Effects of hand catalepsy on subjective trance perception and relative parasympathetic tone in healthy volunteers during pleasant hypnotic session: a randomized controlled study

doi:10.21203/rs.3.rs-3904432/v1

Purpose: This study was designed to evaluate the effects on hand catalepsy on parasympathetic tone assessed using Analgesia/Nociception Index (ANI) and on subjective rating of absorption, dissociation, and time perception among healthy volunteers.

Methods: This was a randomized controlled trial including participants to a medical hypnosis congress in France. Ninety volunteers were randomized in two arms, all receiving a fifteen-minute positive hypnotic trance, with or without hand catalepsy. The relative parasympathetic tone assessed by ANI (Analgesia/Nociception Index), heart rate and respiratory rate were recorded at different times of the study protocol. The actual duration of the hypnotic session, calculated from eye closing to eye opening, was also recorded. At the end of the hypnotic trance, participants subjectively rated their level of absorption and dissociation on a 0-10 scale. They were also asked to estimate the duration of the hypnotic session from eye closing to eye opening.

Results: In total, ninety subjects were included in the study. One subject was excluded because of deviation in the protocol standard, leaving eighty-nine subjects for analysis. Subject characteristics were similar between groups.

There was a statistically different increase in ANI and decrease in both heart rate and respiratory rate over time with no difference with or without hand catalepsy. There was no statistically significant difference in absorption and dissociation subjective scales between groups. The median [Q1-Q3] actual duration of hypnotic sessions was similar between the catalepsy and the control groups (9 [8-10] min vs. 8 [7-10] min, respectively). However, subjects in the catalepsy group estimated a longer duration of the hypnotic session (12 [10-15] min) than in the control group (10 [5-10] min) with a mean ± SD overestimation of 3 ± 4 min (p<0.001).

Conclusion: Parasympathetic comfort increased during the hypnotic trance with no difference between groups. However, adding a hand catalepsy to a pleasant hypnotic trance did not appear to increase feelings of absorption or dissociation but created time distortion on the longer side that could be useful in some clinical settings. Nevertheless, further study is still needed to determine more precisely the physiological and psychological effects on hand catalepsy during the hypnotic trance.

Hand catalepsy

Parasympathetic tone

Hypnosis

Absorption

Dissociation

Time perception

Hand catalepsy is believed to facilitate hypnotic induction and to be associated with dissociative symptoms, although few studies confirm the clinical usefulness and objective effects of this technique which is in common use in hypnosis [1]. Besides, it has been shown that the hypnotic trance state is accompanied by a non-specific increase in parasympathetic tone easily assessed using ANI (Analgesia/Nociception Index) a non-invasive index derived from heart rate variability [2].

We hypothesized that hand catalepsy may have a measurable impact on parasympathetic tone assessed using ANI and on subjective rating of absorption, dissociation, and time perception. We designed this randomized-controlled trial to assess the effects on hand catalepsy on these parameters among healthy volunteers recruited in a French medical hypnosis congress.

Participants

The study participants were a sample of volunteers attending the 7th congress on "Hypnosis and Pain" organized by the French “Émergences” teaching institute, that happened in Saint-Malo, France, in May 2022. The study was initially scheduled for May 2020, but the congress was canceled and postponed two years later because of the COVID pandemics. Participants were informed during the congress opening conference that they could participate in this study by registering to scheduled hypnosis scientific workshops. After oral explanation of the study and written informed consent was obtained, all the subjects registered to the workshops were included. The inclusion criteria for the study included the following: aged eighteen years or older, with or without prior experience in hypnosis as a subject, with decisional capacity to consent to the study, able to communicate verbally, who had given their consent according to the methods described in article L1122-1-1 of the French Public Health Code, and affiliated to a social security scheme or benefiting from such a scheme. The exclusion criteria were people with a visible inability to communicate in French, or with a history of cardiac arrhythmias. The latter was justified using live cardiac monitoring, the results of which could be disrupted by the presence of an arrhythmia. There were no other exclusion criteria. The study was approved by our institutional review board and registered on ClinicalTrials.gov (NCT05306262) in 2022 before enrolling subjects.

