Linear and nonlinear heart rate dynamics in elderly inpatients. Relations with comorbidity and depression

Background. Hospitalization processes are known to increase depressive symptoms arising among elderly population. Meanwhile, dysregulation of cardiac autonomic function has been suggested to link depression and cardiovascular mortality. In this context, analysis of heart rate variability (HRV) is emerging as a powerful mortality risk stratifier clinical tool. The purpose of the study was to examine the relationship among HRV, depression, and comorbidity risk among an elderly inpatient population. Material and methods. Twenty-six subjects (aged 78 +/- 9 years) were recruited from the Short-Term Stay Unit at the Hospital General de Alicante. Before joining a Physical Activity Program aimed to prevent functional impairment and after medical selection and written consent, inpatients were tested for heart rate variability, Yesavage Geriatric Depression Scale, and Charlson comorbidity index score. Results. Men compared to women showed a significantly larger CCI score. Short-term scaling exponent (alpha(1)), derived from detrended fluctuation analysis, showed a negative correlation with Charlson comorbidity index. Conversely, a positive correlation was found between sample entropy (SampEn) and Yesavage Scale. Conclusions. On the one hand, fractal analysis of HRV confirms to be useful as a risk stratifier tool. On the other hand, SampEn is proposed to be reflecting a non-neurally generated complexity when accompanied with low values of alpha(1). Accordingly, in this regime, it would be indicative of a paradoxical gradual reduction in cardiac autonomic control, accentuated with the severity of depressive symptoms.