| ventilation/perfusion ratio | The ratio of alveolar ventilation to simultaneous alveolar capillary blood flow in any part of the lung; because both ventilation and perfusion are expressed per unit volume of tissue and per unit time, which cancel, the units become liters of gas per liter of blood. (05 Mar 2000) |
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| mass-action ratio | The ratio of the product of all of the product concentrations divided by the product of all of the reactant concentrations of a particular reaction; when the reaction has been completed (i.e., t = ∞), then this ratio is equal to the equilibrium constant. (05 Mar 2000) |
| case fatality ratio | The mortality rate of a disease, usually expressed per 100 cases. (05 Mar 2000) |
| CD4:CD8 ratio | The ratio of CD4 to CD8 cells. A common measure of immune system status that is around two in healthy individuals. The ratio of T-lymphocytes that express the CD4 antigen to those that express the CD8 antigen. This value is commonly assessed in the diagnosis and staging of diseases affecting the immune system including HIV infection. (12 Dec 1998) |
| reproductive ratio | <epidemiology> 1. Basic reproductive ratio , Ro , a dimensionless parameter which encapsulates the biological details of different transmission mechanisms. For microparasites, Ro , is defined as the average number of secondary cases of infection to which one primary case gives rise throughout its infectious period if introduced into a defined population consisting solely of susceptible individuals. For macroparasites, Ro , is the average number of female offspring (or just offspring in the case of hermaphroditic species) produced throughout the lifetime of a mature female parasite, which themselves achieve reproductive maturity in the absence of density-dependent constraints on the parasite establishment, survival or reproduction. Also known as the basic reproduction rate, number. 2. Effective reproductive ratio , R , The number of secondary cases (microparasites) or female offspring (macroparasites) produced in a host population not consisting entirely of susceptible individuals (microparasites) or within which density dependent constraints limit parasite population growth (macroparasites). Under conditions of stable endemic infection, R=1. (05 Dec 1998) |
| respiratory exchange ratio | The ratio of the net output of carbon dioxide to the simultaneous net uptake of oxygen at a given site, both expressed as moles or STPD volumes per unit time; in the steady state, respiratory exchange ratio is equal to the respiratory quotient of metabolic processes. (05 Mar 2000) |
| mendelian ratio | The ratio of progeny with a particular phenotypes or genotypes expected in accordance with Mendel's law among the offspring of matings specified as to genotype or phenotype. (05 Mar 2000) |
| M:E ratio | The ratio of myeloid to erythroid precursors in bone marrow; normally it varies from 2:1 to 4:1; an increased ratio is found in infections, chronic myelogenous leukaemia, or erythroid hypoplasia; a decreased ratio may mean a depression of leukopoiesis or normoblastic hyperplasia depending on the overall cellularity of the bone marrow. (05 Mar 2000) |
| grid ratio | In a radiographic scatter-absorbing grid, the ratio of the height to the width of the gaps between lead strips; a higher grid ratio removes more scattered radiation but requires more careful X-ray tube positioning to avoid grid cutoff of the primary radiation beam. (05 Mar 2000) |
| gyromagnetic ratio | In nuclear magnetic resonance, the ratio of the magnetic dipole moment of the nucleus to the nuclear spin angular momentum; the gyromagnetic ratio is a unique value for each type of nucleus. Synonym: magnetogyric ratio. (05 Mar 2000) |
| molecular weight ratio | The sum of the atomic weight's of all the atoms constituting a molecule; the mass of a molecule relative to the mass of a standard atom, now 12C (taken as 12.000). Relative molecular mass (Mr) is the mass relative to the dalton and has no units. See: atomic weight. Synonym: molecular mass, molecular weight ratio, relative molecular mass. (05 Mar 2000) |
| P/O ratio | A measure of oxidative phosphorylation; the ratio of phosphate radicals esterified (forming adenosine 5'-triphosphate from adenosine 5'-diphosphate) to atoms of oxygen consumed by mitochondria; normally, the ratio is 3 (starting from NADH). Synonym: P/O quotient. (05 Mar 2000) |
| hand ratio | The ratio of the length of the hand (measured on the dorsum from the styloid process of the ulna to the tip of the third finger) to the width across the knuckles. (05 Mar 2000) |
| segregation ratio | In genetics, the proportion of progeny of a particular genotype or phenotype from actual matings of specified genotypes. The test of a Mendelian hypothesis is the comparison of the segregation rate with the Mendelian rate. (05 Mar 2000) |
| sex ratio | The number of males per 100 females. (12 Dec 1998) |