This study was conducted across two months at a Wellness Center where free group meditation with Himalayan Singing Bowls is offered twice a month to anyone who is interested. The participants who volunteered to join the study signed informed consent. Ethics committee approval was not required since the free meditation is open to the public and the interventions were non-invasive, consistent with earlier work in this area 1318. A room with good soundproof interiors was used while maintaining 25 Degree Centigrade temperature (Figure 2). This ensured the minimum impact of outside sound and a pleasant indoor temperature. The exclusion criteria included the presence of (a) chronic disease (b) epilepsy (c) pacemaker in the body and (d) metal parts due to any surgery inside the body.

Total 105 subjects signed the informed consent form for PANAS forms, 21 subjects signed POMS form and 20 subjects agreed to undergo the measurements of HRV. Those who agreed for PANAS and POMS completed the self-administered survey 5 minutes before and 5 minutes after the meditation and individuals who agreed to wear the HRV device wore it throughout the meditative practice lasting 40 minutes.

The meditation took place from sharp 7:00 PM to 7:40 PM, twice a month and on the dates communicated in advance. The participants were instructed to sit in a cross-legged meditative posture on a meditation chair that provides back support. After completing the signed consent, the participants were given brief instructions specifying the duration of the meditation (exactly 40 mins) and required to focus the attention on the sound vibrations of the singing bowl or observe their breath - especially when their mind gets diverted. The meditation is conducted by a trained therapist with the use of (a) 7 handmade singing bowls ranging from 18cm to 29cm diameter and (b) one Ting-Sha (as shown in Figure 3) 19. No gongs or other music or sound instruments were used. Participants were instructed to do three humming sounds at the beginning and end of the meditation and throughout the process, they are requested to keep the eyes closed while maintaining the attention on observation of the sound vibrations or their own breath. No other instructions are given. In the beginning, after the three humming sounds, the participants were instructed to follow the session leader s instruction on progressive muscle relaxation (PMR), lasting maximum 3 mins requesting the participants to relax all body parts starting with toes, legs and so on. For the balance of the session, only the sound vibrations of the bowls and Ting-Sha were used, i.e. No more verbal instructions were provided. As mentioned earlier, the sessions ended with three humming sounds. At the end of the session, the participants were requested to slowly observe the changes in the mind and the body and open the eyes when they were comfortable. The lights in the room were closed throughout the meditation. During the mediation, the sound vibrations of the bowl followed a simple pattern of maintaining a gap of about 4-5 seconds between the successive hitting of the bowl and periodically, all the bowls were hit a bit faster to create louder sound from all bowls together (every 8-10 minutes). The bowls were hit by a hammer and the rimming used a wooden stick covered by leather at one end. The entry to the room was closed throughout the practice and air conditioning was maintained at a constant temperature (Figure 2 shows the room). The bowls (shown in Figure 3) were placed in one corner of a long room with a seating capacity of 20 individuals.

The psychological parameters were captured using PANAS and abbreviated POMS forms. The HRV data were collected to measure physiological parameters using the Emwave Pro device (HeartMath, LLC) with PPG (Photoplethysmogram) ear sensor during the entire session. The HRV data was analyzed using Kubios HRV premium software on a Windows 10 PC. The features available in Kubios HRV Premium software (version 3.3.0) were used to export the parameters in a. txt file which included Heart Rate, Stress Index and RMSSD. Each .txt file was tabulated and analyzed using Microsoft Excel pivot table. The data was integrated for each of the 5 minutes of the 40 minute long sessions. Microsoft Excel features, specifically function TTEST, were used to do statistical analysis of the data. The analysis used Paired T-test to compare the changes between various intervals for each method (details are captured in the results).

77 out of the 105 subjects who filled up PANAS forms properly were included in the study. 17 participants completed the abbreviated POMS forms to assess Tension (TEN), Anger (ANG), Fatigue (FAT), Depression (DEP), Confusion(CON), Esteem Related Affect (ERA) and Vigor (VIG). All the forms were filled by the participant before and after the meditation and entered into Microsoft Excel sheet for further analysis. 15 participants completed the full HRV recording during the meditation process to measure the physiological parameters like heart rate, and stress index, etc.

