95. MECHANICS OF BREATfflNG 



Although a large literature has accumulated on the mechanics of breathing, comparison of results often is difficult 

 because of differences in experimental technique. Measurements of lung compliance may yield different results 

 when the elastic pressure changes are measured during spontaneous or rapid breathing, as against those measured 

 under true static conditions when air flow is stopped for a second or more. An additional complication in measure- 

 ments of compliance arises because the pressures observed during slow volume changes depend on the previous 

 degree of expansion of the lungs. (Part I illustrates slow pressure-volume changes in the cat; similar lung behavior 

 has been observed for other mammals, including man.) Thus lung compliance determinations depend on whether 

 measurements are made (1) from the normal resting volume. (2) after a deep inspiration, or (3) with the functional 

 residual capacity decreased, either voluntarily or involuntarily, from effects of posture or anesthetics. Most of the 

 measurements given in the tables below have been made from the resting lung volume, usually in sitting individuals. 

 The reservations cited above apply also to measurements of lung resistance; furthermore, the measured resistance 

 may depend on the lung volume, as well as on the frequency of breathing. 



Contributor: Radford, E. P., Jr. 



Parti; SLOW PRESSURE- VOLUME CURVES: CAT 



Cat, weighing 3.7 kilograms, lungs exposed, lay in tank respirator; lung volume changes were produced by slowly 

 decreasing tank pressure. Three different inflation curves were obtained after the lungs had been allowed to deflate 

 to various pressures. Each inflation or deflation curve required 20-30 seconds. 



350 



E 



a 



•3 



> 



20 



25 



5 10 15 



Pressure, cm H2O 

 /I / Lungs allowed to collapse completely and immediately reinflated slowly. /2/ Lungs deflated to a pressure 

 of 0.6 cm H^O after a maximum inflation, then reinflated. /3/ Lungs deflated to 2 cm H^O and immediately 

 reinflated. /4/ Deflation (following procedures used in obtaining Curve 1), shown for comparison. 



Contributor: Radford, E. P., Jr. 



Reference : Radford, E. P., Jr., "Tissue Elasticity," p 186, Baltimore: American Physiological Society, 1957. 



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