Contact
Write as you would to an almanac keeper: one step, one chapter, named plainly.

Every set of guides has a step it leaves out. If a step before your appointment, scan or vein visit never got explained, this is the page to name it on.
Name the step that got skipped
Describe the moment where the instructions went quiet. It might be what to gather, what to do first, or what happens next. Keep it to the one step. A narrow question is easier to place in the sequence than a broad one.
Four pages to open before you write
Reading what public sources already say can sharpen the question. For tests, there are the MedlinePlus Medical Encyclopedia entries on a Doppler ultrasound exam of an arm or leg and on plethysmography. For the diagnosis side, the NHLBI, NIH publishes pages on peripheral artery disease diagnosis and on venous thromboembolism diagnosis.
Then the form
When the step is named and the reading is done, use the form on this page to put the question in writing.