nitrogen
(N) [ni´tro-jen] a chemical element, atomic number 7, atomic weight 14.007. (See Appendix 6.) It is a gas constituting about four-fifths of common air; chemically it is almost inert. It is not poisonous but is fatal if breathed alone because of oxygen deprivation. It is soluble in the blood and body fluids, and can cause serious symptoms when released as bubbles of gas by rapid decompression (see
bends). Nitrogen occurs in proteins and amino acids and is thus present in all living cells.
nitrogen 13 a radioactive isotope of nitrogen having a half-life of 9.97 minutes and decaying by positron emission; it is used as a
tracer in
positron emission tomography.
nitrogen balance the state of the body in regard to the rate of
protein intake and protein utilization. When protein is metabolized, about 90 per cent of its nitrogen is excreted in the urine in the form of
urea,
uric acid,
creatinine, and other nitrogen end-products. The remaining 10 per cent of the nitrogen is eliminated in the feces. A
negative nitrogen balance occurs when more protein is used by the body than is taken in. A
positive nitrogen balance implies a net gain of protein in the body. Negative nitrogen balance can be caused by such factors as
malnutrition, debilitating diseases, blood loss, and
glucocorticoids. A positive balance can be caused by exercise,
growth hormone, and
testosterone.
liquid nitrogen nitrogen in liquid form, i.e., below −195.79°C; used as a coolant, such as in thermographic equipment.
nitrogen mustards a group of toxic, blistering
alkylating agents that are cell cycle phase nonspecific; it includes nitrogen mustard itself (
mechlorethamine hydrochloride),
chlorambucil,
cyclophosphamide,
ifosfamide, and
melphalan. Some have been used as antineoplastic
agents in certain forms of cancer; they do not cure these conditions, but ease their effects by destroying mitotic cells (those newly formed by division), thereby affecting malignant tissue in its early stage of development, and leaving normal tissue unaffected. They are especially useful in treatment of leukemia, in which they reduce the leukocyte count, and in cases in which the malignant disease is widespread throughout the body and therefore cannot be effectively treated locally by surgery or radiotherapy. In cases of lung cancer, mechlorethamine hydrochloride is usually injected directly into the lungs via the pulmonary circulation. Side effects, which tend to limit the usefulness of these drugs, include nausea, vomiting, and a decrease in bone marrow production.
nonprotein nitrogen (NPN) the nitrogenous constituents of the blood exclusive of the protein bodies, consisting of the nitrogen of urea, uric acid, creatine, creatinine, amino acids, polypeptides, and an undetermined part known as rest nitrogen. Measurement of this is used as a test of renal function, but has been largely replaced by measurement of specific substances, such as
urea and
creatinine.
nitrogen washout test a test for
vital capacity of lungs; with the patient inhaling pure oxygen, the volume of exhaled nitrogen is obtained for each breath until it falls below 1 per cent of the gas being exhaled (usually about seven minutes' time); the total volume of nitrogen that has been exhaled at this point is assumed to be 0.8 of the vital capacity.
nitrogen washout test, single breath the patient inhales a vital capacity's volume of pure oxygen and then slowly exhales. The nitrogen content of the exhalation is measured over the entire breath and a curve is generated; different parts of the curve represent nitrogen concentrations of gas in different components of the total lung capacity, and can be analyzed for irregularities. Called also
single breath test.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.