If you're overweight and have difficulty breathing during sleep, you may be interested in learning about obesity hypoventilation syndrome. What is obesity hypoventilation syndrome? How does it relate to standard obstructive sleep apnea? Why is it sometimes called Pickwickian syndrome?
Definition of Obesity Hypoventilation Syndrome
First, people with obesity hypoventilation syndrome are, by definition, obese. This means that an affected person has a body mass index (BMI) greater than 30. The BMI is calculated using your height and weight, and it provides a means to categorize people based on body size. A person is considered to fall in the normal range if they have a BMI under 25. Many people with obesity hypoventilation syndrome have extremely high BMIs, often greater than 50.
The second key component of the syndrome is hypoventilation. Ventilation refers to breathing, especially the ability to take in oxygen and expel carbon dioxide. Carbon dioxide is a waste product our bodies create and the lungs help us to rid ourselves of it. When breathing occurs less than it should, it is called hypoventilation. This may occur for two reasons: too little air volume is moved or the frequency of breaths is insufficient.
When hypoventilation occurs, the levels of carbon dioxide in the blood increase. This changes the acidity of the blood, and this can cause important consequences. At high levels, the carbon dioxide can lead to drowsiness and, at the most extreme levels, unconsciousness and coma. There are various causes of hypoventilation. When seen in the setting of obesity alone, as it often may be, it is called obesity hypoventilation syndrome.
Obesity Hypoventilation Syndrome and Sleep Apnea
People with obesity hypoventilation syndrome are not only obese. They may have other physical signs that suggest the condition. The retained carbon dioxide may cause color changes in the skin, either appearing red or flushed (florid) or dusky blue (cyanotic). Afflicted people may more commonly have a large neck, narrow airway, and signs of heart failure (including swelling in the feet).
Importantly, obesity hypoventilation syndrome commonly overlaps with obstructive sleep apnea. It is estimated that 4 to 20% of people with obstructive sleep apnea have obesity hypoventilation syndrome. There are many symptoms that can be found in both conditions, including:
- Loud snoring
- Gasping or snorting
- Excessive daytime sleepiness
- Poor concentration
- Memory problems
One key symptom that distinguishes obesity hypoventilation syndrome from obstructive sleep apnea is difficulty breathing after exertion. People with run-of-the-mill sleep apnea will not necessarily find themselves short of breath after routine activity, such as climbing a flight of stairs, walking on level ground, or engaging in moderately strenuous activity. Those with obesity hypoventilation syndrome may quickly find themselves huffing and puffing with only modest physical efforts.
This suggests that people with this condition are barely breathing normally at baseline, and taxing their system with exercise quickly pushes things into a strained state. If obesity hypoventilation syndrome goes untreated, there is a high risk of suffering from fatal consequences. When recognized, it is considered a medical emergency.
A Word on Pickwickian Syndrome
Some people refer to obesity hypoventilation syndrome as Pickwickian syndrome. Why is it sometimes called this?
Pickwickian syndrome refers to a character in a book by Charles Dickens called The Posthumous Papers of the Pickwick Club. This character was named Joe and he is described as "a wonderfully fat boy -- habited as a serving-lad, standing upright on the mat, with his eyes closed as if in sleep."
It is believed that Dickens may have been describing someone who we would now say has obesity hypoventilation syndrome.
Bickelmann, AG et al. "Extreme obesity associated with alveolar hypoventilation; a Pickwickian syndrome." Am J Med 1956;21:811.
Dickens, C. "The posthumous papers of the Pickwick club." Harper and Brothers 1873;311.
Martin, TJ et al. "Alveolar hypoventilation: A review for clinicians." Sleep 1995;18:617.
Mokhlesi, B et al. "Obesity hypoventilation syndrome: prevalence and predictors in patients with obstructive sleep apnea." Sleep Breath 2007;11:117.
Mokhlesi, B et al. "Assessment and management of patients with obesity hypoventilation syndrome." Proc Am Thorac Soc 2008;5:218.
Piper, AJ et al. "Current perspectives on the obesity hypoventilation syndrome." Curr Opin Pulm Med 2007;13:490.