Sleep Physiology and Disorders - Overview and Practice Questions

Sleep Physiology: Overview and Practice Questions

by | Updated: Nov 8, 2023

According to, over 50 million people in the United States are affected by sleep disorders. This is why it’s important for respiratory therapists and medical professionals to develop an understanding of sleep physiology and the most prevalent sleeping disorders.

This guide was designed to help make the learning process easier for you. It contains practice questions for your benefit as well. So, if you’re ready, let’s get started.

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What is a Sleep Physiology?

Sleep physiology refers to the study of how and why we sleep. Simply put, sleep is a state in which there is an absence of wakefulness that is metabolically regulated and essential for human life.

Though we may not be consciously aware of it, our bodies need sleep just as much as they need air, food, and water.

There are many different theories as to why we need sleep, but the most widely accepted one is that sleep allows our bodies to recover from the day’s activities. Sleep also helps to consolidate our memories and helps to keep our body systems functioning properly.

Hospital patient with sleep apnea

What is a Sleep Disorder?

A sleep disorder is a condition that affects the quality, duration, timing, or impact of a patient’s ability to sleep or function properly while awake.

Common Sleep Disorder Examples:

  • Insomnia
  • Sleep Apnea
  • Restless Leg Syndrome
  • Hypersomnia
  • Narcolepsy
  • Sleepwalking
  • Parasomnia

Sleep apnea is the most common disorder that Respiratory Therapists see in patients. However, it is important to be familiar with each of the other sleep disorders listed.

Sleep Apnea

Sleep apnea is a disorder characterized by repeated episodes without breathing while asleep that last for at least 10 seconds or longer.

It has been estimated to affect around 25% of the population between 30 and 70 years of age. There are two primary types of sleep apnea:

  1. Obstructive sleep apnea
  2. Central sleep apnea

Of the two, obstructive sleep apnea is the most common. Keep reading for a brief overview of both types. 

Obstructive Sleep Apnea

Obstructive Sleep Apnea (OSA) is a disorder characterized by the absence of breathing while asleep that is caused by a blockage of the upper airway. It is often associated with obesity.

With that type, breathing efforts are being made by the patient, but the airflow is blocked in the back of the throat.


Some examples of the common causes of obstructive sleep apnea include the following:

  • Upper airway abnormalities
  • Tonsillar hypertrophy
  • Large neck
  • Small chin
  • Increased soft tissue around the neck

A diagnosis of obstructive sleep apnea can be made using a sleep study, also known as polysomnography.

It records the patient’s brain activity, eye movements, muscle activity, and heart rhythm during sleep.


The treatment for obstructive sleep apnea involves the use of noninvasive ventilation (NIV), which applies positive pressure to the airway in order to reduce the number of apnea episodes.

CPAP is the most common type, although BiPAP may be used in some cases.

The use of a specialized mouthpiece can also be helpful to reposition the jaw forward, which opens up the airway so that breaths can flow more freely.

Supplemental oxygen may be indicated in some cases.

If noninvasive treatment methods are not effective, the doctor may recommend a surgical procedure to correct the anatomical abnormalities causing the airway blockage.

Central Sleep Apnea

Central Sleep Apnea (CSA) is a disorder characterized by the absence of breathing while asleep that is caused by a medullary depression that inhibits an inspiratory effort.

It is characterized by a lack of drive to breathe during sleep in which the patient does not make any breathing efforts.

It differs from obstructive sleep apnea because, with that type, breathing efforts are being made by the patient, but the airflow is blocked by an obstruction.

In central sleep apnea, the apnea periods aren’t caused by a blocked airway. They occur because the portion of the brain that controls breathing isn’t functioning properly.

This results in no respiratory effort, insufficient ventilation, and compromised gas exchange.


Some examples of the common causes of central sleep apnea include the following:

  • Stroke
  • Muscular dystrophy
  • Guillain-Barré
  • Amyotrophic lateral sclerosis (ALS)
  • Congestive heart failure
  • Chronic opiate use
  • Congenital abnormalities

A diagnosis for central sleep apnea can also be confirmed using polysomnography.


The treatment for central sleep apnea involves caring for any underlying issue that may be causing the condition.

Noninvasive ventilation (NIV) machines can be used while the patient is sleeping to reduce the periods of apnea. This includes both BiPAP and CPAP devices.

Supplemental oxygen may also be indicated.

