Regulation of Cardiac Autonomic Nervous System Control across Frailty Statuses: A Systematic Review

Abstract

Background: Frailty is a geriatric syndrome that leads to impairment in interrelated physiological systems and progressive homeostatic dysregulation in physiological systems. Objective: The focus of the present systematic review was to study the association between the activity of the cardiac autonomic nervous system (ANS) and frailty. Methods: A systematic literature search was conducted in multiple databases: PubMed/MEDLINE, Embase, Cochrane Library, Web of Science, CINAHL, and ClinicalTrials.gov; the last search was performed in March 2015. Inclusion criteria were: (1) that the studied population was classified for frailty according to a standard definition, such as Fried's criteria; (2) that the study had a nonfrail control group, and (3) that heart rate (HR) and/or heart rate variability (HRV) were parameters of interest in the study. Results: Of the 1,544 articles screened, 54 were selected for full-text review and 6 studies met the inclusion criteria. Assessment of HRV using different standard time domain, frequency domain, and nonlinear domain approaches confirmed the presence of an impaired cardiac ANS function in frail compared to nonfrail participants. Furthermore, HR changes while performing a clinical test (e.g., the seated step test or the lying-to-standing orthostatic test) were decreased in the frail group compared to the nonfrail group. Conclusions: The current systematic review provides evidence that the cardiac ANS is impaired in frail compared to nonfrail older adults, as indicated by a reduction in the complexity of HR dynamics, reduced HRV, and reduced HR changes in response to daily activities. Four out of 6 included articles recruited only female participants, and in the other 2 articles the effect of gender on impairment of cardiac ANS was insufficiently investigated. Therefore, further studies are required to study the association between cardiac ANS impairments and frailty in males. Furthermore, HRV was studied only during static postures such as sitting, or without considering the level of activity as a potential confounder. Accordingly, simultaneous measurement of both physiological (i.e., HRV) and kinematic (e.g., using wearable sensor technology) information may provide a better understanding of cardiac ANS impairments with frailty while controlling for activity.

Prevalence of Ventricular Ectopy in Older Adults across Different Frailty Levels

“…Frail people are more vulnerable to acute and chronic conditions such as cardiac surgery and heart disease (e.g., myocardial infarction and heart failure) [3,4]. Also, frailty is higher in older adults with cardiovascular disease [3,5].…”

Statistical study of the fluctuations in the heart rhythm in subjects of different ages, in rest and with physiological stress

“…A system may look resilient in resting conditions, but if their circumstances change dramatically, it will collapse. It has been proposed to quantify frailty and resilience by the statistical study of the evolution in time (or time series) of a key variable of the system [1,2].…”

“…The human body is resilient in youth and health, but can become frail with disease or ageing. Frailty is usually studied from a clinical point of view [6,7], but recently it has been proposed to study the physiological origins of age-associated frailty [6], e.g., by evaluating the state of the autonomous nervous system which is one of the major adaptive systems of the human body, and which can be assessed in a non-invasive way by measuring the variability of the heart rate [2,1].…”

“…It has been found that with aging, HRV decreases and younger people tend to have a larger HRV response in the face of stressors [8]. HRV as a function of age-associated frailty has been studied mostly in a resting state; some studies have considered HRV in some specific stressed conditions, such as standing upright or the seated step test, and for frail subjects impaired ANS function and a decrease of heart rate response in the face of stressors has been found; however, responses from resting to different stressed conditions have not been studied systematically [2].…”

“…Recently, it has been proposed to quantify frailty or resilience by a statistical study of time series [1]. One of the most studied physiological variables is heart rate variability (HRV), that has been associated to physiological frailty [2]. In this work, we carried out short cardiovascular monitoring (5 minutes) and studied the ANS response in the face of different stressors.…”