JC16 (Medicine) - Sleep apnea

Question 1

Causes of daytime sleepiness

Answer 1

□ ↓sleep duration: sleep deprivation, disturbance of sleep-wake cycle

□ ↓sleep quality:
→ Respiratory: sleep apnoea (central, obstructive), obesity-hypoventilation syndrome
→ Neurological: periodic limb movement syndrome

□ Normal sleep:
→ Neurological: narcolepsy, fibromyalgia, neurological lesions
→ Others: drugs, idiopathic hypersomnolence (rare)

□ Others: depression, other medical conditions

Question 2

List night-time symptoms due to sleep apnea

Answer 2

1) Sleep choking, unusual body/limb movements → arousals following apnoeic episodes
2) Snoring → obstructed airflow
3) Witnessed apnoeic episodes: witnessed pausing of breathing

Question 3

Name of clinical assessment chart for day-time sleepiness

Answer 3

Epworth sleepiness scale

- Assess likelihood to feel sleepy in situations of different activity levels

Question 4

Risk factors of daytime sleepiness

Answer 4

Nasal obstruction

Obesity

Recurrent tonsillitis in childhood

Medical conditions: acromegaly, hypothyroidism, vocal cord palsy, goitre

Drug Hx: use of hypnotics, alcohol

Question 5

Complications of chronic sleep deprivation

Answer 5

□ Risk assessment: driving, operation of heavy machinery, any previous accidents

□ Complications: HTN, ischaemic heart disease, DM

Question 6

List specific P/E for daytime sleepiness

Answer 6

□ Body habitus: weight, height, neck circumference

□ Craniofacial features, eg. short thick neck, receding chin (micronagthia), syndromic facies

□ Oropharyngeal features, eg. macroglossia, enlarged tonsils/uvula, excessive pharyngeal tissue
→ Examination: anterior rhinoscopy, throat examination and nasal endoscopy

□ Thyroid examination: hypothyroidism and goitre

□ BP/P: sleep apnoea is a secondary cause of hypertension

Question 7

Factors affecting sleep patterns

Answer 7

(1) Age
(2) Prior sleep history
(3) Circadian rhythms
(4) Drug ingestion
(5) Pathological states

Question 8

Outline the physiological feedback loop that control breathing during sleep

Answer 8

(1) Respiratory centre
(2) Chemical, mechanical and CNS information
(3) Respiratory muscles (upper airways, diaphragm and others)

Question 9

Describe the normal sleep cycle of REM and NREM sleep

Answer 9

Normal sleep cycle: enter sleep in NREM → alternate between REM and NREM with cycles of 90min

□ REM: ~25% of sleep time, increase in later hours of sleep

□ NREM: Light (stage 1/2) vs deep sleep (stage 3/4, slow wave on EEG)

Question 10

Compare REM and NREM sleep

• Body movement
• EEG
• Dreaming or non-dreaming

Answer 10

REM:
→ Dreaming
→ Brainstem/motor neurones inhibited, body paralyzed
→ Active vitals/EEG

NREM:
→ Decrease mental activity, regulatory body function only
→ Body movable

Question 11

Compare breathing patterns between REM and NREM sleep

Answer 11

NREM: Low tidal volume, Normal respiratory rate

REM: erratic, shallow breathing (ataxic)

Question 12

Explain why ventilation in sleep is decreased

Answer 12

1) Respiratory centre: suppressed arousal response
2) Chemoreceptor reflex: Lower sensitivity to O2 and CO2 → Decrease ventilatory response to hypoxia/hypercarbia

3) Resp apparatus:
- Decrease muscle contraction from intercostal muscles
- Recumbency → diaphragm pushed up → ↓FRC

Question 13

Explain why hypoxia and hypercapnia does not lead to sleep apnea in normal individual

Answer 13

In normal healthy lungs, there will be

• Mild ↓pO2 but still normal w/o ↓SaO2 (note plateau in HbO2 curve)
• Mild ↑pCO2 but still normal

In diseased lungs, baseline is already abnormal → may have hypoxia/hypercapnia in sleep

Question 14

Definition of Apnea

Answer 14

Apnoea: complete cessation of airflow at nose/mouth lasting ≥10s

Question 15

Definition of Hypopnea

Answer 15

Hypopnoea: decrease airflow with ≥3-4% decrease SaO2

and >10s/episode

Question 16

Metric to measure severity of sleep apnea/ hypopnea

Answer 16

Apnoea-hypopnoea index (AHI): number of apnoeic/hypopnoeic episodes per sleep hour

Normal = <5;
Mild OSA = 5-15;
Moderate OSA = 15-30;
Severe OSA = >30

Question 17

Differentiate obstructive and central sleep apnea

Answer 17

Obstructive: apnoea due to functional obstruction of upper airways
→ With arousal response

Central: apnoea due to abnormalities of ventilatory drive
→ No arousal response
→ Defect in central (Low ventilatory drive) or peripheral (Low muscle contraction)
→ Causes: central neurological lesions, neuropathies, NMJ disease, muscle diseases

Question 18

List anatomical abnormalities that cause obstructive sleep apnea

Answer 18

Anatomical abnormalities may predispose to functional obstruction

→ Micronagthia (undersized jaw)
→ Macroglossia (tongue fall back on supine posture)
→ Enlarged tonsils or adenoids: important factor in children (∵small airway)
→ Redundant pharyngeal tissues due to fatty infiltration (obesity)

