Chapter 10: Normal Sleep and Sleep Disorders
I. Normal Awake and Sleep States
Understanding normal sleep is essential for diagnosing sleep disorders.
A. The Circadian Cycle
Humans have an internal biological clock that governs the sleep-wake cycle. In the absence of external time cues (like sunlight), this circadian cycle runs on a rhythm closer to 25 hours, not 24. These external cues, called zeitgebers (German for "time-givers"), help synchronize our internal clock with the 24-hour day.
B. The Awake State
- EEG Waves: An electroencephalogram (EEG) of an awake person shows two main types of brain waves:
- Beta Waves: Fast, low-amplitude waves seen during active mental concentration.
- Alpha Waves: Slower waves seen when a person is relaxed with their eyes closed.
- Sleep Latency: The time it takes to fall asleep is normally less than 10 minutes.
C. The Sleep State and Sleep Architecture
Sleep is divided into two major types: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. A typical night's sleep cycles through these stages in a predictable pattern called sleep architecture.
| Sleep Stage | Associated EEG Pattern | % of Sleep Time (Young Adults) | Key Characteristics |
|---|---|---|---|
| Awake | Beta & Alpha Waves | — | Relaxed with eyes closed (alpha), mentally active (beta). |
| NREM Stage 1 | Theta Waves | 5% | Lightest stage of sleep; transition from wakefulness. Slowed pulse and breathing. |
| NREM Stage 2 | Sleep Spindles & K-complexes | 45% | Largest percentage of sleep time. Bruxism (tooth grinding) can occur. |
| NREM Stages 3 & 4 (Delta Sleep) | Delta Waves (Slow-Wave Sleep) | 25% | Deepest, most restorative sleep. Sleep disorders like sleepwalking (somnambulism), night terrors, and bed-wetting (enuresis) occur here. |
| REM Sleep | "Sawtooth" waves (Beta, Alpha, Theta) | 25% | Dreaming occurs. Body is paralyzed (skeletal muscle atonia), but brain is highly active. Increased pulse, respiration, and blood pressure. Penile and clitoral erection. |
Key Features of Sleep Cycles:
- A complete sleep cycle (from Stage 1 to REM) lasts about 90 minutes.
- REM Latency: The time from falling asleep to the first REM period is normally about 90 minutes.
- Distribution of Sleep Stages: Most Delta (deep) sleep occurs in the first half of the night. REM periods become longer and more frequent in the second half of the night.
- REM Rebound: If a person is deprived of REM sleep on one night (e.g., due to sedative use or frequent awakenings), they will experience an increased amount of REM sleep the following night.
D. Neurotransmitters and Sleep
- Acetylcholine (ACh): Increases both sleep efficiency and REM sleep.
- Dopamine: Decreases sleep efficiency. Antipsychotics that block dopamine can improve sleep.
- Norepinephrine: Decreases both sleep efficiency and REM sleep.
- Serotonin: Increases both sleep efficiency and Delta sleep.
E. Sleep Changes with Age
Sleep architecture changes significantly across the lifespan. Elderly individuals experience a significant reduction in Delta (deep) sleep and more frequent nighttime awakenings, leading to poor sleep quality and daytime fatigue.
| Sleep Measure | Typical Young Adult | Depressed Young Adult | Typical Elderly Adult |
|---|---|---|---|
| Sleep Latency | About 10 min | >10 min (increased) | >10 min (increased) |
| REM Latency | About 90 min | About 45 min (shortened) | About 90 min (no change) |
| Sleep Efficiency | About 100% | <100% (decreased) | <100% (decreased) |
| Percentage Delta | About 25% | <25% (decreased) | <25% (decreased or absent) |
| Percentage REM | About 25% | >25% (increased total) | <25% (decreased) |
II. Classification of Sleep Disorders
The DSM-5 categorizes sleep disorders into several main groups.
- Sleep-Wake Disorders: Problems with the timing, quality, or amount of sleep. Includes insomnia, hypersomnolence, and narcolepsy.
- Breathing-Related Sleep Disorders: Disrupted sleep due to breathing problems, primarily sleep apnea.
- Parasomnias: Abnormal behaviors or physiological events that occur during sleep. Includes bruxism (tooth grinding), sleepwalking, sleep terror disorder, and nightmare disorder.
III. Major Sleep Disorders
A. Insomnia
- Definition: Difficulty falling asleep or staying asleep, leading to daytime sleepiness or impairment.
