Computation of pharyngeal volumes was done as described previously. A computer program using a digitizing pad (Numonics 2210, Montgomeryville, PA) was used. In summary, the pharyngeal airspace was outlined with a computer mouse using the beginning of the soft palate as the superior landmark and the back of the epiglottis as the inferior landmark. An area (in square centimeters) is calculated for each slice and then multiplied by 0.4 cm (the thickness of each slice) to approximate a volume. The sequence is repeated on each slice that involves the airway (n = 7 to 10) and then added together to give a composite volume. In addition, we divided the airway into three separate sections and calculated volumes for each section.
Standard procedures were used to quantitate sleep events. Desaturation was defined as a reduction in oxygen saturation by 4 percent or more. Apnea was a cessation of airflow at the nose and mouth for greater than 10 s. Hypopneas were scored as a decrease in inspiratory flow coupled with desaturation. Sleep period time (SPT) was defined as the time from the onset of sleep to the last awakening in the morning. Total sleep time (TST) was sleep period time less any time the subject was awake after falling asleep. An apnea-hypopnea index (AHI) was defined as all the apneas plus all the hypopneas divided by TST.
The patients did not know that the machine had an internal clock.
At the end of approximately six weeks, the patient returned with his nasal CPAP machine and his diary for the second sleep study. As stated previously, this sleep study was done in the same manner as the initial sleep study with the exception that in some patients the monitoring time prior to the placement of nasal CPAP was longer.
For the first sleep study, after initial monitoring, when it was clear that the patient had OSA, a nasal CPAP mask was applied. Our machine was a commercial brand (SleepEasy III, provided by Respironics, Inc, Monroeville, PA). The pressure was adjusted in each patient individually and was ultimately set at the pressure that abolished most apneas and hypopneas, kept oxygen saturation at more than 90 percent, and eliminated snoring.
The day following their initial sleep study, each patient was given detailed instructions on how to use a nasal CPAP machine and watched an informational video about the use of nasal CPAP (distributed by Respironics). In addition, eight of the 12 subjects slept an additional night (supervised but without polysomnography) at the GVAMC to assure that they could tolerate nasal CPAP.
Chest and abdominal movements were impedance sensed with surface electrodes, airflow was sensed by a combined nasal-oral thermistor (Rochester-Electromed, Tampa, FL), and oxygen saturation was measured with an ear oximeter (3700 pulse oximeter, Ohmeda, Louisville, CO). These were simultaneously recorded on a physiograph (Model DMP-4B, Narco, Houston, TX).
All patients were videotaped using a camera (RCA TC2511 U8) with infrared lighting. Split screen imaging allowed us to view patient and sleep recordings simultaneously.
All patients volunteered for this study and informed consent was obtained. This experimental protocol was approved by the Institutional Review Boards of the J. Hillis Miller Health Center and the Gainesville VA Medical Center.
Patients underwent two sleep studies for this study. All studies were done at the Gainesville VA Medical Center (GVAMC) sleep laboratory. The first sleep study used for analysis was actually the screening study done to diagnose OSA. The second polysomnography was done at the end of the study, which was approximately six weeks later (this time varied slightly for each patient).
Sleep studies were done without nasal CPAP at the initiation of therapy and at the end of six weeks. Magnetic resonance imaging of the upper airway, awake and without nasal CPAP, was also performed at the onset of the study, at two weeks, and at the end of six weeks to see if changes in pharyngeal volume occurred.
Methods and Materials
A total of 12 patients were enrolled in this study, all male. All of the patients had symptoms of daytime hypersomnolence and loud snoring. Patients were enrolled after they had undergone a full night of polysomnography at our VA sleep laboratory.
Nasal continuous positive airway pressure (CPAP) introduced in 1981 by Sullivan et al has revolutionized the treatment of obstructive sleep apnea (OSA). It has been shown conclusively to reduce or abolish the number of apneic and hypopneic events and improve the concomitant oxygen desaturation, decrease snoring, and improve daytime hypersomnolence. For most patients, nasal CPAP is well tolerated; however, recent studies have shown that longterm compliance is not 100 percent.