[trux]

I'd rather suggest to stop bothering with it and stressing with some calculations that will never be exact anyway. Breath up just normally, without any mind control or forcing. Rather than breathing deeply, concentrate on the complete relaxation and it will have much better effect. You can breathe somehow deeper (without forcing), but try keeping the inhalation short (inhalation stimulates tachycardia - increase of the heart rate), hold for 3-5 secs, and then expire very very slowly (expiration stimulates bradycardia - slowing down the HR). Do not try to control the breathing by your ribcage or diaphragm muscles (it adds tension and consumes oxygen), but rather by your lips. Make the expiration about 5 or more times longer that the inhalation, but do not stress about trying to measure it exactly. Simply concentrate just on your relaxation,