Impact of swallowing and ventilation on oropharyngeal cortical representation

Change in Excitability of Cortical Projection After Modified Catheter Balloon Dilatation Therapy in Brainstem Stroke Patients with Dysphagia: A Prospective Controlled Study

Although the modified balloon dilatation therapy has been demonstrated to improve pharyngeal swallowing function post stroke, the underlying neural mechanisms of improvement are unknown. Our aims are (1) to investigate the effect of modified balloon dilatation on the excitability of corticobulbar projections to the submental muscle in dysphagic patients with brainstem stroke and (2) the relation between changes in excitability and pharyngeal kinematic modifications. Thirty patients with upper esophageal sphincter (UES) dysfunction due to unilateral brainstem stroke were recruited into two groups. The patients in dilatation group received modified balloon dilatation and conventional therapies, and those in control were only treated by conventional therapies (twice per day). The amplitudes of bilateral submental motor evoked potentials (MEPs) induced by transcranial magnetic stimulations over bilateral motor cortex, diameters of UES opening (UOD) and maximal displacement of hyoid (HD) were all assessed at baseline and the endpoint of treatments. Repeated ANOVA analysis revealed significant main effect of group, time and MEP laterality on MEP amplitudes (p = 0.02). There were no differences in the pretreatment measures between groups (all p > 0.05). After treatment, the amplitudes of affected submental MEP evoked by ipsilateral cortical pulse as well as UOD and HD were significantly different in dilatation group compared to control (amplitude: p = 0.02, UOD: p < 0.001, HD: p = 0.03). The differences of pre- and post-treatment amplitudes of the affected MEP evoked by ipsilateral stimulation showed a positive correlation with the improvement of HD (dilatation: R ² = 0.51, p = 0.03; control: R ² = 0.39, p = 0.01), rather than UOD in both groups (all p > 0.05). In conclusion, modified balloon dilatation therapy can increase the excitability of affected projection in patients with unilateral brainstem stroke.

Task-concurrent anodal tDCS modulates bilateral plasticity in the human suprahyoid motor cortex

Transcranial direct current stimulation (tDCS) is a non-invasive method to modulate cortical excitability in humans. Here, we examined the effects of anodal tDCS on suprahyoid motor evoked potentials (MEP) when applied over the hemisphere with stronger and weaker suprahyoid/submental projections, respectively, while study participants performed a swallowing task. Thirty healthy volunteers were invited to two experimental sessions and randomly assigned to one of two different groups. While in the first group stimulation was targeted over the hemisphere with stronger suprahyoid projections, the second group received stimulation over the weaker suprahyoid projections. tDCS was applied either as anodal or sham stimulation in a random cross-over design. Suprahyoid MEPs were assessed immediately before intervention, as well as 5, 30, 60, and 90 min after discontinuation of stimulation from both the stimulated and non-stimulated contralateral hemisphere. We found that anodal tDCS (a-tDCS) had long-lasting effects on suprahyoid MEPs on the stimulated side in both groups (tDCS targeting the stronger projections: F_(1,14) = 96.2, p < 0.001; tDCS targeting the weaker projections: F_(1,14) = 37.45, p < 0.001). While MEPs did not increase when elicited from the non-targeted hemisphere after stimulation of the stronger projections (F_(1,14) = 0.69, p = 0.42), we found increased MEPs elicited from the non-targeted hemisphere after stimulating the weaker projections (at time points 30–90 min) (F_(1,14) = 18.26, p = 0.001). We conclude that anodal tDCS has differential effects on suprahyoid MEPs elicited from the targeted and non-targeted hemisphere depending on the site of stimulation. This finding may be important for the application of a-tDCS in patients with dysphagia, for example after stroke.

The effect of swallowing treatments on corticobulbar excitability: a review of transcranial magnetic stimulation induced motor evoked potentials

Transcranial magnetic stimulation (TMS) has been used extensively as a method of investigating the corticomotor physiology of many motor tasks, including healthy and disordered swallowing. Changes in excitability of cortical projections to various swallowing muscles have been documented in response to treatments with TMS induced motor evoked potentials (MEPs). These studies have provided valuable insight into CNS response to swallowing impairment, and more importantly, the adaptations associated with functional recovery. However, unique obstacles are presented when investigating corticobulbar neurophysiology associated with the complex task of swallowing. Stringent methodological control and supplementary outcome measures are required to ensure robust and clinically applicable findings. This article offers a tutorial for the researcher who may be considering the use of TMS for investigating changes in cortical excitability associated with various swallowing paradigms. Included is a review of the mechanisms of TMS and what can be measured with this technique, a summary of existing research using MEPs to investigate swallowing, a review of methodological factors that may influence outcomes, and proposed directions for new areas of research.

Modification in swallowing and ventilation co-ordination during hypercapnia, hypoxia, and tachypnea in unrestrained animals

BACKGROUND

It has been demonstrated that aspirations could occur during respiratory failure, explained by a lack of co-ordination between swallowing and ventilation. To test this hypothesis, we examined the co-ordination of ventilation and swallowing in a completely unrestrained rat model during different level of hypercapnia, during hypoxia, and during tachypnea.

METHODS

A total of 50 male Wistar rats (250-350 g) were studied in a barometric plethysmograph to analyze swallowing and ventilation during swallowing, at different gas concentration [room air (G1), 10% of O2 and 0% of CO2 (G2), 21% of O2 and 5% of CO2 (G3), 21% of O2 and 10% of CO2 (G4), tachypnea (G5)].

KEY RESULTS

During hypoxia, there was no difference between G2 and G1 regarding the swallowing parameters and ventilatory parameters. During hypercapnia, there was an increase in swallowing during inspiration in G4 (16 ± 20%P < 0.01) compared with G1. The analysis of ventilatory parameters during swallowing showed an increase in tidal volume (VT) and mean inspiratory time (VT/TI) (P < 0.001) with no change in respiratory cycle duration (TTOT), inspiratory time (TI), and expiratory time (TE) when compared with G1. During tachypnea (G5), the VT decreased (P < 0.05) without any change in VT/TI.

CONCLUSIONS & INFERENCES

Our results on animal demonstrated that hypercapnia increased swallowing during inspiration, which was not the case for tachypnea or hypoxia, and could explain some aspirations during respiratory failure.