All hypnosis sessions were initially planned to be performed by experienced trainers from the organizing teaching institute, who registered at different slots of the scientific congress, so that they could still enjoy all the other scientific presentations and workshops. Their professions were either physicians (mostly anesthesiologists and psychiatrists) or other healthcare providers (nurses, anesthetic nurses, and psychologists), all trained in medical hypnosis for more than five years. Because some teachers did not all come at their allotted slots, some unexpected professionals were asked to participate in the protocol as hypnosis facilitators. This was easily done because the study protocol was quite simple to perform.

Before randomization, ANI electrodes were placed on the subject’s chest to record the parasympathetic activity throughout the entire experiment. Briefly, ANI is a 0-100 index derived from heart rate variability reflecting the relative parasympathetic tone, with values of fifty and higher corresponding to prominent parasympathetic tone, therefore higher patient comfort [2–4]. A portable pulse oximeter was placed on one finger of each participant using the hand opposite to catalepsy (if any) to record the heart rate (HR) during the experiment. An observer not involved in the hypnotic session assessed the respiratory rate (RR) during the experiment and recorded all measures (ANI, HR, RR) as described further.

Randomization

All participants were randomized in two arms, all receiving a fifteen-minute positive hypnotic trance, with or without hand catalepsy. The randomization process was prepared in advance with sealed consecutive envelopes. When participants joined the study, an envelope was opened, and the arm of randomization was only shown to the hypnosis facilitators. However, because of the informed consent, it was impossible to blind the participants, or the third person conducting the measures. Therefore, this study was open label. For this reason, we wanted to include both subjective and objective assessments.

Measures

At different times of the study protocol, evaluators registered on a paper form the level of ANI, the respiratory rate, the heart rate. They were also asked to time the different moments of their measures since the beginning of the hypnotic induction. At the end of the hypnotic trance, participants subjectively rated their level of absorption and dissociation, and how long they thought the hypnotic trance lasted.

Intervention

The research hypothesis was that, by adding a body dissociation, catalepsy could facilitate and intensify the hypnotic trance, the intensity of which can be monitored and would be proportional to the parasympathetic tone. After randomization, subjects did either benefit from the usual positive hypnotic trance, or from the same hypnotic trance protocol associated with a hand catalepsy. Right after setting up ANI and pulse monitoring (T0), the subjects, who were in a sitting position, were asked about a place or activity that they usually enjoy visiting or practicing. This would serve as the basis for the positive hypnotic fifteen-minute trance. Right after that, the trance was induced and the subjects were asked to close their eyes (T1), another measure was done. Afterwards, the subjects received positive, relaxing, soothing suggestions, linked to the imagined activity that they chose. This period lasted between five to ten minutes. When the subject could report some comfort using a predetermined signal (putting a thumb up or nodding the head), another measure was done (T2), and then the subjects were progressively awakened from the hypnotic trance and another measure was done (T3). Subjects were then asked to subjectively rate their experience on a 0 (none) to 10 (maximal) scale of feeling of absorption and dissociation, then they were asked to subjectively assess the duration of the hypnotic trance in minutes from eye closure to eye opening [5]. Right after that, a final measure was done (T4). The actual duration of hypnosis from eye closing to opening was also recorded in minutes.

Statistical analysis

Based on our previous study showing a mean ± SD ANI value of 84 ± 12 during the hypnotic trance and estimating a 10% increase in ANI using catalepsy (corresponding to a mean ± SD ANI value of 92 ± 12), a total number of eighty subjects (forty in each group) was calculated in order to assess this difference using a unilateral t test with 𝛼=5% and 90% power (PASS^® 11, NCSS, LLC. Kaysville, Utah, USA) [2]. Continuous variables were compared using Mann-Whitney’s U-test or Student’s t-test according to data distribution assessed using Shapiro-Wilk’s test and categorical variables were compared using 𝝌² test. Variation of data during the different time-points were compared between groups using ANOVA for repeated measures. Continuous data are presented as mean ± SD or median [Q1-Q3] and qualitative data as n (%). All analyses were performed using JASP software version 0.17.3 (JASP Team 2023, open source).

