Hemorrhage with a large loss of blood causes
1) no change in blood pressure but a change in respiration
2) a rise in blood pressure due to change in cardiac output
3) no change in blood pressure but a slower heart rate
4) a lowering of blood pressure due to change in cardiac output
The correct answer and explanation is :
Correct Answer:
4) A lowering of blood pressure due to change in cardiac output
Explanation:
Hemorrhage, especially when there is a significant loss of blood, leads to a decrease in blood volume. Since blood pressure (BP) is directly dependent on cardiac output (CO) and peripheral resistance, a large loss of blood reduces the amount of blood returning to the heart (venous return), leading to decreased stroke volume and cardiac output. This, in turn, causes a drop in blood pressure.
Mechanism of Blood Pressure Drop in Hemorrhage:
- Decrease in Blood Volume
- Blood is a crucial component in maintaining BP. A large loss reduces the effective circulating volume, leading to lower venous return and reduced preload.
- Reduced Cardiac Output
- Cardiac output is calculated as CO = Stroke Volume × Heart Rate.
- With less blood returning to the heart, stroke volume decreases, reducing overall cardiac output, which directly lowers blood pressure.
- Compensatory Mechanisms
- Baroreceptor Reflex Activation: The body detects low BP and activates the sympathetic nervous system.
- Increased Heart Rate (Tachycardia): To compensate for low stroke volume, the heart beats faster.
- Vasoconstriction: The blood vessels constrict to maintain perfusion to vital organs.
- Hormonal Response: The release of hormones like epinephrine, ADH (vasopressin), and aldosterone helps retain fluids and constrict blood vessels.
Despite these compensatory mechanisms, if hemorrhage continues without intervention, the drop in blood pressure can lead to shock, where vital organs receive inadequate perfusion, potentially leading to organ failure and death. Therefore, the correct answer is option 4: a lowering of blood pressure due to change in cardiac output.