Cross correlation of heart rate and respiration versus deep breathing. Assessment of new test of cardiac autonomic function in diabetes

Cross correlation is a mathematical function whereby spectral analysis is used to describe the relationship between heart-rate fluctuations (256 R-R intervals) and respiration (simultaneously obtained by pneumotachograph). To assess its usefulness for testing autonomic integrity, cross correlation and deep breathing were compared in 141 diabetic subjects (aged 39 ± 14 yr) and in 77 control subjects (aged 33 ± 13 yr). To characterize patients, Valsalva maneuver, 30:15 ratio, tilt, and handgrip tests were performed in 96 of these patients; 23 had two or more abnormal tests (group A), 28 had one (group B), and 45 had none (group C). Sensitivity to parasympathetic withdrawal was compared in 9 control subjects (aged 26 ± 4 yr) by four sequential 0.01-mg/kg i.v. atropine administrations. Reproducibility was compared in 11 control subjects (aged 25 ± 2 yr) by repeating the tests four times for 2 consecutive days. Considering all 141 patients, cross correlation and deep breathing were