A waveform with slow systolic upstroke and slow diastolic downstroke may occur distal to high-grade stenoses in many vessels .
许多血管高级别的狭窄的远端频谱波形会出现收缩期缓慢的上升支和舒张期缓慢的下降支。
For example , birds clap their wings together at the peak of the upstroke during takeoff - that 's the clatter of a pigeon taking off in the park - and rotate their wings on the way down to get lift .
