Saturday, December 2, 2006

Hypopnea, AHI and the problem of overweight

When breathing is normal the breath airflow is 100% to 70%. Hypopnea is a decrease in breathing when hypopnea-airflow is 69% to 26% of a normal breath. There is the hypopnea index (HI) that can be calculated by dividing the number of hypopneas by the number of hours of sleep. But as far as hypopnea is closely related to apnea (total cessation of breathing) the apnea-hypopnea index (AHI) is commonly used to describe breathing disorders during sleep. AHI is an index of severity that combines apneas and hypopneas. AHI is calculated by dividing the number of apneas and hypopneas by the number of hours of sleep correspondingly.

When the apnea-hypopnea index is positive we generally speak of sleep-disordered breathing (SDB). SBD is a prevalent condition in the US general population that commonly associated with overweight and obesity. Most often problems with weight are caused by metabolism infringements and some eating disorders such as binge eating disorder.

Sleep-disordered breathing and all related diseases (sleep apnea, hypopnea, obesity hyperventilation syndrome, etc.) usually improve when the eating disorders causing overweight and obesity are properly treated. So there is a straight relation between weight loss and improvement in sleep-disordered breathing.

Apnea-hypopnea indexThe figure shows the relationship between weight change and the apnea-hypopnea index. The data demonstrates that changes in AHI are related in a dose-response fashion to changes in body weight. A 10% weight loss is associated with a 26% decrease in the AHI, whereas a 10% weight gain is associated with a 32% increase in the AHI. So there are improvements in sleep-disordered breathing (sleep apnea and hypopnea) in case of weight loss and worsening of the disease in case of weight gain.

You can read more about the subject in Longitudinal study of moderate weight change and sleep-disordered breathing by Peppard PE and others.

Friday, December 1, 2006

Hypopnea in a nutshell: part 2

So in case of hypopnea there is intermittent collapse of the upper airway and reductions in blood oxygen levels during sleep. A sleeping person becomes incapable to breathe normally and awakens with each collapse. As a result the quality of sleep is reduced considerably. If hypopnea is not treated the consequences of the disease can be really deplorable. They include:
  • hypertension,
  • cognitive disfunction,
  • memory loss,
  • coronary artery disease,
  • heart attack,
  • stroke,
  • impotence.
HypopneaThe most common and effective treatment of hypopnea is continuous positive airway pressure or CPAP. A patient puts up a mask over his face (nose or mouth) and an air blower forces air through the upper airway. The air pressure is adjusted in a way to avoid the upper airway tissues from collapsing during sleep. Also mild hypopnea can be treated by losing weight, refusing from alcohol and smoking before sleep, doing certain excercises that strengthen gullet muscles, avoiding sleeping on your back and some more.

Hypopnea in a nutshell: part 1

Hypopnea comes from the Greek roots hypo- (meaning low, under, beneath, down, below normal) and pnoe (meaning breathing). Literally it means underbreathing. In case of hypopnea breathing is shallower or slower than normal. It is a sleep disorder that can be characterized by person's repetitive stops of breathing or low breathing for short periods of time during sleep. Hypopnea is distinct from apnea in which there is a total cessation of breathing.

Hypopnea may disturb a person's quantity and quality of sleep as it often causes a severe sleep breakup. It all results in sleep deprivation and excessive daytime sleepiness, most usual consequences of which are traffic accidents, diminished productivity, emotional problems, etc. Cardiovascular consequences of hypopnea include myocardial infarction, stroke, psychiatric problems, impotence, cognitive disfunction, hypertension, coronary heart disease, and memory loss.

Among the most commong hypopnea symptoms are:
  • Excessive sleepiness
  • Snoring
  • Depression
  • Forgetfulness
  • Mood or behavior changes
  • Trouble concentrating
  • Loss of energy
  • Nervousness
  • Morning headaches
Not everyone who suffers from hypopnea has all these symptoms and not everyone who has these symptoms suffer from hypopnea.