IRS publication 502 - http://www.irs.gov/pub/irs-pdf/p502.pdf page 6 Capital Expenses
Please find there the worksheet for calculating deductible medical expenses. let me know if any clarification needed.
Yes, you may use the same technique to calculate deductible medical expenses for any capital expenses.
Pleas see also on the page 7 - Car:
You can include in medical expenses the cost of special hand controls and other special equipment installed in a car for the use of a person with a disability.
Special design. You can include in medical expenses the difference between the cost of a regular car and a car specially designed to hold a wheelchair.
Cost of operation. You cannot deduct the cost of operating a specially equipped car, except as discussed under Transportation.