MEASUREMENT OF THE CARDIAC OUTPUT 



561 



240 



FIG. 6. Left: relation be- 

 tween capacity of the 

 several parts of the arterial 

 bed per m^ and arterial 

 pressure. Right: sketches 

 to illustrate the calculation 

 of arterial uptake and 

 arteriolar outflow. [From 

 Hamilton (58).] 



transmission time. The uptake of each segment can 

 be read as the difference in volume between that at 

 diastolic pressure and at the pressures as above. Thus 

 we will know the increase in volume of each segment 

 as wrought by the pressure pulse at the instant of 

 semilunar closure. The sum of these will be the arterial 

 uptake. Substituting U, Tc, Ts, and Tw in the above 

 formula, the flow per second per square meter can be 

 closely approximated. 



The simplified pulse contour calculation of the 

 stroke index has been carried out many times and 

 compared with the dye injection method and with the 

 direct Fick procedure. The first set of observations 

 were very encouraging, inasmuch as the correlation 

 between the two methods was R = 0.99. As will be 

 seen in figure 7 there are a few points in which the 

 agreement between the pulse contour method and the 

 standard method is not very good. On getting more 

 comparisons as the method was applied to various 

 physiological problems there appeared a rather larger 

 number of aberrant points (fig. 8). These always 

 showed a large contour stroke index as compared with 

 that calculated from the Fick or dye method, as 

 though the arteries of these dogs had become less 

 distensible than those of normal or dead dogs. This 

 change in distensibility was not signaled by a change 



TABLE 3. Pulse Wave Transmission Times to the 

 Parts of the Arterial Tree at Various Diastolic 

 Pressures for Dog of i§ kg 



in pulse wa\e velocity, a fact which implies that the 

 arteries must have become smaller. The aberrant 

 determinations were all made on dogs that were in 

 bad condition but not all the dogs in this condition 

 showed the discrepancy. It was first discovered in 

 dogs with a rotameter or pump in the great veins 

 (29), and again in dogs suffering from electrolyte 



