Yes Sue, you are smart. I was not smart enough to know the negative effect of it. I thought it would help with dislodging mucus and requested my pulmo and the company sent me one. I'm a very small person 5 feet (104 lbs last year when I got it). So, it hurts a lot and it was not helping with ACT, it was just pounding my chest in one place. I got it in September last year and in March, I cough up a lot of blood (not sure from the vest or from NAC because NAC also causes bleeding). Had to rush to ER and stayed in the hospital for 5 days. So, we need to be very careful with our fragile lungs.