Cardiac Nerve Activity Research Articles

Central command does not decrease cardiac parasympathetic efferent nerve activity during spontaneous fictive motor activity in decerebrate cats

To examine whether withdrawal of cardiac vagal efferent nerve activity (CVNA) predominantly controls the tachycardia at the start of exercise, the responses of CVNA and cardiac sympathetic efferent nerve activity (CSNA) were directly assessed during fictive motor activity that occurred spontaneously in unanesthetized, decerebrate cats. CSNA abruptly increased by 71 ± 12% at the onset of the motor activity, preceding the tachycardia response. The increase in CSNA lasted for 4-5 s and returned to the baseline, even though the motor activity was not ended. The increase of 6 ± 1 beats/min in heart rate appeared with the same time course of the increase in CSNA. In contrast, CVNA never decreased but increased throughout the motor activity, in parallel with a rise in mean arterial blood pressure (MAP). The peak increase in CVNA was 37 ± 9% at 5 s after the motor onset. The rise in MAP gradually developed to 21 ± 2 mmHg and was sustained throughout the spontaneous motor activity. Partial sinoaortic denervation (SAD) blunted the baroreflex sensitivity of the MAP-CSNA and MAP-CVNA relationship to 22-33% of the control. Although partial SAD blunted the initial increase in CSNA to 53% of the control, the increase in CSNA was sustained throughout the motor activity. In contrast, partial SAD almost abolished the increase in CVNA during the motor activity, despite the augmented elevation of 31 ± 1 mmHg in MAP. Because afferent inputs from both muscle receptors and arterial baroreceptors were absent or greatly attenuated in the partial SAD condition, only central command was operating during spontaneous fictive motor activity in decerebrate cats. Therefore, it is likely that central command causes activation of cardiac sympathetic outflow but does not produce withdrawal of cardiac parasympathetic outflow during spontaneous motor activity.

Heart Rate Variability as a Potential Marker for the Recurrence of Atrial Fibrillation after Electrical Cardioversion

Backgound: Cardiac autonomic nerve activity is important in cardiac arrhythmogenesis. We evaluated whether heart rate variability (HRV) with pre and post-DC cardioversion (DCC) could be used as predictors for atrial fibrillation (AF) recurrence after successful DCC. Methods: Forty-one consecutive patients with persistent AF who had HRV evaluation were treated with DCC. Three patients failed sinus conversion and thirty-eight patients (59 ages, 68% men) were enrolled. After successful DCC, post-DCC HRV was measured for 2 to 3 hours before discharge. Results: Twenty-one (55%) patients showed AF recurrence within 2 months after DCC. With HRV measured before DCC, those with recurrence showed higher VLF (10911±6080 vs. 7183±3794 ms2), LF (5781±2921 vs. 3770±1686 ms2), total power (17552±9145 vs. 12030±5540 ms2), and SDANN (173±45 vs. 140±46 ms), whereas MSSD (97±25 vs. 138±261 ms) was lower than those in sinus rhythm (all, p<0.05). LF/HF ratio (3.49±1.36 vs. 4.49±2.29) showed no significant difference. Post-DCC HRV indices did not show any relationship with AF recurrence. There were no clinical and echocardiographic parameters related with AF recurrence except for LA volume (89±16 in sinus vs. 106±18 mm3 in AF recur, p=0.021). Conclusion: Increased HRV measured before DCC was associated with AF recurrence after successful DCC in persistent AF patients, suggesting important role of cardiac autonomic activity for AF recurrence.

