Basilar artery blood flow velocity changes in patients with panic disorder following 35% carbon dioxide challenge

A systematic review and network meta-analysis of carbon dioxide provocation in psychiatric disorders

BACKGROUND

False suffocation alarm hypothesis has been widely used to explain carbon dioxide hypersensitivity in panic disorder (PD). However, hypersensitivity to carbon dioxide has been observed in other psychiatric disorders. We explored the specificity of carbon dioxide inhalation as a panic provocation test among psychiatric disorders via network meta-analysis.

METHODS

A systematic literature search on PubMed, EMBASE, and PsycNET was performed to acquire the studies using the carbon dioxide provocation test in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and checklists. Odds ratios (OR) for a panic attack (PA) induced by the carbon dioxide inhalation tests were extracted from each of the original studies and were pooled using the random-effects model.

RESULTS

Network meta-analysis on a pool of 2181 participants from 41 studies was used to compare the efficacy of carbon dioxide provocation tests among psychiatric disorders. The network meta-analysis showed that the odds for PA in response to carbon dioxide inhalation are higher in patients with PD, premenstrual dysphoric syndrome (PMDD), and social anxiety disorder (SAD) than healthy controls (HC). The odds for PA were not significantly different among patients with generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), major depressive disorder (MDD), and healthy controls (HC).

CONCLUSIONS

The vulnerability to the carbon dioxide provocation test is not limited to PD. The specificity of the test for PD is questionable, as individuals suffering from PMDD and SAD are also significantly more responsive to carbon dioxide inhalation compared to HC, OCD, MDD, and GAD. There may be shared underpinning biological mechanisms between PD, PMDD, and SAD.

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.

Diagnostic Utility of Sodium Lactate Infusion and CO2-35% Inhalation for Panic Disorder

Laboratory measures have played an integral role in diagnosing pathology; however, compared to traditional medicine, psychiatric medicine has lagged behind in using such measures. A growing body of literature has begun to examine the viability and development of different laboratory measures in order to diagnose psychopathologies. The present review examines the current state of development of both sodium lactate infusion and CO2-35% inhalation as potential ancillary measures to diagnose panic disorder (PD). A previously established 3-step approach to identifying laboratory-based diagnostic tests was applied to available literature assessing the ability of both sodium lactate infusion or CO2-35% inhalation to induce panic attacks in PD patients, healthy controls, and individuals with other psychiatric conditions. Results suggest that across the literature reviewed, individuals with PD were more likely to exhibit panic attacks following administration of sodium lactate or CO2-35% compared to control participants. The majority of the studies examined only compared individuals with PD to healthy controls, suggesting that these ancillary measures are underdeveloped. In order to further determine the utility of these ancillary measures, research is needed to determine if panic attacks following administration of these chemical agents are unique to PD, or if individuals with related pathologies also respond, which may be indicative of transdiagnostic characteristics found across disorders.

Characteristics of cardio-Cerebrovascular modulation in patients with generalized anxiety disorder: an observational study

BACKGROUND

Generalized anxiety disorder (GAD) has been shown in previous studies to display abnormal cerebral blood flow velocity (CBFV); however, the characteristics of cardio-cerebrovascular modulation are unknown. We aimed to analyze cardio-cerebrovascular modulation using parameters from a supine-to-standing test.

METHODS

There are 2 parts to this study; in Part 1, 125 participants with Hamilton Anxiety scale scores ≥14 were enrolled, and 33 age- and sex-matched medically and psychiatrically healthy volunteers were recruited as control participants. Patients were divided by score into mild, moderate, and severe anxiety groups. The cardio-cerebrovascular modulation using the parameters of dynamic changes of CBFV and heart rate in response to an orthostatic challenge were investigated. In Part 2, we followed up the severe GAD patients for 6 months and repeated the supine-to-standing test, and severe GAD patients were divided into recovery and non-recovery groups.

RESULTS

In part 1, the GAD group displayed more marked CBFV and heart rate changes than the healthy group, but there was no difference in the CBFV and heart rate changes from the supine to upright position in mild, moderate, and severe anxiety groups. In part 2, The recovery group demonstrated significant improvement in changes in the CBFV and heart rate values from the supine to the upright position after treatment compared with before treatment. In the non-recovery group, the CBFV and heart rate changes were significantly higher than the healthy group regardless of treatment.

CONCLUSIONS

Cardio-cerebrovascular modulation is compromised in patients with GAD, however, this impairment can be restored to normal after the disappearance of anxiety.

Functional t1ρ imaging in panic disorder

BACKGROUND

Abnormal brain pH has been suggested to play a critical role in panic disorder. To investigate this possibility, we employed a pH-sensitive magnetic resonance (MR) imaging strategy (T1 relaxation in the rotating frame [T1ρ]) and conventional blood oxygen level-dependent (BOLD) imaging.

METHODS

Thirteen panic disorder participants and 13 matched control subjects were enrolled in the study. T1ρ and BOLD were used to study the functional response to a visual flashing checkerboard and their relationship to panic symptoms assessed using the Beck Anxiety Inventory.

RESULTS

In response to visual stimulation, T1ρ imaging revealed a significantly greater increase in the visual cortex of panic disorder participants. T1ρ also detected a stimulus-evoked decrease in the anterior cingulate cortex. Blood oxygen level-dependent imaging detected no functional differences between groups. The correspondence between panic symptoms and functional T1ρ response identified significant relationships within the left inferior parietal lobe, left middle temporal gyrus, and right insula. No relationships were found between panic symptoms and the BOLD signal.

