Transit time, mean

Location Average length/diameter (cm) Average surface area (m2) Average pH (range) Enzymes and others Mean transit times Microflora per gram content... 

This definition completely coincides with the characteristic time of the probability evolution introduced in Ref. 32 from the geometrical consideration, when the characteristic scale of the evolution time was defined as the length of rectangle with the equal square, and the same definition was later used in Refs. 33-35. Similar ideology for the definition of the mean transition time was used in Ref. 30. Analogically to the MTT (5.4), the mean square d2(c,x, d) = (f2) of the transition time may also be defined as... 

Note that previously known time characteristics, such as moments of FPT, decay time of metastable state, or relaxation time to steady state, follow from moments of transition time if the concrete potential is assumed a potential with an absorbing boundary, a potential describing a metastable state or a potential within which a nonzero steady-state distribution may exist, respectively. Besides, such a general representation of moments dn(c,xo,d) (5.1) gives us an opportunity to apply the approach proposed by Malakhov [34,35] for obtaining the mean transition time and easily extend it to obtain any moments of transition time in arbitrary potentials, so i9n(c, xo, d) may be expressed by quadratures as it is known for moments of FPT. 

Alternatively, the definition of the mean transition time (5.4) may be obtained on the basis of consideration of optimal estimates [54]. Let us define the transition time i) as the interval between moments of initial state of the system and abrupt change of the function, approximating the evolution of its probability Q(t.X(t) with minimal error. As an approximation consider the following function v /(f,xo, ) = flo(xo) + a (xo)[l(f) — l(f — i (xo))]. In the following we will drop an argument of ao, a, and the relaxation time d, assuming their dependence on coordinates of the considered interval c and d and on initial coordinate x0. Optimal values of parameters of such approximating function satisfy the condition of minimum of functional ... 

In the forthcoming sections we will consider several methods that have been used to derive different integral relaxation times for cases where both drift and diffusion coefficients do not depend on time, ranging from the considered mean transition time and to correlation times and time scales of evolution of different averages. 

In this section we restrict our consideration by potentials of type II only (in this case moments of transition time are moments of decay time). The approach, considered above for derivation of the mean transition time may also be used to obtain higher moments, given by Eq. (5.1). 

For the mean transition time, this fact may be explained in the following way If the transition process is going from up to down, then the probability current is large, but it is necessary to fill the lower minimum by the larger part of the probability to reach the steady state if the transition process is going from down to up, then the probability current is small, and it is necessary to fill the upper minimum by the smaller part of the probability to reach the steady state. 

In addition to more rapid absorption of lipids in animals fed casein, another mechanism that may be operative is decreased clearance of circulating lipids. Rabbits fed a casein-based semipurified diet excreted significantly less cholesterol but more bile acids in their feces than animals fed a commercial diet (18). The total sterol excretion in feces of the animals fed the casein diet was half that of the rabbits fed the stock diet. Huff and Carroll (19) found that rabbits fed soy protein had a much faster turnover rate of cholesterol and a significantly reduced rapidly exchangeable cholesterol pool compared with rabbits fed casein. Similar studies performed in our laboratory revealed that the mean transit time for cholesterol was 18.4 days in rabbits fed soy protein, 36.8 days in rabbits fed casein, 33.7 days in rabbits fed soy plus lysine, and 36.3 days in rabbits fed casein plus arginine. These data suggest that addition of lysine to soy protein... 

Pool A (mg) Pool B (mg) Mean transit time (days)... 

Graff J, Brinch K, Madsen JL. Gastrointestinal mean transit times in young and middle-aged healthy subjects. Clin Physiol 2001 21 253-259. 

Ballinger LN, Cross SE, Roberts MS. 1995. Availability and mean transit times of phenol and its metabolites in the isolated perfused rat liver Normal and retrograde studies using tracer concentrations of phenol. J Pharm Pharmacol 47 949-956. 

A major determinant of the absorption of a compoimd from the colon is the residence in any particular segment of the colon. The time taken for food to pass through the colon accounts for most of the time the food is present in the gut. In normal subjects this is about 78 hr for expulsion of 50% ingested markers but may vary from 18 to 144 hr. Steady-state measurements of mean transit time after ingestion of markers for several days gave a mean transit time of 54.2 hr [10]. 

MAMILLARY MODEL MEAN TRANSIT TIME COMPARTMENTALIZATION Compartments, drug uptake and release, PHARMACOKINETICS COMPENSATION EFFECT COMPETITION PLOT COMPETITIVE BINDING ASSAY COMPETITIVE INHIBITION Competitive inhibitor,... 

MEAN TRANSIT TIME COMPARTMENTAL ANALYSIS MECHANISM-BASED INHIBITOR MEDIATED AMPEROMETRIC BIOSENSOR BIOSENSOR MEDIUM Medium effect,... 

Yamada et al. suggested that benzoate-metabolizing capacity, especially as indicated by the mean transit time value of the serum benzoate, appears to be a better index than the indocyanine green clearance rate for determining hepatic functional reserve in chronic lever disease [40],... 

Thus, if measurements are performed on specimens of differing thicknesses, at identical applied fields, then variations in the relative degree of dispersion should be observed, with thicker specimens being characterized by less dispersive transit pulses (Fig. 3.2). It is interesting to note that a number of analysis (see Ref [8]) have assumed that an increase in electric field in a given specimen will result in an increase in relative dispersion (due to a reduction of the mean transit time). However,... 

Mean In Vivo Dissolution Time For a solid dosage form MDTsoUd = MRT-soiid - MRTsolution. This reflects the mean time for drug to dissolve in vivo. Mean Residence Time The mean time that the drug resides in the body. MRT may also be the mean transit time. MRT = AUMC/AUC. 

The diffusion coefficients of the ions can be determined through time-of-flight techniques. For a liquid crystalline material between two ITO coated plates with an initial voltage V, a sudden increase in the voltage to Vi allows the ionic mean transit time t j and the ion mobility to be determined by the relations [69] ... 

One of the main problems with the IVGTT is its transient nature, because the time it takes to distribute the bolus evenly in the blood is considerable. The mean transit time for the circulation is approx. 1 min [64], but some blood returns fast, while other blood, for example to the legs, may take 10-15 min to return. The result is an initial distribution phase that mimics an uptake, so particularly the initial glucose dependent uptake is overestimated. 

Sorenson et al. (1999) 12 h 65% Mean transit time and cerebral blood flow... 

Fig. 3.8. Graph demonstrating that the perfusion threshold for mismatch tissue to be salvaged from infarction declines with time. These patients all had major reperfusion on follow-up imaging and tissue with severe hypoperfusion (mean transit time 15-s delay) was able to be salvaged from infarction within 3 h, but at 6 h, the threshold for salvage declined to only 3 s delay in mean transit time (Butcher et al. 2003)...

A second, very important parameter is the normalized first momentum of the concentration time curve, which corresponds to the relative mean transit time (rMTT). This parameter is defined by... 

Weisskoff RM, Chesler D, Boxerman JL, Rosen BR (1993) Pit-falls in MR measurement of tissue blood flow with intravascular tracers which mean transit time Magn Reson Med 29 553-558... 

---