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shoulders back and the head up, together with a straightened position of the spine are all essential to deep, full diaphragmatic breathing. The vital capacity is a measure of the greatest volume of air one can take into the lungs in a deep breath. Pulmonary function tests can also measure the timed vital capacity, which shows the degree of elasticity of the lungs, which is impaired early in the development of emphysema. Other breathing capacity measurements can be made and serve as predictors of the development of diseases such as asthma, emphysema, or other chronic conditions. The examination of the chest and lungs, as well as brief comments on diagnostic x-rays are described in chapter one. Lung development just before birth coincides with the production of a detergent-like substance called surfactant. This is deficient in a premature baby and is one of the reasons why hyaline membrane disease may develop. Another enzyme that is usually present in the bronchial tubes is called alpha1antitrypsin. Congenitally deficient in some people, this can lead to the development of early emphysema, particularly in smokers or people exposed occupationally to inhaled particles, such as asbestos or coal dust. A simply performed blood test can determine the existence of this hereditary enzyme deficiency. We turn now to consider some of the common diseases of the respiratory tract. Emphysema Pulmonary emphysema takes the lives of increasing numbers of people each year. Called chronic obstructive pulmonary disease, this condition develops insidiously in people exposed to heavy pollution of the airways. The commonest cause of emphysema today is tobacco smoking. Unfortunately, most individuals do not know that their disease has developed until it is too late to cure the condition. The basic process involved in the development of emphysema first involves the destruction of elastic tissue in the bronchial tubes. Respiration becomes increasingly difficult. Then in later stages many tiny air sacs, called alveoli, lose their walls and coalesce, forming large air sacs or emphysematous blebs. The earliest symptom in developing emphysema is shortness of breath. This is commonly associated with exertion. This exhibits disease risk with decreased ability to carry packages, climb stairs, walk rapidly, or engage in the usual sports. Advanced sufferers of emphysema may develop cyanosis, a bluish tinge around the mouth with a dusky appearance of the nail beds. This sign indicates advanced impairment of oxygen intake with a chronic deficiency in the blood. There is abnormal shunting of blood across the lungs, with resultant deficient oxygenation.