Transcranial direct current stimulation improves the QT variability index and autonomic cardiac control in healthy subjects older than 60 years

Figures & data

Figure 1 Photograph taken during T3 anodal transcranial direct current stimulation (tDCS) in a representative subject.

Note: Photograph by the author.

Figure 2 An example of a 15-minute recording during sham or real anodal transcranial direct current stimulation (tDCS).

Notes: (a) shows in detail the examined electrocardiogram (ECG) and blood pressure variables (b). The following intervals were measured: RR, QT_e (from the Q wave to the T wave end), QT_p (from the Q wave to the T wave peak), and T_e (difference between QT_e and QT_p).

Figure 3 Example of a 5-minute ECG recording: RR, QT_e (from the Q wave to the T wave end), QT_p (from the Q wave to the T wave peak), and T_e (difference between QT_e and QT_p) intervals and relative variability indexes: SDNN, QT_eVI, QT_pVI, and T_eVI.

Abbreviations: ECG, electrocardiogram; SDNN, standard deviation of all R-R intervals.

Figure 4 (A) shows the spectrum for SBP, (B) shows the R–R variability spectrum, and (C) shows the index during sham (left panel) or active tDCS (right panel).

Notes: Alpha indexes: the relationship between the square root of a single spectral component of R–R variability (LF or HF) and the square root of the same spectral component for SBP. The (C) shows the three spectral windows considered: a LF power (0.04–0.15 Hz) and a HF power (0.15–0.40 Hz). R–R and arterial pressure variability were recorded simultaneously during controlled breathing. Note the increased HF_NU and decreased LF_NU and LF: HF during tDCS, a pattern reflecting a sinus vagal increase and sinus sympathetic decrease. LF:HF, ratio between LF and HF.^30,35
Abbreviations: SBP, systolic blood pressure; tDCS, transcranial direct current stimulation; LF, low frequency; HF, high frequency; TP, total power; VLF, very low-frequency; NU, normalized units; PSD, power spectral density.

Table 1 Characteristics of the healthy elderly volunteers who underwent transcranial direct current stimulation

Characteristics	Age <60 years	Age ≥60 years	P-values
Patients, n	29	21
Men/women	12/17	11/10	ns
Age, years	36±11	70±6	<0.0001
Body mass index, kg/m^2	24±3	25±3	ns
Heart rate, beats/min	68±9	66±7	ns
Systolic blood pressure, mmHg	110±17	108±7	ns
Diastolic blood pressure, mmHg	60±10	61±10	ns

Note: Data presented as mean ± standard deviation unless stated otherwise.

Abbreviation: ns, nonsignificant.

Table 2 RR, QT_e, QT_p, and T_e interval data in the healthy elderly volunteers who underwent sham and active tDCS

Variables	Age <60 years	Age ≥60 years	P-values
Sham tDCS
Patients, n	29	21
RR mean, ms	903±126	914±106	ns
RR variance, ms^Citation2	1,552 (1,741)	637 (1,050)	0.014
QTe mean	334±24	346±24*	ns
QTe variance, ms^Citation2	6 (6)	14 (17)	0.020
QTp mean	260±22	267±23	ns
QTp variance, ms^Citation2	16 (13)	25 (21)	ns
Te mean	75±11	79±12*	ns
Te variance, ms^Citation2	21 (20)	36 (34)	ns
QTe →RR, coherence	0.205±0.030	0.202±0.033	ns
QTp →RR, coherence	0.223±0.044	0.212±0.032	ns
Te →RR, coherence	0.206±0.035	0.205±0.029	ns
Te →QTp, coherence	0.683±0.199	0.663±0.134	ns
QTe VI	−1.44 (0.60)	−0.86 (1.15)*	0.004
QTp VI	−0.95 (0.68)	−0.57 (0.85)	0.007
Te VI	0.30 (0.70)	0.68 (0.70)	0.004
Anodal tDCS
Patients, n	29	21
RR mean, ms	897±125	930±130	ns
RR variance, ms^Citation2	1,543 (1,915)	723 (106)	0.004
QTe mean	334±28	353±30*	0.032
QTe variance, ms^Citation2	7 (6)	12 (17)	0.033
QTp mean	256±24	266±28	ns
QTp variance, ms^Citation2	16 (23)	23 (21)	ns
Te mean	78±10	84±11*	0.030
Te variance, ms^Citation2	22 (24)	35 (27)	0.033
QTe →RR, coherence	0.213±0.37	0.204±0.32	ns
QTp →RR, coherence	0.223±0.041	0.211±0.043	ns
Te →RR, coherence	0.205±0.027	0.202±0.025	ns
Te →QTp, coherence	0.726±0.148	0.697±0.129	ns
QTe VI	−1.70 (0.60)	−1.08 (0.93)*	0.006
QTp VI	−1.05 (0.58)	−0.55 (0.68)	0.009
Te VI	0.14 (0.45)	0.69 (0.62)	0.003

