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J Thorac Cardiovasc Surg 2002;123:63-71
© 2002 The American Association for Thoracic Surgery

Cardiopulmonary Support and Physiology

Fractal or biologically variable delivery of cardioplegic solution prevents diastolic dysfunction after cardiopulmonary bypass

From the Departments of Anesthesia,^a Cardiovascular Surgery,^b and Community Health Sciences,^c University of Manitoba, Winnipeg, Manitoba, Canada.

The Crocus Investment Fund and the Industrial Research Assistance Program provided funding. Some of the concepts discussed are protected by US Patents #5,647,350, #5,941,841 and #6,027,498; "Control of Life Support Systems," owned by Biovar Life Support Inc, jointly held by Drs Mutch, Lefevre, the University of Manitoba, and the Crocus Investment Fund.

Received for publication April 23, 2001. Revisions requested June 7, 2001; revisions received June 21, 2001. Accepted for publication June 26, 2001. Address for reprints: W. A. C. Mutch, MD, Professor, Department of Anesthesia, University of Manitoba, A504 Chown Building, c/o 170 Services Building, 744 Bannatyne Ave, Winnipeg, Manitoba, Canada R3C 0W3 (E-mail: amutch{at}ms umanitoba.ca).

Objective: To determine whether myocardial protection is improved by restoring physiologic variability to the cardioplegia pressure signal during cardiopulmonary bypass, we compared cardiac function in pigs in the first hour after either conventional cold-blood cardioplegia (group CC) or computer-controlled biologically variable pulsatile cardioplegia (group BVC).
Methods: Invasive monitors and sonomicrometry crystals were placed, and cardiopulmonary bypass was initiated. The aorta was crossclamped, and cold blood cardioplegic solution was infused intermittently through the aortic root with either conventional cardioplegia (n = 8) or biologically variable pulsatile cardioplegia (n = 8; mean pressure, 75 mm Hg for 85 minutes). The crossclamp was released, cardiac function was restored, and separation from cardiopulmonary bypass was completed. With stable temperature and arterial blood gases, hemodynamics and systolic and diastolic indices were compared at 15, 30, and 60 minutes after cardiopulmonary bypass.
Results: Diastolic stiffness doubled from 0.027 ± 0.016 mm Hg/mm (mean ± SD) at baseline to 0.055 ± 0.036 mm Hg/mm (P = .003) at 1 hour after bypass in group CC, associated with increased left ventricular end-diastolic pressure from 9 ± 2 to 11 ± 2 mm Hg (P = .001), mean pulmonary artery pressure from 14 ± 2 to 20 ± 3 mm Hg (P = .003), and serum lactate levels from 2.0 ± 0.5 to 5.6 ± 2.3 mmol/L (P = .008). Systolic function was not affected. In group BVC diastolic stiffness, left ventricular end-diastolic pressure, and pulmonary artery pressure values were not different from control values at any time after bypass, and serum lactate levels were significantly less than with conventional cold blood cardioplegia. Peak pressure variability with biologically variable pulsatile cardioplegia fit a power-law equation (exponent = –3.0; R² = 0.97), indicating fractal behavior.
Conclusion: Diastolic cardiac function is better preserved after cardiopulmonary bypass with biologically variable pulsatile cardioplegia and fractal perfusion. This may be attributed to enhanced microcirculatory perfusion with improved myocardial protection. A model supporting these results is presented.

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