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J Thorac Cardiovasc Surg 1995;109:810-811
© 1995 Mosby, Inc.

LETTERS TO THE EDITOR

Biophysics of pulsatile perfusion

Division of Cardiothoracic Surgery
The University of Texas
Health Science Center at San Antonio
San Antonio, TX 78284-7841

Reply To the Editor

The comments of Dr. Chiu regarding the greater kinetic energy and, hence, the total energy of pulsatile flow compared with that of steady flow are of course valid. The concept derives from the law of conservation of energy: the greater the magnitude of energy delivered into a system, the greater the magnitude of energy released by the system, in one form or another.

Grossi and colleagues ¹ quantitated the quality, the degree, of pulsatility necessary to significantly reduce hypoxic metabolic acidosis in dogs during cardiopulmonary bypass in 1985. These investigators originated a pulsatility scale that they termed the "Pulse Power Index." Their work is a must for investigators who would study pulsatile versus steady flow.

Other important in vivo data have been published by Trinkle and colleagues, ² who showed that vigorous pulsatile flow in human subjects reduced hypoxic metabolic acidosis compared with steady flow, and by Jacobs and associates, ³ who showed in dogs totally supported by pulsatile flow or steady flow that not only was metabolic acidosis diminished, but also that interstitial fluid accumulation (a routine accompaniment of human cardiopulmonary bypass today) treated with furosemide, hetastarch, mannitol, and human albumin in various centers was also diminished.

It is also possible to demonstrate in vitro several significant differences in pulsatile flow of physiologic morphology versus steady flow. We have done this with standard hemodialyzers, dialyzing water spiked with urea. At identical flow rates (1) mean pressure is significantly higher with pulsatile flow, (2) ultrafiltration volume is significantly greater with pulsatile flow, and (3) urea clearance is significantly greater with pulsatile flow. ⁴

On occasion it has been stated that it is not possible to "define" physiologic pulsatile flow, but certainly it is possible to define pulsatile flow of physiologic morphology. We stand by the numbers previously published in this Journal in February 1994 ⁵ : (1) physiologic rate of pressure rise (dP/dt) of the waveform within the subject's arterial tree (1000 mm Hg/sec or greater); (2) physiologic intraarterial ejection time (no greater than 415 msec - 1.7 x heart rate, after Weissler ⁶;) (3) physiologic pulse pressure; (4) physiologic rate; and (5) physiologic stroke volume.

References

1. Grossi EA, Connolly MW, Krieger KH, et al. Quantification of pulsatile flow during cardiopulmonary bypass to permit direct comparison of the effectiveness of various types of "pulsatile" and "nonpulsatile" flow. Surgery 1985;98:547-54.[Medline]
   
2. Trinkle JK, Helton NE, Bryant LR, Griffen WO. Pulsatile cardiopulmonary bypass: clinical evaluation. Surgery 1970;68:1074-8.[Medline]
   
3. Jacobs LA, Klopp EH, Seamone W, Topaz SR, Gott VL. Improved organ function during cardiac bypass with a roller pump modified to deliver pulsatile flow. J THORAC CARDIOVASC SURG 1969;58:703-12.[Medline]
   
4. Runge TM, Briceno JC, Sheller ME, et al. Hemodialysis: evidence of enhanced molecular clearance and ultrafiltration volume by using pulsatile flow. Int J Artif Organs 1993;16:645-52.[Medline]
   
5. Runge TM, Trinkle JK. Does flow character of cardiopulmonary bypass make a difference? J THORAC CARDIOVASC SURG 1994;107:642-3.
   
6. Weissler AM. Non-invasive cardiology. New York: Grune & Stratton, 1974:307-14.
   

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