Evaluating A Non-Invasive Tissue Perfusion Monitor

Inclusion Criteria: CLTI cohort 1. At least 40 years old 2. Each patient will have documented arterial occlusive disease within 6 weeks of enrolment as determined by an ankle-brachial index (ABI) \< 0.7 but not greater than 1.2, toe-brachial index (TBI) \<0.5, skin perfusion pressure (SPP) less than 30mmHg, OR Transcutaneous oxygen measurement (TCOM) \< 40mmHg in diabetics and \<30mmHg in non-diabetics. 3. The presence of skin breakdown compatible which with an underlying ischemic element (previous minor amputation for gangrene also included) that the Principle Investigator (PI) deems appropriate for the study. 4. Subject has read, understood and signed approved consent, and is willing to participate and comply with the study procedures and requirements. Non-vascular group 1. At least 40 years old 2. Each patient will have documented palpable foot pulses 3. 21 patients will be free of lower limb oedema and 6 patients will have moderate oedema present 4. Subject has read, understood and signed approved consent, and is willing to participate and comply with the study procedures and requirements. Exclusion Criteria: CLTI Cohort 1. Subject on an investigational drug or therapeutic device within 30 days of the study visit, which in the view of the PI may compromise the study results. 2. Presence of a condition that PI considers will compromise the subject's ability to participate in the study. 3. Age \<40 or \>90 4. Inability to straight leg raise to 30 degrees or tolerate calf cuff occlusion. 5. Has smoked cigarettes/e-cigarettes on the day of testing. 6. Has taken caffeine drinks on the day of testing 7. In the last 3 hours the subject has exercised beyond normal daily walking. 8. Inability to have TBI measured (e.g. absence of toe) 9. Signs of active infection causing localised inflammation on the plantar or dorsal surfaces of the foot 10. Pathological skin conditions that may impair the ability of the adhesive sensor pads to adhere. Non-vascular Cohort 1. Subject on an investigational drug or therapeutic device within 30 days of the study visit, which in the view of the PI may compromise the study results. 2. Presence of a condition that PI considers will compromise the subject's ability to participate in the study. 3. Age \<40 or \>90 4. Inability to straight leg raise to 30 degrees or tolerate calf cuff occlusion. 5. Has smoked cigarettes/e-cigarettes on the day of testing. 6. Has taken caffeine drinks on the day of testing 7. In the last 3 hours the subject has exercised beyond normal daily walking. 8. Inability to have TBI measured (e.g. absence of toe) 9. Signs of active infection causing localised inflammation on the plantar or dorsal surfaces of the foot 10. Pathological skin conditions that may impair the ability of the adhesive sensor pads to adhere.