Assessment of postural sway in people living with HIV/AIDS

Introduction: Motor changes are observed in people living with HIV/AIDS. These changes may be associated with the chronicity of infection, continued use of antiretroviral medication, and/ or the presence of comorbidities. Objective: The objective of the present study was to evaluate postural sway in people living with asymptomatic HIV/AIDS under treatment with highly active antiretroviral therapy. Methods: Twenty-seven subjects, recruited at an HIV referral center, aged between 30 and 40 years, participated in the study, divided into two groups: HIV group (n=12) and non-HIV group (n=15). The participants performed an experimental task, remaining on a force platform in a static position, in bipedal support and semi-tandem positions, in conditions with and without vision. Results: The results demonstrated that visual occlusion, when the bipedal base was adopted, generated significant differences in the area of oscillation and mean velocity in both groups. Differences were also observed in the area and mean velocity of both groups when the semi-tandem position was adopted without vision. When comparing the groups, it was possible to identify significant differences in the semi-tandem base with vision. Conclusion: Considering these results, it was found that postural oscillation was higher in the visual occlusion condition for both groups. Concomitant to this, we conclude that in the challenging condition, where the base of support is reduced, the HIV group presents greater oscillation (medial-lateral) than the non-HIV group.


INTRODUCTION
The advent of highly active antiretroviral therapy (HAART) has led to an increase in the life expectancy of people living with HIV/AIDS (PLHA) 1,2 . This has meant that PLHA are more exposed to the chronic effects of continued use of medication and infection [3][4][5] . The present conjuncture causes several alterations in PLHA that can, directly or indirectly, impact on the motor components 6,7 .
Sway has been shown to be sensitive to the effects of continuous exposure to medication 7 . This occurs because prolonged exposure to medication triggers alterations in the metabolic system and Central Nervous System (CNS) 6,[8][9][10] . Changes in these parameters imply in a reduction in muscular strength and efferent neural responses 6,7 .
The fragility that emerges from the progression of infection at more advanced stages is another factor which can provoke changes in sway. In a symptomatic condition (AIDS) the PLHA is vulnerable to the presence of neuropathy and other comorbidities.
This condition can, directly or indirectly, influence postural sway, specifically in more difficult tasks 11,12 . However, the unfolding impacts of HIV and/or HAART on postural sway still do not present consensus 11 . From this perspective, understanding postural sway behavior in PLHA allows prophylaxis strategies to maintain functionality in tasks of daily living 11 . The postural sway of PLHA compared to non-HIV individuals may indicate pathological conditions that are still in an asymptomatic state 3,6 .
Thus, considering the lack of specificity and new nuances of the infection, the objective of the present study was to evaluate the static postural sway of people living with HIV/AIDS under treatment with HAART. It was expected that in light of the new characteristics of the HIV infection, sway in PLHA would be different from that of non-PLHA. Therefore, another hypothesis raised by this study is that the absence of visual information would increase postural instability for both PLHA and non-PLHA.

METHODS
The participants in the present study (PLHA and non-PLHA)  In order to establish greater socioeconomic homogeneity, non-HIV participants were also recruited at the Reference Center, emphasizing that their participation was conditional on the same inclusion criteria as people living with HIV, however, they were required to have a negative serological condition. As this research involves humans, all the procedures adopted were in accordance with the ethical precepts of the country. In the BPYV and STYV conditions, participants were required to keep their gaze fixed on a circular target positioned on the wall two meters from the force platform. For the BPNV and STNV conditions, the participants were required to wear a blindfold that could be withdrawn at any report of discomfort. Lastly, the participants were allowed one attempt to familiarize themselves with the platform and experimental conditions. Two previously trained researchers were present during the trials to ensure the non-occurrence of falls in cases of large postural oscillation.

