Physiology of Sleep Breathing Disorder

Chapter 15: Physiology of Sleep-Disordered Breathing

Objectives

• Explain how the brain regulates sleeping and waking cycles through neurocontrolled chemical mediators.
• Explain why the upper airway anatomy plays such a major role in sleep-disordered breathing (SDB).
• Distinguish among the three stages of nonrapid eye movement sleep and rapid eye movement sleep.
• Identify the six major categories of sleep disorders and the specific classification for SDB.

Additional Objectives

• Differentiate among obstructive sleep apnea, central sleep apnea, complex sleep apnea syndrome, overlap syndrome, hypoventilation syndrome, childhood sleep apnea, and sudden infant death syndrome.
• Explain the effects of SDB on the cardiovascular system.
• Identify the mechanisms of central hemodynamic dysfunction secondary to SDB.
• Classify SDB through the use of the polysomnogram.
• Explain the physiological treatment of SDB using various therapeutic devices and methods.

Introduction to Sleep Breathing Disorders (SBDs)

• One third of human lifetime is spent sleeping.
• SBDs are characterized by:
  • Abnormal respiratory patterns during sleep
  • Poor ventilation quality during sleep
• Key to understanding SDB:
  • Comprehension of the brain’s role in controlling sleep
  • Anatomical and physiological features of the upper airways.

Neurocontrol of Sleep

• Sleep is an active process.
• Polysomnogram (PSG):
  • A diagnostic test evaluating sleep quality.
  • Assesses over 20 physiological parameters and records data throughout sleep cycles from wakefulness to sleep stages (NREM and REM).

Major Brain Regions in Sleep Regulation

• Medulla Oblongata:
  • Connects to the spinal cord; regulates basic life functions.
• Pons:
  • Located superiorly to the medulla; involved in regulating sleep and wakefulness.
• Midbrain (Mesencephalon):
  • Situated just above the pons; plays a role in arousal and sleep regulation.
• Cerebrum (Telencephalon):
  • Composed of five paired lobes within two hemispheres; associated with high-level processing.
• Diencephalon:
  • Nestled between cerebral hemispheres and superior to the brainstem, vital for hormonal regulation and arousal control.

Key Structures in Diencephalon

• Thalamus:
  • Relays sensory information; regulates consciousness and alertness.
• Hypothalamus:
  • Releases melatonin, which is believed to induce sleep by inhibiting arousal centers.
• Optic Chiasm:
  • Involved in visual processing; impacts circadian rhythms.
• Pineal Gland:
  • Produces melatonin; regulates various biological rhythms and processes.

Circadian Rhythm and Sleep Regulation

• “Sleep Clock”:
  • Located in the suprachiasmatic nucleus (SCN) of the hypothalamus, controlling circadian rhythms influenced by light exposure.
• Ventrolateral Preoptic Nucleus (VLPO):
  • Inhibits brain arousal centers; contributes to sleep promotion.
• Neurotransmitters Involved in Arousal:
  • Histamine, serotonin, norepinephrine, acetylcholine, hypocretin (orexin).

Upper Airway Anatomy and Sleep

• Upper Airways Comprised Of:
  • Nose, Pharynx, Larynx.
• Normal Pharyngeal Muscle Tone:
  • Maintains airway patency by preventing the tongue from obstructing the tracheal passage.
• Potential Obstructive Structures:
  • Tongue, soft/hard palate, uvula, tonsils.
• Mallampati Classification:
  • Mallampati Score:
  • Assess oropharyngeal space by visualizing anatomical structures (1-4 classification scale).

Stages of Sleep

• Normal Sleep Cycle:
  • Alternates between NREM and REM stages every 60 to 90 minutes over 4 to 5 cycles in 8 hours.

Non-Rapid Eye Movement (NREM) Sleep Stages

• Stage 1 NREM:
  • Transition to sleep; 5%-10% of total sleep.
• Stage 2 NREM:
  • Characterized by K-complexes and sleep spindles; makes up 40%-50% of sleep duration.
• Stage 3 NREM (Deep Sleep):
  • Involves delta waves; restorative sleep, minimal responsiveness.
• Physiological Changes in NREM:
  • Muscle tone maintained; respiratory rate and tidal volume decrease, causing a rise in PaCO_2 by 2 to 4 mm Hg.

