There is a way to do this, but I don't know what kind of hardware that you have. With an E-series data acquisition board, such as the 6070E, you can set up an analog acquisition to trigger on a falling or rising signal at 0 volts. This "trigger" can then be routed to a counter, which can generate a pulse when this trigger occurs. That should accomplish the task!
There are a couple shipping examples that should help get you started on this application. The first is the Acq&Graph Voltage-Int Clk-HW Trig Restarts VI which creates an analog task that will trigger at a specific voltage level and slope. This task is somewhat limited by time as in order for it to retrigger that task has to be stopped and restarted, this generally takes a few ms. If a trigger occurs during this time, it will be missed.
Another VI that you can refer to is the Gen Dig Pulse-Retriggerable VI, this VI generates a pulse when trigger. The counter task must use a digital trigger, the AnalogComparisonEvent signal is the output of
the analog trigger circuit and is a digital signal. You have to right click on the Terminal I/O
control and select I/O Name Filtering to Include the Advanced Terminals
to see this terminal. This will trigger the pulse each time your analog input task sees an analog trigger.