In his book, Light on Yoga, B.K.S. Iyengar refers to shoulder stand as the "Mother of asanas" and states that the importance of this pose "cannot be over-emphasized". In order to understand the value of the shoulder stand you must first understand the role of the lymphatic and circulatory systems in the body. The lymphatic system is part of the circulatory system and is comprised of a network of lymphatic vessels that carry lymph fluid to the heart. The movement of this fluid is essential for a healthy immune system as it transports white blood cells and nutrients around the body and also assists in elimination of metabolic waste.
When you go into an inversion such as shoulder stand you have several therapeutic actions happening. Possibly the most obvious is the affect of gravity on the body's fluids. As you settle into the pose you notice all of the blood in your body moving downward towards your heart, face and throat. Instantly your thyroid and parathyroid glands are bathed in blood which assists in hormone secretion. Also while you are upside down lymph fluid has an opportunity to move towards the clusters of lymph nodes in the groin, belly and throat which not only helps your body to combat viruses, bacteria and cancerous cells but also to eliminate toxins. Another thing to consider here are the organs in your belly. Being upside down allows your bowels and internal organs to move more freely and have a momentary "lift" from the daily compression caused by prolonged sitting. Iyengar also writes, "It is no overstatement to say if a person regularly practices sarvangasana he will feel new vigor and strength.. new life will flow into him." Not bad just for being upside down for 10 minutes huh?
Now to address how to practice shoulder stand. The photograph below shows a few options ranging from easiest to most difficult. I personally enjoy shoulder stand towards the end of my asana practice after my body has been moving around and warmed up. I also feel it is important to practice with several blankets under the shoulders and arms with the head off of the blankets to avoid any compression in the cervical spine. One thing to note is that shoulder stand is contraindicated for those with high blood pressure and props or alternative therapeutic postures should be used by those with spinal injuries or complication in the cervical spine. This brings us back to that important point of honoring and respecting your body and it's needs! "The rhythm of pausing and surrendering to life is the most daring, for here we can learn to just be."- Donna Farhi.
After your practice and whatever variation of inversion you may choose, take the time to sit and meditate. Observe how your body responds to the postures and what may have arisen for you. A dear friend and yoga teacher Jenny Russo once told me "As things start to change on the outside they also open and evolve on the inside". It is my hopes that your living practice connects you to your highest self and help you to be present with all that you experience upside down or not.