Sama means equal, balance or in the same manner. Vrtti means operation, movement, modification or action. But here, in the context of pranayama, vrtti means four operations that we use for the expansion of the life force.
What are those 4 operations?
4 operations of pranayama are puraka (inhalation), antar kumbhaka (internal breath retention), rechaka (exhalation) and bahir kumbhaka (external breath retention).
In sama vrtti pranayama, we try to achieve the control of all 4 operations but by equalizing their duration/length (time).
Example: if the duration of the inhalation is 6 seconds, we need to make our exhalation, antar kumbhaka, bahir kumbhaka also 6 seconds.
Improves the capacity of the lungs.
Helps to activate the unused alveolis of the lungs.
You will get the control over the respiration/breath.
Helps to harmonize the both hemispheres.
After refining your posture, relax yourself with few belly breathing.
Equalize your exhalation with your inhalation.
When you get the perfect rhythm between inhalation and exhalation, exhalation and inhalation, then start performing the antar kumbhaka. Example: if the length of inhalation and exhalation is 6 seconds, start your antar kumbhaka only from 2 seconds, and slowly increase up to 6 seconds.
When you get the nice rhythm in inhalation, antar kumbhaka and exhalation with equal length, then start performing the external breath retention with just 2 seconds. And slowly increase up to 6 seconds.
Whenever you practice this technique, in the beginning, 3 to 5 rounds practice without kumbhaka. Then, 3 to 5 rounds practice with antar kumbhaka. When your antar kumbhaka become easy and comfortable for you, only then, you can add the bahir kumbhaka. Start with 3 breaths, and gradually, increase your practice up to 9 breaths.
Practice in the guidance of experience teacher.