| Habitual Snorers | Those who snore nearly every night. |
| Headgear | Strap arrangement holding on the mask. |
| Heart Rate or beats per minute (bpm) | pace/speed of the heart measured in beats per minute. 60-80 is considered normal in adults. |
| Hertz (Hz) | Unit of frequency; equal to cycles per second (cps). |
| HH | Hypnogogic Hallucinations |
| Histogram (sleep) | Graph indicating sleep stages thoughout the night. |
| HLA | Human Leukocyte Antigen |
| Home Sleep Test | (HST) This is one way to detect OSA in adults. A home sleep test involves the use of a portable-monitoring system that is small enough for you to take home. It consists of a small recording device sensors belts and related cables and accessories. You apply the sensors to your body and turn on the recording device before going to sleep. The sleep recorder gathers important data as you sleep in your own bed. Standard measurements include airflow respiratory effort blood oxygen saturation and heart activity (EKG). Home sleep tests are classified as Type 2 Type 3 or Type 4. |
| Humidification | Moisture is added to the airflow as an adjunct to CPAP (Continuous Positive Airway Pressure) therapy in treating obstructive sleep apnea (OSA). Humidification can be added to the CPAP by diverting the airflow over or through a cool or heated water reservoir (humidifier) to prevent the upper airway from drying out. |
| Hx | Medical History |
| Hyoid Suspension | A possible surgical procedure sometimes used in the treatment of sleep apnea and/or snoring designed to improve the airway behind the base of the tongue. The hyoid bone is located in the neck where some tongue muscles attach. The hyoid bone is pulled forward in front of the voice box and can open the airway space behind the tongue. |
| Hyperactivity | Typical behavior in a child with a sleep disorder which is causing lack of quality sleep. |
| Hypercapnia | Excessive or elevated carbon dioxide in the blood. |
| Hypercapnia | Having a high level of carbon dioxide in the blood. It can be caused by CSA and OSA. |
| HYPERCAPNIA (high-per-cap-nee-ah) | A raised level of carbon dioxide in the blood. This is the gas normally breathed out which will rise if breathing is inadequate. Usually measured by taking an arterial blood sample.
HYPERSOMNOLENCE (high-per-som-no-lence) |
| Hyperirritability | Extreme irritability; seen in sleep deprived subjects. |
| Hypersomnia | Excessive prolonged sleep |
| HYPERSOMNOLENCE (high-per-som-no-lence) | Technical expression for excessive sleepiness. |
| Hypertension | High blood pressure. |
| Hypnagogic imagery (hallucinations) | Vivid sensory images occurring at sleep onset but particularly vivid with sleep-onset REM periods; feature of narcoleptic REM naps. |
| Hypnagogic startle | "sleep start" or sudden body jerk observed normally just at sleep onset resulting in at least momentary awakening. |
| HYPNOGRAM (hip-no-gram) | The final print out of all the night sleep stages (REM and non-REM). |
| Hypnophobia | Morbid fear of falling asleep. |
| Hypnotics | Sleep-inducing drugs. |
| Hypopharynx | Lowermost portion of the pharynx leading to the larynx and esophagus. |
| Hypopnea | Shallow breathing in which the air flow in and out of the airway is less than half of normal--usually associated with oxygen desaturation. |
| Hypopnea | A partial reduction in breathing of at least 30% that lasts at least 10 seconds during sleep. |
| HYPOPNOEA (high-pop-nee-ah) | A period of underbreathing conventionally for more than 10 seconds. |
| HYPOTHRYOIDISM (high-po-thy-royd-ism) | Also known as myxoedema (mix-ee-dee-ma). When the thyroid gland fails to make enough thyroid hormone. Can present as obstructive sleep apnoea and snoring. |
| Hypoventilation | Reduced rate and depth of breathing. |
| Hypoxemia | Abnormal lack of oxygen in the blood in the arteries. |
| Hypoxemia | Having a low level of blood oxygen saturation. It can be caused by CSA and OSA. Also called hypoxia. |
| Hypoxia | Deficiency of oxygen reaching the tissues of the body. |
| HYPOXIA (high-pox-ee-ar) | When the body is short of oxygen and therefore the level in the blood falls. |
| HYPOXIC DIPS (high-pox-ic) | The falls in oxygen levels seen on the oximeter that usually accompany apnoeas. Also know as desaturations because when it is not hypoxic the blood is described as fully saturated with oxygen. |
| Hz | Hertz (frequency) |
