Cardiovascular strain in peripheral arterial disease. A study with Near Infrared Spectroscopy

Patients with peripheral arterial disease (PAD) are at high cardiovascular risk and are limited by claudication. The relationship between insufficient oxygen delivery to working muscles and cardiovascular response during exercise has not been adequately investigated in PAD patients. Near Infrared Spectroscopy (NIRS) is a tool potentially useful for the study of circulatory disorders, allowing a dynamic evaluation of muscle metabolism . Objectives We studied whether the peripheral metabolic demand during walking affects the cardiovascular response in PAD patients compared to healthy subjects using NIRS. Subjects Fourty-three consecutive untrained patients with claudication (males=39, age 69.5±8.2), and eighteen healthy subjects (males=12, age 33.6±15.8) were studied. Methods At rest ankle-brachial index (ABI) and VO2 at gastrocnemius with arterial occlusion method by NIRS (Oxymon-MKIII, Artinis-The Netherlands) were determined. Subjects performed a level walking incremental treadmill test, with NIRS probes positioned at each calf, up to a speed of 3 Km/h. Variations of total (tHb), oxygenated (O2Hb) and deoxygenated haemoglobin (HHb) and of the differential value (Hbdiff) were recorded and quantified by the calculation of area-under-curve (A) for the range 1.6- 3.0 Km/h. Resting (standing) and final heart-rate were recorded (Heart Rate Monitor, Polar) and the difference (ΔHR) calculated. Results All subjects completed the test. Thirty patients referred claudication. A different muscle metabolism was observed in the legs of PAD patients compared to those of healthy subjects during the test. Patients with PAD showed higher ΔHR(P=0.0001), associated only to ABI of the most diseased leg in a stepwise multiple regression analysis among different independent factors considered (ABI, age, BMI, A-O2Hb, A-HHb). No difference of ΔHR was observed in PAD patients with and without beta-blocker (b-b) therapy. Conclusions During an incremental submaximal test PAD patients showed different muscle metabolism and an exaggerated increase in heart rate compared to healthy subjects. The rise was inversely correlated to the severity of the disease of the worse leg and was not reduced in patients with b-b therapy. The cardiovascular strain induced by PAD, even during the low intensity daily activities, might represent an additional risk factor in patients at unfavourable cardio-vascular outcome.