In total, ninety subjects were included in the study. One subject was excluded because of deviation in the protocol standard (duration of the hypnosis session exceeding twenty minutes), leaving eighty-nine subjects for analysis including seventy-one (70%) women and eighteen (20%) men (Table 1). Among them, fifty-one (57%) were healthcare providers other than physicians and thirty (34%) were physicians (Table 1). Thirty-one subjects (35%) trained in medical hypnosis for less than five years or never, and forty-nine (56%) for more than five years (Table 1). Subject characteristics were similar between groups (Table 1).

There was a statistically different increase in ANI and decrease in both heart rate and respiratory rate over time with no difference with or without hand catalepsy (Figure 1). There was no statistically significant difference in absorption and dissociation subjective scales between groups (Table 2). The median [Q1-Q3] actual duration of hypnotic sessions was similar between the catalepsy and the control groups (9 [8-10] min vs. 8 [7-10] min, respectively). However, subjects in the catalepsy group estimated a longer duration of the hypnotic session (12 [10-15] min) than in the control group (10 [5-10] min) with a mean ± SD overestimation of 3 ± 4 min (p<0.001) (Table 2).

This study shows that using hand catalepsy provides a longer subjective perception of trance duration with no effect on self-rated degrees of dissociation or absorption and on ANI values in healthy volunteers during a pleasant hypnotic session.

To our knowledge, this is the first randomized controlled study assessing the effects of hand catalepsy on subjective trance perception and relative parasympathetic tone. There have been only a few studies assessing the objective effects of catalepsy [1,6–8]. A survey of two-hundred clinicians indicated that they allegedly often used catalepsy to test hypnotic ability in their patients [8]. Our findings lower the scientific validity of the usual taught statement that hand catalepsy would stabilize and deepen the hypnotic process [1]. Surprisingly, no effect of catalepsy was observed on parasympathetic tone and related parameters such as heart and respiratory rates. Indeed, we have previously shown that ANI values increase, and respiratory rate decreases in similar study conditions without catalepsy, and we expected that hand catalepsy would provide signs of higher parasympathetic tone.

However, we observed that hand catalepsy increased the subjective perception of time in our study subjects, which indicates that the use of this technique during hypnotic trances does objectively change the inner process. Therefore, this might be of use if the subjects or patients appear stressed, tachycardic, or if the operator would need that the patient perceives the process of care as longer than it is. For instance, this could help patients that undergo surgeries, as they could perceive fifteen minutes of comfort as actually having been longer than that, therefore bringing more comfort to them.

Our protocol was not perfect, as we had some missing values in the process, for two main reasons: some of the evaluators not having been prepared enough in the study protocol, and some of the evaluators either forgetting or refusing to measure respiratory rate, as they found it “difficult to do at the same time than the rest”. The study protocol would have been more robust if the whole process allowed that the planned facilitators were all present and better prepared, which would have allowed less lost values in the objective respiratory rate measurements mainly. To improve the blinding process, we also could have set up an opaque screen between the evaluators on one hand, and the facilitator/subject on the other.

The applicability of these results for patients is also limited, as most of the subjects were healthcare professionals and not patients. However, as healthcare professionals suffer as much as the general population of pain, anxiety, or other mental ailments, it is safe to hypothesize that we would find the same results among patients.

Lastly, absorption, dissociation and time perception were assessed on self-rated numeric scales for reasons of simplicity but this could be questionable since these scales need further study to be fully validated in clinical practice [5].

