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Intramyocardial distribution of blood flow in hemorrhagic shock in anesthetized dogs
Insights
Hemorrhagic shock can cause irreversible heart damage due to poor coronary blood flow distribution. Mannitol infusion improved coronary flow and reduced myocardial edema in dogs, suggesting a potential treatment for shock-induced heart injury.
Area of Science:
- Cardiovascular Physiology
- Hemorrhagic Shock Research
- Myocardial Ischemia Studies
Background:
- Hemorrhagic shock leads to reduced blood flow and can cause irreversible organ damage.
- The role of coronary blood flow maldistribution in the heart's response to shock is not fully understood.
Purpose of the Study:
- To investigate if coronary blood flow maldistribution contributes to the irreversibility of hemorrhagic shock.
- To evaluate the effects of phenoxybenzamine and hypertonic mannitol on coronary blood flow and myocardial status during shock.
Main Methods:
- Anesthetized dogs underwent induced hemorrhagic shock, maintaining low aortic blood pressure for 3 hours.
- Coronary blood flow (CBF), coronary vascular resistance, and myocardial water content were measured.
- Dogs were pretreated with phenoxybenzamine or received hypertonic mannitol infusions.
Main Results:
- Untreated dogs showed decreased total and left ventricular CBF, increased minimal coronary resistance post-ischemia, and reduced subendocardial:subepicardial flow ratio.
- Mannitol infusion normalized CBF, coronary resistance, and myocardial water content.
- Phenoxybenzamine delayed but did not prevent adverse changes in coronary resistance and subendocardial flow.
Conclusions:
- Hemorrhagic shock may cause subendocardial ischemia, potentially linked to myocardial edema.
- Hypertonic mannitol shows promise in mitigating shock-induced coronary blood flow derangements and myocardial edema.
- Coronary blood flow maldistribution appears to be a significant factor in the cardiac consequences of hemorrhagic shock.
Abstract:
In 34 anesthetized, open-chest dogs aortic blood pressure was kept at 35-40 mmHg for 3 h to determine if maldistribution of coronary blood flow (CBF) could contribute to the irreversibility of hemorrhagic shock. Six dogs were pretreated with phenoxybenzamine (PBZ) and 11 dogs (3 with PBZ) received hypertonic mannitol infusions in late hemorrhage. Changes of heart rate, cardiac output, and peripheral resistance were similar to those described by others. In untreated dogs total and left ventricular CBF fell, as did coronary vascular resistance. However, minimal coronary resistance after transient ischemia rose progressively and the ratio of subendocardial:subepicardial flow fell, as did the percentage of diastolic coronary flow. Mannitol infusion returned CBF and steady-state and minimal postischemic coronary resistance to control values and also returned to normal the increased myocardial water content found in late hemorrhage. Phenoxybenzamine delayed but did not prevent the rise of coronary vascular resistance or decreased subendocardial flow. These studies suggest that there may be subendocardial ischemia, possibly due to myocardial edema, in hemorrhagic shock.