Lecture 19 - Pathophysiology Of Sleep Apnoea

Question 1

Apnoea definition

Answer 1

• cessation of airflow at the mouth and nose for over 10 sec during sleep
• reduction in the peak aiflow excursion on an oro-nasal thermal sensor of 90% of the pre-event baseline

Question 2

Hypopnoea definition

Answer 2

• reduction in amplitude of airflow or thoraco-abdominal wall movement of >30% of pre-event baseline measurement
• the amplitude reduction is associated with either oxygen desaturation of 3% or an arousal
• the duration of the 30% drop in signal excusrion lasts 10 sec +
• at least 90% of the events duration must meet the amplitude reduction criteria

Question 3

Respiratory effort related arousal

Answer 3

• sequence of breaths lasting >10 sec characterised by increasing respiratory effort or by flattening of the inspiratory portion of the nasal pressure signal
• event needs to lead to arousal from sleep
• sequence of breaths does not meet criteria for an apnoea or hypopnoea

Question 4

Central apnoea

Answer 4

• apnoea accompanied by an absence of diaphragm EMG and thoraco-adominal wall movement
• no effort to breathe, its a drive problem

Question 5

• Obstructive apnoea

Answer 5

• apnoea with continued or raised EMG diaphragm activity and/or thoraco-abdominal wall movement
• paradoxical thoraco-abodminal movement may occur
• difficulty breathing

Question 6

Mixed apnoea

Answer 6

• apnoea with. Both central and obstructive componets, with central component for at least one respiratory cycle length
• more related to obstructive

Question 7

Obstructive sleep apnoea clinical syndrome

Answer 7

• characterised by recurrent upper airway obstruction during sleep
• spectrum: normal ->snoring -> OSA

Syndrome:

• recurrent episode of apnoea and hypopnoea
• respiratory disturbance index of over 5 events per hour of sleep
• symptoms of functional impairment

Question 8

OSA diagnostic criteria

Answer 8

1) Excessive daytime sleepiness unexplained by other factors
2) 2+ of choking during sleep, recurrent nocturnal awakening, unrefreshing sleep, daytime fatigue, impaired concentration, memory disturbances
3) overnight monitoring demonstrates 5+ apnoeas and hypopnoes per hour of sleep

• must have 1 or 2, + 3

Question 9

OSA consequences

Answer 9

• fragmentation of sleep
• hypersomnolence
• cognitive dysfunction
• memory loss
• emotional disturbances
• social disharmonhy
• pulmonary and systemic hypertension
• cardiac arrythmias, AF
• myocardial infarction and stroke
• decreased survival

Question 10

Factors contributing to upper airway obstruction during sleep: pharyngeal airway

Answer 10

• anterior wall has no body or cartilaginous support and depends on upper airway muscle activity to maintain patency
• these muscles are normally activated in a rhytmical fashion during each inspiration

Question 11

Balance of forces

Answer 11

• upper airway patency depends on a balance of collapsing and dilating forces
• collapsing forces: negative airway pressure generated by the inspiratory acrtivity of the diaphragm
• dilating force: upper airway dilator muscle activity
• collapse occurs when the force produced by the muscles, for a given cross-sectional area of the upper airways, is exceeded by the negative airway pressure

Question 12

Causes of upper airway obstruction

Answer 12

• anatomical narrowing of the upper airway
• excessive loss of upper airway muscle tone
• defective upper airway protective reflexes
• increased loop gain promotes an unstable airway
• frequent arousal destabilise airway

Question 13

Site of airway obstruction

Answer 13

• alway s between choanae and epiglottis
• generally behind uvula and soft palate (nasopharynx)
• also behind tongue (oropharynx)
• collapse at the level of the epiglottis is unusual
• multi-level collapse is usual`

Question 14

Factors promoting OSA

Answer 14

• Sex: males have higher pharyngeal resistance
• Age: pharyngeal resistance increases with age, and so does risk of OSA
• obesity: strong association between obesity and OSA, may relate to fat deposition in pharyngeal walls, neck or abdomen
• Genetics: familial association exists
• Ethanol reduces upper airway muscle tone, so it increases frequency and duration of apnoeas
• Cranio-facial anatomy: retrognathia and enlarged tonsies

