CSA – Central sleep apnea (CSA) or central sleep apnea syndrome (CSAS)

It is an asleep-related disorder characterized by a decrease or absence of breathing effort, often lasting from 10 to 30 seconds, occurring intermittently or cyclically. This condition is typically accompanied by a decrease in blood oxygen saturation. CSA commonly arises from instability within the body’s feedback mechanisms responsible for regulating respiration.

Signs and symptoms

In a healthy individual during sleep, breathing occurs in a regular pattern, maintaining relatively stable levels of oxygen and carbon dioxide in the bloodstream. Following exhalation, oxygen levels in the blood decrease while carbon dioxide levels increase. To replenish oxygen and remove excess carbon dioxide, the body requires the exchange of gases with fresh air in the lungs.

Specialized receptors in the body, known as chemoreceptors, detect changes in oxygen and carbon dioxide levels and send nerve impulses to the brain. In response, the brain signals reflexive actions, such as opening the larynx (widening the space between the vocal cords) and activating muscles in the rib cage and diaphragm. These actions expand the chest cavity, creating a slight vacuum within the lungs, which allows air to rush in and fill the lungs.

During sleep, the brain usually tells us to breathe regularly. But in pure central sleep apnea, this system gets out of balance. As a result, the brain forgets to tell us to take a breath, causing us to miss one or more breaths.

During a central sleep apnea episode, the body’s feedback mechanism for monitoring carbon dioxide levels does not react quickly enough to maintain a steady respiratory rate. As a result, the respiratory system alternates between periods of apnea (breathing pauses) and hyperpnea (rapid or deep breathing), particularly following an awakening during a breathing pause.

During an apneic episode, the individual stops breathing for up to two minutes before resuming breathing. There is no effort made to breathe during this pause, characterized by the absence of chest movements or muscular struggle. Awakening during an apneic episode may lead to cognitive struggle and panic due to elevated carbon dioxide levels.

Even in severe cases of central sleep apnea, breathing pauses typically result in irregular breathing patterns rather than a complete cessation of breathing over the medium term. After an apneic episode, breathing may become faster and more intense (hyperpnea) for a period, serving as a compensatory mechanism to eliminate retained waste gases and absorb more oxygen. This helps restore normal breathing patterns by replenishing oxygen to the breathing muscles.

Additional Effects

The effects of low oxygen levels (hypoxia) and high carbon dioxide levels (hypercapnia), whether due to apnea or other causes, have further impacts on the body. These effects vary depending on how long breathing is interrupted, the frequency of these interruptions, and whether other underlying conditions exacerbate the effects of apnea.

When breathing is interrupted, whether due to sleep apnea or other factors, it affects the body in several ways:

• Brain cells need oxygen to work properly. If oxygen levels drop for too long, it can lead to brain damage or even death, although this is rare with central sleep apnea.
• Severe drops in oxygen levels can trigger seizures, even in people without epilepsy.
• In severe cases of sleep apnea, the skin may turn bluish due to low oxygen levels.
• Other health conditions can make the effects of sleep apnea worse:
• Epilepsy can cause seizures triggered by low oxygen levels during apnea.
• Heart disease can lead to chest pain, irregular heartbeats, or heart attacks.
• Prolonged apnea episodes can increase carbon dioxide levels in the blood, causing respiratory acidosis.
• Some medications, like sedatives or painkillers, can make sleep apnea worse, even at normal doses.
• Babies placed on their backs to sleep are less likely to experience breathing problems, reducing the risk of sudden infant death syndrome (SIDS).
• Premature babies are more likely to have sleep apnea, but they usually outgrow it with careful monitoring and treatment.

To diagnose sleep apnea, a physician’s evaluation is necessary, often involving a sleep study either in a lab setting or at home. During these tests, the patient’s breathing patterns are closely monitored while at rest to measure the frequency and duration of breathing pauses. In polysomnography (PSG – a sleep study) interruptions in breathing, along with drops in blood oxygen levels and increases in carbon dioxide, are observed.

For adults, a pause lasting at least 10 seconds is typically considered an apnea. However, in children, who breathe more rapidly, shorter pauses may still be classified as apneas. Hypopneas, characterized by a 30% reduction in airflow for over ten seconds followed by drops in oxygen saturation, are also noted in adults.

The Apnea-Hypopnea Index (AHI) is stated as the number of apneas or hypopneas per hour of sleep.

Central sleep apnea is marked by a cessation of airflow without accompanying attempts to breathe, as evidenced by the absence of rib cage and abdominal movements on polysomnograms. In contrast, obstructive sleep apnea may involve increased effort in breathing, as the individual instinctively tries to overcome airway obstruction.

Treatment

regulates airflow and airway pressure:

• CPAP
• BiPAP

The Modern devices also have a CSA detection sensor that can automatically by learning the patient adjust the airflow and so the pressure.

CSA detection – Central sleep apnea (CSA) detection is an advanced technology that uses the forced oscillation technique (FOT) to determine whether a patient’s airway is open during an apnea.

FOT – Forced oscillation technique (FOT) is a method to characterize the mechanical properties of the respiratory system over a wide range of frequencies.

Difference between Central sleep apnea (CSA) and obstructive sleep apnea (OSA):

Central sleep apnea (CSA) occurs because the brain doesn’t send proper signals to the muscles that control breathing. This condition is different from obstructive sleep apnea (OSA), in which breathing stops because the throat muscles relax and block the airway. Central sleep apnea is less common than obstructive sleep apnea.

Epidemiology

Central sleep apnea (CSA) is less common than obstructive sleep apnea (OSA). In one study, CSA is stated to have a prevalence of 0.9% in comparison to OSA.

Many factors increase the risk of developing CSA. Chronic opioid use produces a mean prevalence in central sleep apnea development of 24%. An estimated 10% of chronic kidney disease (CKD) patients have a CSA diagnosis. Stroked patients show a 70% development rate of CSA within 72 hours of the stroke event, although CSA was detected in less than 17% after 3 months of follow-up. A study showed the incidence of CSA in heart failure patients to be 0.9%.

Infancy

During infancy, central sleep apnea (CSA) is often observed in preterm, newborn, and early stages of development. However, the risk tends to decline as individuals age and their central nervous system matures.

Among preterm infants born before 29 weeks, approximately 25% of apnea-related events originate from central factors.

Childhood

Central sleep apnea (CSA) is less common after 2 years of age. The prevalence of CSA in healthy children aged 10 to 18 years is 30%. Children with underlying medical conditions fall under a prevalence rate of 4-6%. For children diagnosed with Prader-Willi syndrome (PWS), CSA is more common and can occur in up to 53% of cases.

Adulthood

The rate of sleep apnea is higher in adults over the age of 65 years, due to older individuals having higher risks of developing CSA due to pre-existing medical conditions.