Dr. Subramanian Suriyan shares expert pointers on how to identify the right patients for sleep study (polysomnography). He also details on the criteria for severity assessment of obstructive sleep apnoea (OSA), a common, yet underdiagnosed sleep disorder.

Obstructive Sleep Apnoea (OSA) is a serious sleep disorder which is common but underdiagnosed or diagnosed late because of its clinical presentation where the patients have varied symptoms, not related directly to the disease. OSA is a sleep-related breathing disorder where there is repeated cessation of breathing during sleep.

Among the various types of apnoea, obstructive sleep apnoea is the most common type of apnoea. Its varied clinical presentation necessitates the knowledge of the diseases among the treating physicians which enables early diagnosis and hence modifies the disease outcome.

---

---

Pathophysiology

Obstructive sleep apnoea occurs when the muscles in the posterior pharyngeal wall supporting the soft palate, uvula, and the tongue relaxes too much to allow normal breathing. This causes the airway narrowing during inspiration. If the breathing is inadequate for more than 10 seconds it may lower the level of oxygen in the blood and cause a buildup of carbon dioxide. The brain senses this hypoxia and briefly rouses from sleep to reopen the airway.

The awakening is usually so brief that patients don't remember it. This can repeat for five to 30 times or more each hour, all night long. These disruptions impair the ability to reach the desired deep, restful phases of sleep and make the person feel sleepy during the waking hours. People with obstructive sleep apnoea may not be aware that their sleep was interrupted. In fact, many people with this type of sleep apnoea think they sleep well all night.

---

Physiology behind OSA

Transmural pressure is the difference between intraluminal pressure and the surrounding tissue pressure. If transmural pressure decreases, the cross-sectional area of the pharynx decreases. If this pressure passes a critical point, pharyngeal closing pressure is reached. Exceeding pharyngeal critical pressure causes tissues collapsing inward. The airway is obstructed.

Normal vs. obstructed breathing

Normal	Obstructed
Mouth closed	Mouth open
Tongue in normal forward position	Tongue collapsed in throat
Airway clear	Airway blocked
Breathing through the nose	Breathing through the nose and mouth

 

---

Aetiology: Structural factors

• Anatomic variations (e.g. facial elongation)
• Retrognathia and micrognathia
• Mandibular hypoplasia
• Inferior displacement of the hyoid
• Adenotonsillar hypertrophy
• Pierre Robin syndrome
• Down syndrome, Marfan syndrome
• High, arched palate (particularly in women)
• Nasal obstruction- polyps, septal deviation, tumours, trauma, and stenosis
• Retro palatal obstruction- elongated posteriorly-placed palate and uvula
• Retroglossal obstruction- macroglossia and tumour

Aetiology: Non-structural factors

• Obesity
• Male sex (male/female 2:1)
• Age
• Postmenopausal state
• Alcohol use
• Sedative use
• Smoking
• Supine sleep position

Neuromuscular factors

1. Decreased neuromuscular activity in the UA, including reflex activity
2. Reduced ventilatory motor output to upper airway muscles

---

Signs and symptoms of obstructive sleep apnoea include:

• Loud snoring
• Excessive daytime sleepiness
• Observed episodes of cessation of breath during sleep
• Intermittent awakenings accompanied by gasping
• Awakening with a dry mouth or sore throat
• Morning headache
• Difficulty in concentrating during the day
• Mood changes, such as depression or irritability, decreased libido
• High blood pressure

---

Clinical consequences of OSA

• Systemic hypertension
• Cardiac arrhythmias
• Myocardial ischaemia
• Cerebrovascular disease
• Pulmonary hypertension
• Cor pulmonale

Non-clinical consequences of OSA

• Increased motor vehicle crashes
• Increased work-related accidents
• Poor job performance
• Depression
• Family discord
• Decreased quality of life

---

Diagnosis

General examination of the patients with OSA is more commonly associated with obesity (BMI>30 kg/m²) but not always, an enlarged neck circumference (men: >17 inches; women: >15 inches), and hypertension.

Evaluate the upper airway in all patients particularly in non-obese adults with symptoms consistent with OSA.

Other examination findings may include the presence of:

• Abnormal Mallampati score
• Narrowing of the lateral airway walls- independent predictor in men but not women
• Enlarged tonsils
• Retrognathia or micrognathia
• High-arched hard palate
• Hypertension, type 2 diabetes mellitus
• Pulmonary hypertension, congestive heart failure
• Metabolic syndrome 

---

Selection of patients for Polysomnography (sleep study)

All patients with a history of snoring and excessive daytime somnolence as well as individuals who have high-risk jobs (pilots, truck, or bus drivers) and experience excessive daytime somnolence should undergo diagnostic testing for OSA. Lack of excessive daytime sleepiness or absence of obesity does not rule out the possibility of clinically significant sleep-disordered breathing or OSA.

There are screening questionnaires such as Berlin Questionnaire, STOP questionnaire, STOP-BANG questionnaire, Epworth sleepiness scale (ESS), SA-SDQ, No SAS questionnaire, OSA50 questionnaire to screen the patients with OSA. Those who are at high risk based on any of the above questionnaires indicate the need for Polysomnography (PSG). There are four levels of sleep testing.

Level 1: In Laboratory, technician-attended, with minimum seven channels and sleep staging

Level 2: A portable monitor with same parameters as level 1 but unattended

Level 3: Portable, unattended with minimum 4 channels including flow, effort, oximetry & HR

Level 4: Fewer than 4 channels, often oximetry with flow or oximetry alone

---

---

Criteria for diagnosis and severity assessment

The third edition of the International Classification of Sleep Disorders defines OSA as a PSG determined obstructive respiratory disturbance index (RDI) ≥5 events/hour associated with the typical symptoms of OSA (e.g. unrefreshing sleep, daytime sleepiness, fatigue or insomnia, awakening with a gasping or choking sensation, loud snoring, or witnessed apnoeas), or an obstructive RDI ≥15 events/hour (even in the absence of symptoms).

A normal cut-off for Apnoea Hypopnoea Index (AHI) has never been clearly defined in an epidemiological study of normal individuals. Most centres recommend a cut-off of 5 to 10 episodes per hour. The severity is defined arbitrarily and it differs between centres. Recommendations for cut-off levels on AHI include 5 to 15 episodes per hour for mild, 15 to 30 episodes per hour for moderate, and more than 30 episodes per hour for severe disease.

---

Treatment options for OSA

Medical

• Behavioural changes
• Medication
• Dental appliances
• Continuous positive airway pressure (CPAP)
• Bi-level positive airway pressure (BiPAP)

Surgical

• Nasal airway surgery
• Palate implants
• Uvulopalatopharyngoplasty (UPPP)
• Tongue reduction
• Genioglossus advancement
• Hyoid suspension
• Maxillomandibular procedures
• Tracheostomy
• Bariatric surgery

Appropriate selection of treatment modalities from the above options tailored for the individual patients is essential for better outcome. Also, a multidisciplinary approach involving the various specialties will be necessary in the management of obstructive sleep apnoea.

---

The detailed clinical aspects of management of OSA will be discussed in the next article.

Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.

The author Dr. Subramanian Suriyan is a Professor of Respiratory Medicine in a reputed medical college in Chennai.