Reliability and validity of cardiovascular and vasomotor autonomic function tests

OBJECTIVE - To determine the reliability and validity of autonomic function tests (AFTs) as clinical tools for diagnosing diabetic autonomic dysfunction. RESEARCH DESIGN AND METHODS - Twenty-one healthy control subjects and 21 insulin-dependent diabetes mellitus (IDDM) patients (11 with no symptomatology and 10 with symptomatic diabetic autonomic neuropathy [DAN]) were matched for age, and administered three standard cardiovascular tests and two new vasomotor tests of autonomic function. Each of the cardiovascular tests (change in heart rate [Δbpm], Valsalva ratio [VR], change in systolic blood pressure [ΔsBP]) and vasomotor tests (total pulse amplitude [TPA] and percent vasoconstriction [%VC]) were repeated within 1 week. Infrared photoplethysmography measured sympathetic-mediated vasomotor function. Reliability was determined by intraclass correlation coefficients. Validity was determined by analysis of variance procedures to test for differences between known groups and by computing sensitivity, specificity, and positive and negative predictive values. RESULTS - All AFTs were reliable, with %VC having highest reproducibility (r = 0.90). AFT scores were not different from time 1 to time 2. After controlling for age, two cardiovascular tests had significantly different values for control subjects and asymptomatic diabetic patients. AFTs, except ΔsBP, were significantly different between symptomatic diabetic patients and asymptomatic diabetic patients after controlling for age and duration of disease simultaneously. Sensitivity, specificity, and predictive values for %VC were comparable to the values for Δbpm and VR. TPA indexes were lower but clinically acceptable. CONCLUSIONS - AFTs were found to be reliable and valid tests for detecting DAN. TPA and %VC are important because they measure an aspect of sympathetic function not assessed by standard cardiovascular AFTs, and they do not depend on the patient's cooperation or ability to exert effort.