Reducing suicidal ideation by biofeedback-guided respiration – heart rate coherence

Figures & data

Table 1. Patient demographics and psychiatric scores.

Variable	MDDSI	MDD	CONT	p Value
N	16	16	29
Gender male, %	5 (31.25%)	3 (18.75%)	12 (41.37%)
Age (y)	37.5 ± 10.37	32.31 ± 6.95	28.00 ± 6.35	0.00**
WC (cm)	95.5 ± 16.64	82.73 ± 10.89	76.24 ± 9.61	0.00*^,**
Height (cm)	164.6 ± 10.22	164.44 ± 8.41	162.28 ± 9.78	0.66
BMI (kg/m^2)	34.77 ± 25.65	24.98 ± 3.27	23.89 ± 3.44	0.03**
BDI	36.06 ± 12.23	33.19 ± 11.55		0.50
GAD7	17.94 ± 11.03	14.56 ± 4.21		0.26
PHQ9	21.06 ± 12.49	18.81 ± 4.48		0.50
Suicidal score	17.35 ± 7.25	0.92 ± 1.75		0.00*

*Significant difference between MDDSI and MDD; **significant difference between CONT and MDDSI.

BMI: body mass index; WC: waist circumference; BDI: Beck depression inventory; GAD7: general anxiety disorder; PHQ-9: patients health questionnaire for depression classification

Figure 1. Tone-entropy for lag 10 between control, MDD and MDDSI.

Table 2. Tone-entropy at different lags (1 to 10).

Parameter	m	MDDSI	MDD	CONT	MDDSI vs. MDD	MDD vs. CONT	CONT vs. MDDSI
		Med ± IQR	Med ± IQR	Med ± IQR	p Value	p Value	p Value
Tone	1	−0.09 ± 0.14	−0.13 ± 0.05	−0.18 ± 0.19	0.01*	0.22	0.00*
	2	−0.17 ± 0.20	−0.22 ± 0.17	−0.37 ± 0.31	0.02*	0.27	0.00*
	3	−0.15 ± 0.26	−0.19 ± 0.14	−0.37 ± 0.33	0.04*	0.30	0.01*
	4	−0.23 ± 0.34	−0.26 ± 0.18	−0.34 ± 0.29	0.02*	0.30	0.01*
	5	−0.22 ± 0.42	−0.29 ± 0.18	−0.40 ± 0.28	0.02*	0.24	0.01*
	6	−0.17 ± 0.38	−0.25 ± 0.18	−0.39 ± 0.28	0.02*	0.15	0.00*
	7	−0.18 ± 0.32	−0.26 ± 0.16	−0.37 ± 0.28	0.01*	0.18	0.00*
	8	−0.20 ± 0.29	−0.26 ± 0.18	−0.43 ± 0.32	0.03*	0.15	0.00*
	9	−0.21 ± 0.31	−0.28 ± 0.20	−0.42 ± 0.32	0.06	0.10	0.01*
	10	−0.21 ± 0.33	−0.28 ± 0.20	−0.40 ± 0.32	0.07	0.08	0.01*
Entropy	1	3.82 ± 0.91	4.12 ± 0.50	5.21 ± 0.62	0.07	0.03*	0.00*
	2	4.01 ± 0.89	4.59 ± 0.51	5.12 ± 0.61	0.09	0.06	0.00*
	3	4.07 ± 0.87	4.78 ± 0.50	4.96 ± 0.62	0.27	0.04*	0.00*
	4	4.60 ± 0.82	4.73 ± 0.46	5.08 ± 0.54	0.15	0.06	0.01*
	5	4.39 ± 0.79	4.82 ± 0.45	5.02 ± 0.52	0.11	0.06	0.00*
	6	4.58 ± 0.81	4.88 ± 0.46	5.10 ± 0.51	0.16	0.02*	0.00*
	7	4.68 ± 0.75	4.82 ± 0.49	4.99 ± 0.52	0.18	0.03*	0.00*
	8	4.69 ± 0.75	4.86 ± 0.41	5.06 ± 0.52	0.15	0.08	0.00*
	9	4.78 ± 0.76	4.81 ± 0.41	5.13 ± 0.51	0.21	0.02*	0.00*
	10	4.78 ± 0.77	4.83 ± 0.41	5.14 ± 0.52	0.17	0.03*	0.00*

Med: median; IQR: inter-quartile range; m: lag.

