Obstructive sleep apnea syndrome

Pathogenesis and classification of apnea

Sleep apnea syndrome is formally classified as a respiratory pathology; however, its key feature is the complete absence of primary lung tissue damage. Respiratory failure here always develops secondarily under the influence of extrapulmonary factors.

Depending on the leading mechanism of development, two variants are distinguished:

• Central type. Occurs due to central nervous system malfunctions when the regulation by the respiratory center is impaired.
• Obstructive type. Occurs in approximately 1% of the population. It is caused by a temporary mechanical obstruction of the upper airways. Risk factors include decreased muscle tone of the soft palate, hypertrophy of the palatine tonsils, adenoids, as well as anatomical abnormalities of the tongue or lower jaw.

Pickwickian syndrome

Within the framework of sleep-related breathing disorders, Pickwickian syndrome is distinguished. The historical background of this condition dates back to the 19th century, when the link between obesity and sleepiness became obvious. The name itself was proposed by physician William Osler after a character from Charles Dickens's novel The Posthumous Papers of the Pickwick Club — a corpulent servant named Joe who suffered from typical manifestations of the syndrome.

The pathology is typical of patients with short stature, pronounced abdominal obesity (fat deposition predominantly in the abdomen), and genetic predisposition. The leading pathophysiological mechanism is marked alveolar hypoventilation. The abundance of adipose tissue sharply limits the normal mobility of the diaphragm and chest wall, leading to the development of restrictive respiratory failure.

Against this background, gas homeostasis is disrupted:

1. Blood oxygen levels drop (hypoxemia).
2. Carbon dioxide concentration increases ($p_aCO_2 > 50$ mmHg).
3. Respiratory acidosis develops.

To compensate for these phenomena, the body triggers enhanced red blood cell production (polycythemia occurs) and increases hemoglobin levels. An important feature of the disease's course is its potential reversibility: with weight loss, symptoms may completely regress.

Clinical presentation

Typically, a patient with obstructive sleep apnea syndrome is a middle-aged, overweight male. However, the pathology can also occur in children and is frequently associated with hypothyroidism.

Symptoms are divided into several groups:

• During sleep: periodic breathing cessations are observed. They are accompanied by loud, straining, "booming" snoring. Long pauses of frightening silence that interrupt snoring are typical, during which the patient does not breathe (sometimes pauses last up to two minutes).
• Daytime manifestations: due to hypoxia, patients experience overwhelming daytime sleepiness. They may suddenly fall asleep right during a conversation, reading, or eating. Typical symptoms also include morning headaches, a sharp decrease in overall performance, and impaired concentration and memory.
• Somatic and cardiovascular manifestations: arterial hypertension is frequently detected, remaining resistant to standard treatment regimens. In severe Pickwickian syndrome, cor pulmonale develops and leg edema appears.

Diagnostics and treatment

To confirm the diagnosis, comprehensive monitoring of physiological parameters during sleep is performed. This includes electroencephalography (EEG, to assess brain activity and sleep stages), spirometry or pneumotachography (recording breathing rate and volume), pulse oximetry (shows the degree of blood oxygen drop), and ECG (detects arrhythmias).

The main goal of obstructive sleep apnea therapy is to prevent sudden cardiac death during sleep.

• Basic measures (lifestyle modification): strict weight loss, as well as complete abstinence from alcohol and sedatives (they further relax airway muscles and depress the respiratory center).
• Instrumental correction: the primary method is CPAP therapy. The essence of the method is that air is delivered into the patient's airways under continuous positive pressure via a facial mask. This flow mechanically overcomes tissue resistance and prevents airway collapse (apnea). As a result, clinical daytime sleepiness decreases and blood pressure normalizes.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Mechanisms of restrictive respiratory failure development
• Pathophysiology of cor pulmonale development in chronic hypoxia
• Differential diagnosis of central and obstructive apnea
• The link between hypothyroidism and obstructive sleep apnea syndrome
• Operating principles and settings of CPAP devices

Other topics in the "Respiratory System" section

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