Several studies have explore the effects of religious changes, such as OM, on physiological parameters such as heart rate, blood pressure and heat rate variability (HRV).
Overall, the effects were considered beneficial.
For example, a brief chanting of OM (5 min) might enhance parasympathetic nervous system activity, promote relaxation, and provide calmness.
Rhythm formulas that involve breathing at 6 breaths per minute induced favorable psychological and possibly physiological effects. Breathing at 6 breaths per minute is very close to so called resonance frequency breathing for most people.
Physiological Effects of Cryptic Ancient Religious Chants. Abhijit. V. Bodne Varsha Patond. Journal of Pharmaceutical Research International, Volume 33, Issue 60B, Page 1042-1048 DOI: 10.9734/jpri/2021/v33i60B34711 Published: 23 December 2021
Effect of rosary prayer and yoga mantras on autonomic cardiovascular rhythms: comparative study. BMJ. 2001 Dec 22; 323(7327): 1446–1449. doi: 10.1136/bmj.323.7327.1446 PMCID: PMC61046 PMID: 11751348
Immediate Effects of OM Chanting on Heart Rate Variability Measures Compared Between Experienced and Inexperienced Yoga Practitioners. Int J Yoga. 2022 Jan-Apr; 15(1): 52–58. Published online 2022 Mar 21. doi: 10.4103/ijoy.ijoy_141_21 PMCID: PMC9015091 PMID: 35444369