Are respiratory abnormalities specific for panic disorder? A meta-analysis

Enhanced interhemispheric resting-state functional connectivity of the visual network is an early treatment response of paroxetine in patients with panic disorder

This study aimed to detect alterations in interhemispheric interactions in patients with panic disorder (PD), determine whether such alterations could serve as biomarkers for the diagnosis and prediction of therapeutic outcomes, and map dynamic changes in interhemispheric interactions in patients with PD after treatment. Fifty-four patients with PD and 54 healthy controls (HCs) were enrolled in this study. All participants underwent clinical assessment and a resting-state functional magnetic resonance imaging scan at (i) baseline and (ii) after paroxetine treatment for 4 weeks. A voxel-mirrored homotopic connectivity (VMHC) indicator, support vector machine (SVM), and support vector regression (SVR) were used in this study. Patients with PD showed reduced VMHC in the fusiform, middle temporal/occipital, and postcentral/precentral gyri, relative to those of HCs. After treatment, the patients exhibited enhanced VMHC in the lingual gyrus, relative to the baseline data. The VMHC of the fusiform and postcentral/precentral gyri contributed most to the classification (accuracy = 87.04%). The predicted changes were accessed from the SVR using the aberrant VMHC as features. Positive correlations (p < 0.001) were indicated between the actual and predicted changes in the severity of anxiety. These findings suggest that impaired interhemispheric coordination in the cognitive-sensory network characterized PD and that VMHC can serve as biomarkers and predictors of the efficiency of PD treatment. Enhanced VMHC in the lingual gyrus of patients with PD after treatment implied that pharmacotherapy recruited the visual network in the early stages.

A History of Suicide Attempt Is Associated with Increased Sympathetic Activation in Bipolar Disorder

OBJECTIVE

Suicide risk in bipolar disorder (BD) is estimated to be up to 20 times higher than in the general population. While there is a large body of evidence suggesting that increased sympathetic activation is associated with disease and death, there is a paucity of research on the role of autonomic nervous system (ANS) dysfunction in patients with BD who have attempted suicide.

METHODS

Fifty-three participants with BD used a wearable device to assess the association between history of suicide attempt, current suicidal ideation, and ANS dysfunction, including measures of heart rate variability (HRV) and respiratory rate. Data were analyzed in a series of unadjusted and adjusted bivariate models of association controlling for relevant variables.

RESULTS

A history of suicide attempts was significantly associated with an increase in respiratory rate (p < 0.01). These results remained significant after adjusting for age, BMI, and current mood state. There was no association between current suicidal ideation and heart rate or respiratory rate. In the frequency domain, HRV parameters suggest reduced parasympathetic (i.e., vagal) activity in participants with a history of suicide attempts and in those with current suicidality, suggesting changes in sympathicovagal balance in BD.

CONCLUSIONS

Our results suggest that changes in the ANS in patients with BD and a history of suicide attempt are not restricted to pure vagally mediated HRV parameters, but rather signal a general ANS dysregulation. This ANS imbalance may be contributing to illness burden and cardiovascular disease. Further research on the relationship between ANS and suicidality in BD is needed.

Cardiorespiratory Assessments in Panic Disorder Facilitated by Wearable Devices: A Systematic Review and Brief Comparison of the Wearable Zephyr BioPatch with the Quark-b2 Stationary Testing System

Abnormalities in cardiorespiratory measurements have repeatedly been found in patients with panic disorder (PD) during laboratory-based assessments. However, recordings performed outside laboratory settings are required to test the ecological validity of these findings. Wearable devices, such as sensor-imbedded garments, biopatches, and smartwatches, are promising tools for this purpose. We systematically reviewed the evidence for wearables-based cardiorespiratory assessments in PD by searching for publications on the PubMed, PsycINFO, and Embase databases, from inception to 30 July 2022. After the screening of two-hundred and twenty records, eight studies were included. The limited number of available studies and critical aspects related to the uncertain reliability of wearables-based assessments, especially concerning respiration, prevented us from drawing conclusions about the cardiorespiratory function of patients with PD in daily life. We also present preliminary data on a pilot study conducted on volunteers at the Villa San Benedetto Menni Hospital for evaluating the accuracy of heart rate (HR) and breathing rate (BR) measurements by the wearable Zephyr BioPatch compared with the Quark-b2 stationary testing system. Our exploratory results suggested possible BR and HR misestimation by the wearable Zephyr BioPatch compared with the Quark-b2 system. Challenges of wearables-based cardiorespiratory assessment and possible solutions to improve their reliability and optimize their significant potential for the study of PD pathophysiology are presented.

