Altered accelerator pedal control in a driving simulator in people with diabetic peripheral neuropathy

Abstract

Aim: To investigate whether the sensory-motor impairment attributable to diabetic peripheral neuropathy would affect control of the accelerator pedal during a driving simulator task.

Methods: A total of 32 active drivers, 11 with diabetic peripheral neuropathy (mean ± sd age 67±5.0 years), 10 with diabetes but no neuropathy (diabetes group; mean ± sd age 62±10 years), and 11 healthy individuals without diabetes (healthy group; mean ± sd age 60±11 years), undertook a test on a dynamometer to assess ankle plantar flexor muscle strength and ankle joint proprioception function of the right leg, in addition to a driving simulator task. The following variables were measured: maximal ankle plantar flexor muscle strength; speed of strength generation (Nm/s); and ankle joint proprioception (ankle repositioning error, degrees). In the driving simulator task, driving speed (mph), accelerator pedal signal (degrees) and the duration of specific 'loss-of-control events' (s) were measured during two drives (Drive 1, Drive 2).

Results: Participants with diabetic peripheral neuropathy had a lower speed of strength generation (P<0.001), lower maximal ankle plantar flexor muscle strength (P<0.001) and impaired ankle proprioception (P=0.034) compared to healthy participants. The diabetic peripheral neuropathy group drove more slowly compared with the healthy group (Drive 1 P=0.048; Drive 2 P=0.042) and showed marked differences in the use of the accelerator pedal compared to both the diabetes group (P=0.010) and the healthy group (P=0.002). Participants with diabetic peripheral neuropathy had the longest duration of loss-of-control events, but after one drive, this was greatly reduced (P=0.023).

Conclusions: Muscle function, ankle proprioception and accelerator pedal control are all affected in people with diabetic peripheral neuropathy, adversely influencing driving performance, but potential for improvement with targeted practice remains possible.

Figure 1

Example from a single participant's steering wheel signal to illustrate how the ‘loss‐of‐control events’ (quantified in seconds) were identified from the steering wheel signal (degrees) during driving. Portions of the wheel signal (Start–End) that abruptly exceeded the range seen during normal driving in terms of amplitude and/or frequency were identified. These periods were then summed and quantified as the total duration (seconds) in one single drive, and then normalized for the number of participants in each group (to obtain seconds per person).

Figure 2

(a) Speed of strength generation (SSG). (b) Maximal strength values. (c) Ankle repositioning error (ARE). All motor function testing was performed on the right leg using a joint angle of 10° plantar flexion in the three groups: healthy participants, participants with diabetes but no neuropathy, and participants with diabetic peripheral neuropathy (DPN). Values are mean and sd, n=32. *Significantly different, P<0.05.

Figure 3

(a) Driving speed (mph) during the first drive (black bars) and second drive (white bars) for each group: healthy participants; participants with diabetes but no neuropathy; and participants with diabetic peripheral neuropathy (DPN). (b) Duration of the loss‐of‐control events (seconds per person) during the first (Drive 1) and second (Drive 2) drives. Values are mean and sd, n=32. *Significantly different, P<0.05.

Figure 4

Accelerator pedal position frequency distribution plots. Each bar represents the time (seconds) the accelerator pedal spent in a specific position, from 0 (no pressure on the pedal) to a maximum of –20° (maximal pressure applied on the pedal) during driving. The graphs on the left side represent the original frequency distribution plots of each group: Healthy individuals (Healthy), people with diabetes but no neuropathy (Diabetes), and people with diabetic peripheral neuropathy (DPN); on the right side the ‘difference plots’ are obtained by subtracting one group plot from another. The change in colour indicates the significantly different DPN group's pedal use when compared to those of the Healthy and Diabetes groups (P<0.005). The upper panel represents the comparison between DPN and Healthy groups, while the lower panel represents the comparison between DPN and Diabetes groups.