Then the person expires through a rapidly recording nitrogen meter, which makes the record shown in the figure. Some oxygen also mixes with the alveolar air but does not completely replace this air.
Rate of Alveolar Ventilation fills the entire dead space with pure oxygen. These problems are discussed further in Chapter 39 in relation to pulmonary gaseous exchange and in Chapter 42 in relation to certain pulmonary diseases. In a normal person, the anatomic and physiologic dead spaces are nearly equal because all alveoli are functional in the normal lung, but in a person with partially functional or nonfunctional alveoli in some parts of the lungs, the physiologic dead space may be as much as 10 times the volume of the anatomic dead space, or 1 to 2 liters. When the alveolar dead space is included in the total measurement of dead space, this is called the physiologic dead space, in contradistinction to the anatomic dead space. On occasion, some of the alveoli themselves are nonfunctional or only partially functional because of absent or poor blood flow through the adjacent pulmonary capillaries.Therefore, from a functional point of view, these alveoli must also be considered dead space. The method just described for measuring the dead space measures the volume of all the space of the respiratory system other than the alveoli and their other closely related gas exchange areas this space is called the anatomic dead space. This record can be used to calculate dead space, as discussed in the text.Īnatomic Versus Physiologic Dead Space. Record of the changes in nitrogen concentration in the expired air after a single previous inspiration of pure oxygen. In making this measurement, the subject suddenly takes a deep breath of oxygen.This Air expired (ml) A simple method for measuring dead space volume is demonstrated by the graph in Figure 37-7. Therefore, the dead space is very disadvantageous for removing the expiratory gases from the lungs. On expiration, the air in the dead space is expired first, before any of the air from the alveoli reaches the atmosphere. This air is called dead space air because it is not useful for gas exchange. Some of the air a person breathes never reaches the gas exchange areas but simply fills respiratory passages where gas exchange does not occur, such as the nose, pharynx, and trachea.
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