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Winters and Hypertension
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The Raynaud phenomenon (RP) is a condition in which some of the body's blood vessels (most commonly those in the fingers and toes) constrict in an exaggerated way in response to cold or emotional stress.

Normally, the vessels that supply blood to the skin constrict or narrow in response to cold temperatures. This reaction, called "vasoconstriction," decreases blood flow to the skin, which helps to minimize heat loss from the warm blood and therefore preserve a normal internal or "core" temperature. In warm temperatures, these same blood vessels dilate or widen, increasing the flow of blood to the skin surface, thus allowing heat to leave the body, and keeping the core body temperature from rising to a dangerous level.

The blood vessels in the skin that react to temperature changes are called "thermoregulatory" vessels. They are primarily controlled by the sympathetic nervous system, which is the same system that reacts when we are stressed or upset emotionally. This explains why both cold and emotional stress can trigger vasoconstriction of these blood vessels, causing cold fingers and toes.

In people with RP, the mechanisms that control vasoconstriction are thought to be altered or defective. The vessels constrict in an exaggerated way in response to cold and emotional or physical stress, causing what is called Raynaud's phenomenon or a Raynaud's attack. There are three phases of the event represented by skin color changes. First, severe vasoconstriction reduces blood flow to the skin of the affected areas, causing the skin surface to feel cold to touch and to have a white color. The pale white color is due to virtually no blood flow to the skin. The skin then typically becomes a purplish-blue color (called acrocyanosis), as a reduced flow of blood through the skin returns. When the vessel fully recovers, it dilates, allowing blood flow to resume; the skin may blush, becoming very pink or red.