Recent evidence indicates that poor autonomic regulation, indexed by decreased heart period variability (HPV), is associated with decreased working memory. HPV analyses are computed on the interbeat interval time series derived from the electrocardiogram (EKG). Unfortunately, the duration of the data collection and the issue of the size of ambulatory monitors with sufficient storage capacity for multi-day records is somewhat problematic. In the present paper we describe a system that allows for the collection of large amounts of high quality data using a small data collection device. The recording system consists of a miniature, single-module electrocardiogram-recording device. This module consists of an integrated three-electrode device that is attached to the chest of the subject. A low power 8-bit micro-controller detects the R-spike and stores the time between R-spikes in milliseconds on a 512 KB EEPROM. This system can record continuously for over four days. This system will allow the recording of cardio-dynamics in the field and provide highly reliable data across multiple days. The use of this device to assess physiological function in military operations would allow researchers to examine longer data records across several contexts and to understand the role of changes in autonomic function as they relate to performance.
In the present paper we describe a model of neurovisceral integration in which a set of neural structures involved in cognitive, affective, and autonomic regulation are related to heart rate variability (HRV) and cognitive performance. We will provide pharmacological and neuroimaging data in support of the neural structures linking the central nervous system to HRV. Next, we will review a number of studies from our group using military cadets showing that individual differences in HRV are related to performance on tasks associated with executive function and prefrontal cortical activity. In the first study, individual differences in resting HRV we related to performance on executive and non-executive function tasks. The results showed that greater HRV was associated with better performance on executive function tasks. In the second study we add a stressor (shock avoidance) to the previous paradigm and show that those with greater HRV were more stress tolerant. Specifically, those with greater HRV were not adversely affected by the added stressor. In the last experiment, HRV was manipulated by physical detraining. Again, those that maintained their HRV at the post-test showed better performance on executive function tasks. We propose that these findings have important implications for the development of biomarkers related to performance in modern warfighters.