Obstetric anesthesia and postpartum mental health: implications from delivery to long-term recovery.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by progressive motor and non-motor symptoms. Impaired balance and anxiety have been prioritized as issues that need to be addressed for motor and non-motor symptoms, respectively. Anxiety is one of the most common non-motor symptoms in people with PD (PwPD), affecting up to 40% of patients. Moreover, anxiety could exacerbate balance control and the development of freezing of gait (FOG). For example, anxious PwPD exhibit larger weight-shifting errors and shorter margins of stability than non-anxious PwPD. In the clinic, PwPD often complain that space constraints (i.e., narrow or crowed spaces) induce higher anxiety and deteriorate their balance. Studies have also reported that PwPD have higher anxiety scale score when they walk on a narrow plank than on a wide plank in a virtual reality environment, and freezers have a decreased step length and increased step length variability when walking through a narrow doorway (67.5 cm wide) compared with normal-size (90 cm wide) and wide (180 cm wide) doorways. Although anxiety is often treated with medicines, studies have proposed that pharmacological treatment for anxiety may lead to higher postural instability and fall incidence in PwPD. Thus, non-pharmacological interventions, such as cognitive behavioral therapy, physical exercise, and neuromodulation techniques, have been proposed as alternative approaches for anxiety symptoms. Vagus nerve stimulation (VNS) is a promising neuromodulation technique that bridges emotional and motor systems through afferent projections to the nucleus tractus solitarius and locus coeruleus that involve arousal, attention, and emotional regulation. Both animal and human studies have provided evidence that VNS is a promising therapeutic technique for tackling anxiety. A pilot trial of implanted VNS in treatment-resistant anxiety disorders showed modest acute effects, with longer-term benefits observed in patients with obsessive-compulsive disorder. Transcutaneous VNS (tVNS) has been proposed as a safer clinical intervention for anxiety. Recent studies have also shown that tVNS may have potential for improved walking in PwPD. Marano and colleagues reported that a single session of tVNS could increase walking speed and stride (or step) length and reduce step variability for PwPD in either an on-medication or off-medication state. In addition, after a 7-day tVNS intervention (30 min/session, 2 sessions/day), PwPD had improved walking performance with decreased oxyhemoglobin in the motor and somatosensory cortices. Although tVNS shows potential for reducing anxiety or improving balance, research examining the concurrent benefits of tVNS for anxiety modulation and balance control remains limited. In particular, no study has investigated the effect of tVNS on balance control in anxious PwPD under space constraints. Given the limited evidence in this area, the present study was exploratory in nature and aimed to generate preliminary evidence regarding the effects of tVNS on anxiety and balance control under space constraints in anxious PwPD. Space-related deterioration of balance and anxiety in PwPD is often observed clinically; however, studies have seldom examined this issue, and those that have done so have primarily focused on walking tasks. Moreover, the association between balance control and anxiety symptoms in PwPD remains insufficiently understood. Impairments in weight-shifting have been identified as one of the most common FOG-related postural deficit, and incorrect weight-shifting may increase the risk of falls in PwPD. Accordingly, present exploratory study focused on the effects of tVNS on weight-shifting control and related anxiety levels in anxious PwPD, particularly under space constraints. We hypothesized that 1) space constraints would decrease the accuracy and amplitude of weight-shifting movement in anxious PwPD, and 2) tVNS would reduce anxiety levels and improve weight-shifting control in anxious PwPD, especially under space constraints.