Final answer:
Increased blood viscosity is the physiological change that increases resistance to blood flow, contributing to high blood pressure and an increased risk of stroke.
Step-by-step explanation:
The physiological change that increases the resistance of blood flow, making it more difficult for the heart to pump and contributing to high blood pressure and an increased risk of stroke, is increased blood viscosity. Viscosity is the thickness of fluids that affects their ability to flow, and when blood viscosity increases, resistance to blood flow also increases. This can lead to hypertension and a higher risk of stroke.
Conditions that can cause an increase in blood viscosity include polycythemia (an increase in red blood cell count) and certain liver abnormalities that affect plasma protein levels.
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