Nonlinear Conte-Zbilut-Federici (CZF) Method of Computing LF/HF Ratio: A More Reliable Index of Changes in Heart Rate Variability

  • Vernon Bond, Jr (Department of Recreation, Human Performance & Leisure Studies, and Exercise Science & Human Nutrition Laboratory, Howard University Cancer Center) ;
  • Curry, Bryan H (Division of Cardiology, Department of Medicine, Howard University College of Medicine & Howard University Hospital) ;
  • Kumar, Krishna (Department of Pharmaceutical Sciences, College of Pharmacy, Howard University) ;
  • Pemminati, Sudhakar (Departments of Pharmacology, American University of Antigua College of Medicine and Manipal University) ;
  • Gorantla, Vasavi R (Behavioral Science & Neuroscience, American University of Antigua College of Medicine) ;
  • Kadur, Kishan (Medical Physiology, American University of Antigua College of Medicine) ;
  • Millis, Richard M (Medical Physiology, American University of Antigua College of Medicine)
  • Received : 2016.06.03
  • Accepted : 2016.08.10
  • Published : 2016.09.30


Objectives: Acupuncture treatments are safe and effective for a wide variety of diseases involving autonomic dysregulation. Heart rate variability (HRV) is a noninvasive method for assessing sympathovagal balance. The low frequency/high frequency (LF/HF) spectral power ratio is an index of sympathovagal influence on heart rate and of cardiovascular health. This study tests the hypothesis that from rest to 30% to 50% of peak oxygen consumption, the nonlinear Conte-Zbilut-Federici (CZF) method of computing the LF/HF ratio is a more reliable index of changes in the HRV than linear methods are. Methods: The subjects of this study were 10 healthy young adults. Electrocardiogram RR intervals were measured during 6-minute periods of rest and aerobic exercise on a cycle ergometer at 30% and 50% of peak oxygen consumption ($VO_{2peak}$). Results: The frequency domain CZF computations of the LF/HF ratio and the time domain computations of the standard deviation of normal-to-normal intervals (SDNN) decreased sequentially from rest to 30% $VO_{2peak}$ (P < 0.001) to 50% $VO_{2peak}$ (P < 0.05). The SDNN and the CZF computations of the LF/HF ratio were positively correlated (Pearson's r = 0.75, P < 0.001). fast Fourier transform (FFT), autoregressive (AR) and Lomb periodogram computations of the LF/HF ratio increased only from rest to 50% $VO_{2peak}$. Conclusion: Computations of the LF/HF ratio by using the nonlinear CZF method appear to be more sensitive to changes in physical activity than computations of the LF/HF ratio by using linear methods. Future studies should determine whether the CZF computation of the LF/HF ratio improves evaluations of pharmacopuncture and other treatment modalities.


Supported by : Howard University


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