Your nose knows, you know

This is an extract from this wonderful book:

We don't usually appreciate the nose until it becomes blocked... This unsung heroine of our anatomy does more for us than sniff out pleasant and unpleasant aromas, the nose prepares the air before it enters the delicate lung tissue so that it is just the right temperature and humidity. Air drawn into the nose is separated into right and left caverns, and is swirled through nasal hair and along passage ways lined with a light blanket of mucous that serves to catch any dust, bacteria or other tiny particles... The air then enters a three-storied chamber. The brain, eyes and optic nerves are just above the top chamber, the nasal cavity occupies the middle chamber and the bottom chamber is just above the roof of the mouth. These chambers are called turbinates and the aerodymamics of their curved walls causes the air to swirl around and around, passing over a much greater surface area than it would otherwise. While the air is doing the Viennese Waltz in your turbinates it is picking up moisture so that it will be just the right humidity before entering the lungs. Up to two quarts of water are supplied by the turbinates each day. By the time the air has passed through these chambers it has also reached body temperature.

We also know that air alternately enters the nose through the left and right nostrils during the course of the day. Blood shifts from one nostril to the other every 90 minutes or so, causing one nostril to become more congested. Scientific studies show that when the left nostril is open the right hemisphere of the brain is more dominant, activating the more creative feeling side of the mind. When the right nostril is open the left hemisphere of the brain in dominant, facilitating more analytical, rational and intellectual mind activity. Yogis observed this phenomenon thousands of years ago and developed a sophisticated practice called "alternative nostril breathing" or nadi shodhanam, in which they deliberately changed the flow of air through the nostrils to balance their psychophysiology. They believed that when the right nostril was open the surya, or sun/heating element, was dominant, and that when the left nostril was open chandra, or moon/cooling element, was dominant. By opening and closing the nostrils in varying patterns one could adjust the physiology of the body just like regulating a hot and cold faucet to produce warm water. Although present research on the subject is controversial, many believe that the right nostril dominance stimulates the arousal-producing sympathetic nervous system and left nostril dominances elicits the relaxation-producing parasympathetic system. By alternating the flow of air in a regulated way yogis could have been trying to create an equilibrium in the two sides of the autonomic nervous system and a balance between excitation and relaxation.