Parasympathetic Nervous System: A Case Study

One candidate biological system that may function to optimize social connections is parasympathetic activity, often conceptualized as the functioning of the vagus nerve and measured as respiratory sinus arrhythmia (RSA) or high-frequency heart rate variability (HF-HRV) at rest. The longest autonomic nerve in the human body, the vagus contributes to the innervation of the viscera, including the heart. Measures of cardiac vagal function like RSA have been used as a proxy for the parasympathetic nervous system’s ability to offset the effects of the sympathetic nervous system to maintain growth and restorative functions (a “vagal brake”; Porges, 2007). For example, in neonates—a developmental period when growth functions are most critical—high-risk …show more content…
Although heart rate is under the influence of several different nerves, the vagus is partly responsible for the variability in heart rate associated with respiration. This respiratory sinus arrhythmia (RSA) is characterized by a slowing of the heart rate during exhalation and an increase in heart rate during inhalation. Vagal influence on heart rate variability has been quantified in a multitude of ways. One of these methods, spectral analysis, utilizes a Fourier-transform equation to decompose the heart period waveform into power bands that correspond to frequencies. Specifically, the “high-frequency power band” (HF-HRV) corresponds to the frequency range of .15 to to .40 Hz, and is thought to reflect variability in heart rate due to respiration, as well as the influence of the vagus nerve (Berntson et al., 1997). Another common technique to obtain vagally-influenced heart rate variability is a peak-to-valley procedure, which uses both heart rate and respiratory data to derive a measure of RSA (Grossman, 1983). While it is not currently feasible to quantify global parasympathetic activity, RSA is a relatively easy, non-invasive measure of parasympathetic control of the