In 34 normal subjects, none of the 12 correlation coefficients between low frequency power of heart period variability and plasma catecholamines during psychological stress achieved significance.
Observational (n=34)
Do indices of heart period variability correlate with circulating catecholamines as measures of cardiac sympathetic activity during mental stress in normal subjects?
Low-frequency heart period variability does not correlate with plasma catecholamines during psychological stress, suggesting it is not a reliable index of cardiac sympathetic activity in this setting.
Heart rate increases during psychological stress are the product of cardiac sympathetic activation and parasympathetic withdrawal. Levels of plasma epinephrine (E) and norepinephrine (NE) have a long history as indicators of cardiac adrenergic activity and, accordingly, generally increase in response to psychological challenge. Recently, several investigators have suggested that indices derived from power spectral analysis of heart period variability (HPV) also may provide estimates of cardiac sympathetic nervous system activity. These indices include power in the low frequency band (0.04-0.15 Hz, LF), and the ratio of low to high frequency (0.15-0.50 Hz, HF) power (LF/HF). The relationship between spectral and neurohumoral indices during psychological stress has not been investigated. This issue was addressed by studying spectrally defined measures of HPV and levels of plasma E and NE in 34 normal subjects who participated in a study of responsiveness to a psychologically challenging arithmetic task. Heart rate (HR), LF and HF power, the LF/HF ratio, and blood pressure were measured during the 5-minute baseline and 5-minute task periods. Integrated samples of forearm venous blood were collected for both periods. E and NE were analyzed by high performance liquid chromatography. The task produced significant increases in HR, systolic and diastolic pressures, and NE. Of the 12 Pearson correlation coefficients used to examine the relationships between power spectral measures and catecholamines for the baseline, task, and delta values, none achieved statistical significance, suggesting little relationship between neurohumoral and spectral estimates of cardiac sympathetic activity. We conclude that under conditions of psychological stress, LF power provides no useful information about cardiac sympathetic activity, both because power in this frequency band falls whereas HR rises and because there is no relationship between LF power and plasma NE.
Sloan et al. (Mon,) conducted a observational in Normal subjects (n=34). Psychologically challenging arithmetic task vs. Baseline was evaluated on Pearson correlation coefficients between power spectral measures of heart period variability and plasma catecholamines. In 34 normal subjects, none of the 12 correlation coefficients between low frequency power of heart period variability and plasma catecholamines during psychological stress achieved significance.
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