Autonomic contributions to attentional modulation of the cardiac defense response.

The cardiac defense response to aversive auditory stimulation is characterized by two acceleration/deceleration heart rate components. The first component is ascribed to attentional processes that facilitate detection and processing of potential threat, and the second one to protective actions. This study investigated attentional modulation of the cardiac defense response and the role of autonomic cardiac control therein. In 60 healthy subjects, the cardiac defense response was elicited, while electrocardiography, impedance cardiography and continuous blood pressure recordings were accomplished. Pre-ejection period represented sympathetic, heart rate variability parasympathetic, and systolic blood pressure sympathetic and parasympathetic, control. Half of the subjects performed a visual search task following the noise stimulus; the other half was exposed to the stimulus without any subsequent task. Task execution was associated with potentiation of the second heart rate acceleration/deceleration component of the defense response. Moreover, there was a greater systolic blood pressure decline during the second component. While pre-ejection period was unaffected by the task, the heart rate variability response was smaller overall in subjects performing the task. The findings suggest mediation of the first acceleration/deceleration component of the cardiac defense response by parasympathetic cardiac control; sympathetic and parasympathetic mechanisms contribute to the second component. While sympathetic control was unaffected by attentional demands, the potentiation of the cardiac defense response due to demands on external attention may relate to increased parasympathetic withdrawal.