Sleep Disorders and Physiology Practice Questions:

1. What is the circadian rhythm?
A biologic rhythm that serves as our 24-hour internal clock

2. What is NREM sleep?
Non-rapid eye movement sleep

3. What is REM sleep?
Rapid eye movement sleep

4. What is Sundown syndrome
An onset of confusion and agitation that affects people with dementia

5. What is insomnia?
A disorder characterized by the inability to fall asleep or remain asleep

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6. What drugs can disrupt sleep?
Alcohol, amphetamines, antidepressants, beta-blockers, bronchodilators, caffeine, decongestants, narcotics, and steroids

7. What drugs cause excessive daytime sleepiness?
Antidepressants, antihistamines, beta-blockers, and narcotics

8. What are the metabolic adverse consequences of obstructive sleep apnea?
Insulin resistance and altered lipid metabolism

9. What is narcolepsy?
A disorder of excessive daytime sleepiness caused by lack of the chemical hypocretin in the CNS, which regulates sleep

10. What is sleep apnea?
A disorder characterized by frequent periods of apnea while asleep

11. What is parasomnia?
A sleep disorder that involves experiences or physical events that can disrupt your sleep

12. Insufficient sleep is a public health epidemic, and the Center for Disease Control has called for what?
They have called for continued public health surveillance of sleep quality, duration, behaviors, and disorders to monitor for sleep difficulties and their health impact.

13. What is the most important biorhythm?
Circadian sleep-wake rhythm

14. What happens to the natural circadian rhythm as people age?
It is less responsive to external stimuli, such as changes in light during the day.

15. What is the result of endogenous changes in the diminished production of melatonin?
Less sleep efficacy

16. What kind of sleep declines with aging?
REM sleep declines with aging and is a “critical state for sleeping elders” when the brain replenishes neurotransmitters.

17. What are the most notable age-related sleep changes?
An increase in the number of night-time awakenings and lower sleep efficiency.

18. What is the most common sleep disorder worldwide?

19. How does CPAP improve breathing in a patient with OSA?
Pneumatic splinting of the upper airway

20. What are some behavioral techniques to enhance sleep for those with AD?
Sleep hygiene education, daily walking, and increased light exposure

21. How do caregivers of dementia suffer from sleep problems?
Caregivers also experience poor sleep quality, leading to stress and health problems.

22. What are the contributing factors of poor sleep and sleep disorders?
Pain, chronic illness, medications, alcohol use, depression, and anxiety

23. What are some nonpharmacologic interventions of sleep?
Sleep hygiene, relaxation techniques, sleep restriction measures, stimulus control, and
circadian interventions

24. What drugs are specifically used for sleep?
Benzodiazepines represent 17-23% of drugs prescribed to older adults and are one of the most abused drugs in the older population.

25. What sleep disorder affects approximately 25% of older adults?
Obstructive sleep apnea (OSA)

26. What is related to untreated obstructive sleep apnea?
Right heart failure, cardiac dysrhythmias, stroke, type 2 diabetes, and even death

27. What predisposes older adults to OSA?
Age-related decline in the activity of the upper airway muscles resulting in compromised pharyngeal patency

28. How can we treat OSA?

29. What happens in Non-rapid eye movement (NREM) sleep?
It occurs in four stages where the frequency of brain waves and vitals decline.

30. What is stage 1 sleep?
The eyes close and relaxation begins, which is known as a drifting sensation. In this stage, the person can be awakened immediately.

31. What is stage 2 sleep?
Brain waves are more irregular, and awakening is more difficult

32. What is stage 3 sleep?
Sleep deepens, and skeletal muscles are very relaxed. It takes approximately 20 minutes to get to this stage of sleep.

33. What is stage 4 sleep?
It is called “slow-wave sleep,” and vital signs reach their lowest level in this stage. It can be hard to awaken, and sleep-walking can occur in this stage.

34. How much sleep do we need?
Most people need 7-8 hours of sleep

35. How many REM cycles do we have each night?

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36. How many times do we wake up per night?
People normally 4-5 per night, but we don’t remember because the episode lasts fewer than twenty seconds.