Question 19

Describe the pathophysiology of arousal after episodes of sleep apnea

Answer 19

Ventilatory drive drops during sleep
> Decrease responsiveness to changes in blood gas
> Decrease neuromuscular tone of upper airway during sleep
> Increase upper airway obstruction
> Hypoxia and hypercapnia reaches critical point
> Activate chemical receptors
> Activate wakefulness drive and arousal

Question 20

Risk factors of Obstructive sleep apnea

Answer 20

□ Occurs in all ages but peak at middle age (40-50y)

□ Male gender

□ Obesity (50%) (parapharyngeal fat deposits narrow airway)

□ Anatomical predisposition, eg. nasal obstruction, receding chin

□ Underlying acromegaly and hypothyroidism (submucosal infiltration and narrowing of URT)

□ Alcohol and sedatives (relaxes upper airway dilating muscles)

Question 21

S/S of obstructive sleep apnea

Answer 21

• Excessive daytime sleepiness
• Snoring
• Apneoic episodes: witness apnea, Nocturnal choking, Restlessness
• Effects of poor sleep: unrefreshing sleep with morning headache, Irritability, Low concentration, Low performance

Others:

• Low libido
• Nocturia, Enuresis

Question 22

D/dx for sudden arousal with breathing difficulties during sleep

Answer 22

• OSA – ‘choking’ sensation
• PND – may be a/w orthopnoea, does not resolve immediately upon awakening, relieved by sleeping upright
• Asthma – a/w wheezes, Hx of atopy
• Rhinitis with severe nasal blockade

Question 23

Clinical diagnostic criteria of OSA

Answer 23

Suspect OSA if snoring at night plus either one of

□ Excessive daytime sleepiness (EDS)
→ Mild: activity with little attention needed, eg. public transport
→ Moderate: activity with some attention, eg. conference
→ Severe: activity with much concentration, eg. phone call, conversation

□ Meeting any two out of the following:
→ Intermittent nocturnal arousal
→ Nocturnal choking
→ Unrefreshing sleep at wakening
→ Daytime fatigue
→ Impaired daytime concentration

Question 24

Complications of obstructive sleep apnea

Answer 24

□ Sleep fragmentation
→ Car accidents
→ Neurocognitive impairments

□ Sympathetic activation → ↑BP → Secondary hypertension

□ Oxidative stress + release of mediators (hormones, cytokines, adipokines)
→ atherosclerosis + metabolic disturbances
→ Cardiovascular diseases, eg. CAD, HF, arrhythmia, stroke

□ Chronic hypoxaemia → chronic respiratory failure
→ Cor pulmonale (rare except in presence of other conditions, eg. OHS, COPD)

Question 25

Indications for Sleep Study (polysomnography)

Answer 25

→ Suspected OSA

→ Unexplained pulmonary hypertension

→ Recurrent CVS events (eg. CVA, angina, CHF) or poorly controlled HT despite adequate medical therapy

Question 26

List some metrics of polysomnography (what’s measured)

Answer 26

→ EEG, EOG and submental EMG to identify sleep stage and arousal, atonia during REM sleep
→ Lead II ECG for HR and arrhythmias

→ SaO2 for nocturnal desaturations
→ Nasal/oral airflow , thoracic and abdomen belts for respiratory effort

→ Neck microphone for snoring

→ ± leg EMG for leg movement
→ ± body position (by technician)

Question 27

List characteristic obstructive sleep apnea changes on sleep study

Answer 27

→ SaO2: intermittent hypoxia and reoxygenation
→ HR/rhythm: tachy-brady cycles
→ Thoracic movement: intrathoracic pressure swings, paradoxical movement to abdominal distension
→ Sleep architecture: sleep fragmentation
→ Body position: some people may only get OSA at supine position
→ Leg movements: corresponding to periodic arousals

Question 28

General management of OSA

Answer 28

→ Weight reduction if overweight

→ Avoid alcohol and hypnotics

→ Sleep hygiene and posture, eg. lying laterally

→ AVOID CAR-DRIVING

→ Mx of predisposing factors, eg. rhinitis, acromegaly, care after sedation/anaesthesia

→ Monitor for obesity-related conditions, eg. metabolic syndrome, DM, HTN

Question 29

Surgical options for OSA

Answer 29

Surgery for anatomical abnormalities

→ Removal of hypertrophic tonsils/adenoids in children

→ Uvulopalatopharyngoplasty (UPPP):
removal/remodeling of uvula, soft palate and pharynx

→ Faciomaxillary/mandibular surgery

→ Bariatric surgery for obesity-related medical problems

→ Surgical correction of snoring/nasal obstruction

Question 30

Devices for alleviation of OSA

Answer 30

Nocturnal nasal cPAP: application of positive pressure through nasal mask during sleep
→ Most consistently effective treatment of OSA

Mandibular advancement device
→ Device worn during sleep to advance mandible to enlarge URT and modify muscle collapsibility

Expiratory pressure device, i.e. nasal valve (to exert +ve EEP)

Question 31

Specific sleep disorder related to obesity

Answer 31

Obesity hypoventilation syndrome (OHS): awake hypoventilation due to gross obesity

Question 32

Complications of Obesity hypoventilation syndrome

Answer 32

Chronic respiratory failure or CO2 narcosis
Pulmonary HTN and cor pulmonale
Excessive daytime sleepiness

Question 33

Management of obesity hypoventilation syndrome

Answer 33

□ Weight loss and lifestyle modifications

□ Treatment of comorbidities

□ Non-invasive ventilation: CPAP/ BiPAP

□ Pharmacologic and surgical weight reduction if morbidly obese, eg. Orlistat, bariatric surgery