Biological and cognitive theories explaining panic disorder: A narrative review

The current narrative review summarizes and examines several theories of panic disorder (PD) including biological theories, encompassing neurochemical factors, metabolic and genetic theories, respiratory and hyperventilation theories and cognitive theory. Biological theories have informed the development of psychopharmacological treatments; however, they may be limited in their utility given the efficacy of psychological treatments. In particular, behavioral and, more recently, cognitive models have garnered support due to the efficacy of cognitive-behavior therapy (CBT) in treating PD. The role of combination treatments has been found to be superior in the treatment of PD in particular cases, lending support for the need for an integrated approach and model for PD given that the etiology of PD is complex and multifactorial.

Validation Criteria for PETCO2 Kinetics during the Hyperventilation Provocation Test in the Diagnosis of Idiopathic Hyperventilation Syndrome

Background: The hyperventilation provocation test (HPTest) is a diagnostic tool for idiopathic hyperventilation syndrome (HVS), encountered in some long-COVID patients. However, interpretation of the HPTest remains unclear regarding the relevant PETCO2 values to focus on and whether subjective symptoms should be considered. This study aimed to re-evaluate objective HPTest results for diagnosing HVS by determining accurate PETCO2 kinetics in two groups of patients previously screened via the Nijmegen questionnaire (NQ). Methods: The kinetics of PETCO2 during the HPTest were mathematically modeled and compared between 37 HVS patients (NQ ≥23/64) and 37 healthy controls (NQ <23/64) matched for gender, age, and body dimensions. AUC values with sensitivity and specificity were calculated, and analysis was monitored in a validation cohort of 152 routine HPTests. Results: A threshold value of a less than 12.8 mmHg increment of PETCO2 at the 5th minute of the recovery phase of the HPTest diagnosed HVS patients with excellent sensitivity (0.92) and specificity (0.84). These results were confirmed in the validation cohort, highlighting the presence of 24% false positives/negatives when diagnosing on the basis of complaints in the NQ. Conclusions: For HVS diagnosis, we suggest considering the HPTest, which can more reliably reflect the mechanisms of CO2 homeostasis and the response of the respiratory center to a stimulus, regardless of the subjective onset of symptoms.

Intravenous doxapram administration as a potential model of panic attacks in rats

Panic disorder can be categorized into the nonrespiratory or the respiratory subtypes, the latter comprising dyspnea, shortness of breath, chest pain, feelings of suffocation, and paresthesias. Doxapram is an analeptic capable of inducing panic attacks with respiratory symptoms in individuals diagnosed with the disorder; however, its neuroanatomical targets and its effects on experimental animals remain uncharacterized. One of the brain regions proposed to trigger panic attacks is the midbrain periaqueductal gray (PAG). Therefore, in this study, we evaluated the effects of doxapram in Fos (c-Fos) protein expression in the PAG and characterized its cardiorespiratory and behavioral effects on the elevated T maze and in the conditioned place aversion (CPA) paradigms. Doxapram increased Fos expression in different columns of the PAG, increased respiratory frequency, decreased heart rate, and increased arterial pressure when injected via intravenous route. Alprazolam, a panicolytic benzodiazepine, injected via intraperitoneal route, decreased respiratory frequency, whereas URB597, an anandamide hydrolysis inhibitor injected via intraperitoneal route, was ineffective. Doxapram injected via intraperitoneal route induced an anxiogenic-like effect in the elevated T-maze model; however, it failed to induce CPA. This study suggests that the cardiorespiratory and behavioral effects of doxapram in rodents serve as an experimental model that can provide insights into the neurobiology of panic attacks.

