Hypoventilation & hypoxemia.
Ventilation is the process of breathing air in and out. In this process, carbon dioxide is exhaled from the lungs and oxygen enters the blood stream after inspiration of air into our lungs. We ventilate air during both our wakefulness and sleep. In individuals with normal sleep, ventilation is reduced slightly during sleep. Thus, oxygen and carbon dioxide levels do not change significantly to disturb our sleep. Several diseases cause disturbance of ventilation and lead to reduced ventilation or hypoventilation.
Sleep-related hypoventilation is a breathing problem during sleep. It is described by reduced ventilation during sleep. Thus, these patients experience reduced oxygen and increased carbon dioxide in their blood. These two processes disturb sleep of patients with sleep-related hypoventilation. Accordingly, these patients experience fragmented sleep, excessive daytime sleepiness, reduced performance, insomnia and difficulty breathing during their sleep.
Patients often seek treatment because of the aforementioned problems as well as breathing difficulty during sleep and sometimes while awake. A blood test is performed to assess levels of oxygen and carbon dioxide in the blood. Then, a sleep study is performed to confirm reduced ventilation during sleep and to find any other sleep problems such as sleep apneas. Other causes such as obesity, hypothyroidism, lung diseases, neurologic diseases and muscle weakness are also evaluated. Treatments of sleep-related hypoventilation include weight loss and/or cause-specific management. In some cases, using positive airway pressure devices during sleep such as CPAP may be required to guarantee a good oxygen level and ventilation during sleep.
Our body needs oxygen during both wake and sleep. If oxygen levels decrease in our blood, it is called hypoxemia. Sleep-related hypoxemia is a problem of decreased oxygen levels during sleep.
Patients with sleep-related hypoxemia may have symptoms similar to patients with sleep-related hypoventilation including fragmented sleep, excessive daytime sleepiness, reduced performance, insomnia and difficulty breathing in sleep. The diagnosis of hypoxemia is made by performing a sleep study. If no specific cause is found, nocturnal oxygen therapy or positive airway pressure may be prescribed by the physician for treatment. Otherwise, the major cause of hypoxemia would be addressed for management.
In conclusion, both sleep related- hypoventilation and hypoxemia result in disturbed sleep and reduced performance. Thus, if you have symptoms suggestive of these two disorders, further evaluation by a physician is required. If you have these conditions, it is recommended to seek help and follow management plans. Treatment of these two disorders will improve your performance and quality of life, so you will have healthier sleep and a happier life and future.
Arezu Najafi, MD is an Occupational and Sleep Medicine Specialist, Faculty of Occupational Sleep at the Research Center at Tehran University of Medical Sciences in Tehran, Iran. She is also a current Mentee of World Sleep Society’s International Sleep Research Training Program (ISRTP) at University of Pennsylvania. She has been working in the field for seven years.