<qa>  What ischaemia, unwillingness to consent, previous amputation or other inability to- Critical limb ischaemia, unwillingness to consent, previous amputation or other inability to perform CPET on a cycle ergometer, age 18, absence of iliofemoral arterial disease, any standard CPET exclusion based on American Thoracic SocietyEuropean Respiratory Society Guidelines, including severe arthritis or lower limb abnormality precluding exercise testing, severe hypertension at rest, unstable angina or acute coronary syndrome within the previous 6 weeks, terminal illnessadvanced cancer or major psychiatric illness, including dementia, which precludes consent 