Background
The environment surrounding vascular endothelial cells determines the contractile state of vascular smooth muscle. The present investigation examined the interrelationships between 3 factors known to effect skin blood flow (global heat, local heat and electrical stimulation) to see how they interacted.
Material and Method
Twenty two males participated in 3 series of experiments. The mean age was 33.2+/-8.8 years, and mean BMI was 25.6+/-3.7. Three series of experiments were conducted. In the first series, the skin blood flow above the quadriceps was evaluated before and during an electrical stimulus with skin temperature clamped at 20, 30 or 40 degrees C. In the second series, the same experiment was accomplished but with subjects exposed to ambient temperatures of 20, 30 or 40 degrees C. Finally both room and skin temperatures were varied in the same protocol. Skin blood flow was measured with a Laser Doppler Imager.
Results
Factors that caused vasoconstriction of the blood vessels such as cold exposure either locally or globally significantly blocked vasodilatation from other factors. For example, global cooling significantly blocked the response of the skin blood flow to local heat and electrical stimulation. Further, when 2 or more stimuli were applied together, the overall blood flow response was not additive but was exponential.
Conclusions
The endothelial cell appears to be a non linear transducer in its response to external stimuli which can alter local blood flow.

Keywords: Rest, Regional Blood Flow - physiology, Hot Temperature, Skin Temperature, Skin - blood supply, Electric Stimulation, Demography