling to stop breathing rather than throat obstruction. For OSA, the belt around the chest of the type 3 monitor measures the cessation of airflow, along with persistent respiratory efforts. Likewise, with central apnea, the monitor records the cessation of airflow, along with no movement of the chest wall.
"Central apnea is more associated with chronic heart failure and some of these patients will respond to CPAP or to supplemental oxygen, and some will not. That leads me to suggest that there are different mechanisms involved in OSA and central," Kuna said.
With the success of home testing, will the sleep lab become extinct? Not so fast, said Kuna. The sleep lab will remain an integral part of apnea testing for several reasons. Not everyone can be tested at home and home studies are "reduced" studies, which may need confirmation in the lab. In the present study, Kuna and colleagues retested everyone in the lab who had a negative home test. They found some false negatives and are still analyzing the data to determine the reasons.
"As you increase the application of the portable monitors to a wider population, you will potentially have more negative studies coming back from the home. Again, in symptomatic patients, you will need to have additional evaluation to feel confident you haven't missed anything. If portable monitors really take off, it will just bring more people into the sleep lab," he said.
Kuna and at least one cardiologist do not think there will be turf battles regarding OSA testing. "I would not consider sending my patients home with a sleep monitor. I leave that up to a qualified sleep specialist, whether he or she wants to perform in-lab testing or home testing," said Julio A. Chirinos, MD, an assistant professor of medicine at the Hospital of the University of Pennsylvania and director of noninvasive cardiac imaging the Philadelphia VA. Chirinos refers patients suspected of OSA to Kuna.
Chirinos is the chief investigator in the COSA (Cardiovascular Effects of Obstructive Sleep Apnea) study, which is currently recruiting patients. The research will examine whether treatment of OSA decreases heart disease risk factors, including inflammation (C-reactive protein) and insulin resistance. Researchers also will analyze DNA to look for an association between apoE genotypes and both dyslipidemia and inflammation.
Patients will be randomized to CPAP alone, weight loss alone, or a combination of the two therapies. "We know there is a risk of cardiovascular disease when someone has OSA. We don't yet know whether those risk factors will decrease if we treat the apnea," Chirinos said.
The COSA study also will determine the independent effects of CPAP and weight loss on blood vessel function including arterial stiffness and central arterial pressures. These will be evaluated using a brachial artery reactivity test in which artery size and blood flow will be measured with ultrasound.
While Chirinos is encouraged that more cardiologists are aware of the link between OSA and cardiovascular disease, he said that they need better evidence that treatment will result in improved cardiovascular outcomes.