Demographics of the subjects and the number of subjects attended the various data collection methods, i.e. PANAS, POMS, and HRV recorded are captured in Table 1.

PANAS is a self-report psychometric questionnaire that can be used across a diverse sample group, measures two segments or moods of an individual. Each segment has 10 terms in which the subject can rate from 1 to 5. Eventually, we can measure the positive and negative affect of the subject before and after any intervention 2021. PANAS has been widely used in the areas ranging from overall mood change in areas ranging from clinical studies involving patients as well as in the areas involving healthy individuals doing various activities such as creative work 22. PANAS has also been used to measure psychological changes in mood in studies related to meditation and also singing bowls. While PANAS provides valuable insight about the mood, additional validation of the changes in mood via physiological data could add more credibility to the overall conclusion 2324. The abbreviated POMS is a simple and effective self-reported questionnaire to understand changes in specific moods 18. The expectation was to understand the specific impact on positive and negative mood with the use of PANAS and additionally understand the changes in specific moods with the help of abbreviated POMS.

HRV is a beat-to-beat interval between successive heartbeats (also known as RR or NN interval) and indicates a physiological state. It has been used to evaluate the impact of the singing bowl during supine position1317. HRV is also emerging as a meaningful marker of autonomic nervous system imbalance, stress, metabolic syndrome and chronic disease. For this study, we used (a) Heart Rate (b) RMSSD (The RMSSD reflects the beat-to-beat variance in heart rate and is the primary time domain measure used to estimate the vagally-mediated changes reflected in HRV) and (c) Stress Index (The Baevsky s stress index is a rather widely used index of cardiovascular system stress and is strongly linked to sympathetic nervous activity). Together, these three physiological measures provide an understanding of the relaxation process as compared to heart rate alone and provide a more comprehensive perspective about the changes in the autonomic nervous system. Specifically, changes heart rate and stress index could provide an indicator of the reduction in sympathetic nervous system activity. The increase in RMSSD denotes a pronounced parasympathetic nervous system activity 28.

Pre and post meditation data of PANAS for 77 enrolled participants showed a statistically significant increase in the positive affect (pre=33.25, post=36.26, p<0.00) and a statistically significant reduction in the negative affect (pre=19.92, post= 14.21, p<0.00) (Table 2).

The above results confirm the primary objective (a) of the study that there is a statistically significant reduction in negative affect and a similar increase in positive affect.

The study explored the mind-body impact of a single session of seated HSB sound bath meditation. The results indicate significant changes i.e. reduction in negative affect and an increase in positive affect. Unlike the previous study, this study method has generated a positive trend in PANAS with an increase in PA and a decrease in NA18. It is likely that a longer duration intervention may  have contributed to the positive impact on the mood since as shown in Figure 4, the HRV changes during the initial 15 minutes indicate some activation of sympathetic activation due to an increase in stress index along with a decrease in RMSSD. However, after the initial 15 minutes, the overall trend in HRV has changed denoting an increase in parasympathetic nervous system activity along with a decrease in sympathetic activity. While this trend in HRV data does not directly explain the changes in the mood, it still shows a more relaxed body which may have triggered the beneficial changes in the mood.

The findings are significant since both the mind and the body changes are positive and demonstrate a significant psychological and physiological benefit of such a session. Such sessions can be very useful for individuals keen to reduce stress and improve overall mood. Applications could also include individuals facing sleep disruption or an inability to relax or generalized anxiety. Such practice, on a regular basis, could speed up the relaxation response, known to have a profound impact on the mind and the body5. Some creative possibilities for applying sound bath meditation could include pre-surgery relaxation for subjects as well as health care professionals, individuals suffering from depressive mood, anxiety and so on.