| rule of bigeminy | Rule that a ventricular premature beat will follow the beat terminating a long cycle. Sudden prolongation of the ventricular cycle, by changing the refractoriness in the conduction system, causes a peripheral region of bidirectional block to become transiently unidirectional and thus opens potential pathways for reentry to occur. (05 Mar 2000) |
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| rule of nines | Method used in calculating body surface area involved in burns whereby values of 9 or 18 percent of surface area are assigned to specific regions as follows: Head and neck, 9%; anterior thorax, 18%; posterior thorax, 18%; arms, 9% each; legs, 18% each; perineum 1%. (05 Mar 2000) |
| rule of outlet | An obstetric rule for determining whether the pelvic outlet will permit the passage of a foetus; the sum of the posterior sagittal diameter and the transverse diameter of the outlet must equal at least 15 cm if a normal-sized baby is to pass. (05 Mar 2000) |
| Clark's weight rule | An obsolete rule for an approximate child's dose, obtained by dividing the child's weight in pounds by 150 and multiplying the result by the adult dose. (05 Mar 2000) |
| weigert-meyer rule | <radiology> Applies to duplex collecting systems, upper-pole ureter, obstruction most likely to be hydronephrosis, inserts more inferiorly and medially in bladder, may insert into urethra, vagina, etc., males not incontinent: insertion above ext. Sphincter, associated with ureterocele, lower-pole ureter, reflux most likely to be pyelonephritis see also: drooping lily sign (12 Dec 1998) |
| Cowling's rule | An obsolete rule for a child's dose: that fraction of the adult dose obtained by dividing the age of the child at the nearest birthday by 24. (05 Mar 2000) |
| Haase's rule | The length of the foetus in centimeters, divided by 5, is the duration of pregnancy in months, i.e., the age of the foetus. (05 Mar 2000) |
| Haldane's rule | <genetics> if one of the two sexes is missing, sterile, or rare in a population of first-generation hybrids between two different species, then that sex is the heterogametic sex (has two different sex chromosomes, such as XY as opposed to XX). (09 Oct 1997) |
| Prentice's rule | Each centimeter of decentration of a lens results in 1 prism diopter of deviation of light for each diopter of lens power. (05 Mar 2000) |
| Schutz rule | The rate of an enzyme reaction is proportional to the square root of the enzyme concentration; applied specifically to pepsin within a limited range. Synonym: Schutz' law. (05 Mar 2000) |
| His' rule | The duration of pregnancy is calculated from the first day of the first omitted menstrual period; obsolete. (05 Mar 2000) |
| Huckel's rule | <chemistry> The number of depolarised electrons in an aromatic ring is equal to 4n + 2 where n is zero or any positive integer; l-tyrosine, l-phenylalanine, l-tryptophan, and l-histidine (when the imidazole ring is deprotonated) obey this rule. (05 Mar 2000) |
| Nagele's rule | Means of estimating date of delivery by counting back three months from the first day of the last menstrual period and adding seven days. (05 Mar 2000) |
| New Hampshire rule | Pioneering American test of criminal responsibility (1871): "if the [criminal] act was the offspring of insanity, a criminal intent did not produce it." (05 Mar 2000) |
| Durham rule | An American test of criminal responsibility (1954): "an accused is not criminally responsible if his unlawful act was the product of mental disease or mental defect." (05 Mar 2000) |