1. Baseline characteristics of the participants
The primary sample size for this cross-sectional study was 260 containing 126 cognitive normal control and134 MCI. The baseline clinical characteristics was shown in Table 1. The data showed that in the overall population, the participants with MCI had higher percentage of female gender, higher body weight as well as BMI, and lower educational level with 6–9 years accounting for 42.5% of the group. The two groups had similar comorbid conditions such as cardiovascular diseases, subjective sleep disorder and family history of AD. The MoCA sores were 26.72 ± 1.98 in NC group and 21.52 ± 2.35 in MCI group, indicating a significant difference between the two groups (P < 0.05). Meantime, there was statistical difference in MMSE scores between them. To balance the significant confounding variables potentially affecting cognitive and gait functions, a matched population at a ratio of 1:1 in NC and MCI group was created using propensity score matching (PSM) method after adjusting gender, age, height, weight, and educational years. Eventually, a total of 212 subjects, 106 in each group, were matched and most of the significant imbalances were removed without yielding other imbalanced variables between the two groups. As expected, significant difference on MMSE and MoCA remained existing between the NC and MCI groups after PSM matching.
Table 1
Baseline characteristics of the overall and matched populations
Characteristics | Overall Population | Propensity Score-Matched (1:1) Population |
NC (n = 126) | MCI (n = 134) | P | NC(n = 106) | MCI(n = 106) | P |
Age (years) | | | 0.122 | | | 0.319 |
50 ~ 59 | 55 (43.7) | 42(31.3) | | 44(41.5) | 33(31.4) | |
60 ~ 69 | 55 (43.7) | 70(52.2) | | 47(44.3) | 56(53.3) | |
70 ~ 79 | 16 (12.7) | 20 (14.9) | | 15(14.2) | 15(14.3) | |
≥ 80 | 0 (0.0) | 2 (1.5) | | 0(0.0) | 1(1.0) | |
Female n (%) | 89 (70.6) | 74 (55.2) | 0.010 | 69(65.1) | 65(61.3) | 0.669 |
Height (cm) | 163.08 ± 7.33 | 163.52 ± 8.11 | 0.647 | 163.56 ± 7.48 | 162.86 ± 7.51 | 0.499 |
Body weight (kg) | 61.46 ± 9.84 | 65.52 ± 10.83 | 0.002 | 63.02 ± 9.95 | 63.96 ± 10.47 | 0.502 |
BMI (kg/m2) | 23.16 ± 2.87 | 24.32 ± 2.97 | 0.002 | 23.54 ± 2.86 | 24.04 ± 3.06 | 0.210 |
Education n (%) | | | < 0.001* | | | 0.068 |
< 6 years | 12 (9.5) | 13 (9.7) | | 12(11.3) | 10(9.4) | |
6–9 years | 25 (19.8) | 57 (42.5) | | 25(23.6) | 43(40.6) | |
9–12 years | 53 (42.1) | 46(34.3) | | 50(47.2) | 37(34.9) | |
> 12 years | 36 (28.6) | 18 (13.4) | | 19(17.9) | 16(15.1) | |
Martial status (%) | | | 0.442 | | | 0.318 |
Single | 0(0.0) | 1(0.8) | | 0(0.0) | 1(0.9) | |
Married | 121 (96.0) | 122 (91.0) | | 102(96.2) | 95(89.6) | |
Divorced | 1(0.8) | 2(1.5) | | 1(0.9) | 2(1.9) | |
Widowed | 4(3.2) | 9(6.7) | | 3(2.8) | 8(7.5) | |
Living alone n (%) | 9 (7.1) | 15(11.2) | 0.259 | 7(6.6) | 14(13.2) | 0.167 |
Exercise n (%) | | | 0.156 | | | 0.149 |
Never | 8(6.3) | 6(4.5) | | 6(5.7) | 5(4.7) | |
< 3 times/week | 49(38.9) | 39(29.1) | | 43(40.6) | 30(28.3) | |
> 3 times/week | 69(54.8) | 89(66.4) | | 57(53.8) | 71(60.7) | |
Smoking n (%) | 31 (24.6) | 48 (35.8) | 0.075 | 31(29.2) | 32(30.2) | 0.358 |
Alcohol use n (%) | 29 (23) | 40 (29.9) | 0.326 | 28(26.4) | 27(25.5) | 0.809 |
Hypertension n (%) | 46(53.6) | 57(42.5) | 0.321 | 44(41.5) | 44(41.5) | 1.000 |
Diabetes n (%) | 11 (8.7) | 20 (14.9) | 0.123 | 9(8.5) | 17(16.0) | 0.094 |
Hyperlipemia n (%) | 38 (30.2) | 41(30.6) | 0.939 | 33(31.3) | 31(29.2) | 0.881 |
Coronary arterial disease (%) | 20 (15.9) | 18(13.4) | 0.578 | 17(16.0) | 14(13.2) | 0.698 |
Sleep disorder n (%) | 67 (53.2) | 65 (48.5) | 0.452 | 59(55.7) | 54(50.9) | 0.582 |
Family history n (%) | 14 (11.1) | 10 (7.5) | 0.310 | 10(9.4) | 10(9.4) | 1.000 |
MMSE | 28.91 ± 1.17 | 27.35 ± 1.65 | < 0.001 | 28.90 ± 1.05 | 27.30 ± 1.64 | < 0.001 |
