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Brain, Vol. 116, No. 2, 485-492, 1993
© 1993 Oxford University Press
research-article |
Vagolytic effect of diabetes mellitus
Department of Physiology, University of Zimbabwe Harare, Zimbabwe
Correspondence to:
Correspondence to: Dr P. O. O. Julu, Clinical Neurophysiology, Institute of Neurological Sciences, Southern General Hospital, Glasgow G51 4TF, Scotland.
The amplitude of respiratory sinus arrhythmia was quantified as the ratio of the longest to the shortest R—R intervals in electrocardiograms recorded during deep inspirations and forced expirations in the supine position. The mean of the absolute differences between consecutive R—R intervals recorded during normal quiet breating in a supine position was also calculated. Since these two tests measure only cardiac parasympathetic function, they were used to assess the resting vagal tone in 165 patients with diabetes mellitus and 116 healthy volunteers (controls). The frequency distribution curve of resting vagal tone was Gaussian in the controls and was also negatively correlated with age and height. The frequency distribution curve of resting vagal tone was skewed in the diabetic population where a majority of patients had low vagal tone. The correlation of vagal tone with age was stronger than in controls, but there was no correlation of vagal tone with height in diabetic patients. The mean resting vagal tone in diabetic patients was reduced by 40%, and the whole frequency distribution curve was also shifted to the left by 40% relative to the control curve. It is concluded that there is a substantial impairment of cardiac vagal function in most diabetic patients, contrary to current belief. Clinical tests which include measurement of vagal tone may give a bias towards low values in diabetic patients because of the shift to the left in the distribution curve of vagal tone in the diabetic population. It may therefore be necessary to measure resting vagal tone separately using one of the two tests described here for critical interpretation of results of autonomic function test in diabetic patients.
Received August 20, 1991. Revised February 9, 1992. Accepted November 11, 1992.
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