167O HANDBOOK OF PHYSIOLOGY ^ CIRCULATION II 



fig. 3. Richard Lower (163 1-1691). In his book, Tractatus 

 De Corde, he described his experiments with Hooke's respiration 

 pump. These experiments proved that venous blcod becomes 

 arterialized in traversing the lungs and that bleed absorbs a 

 vital chemical substance from the air (172). 



was involved in the transport of oxygen from the lungs 

 to the tissues (90a, 144). 



Analysis of Pulmonary Hemodynamics 



Although certain aspects of the regulation of the 

 pulmonary circulation — such as the influence of the 

 respiration — were under experimental scrutiny by the 

 middle of the eighteenth century (180), the system- 

 atic study of pulmonary hemodynamics could not 

 begin without practical methods for measuring pul- 

 monary vascular blood pressures and flow (189, 433). 

 These became available about a century later: pul- 

 monary arterial pressures were first measured in the 

 laboratory of Carl Ludwig (fig. 4) in the i85o's, by 

 using the recording mercury manometer in open-chest 

 dogs (27); shortly thereafter, more elaborate measure- 

 ments were made in the intact horse (90a, 91). In 

 1870, A. Fick (fig. 4) pointed out how measurements 

 of respiratory gas exchange could be used to calculate 

 the volume rate of pulmonary blood flow (130). But, 

 without ready access to mixed venous blood, the 

 direct Fick principle offered little promise of becoming 

 a popular method for measuring the pulmonary blood 

 flow in either the intact animal or man. 



fig. 4. Pioneers in hemodynamic measurements. Left: Carl Ludwig (1816-18951 introduced 

 graphic recording of blood pressure in 1847. Right: Adolph Fick (1829-1901), student of Ludwig, 

 in 1870 described the use of respiratory gas exchange for the measurement of cardiac output in intact 

 animal or man. [After Rothschuh (361).] 



