While eupnoea is normal breathing, hypopnea is an abnormal type of breathing when the airflow is labored because of some pathology of the respiratory system. In other words it’s underbreathing. Hypopnea comes from the Greek roots hypo- (meaning low, under, beneath, down, below normal) and pnoe (meaning breathing). Among other abnormal breathing patterns are: bradypnea – rare and slow breath, dyspnea - intense breath with a shortness, sometimes with cyanosis, hyperpnea – the increased amplitude of breathing at the normal rate, tachypnea – quickened and fast breathing, oligopnea – weakening of respiratory movements accompanied with reduction of breath. Hypopnea is often confused with apnea. But while hypopnea is a reduced amplitude of breathing at the normal rate, apnea is a total cessation of breathing.

Hypopnea can occur during sleep. In this case it may turn into a serious sleeping disorder. Sleep hypopnea can be characterized by person's repetitive stops of breathing or low breathing for short periods of time during sleep. Speaking in anatomical terms, there is intermittent collapse of the upper airway and reductions in blood oxygen levels during sleep. Thus, a sleeping person becomes incapable to breathe normally and awakens with each collapse. Quantity and quality of sleep is lowered, what results in sleep deprivation and excessive daytime sleepiness. The most usual physiological consequences of hypopnea are cognitive disfunction, coronary artery disease, myocardial infarction, hypertension, memory loss, heart attack, stroke, impotence, psychiatric problems. People suffering from sleep hypopnea increase considerably the overall number of traffic accidents. Their productivity is diminished and they have constant emotional problems and strains.

The most common hypopnea symptoms are: loss of energy, forgetfulness, excessive sleepiness, snoring, lack of concentration, depression, rapid changes in mood and behavior, morning headaches, nervousness.

There is the so called hypopnea index 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 most often we speak of the apnea-hypopnea index (AHI). AHI is an index of severity that combines apneas and hypopneas. It is calculated by dividing the number of apneas and hypopneas by the number of hours of sleep correspondingly. When AHI is positive we usually speak of sleep-disordered breathing or SDB.

Although hypopnea itself is not a mortal disease, if it is not treated properly it may shorten a person’s life considerably by aggravating other diseases. CPAP, or continuous positive airway pressure, is considered to be the most effective treatment of hypopnea. It is usually used in case of heavy hypopnea. A patient puts up a mask over his nose or mouth while 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. Mild hypopnea is treated more conservatively. In the majority of cases hypopnea treatment presupposes refusing from alcohol and smoking before sleep, strengthening gullet muscles by doing certain excercises, avoiding sleeping on the back. Also there is a straight relation between weight loss and improvement of breathing while sleeping. It is established that abnormal breathing patterns during sleep such as sleep apnea and hypopnea, obesity hyperventilation syndrome, etc. usually improve when eating disorders causing overweight and obesity are properly treated.