The popularity of breathwork as a therapeutic tool for psychological distress is rapidly expanding. Breathwork practices that increase ventilatory rate or depth, facilitated by music, can evoke subjective experiential states analogous to altered states of consciousness (ASCs) evoked by psychedelic substances. These states include components such as euphoria, bliss, and perceptual differences. However, the neurobiological mechanisms underlying the profound subjective effects of high ventilation breathwork (HVB) remain largely unknown and unexplored. In this study, we investigated the neurobiological substrates of ASCs induced by HVB in experienced practitioners. We demonstrate that the intensity of ASCs evoked by HVB was proportional to cardiovascular sympathetic activation and to haemodynamic alterations in cerebral perfusion within clusters spanning the left operculum/posterior insula and right amygdala/anterior hippocampus; regions implicated in respiratory interoceptive representation and the processing of emotional memories, respectively. These observed regional cerebral effects may underlie pivotal mental experiences that mediate positive therapeutic outcomes of HVB.
Our study was designed to address different objectives through three inter-related experiments: (please see the methods for more details), in 1) HVB was conducted over an online video-conferencing platform with a breathwork facilitator (REMOTE setting). The aim was to characterise the subjective response to remote HVB in a home setting, and inform the choice of the ASC domain to be used as subjective endpoint. In 2), we used pseudo-continuous arterial spin labelling (pCASL) magnetic resonance imaging (MRI) of the brain during HVB to identify the relationship between neural haemodynamic effects of HVB and subjective measures (MRI setting). In 3) HVB was performed in a psychophysiology lab to characterise the relationship between the psychophysiological effects of HVB (autonomic alterations, see ‘psychophysiological session 3’ for more information) and subjective measures (LAB setting).
To our knowledge, no studies have previously reported the relationship between the intensity of ASCs and changes in rCBF induced by HVB practices. Since we could not base our prediction of the regional specificity of such correlations on previous knowledge, we preferred to adopt a whole brain voxelwise exploratory approach. Also, as observations reported on the effects of psychedelics on autonomic nervous system activity have been contrasting [ 18 , 19 ], we could not make precise predictions on the direction of association between HRV and ASCs.
Then we examined the effects of HVB performed by experienced breathwork practitioners in different experimental settings, and investigated peripheral and central neurophysiological mechanisms underpinning ASCs engendered by HVB. The neurobiological endpoints were selected based on well-characterised neurophysiological effects of hyperventilation (reviewed in [ 11 ]). Hyperventilation acutely reduces regional cerebral blood flow (rCBF) through interacting effects of hypocapnia, cerebral alkalosis and hypoxia, resulting in transient perturbation of neurometabolic homeostasis. Further, hyperventilation evokes allostatic changes in action-ready bodily arousal, mediated via the autonomic nervous system via the dominance of sympathetic over parasympathetic drive to the heart and blood vessels. In characterising the neurobiological effects of HVB and associated ASCs, we therefore focused our measurements on two robust indices of neurometabolic and autonomic nervous control: rCBF and heart rate variability (HRV).
First, we characterised the subjective experience of HVB to capture the nature and intensity of evoked experiential phenomena. From these data, we aimed to assess whether these effects could be reliably reproduced in controlled experimental settings in comparison to a remote – and more ecologically valid – condition. These findings informed the choice of the ASC variable, OBN, which was ultimately selected as the most widely reported experiential phenomena to identify the critical neurobiological effects of HVB.
The therapeutic potential of HVB practices is suggested by a long cultural tradition of use to relieve symptoms of psychological distress [ 11 , 13 ] and by emerging preliminary evidence of clinical efficacy from controlled trials in affective and trauma-related disorders [ 14 ]. Prolonged hyperventilation/HVB reportedly elicits a wide range of effects on subjective experience that include emotional and psychedelic-like phenomena (ASCs), which range from panic-like sensations to feelings of awe and dissociative symptoms [ 11 ]. The 5D-ASC questionnaire is popularly used in ASC research to retrospectively assess such states [ 15 ]. A key dimension of this scale is ‘Oceanic Boundlessness’ (OBN); a term coined by Freud in 1920 [ 16 ] which describes a set of related feelings including ‘spiritual experience, insightfulness, blissful state, positively experienced depersonalization, and the experience of unity’ [ 17 ]. OBN is considered as a defining aspect of ASCs evoked by psychedelic substances, such as psilocybin. However, the neurobiological mechanisms and subjective experience underlying ASCs induced by HVB have not been studied extensively and remain elusive.
High ventilation breathwork (HVB) encompasses contemplative and therapeutic practices, including Conscious Connected Breathing or Holotropic Breathwork, in which a controlled pattern of volitional breathing increases the rate or depth of ventilation and is typically accompanied by evocative music. Despite their distinct historical roots and delivery modalities, these different HVB practices share a purported ability to elicit acute extraordinary alterations in subjective experience that closely resemble the qualia of altered states of consciousness (ASCs) induced by psychedelic substances [ 1 – 3 ]. Converging evidence demonstrates the potential value of psychedelic treatments for specific difficult-to-treat psychiatric and physiological conditions [ 4 – 7 ]. The induction of ASCs is suggested to be critical to the therapeutic action of psychedelic substances [ 8 – 10 ], for which HVB might therefore offer a non-pharmacological alternative, with fewer legal and ethical restrictions to large-scale adoption in clinical treatment. In line with this, the popularity of HVB as a therapeutic tool for psychological distress is rapidly expanding, indexed by an increased number of scientific investigations, see [ 11 , 12 ] for more details.
Objective 3: To investigate changes in cardiac autonomic drive during HVB and their relationship to the intensity of ASCs, we calculated change in HRV (ΔRMSSD) and HR. Heartbeat timing data were imported from the Firstbeat Bodyguard device into Kubios 3.5.0 HRV scientific 4.1.0 for processing. Raw data contained substantial noise from chest movement. After an initial phase of artefact removal, interbeat interval (IBI) data were smoothed using an automatic noise detection filter at a medium threshold [ 33 ]. A repeated measures ANCOVA with contrasts for different orders of an equation was conducted using HRV and OBN (5D-ASC selected from objective 1) as covariates to explain HRV variance over time, with polynomial contrast applied to identify linear and complex patterns, allowing us to characterise dynamic trends in HRV responses to HVB.
Objective 2: In order to test the correlations between HVB-induced ASCs and rCBF effects, two contrasts between HVB time points (see MRI experimental design in Fig 1 ) were studied using paired-samples t-tests in SPM12 [ 27 ]: contrast 1) between BASELINE and START HVB grey matter CBF; contrast 2) between BASELINE and SUSTAINED HVB grey matter CBF. Following this, voxel-wise maps of changes in pcASL rCBF (ΔrCBF) were calculated for the contrasts between BASELINE versus SUSTAINED HVB, and START versus SUSTAINED HVB. These ΔrCBF maps were then used for voxelwise correlation analysis with the OBN score, selected as the highest-rated 5D-ASC dimension. Voxel clusters were considered significant at a cluster-forming threshold of p < 0.001, corrected for multiple comparisons using family-wise error (FWE) correction, with a significance level of p < 0.05.
For the PANAS-X and VAS, we used an LMM analysis to examine the effects of HVB (pre- versus post-) on setting and the type of question (positive versus negative affect for PANAS; discomfort versus fear for VAS), accounting for subject-specific variability as a random effect. We explored two-way interactions between all the variables and post-hoc tests using the same methods as the previous analyses [ 32 ].
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