Efficacy and Methodology of Remote Heart Rate Variability Biofeedback Interventions for Mental Health: A Systematic Review and Meta-Analysis

Table 2 Meta-regression analyses

Categorical variable	QM	QMp	k	β	SE	p-val
Depression
Practice time	4.475	0.107
Interface	6.721	0.081
HRVB-method	4.572	0.102
Stress
Practice time	2.137	0.343
Interface*	6.542	0.038
Screen on device		5	0.027	0.115	0.815
Smartphone app/other software*		3	0.547	0.215	0.011
HRVB-method	3.115	0.374
HRV
Practice time*	8.291	0.016
20 min or less*		6	0.279	0.132	0.035
Over 20 min		3	0.370	0.189	0.050
Interface*	9.122	0.010
Screen on device**			8	0.443	0.162	0.006
Smartphone app/other software			2	0.454	0.352	0.197
HRV-B method*	9.101	0.011
Maximize resonance*			5	0.488	0.205	0.017
Stepped method			5	0.399	0.215	0.064

Continuous variable	k	QM	QMp	β	SE
Depression
Study duration	10	0.290	0.590
Total practice time	10	0.545	0.460
Number of lab visits	10	1.445	0.229
Practice time per day	10	0.014	0.906
Age of participants	10	0.029	0.865
Gender(% female)	10	1.990	0.158
Stress
Study duration	8	0.000	0.990
Total practice Time	8	1.313	0.252
Number of lab visits*	8	6.346	0.012	0.134	0.053
Practice time per day	8	1.967	0.161
Age of participants	8	0.003	0.957
Gender(% female)*	8	5.885	0.015	− 0.883	0.364
HRV
Study duration	10	0.017	0.897
Total practice time	9	2.23	0.135
Number of lab visits	10	1.527	0.217
Practice time per day	9	0.004	0.947
Age of participants	10	0.543	0.461
Gender(%Female)	10	0.645	0.422

Negative values for psychometric outcomes (Depression and Stress) indicate greater improvement, positive values for HRV indicate greater increase. Bold indicates significance level < 0.05.
k, number of studies; QM, omnibus test of moderators; QMp, p-value of QM; β, slope; SE, standard error. *< 0.05 significance level; **< 0.01 significance level