| continuous time model | <epidemiology> A model in which the system changes continuously over time. Derivatives (e.g. DY/dt ) are the mathematical formalism for describing such continuous change. The differential equation which embodies a model provides the values of these derivatives at any particular time point; calculus or a computer can then be used to move the state of the model forwards in time. Continuous models have the advantage over discrete time models in that they are more amenable to algebraic manipulation, although they are slightly harder to implement on a computer. The same as a differential equation model. (05 Dec 1998) |
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| half-time | The time, in a first-order chemical (or enzymic) reaction, for half of the substance (substrate) to be converted or to disappear. Compare: half-life. (05 Mar 2000) |
| prothrombin time | Measurement of clotting time of plasma recalcified in the presence of excess tissue thromboplastin. Factors measured are fibrinogen, prothrombin, and factors v, vii, and x. It is used for monitoring anticoagulant therapy with coumarins. (12 Dec 1998) |
| sensation time | The minimal time a visual image must be exposed in order to be perceived. (05 Mar 2000) |
| H-R conduction time | Conduction of the cardiac impulse through the ventricular myocardium, represented by the QRS complex in the electrocardiogram. H-R conduction time is from the onset of the first high frequency component of the His bundle electrogram to the onset of the QRS complex of the surface electrocardiogram (normally 43 ± 12 msec); H-V conduction time is from the onset of the first high frequency component of the His bundle electrogram to the onset of the ventricular electrogram (normally approximates the H-R interval but may be a little shorter). Synonym: ventricular conduction. (05 Mar 2000) |
| H-V conduction time | Conduction of the cardiac impulse through the ventricular myocardium, represented by the QRS complex in the electrocardiogram. H-R conduction time is from the onset of the first high frequency component of the His bundle electrogram to the onset of the QRS complex of the surface electrocardiogram (normally 43 ± 12 msec); H-V conduction time is from the onset of the first high frequency component of the His bundle electrogram to the onset of the ventricular electrogram (normally approximates the H-R interval but may be a little shorter). Synonym: ventricular conduction. (05 Mar 2000) |
| sinoatrial conduction time | <cardiology, physiology> The time required for an impulse to travel from the sinoatrial node to the atrium; estimated indirectly during asystole by halving the average interval from the premature beat to the following normal sinus beat of the atrium. (05 Mar 2000) |
| sinoatrial recovery time | <cardiology, physiology> Interval from the last paced P wave to the first succeeding spontaneous P wave (after 2 to 5 minutes of right atrial pacing at 120 to 140 beats per minute, and when expressed as percentage of control cycle length, it normally ranges from 115 to 159%). (05 Mar 2000) |
| space-time clustering | A statistically significant excess of cases of a disease, occurring within a limited space-time continuum. (12 Dec 1998) |
| Stypven time test | A test measuring the clotting time of plasma after addition of Russell's viper venom, useful in evaluating patients with deficiencies in factor X. Origin: Trade name styptic + venom (05 Mar 2000) |
| survival time | The period elapsing between the completion or institution of any procedure and death, the life-span of biologically or physically marked erythrocytes or other cells. (05 Mar 2000) |
| systolic time intervals | See: electromechanical systole, left ventricular ejection time, preejection period. (05 Mar 2000) |
| discrete time model | <epidemiology> A model in which the system jumps from one state to the next at fixed intervals or timesteps. These difference models are simple to understand but often difficult to analyse; Contrast continuous time models. The parameters in such a model refer to the amount of change over the finite timestep; they are sometimes referred to as finite rates. In a (rather precise) sense, a differential equation is what you eventually get from a difference equation when you let the timestep get smaller and smaller and smaller. (05 Dec 1998) |
| doubling time | <cell biology> The time taken for a cell to complete the cell cycle. (10 Oct 1997) |
| Duke bleeding time test | A bleeding time test in which an incision is made in the earlobe and the time until bleeding stops is measured. (05 Mar 2000) |