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heat unit

ABBR: HU. The amount of heat created at the anode during the production of x-ray photons. It is the product of the milliamperage times the seconds of exposure times the kilovoltage peak.

heat wave

An environmental emergency during which ambient temperatures remain above the 99th percentile of normal for 48 hr or more.


(hēvs) Vomiting.

heavy chain disease

ABBR: HCD. Any of several abnormalities of immunoglobulins in which excessive quantities of alpha, gamma, delta, epsilon, or mu chains are produced. The immunoglobulins formed are incomplete, causing, in some cases, distinct clinical signs and symptoms including weakness, recurrent fever, susceptibility to bacterial infections, lymphadenopathy, hepatosplenomegaly, nephrotic syndrome and renal failure, anemia, leukopenia, thrombocytopenia, and eosinophilia. The disease may be diagnosed with immunoelectrophoresis or biopsy of affected organs.

alpha h.c.d. Immunoproliferative small intestinal disease.

gamma h.c.d. A rare heavy chain disease whose hallmark is the production of abnormal immunoglobulins (made of gamma heavy chains) by malignant B-lymphocytes. Clinical findings include lymphadenopathy, hepatosplenomegaly, arthritis, edema of the uvula, and infiltration of the skin and thyroid gland. Treatment includes therapy for the underlying disorders, including the particular type of lymphoma present. SEE: heavy chain disease.

mu h.c.d. A heavy chain disease with presenting symptoms of a lymphoproliferative malignancy, esp. chronic lymphocytic leukemia. Treatment focuses on the underlying disorders.

heavy metals

Metals such as mercury, lead, chromium, cadmium, and arsenic that have known toxic effects on internal organs, such as the kidneys, brain, bone, or retina. SEE: Poisons and Poisoning Appendix.

Heberden nodes

(hē′bĕr-dĕn) [William Heberden, Brit. physician, 1710–1801] Hard nodules or enlargements of the distal interphalangeal joints of the fingers; seen in osteoarthritis.


(heb′ĕ-tood″, heb′ĕ-tud″) [L. hebes, stem hebet-, dull] Dullness or lethargy.

Hebra disease

(heb′ ră) [Ferdinand Ritter von Hebra, Austrian dermatologist, 1816–1880] 1. Erythema mulitforme. 2. Impetigo herpetiformis.


[Gr. hekaton, hundred] In the International System of Units (SI), a prefix meaning 100 times (102).


(hĕk′tō-grăm″) [″ + gramma, small weight] One hundred grams, or 3.527 avoirdupois ounces.


(hĕk′tō-lē″tĕr) [″ + litra, a pound] One hundred liters.


(hĕk-tōm′ĕ-tĕr) [″ + metron, measure] One hundred meters.


Health Plan Employer Data and Information Set.


(hē-don′ik) [Gr. hēdonikos, pleasurable] Pert. to pleasure and its perception.

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