MoCA | 26.72 ± 1.98 | 21.52 ± 2.35 | < 0.001 | 26.22 ± 2.39 | 21.01 ± 2.52 | < 0.001 |
2. Important Feature Selection Of Gait Parameters Associating With Cognitive Function
In this study, a panel of spatiotemporal and kinematic gait parameters as listed in Fig. 1 were measured using a portable sensor in all the enrolled participants. To analyze the association between gait performance and cognitive function in the matched population, all gait parameters (31 gait characteristics) were pooled into a random forest and a LASSO regression model to select important features contributing to MCI in single task and three dual-task modes. As shown in Table 2, in different task modes, top 5 important features based on random forest model were selected and 5 ~ 6 significant features at λmin or λ1SE in LASSO model were shown. For the single task, the common ranked features included variability of stride length and thigh twitch acceleration. While, in double task of serial 100-7 test and naming animals test, DTC and gait cycle of mid stance and terminal swing were common features associated with MCI. In words recall test, only DTC was selected as common feature by the two algorithms. Therefore, selection preference could be observed in different models, and the combined features were further analyzed in each task.
Table 2
Important gait characteristics selection associated with cognitive function in matched populations
Task | Random forest | LASSO regression | The combined features |
Features | Importance | Features | Importance |
Single task | Stride length CV | 0.577 | Thigh swing work | -0.120 | Stride length CV Stride time CV Load response Initial swing Mid swing Thigh twitch acceleration Thigh swing work |
Mid swing | 0.555 | Load response | -0.012 |
Thigh twitch acceleration | 0.531 | Stride length CV | 0.010 |
Stride time CV | 0.524 | Thigh twitch acceleration | 0.001 |
Initial swing | 0.511 | | |
Subsequent 100-7 | Mid stance | 0.592 | Swing time | -0.484 | Stance time CV Swing time Terminal swing Mid stance Thigh swing work DTC |
Thigh swing work | 0.547 | Terminal swing | -0.032 |
Stance time CV | 0.540 | Mid stance | 0.002 |
DTC | 0.534 | DTC | 0.002 |
Terminal swing | 0.528 | | |
Naming Animals | Terminal swing | 0.565 | Stride length | -0.271 | Stride length Stride length CV Terminal swing Mid stance DTC Stride time CV Swing time Swing time CV |
Stride time CV | 0.533 | Swing time | -0.225 |
Swing time CV | 0.528 | Terminal swing | -0.039 |
DTC | 0.526 | Mid stance | 0.013 |
Mid stance | 0.526 | Stride length CV | 0.008 |
| | DTC | 0.003 |
Words recall | Stride time CV | 0.568 | Swing time | -0.117 | Velocity Stride length Stride time CV Swing time DTC Mid stance Terminal swing Thigh swing work Thigh twitch acceleration |
Thigh swing work | 0.543 | Terminal swing | -0.015 |
Velocity | 0.540 | Thigh twitch acceleration | -0.021 |
DTC | 0.532 | DTC | 0.002 |
Stride length | 0.522 | Mid stance | 0.001 |
3. Logistic Regression Analysis Of The Selected Gait Parameters Associating With Mci
To further delineate the association between the above selected important gait features and MCI, an univariate logistic model and a multivariate logistic model adjusting gender, age, height, body weight were created, and the odds ratio (OR) with 95% confidence interval (CI) and testing significance were shown in a forest plot in Fig. 2. In the single task, only stride length CV was identified as a risk factor for MCI in the adjusted logistic model (OR = 1.083, 95% CI: 1.012–1.060, P = 0.021). In serial 100-7 dual task, swing time and terminal swing phase were screened as two independent risk factors for MCI, with shorter swing period and lower terminal swing cycle indicating higher risk of MCI (OR = 0.001, 95% CI: 0-0.484 and OR = 0.792, 95% CI: 0.665–0.942). In dual task of naming animals, in addition to the above variables, mid stance phase, stride length CV and swing time were also contributing factors indicating MCI. When performing a word recall test, DTC, swing time mid stance, and terminal swing independently predicted cognitive impairment. Collectively, the logistic regression analysis suggested that mid stance, terminal swing, and swing time were filtered as common hallmarks of gait predicting cognitive functional decline.
