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Lecture 12

PHGY 210- Lecture 12- Dr. Lauzon.docx

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Department
Physiology
Course
PHGY 210
Professor
Ann Wechsler
Semester
Winter

Description
Lecture Twelve- Friday, January 29 , 2010h B. Static Properties: Elastic propeties of the lungs and chest wall -characterize the propertiesof the lungs: swallow catheter tube, take pressure To evaluate the elastic properties of the respiratory system (chest wall and lungs), we measure changes in the recoil pressure of each separate structure (Figure 36) for a given change in lung volume. Lung volumes can be measured by means of the spirometry (see section 1-I). For the respiratory system, pressures are measured using manometers or pressure transducers, as referenced to atmospheric pressure. "Negative pressure" indicates a pressure below atmospheric, and "positive pressure" indicates a pressure above atmospheric pressure. The recoil pressure of a structure is defined as the pressure difference between the inside and outside of the structure (transmural pressure). The recoil pressure of the chest wall, trans-chest-wall pressure (Pw) is the difference between Ppl and the pressure at the body surface. Ppl can be measured using a flexible balloon introduced into the esophagus. Because the esophagus is located between the two pleural spaces, esophageal pressure provides a close approximation of pleural pressure. The body surface is under atmospheric pressure (bs). Thus, Pw = Ppl – Pbs The recoil pressure of the lungs, transpulmonary pressure (Pl) is measured from the difference between Palv and Ppl. When there is no air flow, closed nose and mouth, Palv and the pressure measured at the mouth are the same. Thus, Pl = Palv - Ppl The recoil pressure of the total respiratory system, the trans-respiratory system pressure (Prs), is measured as the difference between Palv and Pbs: Prs = Palv – Pbs (where Palv=Pl+Ppl and Pbs=Ppl-Pw; by rearranging the 2 equations above) Hence, Prs is the sum of the pressures generated by its two components, lung and chest: Prs = Pl + Pw see picture in slides C. Compliance  second equation you must know for the course (the first being resistance) Compliance of the lungs: The compliance of the lungs, or chest wall, or total respiratory system, is a parameter that refers to the ease with which each of these structures can be distended. The standard procedure for measuring the respiratory system compliance in humans is to determine the static pressure-volume relationship while lung volume is decreased step by step from TLC (figure 37). Compliance is expressed as the volume change in the lungs for a unitary change in pressure, i.e. the slope of the pressure-volume curve in figure 37. The pressure required to maintain a given volume of gas inside the lungs increases as the volume increases, i.e. the slope decreases with increases in lung volume in figure 37. Compliance of the lungs is also altered in diseases such emphysema and fibrosis (figure 37). The pressure difference between the alveoli (Palv) and the pleural space (Ppl) equals the pressure drop across the lung tissues. This is the pressure required to maintain the lungs at a given inflation volume against their tendency to recoil elastically. Thus, Cl = V / (P
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