100 Snoring and Sleep-Related Breathing Disorder
Sleep-related breathing disorder is a spectrum of breathing disorders occurring during sleep and comprises simple snoring, upper airway resistance syndrome and obstructive sleep apnoea.
• Snoring: A noise generated from turbulence due to partial upper airway obstruction during sleep.
• Apnoea: A period of no airflow at the nose or mouth for at least 10 seconds.
• Hypopnoea: Breathing where there is a 30% or greater reduction in normal tidal volume.
• Apnoea–hypopnoea index (AHI): The number of periods of apnoea and hypopnoea per hour.
Sleep apnoea can be obstructive, central or mixed. In obstructive sleep apnoea, there is partial (hypopnoea) or complete (apnoea) upper airway obstruction yet the patient continues to make respiratory efforts to overcome this. In central apnoea, respiratory effort and consequently airflow, ceases for a while. Central apnoea is due to a defect of autonomic control of respiration in the medulla or in the peripheral chemoreceptors resulting in a failure of respiratory drive. It is a symptom of serious neurological disease and is not considered further here.
Obstructive sleep apnoea (OSA) is diagnosed if the AHI is more than 5. Obstructive sleep apnoea is classified as mild (AHI = 5–15), moderate (AHI = 15–30) or severe (AHI > 30).
Upper airway resistance syndrome (UARS) is diagnosed if the AHI is less than 5 but patients have some of the symptoms and signs of OSA. Patients with UARS may progress to OSA if factors that are contributing to UARS are not addressed.
The noise of snoring is produced by vibration of the soft palate and pharyngeal walls caused by turbulent airflow and the Bernoulli effect from a partial obstruction. The obstruction occurs when the negative intra-luminal pharyngeal pressure exceeds the ability of the dilators to hold the pharynx open. Any cause of airway narrowing from nares to glottis can contribute to increased airway resistance. Neuromuscular incoordination interfering with the reflex activity of the pharyngeal dilators associated with inspiration, increased compliance and bulk of pharyngeal tissues, the Venturi effect and the decreased muscle tone associated with sleep can all predispose to upper airway collapse. This obstruction has three effects:
1. Hypoxia, which may cause cardiac dysrhythmias, and if severe and prolonged may lead to pulmonary and systemic hypertension and cor pulmonale.
2. Increased negative intrathoracic pressure and increased cardiovascular strain.
3. Arousal, which is an attempt to overcome the obstruction and caused by increased serum levels of carbon dioxide. Frequent arousal results in poor sleep quality.
Patients with severe OSA have an increased mortality due to cardiovascular disease.
100.2.1 Clinical Features
Snoring and OSA in adults are more common with increasing age, in men (2:1 M/F ratio), in the obese (body mass index [BMI] > 30), in those with a neck size of more than 17 inches and in those with a high alcohol intake. Snoring occurs in 10% of men under 30 years and 40% of men over 60 years, while OSA can be found in approximately 6% of men. In children, it most commonly occurs around the age of 5 when lymphoid hyperplasia is at its greatest. Snoring can be immensely socially disruptive and may lead to marital difficulties. OSA often leads to excessive daytime somnolence, morning headaches, personality change including depression, intellectual deterioration (inattention, memory loss and poor work performance), reduced libido and impotence and an increased risk of causing a road traffic accident. The DVLA should be informed of a diagnosis of OSA; it is the doctor’s responsibility to alert the patient of this need, and it is the patient’s responsibility to carry this out.
It is important to establish whether the patient has simple snoring, UARS or OSA and to identify exacerbating factors, for example, medication causing drowsiness, endocrine disorders such as hypothyroidism or diabetes. One should try to identify the site and level of obstruction including anatomical factors such as retrognathia or benign tonsillar hyperplasia. A thorough history and examination is needed. When taking the history, it is preferable to have the bed partner present.
1. Body mass index This measurement helps define the degree of obesity. It is calculated by dividing the weight in kilograms by the square of the height in metres (kg/m2). A normal BMI is 19 to 25, overweight 26 to 30, obese 30 to 40 and very obese greater than 40. Palatal surgery is less effective in patients with a body mass index of greater than 30. This is probably because these patients are more likely to have OSA caused by multi-segmental or tongue base level collapse.
2. General investigations Full blood count (FBC), thyroid function tests (TFTs), chest radiograph and electrocardiogram (ECG).
3. Epworth sleepiness scale