- Psychological Causes:
- Major Depressive Disorder: The most common psychiatric cause. Key sleep features include terminal insomnia (waking too early), long sleep latency, and short REM latency.
- Bipolar Disorder: Patients in a manic or hypomanic state have trouble falling asleep and require less sleep.
- Anxiety Disorders: Anxious patients often have difficulty falling asleep.
- Physical Causes:
- Use of CNS stimulants (e.g., caffeine).
- Withdrawal from sedatives (e.g., alcohol, benzodiazepines).
- Medical conditions causing pain.
B. Breathing-Related Sleep Disorder (Sleep Apnea)
- Definition: A disorder where the patient repeatedly stops breathing for brief intervals during sleep. This causes low oxygen and high carbon dioxide levels, leading to respiratory acidosis (blood pH < 7.35) and frequent awakenings. The result is severe daytime sleepiness and morning headaches.
- Types:
- Central Sleep Apnea: No respiratory effort is made. More common in the elderly.
- Obstructive Sleep Apnea: Respiratory effort occurs, but an airway obstruction prevents air from reaching the lungs. Much more common, especially in obese, middle-aged men who snore loudly.
C. Narcolepsy
- Definition: A disorder characterized by uncontrollable "sleep attacks" during the day, despite a normal amount of sleep at night.
- Key Features (The Narcolepsy Tetrad):
- Excessive Daytime Sleepiness: The primary symptom.
- Cataplexy: A sudden, complete loss of muscle tone triggered by a strong emotion like laughter or surprise. The person collapses but remains conscious. Occurs in ~70% of patients.
- Hypnagogic/Hypnopompic Hallucinations: Vivid, dream-like hallucinations that occur as the patient is falling asleep (hypnagogic) or waking up (hypnopompic).
- Sleep Paralysis: A brief inability to move or speak immediately upon waking.
- Sleep Pattern: Characterized by a very short REM latency (<10 minutes), meaning patients enter REM sleep almost immediately after falling asleep.
IV. Management of Sleep Disorders
| Disorder | Management Strategies (in order of utility) |
|---|---|
| Insomnia | 1. Sleep Hygiene: Establish a consistent sleep schedule, create a relaxing bedtime ritual, avoid caffeine before bed, and get daily exercise. 2. Psychoactive Agents: Use of sleep agents should be limited. Antidepressants may be used if insomnia is due to depression. |
| Obstructive Sleep Apnea | 1. Weight Loss: If the patient is overweight. 2. Continuous Positive Airway Pressure (CPAP): A mask worn at night that delivers gentle air pressure to keep the airway open. This is the primary treatment. 3. Breathing Stimulants or Surgery: Less common options. |
| Narcolepsy | 1. Stimulant Agents: Medications like modafinil (Provigil) or methylphenidate (Ritalin) are used to manage daytime sleepiness. 2. Scheduled Daytime Naps: Can help the patient feel refreshed by making up for lost REM sleep. |
Knowledge Check Quiz: Sleep Disorders
Question 1
The parents of a 5-year-old boy report that the child often screams during the night. They are particularly concerned because during these disturbances, the child sits up, opens his eyes, and “looks right through them,” and they are unable to awaken him. The child has no memory of these experiences in the morning. During these disturbances, the child’s EEG is most likely to be primarily characterized by:
Question 2
During a sleep study, a physician discovers that a patient shows too little REM sleep during the night. Theoretically, to increase REM sleep, the physician should give the patient a medication aimed at increasing circulating levels of:
Question 3
During a sleep study, a male patient’s EEG shows primarily sawtooth waves. Which of the following is most likely to characterize this patient at this time?
Question 4
During a sleep study, a female patient’s EEG shows primarily delta waves. Which of the following is most likely to characterize this patient at this time?
Question 5
An 85-year-old patient reports that he sleeps poorly. Sleep in this patient is most likely to be characterized by increased:
Question 6
A woman reports that most nights during the last year, she has lain awake in bed for more than 2 hours before she falls asleep. After these nights, she is tired and forgetful and makes mistakes at work. Of the following, the most effective long-term treatment for this woman is:
Question 7
A 22-year-old medical student who goes to sleep at 11 pm and wakes at 7 am falls asleep in the laboratory every day. He tells the doctor that he sees strange images as he is falling asleep. Which of the following is this student most likely to experience?
Question 8
The medical student in the previous question is diagnosed with narcolepsy. The most effective first step in management is: