Dihogo de Matos

Health human functioning requires the integration of a complex network of physiological systems (e.g.,autonomic, cardiovascular, and respiratory systems) that enable the organism to maintain homeostasis in the face of external stressors (e.g., standing from a bed or chair, walking). If these physiological integrations are not well adjusted to reach the task's required demands, both females and males will struggle to perform even activities of daily living (ADLs). Impairment/dysfunction of these physiological systems would expose them to higher risks of frailty, chronic diseases, and falls. For this reason, an orchestrated tight and complex control and regulation of these systems play a critical role in matching physiological demands and supply for homeostasis maintenance. Homeostatic dysregulation compromises these rapid adjustments in the autonomic, cardiovascular, and respiratory regulatory mechanisms and is mostly present in more vulnerable populations (older adults, frail, and people with chronic diseases). Frailty is a condition characterized by the degradation of biological and functional reserves to tolerate stressors resulting in a decreased ability to maintain homeostasis under stress. 

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The autonomic nervous system (ANS) including the cardiac ANS has a crucial role in maintaining homeostasis in almost all physiological functions. This function becomes more pronounced when responding to external stressors such as ADLs. It has been postulated that frail older adults exhibit a progressive homeostatic dysregulation in physiological systems, including the cardiac ANS which could be a factor that accelerates the frailty process. Furthermore, the aging process differs significantly between sexes, where cardiovascular anatomy, hemodynamics, and autonomic nervous system differences have been identified. Studies have shown intriguing findings related to frailty and sex differences. For example, females present lower physiological dysregulation levels, longer life expectancy, despite higher pre-frailty and frailty scores, and higher prevalence of disability than males. This female-male frailty paradox is intriguing and poorly understood. The exact physiological processes that underpin sex differences are unclear and difficult to pinpoint. The assessment of physiological systems can be a useful approach to provide information on the mechanisms involved in the pathogenesis of various diseases and the frailty phenotype. One of these assessments is the analysis of heart rate variability (HRV). The HRV can be useful to diagnose and monitor some impairments that are related to ANS. 

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Currently, there are several mobile and easy-to-use heart rate monitors that allow keeping a record of the HRV. Commercial devices, like Garmin Vivosmart® 4 heart rate monitors, have been used for HRV analysis. Despite the potential benefits of accessing this information, this device has not been evaluated in laboratory conditions. Therefore, this proposal aims to: (1) evaluate the agreement and reliability between HRV analysis derived from Garmin Vivosmart® 4 heart rate monitor and HRV analysis from a standard laboratory electrocardiogram (ECG) during postural transition. (2) determine the sex difference in the HRV analysis in older adults with frailty during orthostatic stress. HRV will be collected via an electrocardiogram (ECG) module (Finapres Medical System, Arnhem, The Netherlands). Data will be recorded and analyzed using LabChart 8.0 (AD Instruments, Colorado Springs, USA). The orthostatic stress test (postural transition) will disturb homeostasis by altering pressure gradient distribution due to changes caused by gravity. Changing posture requires a quick autonomic nervous system and cardiovascular adjustments revealing how these systems contribute to autonomic and cardiovascular regulation. 

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Participants will perform three types of postural transitions: (a) sit-to-stand, (b) lie-to-stand, and (c) lie-to-sit. Each person will complete three trials in a randomized and counterbalanced order by block. The protocol will consist of 10 minutes in the initial posture (lying or sitting), then transitioning to sitting or standing and remaining in that body position for 7 minutes. A 10 min break will be given between each trial. The sample will be composed of 5 females and 5 males older adults living with frailty.

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