1 686 HANDBOOK OF PHYSIOLOGY v-~ CIRCULATION II 



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fig. 17. Simultaneous aortic (AO) and pulmonary arterial (PA) pressure pulses recorded from a 

 human subject with a normal circulation during open thoracotomy. The arrows indicate the be- 

 ginning of ejection and the end of protodiastole in the aorta and pulmonary artery. (Paper speed, 

 25 mm/sec on left; 75 mm/sec on right. Interval between time lines, 0.04 sec.) [After Braunwald 

 etal. (47).] 



values, any of these reference levels will suffice for 

 consecutive measurements in a single experiment. 



Pulmonary Arterial Pressure 



With minor differences, the contour of the pul- 

 monary arterial pulse mirrors that at the root of the 

 aorta: as may be seen in figure 17 (47), the pul- 

 monary arterial pressure pulse is small in amplitude 

 as compared to the aortic pulse and characteristically 

 displays a rapid rise to a rounded peak during systole, 

 a brisk small incisura and a gradual decrease in 

 pressure during diastole (182, 225). The "classical" 

 pulmonary arterial curves are more apt to be recorded 

 in pulmonary hypertensive states than in pulmonary 

 normotensive states; at the lower levels of pulmonary 

 arterial pressure, distorting artifacts are exceedingly 

 common. Not shown are the corresponding records 

 of the velocity of the blood flow: in contrast to the 

 pressure-velocity relationships in the aorta, the 

 pulmonary arterial pressure-velocity curves are 

 quite similar: the velocity of blood flow in the pul- 

 monary artery lags slightly behind the pulmonary 

 arterial pressure (156). 



Ordinarily, the pulmonary arterial mean pressure 

 in man (87), dog (303), cat (132), and the rabbit 

 (239) averages one-fifth to one-sixth that in the 

 systemic circulation. In man, the level of the pul- 

 monary arterial pressure seems to increase slightly 

 with age (101). There is no fixed relationship between 

 the pressures in the two circuits. In man, before the 

 onset of systole, the pulmonary arterial pressure is 

 of the order of 7 to 12 mm Hg; during systole it 

 rises abruptly to 20 to 30 mm Hg; the corresponding 



mean pressure is of the order of 12 to 15 mm Hg 

 (87, 103). In the dog, pulmonary arterial pressures 

 tend to be somewhat higher, so that a mean pressure 

 of 20 mm Hg is not unusual (187). 



Pulmonary Venous and Left Atrial Pressures 



Blood pressures have been recorded directly from 

 the left atrium and pulmonary veins in dog (187) 

 and man (45, 92, 299). The pulmonary venous 

 pressure pulse is a record of left atrial events, indi- 

 cating that the pulmonary arterial pressure pulse has 

 been damped out by the small pulmonary vessels. 

 As in the systemic veins and right atrium, the a, c, and 

 v waves are clearly defined (187); but, in contrast 

 to the right heart, the summit of the v wave is usually 

 the highest part of the pressure pulse, and pressure 

 variations during the cardiac cycle are greater in the 

 left atrium and pulmonary veins. Thus, in both the 

 unanesthetized and anesthetized dog, pulmonary 

 venous pressures during a single cardiac cycle range 

 between 3 and 12 mm Hg (187). In intact, unanes- 

 thetized man the mean left atrial pressure is of the 

 order of 4 to 5 mm Hg (47). Although physiologic 

 observations (121) arc accumulating to support 

 the anatomic impression (56, 392) that the pulmonary 

 venous-left atrial junctions can act as sphincters, 

 final proof, in the form of suitably recorded pulmo- 

 nary venous-left atrial pressure gradients or differences 

 between the contours of the pulmonary venous and 

 left atrial pressure pulses have as yet not been pub- 

 lished. 



Until recently, measurements of left atrial and 

 pulmonary venous pressures in intact animals were 



