I have observed quite few breathing techniques that women used during labour.
Majority adapted their rhythm of breathing naturally and some used breathing techniques they learnt in yoga.
A friend of mine was whistling throughout her contractions as it helped her. I thought that was fascinating. Some hypnobirthing techniques encourage women to make a noise during the exhale which could be a “sshhh” noise or a deep exhale. Indeed, my friend used a whistling technique. I think that having this added sound can help you to focus your mind on something other than the intensity of the labour sensations. Making a noise during the exhale can also work to lengthen it and relax the muscles in the face and jaw. So do not be embarrassed to make noise!
I suggest to practise prenatal yoga as you will learn several exercises to stretch the sides of your body to give more space for your lungs. You will also learn that breathing exercises help you to focus the mind and body, and to regulate your breathing rate and ensure you are getting enough oxygen to your lungs and to your baby.
So here are some tips for you to try:
Generally, the breathing techniques that you learn for your birth places emphasis on your exhaling. For example visualise a white feather floating in front of your face. The aim is to blow away the white feather further and further away from you during a contraction.
You may find useful to use Ujjayi breathing https://www.youtube.com/watch?v=RnubvFv62Ak . This is another way to create sound during the exhale. This breathing technique is sometimes called "the ocean breath". It works by slightly narrowing the back of the throat which constricts the passage of air. It’s important never to hold your breath during labour (or in pregnancy).
Another breathing technique to lengthen the out breath is by counting. Inhale to the count of 3 and exhale to the count of 3 initially, but then gradually lengthen the exhale to the count of 5. You can count in your head or get your birth partner to help you count out loud. Alternatively, instead of counting perhaps focus on the sensation of cold air coming in through the nostrils and warm air leaving your nose and mouth.