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Effect of descending thoracic aorta clamping and unclamping on phasic coronary blood flow
Insights
Investigating aortic blood pressure and coronary blood flow during aortic surgery reveals significant changes. Diastolic coronary blood flow decreases after unclamping, potentially due to active vasodilation and altered zero flow pressure.
Area of Science:
- Cardiovascular Physiology
- Surgical Hemodynamics
- Myocardial Ischemia Research
Background:
- Myocardial infarctions are a risk during aortic surgery, often linked to aortic clamping and unclamping.
- Understanding the relationship between aortic blood pressure and coronary blood flow is crucial for mitigating surgical risks.
Purpose of the Study:
- To investigate the aortic blood pressure (AoBP)-coronary blood flow (CBF) relationship during thoracic descending aorta clamping and unclamping.
- To analyze hemodynamic parameters and phasic circumflex CBF in dogs under these surgical conditions.
Main Methods:
- Recorded hemodynamic parameters and phasic circumflex CBF in 15 anesthetized dogs.
- Performed thoracic descending aorta clamping and unclamping.
- Analyzed changes in mean aortic blood pressure (MAoBP), left-ventricular power (Wtc), aortic blood flow (AoBF), heart rate, and coronary blood flow (CBF) including diastolic CBF (DCBF).
Main Results:
- Aortic clamping increased MAoBP and Wtc, with a larger rise in systolic than diastolic CBF.
- Aortic unclamping initially decreased DCBF by 50% with decreasing diastolic blood pressure (DBP), followed by a DCBF increase.
- A linear relationship between DCBF and DBP was observed, indicating a change in diastolic zero flow pressure (PfO) of +40 mm Hg during clamping.
Conclusions:
- The observed decrease in DCBF during unclamping may be attributed to the altered diastolic zero flow pressure (PfO).
- The decrease in DCBF, coupled with increased left-ventricular power (Wtc), suggests a delayed active coronary vasodilation following aortic unclamping.
Abstract:
Myocardial infarctions during aortic surgery often occur after aortic clamping and unclamping. In order to investigate the aortic blood pressure (AoBP)-coronary blood flow (CBF) relationship, hemodynamic parameters and phasic circumflex CBF in 15 anesthetized and open-chest dogs during clamping and unclamping of the thoracic descending aorta have been recorded. During clamping, mean aortic blood pressure (MAoBP) rose from 97 + 17 to 150 + 42 mm Hg (P less than 0.001), and total combined left-ventricular power (Wtc) from 692 + 232 to 923 + 402 mW (P less than 0.001) while the ascending aortic blood flow (AoBF) and heart rate did not change significantly. The mean circumflex blood flow (MCBF) increased from 67 + 30 to 88 + 30 ml/min. The increase in systolic coronary blood flow (+73%) was larger than that in diastolic coronary blood flow (DCBF) (19%). The late coronary resistances were increased 39%. Conversely, after unclamping, MAoBP decreased while AoBF and Wtc increased. During the first cardiac cycles after aortic unclamping DCBF decreased 50% with a decrease in the diastolic blood pressure (DBP). Four cycles later, DCBF reincreased while DBP kept on decreasing. This may be related to an active coronary vasodilatation. A linear relationship between DCBF and DBP has been obtained during acute change in DBP due to clamping or unclamping. From these linear relationships, the change in diastolic zero flow pressure (PfO) has been found to be about + 40 mm Hg during clamping. This change in PfO may be responsible for the observed large fall in DCBF during unclamping. The decrease in DCBF associated with the increase in Wtc accounts for the delayed active vasodilatation.