Sleep-Disordered Breathing and CPAP Workup

Updated: Mar 02, 2022
  • Author: Vittorio Rinaldi, MD; Chief Editor: Zab Mosenifar, MD, FACP, FCCP  more...
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Laboratory Studies

The relation between snoring, obstructive sleep apnea (OSA), and hypothyroidism has been confirmed by many authors. Thyroid-stimulating hormone (TSH) levels should be determined in patients who are newly diagnosed with sleep-disordered breathing (SDB) because SDB is relatively common among patients with hypothyroidism. Significant increases in homocysteine levels have been observed in OSA syndrome (OSAS) patients with cardiovascular disease.


Imaging Studies

Radiologic and diagnostic studies have been used to identify the obstruction site, to direct surgical intervention, and to predict outcomes of sleep apnea surgery. These studies include lateral cephalometric radiography, computed tomography (CT), magnetic resonance imaging (MRI), asleep fluoroscopy, asleep and awake endoscopy with Mueller maneuver, upper-airway manometry, and acoustic reflection techniques. [43]

Most of those techniques have limitations (dynamic and tridimensional evaluation) with respect to the investigation of the mechanism of occlusion. Ultrafast MRI provides a reliable and noninvasive method for static and dynamic evaluation of the soft-tissue structures surrounding the upper airway during the respiratory cycle in wakefulness and sleep.


Epworth Sleepiness Scale

The Epworth Sleepiness Scale is a questionnaire filled out by the patient that is used to provide a standardized semiquantitative subjective assessment of daytime sleepiness.

In this questionnaire, patients are instructed to rate the chance of dozing off in a number of different situations. They are to choose the most appropriate ranking for each of these situations, working out how they would probably respond if it is something they have not actually done recently. Scoring for the Epworth Sleepiness Scale is shown in Table 1 below.

Table 1. Epworth Sleepiness Scale Questionnaire (Open Table in a new window)


0 - Would never doze off

1 - Slight chance of dozing off

2 - Moderate chance of dozing off

3 - High chance of dozing off

Score situation

_____ Sitting and reading

_____ Watching TV

_____ Sitting inactive in a public place (eg, theater, meeting)

_____ As a passenger in a car for an hour without break

_____ Lying down to rest in the afternoon when circumstances permit

_____ Sitting and talking to someone

_____ Sitting quietly after a lunch without alcohol

_____ In a car, while stopped for a few minutes in the traffic

_____ Total*

*A total score of 0-5 is supernormal; 5-10 is normal; 10-15 is sleepy; 15-20 is very sleepy; and >20 is dangerously sleepy (arrange transportation for patient)



Polysomnography (PSG) is the criterion standard diagnostic test for OSAS. A respiratory event suggestive of OSAS is defined as a decrease in nasal and oral airflow, alone or with thoracoabdominal movements, of more than 90% (apnea) or of more than 50% but less than 90% (hypopnea) that lasted for at least 10 seconds. A decrease in arterial oxygen saturation of 4% or more is considered significant oxygen desaturation. [44]

Information from PSG is reported in the form of the respiratory disturbance index (RDI; also referred to as the apnea-hypopnea index [AHI]). The RDI is the number of apneas or hypopneas 10 seconds or longer occurring per hour of sleep. A normal RDI is less than 5. An RDI less than or equal to 5 is suggestive of simple snoring with no OSAS. An RDI greater than 5 and less than or equal to 15 is suggestive of mild OSAS. An RDI greater than 15 and less than or equal to 30 is suggestive of moderate OSAS. Finally, an RDI greater than 30 is suggestive of severe OSAS.

The loudness and persistence of snoring (constant versus intermittent) are usually reported. Body position is also recorded so one can determine what position (usually supine) and in what sleep phase (usually rapid-eye-movement [REM] sleep, when muscle tone is most relaxed) the patient is in when respiratory events occur.

In-laboratory PSG is the criterion standard for diagnosing OSAS. However, PSG has several limitations, including the necessity of performing the test in a sleep laboratory, high costs, the considerable technical expertise required, and the long analyzing time needed by the operator. In addition, the examination often must be repeated because of the interference of monitoring electrodes with the physiologic sleep of the patient (“first night effect”). Therefore, timely access to PSG is often a problem.


