I am 5’4” tall and weigh 110 pounds. I had the Hill-Rom Monarch for about nine months. I am told it comes in only one size. I tried everything to make it work, but it was simply too big. The pods are supposed to fit on your lungs or they do not work. The back lower pods hit me in the kidneys (although they were too wide to fit on my back fully). That caused back pain. The front lower pods hit my stomach. When they added shoulder pads, the top pads were too high. They wound up turning off more than half of the pods. The third representative who called finally came out and took a look; he said the vest did not fit AT ALL. They switched me to the Vest APX in December. It comes in different sizes. I am wearing a 30-34”. It fits comfortably and is adjustable. Although you can’t walk around with it, the hoses detach easily if you need them to. I highly recommend. My next scan will tell whether it has improved the mucus plugging, but I do believe it has improved my breathing. Pay careful attention if they try to fit you with the Monarch. If you are my size, it will not really fit.