1302 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



fiu. 14. Cybulski's modification of the Pitot meter. [From 

 Muller (95).] 



pressure elevation which acts upon the adjacent limb of 

 the differential water manometer. 



Broemser's differential sphygmograph (14) was 

 built for application on unopened arteries. The instru- 

 ment (fig. 15) consists of a double sphygmograph 

 capsule, the two lower openings of which are covered 

 with thin rubber diaphragms. The planes of the dia- 

 phragms form an obtuse angle to each other. The air- 

 filled capsules are connected to an optical differential 

 manometer as well as to a simple optical manometer. 

 When the lower end of the instrument is pressed 

 against an artery so that one diaphragm is directed 

 upstream, the other downstream, a wedge-shaped 

 inflection of the vessel wall is produced, and the blood 

 pressure bulges the diaphragms into the capsules. Due 

 to the pressure difference effected by the blood flow, 

 the upstream diaphragm will bulge more than the 

 downstream one; thus a flow-related deflection of the 

 differential manometer takes place, while the deflec- 

 tion of the simple manometer is proportional to the 

 blood pressure. The function of this device may be 

 derived partly from the Venturi and partly from the 

 Pitot principle in that the wall inflection is typical of 

 the Venturi meters while the inclination of the dia- 

 phragms to the vessel axis results in a Pitot effect. The 

 calibration curve determined by perfusion of excised 

 arteries or of elastic tubes is almost quadratic. Al- 

 though the records obtained with this device from the 

 ascending and abdominal aorta of rabbit, cat, and 



dog show the typical contours known from other 

 flowmeter registrations, the instrument did not find 

 frequent application. This may be due to the fact that 

 its exact positioning and its calibration in situ are 

 difficult. 



Besides historical notes, Muller (95) published a 

 theoretically and experimentally based criticism of 

 Pitot meters. He stated that the arguments raised by 

 previous investigators against these meters are, on the 

 whole, not justified. Pieper & Yogel (101) calculated, 

 for the device shown in figure 1 1 , the distortions due 

 to term III of equation 8 at various distances L. Al- 

 though, on the one hand, L should be kept as small as 

 possible so as to minimize C' 3 , the flow sensitivity of 

 the device (term II) is, on the other hand, also dimin- 

 ished when opening 2 is placed too near to 1 . The 

 optimal L must therefore be found by compromise. 

 Hardung (57) came to the conclusion that, for instru- 

 ments such as shown in figure 10, term III can theo- 

 retically be eliminated by placing the upstream-facing 

 opening at a certain optimal distance from the long 

 axis of the lateral tube. 



A new and interesting catheter-tip method for re- 

 cording the blood velocity in great central arteries was 

 developed by Fry et al. (46-48). The tip of the double- 

 lumen catheter used has two openings, both facing in 

 lateral direction and placed several centimeters apart. 

 Here the difference of the pressures acting on the 

 openings ("axial pressure gradient") is due neither to 

 a Venturi nor to a Pitot effect so that only the terms 

 I and III of equation 8 are involved. While, in the 

 aforementioned instruments, term III is a very un- 

 desired source of distortions, this very term plays the 

 main role in Fry's method. For this reason, the co- 

 efficient Ci is purposely made very large by choosing a 

 great distance between the openings. It is obvious 

 that the time course of the pressure difference itself, 

 which is picked up by an electrical differential manom- 



fic. 15. Differential sphygmograph 

 of Broemser for application to unopened 

 arteries. Thin lines at the lower ends = 

 rubber diaphragms. Upper ends con- 

 nected to differential and adding 

 manometers. [From Broemser (14)] 



