Auditory, Visual and Postural Reaction Time Among Middle Aged Type 2 Diabetics and Healthy Individuals – A Cross-Sectional Study

iabetes mellitus (DM) is a group of metabolic diseases characterized by high blood sugar either because the body does not produce enough insulin or because cells do not respond to the insulin that is produced. (1) According to International Diabetes Federation, globally an estimated 425 million adults are living with DM of which 74 million cases are Indians. The average age of onset is 42.5 years (2). Balance is defined as the ability to maintain the body‟s center of gravity within its Base of Support (BOS) and can be categorized by either static or dynamic balance (3). Both static and dynamic balance requires effective integration of visual, vestibular, and proprioceptive inputs to produce an efferent response to control the body within its BOS (4-5). Type 2 DM may involve peripheral as well as central nervous system and can often D 1. Assistant Professor, MGM College of Physiotherapy and Hospital. Affiliated to Maharashtra University of Health Sciences (MUHS) Nasik, India. 2. BPT, MGM College of Physiotherapy and Hospital. Affiliated to Maharashtra University of Health Sciences (MUHS) Nasik, India.


Introduction
iabetes mellitus (DM) is a group of metabolic diseases characterized by high blood sugar either because the body does not produce enough insulin or because cells do not respond to the insulin that is produced. (1) According to International Diabetes Federation, globally an estimated 425 million adults are living with DM of which 74 million cases are Indians. The average age of onset is 42.5 years (2).
Balance is defined as the ability to maintain the body"s center of gravity within its Base of Support (BOS) and can be categorized by either static or dynamic balance (3). Both static and dynamic balance requires effective integration of visual, vestibular, and proprioceptive inputs to produce an efferent response to control the body within its BOS (4)(5). Type  cause changes in the somatosensory, vestibular, visual and auditory systems affecting reaction time (RT) of an individual (1). RT has physiological significance and is a simple and non-invasive test for peripheral as well as central neural structures. Limited reports are available from India showing the effects of diabetes on the processing of signals and also on peripheral nerves. Keeping this in mind, the present study was planned. The aim of the present study was to compare Visual, Auditory and Postural RT among middle aged Type 2 diabetics and Healthy individuals.

Materials and Methods
Sample size n= 98 per each group was calculated using G-power software keeping confidence level 95% and error 5%. 258 participants were screened from three tertiary care health set-up and 200 participants met the inclusion and exclusion criteria. Written informed consent was obtained before commencement of study. Inclusion criteria were age group 45-60 years, both males and females, BMI ranging from 18.5-29.9 kg/m 2 , visual acuity normal or corrected: 6.6 or 5.6) and auditory acuity normal: 0-20 dB. 100 clinically diagnosed patients of T2DM who are on oral medication and of duration more than 5 years were included in the diabetic group and 100 healthy participants were included in the healthy group. Participants on insulin, reduced sensory and pain perception in the extremities of limbs, H/O neurological, cardiovascular, respiratory, chronic and acute musculoskeletal conditions that can affect the test and H/O Smokers and Alcoholics were excluded.

ART
Test was done using Inquisit 4.0 computer software released in 2013 by Millisecond Software in Seattle, Washington. The participant to be tested sits on a chair in front of the computer screen and is asked to wear the earphone which is attached to the computer. A white screen appears and only sound can be heard, the participant"s task is to press the spacebar with his/her dominant hand as soon as the sound is presented. Fastest, slowest and average RT was recorded.

VRT
Test was also done using Inquisit 4.0 computer software. The participant to be tested sits on a chair in front of the computer screen. A fixation cross is presented on the screen that is followed after variable time intervals by a visual target stimulus (here red circle). The participant"s task is to press the spacebar as soon as the fixation cross is converted into red circle. Fastest, slowest and average RT is recorded.

In RDT
The participant was made to sit with their dominant forearm resting on a flat horizontal table surface, with the open hand at the edge of the surface. When the examiner suspends and releases the ruler vertically the participant is instructed to catch it as quickly as possible. The distance the ruler fell was recorded in centimeter. Three readings were taken and the mean was calculated. This distance was converted into time by using the formula, t=√ where, d is the distance travelled by the ruler and g is the acceleration of gravity (9.8 m/s²).

Balance test using Wobble disc board
 WB stance wide base of support (BOS): The participant has to stand on WB with legs apart so that the feet touch the edge of the board and try to maintain the balance so that they don"t fall.  WB stance narrow BOS: The participant has to stand on WB with legs together so that the feet is in the center board and try to maintain the balance so that they don"t fall.
Downloaded from ijdo.ssu.ac.ir at 5:44 IRDT on Sunday June 6th 2021 TUGT The person to be tested has to stand up from a chair and walk 3 meters, turn around and walk back. Timer starts when the therapist says "Go" and stopped when the patient"s pelvis touches the chair. Three readings were recorded and the mean was calculated.

