“Walking disability,” as used in N.H. Rev. Stat. § 261:88, means a severe physical impairment including partial paralysis, lower limb amputation, chronic heart disease, emphysema, arthritis, rheumatism or other debilitating condition:
I. Which limits personal mobility and results in an inability to travel without the use of a wheelchair, crutch, walker, prosthetic, orthotic or other assistive device, and which is verifiable by a comparable disability rating from the Department of Veterans Affairs, Social Security Administration, or Workers’ Compensation Board;
II. Caused by a cardiovascular impairment to the extent that functional limitations are rated in either class III or class IV standards as accepted by the American Heart Association; or
III. Caused by lung dysfunction to the extent that the person‘s forced respiratory expiratory volume in one second, as measured by spirometry, is less than one liter, or the person’s arterial oxygen tension (pO₂) is less than 60 mm/Hg in room air at rest.