Cognitive dysfunction mediates the effects of poor physical fitness on decreased functional independence in heart failure

Abstract

Aim: Heart failure (HF) patients require assistance with activities of daily living (ADL). Poor physical fitness has recently been identified as a contributor to the high rates of disability in HF, though the mechanisms for such effects are unclear. Although not previously examined, decreased fitness might adversely impact ADL in HF through its known association with cognitive impairment, a key correlate of self-care abilities in this population. We sought to test this possibility using a model-based approach.

Methods: A total of 197 patients with HF completed a physical fitness test and a neuropsychological test battery. A total ADL composite was derived from the Lawton Brody scale. Structural equation modeling tested whether cognitive function mediated the association between physical fitness and total ADL.

Results: Fitness was reduced, and cognitive dysfunction and impaired ADL were prevalent. The initially significant association between fitness and total ADL was attenuated when cognitive function was introduced as a mediator. This model showed good fit (comparative fit index=0.91: root mean-square error of approximations=0.077) with a significant indirect pathway between physical fitness and total ADL through cognitive function: Decreased physical fitness was associated with cognitive dysfunction (β=0.35), which predicted greater assistance with ADL (β=0.22).

Conclusions: Poor physical fitness might lead to decreased functional independence in HF through its negative effects on cognitive function. Prospective studies are required to confirm our findings, identify other mechanisms by which poor fitness impacts ADL, and examine whether exercise interventions can improve cognition and help preserve ADL independence in HF.

Keywords: activities of daily living; cognitive function; heart failure; physical fitness.

Figure 1. Cognitive Function Mediates the Effects of Physical Fitness on ADL Function in Patients with Heart Failure (N = 197)

Notes. The pathway between cognitive function and Digits was fixed. Standardized parameters estimates are presented in the model; significance levels for these paths are based on the unstandardized estimates. Pathways connected hypertension (β = −0.17) and type 2 diabetes mellitus (β = −0.21) demonstrated significant effects on the latent construct cognitive function. They were not included in the Figure for ease of presentation. Abbreviations—2MST = 2 minute step test; TMTA = Trail Making Test A; TMTB = Trail Making Test B; Digits = Digit Symbol Coding; LNS = Letter Number Sequencing; CVLT= California Verbal Learning Test Long Delay Recall; ADL = Activities of Daily Living *p < .05