Respiratory Rate and Pulse Rate
First you need to lower your breathing rate. Normal people breathe about 18 times a minute, but less than 10 is good. Don't count your breath in seconds, count seconds in your breath. If you can count to five and feel that your breath is coming in without difficulty, start adjusting to your body from then on. This is possible if you know your body deeply.
You shouldn't be in a hurry just because you want to reap the results of training quickly. Both zazen and meditation are for the purpose of relaxing the body. The main purpose of the lotus position is also relaxation. It is because of relaxation that Shakyamuni sat cross-legged under the Bodhi tree. Breathing in an unrelaxed state is poison. What will happen if you increase your breathing training without knowing that bubbles will form in your blood while breathing in the first few seconds, causing a circulatory disorder? The body will become more and more stiff due to cell inflammation. Never artificially breathe. It is also forbidden to try hard here and there to lengthen the breath. If you want to drop your breathing rate, you need to raise the oxygen tank first. Again, relaxation comes first.