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HANDBOOK OF PHYSIOLOGY 



CIRCULATION I 



TABLE I . Factors for tfie Prediction of Stroke Volume, 

 per m^ Body Surface, from the Pulse Pressure 



this pressure level a given stroke volume produces a 

 gradually increasing pulse pressure. 



Study of the plot shows that there is a group of de- 

 terminations scattered rather uniformly about the 

 line of identity and a group which includes about half 

 of the cases of congestive failure (C) who display a 

 much larger pulse pressure than would be predicted 

 from their Fick stroke volume. It is a matter of clinical 

 observation that pulse pre.ssure readings are more 

 nearly normal than are stroke volume measurements 

 in congestive failure, but we have no clue as to what 

 makes the arterial tree in these cases less distensible 

 than in other diseases or than the normal. 



The agreement between the stroke volume as 

 measured by the Fick and dye dilution methods (see 

 below) and as derived from the pulse pressure is far 

 from perfect. However, it compares well with those 

 derived from ballistocardiography and other methods 

 (see below) which can be applied to the intact man 

 and which measure the beat-to-beat variations in the 

 stroke volume. Furthermore, since it includes 

 measurements taken on patients with various dis- 

 eases, during exercise and anxiety, it is reasonable to 

 assume that changes in arterial distensibility, as 

 caused by these factors, are not great enough to hide 

 a significant relation between stroke volume and pulse 

 pressure. 



Nevertheless, improvement in calculation of stroke 

 volume from pulse pressure may well be sought by 

 correcting the average empirical ratio by a constant 

 derived by a Fick or dye measurement on the par- 

 ticular individual. Thus if the crude pulse pressure 

 relation as given above overestimates the stroke 

 volume by 10 per cent in a certain individual at rest, 

 a 10 per cent lowering of the pulse pressure figure 

 during exercise or during the effect of tilting, or of a 

 drug, can be expected to come closer to the true 

 experimental figure than the uncorrected estimate. 



10 20 30 40 50 60 70 80 



FIG. 5. Relation between stroke inde.x as calculated from 

 the Fick procedure and that derived from a simultaneous pulse 

 pressure measurement. C = patients with congestive circula- 

 tory failure. [From Remington et al. (112).] 



A procedure using this principle has been worked 

 out by Warner et al. (136), who assumed that the 

 arterial uptake was proportional to the systolic area 

 (pressure X time) above end diastolic pressure, times 

 a constant derived from a known stroke volume in the 

 same individual imder resting (steady state) condi- 

 tions. Introduction of experimental conditions pro- 

 duces a change in the pressure pulse, the systolic area 

 of which multiplied by the same constant gives the 

 uptake under the new conditions. The uptake plus 

 the systolic drainage gives the stroke \olumc, and the 

 systolic drainage is the uptake times the fraction S.A. ' 

 D.A. where S.A. and DA. are the systolic and 

 diastolic areas of the pulse curve above an arbitrary 

 ■20 mm Hg and corrected for transmission to the pe- 

 riphery. 



PULSE CONTOUR METHOD 



The best application of tlie pulse pre.ssure method of 

 calculating the cardiac output is not to man, who.se 

 variable age and susceptibility to arterial disease 

 must necessarily cause changes in arterial distensi- 

 bility. These may account for much of the scatter seen 

 in figure 5. The laboratory dog, on the other hand, is 

 a young animal as a result of hazards which surround 

 him, and only rarely is he afflicted with arterial dis- 

 ease. The arteries from many dogs have been cut inio 



