Found more info, for those interested.
Unfortunately, CART is not yet available to the public. Dr. Meuret and others are hoping to devise a capnometry machine for at-home use, but it will take time. Until then, here are her suggestions on how to breathe shallowly, which will help decrease panic and anxiety...
Never breathe deeply when you start to feel anxious. Although it feels counterintuitive, concentrate on taking shallow breaths only.
Breathe only through your nose—this will make it easier to keep your breath shallow.
Breathe from the abdomen but so lightly that you experience almost no movement in your belly or anywhere else in your body.
Time yourself—try to take nine breaths per minute, which is somewhat slower than normal breathing.
Dr. Meuret had one more bit of conventional wisdom to lay to rest. If you find yourself hyperventilating, do not breathe into a paper bag—not only does it not help with panic, but the oxygen deprivation that results from it can be dangerous for people with lung or cardiac disease. Instead, try the techniques mentioned above.