To understand the pathophysiology of central sleep apnea, you must first understand how normal respiration works.
Normal Ventilation
Normally the body’s ventilation is strictly regulated to ensure that the levels of Carbon Dioxide and Oxygen are within the proper ranges. This is achieved by a feedback system (many feedback loops) which uses peripheral chemoreceptors, central chemoreceptors intrapulmonary receptors, respiratory muscles and lastly the brain stem (which sends the signal for breathing).
When you are awake, you have conscious control over your breathing i.e. you can control when you inhale and when you exhale to a certain extent. When you are asleep however, this changes; the conscious control is lost and the control of ventilation passes onto the chemical control (the major stimulus being Carbon Dioxide concentrations). Central sleep apnea is observed at the highest frequency in patients during the NREM or non-rapid eye movement stage of sleep (the stage where conscious control of breathing is at its lowest level). The body has an internal set point regarding the concentration of carbon dioxide which should be present inside the body at all times, when the real concentration of carbon dioxide falls below this level, it can induce apneas.
Pathophysiological Phenomenon which Cause Central Sleep Apnea
- Ventilatory Instability: This mechanism is the root cause behind CSB-CSA, high altitude central sleep apnea and lastly primary CNS. Since ventilation is controlled by feedback loops, it is prone to instabilities. How the system reacts to these instabilities (with too much force or too less force) determines if normal breathing will be present or apneas will occur. If the body responds with too much force in a rapid and highly intense manner or if it responds slowly in a gradual manner it can cause the apnea to occur.
- Depression of the Brain Stem: This type of central sleep apnea is more commonly found in people. The brain stem contains many different parts which work together to allow a person to breathe normally and smoothly throughout the night. However if you sustain heavy trauma to the brain or if you suffer from a central nervous system disease such as a tumor or brain haemorrhage, the functioning of the brain stem may be lowered which can cause your central sleep apnea. Other medical problems which cause this are stokes and medication which may either overexcite or depress the receptors present in the brain stem.