Screening Questionnaires

Because PSG is expensive and not widely available, there has been extensive interest in alternative diagnostic approaches, such as clinical prediction rules and portable monitors. A limited number of questionnaires are available to detect some sleep disorders, but those instruments do not achieve the reliability of PSG, which remains the recommended method of assessing patients with suspected sleep disorders. The role of those questionnaires is mainly to serve as a screening tool for identifying patients at risk for OSAS. [45, 46, 47, 48]

Many questionnaires have been developed for screening OSAS. The Rome Questionnaire (RQ) is a seven-item questionnaire useful in identifying adult patients at risk for OSAS. The RQ, together with the body mass index (BMI), is reported to be a useful tool for selecting patients at higher risk for moderate-to-severe OSAS, who need a prompt PSG evaluation. [49]


Home Sleep Testing and Ambulatory Monitors

Home sleep testing pursues the goal of simplify the diagnosis of sleep apnea while retaining the essential recording features of PSG. There is some evidence to suggest that home sleep studies have benefits in terms of time and cost, but for diagnostic reliability, an in-laboratory sleep study may be required in more than half of the cases.

Various types of ambulatory (to be used at home) monitors can measure parameters such as airflow, chest, and abdomen movements (as indicators of respiratory effort); oxygen desaturations; snoring; pulse; and body position. [50, 51]

Although the data from such studies are not as detailed or accurate as those obtained from an overnight PSG, these studies can often be used to differentiate primary snoring from snoring with apneas and can usually provide an indication of the frequency with which apneas are occurring. In contrast, techniques that measure only one parameter (eg, home oximetry alone) seem to be less accurate than those that track several measurements.

The EdenTrace portable monitor measures nasal and oral air flow using thermistors, chest wall impedance, oxygen saturation with finger pulse oximetry, heart rate, and movement detected by electrical comparison of the signals from electrocardiography and pulse oximetry.

The MESAM IV system evaluates SDB on the basis of analysis of snoring, heart rate, and saturation change. Even if in many studies there is a good agreement between the RDI measured in the laboratory and that measure with home sleep testing, there is a risk that ambulatory diagnostic procedures may alter patients' relationship with their disease, the medical staff, or both in such a way that their subsequent compliance with treatment may be decreased.

The Nightwatch system has the ability to calculate the RDI. It records eye movement (one channel, piezo electrode), leg movement (one channel, piezo electrode), (finger pulse oximeter), nasal oral airflow (thermistor), chest and abdominal movements (piezo electrodes), body position and movement (mercury gauge placed on the chest), and heart rate.

The Nightwatch system also has the ability to send 2-minute portions of the complete recording to the laboratory for analysis so that signal quality can be assessed and transducer function corrected if necessary. However, further studies are necessary before this technology can be put into widespread use.

With the aim of developing a simpler, cheaper, and more accessible method for the diagnosis of OSAS, the peripheral arterial tonometer (PAT) has been proposed for use in ambulatory diagnosis of OSAS. The portable monitoring device WatchPAT 200 detects obstructive events by identifying the changes in sympathetic activity associated with the termination of the events. The wrist-worn device WatchPAT 200, compared with standard PSG, has been reported to be able to detect OSAS on the basis of the RDI with comparable accuracy. [52]


Acoustic Snoring Analysis

Acoustic analysis of snoring sounds may help differentiate between primary snoring and OSA. Various researchers have investigated the combination of clinical variables such as neck and chest circumference, BMI, and resting room air oxygen saturation; however, none of these has been shown to differentiate consistently between primary snorers and patients with significant apneas and desaturations during sleep.


Sleep Endoscopy

Drug-induced sleep endoscopy (DISE) is a safe and reliable technique for determining the pattern of upper-airway obstruction and the contribution of specific structures to airway obstruction. [53]

Identifying the site and the dynamic pattern of obstruction is mandatory in therapeutic decision-making, especially if a surgical therapeutic option is being considered. [54]

The nose-oropharynx-hypopharynx-larynx (NOHL) classification, which could be applied during awake and sleep endoscopy, allows a simple, quick, and effective evaluation of grade and patterns of upper-airway collapse. [55]


Histologic Findings

The histology of the soft palate and uvula in snorers and patients with OSAS has been investigated by many authors. [56, 57]  Some authors observed muscular atrophy, dilatation and congestion of the blood vessels, lymphocytic infiltrations, and hypertrophy of superficial salivary glands localized between the muscle bundles and epithelium. Those histopathologic changes were related to the influence of the vibration on the soft palate and uvula and were considered responsible for the excessive flaccidity of these structures.

Other authors found contents of glands, muscle, fat, blood vessels, and the epithelium in the uvula and the soft palate to be similar in OSAS patients and control subjects.