水温27℃, 34℃, 38℃における短時間水浸が心臓自律神経系活動に及ぼす影響

水温27℃, 34℃, 38℃における短時間水浸が心臓自律神経系活動に及ぼす影響

The effect of yoga training on the automatic cardiac nerve activity

The effect of yoga training on the automatic cardiac nerve activity

Intrinsic Cardiac Nerve Activity and Paroxysmal Atrial Tachyarrhythmia in Ambulatory Dogs

Little is known about the relationship between intrinsic cardiac nerve activity (ICNA) and spontaneous arrhythmias in ambulatory animals. We implanted radiotransmitters to record extrinsic cardiac nerve activity (ECNA; including stellate ganglion nerve activity and vagal nerve activity) and ICNA (including superior left ganglionated plexi nerve activity and ligament of Marshall nerve activity) in 6 ambulatory dogs. Intermittent rapid left atrial pacing was performed to induce paroxysmal atrial fibrillation or atrial tachycardia. The vast majority (94%) of ligament of Marshall nerve activity were preceded by or coactivated with ECNA (stellate ganglion nerve activity or vagal nerve activity), whereas 6% of episodes were activated alone without concomitant stellate ganglion nerve activity or vagal nerve activity. Paroxysmal atrial fibrillation and atrial tachycardia were invariably (100%) preceded (<5 seconds) by ICNA. Most paroxysmal atrial tachycardia events (89%) were preceded by ICNA and sympathovagal coactivation, whereas 11% were preceded by ICNA and stellate ganglion nerve activity-only activation. Most paroxysmal atrial fibrillation events were preceded only by ICNA (72%); the remaining 28% were preceded by ECNA and ICNA together. Complex fractionated atrial electrograms were observed during ICNA discharges that preceded the onset of paroxysmal atrial tachycardia and atrial fibrillation. Immunostaining confirmed the presence of both adrenergic and cholinergic nerve at ICNA sites. There is a significant temporal relationship between ECNA and ICNA. However, ICNA can also activate alone. All paroxysmal atrial tachycardia and atrial fibrillation episodes were invariably preceded by ICNA. These findings suggest that ICNA (either alone or in collaboration with ECNA) is an invariable trigger of paroxysmal atrial tachyarrhythmias. ICNA might contaminate local atrial electrograms, resulting in complex fractionated atrial electrogram-like activity.

Clinical prognostic significance of heart abnormality and heart rate variability in patients with stroke

Objective: To investigate the difference of heart rate variability (HRV) and serum creatine kinase isoenzyme (CK-MB) activity between right-sided and left-sided stroke, and the relative impact of cardiac autonomic imbalance and heart abnormality on death by serum CK-MB activity and fractal dimension (FD) detection in patients with stroke.Methods: Three hundred and twenty-seven patients (mean age: 61·12 ± 9.74 years) with an acute first-ever stroke underwent a comprehensive clinical investigation and laboratory tests, and were followed up for 1 month. Serum CK-MB activity and FD of heart rate variability were detected on the next day after admission.Results: During the 1 month follow-up period, 42 out of 327 (12·84%) patients had died. Among all the variables analysed, FD decreased and serum CK-MB activity increased after stroke, and decreased FD was more common in the right-sided stroke. This study also demonstrated that acute phase increased serum CK-MB activity [odds ratio (OR)=0·226, 95% CI: 0·103–0·493, p= 0·000) and decreased FD (OR=0·276, 95% CI: 0·135–0.567, p=0·000) had been linked with the risk of death.Conclusions: Right-sided stroke and left-sided stroke had different influences on cardiac autonomic nerve activity. Acute phase increased serum CK-MB activity and decreased FD are well-established prognostic factors of death in patients with stroke. Assessment of FD and serum CK-MB activity may provide additional information on the risk of death in stroke patients.

