ssment of Autonomic Function in Humans by Heart Rate Spectral Analysis," American Journal of Physiology 248 (1985): H151-H153. 25 U. I. Zulficiar, D. A. Jurivich, W. Gao, and D. H. Singer, "Relation of High Heart Rate Variability to Healthy Longevity," American Journal of Cardiology 105, no. 8 (Apr 15, 2010)