Low Heart Rate Variability in Healthy Young Adult Males

Abstract

The autonomic nervous system coordinates a person’s responsiveness to physiological and environmental stressors. Attenuated respiratory sinus arrhythmia (RSA) with small standard deviation of the normal-normal electrocardiogram RR intervals (SDNN) is found in subjects with low heart rate variability (HRV) by time domain analysis (Montano et al., 2009). Low HRV is also characterized by sympathovagal balance shifted toward sympathetic predominance observed as an increase in the low frequency/high frequency ratio by frequency domain (fast Fourier transform) spectral analysis (Montano et al., 2009). However, interand intra-individual spectral changes are highly variable (Taverner et al., 1996) and the physiological significance is not always clear. Paced breathing at 0.2 Hz normally shifts sympathovagal balance toward greater vagal and less sympathetic activity (Driscoll and Dicicco, 2000) because of increased tidal volume and/or minute ventilation (Pinna et al., 2006). Sympathovagal imbalance related to low HRV is a risk factor for hypertension and various other cardiovascular and non-cardiovascular diseases (Kuch et al., 2001; Montano et al., 2009). Epidemiological studies estimate that the prevalence of hypertension ranges from 8% in an urban adolescent population (Rabinowitz et al., 1993) to 43% in black physicians twenty-two years after medical school (Gillum, 1999). However, no studies have determined the incidence and behavioral significance of sympathovagal imbalance in healthy young adult African-Americans. Abnormal autonomic responsiveness to environmental stressors is thought to be an important factor in the evolution of essential hypertension (Fauvel et al., 1996; Mezzacappa et al., 2001; Lucini et al., 2002a; 2002b) and African-American males are a subpopulation at high risk for such hypertension (Gillum, 1979; Kaplan, 1994; Gillum, 1999). The present study was, therefore, designed to determine whether sympathovagal imbalance related to low HRV occurs in a population of healthy young adult African-American males and whether it is an indicator of abnormal responsiveness to environmental stressors.