The association between diabetic complications and exercise capacity in NIDDM patients

Exercise capacity has been used as a noninvasive parameter for predicting cardiovascular events. It has been demonstrated previously in NIDDM patients that several risk factors (i.e., obesity, smoking, hypertension, and African-American race) are associated with an impaired exercise capacity. We studied 265 male and 154 female NIDDM patients who underwent graded exercise testing with expired gas analyses to determine the possible influences of diabetic neuropathy, nephropathy, and retinopathy on exercise capacity.

Univariate and multiple linear regression analyses were performed to determine the relationship between diabetic neuropathy, urinary albumin excretion (UAE), and retinopathy with respect to peak oxygen consumption (VO2). Neuropathy was assessed by neurological symptom and disability scores, autonomic function testing, and quantitative sensory exams involving thermal and vibratory sensation. Three categories of UAE were used: normal albuminuria (< 20 micrograms/min), microalbuminuria (20-200 micrograms/min), and overt albuminuria (> 200 micrograms/min). Retinopathy was assessed by stereoscopic fundus photographs. Multiple linear regression analyses were then performed controlling for age, sex, length of diagnosed diabetes, duration of hypertension, race and ethnicity, GHb, BMI, and smoking to determine whether there was an independent effect of these diabetic complications on exercise capacity.

Univariate analyses revealed that the presence of diabetic retinopathy (P = 0.03), neuropathy (P = 0.002), microalbuminuria (P = 0.04), and overt albuminuria (P = 0.06) were associated with a lower peak VO2. Multiple linear regression analyses were performed to determine independent relationships with peak VO2. The results revealed that increasing retinopathy stage (Parameter estimate [PE] = -0.59 +/- 0.3 ml.kg-1.min-1; P = 0.026) and increasing UAE stage (PE = -0.62 +/- 0.3 ml.kg-1.min-1; P = 0.04) were associated with a decrease in peak VO2.

In the present study of NIDDM subjects, a significant independent association was demonstrated between diabetic nephropathy and retinopathy with exercise capacity. These results were obtained controlling for age, sex, length of diagnosed diabetes, hypertension, race, and BMI. Thus the findings in this large NIDDM population without a history of coronary artery disease indicate a potential pathogenic relationship between microvascular disease and exercise capacity.