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HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



left atrial pressure. Authors, arguing that this is an 

 unphysiological measurement, have usually founded 

 their conclusions on dog experiments, where it may 

 be difficult to get a true wedge tracing, or on unsuc- 

 cessful clinical studies. Careful studies have, on the 

 other hand, definitely shown that the true pulmonary 

 arterial wedge pressure tracing has all the characteris- 

 tics of the left atrial tracing, only slightly delayed, 

 with a mean pressure that closely follows the left 

 atrial mean pressure. It has also been demonstrated, 

 by occluding the pulmonary artery with a balloon, 

 that the pressure waves registered from the wedge 

 position are not merely a distorted pulmonary arterial 

 pulse. In this connection it is of interest that Mac- 

 Callum & McClure (144), in 1906, demonstrated that 

 the increased \' wave of mitral incompetence could 

 traverse the pulmonary vascular bed in the retro- 

 grade direction. There is a possibility that in some 

 cases the tracing obtained through a wedged pulmo- 

 nary arterial catheter is more representative of the 

 over-all events in the left atrium during the cardiac 

 cycle than the tracing obtained through a needle or 

 thin catheter placed within the atrium and subject to 

 direct influences giving rise to errors (i.e., jet effect of 

 mitral regurgitation). It should be stressed, however, 

 that it may be impossible to obtain a true wedge 

 pressure tracing in a certain number of cases (from 

 10 to 30%). It is furthermore impossible to obtain 

 more information from the wedge pressure tracing 

 than from the left atrial record, and its use for diag- 

 nostic purposes is thus limited. 



LEFT ATRIAL PRESSURE IN MITRAL VALVE DISEASE. In 



mitral valvular disease the normal train of events in 

 the left atrial pulse is changed more or less markedly 

 due to the extent of the valvular alteration, the time 

 the valvular disease has lasted, and the presence or 

 absence of other factors of importance for the atrial 

 or ventricular performance [the prevailing heart 

 rhythm and rate, the state of the myocardium, hyper- 

 volemia, etc. (80, 98)]. 



Mitral stenosis. In early mitral stenosis the atrial 

 contraction produces a giant a wave, with a slight 

 elevation of the left atrial mean pressure, otherwise 

 the curve is normal. In cases more advanced, but 

 still in sinus rhythm, the a-c complexes and v waves 

 are of similar amplitude, the mean pressure is ele- 

 vated, the pulse pressure is narrow, the y descent is 

 slow, and diastasis is absent. In some of these cases the 

 main feature is the prominent c wa\e. When atrial 

 fibrillation supervenes, the picture is complicated and 

 more difhcult to analvze. Besides the absence of the a 



wave the striking changes from normal are the promi- 

 nent positive c wave and the absent negative x wave. 

 In the absence of atrial contraction, and thus relaxa- 

 tion of this chamber, no x wave can be seen. Immedi- 

 ately following the c wave there is a gradual rise in 

 pressure forming a definite v wave. This type of tracing 

 is apparently characteristic of either right or left 

 atrial curves in the presence of atrial fibrillation and 

 may not have anything to do with vahular stenosis 

 per se (5, 165). 



Mitral insiifficierny. The findings described by W'ig- 

 gers & Fell (204) during the acute phase of the pro- 

 duction of marked mitral regurgitation are not always 

 found in long-standing mitral insufficiency, probably 

 due to secondary changes that have occurred, modify- 

 ing the pressure-pulse response. After the establish- 

 ment of mitral incompetence they found that the 

 left atrial pressure was elevated only slightly during 

 the isometric phase and that it fell quite normally 

 during the latter portion of this phase. During systolic 

 ejection the atrial pressure rose rapidly, producing a 

 greatly elevated plateau. This increase in atrial 

 pressure did not end with the onset of diastole, but 

 continued for about 0.08 sec into diastole, i.e., 

 throughout the protodiastolic and isometric relaxa- 

 tion phases. 



In clinical mitral insufficiency in man the left 

 atrial pressure pulse may undergo all degrees of 

 changes, from virtually none to a tracing similar to 

 the one recorded from the left ventricle. In the former 

 case with slight regurgitation the most conspicuous 

 finding is increase in amplitude of the i' waves, that 

 rises far abov'e the a-c complexes. The y descent is 

 rapid and brief, and diastasis is evident. In the latter 

 case there is an early rise in left atrial pressure simul- 

 taneous to the ventricular systole, absence of a spiked 

 c wave, and no pressure rise that appears to be similar 

 to a V wave (fig. 3). 



The changes in contour of left atrial pressure pulse 

 curve also incorporate disappearance of the down 

 slope following the c wave with a steep rise to the v 

 peak. This rise begins at the c wave and is therefore 

 initiated early in systole. The descending limb of the 

 V wave (the v descent) drops sharply early in 

 diastole (in the absence of concomitant stenosis). 

 During the latter part of diastole, to the a wave in 

 normal sinus rhythm or to the end-diastole in atrial 

 fibrillation, there is sometimes a slight gradual 

 increase in pressure. The degree of incompetence of 

 the mitral valve is the factor of greatest importance 

 for the difference between the ventricular type and 

 the enlarged v wave type of atrial curve. The mean 



