Bhramari is directly related to the throat center and to the organs in the region - the most important of which are the thyroid and thymus glands. Let's take the effect of bhramari on the thymus.
This gland is indirectly involved in the production of white blood cells, also known as lymphocytes. Called T-cells the the rhymus weighs about 15 grams at birth; by the time we are twelve, it gets doubled in size. As we enter adulthood, however, it begins to shrink, and by the time we are in our thirties, it is quite small and is buried in a layer of fatty cells.
At this stage, according to modern science, the thymus no longer has an important role to play in maintaining our health. The job of manufacturing T-cells has been largely taken over by the lymph nodes and the spleen.
According to yoga science however, the thymus, and more significantly the energy of the region surrounding it, continues to play a pivotal role in maintaining the resistance of both the body and mind to adverse, harmful conditions. In the early part of life, the growing thymus enables a child to have a strong immune system and to exhibit almost limtless mental creativity. But as soon as nature imposes a ban on physical growth, the thymus assumes a more subtle and powerful role, it shifts from maintaining physical immunity to disease to supporting emotional maturity.
Now you can see how bhramari pranayama can restore the normal health of the thymus. On the one hand, this healthy thymus can continue guiding the lymph nodes and the spleen to perform their immune-system functions appropriately. On the other hand, it can focus on performing a more subtle function; it can enable us to cultivate the virtues of patience, fortitude, forgiveness and compassion, and thereby help the mind defend itself against psychological foes. Both of these functions have a positive effect on our health.
This is the significance both physical and spiritual - of bhramari paranayama.