access c++ objects from another file in Arduino

In my Arduino file, TimerTest.ino

#include "Arduino.h"
#include "Pulse.h"
#include <elapsedMillis.h>

elapsedMillis timeElapsed ; 
Pulse trigger(45,60) ; //45 is pin number, 60 is pulse interval in msec

When I defined Pulse.cpp

#include "Arduino.h"
#include "Pulse.h"

Pulse::Pulse(int pin, long interval)
{
  _pin = pin ;
  pinMode(_pin, OUTPUT);
  _interval = interval);
}

void Pulse::PulseOut()
{
  if(timeElapsed > _previousTime + _interval)
    digitalWrite(_pin,LOW);
} 

I got a compiler error saying that timeElapsed is not in this scope of this file, I don't know enough c++ to understand the access mechanism, can somebody point me to the right solution.