Nitric oxide (NO) is a signaling molecule. NO is made by many types of cells throughout the body. Nitric oxide is naturally released in the respiratory tract. Its produced in the paranasal sinuses and airways. NO aids in proper ventilation. Proper ventilation is essential for maintaining the integrity of the sinuses. NO helps alleviate chronic inflammation or infection of the nose and sinuses. NO also improves pulmonary function in healthy individuals. It improves oxygen delivery into the lungs by causing bronchodilation, relaxing the smooth muscles in the trachea and widening of the bronchi and bronchioles in the lungs.
Nitric oxide regulates cardiovascular function. NO relaxes the smooth muscle cells around the arteries, widening them which results in a decrease in blood pressure and increased blood flow to the organs.
NO is known to be broadly antifungal, antiviral and antibacterial. When NO is produced in white blood cells (such as macrophages), the gas reacts chemically with molecules in invading bacteria, parasites, and viruses, altering their function, destroying or inhibiting their replication and spread.
Humming increases levels of nitric oxide 15-fold. In addition, humming slows the breath down to a frequency of 6 breaths or less per minute evoking the relaxation response. Humming slows the heart rate as well. As you exhale you expel the air in your lungs. the diaphragm moves up, the lungs get smaller. the heart has less space and shrinks. A signal is sent from the sinoatrial node in the heart to the brain which sends a message back to the heart through the vagus nerve signaling the heart to slow down.
Metabolism slows, the breath slows, heart rate slows. The mind settles.
Monks have been chanting for thousands of years. This is the science behind the practice.