Cerebral blood flow autoregulation is impaired in schizophrenia: A pilot study

[Cerebral hemodynamic disorders in patients with schizophrenia with concomitant metabolic syndrome]

OBJECTIVE

To identify the differences or comparability of parameters of cerebral hemodynamics between patients with schizophrenia with or without concomitant metabolic syndrome (MS).

MATERIAL AND METHODS

The study included 94 patients with schizophrenia (48 men and 46 women). A control group consisted of 40 mentally and somatically healthy individuals (17 men and 23 women) comparable in sex and age to the main group of patients. The diagnosis of metabolic syndrome was carried out according to the criteria of the International Diabetes Federation (IDF). Assessment of cerebral hemodynamics was carried out by 4 - channel rheoencephalography (REG) at rest with closed eyes. Data analysis was carried out using the Kraskel-Wallis ANOVA criterion with the procedure of automatic a posteriori pairwise comparison, the χ2 criterion and Spearman correlation analysis.

RESULTS

According to the IDF criteria, 37 (39.4%) patients were diagnosed with MS. REG results revealed significantly (p<0.05) lower indicators of blood filling in the carotid basin, elasticity of the wall of the main arteries, the tone of small-caliber arteries and arterioles, as well as higher values of the tone of medium-caliber arteries in the carotid and vertebrobasilar basins, in both groups of patients with schizophrenia compared with the control group. In patients with schizophrenia with MS, compared with patients without MS, there were lower indicators of blood filling (p=0.044 and p=0.016) and elasticity of the wall of the main arteries (p=0.044 and p=0.028) in the carotid basin on the left and right sides.

CONCLUSION

The presence of MS in patients with schizophrenia was accompanied by more pronounced disorders of cerebral blood flow in the form of a decrease in blood filling and elasticity of the wall of the main arteries in the carotid basin. The results indicate that patients with schizophrenia with MS should be considered as a group at increased risk of cerebrovascular diseases.

Tryptophan challenge in individuals with schizophrenia and healthy controls: acute effects on circulating kynurenine and kynurenic acid, cognition and cerebral blood flow

Cognitive impairments predict poor functional outcomes in people with schizophrenia. These impairments may be causally related to increased levels of kynurenic acid (KYNA), a major metabolic product of tryptophan (TRYP). In the brain, KYNA acts as an antagonist of the of α7-nicotinic acetylcholine and NMDA receptors, both of which are involved in cognitive processes. To examine whether KYNA plays a role in the pathophysiology of schizophrenia, we compared the acute effects of a single oral dose of TRYP (6 g) in 32 healthy controls (HC) and 37 people with either schizophrenia (Sz), schizoaffective or schizophreniform disorder, in a placebo-controlled, randomized crossover study. We examined plasma levels of KYNA and its precursor kynurenine; selected cognitive measures from the MATRICS Consensus Cognitive Battery; and resting cerebral blood flow (CBF) using arterial spin labeling imaging. In both cohorts, the TRYP challenge produced significant, time-dependent elevations in plasma kynurenine and KYNA. The resting CBF signal (averaged across all gray matter) was affected differentially, such that TRYP was associated with higher CBF in HC, but not in participants with a Sz-related disorder. While TRYP did not significantly impair cognitive test performance, there was a trend for TRYP to worsen visuospatial memory task performance in HC. Our results demonstrate that oral TRYP challenge substantially increases plasma levels of kynurenine and KYNA in both groups, but exerts differential group effects on CBF. Future studies are required to investigate the mechanisms underlying these CBF findings, and to evaluate the impact of KYNA fluctuations on brain function and behavior. (Clinicaltrials.gov: NCT02067975).

Cerebral blood flow self-regulation in depression

BACKGROUND

Depression is a common neuropsychiatric disease with a high prevalence rate. Sleep problems, memory decline, dizziness and headaches are the most common neurological symptoms in depressed patients. Abnormality of cerebral blood flow (CBF) has been observed in depressive patients, but those patients did not have intracranial structural damage. Both of those phenomena might be related to cerebral blood flow self-regulation (CBFSR: cerebral blood flow self-regulation). CBFSR can maintain CBF relatively stable in response to changes in neurological and metabolic factors. Therefore, this review aimed to discuss CBFSR in depression.

METHODS

We searched for keywords such as "depression", "cerebral blood flow", "cerebral autoregulation", "cerebrovascular reactivity" and the words related to depression. We analyzed whether there is a change in the CBFSR in depression, further explored whether there is a relationship between the pathogenesis of depression and the CBFSR, and discussed the possible mechanism of impaired CBFSR in patients with depression.

RESULTS

Discovered by the literature review, CBFSR is significantly impaired in depressed patients. The level of circulating markers of endothelial dysfunction, nitric oxide, inflammatory cytokines, glucocorticoid and monoamine neurotransmitters is mostly abnormal in depression, which affected the CBFSR to varying degrees.

LIMITATIONS

Limitations include the small number of direct studies about depression and CBFSR mechanisms.

