Cardiovascular reactivity during stress induction differentiates ADHD subtypes

Attention-Deficit Hyperactivity Disorder (ADHD) is one of the most pervasive childhood mental health problems in Canada. Research examining how autonomic physiological systems are associated with ADHD has been inconclusive, often yielding contradictory results. One confounding issue may be the very high prevalence of comorbid problems in children with ADHD. Another issue may be the heterogeneity of symptom sets exhibited by children with ADHD. Children's ability to self-regulate their physiological arousal under conditions of challenge or stress is likely to be influenced by comorbid problems and ADHD subtype. In this investigation, 142 elementary school-aged children with ADHD wore cardiac monitors while undergoing a stress-inducing event: having their blood drawn in a hospital clinic. Continuously recorded cardiac inter-beat intervals were used to assess heart rate (arousal), vagal tone (parasympathetic regulation), and SNS Index (sympathetic regulation). Parental reports of comorbid problems were assessed using the CPRS-R and the DISC-IV. Comorbid disruptive behavior disorders and anxiety disorders did not strongly predict cardiac reactivity. Significant variability in cardiovascular reactivity distinguished between ADHD subtypes; in particular, children with hyperactive-impulsive problems showed strongly atypical vagal and SNS reactivity. These results have implications for the diagnosis and treatment of ADH