Frailty and the degradation of complex balance dynamics during a dual-task protocol

Abstract

Background: Balance during quiet stance involves the complex interactions of multiple postural control systems, which may degrade with frailty. The complexity of center of pressure (COP) dynamics, as quantified using multiscale entropy (MSE), during quiet standing is lower in older adults, especially those with falls. We hypothesized that COP dynamics from frail elderly individuals demonstrate less complexity than those from nonfrail elderly controls; complexity decreases when performing a dual task; and postural complexity during quiet standing is independent of other conventional correlates of balance control, such as age and vision.

Methods: We analyzed data from a population-based study of community-dwelling older adults. Frailty phenotype (nonfrail, prefrail, or frail) was determined for 550 participants (age 77.9 +/- 5.5 years). COP excursions were quantified for 10 trials of 30 seconds each. Participants concurrently performed a serial subtraction task in half of the trials. Complexity of balance dynamics was quantified using MSE. Root-mean-square sway amplitude was also computed.

Results: Of the 550, 38% were prefrail and 9% were frail. Complexity of the COP dynamics in the anteroposterior direction was lower in prefrail (8.78 +/- 1.91 [mean +/- SD]) and frail (8.38 +/- 2.13) versus nonfrail (9.20 +/- 1.74) groups (p < .001). Complexity reduced by a comparable amount in all three groups while performing the subtraction task (p < .001). Quiet standing complexity was independently associated with frailty after adjusting for covariates related to balance while sway amplitude was not.

Conclusion: Cognitive distractions during standing may further compromise balance control in frail individuals, leading to an increased risk of falls.

Figures

Figure 1.

Power spectral density of center of pressure (COP) time series from a nonfrail participant (black) and of the calibration signal (gray) in the anteroposterior (AP) and mediolateral (ML) directions. The signal-to-noise ratio between 7.5 and 60 Hz in the AP direction (top) is more than 10, but in ML direction, it is less than 1. Therefore, no further analyses of the COP time series in the ML direction were performed.

Figure 2.

Anteroposterior (AP) center of pressure time series from representative nonfrail and frail participants, root-mean-square (RMS) values, multiscale entropy (MSE) curves and CI values. Both the original and the high-pass filtered time series are presented during quiet stance and dual task. The RMS amplitudes were calculated for the original signals. The MSE plots and the CI values were derived from the high-pass filtered time series.

Figure 3.

Multiscale entropy (MSE) analysis of COP sway dynamics for the nonfrail, prefrail, and frail groups during quiet standing and dual-task conditions. The MSE curves were obtained by connecting the group mean values of sample entropy for each scale. The error bars represent standard errors. The MSE curves for the surrogate shuffled time series (see text) are also presented.

Figure 4.

Complexity indices (CI) for nonfrail, prefrail, and frail groups during quiet standing and dual-task conditions. Solid bars and error bars represent group mean values and standard errors, respectively. The CI for the frail (p = .003; post hoc LSD) and prefrail (p < .001) groups were lower than for the nonfrail group and dropped further with dual task (p < .001). Prefrail and frail groups were not different (p = .2).