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Relationship between perfusion pressure and myocardial microcirculation in the beating empty or spontaneously
Insights
In spontaneously fibrillating hearts (SFH), low perfusion pressures during cardiopulmonary bypass can cause underperfusion of the left ventricular endocardium. Myocardial oxygen consumption is higher in SFH compared to beating empty hearts (BEH).
Area of Science:
- Cardiovascular Physiology
- Surgical Perfusion
Background:
- Cardiopulmonary bypass (CPB) requires careful management of perfusion pressure to ensure adequate organ perfusion.
- Understanding the impact of varying perfusion pressures on myocardial blood flow and oxygen consumption is crucial for optimizing CPB strategies.
Purpose of the Study:
- To investigate the effects of graded perfusion pressures (30, 60, 90 mmHg) during CPB on coronary flow distribution and myocardial oxygen consumption.
- To compare these effects between beating empty hearts (BEH) and spontaneously fibrillating hearts (SFH).
Main Methods:
- Utilized the tracer microsphere technique in twelve mongrel dogs under normothermic conditions.
- Assessed coronary blood flow, myocardial oxygen consumption (MVO2), and regional flow distribution (left and right ventricles).
- Compared outcomes between BEH and SFH at different perfusion pressures.
Main Results:
- In SFH, subendocardial (ENDO) to epicardial (EPI) flow ratio in the left ventricle (LV) decreased significantly at 30 and 60 mmHg, indicating underperfusion.
- Right ventricular (RV) flow distribution relatively increased in both BEH and SFH, with no significant decrease in RV ENDO/EPI ratio at 30 mmHg.
- Coronary blood flow and MVO2 were higher in SFH than BEH, and increased with perfusion pressure in both groups.
- MVO2 remained constant in BEH but increased with pressure in SFH.
Conclusions:
- Low perfusion pressures (30 and 60 mmHg) during CPB can induce left ventricular subendocardial underperfusion in spontaneously fibrillating hearts.
- The findings highlight the importance of maintaining adequate perfusion pressure to ensure optimal myocardial oxygen supply, particularly in the endocardium.
- Differences in cardiac activity (BEH vs. SFH) significantly influence myocardial response to perfusion pressure variations.
Abstract:
The influence of graded perfusion pressure (30, 60, and 90 mmHg) at cardiopulmonary bypass were studied on beating empty hearts (BEH) or spontaneously fibrillating hearts (SFH) in the normothermic state. The adequacy and distribution of coronary flow and the myocardial oxygen consumption (MVO2) were examined using the tracer microsphere technique in twelve mongrel dogs. In the SFH, the left ventricular (LV) endocardium (ENDO)/epicardium (EPI) flow ratio indicated significant decrease at 30 and 60 mmHg (0.83 +/- 0.05 and 0.86 +/- 0.06, p less than 0.005, respectively), but was recovered to control value at 90 mmHg (1.01 +/- 0.13). In the BEH, these low perfusion pressures did not result in an abnormal flow distribution in the LV (1.03 +/- 0.03 at 30 mmHg). The flow distribution to the right ventricle (RV) relatively increased in both the BEH and the SFH (p less than 0.001). The ENDO/EPI ratio of the RV did not decrease at 30 mmHg in both groups (1.11 +/- 0.03 in BEH and 1.16 +/- 0.08 in SFH). Coronary blood flow and MVO2 were significantly higher in the SFH than in the BEH. Coronary blood flow increased significantly with increase in the perfusion pressure, in both groups. The MVO2 was constant in the BEH, regardless of the perfusion pressure, but increased in the SFH at increasing pressure. These results show that in the SFH, subendocardial underperfusion of the LV is induced at the perfusion pressure of 30 and 60 mmHg.