Heart Rate or Heart Rate Variability? Evidence from Breath Suspension

Abstract

Dear Editor:

Studies have assessed changes in autonomic variables in terms of heart rate variability (HRV) during meditation, but their results have been conflicting. Recently, Telles and colleagues' excellent study¹ compared changes in HRV measures during the first four meditative states—cancalata (random thinking), ekagrata (nonmeditative focusing), dharana (meditative focusing), and dhyana (effortless meditation)—described in traditional yoga texts. Their results revealed that the discrepancy in changes in HRV measures might be due to the different stages. At the end of the Discussion section, the authors mention the ultimate state in yoga, samadhi, which manifests with breath suspension. They did not explore this advanced meditative state in their study. Therefore, we would like to share our results about changes in HRV measures during breath suspension.

We collected and compared HRV measures in time and frequency domains, along with heart rate and blood pressure, during random thinking, breath meditation, and the advanced meditative stage with breath suspension in 10 meditative sessions conducted by an experienced meditator. The results (Table 1) show that none of HRV measures of time and frequency domains differed significantly during meditation. In contrast, heart rate and systolic blood pressure reliably decreased as meditation advanced. Because the meditation technique used in this study is close to meditative focusing, the results are concordant with the dharana state described in Telles and colleagues' study.

Table 1.

Comparisons of Heart Rate, Blood Pressure, and Heart Rate Variability Measures During Random Thinking, Breath Meditation, and Advanced Meditative Phase with Breath Suspension

Measure	Random thinking	Breath meditation	Advanced meditation with breath suspension	p-Value
Heart rate (beats/min)	73.6±7.0	67.3±6.2	64.1±5.2	0.000, R>B, R>A, B>A
SBP (mm Hg)	134.1±7.7	118.8±8.2	117.0±5.2	0.000, R>B, R>A
DBP (mm Hg)	87.5±3.0	90.5±5.7	86.1±6.6	0.011, B>A
RMSSD (ms)	48.3±24.9	30.1±5.2	34.8±6.3	0.067
pNN50 (%)	18.0±13.4	9.4±6.1	12.9±5.6	0.150
nuHF (%)	51.2±12.2	45.1±9.1	45.6±16.7	0.975
nuLF (%)	48.8±12.2	54.8±9.0	54.3±16.6	0.975
LF/HF	1.07±0.58	1.29±0.48	1.45±0.81	0.905

Data are presented as mean±standard deviation.

A, advanced meditation with breath suspension; B, breath meditation; DBP, diastolic blood pressure; LF/HF, low frequency–to–high frequency ratio; ms, mini-second; nuHF, normalized unit of high frequency; nuLF, normalized unit of low frequency; pNN50: proportion of the number of pairs of successive normal/normal intervals that differ by more than 50 ms, divided by total number of normal/normal intervals; R, random thinking; RMSSD, root-mean-square of the successive differences of normal/normal intervals; SBP, systolic blood pressure.

By using a device to monitor the chest circumstance of the meditator, the current study confirmed that the timing of breath suspension coincided with the subjective experience of breath suspension, complete quiescence, and absence of self-boundary. HRV measures, on the other hand, did not concord with the subjective experience of pure quiescence. Because other authors have argued that HRV is not an index of autonomic control of the circulation,² whether HRV can be an ideal index of sympathetic or parasympathetic activities remains questionable. According to the current results, the variations of HRV measures, manifested as the ratio of standard deviation to mean, are much greater than those of heart rate and blood pressure. This has also been shown in previous studies.^1,3,4 According to this view, HRV measures cannot be accurate indexes.

The current results suggest that heart rate itself is a better HRV measure for meditation and agree with findings from Mukherjee et al.⁵ These authors examined the sensitivity to mental effort and reliability of various HRV measures. Their data revealed that heart rate was the most sensitive and reliable measure, followed by measures of time domain; HRV measures of frequency domain were much less sensitive and reliable. Therefore, Mukherjee and colleagues suggested that heart rate can be considered a strong and reliable outcome measure in mental effort tasks and that heart rate is the most sensitive measure of HRV in cognitive function tasks. The current data reported here also support this point.

Footnotes

Disclosure Statement

No competing financial interests exist.

References

Telles

, Raghavendra

, Naveen

, et al. Changes in autonomic variables following two meditative states described in yoga texts. J Altern Complement Med, 2013; 19:35–42.

Taylor

, Studinger

Counterpoint: cardiovascular variability is not an index of autonomic control of the circulation. J Appl Physiol, 2006; 101:678–681; discussion 681.

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Inward-attention meditation increases parasympathetic activity: a study based on heart rate variability. Biomed Res, 2008; 29:245–250.

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, Chang

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, et al. Fifteen minutes of chair-based yoga postures or guided meditation performed in the office can elicit a relaxation response. Evid Based Complement Alternat Med, 2012; 2012:501986.

Mukherjee

, Yadav

, Yung

, et al. Sensitivity to mental effort and test-retest reliability of heart rate variability measures in healthy seniors. Clin Neurophysiol, 2011; 122:2059–2066.