Getting Your Results

What happens to the sleep study information

Once your sleep study is completed, the data that has been collected is reviewed in detail. Information concerning your sleep (time to fall asleep, time asleep, arousals from sleep, sleep staging), presence of apneas, and their frequency, and distribution during sleep, oxygen levels during sleep, and body position and movements are tabulated and reported in a statistical format. The raw data (16 channels of information including EEG waveforms, EKG tracing, chin muscle tone, respiratory effort, position, oximetry, leg movements) is reviewed by Dr. Cocanower in its’ entirety. The review of your study raw data, and the statistical information concerning your sleep, are used to interpret the sleep study. The sleep study results must be considered in the context of a patients’ symptom complex, medical history, and physical exam, to make proper clinical decisions regarding the significance of any findings, or the need for treatment. Your sleep study results and interpretation will be forwarded to the physician ordering the study, and a copy sent to you.

Getting my sleep study results

Your physician may choose to discuss the results of your sleep study with you, or may arrange a consultation with Dr. Cocanower to review the study results with you. It is the recommendation of Sleep Medicine Associates that all patients studied in the laboratory be seen be seen by Dr. Cocanower in consultation, or Lindsay Lang, NP for follow-up, to facilitate the highest level of sleep care.

What do my sleep study results mean?

What is normal?
When evaluating sleep apnea, the apnea-hypopnea index (AHI) is used as an indicator of the severity of sleep apnea. The apnea-hypopnea index represents the number of abnormal breathing episodes (apneas and hypopneas) that occur in one hour of sleep. An apnea-hyponpea index of 5/hr. or less is considered normal; 5-14 mild obstructive sleep apnea; 15-29/hr. moderate obstructive sleep apnea; more than 30/hr. severe. It is important to consider a patients’ entire clinical history, including symptoms, and the presence of other medical conditions that may be due to sleep apnea, when making decisions about the significance of the AHI. Individuals vary in the symptoms they express due to sleep disruption due to obstructive sleep apnea (individual susceptibility), with some having prominent sleepiness associated with mild sleep apnea, and others minimal symptoms even though they may have severe obstructive sleep apnea.

What is obstructive sleep apnea?
The hallmark symptoms and findings of obstructive sleep apnea are loud snoring, “stop-breathing” events during sleep, and daytime sleepiness. This common sleep disorder, estimated to affect more than 20 million Americans, is typically unrecognized by those affected, and often by physicians and healthcare personnel. Seen in all age groups, and both sexes, this under-recognized problem can contribute to high blood pressure, and an increased risk of heart attacks and strokes. A number of other symptoms that can be associated with sleep apnea, and that are often not recognized as such, include headaches on awakening, dry mouth on awakening, sweating during sleep, difficulty staying asleep, waking frequently during the night to urinate, mood and memory problems, worsened heartburn and reflux at night, and sexual dysfunction. The disorder is characterized by obstruction of the upper airway (typically at the level of the throat), that reduces partially, or completely, the flow of air through the throat into the lungs. This process is associated with an increase in breathing effort, and typically a drop in the body’s blood oxygen level, resulting in an arousal, or awakening from sleep. Those with the disorder often complain of being tired and worn out, and not being refreshed by sleep, that results from their sleep being interrupted up to hundreds of times in a night, even without the affected person being aware of these interruptions. Though seen most often in those who are overweight, thin persons are also affected. Sleep testing is usually performed to document the presence of the disorder so that appropriate treatment can be initiated. Treatment options include the use of a nasal mask device (continuous positive airway pressure, or CPAP), upper airway surgical procedures, and oral appliances. Positioning techniques can be used for some patients. Weight control is useful in all patients who are overweight with OSA.

What is an obstructive apnea?
An obstructed apnea is defined by a 90% reduction of airflow through the upper airway (nose/mouth/throat) lasting at least 10 seconds. This ineffective breathing results in an increase in respiratory effort, and a reduction in the amount of oxygen in the blood available to the body’s tissues. An obstructed apnea is terminated by an arousal, or interruption in sleep. Blood pressure and heart rate generally increases following an apnea. Sleep fragmentation associated with repetitive apneas can result in daytime sleepiness.

What is a central apnea?
A central apnea is characterized by absence of respiratory effort for at least 10 seconds, associated with an arousal, or interruption of sleep. Central apneas can be observed as part of the spectrum of respiratory abnormalities seen in obstructive sleep apnea, and are also seen following arousals from sleep in the wake/sleep transition, and as part of periodic breathing that can be seen in heart failure and following strokes. A pure form of central sleep apnea can be seen as a more rare condition in infants.

