Hemorrhage with a large loss of blood causes
no change in blood pressure but a slower heart rate
a lowering of blood pressure due to change in cardiac output
a rise in blood pressure due to change in cardiac output
no change in blood pressure but a change in respiration
The correct answer and explanation is :
The correct answer is:
“A lowering of blood pressure due to change in cardiac output.”
Explanation:
Hemorrhage with a large loss of blood leads to a decrease in blood volume, which directly affects cardiac output and blood pressure. Cardiac output (CO) is the amount of blood the heart pumps per minute and is determined by stroke volume (SV) and heart rate (HR):
[
CO = SV \times HR
]
When significant blood loss occurs, stroke volume decreases because there is less blood available to be pumped by the heart. Initially, the body attempts to compensate by increasing the heart rate (tachycardia) through the activation of the sympathetic nervous system (SNS). However, if the hemorrhage continues, the compensatory mechanisms become insufficient, leading to a drop in cardiac output and blood pressure.
Physiological Responses to Hemorrhage:
- Decrease in Blood Volume: Large blood loss reduces venous return to the heart, leading to a drop in preload (the initial stretching of the heart before contraction).
- Decreased Stroke Volume and Cardiac Output: Less blood returning to the heart means less blood ejected with each heartbeat. Since CO depends on stroke volume, it decreases.
- Blood Pressure Drop: Blood pressure (BP) is proportional to cardiac output and systemic vascular resistance (SVR). As CO falls, BP also decreases.
- Compensatory Mechanisms: Initially, the SNS triggers vasoconstriction and increases heart rate to maintain BP. However, if hemorrhage continues, BP continues to drop, leading to hypovolemic shock.
Thus, the most accurate response is a lowering of blood pressure due to change in cardiac output because severe hemorrhage leads to decreased CO, which in turn results in hypotension (low blood pressure).