Aim: To determine whether the lactate threshold during CPET is influenced by the presence of haemodynamically significant PAD.

Assumption: Correction of haemodynamically significant PAD results in an increased LT, measured by CPET.

Design: Prospective study Population: Thirty patients scheduled to undergo surgical or percutaneous treatment of iliofemoral arterial disease for intermittent claudication.

Patients scheduled to undergo surgery or angioplasty of the iliofemoral segment for intermittent claudication will be screened for inclusion. Consenting patients will undergo ABI measurements and CPET before treatment and four weeks after treatment. Study measures will be performed in the respiratory physiology laboratory at University Hospital Aintree. Demographic and medical details will be recorded including gender, age, smoking history and pack years, medical history and treatment and BMI. A record will be made of patuients' latest full blood count which will be routinely available in all participants before the procedure. Ankle-brachial index will be recorded. The subjects will undergo full CPET. This includes recording of baseline spirometry, full ECG monitoring throughout the test, measurement of ventilator parameters and recording of Borg breathlessness and leg fatigue score every minute. At the end of the test the reason for cessation will be documented. The test will be incremental with a 10-20W ramp determined according to baseline MVV aiming for the subject to exercise for 10-12 minutes. The test will involve 3 minutes rest, 2 minutes free-pedal followed by continuous ramping until volition. Recording will continue for 5 minutes recovery

Inclusion Criteria:

• Written informed consent, ability to perform a CPET on a cycle ergometer, intermittent claudication as presenting complaint, age ≥18, iliofemoral arterial disease

Exclusion Criteria:

• 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 Society/European 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 illness/advanced cancer or major psychiatric illness, including dementia, which precludes consent