Figure 2
Vascular arterial, venous and arteriovenous flow curves . Mean arterial, venous and arteriovenous flows are represented over two successive cardiac cycles (CC) in one patient. The arterial blood flow peaks and troughs are represented. The difference in amplitude (ΔF = Fmax - Fmin) and latency ((ΔT = Tmin - Tmax) between these 2 features is also shown. The arterial pulsatility index (defined as ΔF/ΔT) corresponds to the slope of the arterial flow curve at the beginning of systole. The arterial pulse volume (defined as ΔF × ΔT/2) corresponds to the systolic arterial inflow volume. The arteriovenous flow curve results from the difference between the arterial and the venous flow curves over a given CC. Integration of the area under the curve yields the arteriovenous stroke volume, which represents the volume blood carried into the cranium (the input cerebral blood volume) or expulsed caudally (the output cerebral blood volume) from the cranium over the course of the CC. The difference in latency between the arterial and venous flow peaks (in milliseconds or as a percentage of the CC) corresponds to the arteriovenous delay (AVD).