Sleep Diagnostic Tests

Sleep Tests

Many patients who see me present with two ends of the spectrum in sleep disorders, they usually have 2 main complaints:

"Doc, I'm so tired but I just can't fall asleep!" or

"Doc, I sleep 8 hours, but I'm still so tired, I can't keep awake!"

These sleep disorders range from insomnia (unable to fall asleep) to obstructive sleep apnea (excessive daytime tiredness, unable to keep awake).

Many patients who see me present with two ends of the spectrum in sleep disorders, they usually have 2 main complaints: "Doc, I'm so tired but I just can't fall asleep!" or "Doc, I sleep 8 hours, but I'm still so tired, I can't keep awake!" These sleep disorders range from insomnia (unable to fall asleep) to obstructive sleep apnea (excessive daytime tiredness, unable to keep awake).

Answer some of these questions:

  1. I have been told that I snore
  2. I have been told that I hold my breath when I sleep
  3. . I wake up choking, gasping, or have difficulty breathing at night
  4. I wake up in the middle of the night with palpitations (fast heart beat)
  5. I am told that I kick violently at night
  6. I feel very tired during the day despite sleeping for 6 to 7 hours per day
  7. I wished I had more energy
  8. I get morning headaches often
  9. I noticed that I am grumpy and irritable lately
  10. I often feel sleepy and have trouble staying awake at meetings
  11. I frequently awake with a dry mouth and throat
  12. I have high blood pressure
  13. I am slightly overweight
  14. I have frequent sore throats
  15. I have "sinus" problems on most mornings of the week
  16. I have fallen asleep while driving
  17. I often feel like I'm in a daze
  18. I have difficulty falling asleep
  19. I feel sad and depressed
  20. Sometimes I can't keep my legs still at night; I just have to move them to feel comfortable.

In general, with more than 5 answers as positive (yes), one should seek a sleep specialist consult. It might indicate that you could have a sleep disorder.

Sleep Assessment Tests

To say that a patient has high blood pressure, one would have to take the blood pressure reading; to say that a patient has diabetes, one would have to take a glucose blood test. Similarly, to diagnose a patient with a sleep disorder, one would have to perform a sleep assessment test.

There are 2 main types of sleep test:

  1. in hospital overnight sleep test (in-patient)
  2. at home overnight sleep test (done in the patient's own home)

Depending on the type of sleep disorder suspected, the sleep specialist would order the appropriate sleep test. The type of sleep test ordered would be dependent on the number of parameters required.

Overnight Hospital Sleep Test

The in hospital overnight attended (monitored by a sleep technician throughout the night) sleep test comprises of multiple parameters including:

  • Electroencephalogram (EEG) – monitoring brain waves,
  • Electrooculogram (EOG) – monitoring eye movements,
  • Electromyogram (EMG) – muscle tone in the chin
  • Electrocardiogram (ECG) – heart muscle electrical activity,
  • Nasal/Oral Airflow – thermistor or pressure transducer in the nose and mouth,
  • Respiratory Effort – monitoring the chest and abdominal movements and effort,
  • Oxygen Saturation – monitoring the amount of oxygen in the blood
  • Body Position – surveillance of the patient's sleeping position
  • Video monitoring system – monitoring the entire night's sleep.

With these parameters, the sleep specialist would be able to determine the sleep stage (dream sleep versus non-dream sleep), the stoppages of breathing, and whether there is continued chest / abdominal effort to breathe.

Apnea – stoppage in breathing by more than 10 seconds duration

Obstructive – some form of obstruction in the upper airway

With obstructive sleep apnea, there would be no nasal or oral airflow (stoppage in breathing), but there would be PERSISTENT EFFORT by the patient to breathe (body trying to breathe despite an obstructed airway).

In central apnea, there would be no nasal or oral airflow (stoppage in breathing), and also NO CHEST AND ABDOMINAL EFFORT to breathe (brain forgetting to breathe).

Although the in hospital overnight sleep test is useful, it suffers from a few disadvantages namely:

  • limited resources,
  • limited recording beds,
  • high cost,
  • long waiting lists,
  • intensive labor requirements (requiring a sleep technician overnight),
  • difficult for elderly or sick patients to travel to the hospital and spend the night in the sleep laboratory,
  • many patients often find the PSG equipment too cumbersome and
  • first night effect (due to new environment, patients might not be able to sleep at all)

Hence, due to these short-comings of the in hospital overnight sleep test, many sleep specialists have moved away from asking the patient to stay in hospital for the sleep test and have evaluated various other methods to monitor the patient's sleep in the comfort of his own home.

Home Based Overnight Sleep Test (done in the patient's own home)

A number of home based overnight sleep test (done in the patient's own home) designed to assess the severity of OSA have emerged. These devices serve to aid the doctor in decision-making and minimize inconvenience to the patient.

The ideal home based overnight sleep test device for OSA should be

  • not expensive,
  • easily accessible,
  • easily used with the minimal instructions,
  • have no risk or side effects to the patient, and be
  • safe and accurate.

It should be capable of being issued by relatively unskilled staff, and done at home by the patient him or herself.

A wrist-worn device known as the Watch PAT has been used to detect OSA. The PAT (peripheral arterial tonometry) technology represents a unique and relatively new concept of noninvasive measurement of stress levels that appears to be very accurate for detecting sleep-disordered events. This is a self-contained device worn around the wrist. It is lightweight and silent, easy to use, portable, and accurate, which is essential for a practical ambulatory device. Two finger probes extend from the main body of the device. One is the optico-pneumatic (light and pressure) sensor that detects the peripheral arterial tonometry (PAT) signal (stress level in the finger); the other measures arterial oxygen saturation (amount of oxygen in the blood). The body of the device also contains an actigraph (which measures and detects muscle tension and tone), which is used to differentiate sleep stages from wakefulness.

Simplistically speaking, the Watch PAT looks at any desaturation in oxygen level in the blood and correlates this with the arterial tone in the finger probe.

  • Low Oxygen level + no stress in the finger tone = central apnea event
  • Low Oxygen level + high stress in the finger tone = obstructive apnea event

Pang K.P. and his researchers found that this wrist worn device had very close correlation and accuracy with the in hospital overnight sleep test. As discrete obstructive airway events (i.e. stoppages in breathing) causes stress to the heart, lungs and brain, this increases arousal from sleep, stress activation and hence these events would markedly increase peripheral arterial tone (finger tone) signal. Many other authors have also found good correlation between the Watch PAT and the overnight sleep study in the hospital.