The breathing in men and women is very irregular. In exhalation the Prana goes out 16 digits and in inhalation only 12 digits, thus losing 4 digits. But if you inhale for 16 digits as in exhalation then you will have rhythmical breathing. Then the power Kundalini will be aroused. By the practice of rhythmical breathing you will enjoy real good rest. You can control the respiratory centre that is situated in medulla oblongata and other nerves also, because the centre of respiration has a sort of controlling effect on other nerves. He who has calm nerves has a calm mind also.
If the units of exhalation and inhalation are the same, you will have rhythmical breathing. If you inhale till you count 6 OMs, exhale also till you count 6 OMs. This is breathing in and out in a measured manner. This will harmonise the whole system. This will harmonise the physical body, mind, Indriyas and will soothe the tired nerves. You will experience full repose and calmness. All the bubbling emotions will subside and the surging impulses will calm down.
There is another variety of modification of rhythmic breathing. Inhale slowly through both nostrils for 4 OMs; retain the breath for 8 OMs (internal Kumbhaka); exhale slowly through both nostrils for 4 OMs: and retain the breath outside (external Kumbhaka) for 8 OMs.
Repeat the above process a number of times according to your strength and capacity. You can gradually increase the duration of inhalation and exhalation after some practice 8 OMs and the period between breaths to 16 OMs. But never try to increase the duration until you are sure that you have power and strength to do so. You must experience joy and pleasure in doing the same. You should not feel any undue strain. Pay considerable attention to keep up the rhythm. Remember that the rhythm is more important than the length of breath. You must feel the rhythm throughout your whole body. Practice will make you perfect. Patience and perseverance are needed.