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PathogenesisWhen 10-25% of the blood is lost the stroke volume falls and arterial blood pressure is maintained due to sympathetic increases in heart rate and vasoconstriction. Vasoconstriction causes increased diastolic pressure and narrow pulse pressure. Since blood pressure consists of cardiac output and systemic vascular resistance, an increase in the resistance can maintain arterial pressure for a short time, despite decreased output.
Cardiac ouput and arterial pressure fall to 0% when 30-40% of total blood volume has been lost. |