Abstract
This study was designed to assess which of the currently available methods for measuring R-R interval variation is the most suitable as a test of cardiac parasympathetic function. The relationship between the R-R interval variation and diabetic complications was also examined.
The following measurements of R-R interval variation were made in 36 maturity onset diabetics and 36 controls:(1) standard deviation (SD) and coefficient of variation (CV) of 100 successive R-R intervals during supine rest, supine deep breathing, and quiet standing in each person;(2) mean difference between the shortest and longest R-R intervals during deep breathing at six breaths per minute;(m (max-min)); and (3) ratio of the longest (C) to shortest (B) R-R interval after standing (C/B ratio).
The results showed that heart rate can affect SD, and that an unfixed respiratory rate can affect SD and CV during supine rest or quiet standing. The R-R interval variation was smaller while standing than while lying. The C/B ratio was less effective than the other measurements. It was concluded the most practical method is measuring CV or m (max-min) during deep breathing with the subject lying. There was no relationship between the R-R interval variation and sodium intake.
Diabetics who had retinopathy (>Scott III), continuous proteinuria (>150mg/day), or decreased Achilles tendon reflexes showed smaller R-R interval variations than controls. In diabetes, the R-R interval variation was correlated with blood pressure changes after standing, indicating coexistence of sympathetic and parasympathetic nervous dysfunction.