Rapid Eye Movement (REM) Sleep

• Physiological Characteristics:
  • Loss of core temperature regulation; increased cerebral blood flow.
  • Blood Pressure Variability:
  • Can elevate during REM sleep and poses risks for patients with pulmonary/cardiac diseases.
• Sleep Architecture Representation:
  • Sleep histogram shows cycling through various sleep stages.
  • Poor hygiene leads to fragmented cycles.

Sleep Disorders Classification

• One in six Americans experiences sleep disorders.
• Categories of Sleep Disorders:
  1. Dyssomnias (most common): Obstructive Sleep Apnea (OSA), Central Sleep Apnea (CSA), Complex Sleep Apnea Syndrome (CompSAS).
  2. Parasomnias.
  3. Medical or psychiatric conditions causing sleep disorders.
  4. Sleep sickness.
  5. Snoring.
  6. Sudden Infant Death Syndrome (SIDS).

Obstructive Sleep Apnea (OSA)

• Prevalence:
  • Most common SBD in the U.S.; majorly anatomical.
• Structural Issues Impacting OSA:
  • Macroglossia, micrognathia, deviated septum, retrognathia.
• Symptoms:
  • Episodes of suffocation; risk factors characterized by supine sleeping positions.
• Consequences of Untreated OSA:
  • Can lead to health issues like hypertension, decreased performance, psychological problems, and cardiovascular complications.

Central Sleep Apnea (CSA)

• Definition:
  • Lack of airflow with absences of thoracic-abdominal effort for at least 10 seconds; about 10% of all adult SDB.
• Causes of CSA:
  • Stroke, brainstem damage, encephalitis, and chronic heart failure.
• Common Signs:
  • Cheyne-Stokes respirations; can occur in infants, particularly premature babies.

Complex Sleep Apnea Syndrome

• Definition:
  • A blend of OSA and CSA in the same patient.

Sudden Infant Death Syndrome (SIDS)

• Definition:
  • The unexplained sudden death of an infant <1 year after a thorough investigation.
  • Risk factors include prone sleeping position and maternal habits.

Cardiovascular Effects of Untreated SDB

• Primary Cardiovascular Risk Factors:
  • Pulmonary Vasoconstriction, Hypotension, Increased Heart Rate, Stroke, Myocardial Infarction.
• Causal Factors in Cardiovascular Disease:
  • Associated with hypertension, heart failure, and arrhythmias.

Diagnosing Sleep-Disordered Breathing (SDB)

• Polysomnogram Characteristics:
  • Gold standard diagnostic tool; records 17 physiological channels.
  • Main Measurement: Apnea-Hypopnea Index (
    ;AHI
    ;):
  • Adults: AHI > 5 per hour with SpO2 drop > 4%.
  • Children: AHI > 1 with etCO2 > 53 mm Hg or SpO2 < 92%.
• Severity Classification of SDB based on AHI:
  • Mild: AHI 5-20
  • Moderate: AHI 21-40
  • Severe: AHI > 40.

Treatment of Sleep-Disordered Breathing (SDB)

• Four Major Categories of Treatment:
  1. Positive Airway Pressure (PAP) Therapy:
  • Devices and masks; crucial for proper fitting.
  1. Oral Appliances:
  • Mandibular advancement devices to reposition the jaw forward.
  1. Implantable Upper Airway Stimulation:
  • Such as the Inspire UAS system; provides nerve stimulation to name muscle.
  1. Surgical Interventions:
  • Procedures such as uvulopalatopharyngoplasty (UPPP) or glossectomy may be utilized; their effectiveness can be controversial.
• Positioning Therapy:
  • Avoiding the supine position using specific devices.
• Drug Therapy:
  • Effective treatments are still under exploration.

Concept Questions

• 15-1: What part of the brain controls sleep and wakefulness?
• 15-2: How does oropharyngeal anatomy affect breathing during sleep?
• 15-3: What is the Mallampati score and how is it relevant?
• 15-4: Explain the differences between NREM stages 1, 2, and 3.
• 15-5: Describe physiological changes during REM sleep.
• 15-6: To what major category do OSA, CSA, and CompSAS belong?
• 15-7: Define apnea vs hypopnea events.
• 15-8: Effects of hypoxia and hypercapnia on the cardiovascular system; consequences of untreated SDB.
• 15-9: Outline the diagnostic process for SDB.
• 15-10: Discuss treatment categories for SDB and the most common methods.