Acquisition of optical coherence tomography angiography metrics during hemodialysis procedures: A pilot study

BACKGROUND AND AIMS

The observation of optical microcirculation gives us an extraordinary way to directly assess in vivo the responses of human circulation to stress stimuli. We run a pilot study to analyze optical coherence tomography angiography (OCT-A) metrics at determined time-points during a hemodialysis (HD) session to understand how these metrics gradually change and to evaluate possible correlations with patients' characteristics.

METHODS

After the eligibility screening, 15 patients (23 eyes) were included in the study. OCT-A parameters were collected at established time-points: Before treatment (t0), at first hour (t1), at second hour (t2), at third hour (t3), and finally at the end of HD treatment (t4). Patients were finally shared in hypotensive group if they occurred in a hypotensive episode during subsequent month methods or no hypotensive group. The instrument software automatically segmented OCT-A scans into four en-face slabs: The superficial capillary plexus (SCP), the deep capillary plexus (DCP), the outer retinal plexus and the choriocapillaris plexus. In this study we focus on SCP, DCP plexuses.

RESULTS

Overall, the majority of ophthalmic parameters remained unaffected and comparable at dialysis end; a significant reduction being observed at the end vs. starting of HD only for deep capillary plexus (DCP: Whole, fovea, and parafovea) and for central choroid thickness (CCT) (p < 0.05). An overall trend during the session showed in general a decrease with a significance in particular for DCP (whole, fovea, and parafovea) and for CCT (P = 0.006). In the hypotension group, Superficial capillary plexus (SCP: Fovea and parafovea) significantly increased comparing post vs. pre-dialysis values while CCT significantly decreased. Analyzing the trend during treatment only CCT maintained a significant trend (p for trend = 0.002). In the no-hypotension group, neither pre- vs. post-analysis and trend analysis showed a statistical significance.

CONCLUSION

Main achievement of our study was to measure, for the first time in literature, single parameters at different time-points of a HD session. As a result of this process we did not notice a brusque decreasing or increasing of OCT-A metrics but we can characterize the different effect of HD on the two distinct areas distinguishing ocular vessels: Retinal and choroidal circulation. As interesting sub-analysis, Hypotensive group showed for CCT a decreasing trend with a difference statistically significant respect to the group with no-hypotension maintaining a constant trend. In our opinion, these results suggest the role of autonomic system on vessel control in patients affected by uremia.

Mirroring the Social Aspects of Speech and Actions: The Role of the Insula

Action and speech may take different forms, being expressed, for example, gently or rudely. These aspects of social communication, named vitality forms, have been little studied in neuroscience. In the present functional magnetic resonance imaging study, we investigated the role of insula in processing action and speech vitality forms. In speech runs, participants were asked to listen or imaging themselves to pronounce action verbs gently or rudely. In action runs, they were asked to observe or imaging themselves to perform actions gently or rudely. The results showed that, relative to controls, there was an activation of the dorso-central insula in both tasks of speech and action runs. The insula sector specific for action vitality form was located slightly more dorsally than that of speech with a large overlap of their activations. The psycho-physiological interaction analysis showed that the insular sector involved in action vitality forms processing is connected with the left hemisphere areas controlling arm actions, whereas the sector involved in speech vitality forms processing is linked with right hemisphere areas related to speech prosody. We conclude that the central part of the insula is a key region for vitality forms processing regardless of the modality by which they are conveyed or expressed.

Language for action: Motor resonance during the processing of human and robotic voices

In this fMRI study we evaluated whether the auditory processing of action verbs pronounced by a human or a robotic voice in the imperative mood differently modulates the activation of the mirror neuron system (MNs). The study produced three results. First, the activation pattern found during listening to action verbs was very similar in both the robot and human conditions. Second, the processing of action verbs compared to abstract verbs determined the activation of the fronto-parietal circuit classically involved during the action goal understanding. Third, and most importantly, listening to action verbs compared to abstract verbs produced activation of the anterior part of the supramarginal gyrus (aSMG) regardless of the condition (human and robot) and in the absence of any object name. The supramarginal gyrus is a region considered to underpin hand-object interaction and associated to the processing of affordances. These results suggest that listening to action verbs may trigger the recruitment of motor representations characterizing affordances and action execution, coherently with the predictive nature of motor simulation that not only allows us to re-enact motor knowledge to understand others' actions but also prepares us for the actions we might need to carry out.

Understanding the internal states of others by listening to action verbs

The internal state of others can be understood observing their actions or listening to their voice. While the neural bases of action style (vitality forms) have been investigated, there is no information on how we recognize others' internal state by listening to their speech. Here, using fMRI technique, we investigated the neural correlates of auditory vitality forms while participants listened to action verbs in three different conditions: human voice pronouncing the verbs in a rude and gentle way, robot voice pronouncing the same verbs without vitality forms, and a scrambled version of the same verbs pronounced by human voice. In agreement with previous studies on vitality forms encoding, we found specific activation of the central part of insula during listening to human voice conveying specific vitality forms. In addition, when listening both to human and robot voices there was an activation of the posterior part of the left inferior frontal gyrus and of the parieto-premotor circuit typically described to be activated during observation and execution of arm actions. Finally, the superior temporal gyrus was activated bilaterally in all three conditions. We conclude that, the central part of insula is a key region for vitality forms processing allowing the understanding of the vitality forms regardless of the modality by which they are conveyed.