Decreased cardiac parasympathetic nerve activity of pregnant women during foot baths

This study aimed to examine the effect of foot baths on the cardiac parasympathetic outflow of five pregnant (31-32 weeks; mid-pregnancy) women and 16 non-pregnant women. The cardiac parasympathetic outflow was assessed by using the respiratory variability of the R-R interval under controlled breathing according to three different methods: (i) respiratory sinus arrhythmia; (ii) a respiratory-synchronized component of the power spectrum of R-R interval variability with a fast Fourier transform; and (iii) a high-frequency component (HF at 0.15-0.40 Hz) of the power spectrum of R-R interval variability with a maximum entropy method. The rate and amplitude of spontaneous respiration and arterial blood pressure at rest were the same between the non-pregnant and pregnant women. However, the baseline R-R interval was shorter and the respiratory-synchronized and HF components of the power spectrum of R-R interval variability were smaller in the pregnant women, indicating a decreased baseline cardiac parasympathetic outflow with mid-pregnancy. Although a foot bath for 15 min did not significantly affect the systemic hemodynamics and body temperature of both groups, the foot bath reduced the respiratory arrhythmia and the respiratory-synchronized and HF components of the power spectrum of R-R interval variability in both groups. The reduction in the respiratory R-R interval became more prominent in the pregnant group. A foot bath, used as part of midwives' daily nursing care, is able to decrease the cardiac parasympathetic outflow of pregnant women.

The effects of adrenalectomy and autonomic blockades on the exercise tachycardia in conscious rats

Heart rate (HR) during exercise is controlled by cardiac sympathetic (CSNA) and vagal (CVNA) efferent nerve activity and plasma catecholamines. To determine their relative contribution to the exercise tachycardia, we examined the effects of adrenalectomy (ADX) and autonomic blockades on the HR response during treadmill exercise for 32 min in 13 conscious rats. The baseline HR was not influenced by ADX, suggesting no significant role of adrenal catecholamines on the baseline HR. Since the baseline HR was increased 61 beats/min by atropine methyl nitrate (1.5 mg/kg) and decreased 26 beats/min by atenolol (3 mg/kg), CVNA determined the baseline HR more than CSNA. ADX did not affect the immediate increase in HR at 0–12 s from the exercise onset but reduced the subsequent increase in HR at 13–30 s. These increases in HR at the early period of exercise were more blunted by atenolol than atropine. On the other hand, the peak tachycardia response of 99 ± 8 beats/min at the end of exercise, which was the same between the intact and ADX conditions, was blunted to 73% by atenolol, to 77% by atropine, and to 35% by combined atenolol and atropine, respectively. In conclusion, it is likely that the tachycardia at the beginning of dynamic exercise is predominantly determined by the cardiac autonomic nerve activity, especially by a prompt increase in CSNA, and that the hormonal mechanism due to adrenal epinephrine contributes to a further increase in HR approximately in 13 s from the onset of exercise.

Influence of ageing on carotid baroreflex peak response latency in humans

The stability of a physiological control system, such as the arterial baroreflex, depends critically upon both the magnitude (i.e. gain or sensitivity) and timing (i.e. latency) of the effector response. Although studies have examined resting arterial baroreflex sensitivity in older subjects, little attention has been given to the influence of ageing on the latency of peak baroreflex responses. First, we compared the temporal pattern of heart rate (HR) and mean arterial blood pressure (BP) responses to selective carotid baroreceptor (CBR) unloading and loading in 14 young (22 +/- 1 years) and older (61 +/- 1 years) subjects, using 5 s pulses of neck pressure (NP, +35 Torr) and neck suction (NS, -80 Torr). Second, CBR latency was assessed following pharmacological blockade of cardiac parasympathetic nerve activity in eight young subjects, to better understand how known age-related reductions in parasympathetic nerve activity influence CBR response latency. In response to NP, the time to the peak increase in HR and mean BP were similar in young and older groups. In contrast, in response to NS the time to peak decrease in HR (2.1 +/- 0.2 vs. 3.8 +/- 0.2 s) and mean BP (6.7 +/- 0.4 vs. 8.3 +/- 0.2 s) were delayed in older individuals (young vs. older, P < 0.05). The time to peak HR and mean BP were delayed in young subjects following cardiac parasympathetic blockade (glycopyrrolate). Collectively, these data suggest that ageing is associated with delayed peak cardiovascular responses to acute carotid baroreceptor loading that may be, in part, due to age-related reductions in cardiac parasympathetic tone.

