15: Sleep Related Breathing Disorders

Question 1

Normal control of breathing during NREM sleep

Answer 1

• Dependence on metabolic control
• Loss of voluntary/behavioral control
• Permissive respiratory periodicity
• Alveolar hypoventilation
  
  • V_E decreased by ~1.5 Lpm
  • PaCO2 increased by 3-6mmHg
• ↑upper airway resistance

Question 2

Normal control of breathing during REM sleep

Answer 2

• Decreased/absent metabolic response
• Inhibition/paralysis of postural muscles including UA and accessory breathing muscles
• Irregular, shallow respiration/apnea
• All may result in severe hypoventilation/hypoxemia

Question 3

General classification of sleep-related breathing disorders

Answer 3

• Central sleep apnea syndromes
  
  • Due to Cheyne-Stokes breathing
  • Due to drug or substance
• Obstructive sleep apnea syndromes
  
  • Adult obstrutive sleep apnea
  • Pediatric obstructive sleep apnea
• Sleep-related hypoventilation/hypoxemic syndromes
  
  • “Central” alveolar hypoventilation syndromes

Question 4

Risks with sleep-related breathing disorders

Answer 4

• Cardiovascular:
  
  • HTN
  • HF
  • Dysrhythmia
• Stroke
• Pulmonary:
  
  • COPD
  • Overlap syndrome
  • Hypoventilation syndromes
  • Parenchymal lung dz
  • PHTN

Question 5

Apnea

Answer 5

• Cessation of airflow ≥ 10 sec
• Central, obstructive or mixed

Question 6

Hypopnea

Answer 6

• Discrete reduction (not absence) in airflow and respiratory effort
• Lasts ≥ 10 seconds
• Typically with SpO2 decrease of 3-4% and/or arousal from sleep
• Obstructive or non-obstructive

Question 7

Types of apneas

Answer 7

• Obstructive: with ventilatry effort; associated with upper airway obstruction
• Central: without ventilatory effort
• Mixed: begins with central apnea, ends as obstructive

Question 8

Sleep apnea indexes

Answer 8

• Apnea index (AI): #apneas/hr
• Apnea-hypopnea index (AHI): #apneas+hypopneas/hr

Question 9

Obstructive sleep apnea syndrome (OSAS)

Answer 9

• AHI ≥ 5 w/ excessive daytime sleepiness
• Prevalence: 24% men (30-60yo), 9% women, 80% undiagnosed

Question 10

Acute consequences of obstructive apneas

Answer 10

• Abrupt arousal from sleep
• O2 desat
• Systemic BP swings
• ↓CO
• ↑RV, LV afterload
• ↑PA pressure
• ↑myocardial O2 demand + ↓coronary blood flow
• ↑arterial stiffness
• ↑vagal, sympathetic surges

Question 11

OSA clinical manifestations

Answer 11

• Snoring alternating w/ periods of silence
• XS daytime sleepiness/increased risk of MVA
• poor sleep quality/insomnia
• awaking sensation of choking/gasping
• morning HA/dry mouth/poor memory/concentration

Question 12

OSA cardio/cerebrovascular associations

Answer 12

• Systemic HTN
  
  • AHI 5-29.9: ≥ 20% XS risk HTN
  • AHI ≥ 30: 37% XS risk HTN
• ↓LV function
• Stroke (during sleep 48% of time)
• Sudden death nocturnally
• ↑risk all-cause and CAD-related mortality

Question 13

OSA management

Answer 13

• Wt loss
• Sleep positioning (avoid supine)
• Alcohol/sedative avoidance
• Oral devices
• Surgery (?)
• Continuous positive airway pressure (CPAP)
  
  • ​pressure settings determined by titration during **polysomnography **(typically 6-16 cm H2O)
  • ↑QOL, LVEF; ↓AI, AHI, daytime sleepiness; improved BP, no data on mortality

Question 14

Cheyne-Stokes Breathing with Central Sleep Apnea (CSB/CSA)

Answer 14

• Periodic breathing occurs in various disease states
• Pathogenesis:
  
  • Stimulation of vagus nerve receptors in the lung, 2/2 pulmonary congestion or reduced lung compliance
  • Hyperventilation –> hypocapnia; respiratory mechanism overresponds to CO2 –> breathing ceases, and the cycle repeats
    
    • Increased chemoreceptor drive and delayed feedback gain
• In CHF: asphyxia, arousal, disrupted sympathovagal balance, acute systemic and pulmonary pressure responses, increased complex ventricular arrhythmias
• Treatment: Treat CHF (lower filling pressure w/ diuresis, ACE inhibitors, beta blockers, heart transplant); O2 alone (prevent SaO2 decreases, decrease apnea frequency [O2 flow must be sufficient enough to increase PaCO2]); PAP (↑intrathoracic pressure, ↓transmural pressure [↓preload, afterload]), ↓inspiratory muscle work) –> ↑PaCO2 above apneic threshold

Question 15

Central hypoventilation syndrome (CHS)

Answer 15

• Sleep-related nonobstructive alveolar hypoventilation
• “Ondine’s curse”
• Absent respiratory response to hypoxia or hypercapnia, mildly elevated PaCO2 while awake, and markedly elevated PaCO2 during non-REM sleep
• Congenital and acquired
• Infarct/reduced respiratory affernt input to dorsal respiratory group of medullary neurons, nucleus tractus solitarius

Question 16

Cluster Breathing

Answer 16

• Groups of quick, shallow inspirations followed by regular or irregular periods of apnea
• Associated with opioids, brain stem damage due to strokes, trauma or increased ICP; also reported in bihemispheric infarction