Statistical analysis
The statistical analysis was done in SPSS 16 software. All data sets analyzed passed a normality test, therefore a parametric test was used. For comparing diabetic and healthy group "Independent sample T-test" was done. For all tests, the level of significance used was P-value< 0.05.

Ethical considerations
Ethical approval was obtained for the crosssectional study from institutional ethical review board committee (N-EC/2019/SC/04/ 68).

Demographic information participants
There were200 participants participated in this study out of which 100 were diabetic and 100 were healthy.  (Table 1).

Comparing the reaction time between diabetic and healthy participants.
ART Total: P-value≤ 0.0001 for fastest ART and average ART shows that the test is statistically significant (P-value< 0.05), where ART in healthy group was faster compared to diabetic group. Fast ART: P-value= 0.334 for fastest ART among diabetic females and males, and P-value= 0.764 among healthy females and males shows that the test is not statistically significant (P-value> 0.05) in both the groups. However, P-value= 0.001 for fastest ART among female diabetic and healthy participants, and P-value= 0.011 among male diabetic and healthy participants in both the groups shows that the test is statistically significant (P-value< 0.05). Slow ART: P-value= 0.200 for slowest ART among diabetic females and males, shows that the test is not statistically significant (P-value> 0.05), while P-value= 0.023 among healthy females and males shows that the test is statistically significant (P-value< 0.05). However, P-value= 0.011 for slowest ART among female diabetic and healthy participants shows that the test is statistically significant (P-value< 0.05), while P-value= 0.546 among male diabetic and healthy participants shows that the test is not statistically significant (P-value> 0.05). Average ART: P-value= 0.646 for average P-value= 0.731 among female diabetic and healthy participants, and P-value= 0.239 among male diabetic and healthy participants in both the groups also shows that the test is not statistically significant (P-value> 0.05).
No. of times edges touches floor: P-value= 0.000 among diabetic and healthy groups shows that the test is statistically significant (P-value< 0.05), where the edges of the WB touched the floor more times in the diabetic group compared to healthy group. P-value= 0.784 among diabetic females and males, and P-value= 0.580 among healthy females and males shows that the test is not statistically significant (P-value> 0.05) in both the groups. However, P-value= 0.001 among female diabetic and healthy participants, and P-value= 0.001 among male diabetic and healthy participants shows that the test is statistically significant (P-value< 0.05), where the females and males in the diabetic group touched the edges of the WB more times than healthy females and males. TUGT: P-value= 0.023 for TUGT shows that the test is statistically significant (P-value<0.05), where the healthy group performed better than diabetic group. P-value= 0.485 for TUGT among diabetic females and males, and P-value= 0.369 among healthy females and males shows that the test is not statistically significant (P-value> 0.05) in both the groups. However, P-value= 0.029 for TUGT among female diabetic and healthy participants shows that the test is statistically significant (P-value< 0.05), while P-value= 0.305 among male diabetic and healthy participants shows that the test is not statistically significant (P-value> 0.05) ( Table  2).

