.
Vasoconstrictors are often given to raise blood pressure. That they do is seductively reassuring. We should expect vasoconstrictors to also immediately increase the resistance to blood flow and worsen it. We cannot see this happening. Generally we cannot measure or perceive reduced blood flow. We might see in the short term an initial rise in blood pressure which is easily measured, mistakenly reassuring, but we should expect the worsening of perfusion. We won’t be able to measure or test it. It is however a basic law of thermodynamics. Flow is inversely related to the resistance everywhere in the universe.
The fallacy of our conclusion is inherent in the urgency of the situation. We believe what we can see rather than what we know.