Differences in responses of platelets to fluid shear stress in patients with peripheral artery disease (PAD) and coronary artery disease (CAD).

Information on differences in platelet function between patients with peripheral arterial disease (PAD) and patients with coronary artery disease (CAD) is limited. We sought to examine the differences in the platelets response to shear stress in patients with PAD compared to those with CAD. Men with symptomatic PAD (ankle brachial index [ABI] < 0.9; n = 29) were compared with similarly aged men with CAD (post coronary artery bypass grafting; n = 40) but without PAD. All participants were on aspirin, and none were on clopidogrel. We measured changes in shear-induced platelet aggregation (SIPA) and shear-induced P-selectin expression (SIPE) under fluid shear rates of 5000 and 10,000 s(-1)which are typically found in arterioles and stenosed arteries, respectively. Aggregation was also induced by a combined stimulation of collagen, fluid shear stress, and adenosine diphosphate (ADP) or epinephrine using a platelet function analyzer (PFA-100) as well as optical aggregometry (arachidonic acid, collagen and epinephrine). Analyses of covariance adjusted for age, aspirin dose, and statin use were used to estimate differences between the groups. Values of SIPA at fluid shear rates of 5000 and 10,000 s(-1) were significantly higher in the PAD group, while there were no differences between the PAD and CAD groups in SIPE at both fluid shear rates. However, baseline shear-induced P-selectin expression was higher in patients with PAD than CAD (mean fluorescence intensity [MFI] = 2.93 +/- 1.37 vs.1.94 +/- 0.67; p = 0.01), while the percentage increases in SIPA and SIPE at fluid shear rates of 5000 and 10,000 s(-1) were significantly higher in patients with CAD when compared to PAD (p < 0.001 for all comparisons). Although there were several similarities in platelet function between men with PAD and men with CAD, significant differences in platelet responses to shear stress were observed in men with PAD when compared to those with CAD. Although the mechanism for these observed differences are not clear, we hypothesize that in vivo platelet activation in PAD patients may contribute to the differences and will need to be further investigated.

Unsupervised walking therapy and atherosclerotic risk-factor management for patients with peripheral arterial disease: a pilot trial.

BACKGROUND: Although only a small percentage of patients with peripheral arterial disease (PAD) have claudication, many more suffer from atypical leg symptoms. PURPOSE: This pilot trial evaluated a risk-factor modification program to improve walking ability in patients with PAD and leg symptoms other than intermittent claudication. METHODS: Patients 18 years or older with an ankle-brachial index (ABI) of 0.50 to 0.89 completed a baseline assessment of current walking ability, physical activity level, health-related quality of life, glycosylated hemoglobin values, and fasting lipid profiles. Patients were randomized to usual care (control group) versus usual care plus an educational intervention on risk-factor management (intervention group). We compared functional outcomes between and within groups using the Student's t test and control and intervention group outcomes at 12 weeks using analysis of covariance with the baseline value as the covariate. RESULTS: We randomized 50 patients into two treatment arms. There was no difference in the mean age of patients in each group. At baseline, mean ABI for the control versus the intervention group was 0.72 (SD = 0.10) and 0.75 (SD = 0.10), respectively, and mean stair-climbing values did not differ between groups. At 12 weeks, mean stair-climbing values were 40.2 (SD = 30.2) for the control and 61.2 (SD = 32.8) for the intervention group. The difference in adjusted mean walking distance between groups at 12 weeks was not significant. Analysis of covariance associated assignment to the intervention versus the control arm with a significant increase at 12 weeks in the ABI (p = .008) and stair-climbing ability (p = .02). CONCLUSIONS: Patients in the intervention group improved objective measures of blood flow and reported stair-climbing ability.