What is a mixed apnea?
A mixed apnea begins as a central apnea (absence of respiratory effort), and ends with an obstructed apnea (respiratory effort against a closed airway ie. at least 90% airflow reduction), and lasts at least 10 seconds. This frequently is seen as part of the spectrum of abnormal respiration seen in obstructive sleep apnea.

What is a hypopnea?
A hypopnea is defined by at least a 50% reduction of airflow through the upper airway (nose/mouth/throat) lasting at least 10 seconds. This ineffective breathing results in an increase in respiratory effort, and a reduction in the amount of oxygen in the blood available to the body’s tissues. A hypopnea is terminated by an arousal, or interruption in sleep. Blood pressure and heart rate generally increases following a hypopnea. Sleep fragmentation associated with repetitive hypopneas can result in daytime sleepiness.

What is the AHI?
The apnea/hypopnea index or AHI represents the number of apnea and hypopnea episodes that occur per hour of sleep. During a sleep study the number of breathing interruptions (apneas and hypopneas) are identified and counted. The AHI is the measure most commonly used to determine the severity of sleep apnea. According to the American Academy of Sleep Medicine, an AHI of 6 to 14 indicates mild sleep apnea, an AHI of 15-30 moderate sleep apnea, and an AHI >30 severe sleep apnea.

About Sleep Stages
Sleep is by convention categorized as non-rapid eye movement (NREM), or rapid eye movement (REM) sleep. REM sleep is also called “active sleep,” and is the sleep associated with dreaming. The brain waves in REM sleep resemble that of wake, and it is in this stage of sleep that muscle tone, or strength is lowest, and rapid bursts of side to side eye movements can be observed. REM sleep is not considered to be the “deepest” stage of sleep and comprises approximately 20% of sleep.

NREM sleep is comprised of four stages of sleep, ranging from lightest (Stage 1), to deepest (Stage 4). Stage 1 sleep normally comprises <5% of sleep; Stage 2 is deeper, and comprises 50-60% of sleep; Stages 3 and 4 are the deepest sleep and comprise 15-20% of sleep. Recent changes in sleep scoring have resulted in Stage 3and 4 being combined into one as Stage 3 sleep. A normal sleep cycle lasts approximately 90 minutes, and will typically include sleep from all 4 NREM stages, and REM sleep. Stage 3-4 sleep is more prominent early in the night of sleep, and REM sleep more prominent late in a night of sleep. It is not uncommon to have some change in the distribution of sleep stages during a sleep study (more light stage sleep, and less deep sleep) due to the unfamiliar environment of a sleep center, and to disruption in sleep caused by the monitoring leads and sensors.

What does oxygen desaturation mean?
Air breathed into the lungs provides oxygen that is absorbed through an extensive network of fine blood vessels (capillaries) that line the alveoli (small air sacs in the lung). This oxygen is pumped from the heart to the tissues of the body to be used to facilitate efficient functioning of the cells of the tissues. Oxygen is used by the cells to carry on vital basic tissue functions. Blood that has delivered oxygen to the body’s tissues returns to the lungs to pick up more oxygen. If the upper airway (throat) obstructs, the amount of air that enters the lung is reduced, and consequently, the amount of oxygen available to the tissues for efficient vital functions is reduced. Inefficient cell functioning occurs, with build up of harmful products that can damage cells, and tissues. An oximeter is typically worn on the finger during a sleep study, and is used to measure the saturation of oxygen on the carrying molecules (hemoglobin) in the blood. Normally, hemoglobin carries more than 90% of the blood it is able to carry. When the airway obstructs, the saturation of oxygen on the hemoglobin will typically drop, resulting in a lower saturation reading noted on the oximeter.

If I have sleep apnea, what next?
If sleep apnea outside the range of normal (>5/hr.) has been observed during your sleep study, it will be important to consider available treatment options. During a consultation with Dr. David A. Cocanower, the findings of your sleep study will be reviewed, treatment options discussed in detail, and recommendations made, taking into consideration your symptoms, and exam findings, and medical history. It is important to keep in mind that individuals vary in symptoms they may experience with obstructive sleep apnea, and that the presence of symptoms in mild sleep apnea, ie. sleepiness, will make treatment appropriate, and that absence of significant symptoms in the context of severe sleep apnea does not mean treatment is not necessary. Direct testing patients will need to be proactive in ensuring that they understand their sleep study results, and treatment options that may be appropriate for the management of any sleep disorder that is identified. This may involve returning to the primary care physician, or specialist who ordered the study to review the study findings, or scheduling a consultation with the physician, or nurse practitioner at Sleep Medicine Associates.