Discussion
The results of our study suggested that; the fastest ART and average ART values were statistically significant among diabetic and healthy groups, where the healthy group performed better than the diabetic group. The delay in DM group may be due to increase in blood glucose level that increases blood viscosity leading to circulatory disorders affecting both large and microscopic size blood vessels, especially involving stria vascularis that in turn causes damage at multiple neural units (hair cells) at structural level. The extent of tissue ischemia and hypoxia in DM group can lead to beginning of auditory nerve damage and hence delayed ART (6). Similar studies found a 30ms difference in ART values between diabetics and the control group (7). Our study result states that fastest VRT, slowest VRT and average VRT were statistically significant among diabetic and healthy groups, where the healthy group performed better than the Diabetic group. The delay in DM group may be due to constant hyperglycemia causing narrowing of the retinal arteries resulting into reduced retinal blood flow leading to dysfunction of neurons at inner retina which later extends to outer retina as well. This may cause beginning of retinal dysfunction and degeneration of the neurons and glial cells resulting in delayed response (8)(9). Similar studies show doubling of VRT in diabetics versus that measured in healthy individuals (17).
Our study results states VRT is more delayed than ART in both the groups, (10-13) the common reason on comparison with healthy individuals could be due to increase in blood glucose level in DM group, that causes glucose oxidation and release of free radicals (like peroxynitrite) leading to axonal fragmentation and degeneration of both type nerve fibers, decreasing nerve diameter and delayed transmission of nerve impulses leading to delayed response (10,(13)(14)(15). RT is dependent on several factors from arrival of stimuli, processing unit to muscle response depending on different parameters (16). In VRT, the arrival of stimulus involves 6 step chemical changes that convert photons to bioelectric stimuli along with activation of many collateral pathways in association with visual areas. Whereas ART involves single step chemical changes that convert pressure wave to bioelectric stimuli. Studies have shown that auditory stimulus takes only 8-10 milliseconds to reach the brain, whereas visual stimulus takes 20-40 milliseconds in healthy individuals (17). In DM, dysfunction and degeneration of retinal cells causes delay in 6 step chemical changes to bioelectrical stimuli along with delay in activation of associated pathways leads to reduced and delayed VRT when compared to ART, ART response is much quicker among diabetic group. Our findings are supported by many recent studies stating that ART is significantly faster than VRT among diabetic individuals when compared to healthy groups (18)(19).
Our study showed that RDT was not statistically significant. This states that there is no marked change in hand-eye coordination among diabetic and healthy groups. A comparative study by S. Bhat and S. Kumar between middle age and geriatric type 2 diabetic groups concluded the RT and coordination among middle aged DM group was significantly faster than geriatric DM group (20). The mean time taken by middle aged group was 0.19 (±0.01) seconds (20) which was in hand with our study that is 0.18 (±0.27) seconds.
In the present study, the result for WB stance wide BOS and narrow BOS-1 st time edge touches floor in both diabetic and healthy groups is not statistically significant. WB stance wide BOS and narrow BOS -number of times the edges touch the floor is statistically significant in both the groups. This could be associated with beginning of somatosensory dysfunction in lower limb among diabetic group that decreases ankle joint proprioception and vibration senses that leads to inappropriate timing and faulty activation of ankle strategy on dynamic wobble board surface. This in-coordination along with hyper activation of hip strategy (21) caused repetitive touching of edge of WB to the floor in DM group. The reason for delayed postural reaction and reduced balance performance could be due to initiation of somatosensory dysfunction leading to delayed response from CNS, late activation of ankle-hip strategies causing impaired dynamic balance in DM group leading to high risk of falls (22)(23). This study finding is supported by El-Kader who conducted study on elderly type 2 diabetics stating, reduced balance performance and high risk of fall using Biodex Balancing System (24). According to our result there was a statistical significance among diabetic and healthy groups in TUGT suggesting time taken in diabetic group was longer compared to healthy group when surface is static. This could be due to somatosensory dysfunction and poor contraction of leg muscle strength could be the reason for decrease in speed while performing the test in DM group. Supported by a  (25). It was also observed that along with slowness in speed, time taken during turning phase was relatively more in diabetic group than healthy group. This could be due to in the early stage, poor glycemic control in DM group that causes somatosensory and vestibular dysfunction. Vascular damage to vestibular systems leads to degeneration of type 1 hair cells, nerve myelin sheath thinning, reduced axonal fiber diameters eventually causing beginning of vestibular dysfunction. Similar results were found by Alvarenga et al. stating elderly with diabetes presented worse performance in both functional mobility and dual task, whereas in our study middle aged diabetic group were only included and showed similar when compare with healthy group suggesting high risk of falls among diabetic group (26). We found that among diabetic and healthy group RT was not statistically significant whereas within diabetic and healthy group RT was statistically significant in males and females for ART, VRT, TUGT (females) and WB test, suggesting DM affects equally irrespective of gender causing delayed RT later resulting in impaired balance and high risk of falls. The gender component is contradictory with a recent study concluding the impairments due to diabetes strongly affect women than men (27)(28). Our study included 42% women in diabetic group with normal BMI this could be one of the reasons where no significant changes were seen in terms of RT. In our study we had included middle aged T2DM participants who showed delay in ART, VRT, Ruler drop test, WB test and TUGT when compared to healthy participants. Although there was a significant difference in all the components and test, all the participants didn"t show any clinical signs and symptoms in terms with vision, auditory function and balance impairment. This finding is suggesting the vascular damage caused by DM is slow and severe over the time. Delayed RT in middle age type II DM could be consider as one of the signs for beginning of pathological changes occurring in visual, auditory and balance function which could result in functional impairment. The limitation of our study was use of simple RT to assess visual, auditory and hand-eye coordination. Consideration of Choice RTs could show variation in the result as it"s more functional based. In ruler drop test, use of 12 inches ruler (30 cm) could be one of the drawbacks as few participants were unable to catch hold of ruler on command (the trial was repeated until they catch it). Also, the minimal unavoidable human error during the test while measurement of distance travelled by the ruler. This could be the reason there was no significant difference seen in the test. Clinical implication of the study would be early balance assessment should be considered at the time of diagnosis of T2DM. Conventional balance intervention should be considered and recommended to the patients after the diagnosis of T2DM irrespective of age and gender to prevent long term deterioration in balance and to reduce risk of falls. Future recommendation from our study could be adding up intervention and finding its effect among DM population in terms of RT.

Conclusions
Our study concludes that in diabetic group there was a significant delay in VRT, ART and postural RT when compared to healthy individuals due to reduced response of sensory stimuli and receptor in visual, auditory, somatosensory and vestibular system. There was no significant difference in Ruler drop test between both the groups. There was no significant difference in terms of gender in RT stating DM impairments affects equally in all gender.
IRANIAN JOURNAL OF DIABETES AND OBESITY, VOLUME 13, NUMBER 1, SPRING 2021 Funding self-funded study.