Fractal correlation property of heart rate variability in chronic obstructive pulmonary disease

Tatiana D Carvalho^1,2, Carlos Marcelo Pastre¹, Moacir Fernandes de Godoy³, Celso Fereira², Fábio O Pitta^1,4, Luiz Carlos de Abreu⁵, Ercy Mara Cipulo Ramos¹, Vitor E Valenti^2,5, Luiz Carlos Marques Vanderlei^1
1Departamento de Fisioterapia da Faculdade de Ciências e Tecnologia, Universidade Estadual Paulista, Presidente Prudente, São Paulo, Brasil; ²Departamento de Medicina, Disciplina de Cardiologia, Universidade Federal de São Paulo, São Paulo, Brasil; ³Departamento de Cardiologia e Cirurgia Cardiovascular, Faculdade de Medicina de São José do Rio Preto, São José do Rio Preto, São Paulo, Brasil; ⁴Laboratório de Pesquisa em Fisioterapia Pulmonar, Departamento de Fisioterapia, Universidade Estadual de Londrina, Londrina, Brasil; ⁵Departamento de Morfologia e Fisiologia da Faculdade de Medicina do ABC, Santo André, Brasil

Background: It was reported that autonomic nervous system function is altered in subjects with chronic obstructive pulmonary disease (COPD). We evaluated short- and long-term fractal exponents of heart rate variability (HRV) in COPD subjects.
Patients and methods: We analyzed data from 30 volunteers, who were divided into two groups according to spirometric values: COPD (n = 15) and control (n = 15). For analysis of HRV indices, HRV was recorded beat by beat with the volunteers in the supine position for 30 minutes. We analyzed the linear indices in the time (SDNN [standard deviation of normal to normal] and RMSSD [root-mean square of differences]) and frequency domains (low frequency [LF], high frequency [HF], and LF/HF), and the short- and long-term fractal exponents were obtained by detrended fluctuation analysis. We considered P < 0.05 to be a significant difference.
Results: COPD patients presented reduced levels of all linear exponents and decreased short-term fractal exponent (alpha-1: 0.899 ± 0.18 versus 1.025 ± 0.09, P = 0.026). There was no significant difference between COPD and control groups in alpha-2 and alpha-1/alpha-2 ratio.
Conclusion: COPD subjects present reduced short-term fractal correlation properties of HRV, which indicates that this index can be used for risk stratification, assessment of systemic disease manifestations, and therapeutic procedures to monitor those patients.

Keywords: pulmonary disease, chronic obstructive, heart rate, nervous system, cardiology