CONCLUSION

CBFSR is impaired in depression. The underlying mechanisms include endothelial dysfunction, overactivation of microglia and changes of cytokines, hyperactivation of the HPA axis, increased oxidative stress, monoamine neurotransmitter disorders, etc. These deepened our understanding of the clinical symptoms of depressed patients.

Reliability and validity of the mean flow index (Mx) for assessing cerebral autoregulation in humans: A systematic review of the methodology

Cerebral autoregulation is a complex mechanism that serves to keep cerebral blood flow relatively constant within a wide range of cerebral perfusion pressures. The mean flow index (Mx) is one of several methods to assess dynamic cerebral autoregulation, but its reliability and validity have never been assessed systematically. The purpose of the present systematic review was to evaluate the methodology, reliability and validity of Mx.Based on 128 studies, we found inconsistency in the pre-processing of the recordings and the methods for calculation of Mx. The reliability in terms of repeatability and reproducibility ranged from poor to excellent, with optimal repeatability when comparing overlapping recordings. The discriminatory ability varied depending on the patient populations; in general, those with acute brain injury exhibited a higher Mx than healthy volunteers. The prognostic ability in terms of functional outcome and mortality ranged from chance result to moderate accuracy.Since the methodology was inconsistent between studies, resulting in varying reliability and validity estimates, the results were difficult to compare. The optimal method for deriving Mx is currently unknown.

A systematic review of ultrasound imaging and therapy in mental disorders

BACKGROUND

Increasing evidence suggests that ultrasound (US) imaging may provide biomarkers and therapeutic options in mental disorders. We systematically reviewed the literature to provide a global overview of the possibilities of US for psychiatry.

METHODS

Original English language articles published between January 2000 and September 2019 were identified through databases searching and analyzed to summarize existing evidence according to PRISMA methodology.

RESULTS

A total of 81 articles were included. Various US techniques and markers have been used in mental disorders, including Transcranial Doppler and Intima-Media Thickness. Most of the studies have focused on characterizing the pathophysiology of mental disorders, especially vascular physiology. Studies on therapeutic applications are still scarce.

DISCUSSION

US imaging has proved to be useful in characterizing vascular impairment and structural and functional brain changes in mental disorders. Preliminary findings also suggest potential interests for therapeutic applications. Growing evidence suggests that US imaging could provide a non-invasive, portable and low-cost tool for pathophysiological characterization, prognostic assessment and therapeutic applications in mental disorders.

Excess Glutamate May Cause Dilation of Retinal Blood Vessels in Glutamate/Aspartate Transporter-Deficient Mice

Purpose

To investigate the longitudinal findings of fundus features and spectral-domain optical coherence tomography (SD-OCT) to characterize the morphologic features in a mouse model of defective glutamate/aspartate transporter (GLAST^−/− mice).

Materials and Methods

The fundus findings and SD-OCT images were longitudinally recorded at five time points from postnatal (P) 22 to P156 in GLAST^−/− mice. As a control wild type, age-matched C57BL/6J mice were employed. The mouse retina was subdivided into five layers, and the thickness of each layer was longitudinally measured by InSight® using SD-OCT pictures. The SD-OCT findings were compared with the histologic appearances. The diameter of the retinal blood vessels was measured by the ImageJ® software program using SD-OCT images. The data were statistically compared between both age-matched mouse groups.

Results

The retinal blood vessels appeared more dilated in GLAST^−/− mice than in wild-type mice. This tendency was statistically significant at all time points after P44 by analyses using SD-OCT images. The ganglion cell complex (GCC) and outer nuclear layer (ONL) were significantly thinner in GLAST^−/− mice at all time points after P80 than in the wild-type mice. This tendency was more clearly indicated by SD-OCT than histologic sections.

Discussion

In the present study, we found for the first time the dilation of the retinal blood vessels and the thinning of the ONL in GLAST^−/− mice, in addition to the thinning of the GCC.

Comparing Different Recording Lengths of Dynamic Cerebral Autoregulation: 5 versus 10 Minutes

We compared the dynamic cerebral autoregulation (dCA) indices between 5- and 10-minute data lengths by analyzing 37 patients with ischemic stroke and 51 controls in this study. Correlation coefficient (Mx) and transfer function analysis were applied for dCA analysis. Mx and phase shift in all frequency bands were not significantly different between 5- and 10-minute recordings [mean difference: Mx = 0.02; phase shift of very low frequency (0.02–0.07 Hz) = 0.3°, low frequency (0.07–0.20 Hz) = 0.6°, and high frequency (0.20–0.50 Hz) = 0.1°]. However, the gains in all frequency bands of a 5-minute recording were slightly but significantly higher than those of a 10-minute recording (mean difference of gain: very low frequency = 0.05 cm/s/mmHg, low frequency = 0.11 cm/s/mmHg, and high frequency = 0.14 cm/s/mmHg). The intraclass correlation coefficients between all dCA indices of 5- and 10-minute recordings were favorable, especially in Mx (0.93), phase shift in very low frequency (0.87), and gain in very low frequency (0.94). The areas under the receiver operating characteristic curve for stroke diagnosis between 5- and 10-minute recordings were not different. We concluded that dCA assessed by using a 5-minute recording is not significantly different from that using a 10-minute recording in the clinical application.