Definitions• Apnea It is defined by American Academy of Sleep Medicine (AASM) as the airflow (measured by the oronasal thermal sensor) reduction by 90% for >10s or for 90% of the duration of the event.
• HYPOPNEA Hypopnea is defined by a consensus conference(Chicago Criteria) as including one of three features:A. Substantial reduction in airflow (>50%),B. Moderate reduction in airflow (<50%) with desaturation (>3%)C.Moderate reduction in airflow (<50%) with EEG evidence of arousal.
• AASM provide two definitions of hypopnoea (A and B)A. At least 30% reduction in airflow accompanied by a fall in oxygen saturation of 4% or more. (Recommended)B. At least 50%reduction in airflow accompanied by an arousal or a fall in oxygen saturation of 3% or less.(Alternative)
• RERA ( Respiratory Effort Related Arousal) It is defined as increasing respiratory effort for 10 seconds or longer leading to an arousal from sleep but one that does not fulfill the criteria for a hypopnea or apnea.• AROUSAL RESPONSE Arousal response has an important role in termination of sleep, inducer of cough reflex, life saving gestures, termination of apnea episode etc. BUT associated with1. Fragmentation of sleep2. Sympathetic surge that is associated with various cardiovascular events
• AHI (Apnea Hypopnea Index) Apnea and Hypopnea episodes are measured by an index known as Apnea Hypopnea Index (AHI)- No. of Apnea or Hypopnea episodes per Hr of sleep.• Up to 5 AHI’s can occur during sleep in normal individuals and is considered irrelevant.• > 5 AHI are clinically relevant and they are sub classified as mild (5-15) moderate (15-30)and severe (>30).
SLEEPSleep predominantly occurs in two stages1. REM2. NREM• Both have different effects on blood pressure heart rate and respiration• Adults usually spend 70-80% sleep in NREM while children and aged usually spend 70% of sleep in REM.Physiological effects of these stages are as follows
STAGES OF SLEEP• It is characterized by two stages which alternates during whole of sleep1. NREM ( Non Rapid Eye Movement ):-• 90-120 mnts. (each cycle)• 75% of total duration.• It is further classified into 4 stages as I, II, III,IV. Stage IV is deepest sleep ( slow wave sleep)• In general NREM is characterized by reduction in sympathetic outflow and increase in parasympathetic outflow. (↑ Vagal tone)• Leads to ↓ B.P. , ↓H.R. , ↓C.O. ↓ Tidal ventilation and minute ventilation. Control of ventilation is majorly by chemical means (compared with values when person is awake)
Stages of sleep cont…2. REM ( rapid eye movement sleep)• 10-20 mnts duration. alternates with NREM sleep .• Makes 15-20% of total sleep duration• It is characterized by loss of all sensory inputs and motor outputs of brain but brain is metabolically active, rapid rolling type eye movements, dreaming, awakening, paralysis, c onsolidation of memory, satisfaction of sleep.
Continued..• Return of sympathetic tone causes ↑ in H.R., B.P. and C.O. to the values similar to wakefulness• Phasic activity that occurs in bursts• Causes both ↑ and ↓ in H.R. and predisposes to MI and Asystole resp.• Ventilation is reduced than NREM. v High propensity of apnea,
SLEEP APNEA• It is further classified as1. OBSTRUCTIVE2. CENTRAL3. MIXED
Types contd..• OBSTRUCTIVE It is most common type, occurs because of collapse of upper airways at intervals during sleep• CENTRAL It occurs because of problem in brain or its neural pathways stimulating and controlling breathing without any change in the physical status of the airways.• MIXED Absence of thoracoabdominal movements during initial part of airflow cessation but appear gradualy as the episode terminates.
Collapse of airways Apnea (↑PCO2,↓PO2 ) Sympathetic surge AwakeningOpenning of airwaysTermination of episode
Structural factorsStructural factors related to craniofacial bony anatomy that predispose patients with OSA to pharyngeal collapse during sleep include the following:• Innate anatomic variations• Retrognathia and micrognathia• Mandibular hypoplasia• Inferior displacement of the hyoid
• Adenotonsillar hypertrophy, particularly in children and young adults• Pierre Robin syndrome• Down syndrome• Marfan syndrome• Prader-Willi syndrome• High, arched palate (particularly in women)• Brachycephalic head form - Associated with an increased AHI in whites but not in African Americans.
