Spirometer ... Blow in the horn ... test the pulmonary system (lungs) strength by the gauge and the endurance(capacity) by timing how long the propeller spins. ?
Maybe yours didn't have the lamp ?
There doesn't seem to be many out there. Perhaps used more in Spain or Mexico ?
They describe it this way:
"El espirómetro se utiliza para medir la capacidad respiratoria pulmonar."