Mean transit time (MTT) is the average amount of time the blood spends in the capillary bed. A capillary bed is made up of numerous capillaries of different lengths, so the time spent in the tissue has a distribution. The unit of measurement is seconds. Typical values for the normal brain are in the range of 3 - 5 s, whereas in acute cerebral infarction MTT is increased.
According to the central volume principle, it is important to note close relationship between the CBF, CBV, and MTT. This relationship is:
This relationship can easily be explained with the simple case of flow through a single capillary. Flow is defined as the motion of a volume of fluid over time and velocity as distance over time. If the distance is measured along the capillary vessel, and the velocity is the speed of the fluid in this vessel, this relationship can be multiplied by the cross-sectional area of the capillary. This converts the distance to a volume and the velocity to a flow.
Was this article helpful?