Innate anatomical variations in OSA• Presence of excessive soft tissue for given craniofacial anatomy• Large tongue• Longer soft palate• Less lateral dimensions• Increased parapharyngeal pad of fats• Sedative use• Smoking
Nonstructural risk factors Nonstructural risk factors for OSA include the following:• Obesity• Central fat distribution• Male sex• Age• Postmenopausal state• Alcohol use
Nonstructural factors contd…• Sedative use• Smoking• Habitual snoring with daytime somnolence• Supine sleep position
Etiology contd.. Other conditions associated with the development of OSA are as follows:• Hypothyroidism• Neurologic syndromes• Stroke• Acromegaly• Environmental exposures
Neuropsychological usually day time symptoms• Excessive daytime sleepiness- initially to passive events , directly related to severity• Fatigue• Decreased energy• Inability to concentrate• Irritability• Mental clouding• Early morning headache
Cardio respiratoryRelated to apneic events, occurs nocturnal• Snoring- most common symptom, present for many years, patient may be unaware, interrupted periodically by silence.• Awakening with choking, gasping or air hunger• Nocturia• Insomnia• Unrefreshing sleep, mental clouding, early morning headache• PND• Symptoms of HTN, Stroke, Acute anginal events
Investigation and diagnosis• Middle aged or elderly man or woman (postmenopausal)• Overweight, hypertensive• Comes with C/O unrefreshing sleep, snoring, choking and daytime sleepiness• It can be suspected in any of the primary cardiovascular events previously mentioned
Physical examination• Age• Neck circumference• BMI• Visualization of pharynx to assess crowding• Soft tissue dimensions and craniofacial abnormalities• Blood pressure
PSG• AASM guidelines for the indications and performance of PSG include the following:• Sleep stages are recorded via an EEG, electrooculogram, and chin electromyogram (EMG).• Heart rhythm is monitored with a single-lead ECG.• Leg movements are recorded via an anterior tibialis EMG.• Breathing is monitored, including airflow at the nose and mouth (using both a thermal sensors and a nasal pressure transducer), effort (using inductance plethysmography), and oxygen saturation.• The breathing pattern is analyzed for the presence of apneas and hypopneas, determined according to definitions standardized by the AASM.
• PSG can be done in home by portable PSG devices - unattended, cheap. Sleep stage, sleep position, RERA cant be measured and negative study cant exclude OSA.• In lab or attended PSG – gold slandered1. Standard PSG- evaluation and severity of OSA on night 1 pt again comes on next day for CPAP monitoring.2. Split night study-both can be done in single night, cost effective ,user friendly , OSA evaluation in 1st half and CPAP monitoring in 2nd half.
Treatment• General measures• Specific medical therapies• Intraoral devices• Surgical intervention
• General measures1. Weight reduction2. Maintenance of position during sleep3. Avoidance of alcohol and sedatives• No any pharmacological agent is recommended
• Specific medical therapies include1.Behavioral therapy2.CPAP• CPAP – acts as a airway pneumatic splint• Maintains positive press throughout in all stages of sleep• Can be given by nasal mask, nasal inserts and full face mask
Intraoral devices• Used in patients intolerant to OSA1. Tongue retaining devices2. Palatal lifting devices3. Mandibular advancements technique
Obesity hypoventilation syndrome• it is defined by morbid obesity(BMI>40Kg/M2 )• chronic hypoventilation with hypercapnia even during wakefulness (PACO2 >45mmHg )• Sleep disordered breathingIt is different from OSA and defect lies at three levels1. Excessive load on respiratory system-high upper airway resistance, low FRC, altered resp. muscle movements ,and altered resiratory mechanics2. Reduced central resp. drive3. Sleep disordered breathing• As defect lies at different levels only CPAP does not suffice• Weight reduction and nocturnal non invasive ventilation is the treatment of choice