Instrument
The instrument used in the present study was a Bertec Corporation ® brand load cell, model 4060-08, size (LxWxH) 60cm x 40cm x 5cm, with a 1000Hz sampling frequency and a capacity of 220 Kg.
The center of pressure (COP) data provided by the platform were exported to Matlab software where they were analyzed using a specific routine, smoothed by means of a 4 th order Butterworth low pass filter and a defined cut-off frequency of 5Hz, through residual analysis.
The variables calculated from the COP provided by the platform were: the area of oscillation (cm 2 ) being calculated by means of 95% of the ellipse, which, in turn, is obtained by means of the dispersion measurements of the COP; the mean amplitude (cm), which refers to the distance between the minimum and maximum displacement in the anterior-posterior and medial-lateral directions of the COP; and the mean velocity (cm/s), which represents the COP total displacement over time.

Statistical Analysis
The independent variables under analysis were the groups,

DISCUSSION
The objective of the present study was to evaluate the pos- The data also allowed us to identify that visual information is essential for the maintenance of postural sway for both PLHA and non-PLHA. In this context, the hypothesis that the PVHA sway would be different from the non-PLHA was accepted, and that occlusion of visual information is a factor which increases sway in both groups.
Previous studies have identified that the postural sway of PLHA may be compromised by several factors, in addition to being a condition present in asymptomatic individuals 11,[13][14][15] . The scholars 6,15 have suggested that increased postural oscillation is associated with manifestations of HIV in the central nervous system (CNS). These manifestations tend to affect the subcortical structures and the infratentorial brain system, compromising efferent signals 6,15,16 .
On the other hand, some authors associate HAART with generalized toxicity in the organism 8,9 , stemming from the continued use of HAART and impacting muscle function, the sensory system, and fat distribution 8,9 . This variability in the condition implies in the maintenance of sway 10,13,15 .
The results presented above interact with the present study, since the GHIV presented greater ML amplitude than the GNHIV in the STYV condition. In terms of neural control, a high amplitude of ML demands a proximal-distal muscular response to maintain balance 17 . This response is adjusted by the hip strategy in order to respond to the disturbance generated by a reduction in the support base 18 .
The hip strategy controls sway dependent on the torques generated by the trunk and hip muscles. In this context, the force generated by these muscle groups becomes indispensable for torque to restore or maintain balance 19,20 .
The fact that the difference in intragroup ML amplitude occurs in a condition with visual information available suggests changes in the neuro-muscular control mechanisms 17,20 . This condition can be better understood when considering that the GNHIV did not present differences between BPYV and BPNV.
On Maintenance of balance using a muscular strategy depends initially on the sensory information. Studies [21][22][23][24][25] indicate that the reduction or manipulation of sensory information results in increased postural sway. This is because the muscular response to disturbances is intrinsically conditioned to the sensory perception 20,26 . Specifically, the reduction in visual information has been related to the postural sway of several populations [27][28][29] , this being the most reliable information for humans, as its relevance for the maintenance of balance can reach 50% in challenging conditions 23 .
The results of the present study showed the importance of visual information for both groups (GHIV and GNHIV). With the occlusion of visual information, there was greater instability in all experimental tasks. In the absence of sensory information, the central nervous system (CNS) has the ability to modulate the participation of sensory channels to maintain balance 28,29 however, this modulation does not completely compensate for suppression of vision 30,31 .
In summary, the present research accepted the initial hypothesis that postural balance of the GHIV under continuous HAART use differs from GNHIV. Concomitantly, the hypothesis that the absence of visual feedback would generate greater sway in both groups was also accepted.
Some limitations should be considered in order to better understand our results, for example: the sample size, which does not allow our results to be generalized; and the median age of the GHIV, as younger adults could better adapt to the experimental tasks. However, the present study has some significant points such as: intragroup and intergroup homogenization and the sensitivity of the instrument used to evaluate postural sway.
Finally, we believe that these findings are relevant to specialists and non-specialists in this area. The results corroborate with previous research, evidencing the need for better understanding of the changes in balance and impacts on the quality of life in PLHA.
For this, we suggest the investigation of the muscular strategies adopted in day-to-day tasks, through electromyography, in addition to the realization of linear regression to map the variables that can impact balance.