• Choose a category
• All
• Classic-Fiction

By Root 626 0

thus increasing their volume as air is drawn in automatically from the outside (Figure 2). The air that we inhale is composed of about 20 percent oxygen and .03 percent carbon dioxide; the rest is nitrogen. During exhalation, the rib muscles relax, the sternum moves downward, the diaphragm relaxes upward (regaining its full dome-like curvature), and the old air is expelled upward through the trachea as the lungs recede from the walls of the chest and shrink back to their original size (Figure 3). The exhaled air consists of 16 percent oxygen and 4 percent carbon dioxide. It is saturated with water vapor produced by metabolic activity.

The Movement of Air through the Respiratory System

As air enters our nose, particles of dust and dirt are filtered out by the hairs that line our nostrils. As the air continues on through the nasal passages it is warmed and humidified by the mucous membranes of the septum, which divides the nose into two cavities. If too many particles accumulate on the membranes of the nose, we automatically secrete mucus to trap them or sneeze to expel them. In general, air does not move through the nasal passages equally at the same time. Usually when the left nostril is more open, the right one is more congested and vice versa. This occurs because the flow of blood shifts back and forth between the nostrils in a rhythm that takes approximately one and a half to two hours.6

Figure 2

Figure 3

After passing through the nose, the air then flows down past our pharynx, the cavity at the back of our mouth where the nose and mouth are connected, and where swallowing and breathing are coordinated by the pharyngeal plexus (under the control of the lower brain stem). Here the air passes through the lymphoid tissue of the adenoids and tonsils at the back of the nose and throat, where bacteria and viruses are removed. The air then moves past the larynx, which helps the vocal cords use air to produce sound, and then continues downward into the tube of muscle called the trachea, which separates into two bronchi serving the lungs (Figure 4). The trachea and bronchi are lined with mucus-secreting cells that trap pollutants and bacteria. As the air flows through the bronchi, tiny hairlike lashes called cilia massage the mucus and any remaining debris away from the lungs and upward toward the trachea, over the larynx, and finally into the esophagus. When too many particles, chemicals, or clumps of mucus accumulate in the bronchi, they trigger a coughing spasm—a powerful muscle contraction and bronchial constriction which can generate a wind force stronger than a tornado—to expel this toxic material.

In the lungs, the bronchi divide into smaller and smaller branches called bronchioles. The bronchioles, which have muscular walls that can constrict air flow through contraction, end in some 400 million bubble-like sacs called alveoli. It is in the alveoli that the life-giving exchange between oxygen and carbon dioxide occurs—where fresh oxygen enters the circulatory system to be carried throughout the body by hemoglobin molecules in the blood, and where gaseous waste products such as carbon dioxide are returned by the blood for elimination through exhalation.

THE PHASES OF BREATHING

Depending on the demands of what we are doing at the moment (lying down, sitting, walking, running) and on our specific psychological state (peaceful, angry, stressed out, happy), our breath can range from fast to slow and from shallow to deep, emphasizing one or more of the three fundamental phases of the breathing process: diaphragmatic, thoracic, and clavicular. In deep breathing, for example—what is often referred to as “the yogic complete breath,” all three phases come into play. According to Alan Hymes, M.D., a cardiovascular and thoracic surgeon who is a pioneer in the field of breath research, this form of breathing “is initiated by diaphragmatic contraction, resulting in a slight expansion of the lower ribs and protrusion of the upper abdomen, thus oxygenating the lower lung fields. Then the middle portions of the