| MHR | major histocompatibility region; malignant hyperthermia resistance; maternal heart rate; maximal hea... |
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| MMFR | maximum midexpiratory flow rate; maximal midflow rate |
| MMR | mass miniature radiography; masseter muscle rigidity; maternal mortality rate; measles-mumps-rubella... |
| MPR | mannose 6-phosphate receptor; marrow production rate; massive preretinal retraction; maximum pulse r... |
| MRR | marrow release rate; maximum relation rate |
| rate constants | Proportionality constants equal to the initial rate of a reaction divided by the concentration of the reactant(s); e.g., in the reaction A → B + C, the rate of the reaction equals -d[A]/dt = k1[A]. The rate constant k1 is a unimolecular rate constant since there is only one molecular species reacting and has units of reciprocal time (e.g., sec-1). For the reverse reaction, B + C → A, the rate equals -d[B]/dt = d[A]/dt = k2[B][C]. The rate constant k2 is a bimolecular rate constant and has units of reciprocal concentration-time (e.g., m-1 sec-1). Synonym: velocity constants. (05 Mar 2000) |
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| rate, death | The number of deaths in the population divided by the average population (or the population at midyear) is the crude death rate. In 1994, for example, the crude death rate per 1,000 population was 8.8 in the united states, 7.1 in Australia, etc. A death rate can also be tabulated according to age or cause. (12 Dec 1998) |
| rate equation | A mathematical expression for a chemical, radiochemical, or enzyme-catalyzed reaction. (05 Mar 2000) |
| rate, erythrocyte sedimentation | A sedimentation rate, or sed rate , is a blood test that detects and is used to monitor inflammation activity. It is measured by recording the rate at which red blood cells (rbcs) sediment in a tube over time. It increases (the rbcs sediment faster) with more inflammation. (12 Dec 1998) |
| rate, foetal mortality | The ratio of foetal deaths divided by the sum of the births (the live births + the foetal deaths) in that year. In the united states, the foetal mortality rate plummeted from 19.2 per 1,000 births in 1950 to 9.2 per 1,000 births in 1980. (12 Dec 1998) |
| rate, heart | Number of heart beats per minute. The normal resting adult heart beats regularly at an average rate of 60 times per minute. (young children's hearts beat faster). The speed of the heartbeat (heart rate) is governed by the speed of electrical signals from the pacemaker of the heart, the sa node, located in the right atrium (upper chamber of the heart). The electrical signals from the sa node travel across the atria and cause these two upper heart chambers to contract, delivering blood into the lower heart chambers, the ventricles. The electrical signals then pass through the av node to reach the ventricles. Electrical signals reaching the ventricles cause these chambers to contract, pumping blood to the rest of the body, generating the pulse. During rest, the speed of electrical signals originating from the sa node is slow, so the heart beats slowly. During exercise or excitement, the speed of signals from the sa node increases, and the heartbeat quickens. (12 Dec 1998) |
| rate, infant mortality | The number of children dying under a year of age divided by the number of live births that year. The infant mortality rate in the united states, which was 12.5 per 1,000 live births in 1980, fell to 9.2 per 1,000 live births in 1990. (12 Dec 1998) |
| rate-limiting step | <biochemistry> The slowest step in a metabolic pathway, or the step in an enzymatic reaction that requires the greatest amount of energy to initiate. (17 Dec 1997) |
| rate, maternal mortality | The number of maternal deaths related to childbearing divided by the number of live births (or by the number of live births + foetal deaths) in that year. The maternal mortality rate in the united states in 1993 (and 1994) was 0.1 per 1,000 live births, or 1 mother dying per 10,000 live births. (12 Dec 1998) |
| rate meter | A device that continuously displays the magnitude of events averaged over varying time intervals. (05 Mar 2000) |
| rate, neonatal mortality | The number of children dying under 28 days of age divided by the number of live births that year. The neonatal mortality rate in the united states, which was 8.4 per 1,000 live births in 1980, declined to 5.8 per 1,000 live births in 1990. (12 Dec 1998) |
| rate, pulse | The pulse rate is most often taken at the wrist. It measures the number of pulsations in the radial artery each minute. (12 Dec 1998) |
| rate, respiratory | The number of breaths per minute (or, more formally, the number of movements indicative of inspiration and expiration per unit time). In practice, the respiratory rate is usually determined by counting the number of times the chest rises (or falls) per minute. By whatever means, the aim is to determine if the respirations are normal, abnormally fast (tachypnea), abnormally slow (technically termed bradypnea), or nonexistent (apnea). (12 Dec 1998) |
| rate schedule | A price list showing how the electric bill of a particular type of customer will be calculated by an electric utility company. (05 Dec 1998) |
| rate, sed | A sedimentation rate, or sed rate , is a blood test that detects and is used to monitor inflammation activity. It is measured by recording the rate at which red blood cells (rbcs) sediment in a tube over time. It increases (the rbcs sediment faster) with more inflammation. (12 Dec 1998) |