37. What are the 4 EEG brain waves?
Delta <4Hz, Theta 4-8 Hz, Alpha 8-13Hz, and Beta >13 Hz

38. Which waves are seen in deep sleep?
Delta waves

39. What are the three main sleep stages?
Wakefulness, REM, and Non-REM

40. Which of the following physical exam findings is associated with obstructive sleep apnea?
Large tonsils

41. How long is a sleep cycle?
90-110 minutes

42. Which of the following parameters is NOT typically monitored with polysomnography?
Exhaled PCO2

43. Which of the following is NOT a common side effect of positive-pressure therapy?

44. Which of the following is NOT a parameter used to confirm the metabolic syndrome associated with obstructive sleep apnea?
Low triglycerides

45. Which of the following medical therapies is considered first-line treatment for obstructive sleep apnea (OSA)?
Continuous positive airway pressure (CPAP)

46. What is the function of melatonin?
It causes sleep craving.

47. What are the two main groups of primary sleep disorders?
Dyssomnia and parasomnia

48. What are the three causes of secondary sleep disorders?
(1) Medical – COPD, asthma, and chronic pain. (2) Drugs – caffeine, nicotine, and amphetamines. (3) Psychiatric – which are mood and anxiety disorders

49. What are some examples of dyssomnia?
Insomnia, hypersomnia, and narcolepsy

50. How is insomnia treated?
It can be treated with good sleep habits, psychological approaches, and medications.

51. Name one sleep-related movement disorder?
Restless leg syndrome

52. What is restless leg syndrome?
A disorder characterized by the irresistible urge to move with disagreeable leg sensation

53. Who gets restless leg syndrome?
It occurs in 4% of men and 5-6% of women.

54. What is PLM?
PLM stands for “periodic limb movement,” and it occurs in 80% of patients with restless leg syndrome.

55. What are the symptoms of PLM?
Insomnia, excessive daytime sleepiness, and many small awakenings during the night

56. What is the treatment for restless leg syndrome?
Dopaminergic therapy

57. What is hypersomnia, and what is it caused by?
Excessive daytime sleepiness due to insufficient sleep syndrome, depression, neurological disorders, and drug side effects

58. Which of the following conditions is NOT associated with untreated obstructive sleep apnea?
Heart failure

59. What is a hypnagogic hallucination?
A vivid, dream-like experience that occurs at the beginning or end of sleep

60. What is sleep paralysis?
It is characterized by the inability to move during the sleep/wake transition. In this case, the patient is fully oriented, but there is persistent imagery from a dream.

61. What medications can be used for the treatment of narcolepsy?
Modafinil, Methylphenidate, and Sodium Oxybate

62. Why do long, vivid dreams sometimes occur near the morning?
Morning is when REM sleep lasts the longest, and REM is when one experiences the most dreaming.

63. Which of the following factors has been shown to positively correlate with obstructive sleep apnea?
Obesity of the upper body

64. What are the symptoms of obstructive sleep apnea?
Excessive daytime sleepiness, loud snoring, dry mouth, sore throat, and frequent headaches in the morning

65. How do you diagnose obstructive sleep apnea?
It is diagnosed with an overnight sleep study.

66. What alternative methods can be used to treat OSA?
Weight reduction, soft palate reduction, and tonsil surgery

67. What are the four types of parasomnia?
Nightmares, night terrors, sleep enuresis, and somnambulism

68. What are some examples of non-REM parasomnia?
Night terrors, sleepwalking, and confusional arousal

69. What are some examples of REM sleep parasomnia?
Isolated sleep paralysis and nightmares

70. What are night terrors?
Recurrent episodes of abrupt awakening with intense fear that usually are accompanied by a scream

71. What is the cause of night terrors?
Incomplete arousal from NREM sleep which is genetic and environmentally influenced.

72. What is the prevalence of night terrors?
30-40% of people have at least one episode as a child. They occur less often during adolescence but can return in your 20s-30s.

73. What is sleepwalking?
It is an automatic behavior at night where the sufferer is unresponsive to his surroundings and other people. It most commonly involves walking around but can also include other behavior such as dressing, washing, making tea, and arranging possessions.

74. What is the prevalence of sleepwalking?
It occurs at a rate of 15-20% in children and 3-4% in adults.

75. What is the cause of sleepwalking?
Sleep deprivation, stressful events, moonlight, alcohol, and moving

76. What are nightmares?
Distressing dreams where the sufferer is oriented and can vividly describe their dream contents; they are more common in patients with depression and PTSD

77. What is REM sleep behavior disorder?
It is a violent, short-duration complex behavior that occurs at night. The subject remembers the dream that may be unpleasant.

78. What is the prevalence of REM sleep behavior disorder?
It occurs mostly in men >50 years old.

79. What is the treatment for REM sleep behavior disorder?
It can be treated with drugs such as clonazepam, agomelatine, melatonin, pramipexol, and clonidine.