CONCLUSIONS

The data suggest greater activity-evoked T1ρ changes in the visual cortex and anterior cingulate cortex of panic disorder participants. These observations are consistent with a pH dysregulation in panic disorder. In addition, our data suggest that T1ρ imaging may provide information about panic disorder that is distinct from conventional BOLD imaging and may reflect abnormalities in pH and/or brain metabolism.

Brain Circulation during Panic Attack: A Transcranial Doppler Study with Clomipramine Challenge

Introduction. Cerebral blood flow has been well studied in patients with panic disorder, but only few studies analyzed the mechanisms underlying the onset of a panic attack. The aim of the present study was to monitor the cerebral hemodynamics modifications during a panic attack. Materials and Methods. 10 panic disorder patients with recent onset, fully drug naïve, were compared to 13 patients with panic disorder with a previous history of treatment and to 14 controls. A continuous bilateral monitoring of mean flow velocities in right and left middle cerebral arteries was performed by transcranial Doppler. Clomipramine was chosen as challenge. Results. Eight out of 10 patients drug naïve and 6 control subjects out of 13 had a full blown panic attack during the test, whereas none of the patients with a history of treatment panicked. The occurrence of a panic attack was accompanied by a rapid decrease of flow velocities in both right and left middle cerebral arteries. Discussion. The bilateral acute decrease of mean flow velocity during a panic attack suggests the vasoconstriction of the microcirculation of deep brain structures perfused by middle cerebral arteries and involved in the so-called "fear circuitry," thus suggesting that cerebral homeostatic dysfunctions seem to have a key role in the onset of a panic attack.

Anxiety, pCO2 and cerebral blood flow

This study examined the effect of anxiety on cerebral blood flow at different levels of pCO2 in healthy participants (N=29). Three types of breathing were used to manipulate pCO2 in a within-subject threat-of-shock paradigm: spontaneous breathing, CO2-inhalation and hyperventilation resulting in normo-, hyper- and hypocapnia. Transcranial Doppler ultrasonography was used to measure CBF velocity (CBFv) in the right middle cerebral artery, while breathing behavior and end-tidal pCO2 were monitored. During normocapnia, elevated anxiety was clearly associated with increased CBFv. Consistent with the cerebral vasoconstrictive and vasodilating effects of, respectively, hypo- and hypercapnia, we observed a positive linear association between CBFv and pCO2. The slope of this association became steeper with increasing anxiety, indicating that anxiety enhances the sensitivity of CBFv to changes in pCO2. The findings may elucidate conflicting findings in the literature and are relevant for brain imaging relying on regional cerebral blood flow.

Hypersensitivity to hypercapnia: definition/(s)

Empirical evidence indicates that panic disorder (PD) patients experience hypersensitivity to hypercapnia, a condition in which the blood level of carbon dioxide exceeds the normal value. The importance of this research line is substantial and indeed, hypercapnic hypersensitivity has been advanced as a possible endophenotype of panic. Definitions of "hypersensitivity," however, have varied. The purpose of this brief review is to delineate and critique different definitions of hypercapnic hypersensitivity. Several definitions - panic attack rate, panic symptoms including dyspnea, subjective anxiety, and respiratory disturbance - are explored. The review concludes that although no ideal definition has emerged, marked anxiety post-hypercapnia has substantial support as a putative trait marker of PD. The term "subjective hypersensitivity" (Coryell et al., 2001) is re-introduced to denote pronounced anxiety post-hypercapnia and recommended for use along with its previous definition: increased self-reported anxiety measured on a continuous visual analog scale, already widely in use. Due to the well-established link between panic and respiration, definitional candidates focusing on aberrant respiratory response - less investigated as trait markers of PD in high risk studies - warrant scrutiny as well. Several reasons why definitional clarity might be beneficial are presented, along with ideas for future research.

Feeling lightheaded: the role of cerebral blood flow

OBJECTIVE

The main aims of this study were a) to investigate the relationship between lightheadedness and cerebral blood flow velocity (CBFv) during hyperventilation-induced hypocapnia, and b) to investigate whether and why the relationship between lightheadedness and CBFv may change after several episodes of this sensation.

METHODS

Three hypocapnic and three normocapnic overbreathing trials were administered in a semirandomized order to healthy participants (N = 33). Each type of breathing trial was consistently paired with one odor. Afterward, participants were presented each odor once in two spontaneous breathing and in two normocapnic overbreathing trials. CBFv in the right middle cerebral artery was measured by transcranial Doppler ultrasonography (TCD). Also breathing behavior and self-reported lightheadedness were measured continuously. Each trial was followed by a symptom checklist.

RESULTS

Self-reported lightheadedness was closely related to changes in CBFv in the hypocapnic overbreathing trials. During the subsequent normocapnic trials, however, participants experienced more lightheadedness and "feeling unreal" to the odor that had previously been paired with hyperventilation-induced hypocapnia. These complaints were not accompanied by changes in end-tidal CO(2) nor in CBFv.

CONCLUSIONS

The results show that lightheadedness is associated with changes in CBFv but that after a few episodes, the underlying mechanism for this symptom may shift to perceptual-cognitive processes. These findings may help to understand why lightheadedness occurs during emotional distress and panic. In addition, altered cerebral blood flow is unlikely to play a primary precipitating role in recurrent symptoms of lightheadedness.