4. Comparison Of Gait Parameters Between Normal Aging People And Cognitive Impaired Population
Based on the above results, we further traced and compared the changes of these filtered gait parameters in the two groups. As shown in the scatter-box plots in Fig. 3, stride length CV obviously increased in MCI subjects in the condition of single task and naming animals dual task test compared with NC group (P = 0.024 for each comparison). Although elevated stride length CV was also found in MCI under the dual tasks of serial 100-7 and words recall, it didn’t reach statistical significance. Mid stance and terminal swing phase are two temporal gait parameters accounting for approximately 18% and 11% of the whole gait cycle for normal adults, respectively. In our study, the mean mid stance of NC group was 19.59% in performing single task, which was not differed from MCI group of 19.73 ± 2.51% (P = 0.066). In the three dual tasks, the mean mid stance (%) of MCI group increased to 20.46% in serial100-7 test, 20.39% in naming animals test and 20.42% in words recall test, which were all significantly higher than that in NC group. For the terminal swing, the two groups had comparable percentage under single task condition; reduced terminal swing was found in MCI group than NC group when performing dual tasks. Likewise, there was no significant difference in the mean swing time between NC and MCI in single task; however, MCI group exhibited significantly decreased swing time than NC when performing the three cognitive tasks.
5. Effects Of Different Dual Cognitive Tasks On The Performance Of Gait Test
To elucidate the effect of different cognitive tasks on the performance of gait test, we compared the the above screened gait parameters, velocity and DTC between single task and three dual tasks as illustrated in Fig. 4. The ANOVA analysis revealed that there was statistical difference in the stride length CV among the different tasks both in NC group and MCI group (F = 8.819, P < 0.001 and F = 3.225, P = 0.026), and subjects tended to have higher stride length CV when performing the dual task gait tests, particularly in finishing the words recall test. The percentage of mid stance didn’t differ significantly under the four modes of tasks either in NC or MCI group. Statistical difference on percentage of terminal swing phase was shown among the four task modes in NC group (F = 3.96, P = 0.008) with significantly higher values in counting backward by 7 test and enumerating different animals. Whereas, this difference was not shown in MCI group. Besides, participants had higher expenditure in swing time when performing the dual tasks either in NC or MCI groups (F = 44.11, P < 0.001 and F = 18.32, P < 0.001, respectively), with a stepwise increase between serial 100-7 and naming animals, especially higher in words recall test than the other two dual tasks (both P < 0.05). Because velocity was an important hallmark parameter of gait, we then evaluated the changes of velocity under different tasks. Notably, slower speed was monitored in dual tasks in both NC and MCI groups, and the mutual comparison following ANOVA suggested much lower velocity in words recall test comparing with counting backward by 7 test and enumerating different animals test (both P < 0.05). Likewise, significantly higher DTC on velocity was required when finishing the words recall test than the others in both NC and MCI groups.