Intrinsic Cardiac Nerve Activities and Spontaneous Onset of Atrial Tachyarrhythmia

Intrinsic cardiac ganglionated plexuses are known to play important roles in cardiac arrhythmogenesis. We sought to directly record intrinsic cardiac nerve activity (ICNA) and extrinsic cardiac nerve activity (ECNA) simultaneously and to test the hypothesis that ICNA always precedes the onset of spontaneous atrial tachyarrhythmia.

Emotion‐related Changes in Heart Rate and Its Variability during Performance and Perception of Music

The present study investigated the differential effects of emotions evoked by music on heart rate (HR) and its variability (HRV) during the playing of music on the piano compared to those in persons listening to the same music. Thirteen elite pianists underwent experiments under expressive piano playing, nonexpressive piano playing, expressive listening, and nonexpressive listening conditions. The expressive conditions produced significantly higher levels of HR and low-frequency component of HRV, as well as a lower level of its high-frequency component. A greater modulation of these was also revealed for performance than perception. The findings suggested that musical performance would lead to a greater effect of emotion-related modulation in cardiac autonomic nerve activity than musical perception.

Effect of spinal cord stimulation on cardiac adrenergic nerve function in patients with cardiac syndrome X

In patients with cardiac syndrome X (CSX) who present with refractory angina episodes, spinal cord stimulation (SCS) has beneficial effects. The mechanisms of SCS, however, remain speculative. We assessed the effects of SCS on cardiac sympathetic function in these patients. We studied 11 CSX patients treated by SCS for refractory angina (mean age, 60 +/- 9 years; 5 men and 6 women), both during SCS therapy (SCS-ON) and after withdrawal of SCS therapy (SCS-OFF), using a randomized crossover design. Planar and single photon emission computed tomography iodine 123 metaiodobenzylguanidine (MIBG) myocardial scintigraphy and technetium 99m sestamibi (MIBI) bicycle exercise stress testing were performed at the end of each period. Compared with 10 healthy control subjects, CSX patients showed a lower heart-mediastinum ratio for MIBG uptake (2.19 +/- 0.3 vs 1.69 +/- 0.3, P = .001) and a higher cardiac MIBG uptake score (4.0 +/- 2.5 vs 19.7 +/- 27, P = .08). There were no differences in CSX patients during the SCS-ON and SCS-OFF phases of the study in heart-mediastinum ratio (1.74 +/- 0.3 vs 1.69 +/- 0.3, P = .13), cardiac washout rate of MIBG (42.9% +/- 14% vs 43.3% +/- 14%, P = .08), or MIBG defect score (18.7 +/- 25 vs 19.7 +/- 27, P = .22). Reversible perfusion defects during the SCS-OFF phase were detected in 8 patients; an improvement in perfusion defects was observed in 2 patients (25%) during the SCS-ON phase. Our data confirm the presence of abnormal cardiac adrenergic nerve function in CSX patients. SCS was unable to result in significant improvement of cardiac MIBG uptake abnormalities, suggesting that its therapeutic effects are unlikely to be mediated by modulation of cardiac adrenergic nerve activity.

Power Spectral Analysis of Heart Rate Variability: Normal Values of Subjects over 60 Years Old

Power spectral analysis of heart rate variability (HRV) provides a non-invasive method of estimating cardiac autonomic nerve activity. It has been reported that HRV decreases with age. The purpose of this study was to assess the values of and determine the reliability of HRV in healthy older people. The study found lower and highly variable values of HRV. It was concluded that the reliability of HRV in older subjects might need to be reinvestigated and only normalized values of HF and LF might be useful. Larger study groups and different recording periods of HRV are needed.

