Resting parasympathetic status and cardiovascular response to orthostatic and behavioral challenges in type I insulin-dependent diabetes mellitus

Alterations in cardiac autonomic innervation are commonly seen in individuals with diabetes mellitus. In this study, we used a cluster analysis to quantitatively separate individuals with Type I insulin-dependent diabetes mellitus (1DDM) on the basis of assessment of autonomic mediation of resting cardiac function and compared these two IDDM groups with nondiabetic control subjects. One group, termed IDDM-1, exhibited respiratory sinus arrhythmia and resting heart rale (HR) at the same level as controls. A second group, termed IDDM-2, displayed significantly reduced respiratory sinus arrhythmia and elevated resting HR, indicating reduced parasympathetic cardiac input. Noninvasive physiological assessment of the subjects’ response to orthostatic maneuvers (supine, seated, upright tilt) and behavioral stressors (speech preparation, speech talking, mirror tracing, cold pressor) revealed abnormalities in cardiovascular regulation in the IDDM groups. Specifically, under supine resting conditions the IDDM-2 group exhibited reduced myocardial contractility and stroke volume. HR was accelerated in these subjects but not enough to compensate for the decreased stroke volume, and therefore cardiac output was not maintained at normal levels. Consequently, total peripheral resistance and hlood pressure were elevated in thcse subjects. Thus. for the IDDM-2 subjects, these data sugges that blood flow to the periphery is being sacrificed In maintain flow to the heart, lungs, and brain, which cannot sustain themselves anaerobically. The IDDM subjects, when compared with the control subjects, responded with similar magnitude and pattern of cardiovascular response to the behavioral stressors that selectively challenged the heart, vasculature, or both. However, the cardiovascular pattern produced by the IDDM subjects to the seated and uprigh postural challenges suggests that the IDDM-1, and to a certain extent the IDDM-2 subjects, evidenced difficulty in regulating vasomotor and/or venomotor tone to maintain blood pressure levels. Therefore, this study demonstrates a quantitative method for assessing resting parasympathetic status that distinguishes a group of IDDM subjects with abnormal resting cardiovascular regulation and response to challenge. This work was supported by Grants POI-HL36588 and T32-HL07426 from the National Heart, Lung, and Blood Institute, National Institutes of Health, U.S. Public Health Service