hey all. I recently purchased a peak flow meter to measure the capacity of my lungs since I'm paranoid about them functioning properly. this is the first day I've used it and I've used it a lot, I get episodes of shortness of breath from my acid reflux and such. when I was exhaling I felt a stabbing pain right beneath my heart which freaked me out. Could it just be from strain? It definitely hurts when I press down on it