*Statistical significance between group pairs.

Figure 2. Tone-entropy responses while changing lags from 1 to 10 for MDDSI, MDD and Control.

Table 3. Traditional HRV markers for MDDSI, MDD and control.

HRV	MDDSI (Median ± IQR)	MDD (Median ± IQR)	CONT (Median ± IQR)
Mean HR	790.06 ± 90.2*	864.77 ± 140.11	858.06 ± 111.43
SDHR	45.00 ± 19.45*	40.90 ± 11.65**	61.17 ± 22.03
RMSSDHR	25.76 ± 19.50*	39.54 ± 13.86***	54.36 ± 21.00
VLF	964.71 ± 710.30	869.87 ± 450.50	1375.04 ± 1087.45
LF	614.54 ± 759.02*	723.66 ± 436.20	1000.52 ± 598.34
HF	412.33 ± 610.30*	566.70 ± 440.00	1154.90 ± 1240.30
LF/HF	2.12 ± 1.40	2.4 ± 1.89	2.1 ± 2.0

Data is given as median ± IQR.

HRV: heart rate variability; HR: heart rate; SDHR: standard deviation of heart rate; RMSSDHR: root mean square of standard deviation of heart rate; VLF: very low frequency; LF: low frequency; HF: high frequency.

*^, ** and ***: Mean significant differences between CONT vs. MDDSI, MDD vs. CONT and MDDSI vs. MDD pairs, respectively.

Table 4. Cardiorespiratory and HRV variables.

	Control	MDD	MDDSI
RRI (ms)	859 ± 102**	794 ± 92	754 ± 100
fR (breaths/min)	15 ± 5**	19 ± 4	24 ± 5
ARSA (ms)	23 ± 3.2**	20 ± 2.5	19 ± 2
Normalized nARSA (%) (ARSA/RRI)	3.0 ± 0.6**	2.8 ± 0.4***	2.0 ± 0.2
λ	0.79 ± 0.6**	0.51 ± 0.4***	0.43 ± 0.7

Data shown as (median ± IQR).

RRI: interbeat interval; MDD: major depressive disorder; MDDSI: major depressive disorder with suicidal ideation; f_R: breathing frequency; A_RSA: amplitudes of RSA; nA_RSA: normalized amplitude of RSA; λ: phase coupling coefficient.

Significant difference (p < 0.05) between **MDDSI/Control, ***MDD/MDDSI.

Table 5. Correlation coefficients (r) of time domain and multi-lag T-E features with Phase synchronization parameter (λ).

Lag, m	Feature	CONT	MDD	MDDSI
		λ	λ	λ
1	Entropy	0.51*	0.42*	0.28
	Tone	−0.07	−0.05	−0.05
2	Entropy	0.53*	0.46*	0.26
	Tone	−0.08	−0.09	−0.09
3	Entropy	0.42*	0.49*	0.29
	Tone	0.11	−0.10	−0.12
4	Entropy	−0.29	−0.37	0.23
	Tone	0.12	−0.11	−0.01
5	Entropy	−0.21	−0.34	−0.39*
	Tone	0.12	0.14	0.14
6	Entropy	−0.29	−0.47*	−0.44*
	Tone	0.15	0.17	0.16
7	Entropy	−0.28	−0.43*	−0.43*
	Tone	0.01	0.01	0.01
8	Entropy	−0.25	−0.40*	−0.47*
	Tone	0.31	0.11	0.11
9	Entropy	−0.19	−0.45*	−0.53*
	Tone	0.39*	0.21	0.26
10	Entropy	−0.22	−0.48*	−0.55*
	Tone	0.38	0.22	0.22
HRV	MeanHR	−0.19	−0.28	−0.28
	SDHR	0.61*	0.29	0.29
	RMSSDHR	0.51*	0.47*	0.31
	VLF	−0.01	0.04	0.04
	LF	−0.41*	−0.34	−0.25
	HF	0.61*	0.44*	0.24

HRV: heart rate variability; HR: heart rate; SDHR: standard deviation of heart rate; RMSSDHR: root mean square of standard deviation of heart rate; VLF: very low frequency; LF: low frequency; HF: high frequency; λ: phase coupling coefficient.

*Significant correlation (p < 0.05).

Data availability

Data is available on request from the corresponding author.