Accelerometer approach for anticipatory postural adjustments assessment during step initiation in patients with leprosy

Abstract

Anticipatory postural adjustments (APAs) involve a complex coordination of sensorimotor information that can be impaired in diseases that affect nerve conduction. Assessing APAs typically requires costly video recording technology, posing a challenge to the study of postural changes. This hurdle is compounded in impoverished communities affected by diseases such as leprosy, which often receive limited government support. Recent years have seen the validation of inertial sensors in wearable devices and smartphones for APA analysis in diverse populations, including adults, the elderly and people with Parkinson's disease. This progress offers economically efficient alternatives for the study of APA in leprosy. Do patterns of activation of anticipatory postural adjustment differ between leprosy patients and healthy controls? We also investigated the validity and replicability of APAs recorded in leprosy patients using inertial measurements and video capture recordings. Thirty healthy individuals in the control group and 30 individuals with leprosy in the leprosy group performed ten gait initiation trials. To record the APA for gait initiation, the participants stood on a 2 m platform. Each participant was informed that the experimenter would give an signal, after which the participant would initiate a two-step walk on the platform. Inertial recordings (low-cost method) and video capture recordings (gold-standard method) from center of mass displacements were used to extract the APA before gait initiation. The results show that APAs are similar between groups (control and leprosy), but leprosy patients have less consistent APAs. In addition, this study highlights the reproducibility and high correlation between the values of variables obtained from both instruments, the video recording as gold standard method and portable digital inertial sensor as a low-cost alternative method. These promising findings support the use of affordable inertial sensors to track and record APAs in underserved populations that lack easy access to gold standard methods such as video recording. This approach has the potential to improve the therapeutic care and rehabilitation of these patients. Although not currently part of official protocols for leprosy patients, this assessment method could prove particularly valuable in situations where significant sensorimotor impairments are suspected or documented.

Keywords: Anticipatory postural adjustments; Gait initiation; Leprosy; Wireless triaxial accelerometer.

Figure 1

Time series of left heel displacement (A) and medio-lateral acceleration at L5 (B) obtained from the image capture system. Dashed line at 0 s represents the moment of heel-off (Tzero), red dashed line indicates the initiation of the initial swing phase (APA), and the interval between this point and Tzero represents APAonset (red arrow). The acceleration interval between the baseline and the maximum acceleration of the Center of Mass (COM) during APA represents APAamp (blue arrow), and the time interval between the initiation of APA and the moment of maximum acceleration of the COM during APA represents PEAKtime (green arrow).

Figure 2

Waveforms of anticipatory postural adjustments (dashed rectangles) obtained from the video capture system in the control group (A), inertial sensor in the control group (B), video capture system in the Leprosy group (C), and inertial sensor in the Leprosy group (D). The black lines represent the grand mean of each data group, and the red area (in controls) and blue area (in leprosy) represent the confidence interval of the records for each data group, considering a significance level of 95%.

Figure 3

Concordance analysis between the same variables measured from the recordings obtained by the video capture (elements in red) and the inertial sensor (elements in blue). Solid lines represent the bias between the measurements, dashed lines represent the limits of agreement, and the shaded areas around the bias indicate the confidence interval of the bias. The bias was considered significant when the confidence interval includes the value zero of bias. (A) Concordance analysis for APA onset from leprosy group. (B) Concordance analysis for APA onset from control group. (C) Concordance analysis for APA amplitude from leprosy group. (D) Concordance analysis for APA amplitude from control group. (E) Concordance analysis for APA time to peak from leprosy group. (F) Concordance analysis for APA time to peak from control group.

Figure 4

Correlation between the measurements obtained with the video capture and the inertial sensor in both study groups. (A) APA onset, (B) APA amplitude, (C) APA time to peak.