Fig. 1. Parameters used to quantify the intensity and duration of the fluorescence traces included the area under the first pass curve 

where Fluo(t) was the corrected first pass fluorescence trace after elimination of the recirculation with an exponential fit (  dashed line ) of the trailing edge of the experimental fluorescence trace, the peak intensity, the full-width at half-maximum (FWHM = duration between points on the curve at which the fluorescence reached half its maximum value), the circulation time (duration between the peak of the first pass fluorescence and the peak of the recirculation), and the mean transit time (average duration of the first pass peak) estimated with the formula

Time 0 was selected as the instant at which the fluorescence intensity departed from the preinjection baseline.