Disruption of estradiol regulation of orexin neurons: a novel mechanism in excessive ventilatory response to CO2 inhalation in a female rat model of panic disorder

Panic disorder (PD) is ~2 times more frequent in women. An excessive ventilatory response to CO2 inhalation is more likely during the premenstrual phase. While ovarian hormones appear important in the pathophysiology of PD, their role remains poorly understood as female animals are rarely used in pre-clinical studies. Using neonatal maternal separation (NMS) to induce a "PD-like" respiratory phenotype, we tested the hypothesis that NMS disrupts hormonal regulation of the ventilatory response to CO2 in female rats. We then determined whether NMS attenuates the inhibitory actions of 17-β estradiol (E2) on orexin neurons (ORX). Pups were exposed to NMS (3 h/day; postnatal day 3-12). The ventilatory response to CO2-inhalation was tested before puberty, across the estrus cycle, and following ovariectomy. Plasma E2 and hypothalamic ORXA were measured. The effect of an ORX1 antagonist (SB334867; 15 mg/kg) on the CO2 response was tested. Excitatory postsynaptic currents (EPSCs) were recorded from ORX neurons using whole-cell patch-clamp. NMS-related increase in the CO2 response was observed only when ovaries were functional; the largest ventilation was observed during proestrus. SB334867 blocked this effect. NMS augmented levels of ORXA in hypothalamus extracts. EPSC frequency varied according to basal plasma E2 levels across the estrus cycle in controls but not NMS. NMS reproduces developmental and cyclic changes of respiratory manifestations of PD. NMS disrupts the inhibitory actions of E2 on the respiratory network. Impaired E2-related inhibition of ORX neurons during proestrus is a novel mechanism in respiratory manifestations of PD in females.

The Importance of Respiratory Rate Monitoring: From Healthcare to Sport and Exercise

Respiratory rate is a fundamental vital sign that is sensitive to different pathological conditions (e.g., adverse cardiac events, pneumonia, and clinical deterioration) and stressors, including emotional stress, cognitive load, heat, cold, physical effort, and exercise-induced fatigue. The sensitivity of respiratory rate to these conditions is superior compared to that of most of the other vital signs, and the abundance of suitable technological solutions measuring respiratory rate has important implications for healthcare, occupational settings, and sport. However, respiratory rate is still too often not routinely monitored in these fields of use. This review presents a multidisciplinary approach to respiratory monitoring, with the aim to improve the development and efficacy of respiratory monitoring services. We have identified thirteen monitoring goals where the use of the respiratory rate is invaluable, and for each of them we have described suitable sensors and techniques to monitor respiratory rate in specific measurement scenarios. We have also provided a physiological rationale corroborating the importance of respiratory rate monitoring and an original multidisciplinary framework for the development of respiratory monitoring services. This review is expected to advance the field of respiratory monitoring and favor synergies between different disciplines to accomplish this goal.

Panic disorder respiratory subtype: psychopathology and challenge tests - an update

Panic disorder (PD) pathophysiology is very heterogeneous, and the discrimination of distinct subtypes could be very useful. A subtype based on respiratory symptoms is known to constitute a specific subgroup. However, evidence to support the respiratory subtype (RS) as a distinct subgroup of PD with a well-defined phenotype remains controversial. Studies have focused on characterization of the RS based on symptoms and response to CO2. In this line, we described clinical and biological aspects focused on symptomatology and CO2 challenge tests in PD RS. The main symptoms that characterize RS are dyspnea (shortness of breath) and a choking sensation. Moreover, patients with the RS tended to be more responsive to CO2 challenge tests, which triggered more panic attacks in this subgroup. Future studies should focus on discriminating respiratory-related clusters and exploring psychophysiological and neuroimaging outcomes in order to provide robust evidence to confirm RS as a distinct subtype of PD.

Biological and Clinical Markers to Differentiate the Type of Anxiety Disorders

The present chapter is an overview of possible biomarkers which distinguish anxiety disorders as classified by the DSM-5. Structural or activity changes in the brain regions; changes in N-acetylaspartate/creatine, dopamine, serotonin, and oxytocin; hearth rate variability; hypothalamic-pituitary-adrenal axis activity; error-related negativity; respiratory regulation; and genetic variants are proposed. However, their clinical utility is questionable due to low specificity and sensitivity: the majority does not distinguish subjects with different anxiety disorders, and they might be influenced by stress, comorbidity, physical activity, and psychotropic medications. In this framework, the staging model, a clinimetric tool which allows to define the degree of progression of a disease at a point in time and where the patient is located on the continuum of the course of the disease, is proposed since several DSM anxiety disorders take place at different stages of the same syndrome according to the staging model. Thus, a stage-specific biomarker model for anxiety disorders is hypothesized and illustrated.

