Home sleep monitoring plays a huge role at The Center for Sound Sleep.  While neither the American Academy of Sleep Medicine or insurance companies recognize home sleep monitoring as an “official” diagnosis for any sleep-related breathing disorder, home monitoring is nevertheless a valid way to obtain an enormous amount of information about someone’s sleep.

 

At The Center for Sound Sleep, we use an instrument called a Watch PAT to assess whether or not a patient is experiencing restful breathing during sleep.  This sophisticated device uses several things to monitor sleep.  The green finger probe shown on the index finger in this photo measures peripheral arterial tone or PAT.   The blood vessels in the fingers of the body experience the same phenomenon that all peripheral blood vessels under stress do, they restrict or contract.  When someone experiences a respiratory event during sleep, they unknowingly experience a stressful event.  Our greatest moment to moment need is oxygen.  Our heart, lungs and circulatory system are designed to take a constant supply of oxygen to all parts of the body.  When anything happens to restrict or stop this flow of oxygen, the blood vessels in the finger respond and this information is picked up by the finger probe as a PAT signal.

In addition to the PAT signal, the Watch PAT uses a pulse/oximeter shown on the ring finger.  This allows us to document oxygen levels and the pulse through the night.  This information is gathered and stored in the sensor worn on the wrist.  This sensor doubles as an actigraph which senses arm motion throughout the night.  Data from the actigraph helps determine whether the data gathered during the night was when the patient was awake or asleep.  Not shown in the photo is a very small body position sensor and snore sensor that are taped to the chest near the throat.

 

The following is an in-depth amount of information about the Watch PAT sleep report.  This information has been placed here as a service to our referring physicians, our patients wanting to understand more about their sleep study or for those who want a greater understanding of sleep physiology and sleep-related breathing disorders.

 

After our patients wear the Watch PAT for a night’s sleep, the instrument is brought back to our office and the accumulated data is downloaded.  The following sleep study shows an extremely healthy sleeping pattern.

 

 

 

This sleep study of a healthy sleeping pattern shown at left may be enlarged by clicking on it.  Notice that even someone with healthy sleep may have some respiratory events (shown by vertical blue lines) throughout the night.  However, the events are so few and spread so far apart throughout the night, that sleep is rarely disturbed.

 

 

 
Contrast this healthy sleeping pattern shown above with that of a patient with severe sleep apnea.  Different sections of this study will be further examined below.

 

  

The Sleep Summary section shows the starting and ending time of the sleep study as well as the actual sleep time.  The actual sleep time is determined by the actigraph worn on the wrist.  The Watch PAT actigraph has a built-in algorithm that knows how much a person’s hand will likely move when they are awake as opposed to the hand movement during sleep.  This allows a very accurate computation of actual sleep time.  This section also shows the total amount of REM (rapid eye movement- the period of sleep when dreaming occurs) time during sleep.  Normal REM time is 20-25% of the night.  This patient’s REM time of 8.4% is very low and due to the extreme number of respiratory events during the night that fragment sleep.

 

The Respiratory Indices section is divided into REM time, NREM (non-REM) time and All Night.  Separating the number of respiratory events into REM time and non-REM time is important because some people have a great deal more respiratory events in REM sleep.  This is because, with the exception of muscles of the eye, the heart and the diaphragm, the body is literally paralyzed during REM sleep.  Because of this, the muscles that normally contract to keep the airway open have no protective ability.

 

In the Sleep Medicine Basics page you will find definitions of the terms apnea, hypopnea, apnea/hypopnea index and respiratory distress index.  The Watch PAT uses slightly different terms.   ODI (Oxygen Desaturation Index) is most like the apnea/hypopnea index or AHI term used in a polysomnogram.  In other words, they both refer to a period of breathing restriction resulting in a 4% drop in blood oxygen levels.  The Watch PAT pAHI refers to a period of breathing restriction resulting in a 3% drop in blood oxygen level, a much more stringent definition.  The Watch PAT pRDI has a similar definition to the polysomnogram RDI.  HOWEVER, the pRDI and the RDI are determined very differently.   It is this difference, in this clinician’s opinion, that causes the Watch PAT to be far more effective than a polysomnogram in identifying non-hypoxic respiratory events that are clinically significant.

 

Watch PAT pRDI vs. Polysomnogram RDI

 
 

When a patient is having a polysomnogram, a non-hypoxic respiratory event is scored when the patient is having enough difficulty breathing that they arouse from a deeper level of sleep. This is better understood by observing the person in the following video struggling for air during sleep.

 

   

 

It is obvious from observing the difficulty breathing that this woman’s sleep is not restful.  After a period of time of breathing through a very restricted upper airway, this person will get fatigued, arouse from this deeper level of sleep to a more shallow sleep where the muscles of the pharynx open the airway and she can breath easier.  In a sleep lab this event is scored as a respiratory effort related arousal.  Then, because her body is craving sleep, she goes back to a deeper level of sleep where the muscles of the upper airway relax, the airway restricts and the cycle starts over.  A bed partner will sometimes describe this pattern as crescendo snoring: snoring that gets progressively louder over time as the airway restricts, stops awhile as the airway is opened in a more shallow sleep, and then progressively louder as deeper sleep is obtained.

 

The Watch PAT non-hypoxic respiratory events are determined by an activation of the PAT signal.  Keep in mind that when airflow is restricted, the body encounters stress.  While this stress may not be great enough to cause an arousal from a deeper level of sleep, it is stressful regardless.  Therefore, the PAT signal is more sensitive in identifying respiratory effort than the scoring requirements used in a polysomnogram.  This explains why many patients are referred to a sleep lab due to their complaints of awakening unrefreshed or daytime sleepiness and fatigue and are told that they snore loudly but they “have no problem”.  This is because they do not have enough respiratory effort related arousals to meet the minimum criteria for a diagnosis.  When these same patients are evaluated with the Watch PAT, significant respiratory effort is usually observed to be assessed as clinically significant.  If these same patients choose to be treated with oral appliance therapy, they almost always notice significant difference in symptoms.

 

 
The Oxygen Saturation Statistics section summarizes the blood oxygen levels recorded throughout the night’s sleep.  For example, this study shows that there were 2 respiratory events during this night’s sleep where the oxygen desaturation was greater than 20%.  In addition this patient had 146.6 minutes of sleep with the oxygen less than 90%, representing 33.7% of the total amount of sleep time!  The mean pulse rate of 79 minutes shows an extremely high amount of stress and effort in trying to maintain an adequate air supply during sleep.

 

The sleep summary data is shown in the form of a chart as seen below.  Click on the image to enlarge.

 
 

 

By carefully looking at the enlarged image you can easily see how the blue respiratory events correlate to yellow snoring events (in this case almost all night).  While most patient’s respiratory events show as single vertical blue lines, the respiratory events in this patient were so close together throughout sleep that they appear as blue bars.  Also shown are oxygen levels in black and pulse rate in red.  This particular patient’s sleep apnea is so severe that there is not a tremendous amount of variation throughout the night.  However, the next sleep study will show how the data that is collected can have greater meaning regarding specific times of sleep.

 

The sleep study data shown at left is an example of one where the patient (who is a sleep lab technician) did not get a diagnosis for obstructive apnea and was told that no treatment was needed.  However, this patient typically awakened 5-6 times throughout the night and disturbed her bed partner’s sleep with her snoring.  Using an oral appliance, she now sleeps soundly though the night, usually without awakening.  Close examination of this study (click on the study to enlarge) shows that her biggest problem is in REM sleep when the muscles of the pharynx are paralyzed.