Fig. 1.

Schematic illustrating common Doppler ultrasound-based procedures to assess resistance vessel function in humans and list of environmental stressors that should be taken into consideration during such studies. As noted in the text, these procedures can be applied to the upper and lower limbs and can also be overlaid. For example, drug infusions can occur in the resting limb but also during exercise or passive limb movement. Likewise, cuff occlusion can also be coupled with exercise to produce a “maximal” hyperemic response. The profile of typical blood flow responses is also illustrated; however, these are largely dependent on the precise stimulus (e.g., intensity of exercise, drug type, and dose, etc.), as well as the subject population studied.