In conclusion, parasympathetic comfort increased during the hypnotic trance in the current study with no difference between groups. However, adding a hand catalepsy to a pleasant hypnotic trance did not appear to increase feelings of absorption or dissociation but created time distortion on the longer side that could be useful in some clinical settings. Nevertheless, further study is still needed to determine more precisely the physiological and psychological effects on hand catalepsy during the hypnotic trance.

Funding

This work was funded by internal sources only. The ANI monitors and electrodes were provided free of charge by MDoloris Medical Systems during the study.

Conflicts of interest

All the authors receive fees from Institut Émergences for teaching hypnosis to other healthcare professionals, in public or private teaching settings. Stéphane Radoykov also received fees from other institutes or universities to teach healthcare professionals. Emmanuel Boselli received honoraria and travel grants from MDoloris Medical Systems, Lille (France) for lectures on ANI. The authors report no other conflict of interest.

Ethics

The study was approved by our institutional review board and registered on ClinicalTrials.gov (NCT05306262) in 2022 before enrolling subjects.

Consent to participate

All participants provided written inform consent to participate to this study.

Author's contributions

EB made substantial contribution to the design of the work and on the acquisition, analysis and interpretation of data for the work, revised the work critically for important intellectual content, approved the final version to be published and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. SR made substantial contribution to the acquisition and interpretation of data for the work, drafted the work, approved the final version to be published and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. XP made substantial contribution to the design of the work and on the acquisition of data for the work, revised the work critically for important intellectual content, approved the final version to be published and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. CV made substantial contribution to the acquisition and interpretation of data for the work, drafted the work, approved the final version to be published and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Acknowledgements

The authors wish to thank Drs Didier Anne, Arnaud Bouzinac, Stéphane Charré, Philippe Houssel, Mathieu Landry, Hervé Musellec, Olivier Fleureaux, Nicolas Fusco, Valérie Fuzier, Olivier Prian, Christian Schmitt, Mrs. Élodie Belz-Guillo, Pascale Hagnéré, Cécile Naudain, Mary Virot and Mr. Jérémy Cuna for their participation in this study.

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Table 1 Subject characteristics. Results are expressed as mean ± SD or n (%).

	Catalepsy (n=44)	Control (n=45)	p
Age, yrs	52 ± 10	49 ± 10	0.27
Gender Female Male	33 (75) 11 (25)	38 (84) 7 (16)	0.79
Weight, kg	68 ± 14	66 ± 13	0.27
Height, cm	168 ± 9	168 ± 7	0.97
Profession Non-physician healthcare provider Physician Other	26 (59) 13 (26) 5 (11)	25 (55) 17 (38) 3 (7)	0.59
Experience in hypnosis None Less than one year One to five years More than five years	1 (2) 2 (5) 15 (34) 26 (59)	4 (9) 2 (4) 16 (36) 23 (51)	0.57

Table 2 Study results. Results are expressed as median [Q1-Q3] or mean ± SD.

	Catalepsy (n=44)	Control (n=45)	p
Absorption (0-10 scale)	8 [7-9]	8 [7-9]	0.97
Dissociation (0-10 scale)	8 [7-9]	8 [6-9]	0.45
Estimated duration of hypnosis^a (min)	12 [10-15]	10 [5-10]	<0.001
Actual duration of hypnosis^b (min)	9 [8-10]	8 [7-10]	0.07
Mean difference (min)	3 ± 4	0 ± 4	0.001

^aEstimated duration of hypnosis session by participants from eye closing (T1) to eye opening (T3). ^bCalculated duration of hypnosis session by investigators from eye closing (T1) to eye opening (T3). ^cDifference between estimated and actual duration of hypnosis.

No competing interests reported.

Effects of hand catalepsy on subjective trance perception and relative parasympathetic tone in healthy volunteers during pleasant hypnotic session: a randomized controlled study

Status:

Version 1

Abstract

Figures

1 Introduction

2 Methods

Measures

Intervention

Statistical analysis

3 Results

4 Discussion

Declarations

Conflicts of interest

References

Tables

Additional Declarations

Status:

Version 1