Toward a personalized therapy for panic disorder: preliminary considerations from a work in progress

Although several treatment options for panic disorder (PD) are available, the best intervention for each individual patient remains uncertain and the use of a more personalized therapeutic approach in PD is required. In clinical practice, clinicians combine general scientific information and personal experience in the decision-making process to choose a tailored treatment for each patient. In this sense, clinicians already use a somehow personalized medicine strategy. However, the influence of their interpretative personal models may lead to bias related to personal convictions, not sufficiently grounded on scientific evidence. Hence, an effort to give some advice based on the science of personalized medicine could have positive effects on clinicians' decisions. Based on a narrative review of meta-analyses, systematic reviews, and experimental studies, we proposed a first-step attempt of evidence-based personalized therapy for PD. We focused on some phenomenological profiles, encompassing symptoms during/outside panic attacks, related patterns of physiological functions, and some aspects of physical health, which might be worth considering when developing treatment plans for patients with PD. We considered respiratory, cardiac, vestibular, and derealization/depersonalization profiles, with related implications for treatment. Given the extensiveness of the topic, we considered only medications and some somatic interventions. Our proposal should be considered neither exhaustive nor conclusive, as it is meant as a very preliminary step toward a future, robust evidence-based personalized therapy for PD. Clearly much more work is needed to achieve this goal, and recent technological advances, such as wearable devices, big data platforms, and the application of machine learning techniques, may help obtain reliable findings. We believe that combining the efforts of different research groups in this work in progress can lead to largely shared conclusions in the near future.

Biological and Clinical Markers in Panic Disorder

OBJECTIVE

Classifying mental disorders on the basis of objective makers might clarify their aetiology, help in making the diagnosis, identify "at risk" individuals, determine the severity of mental illness, and predict the course of the disorder. This study aims to review biological and clinical markers of panic disorder (PD).

METHODS

A computerized search was carried out in PubMed and Science Direct using the key words: "marker/biomarker/clinical marker/neurobiology/staging" combined using Boolean AND operator with "panic." In addition, the reference lists from existing reviews and from the articles retrieved were inspected. Only English language papers published in peer-reviewed journals were included.

RESULTS

Structural changes in the amygdala, hippocampus, cerebral blood level in the left occipital cortex, serotonin 5-TH and noradrenergic systems activation, aberrant respiratory regulation, hearth rate variability, blood cells and peripheral blood stem cells, hypothalamic-pituitary-adrenal axis dysregulation were identified as potential candidate biomarkers of PD. Staging was identified as clinical marker of PD. According to the staging model, PD is described as follows: prodromal phase (stage 1); acute phase (stage 2); panic attacks (stage 3); chronic phase (stage 4).

CONCLUSION

The clinical utility, sensitivity, specificity, and the predictive value of biomarkers for PD is still questionable. The staging model of PD might be a valid susceptibility, diagnostic, prognostic, and predictive marker of PD. A possible longitudinal model of biological and clinical markers of PD is proposed.

Respiratory subtype of panic disorder: Can serum phosphate levels be a possible outcome to group cognitive-behavior therapy?

OBJECTIVE

Panic disorder (PD) respiratory subtype (RS) was described in order to cluster patients according to their symptoms. These patients are characterized by experiencing a relatively high number of noticeable respiratory symptoms during a panic attack (PA) and a higher reactivity to CO₂. In this study, we aimed to evaluate the clinical relevance of this diagnostic category, evaluating if there are different responses to cognitive-behavioral therapy in patients with panic disorder RS as compared to those with the non-respiratory subtype (NRS), using serum phosphate as a biological marker.

METHODS

Patients were assessed by a clinical interview followed by a structured diagnostic interview (M.I.N.I) and classified as RS or NRS based on symptoms. The severity of PD was evaluated throughout the PDSS, CGI, HAM-A, STAI and the BDI rating scales. All patients underwent 12 structured sessions of group-CBT for PD and had their blood collected at baseline and after treatment to assess phosphate levels.

RESULTS

One hundred and thirty-eight patients have been assessed, and 102 were included in this trial. Sixty-nine patients completed the treatment protocol, 42 were classified as RS and 27 as NRS. Both RS and NRS patients improved in all clinical scales (p < 0.001). The mean phosphate levels increased from 2.44 mg/dl ± 0.49 at baseline to 3.38 mg/dl ± 0.52 (p < 0.01) in the RS group as well as from 2.46 mg/dl ± 0.64 at baseline to 3.46 mg/dl ± 0.61 (p < 0.01) in the NSR group.

