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HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



fig. 29. Blood flow and pressure gradient in aortic valve 

 regurgitation without stenosis in a 19-year-old girl. In ascending 

 aorta flow, the zero reference is estimated. The regurgitant 

 blood flow, the envelope of the diastolic murmur, and the pres- 

 sure gradient between ascending aorta and left ventricle follow 

 the contour rule. The blood flow pattern during systole is not 

 greatly altered from that of the normal, in spite of increased 

 stroke volume (see also atrial septal defect, fig. 26). 



to valve closure is not, per se, dependent upon 

 absence of aortic stenosis, but rather upon the degree 

 of flexibility of the valve. If the valve is stiff and 

 immobile, this wave will disappear. If the valve, as 

 in congenital stenosis, is flexible, this wave will 

 persist and also one may differentiate subaortic 

 stenosis or outflow stenosis from valvular stenosis by 

 the presence of a stenosis pattern during systole which 

 retains the normal amplitude of the valve closure 

 wave. 



The severe pressure gradient across the stenotic 

 valve, as shown by the difference in the aortic pressure 

 and ventricular pressure when recorded directly, is 



quite similar in contour to the flow-pulse contour 

 (fig. 28). The murmur, which is harsh, loud and 

 blowing, and is located in the ascending aorta and 

 arch, has an envelope with a contour closely paral- 

 leling that of both the peak of the flow curve and 

 differential pressure curve. Experimental aortic 

 stenosis produced by means of a wire tightened about 

 the ascending aorta at the sinus of Valsalva is shown 

 in figure 5. The effect of varying degrees of stenosis 

 is demonstrated on the flow curve, the aortic arch 

 pressure, and the differential pressure between 

 ventricle and ascending aorta. Also of note here is 

 the heart's ability to maintain a stroke volume in the 

 face of this severe increase in load impedance. Under 

 the conditions of this experiment, in which several 

 heartbeats were allowed for cardiac compensatory 

 mechanisms to act, the left ventricle functions as a 

 constant flow source. Further compensatory mech- 

 anisms brought into play over long periods of time, 

 particularly allowing hypertrophy of the left ventric- 

 ular wall, further enhance the heart's ability to 

 maintain a constant stroke with a severe increase in 

 load impedance. 



Aortic regurgitation causes changes both in the 

 systolic and diastolic contour of the left ventricular 

 ejection pulse (fig. 29). The systolic stroke volume 

 exceeds the normal volume by the amount necessary 

 to compensate for regurgitation during diastole. As a 

 result the flow pulse tends to be somewhat more 

 rounded, but otherwise maintains the general shape 

 of the normal pulse. However, because of the greater 

 stroke volume, there is necessarily a greater accelera- 

 tion and deceleration at the onset and termination of 

 ejection. The valve closure notch disappears, and in 

 its place one sees a sustained backflow deflection. 

 The backflow, diminishing throughout diastole, is a 

 function of the diastolic pressure gradient across the 

 valve, and the size of the regurgitant orifice. The 

 murmur, which has a wide frequency band extending 

 above 100 cps, sounds high pitched and blowing, 

 begins with reversal of the pressure gradient across 

 the valve, usually builds up early in diastole to a 

 maximum, and then follows a decrescendo pro- 

 portional to the backflow. As seen from figure 29, 

 the envelope of the diastolic murmur is similar to the 

 pattern of the diastolic backflow. 



Descending Thoracic Aorta 



Figure 30 illustrates flow in the descending thoracic 

 aorta immediately distal to a ductus arteriosus, before 

 and after the closure of the ductus. The descending 