80. What are some common worsening factors of parasomnia?
Anxiety and depressive disorder

81. What are circadian rhythm disorders?
Disturbances of the normal sleep-wake rhythm

82. What are the symptoms of jet lag?
Daytime fatigue, sleepiness, night-time insomnia, mood changes, problems with concentration, general malaise, and an upset stomach

83. In which direction is jet lag worse?
Eastward travel is worse because the internal rhythm is slightly longer than 24 hours. Therefore, lengthening the day after westward travel is easier.

84. What are brain waves?
Impulses that continuously pass through the brain and show up on monitoring equipment

85. What does EEG stand for?

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86. What are the types of brain waves?
Alpha, beta, theta, and delta

87. What are alpha waves?
They are brain waves that occur when one is awake but in a relaxed state with their eyes closed. Once the person falls asleep or opens their eyes to focus on a task, these waves disappear.

88. What are beta waves?
These are the typical brain waves in a person that is conscious, alert, thinking, and receiving sensory input.

89. What are theta waves?
These are the common brain waves found in children, but disappear in adults.

90. What are delta waves?
These are brain waves that are normally seen only when a person is asleep. If seen in an awake person, it could be an indication of an abnormality.

91. What is sleep?
The state of unconsciousness in which adequate stimulus can arouse and wake a person to consciousness.

92. What does it mean to be awake?
To be conscious, alert, attentive, and mindful of surroundings

93. What is a coma?
A state of unconsciousness that even intense stimuli will not wake a person

94. When do nightmares occur?

95. When does dreaming occur?
In REM sleep, not including nightmares

96. When does a person experience skeletal muscle paralysis?
REM sleep

97. Why do long, sometimes vivid dreams occur near morning?
Morning is when REM lasts the longest, and REM is when one experiences the most dreaming.

98. Has the available evidence shown that bilevel pressure is associated with better patient compliance than conventional CPAP?
No, most patients prefer CPAP over BiPAP.

99. Does central sleep apnea occur more often than obstructive sleep apnea?
No, obstructive sleep apnea occurs more often.

100. The definition of sleep apnea uses what criteria for defining an episode of apnea?
10 seconds

101. In what way do BiPAP units differ from CPAP units?
BiPAP applies different pressure levels on inspiration and exhalation.

102. Do medications work for people with sleep apnea?
No, medications have been proven ineffective for most patients with sleep apnea.

103. Do oral devices help patients with mild cases of sleep apnea?
Yes, oral devices may prove useful for cases of mild obstructive sleep apnea.

104. What is the success rate of Uvulopalatopharyngoplasty?
It is generally less than 50%.

105. What are the criteria to define hypopnea?
A 30% decrease in airflow and 4% oxygen desaturation

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106. What is believed to be the cause of systemic hypertension in patients with sleep apnea?
Increased sympathetic tone

107. What is considered to be the major problem with the use of CPAP in patients with obstructive sleep apnea?
Patient compliance

108. What is the amount of CPAP that is typically required to abolish upper airway obstruction in patients with OSA?
7.5 to 12.5 cmH2O

109. What is the primary cause of obstructive sleep apnea?
A small or unstable pharyngeal airway

110. What percent of the adult population is believed to have obstructive sleep apnea?
2% to 4%

111. What term is used to describe a significant decrease in airflow during sleep but not a complete cessation of breathing?

112. What term is used to describe CPAP units that use a computer to adjust CPAP levels as needed by the patient during sleep?

113. What value for the apnea-hypopnea index (AHI) is consistent with moderate obstructive sleep apnea?
15 to 30

114. Which of the following behavioral interventions is least useful for the treatment of sleep apnea?
Avoidance of daytime naps

115. Which of the following characteristics is not typically associated with sleep apnea?
Excessive daytime sleepiness

Final Thoughts

As previously mentioned, learning about the physiology of sleep and the different sleep disorders is essential for Respiratory Therapists and medical professionals. Hopefully, the information in this guide can help you do just that.

We have a similar guide on obstructive lung diseases that I think you will enjoy. Thank you so much for reading, and as always, breathe easy, my friend.

Written by:

John Landry, BS, RRT

John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.


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  • “Clinical Practice Guidelines for Sleep Disorders.” PubMed Central (PMC), 1 Jan. 2017,
  • “Diagnosis and Treatment of Sleep Disorders: A Brief Review for Clinicians.” PubMed Central (PMC), 1 Dec. 2003,
  • Egan’s Fundamentals of Respiratory Care. 12th ed., Mosby, 2020.
  • Wilkins’ Clinical Assessment in Respiratory Care. 8th ed., Mosby, 2017.
  • Clinical Manifestations and Assessment of Respiratory Disease. 8th ed., Mosby, 2019.

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