LIMITATIONS

Small sample size and the lack of assessment of other clinical and physiological parameters, such as respiratory variables.

CONCLUSION

Our findings suggest that both RS and NRS benefit from group CBT and that there was a change in phosphate levels after effective treatment in both groups. Our data support the idea that there is a reversal of the conditions that promote hypophosphatemia as chronic hyperventilation after CBT treatment, whereas it is in disagreement to the presence of two different PD subtypes based on phosphate levels once their rates did not differ at baseline and had a similar increase after effective treatment.

Are there advances in pharmacotherapy for panic disorder? A systematic review of the past five years

INTRODUCTION

Several effective medications are available for treating panic disorder (PD). However, outcomes are unsatisfactory in a number of patients, suggesting the usefulness of expanding the array of antipanic drugs and improving the quality of response to current recommended treatments.

AREAS COVERED

The authors have performed an updated systematic review of pharmacological studies (phase III onwards) to examine whether advances have been made in the last five years. Only four studies were included. D-cycloserine no longer seemed promising as a cognitive-behavioral therapy (CBT) enhancer. Some preliminary findings concerning the optimization of recommended medications deserved consideration, including: the possibility that SSRIs are more effective than CBT alone in treating panic attacks, combined therapy is preferable when agoraphobia is present, and clonazepam is more potent than paroxetine in decreasing panic relapse.

EXPERT OPINION

Given the lack of novel treatments, expanding a personalized approach to the existing medications seems to be the most feasible strategy to improve pharmacotherapy outcomes regarding PD. Recent technological progress, including wearable devices collecting real-time data, 'big data' platforms, and application of machine learning techniques might help make outcome prediction more reliable. Further research on previously promising novel treatments is also recommended.

Is panic disorder a disorder of physical fitness? A heuristic proposal

Currently, panic disorder (PD) is considered a mental disorder based on the assumptions that panic attacks (PAs) are “false alarms” that arise from abnormally sensitive defense systems in the central nervous system and that PD is treated with therapies specifically acting on anxiety or fear mechanisms. This article aims to propose an alternative perspective based on the results of some experimental studies. Our heuristic proposal suggests not only that PD may be a mental disorder but also that patients with PD have real abnormal body functioning, mainly involving cardiorespiratory and balance systems, leading to a decline in global physical fitness. PAs, as well as physical symptoms or discomfort in some environmental situations, may be “real alarms” signaling that the adaptability resources of an organism are insufficient to respond appropriately to some internal or external changes, thus representing the transient conscious awareness of an imbalance in body functioning. The antipanic properties of several modern treatments for PD may include their beneficial effects on body functions. Although anxiety or fear mechanisms are evidently involved in PD, we hypothesize that a reduction of physical fitness is the “primum movens” of PD, while anxiety or fear is induced and sustained by repeated signals of impaired body functioning. We propose considering panic in a broader perspective that offers a central role to the body and to contemplate the possible role of somatic treatments in PD.

Management of Treatment-Resistant Panic Disorder

PURPOSE OF REVIEW

Purpose of Review Management of treatment-resistant (TR) panic disorder (PD) is an unresolved issue. In this paper, we provide a brief summary of previous findings, an updated (2015-2017) systematic review of pharmacological/non-pharmacological studies, and our personal perspective on this topic.

RECENT FINDINGS

Recent Findings We found a very limited number of recent findings. Quetiapine extended-release augmentation has not been found to be beneficial, in comparison to placebo, in non-responders to previously recommended pharmacotherapy. In non-responders to cognitive behavioral therapy (CBT), switching to paroxetine/citalopram has been found to be more effective than continuing CBT. Acceptance and commitment therapy (ACT) has shown some improvement in patients' resistance to previous psychological/pharmacological interventions compared with a waiting-list condition.

SUMMARY

Summary Previous and recent findings regarding the treatment of TR PD suffer from several methodological limitations. Available studies provide insufficient evidence to support the use of medications alternative to the recommended medications; the efficacy of ACT needs confirmation with more rigorous methodology. Prolonged pharmacotherapy may produce significant improvement in patients with unsatisfactory response to short-term pharmacotherapy, while switching to pharmacotherapy may help non-responders to CBT. We discuss our personal perspective on the definition of "treatment resistance" as it relates to PD and provide personalized intervention strategies to increase favorable clinical outcomes based on our clinical expertise and review of experimental studies on the pathophysiology of PD.