Question 15

Reduced upper airway size leads to

Answer 15

• increased upper airway resistance
• more negative pharyngeal pressure during inspiration - can lead to collapse
• increased transmural collapsing pressure
• upper airway occlusion during sleep

Question 16

Anatomical abmnormalities associated with OSA

Answer 16

• adenotonsillar enlargment
• micrognathia
• infiltration of muslces and soft tissue: myxoedema in hypothyroidism, acromegaly, neoplastic processes, mucopolysaccharisosis
• nasal obstriction -> icnreases negative pressure, but not a strong association with sleep apnoea

Question 17

Effect of NREM sleep on muscle activity

Answer 17

• genioglossus and diaphragm maintain normal activity
• palatoglossus, levator palatini and tensor palatini all reduce activity
• tensor palatini has the most reduced activity and it is the most important muscle for OSA because it is the one that pulls the soft palate away from the tongue, opening up the airways

Question 18

Upper airway muscle and sleep in normal

Answer 18

• upper airway remains patent in normal subjects despite decrements in upper airway muscle activity during sleep
• upper airway muscle respond to negative airway pressure by reflex activation
• during sleep, this reflex response to negative pressure is diminished or absent

Question 19

Upper airway muscle and sleep in OSA patients

Answer 19

• during wakefulness, OSA patients compensate for inadequate airway anatomy by increasing pharyngeal dilator muscle activity
• this neuromuscular compensation mechanism is driven by reflex responses to negative airway pressure
• loss of neuromuscular compensation during sleep leads to airway occlusion in OSA patients

Question 20

Control of breathing and OSA

Answer 20

• reduced hypercapnic ventilatory response in OSA
• imbalance of upper airway muscle activity and diaphragm activity during sleep - favors upper airway collapse
• hypoxia causes periodid breathing and may lead to hypocapnia, which predisposes to further apnoea
• impaired resistive load detection in OSA patient

Question 21

Arousal and OSA

Answer 21

• arousal from sleep is responsible for terminating obstructive events: airway occlusion, hypoxia and hypercapnia all play a part
• arousal do not usuallylead to complete awakening
• impaired arousal responses will lead to more profound and prolonged apnoeas
• arousal may lead to hyperventilation post-apnoea, leading to hypocapnia and reduced ventilatory drive, predisposing to recurrent upper airway occlusion

Question 22

3 types of central apnoea

Answer 22

• due to hyperventilation (low CO2)
• due to hypoventilation (high CO2)
• due to cheyne stokes respiration associated with cardiac failure

Question 23

Central apnoea due to hyperventilation

Answer 23

• respiration during NREM is critically dependent on PaCO2
• central apnoea results if arterial PaCO2 is lowered below ethe apnoeic threshould

EVENTS

• stimulus induces hyperpnoea
• hyperpnoea causes ventilatory overshoot and hypocapnia, causing central apnoea
• central apnoea causes PaCO2 to rise, restoring rhtymic respiration with or without arousal
• hyperpnoea, ventilatory overshoot, hypocapnia and further central apnoea follows

Question 24

Syndromes with hypercapnia

Answer 24

• dominant central apnoea with no cardiac disease
• more regular pattern of panoeas
• abnormally. High awake ventilatory responses
• disinhibition of brainstem respiratory reflexes may result in extreme sensitivity of the respiratory controller to CO2
• may be precipitated by stroke and frontal lobe syndrome
• may not be any identifiable neurological diseae

Question 25

Central apnoea due to hypoventilation

Answer 25

• less common
• occurs in patients with marginal ventilatory statys
• wakefulness stimulus to breathe disappears during sleep, resulting in alveolar hypoventilation and cental pnoeas
• ventilation is restored by arousal from sleep, but declines during sleep

Question 26

Syndromes with hypocapnia

Answer 26

• alveolar hypoventilation in sleep
• reduced tidal volume rather than discrete apnoeas
• irregular pattern of decreased tidal volumes, central apnoea and arousal
• abnormally low awake ventilatory response

Question 27

Syndromes with cardiac failure

Answer 27

• congestive cardiac failure predisposes to central apnoea and Cheyne-stokes breathing
• induces overall alveolar hyperventilation
• up to 80% of patients may have sleep disordered breathing
• delayed circulation time with fluctuation of arterial CO2 is thought to dominate the mechanism