Notes: Values expressed as mean ± SD or median (interquartile range 75th percentile to 25th percentile).

* P<0.05 sham vs tDCS. QT_e, QT interval (from q to end of T wave); QT_p, QT_p interval (from q to peak of T wave); T_e, T_e interval (from peak to end of T wave).

Abbreviations: tDCS, transcranial direct current stimulation; ns, nonsignificant; SD, standard deviation.

Table 3 Power spectral analysis of RR and SBP data in the healthy elderly volunteers who underwent sham and active tDCS

Variables	Age <60 years	Age ≥60 years	P-values
Sham tDCS
Patients, n	29	21
LFRR, ln ms^Citation2	6.02±0.89	5.15±1.49	0.014
HFRR, ln ms^Citation2	5.65±1.07	4.32±1.43	0.001
LFRR, nu	51 (22)	63 (25)*	ns
HFRR, nu	42 (24)	26 (24)*	ns
LF/HFRR	1.15 (1.65)	2.6 (3.47)*	ns
LFSBP, mmHg^Citation2	6 (10)	9 (17)	ns
α LF, mmHg/ms	7 (8)	6 (4)	0.020
α HF, mmHg/ms	11 (8)	6 (5)*	0.002
SBPfinomer, mmHg	110±17	108±28	ns
DBPfinomer, mmHg	52±14	51±15	ns
Stroke volume, mL	69±12	52±14	0.001
Cardiac output, L/m	4.47±0.87	3.45±1.06	0.001
Systemic peripheral resistance, u	1,579 (740)*	2,155 (1,181)*	0.01
Anodal tDCS
Patients, n	29	21
LFRR, ms^Citation2	6.25±0.91	5.26±1.32	0.003
HFRR, ms^Citation2	5.64±1.13	4.90±1.71	ns
LFRR, nu	59 (23)	52 (24)*	ns
HFRR, nu	36 (21)	40 (23)*	ns
LF/HFRR	1.67 (2.18)	1.23 (1.70)*	ns
LFSBP, mmHg^Citation2	6 (5)	7 (6)	ns
α LF, mmHg/ms	9 (6)	6 (7)	0.018
α HF, mmHg/ms	13 (10)	8 (10)*	ns
SBPfinomer, mmHg	102±14	92±28	ns
DBPfinomer, mmHg	45±14	44±15	ns
Stroke volume, mL	72±14	53±16	0.001
Cardiac output, L/m	4.67±0.97	3.44±0.97	0.001
Systemic peripheral resistance, u	1,296 (428)*	1,600 (1,111)*	0.038

Notes: Values are expressed as mean ± SD or median (interquartile range 75th percentile to 25th percentile).

* P<0.05 sham vs tDCS.

Abbreviations: SBP, systolic blood pressure; tDCS, transcranial direct current stimulation; LF, low frequency power; HF, high frequency power; ns, nonsignificant; nu, normalized units; DBP, diastolic blood pressure; SD, standard deviation.

Figure 5 QT_eVI during sham or anodal tDCS in volunteers younger and older than 60 years.

Notes: In the box plots, the central line represents the median distribution. Each box spans from 25th to 75th percentile points, and error bars extend from 10th to 90th percentile points.
Abbreviations: QT_eVI, QT_e variability index; tDCS, transcranial direct current stimulation; ns, nonsignificant.

Figure 6 Relationship between QT_e variability index (QT_eVI) and age in healthy control subjects during sham or active transcranial direct current stimulation (tDCS).

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