Long-lasting bradypnea induced by repeated social defeat

Repeated social defeat in the rat induces long-lasting cardiovascular changes associated with anxiety. In this study, we investigated the effects of repeated social defeat on breathing. Respiratory rate was extracted from the respiratory sinus arrhythmia (RSA) peak frequency of the ECG in rats subjected to social defeat for 4 consecutive days. Respiratory rate was recorded under anesthesia 6 days (D+10) or 26 days (D+30) after social defeat. At D+10, defeated (D) rats spent less time in the open arms of the elevated plus maze test, had heavier adrenal glands, and displayed bradypnea, unlike nondefeated animals. At D+30, all signs of anxiety had disappeared. However, one-half of the rats still displayed bradypnea (DL rats, for low respiratory rate indicated by a lower RSA frequency), whereas those with higher respiratory rate (DH rats) had recovered. Acute blockade of the dorsomedial hypothalamus (DMH) or nucleus tractus solitarii (NTS) 5-HT3 receptors reversed bradypnea in all D rats at D+10 and in DL rats at D+30. Respiratory rate was also recorded in conscious animals implanted with radiotelemetric ECG probes. DH rats recovered between D+10 and D+18, whereas DL rats remained bradypneic until D+30. In conclusion, social stress induces sustained chronic bradypnea mediated by DMH neurons and NTS 5-HT3 receptors. These changes are associated with an anxiety-like state that persists until D+10, followed by recovery. However, bradypnea may persist in one-half of the population up until D+30, despite apparent recovery of the anxiety-like state.

The presence of respiratory disorders in individuals with low back pain: A systematic review

BACKGROUND

Inspiratory muscles, such as the diaphragm, play a key role in both respiration and spinal control. Therefore, diaphragm dysfunctions are often related to low back pain (LBP). However, few is known on the association between the presence of LBP and the presence of respiratory disorders (RD).

OBJECTIVES

To perform a systematic review on the relation between RD and LBP.

STUDY DESIGN

Systematic review.

METHODS

Two reviewers searched on PubMed/MEDLINE for studies concerning LBP and RD, from 1950 up to January 2016. The search string consisted of the following key words: low back pain, dyspnea, respiratory problems, lung diseases, comorbidity, pulmonary disease, chronic obstructive, smoking, asthma, allergy, sinusitis, respiratory tract infection and hyperventilation. The aim was to evaluate a potential correlation, co-occurrence or causality between RD and LBP.

RESULTS

A total of 16 articles were included. A significant correlation between the presence of LBP and the presence of RD such as dyspnea, asthma, different forms of allergy, and respiratory infections was found. No correlation was found between Chronic Obstructive Pulmonary Disease (COPD) and LBP, and no articles were found on the correlation between hyperventilation and LBP.

CONCLUSIONS

This is the first study providing an overview of the literature on the relation between LBP and RD. Immunological, biomechanical, psychosocial and socio-economic factors might explain this correlation. Smoking is likely to contribute. Future studies must reveal the causative relationship.

LEVEL OF EVIDENCE

Therapy, level 2a.

A linear model for event-related respiration responses

BACKGROUND

Cognitive processes influence respiratory physiology. This may allow inferring cognitive states from measured respiration. Here, we take a first step towards this goal and investigate whether event-related respiratory responses can be identified, and whether they are accessible to a model-based approach.

NEW METHOD

We regard respiratory responses as the output of a linear time invariant system that receives brief inputs after psychological events. We derive average responses to visual targets, aversive stimulation, and viewing of arousing pictures, in interpolated respiration period (RP), respiration amplitude (RA), and respiratory flow rate (RFR). We then base a Psychophysiological Model (PsPM) on these averaged event-related responses. The PsPM is inverted to yield estimates of cognitive input into the respiratory system. This method is validated in an independent data set.

RESULTS

All three measures show event-related responses, which are captured as non-zero response amplitudes in the PsPM. Amplitude estimates for RA and RFR distinguish between picture viewing and the other tasks. This pattern is replicated in the validation experiment.

COMPARISON WITH EXISTING METHODS

Existing respiratory measures are based on relatively short time-intervals after an event while the new method is based on the entire duration of respiratory responses.

CONCLUSION

Our findings suggest that interpolated respiratory measures show replicable event-related response patterns. PsPM inversion is a suitable approach to analysing these patterns, with a potential to infer cognitive processes from respiration.