A study from the Johns Hopkins Sleep Disorders Center published online in the Thoracic Society’s American Journal of Respiratory and Critical Care Medicine has shown that hypoglossal nerve stimulation (HGNS) produced marked dose-related airflow increases in patients suffering from obstructive sleep apnea (OSA) without waking them up. According to the study, HGNS has demonstrated its potential therapeutic efficacy for a wide spectrum of sleep apnea severities. HGNS also provides an alternative to continuous positive airway pressure (CPAP), the currently common treatment for moderate to severe OSA, which is often of limited effect, simply because of poor patient compliance.
Alan R. Schwartz, MD, medical director of the Sleep Center at Johns Hopkins Bayview Medical Center states:
“With HGNS, airflow increased in all of our patients, and increased progressively with stimulus amplitude. The increases in airflow we observed were of sufficient magnitude to eliminate inspiratory airflow limitation (IFL) in the majority of patients.”
The device, manufactured by Apnex Medical, Inc. which also supported the study, acts like a pacemaker, by monitoring breathing patterns, and is activated during sleep to stimulate the hypoglossal nerve, controlling muscles in the upper airway.
For the study, researchers enlisted 30 middle-aged patients with moderate to severe obstructive sleep apnea; they had a novel HGNS system implanted.
In the study period, the current was increased level by level during non-REM sleep, and the frequency and pulse width were fixed. The researchers measured maximal inspiratory airflow (Vlmax) and IFL at each current level, during which stimulation was applied on alternate breaths to compare responses in inspiratory airflow next to unstimulated breaths.
The results showed that HGNS produced linear increases in VImax as the current was raised, with a significant rise of the average VImax from 215±21ml/s during off stimulation to 509±37mL/s on stimulation. They observed an increase of Vlmax in all 30 patients, with all achieving normal or near-normal levels of airflow, whilst in 17 patients (57%) IFL was completely eliminated.
Dr. Schwartz commented:
“In our study, acute unilateral stimulation of the hypoglossal nerve during sleep in patients with obstructive sleep apnea resulted in progressive increases in inspiratory airflow with increasing stimulation intensity, and inspiratory flow limitation was completely eliminated in the majority of patients. Of note, inspiratory airflow returned to baseline levels on alternating unstimulated breaths, suggesting that HGNS has a direct effect on lingual muscles and airway patency without arousing patients from sleep.”
The authors noted that that inspiratory efforts were not monitored by the esophageal manometry and flow response was not measured in all body positions and sleep stages (a limitation of the study). They also did not assess the long-term impact of HGNS therapy.
Dr. Schwartz concluded:
“Our findings extend previous findings on the effects of HGNS on airflow in obstructive sleep apnea by characterizing flow responses over a range of stimulus amplitudes and demonstrating greater increases in airflow. The magnitude of the increases in airflow we observed indicate that HGNS can provide substantial relief of upper airway obstruction during sleep in these patients across a wide range of disease severity.”