Myocardial sympathetic innervation in patients with impaired glucose tolerance: relationship to subclinical inflammation

This study was designed to assess cardiac adrenergic nerve activity, using iodine (I)-123-labeled metaiodobenzylguanidine (MIBG), in patients with impaired glucose tolerance (IGT) and to investigate its relation to circulating levels of proinflammatory cytokines. We studied 22 patients with IGT (aged 34-68 years) and 18 age-matched healthy controls, using I-123 MIBG cardiac imaging. The early (10 min) and late (4 h) heart to mediastinum MIBG uptake (H/M) ratio and washout were calculated. Levels of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-a), and its soluble receptor [soluble TNF receptor II (sTNFRII)] were measured by immunoassay of blood samples from patients and controls. The early and late MIBG uptake was lower (both P<.001) and the WR was higher (P<.001) in patients than in controls. The analysis showed innervation defects in 20 of the 22 patients. Nearly half (45.4%) showed severe adrenergic innervation defects in both the inferior wall and the apex. Regarding cytokines, patients showed significantly elevated TNF-a (P=.005), sTNFRII (P<.001), and IL-6 (P<.001) levels compared to controls. IL-6 and sTNFRII were found to correlate with the WR (r=0.468, P=.028 and r=0.455, P=.034, respectively). Patients with IGT show reduced MIBG cardiac uptake with a segmental pattern. The reduced cardiac sympathetic innervation was related to the elevated proinflammatory cytokine levels and could be considered an index of early atherosclerotic process in these patients.

Control of heart rate variability by cardiac parasympathetic nerve activity during voluntary static exercise in humans with tetraplegia

Heart rate (HR) is controlled solely by via cardiac parasympathetic outflow in tetraplegic individuals, who lack supraspinal control of sympathetic outflows and circulating catecholamines but have intact vagal pathways. A high-frequency component (HF; at 0.15-0.40 Hz) of the power spectrum of HR variability and its relative value against total power (HF/Total) were assessed using a wavelet transform to identify cardiac parasympathetic outflow. The relative contribution of cardiac parasympathetic and sympathetic outflows to controlling HR was estimated by comparing the HF/Total-HR relationship between age-matched tetraplegic and normal men. Six tetraplegic men with complete cervical spinal cord injury performed static arm exercise at 35% of the maximal voluntary contraction until exhaustion. Although resting cardiac output and arterial blood pressure were lower in tetraplegic than normal subjects, HR, HF, and HF/Total were not statistically different between the two groups. When tetraplegic subjects developed the same force during exercise as normal subjects, HF and HF/Total decreased to 67-90% of the preexercise control and gradually recovered 1.5 min after exercise. The amount and time course of the changes in HF/Total during and after exercise coincided well between both groups. In contrast, the increase in HR at the start of exercise was blunted in tetraplegic compared with normal subjects, and the HR recovery following exercise was also delayed. It is likely that, although the withdrawal response of cardiac parasympathetic outflow is preserved in tetraplegic subjects, sympathetic decentralization impairs the rapid acceleration of HR at the onset of exercise and the rapid deceleration following exercise.

Vagal nerve activity contributes to improve the efficiency of pulmonary gas exchange in hypoxic humans

The aim of this study was to test our hypothesis that both phasic cardiac vagal activity and tonic pulmonary vagal activity, estimated as respiratory sinus arrhythmia (RSA) and anatomical dead space volume, respectively, contribute to improve the efficiency of pulmonary gas exchange in humans. We examined the effect of blocking vagal nerve activity with atropine on pulmonary gas exchange. Ten healthy volunteers inhaled hypoxic gas with constant tidal volume and respiratory frequency through a respiratory circuit with a respiratory analyser. Arterial partial pressure of O(2) (P(aO(2))) and arterial oxygen saturation (S(pO(2))) were measured, and alveolar-to-arterial P(O(2)) difference (D(A-aO(2))) was calculated. Anatomical dead space (V(D,an)), alveolar dead space (V(D,alv)) and the ratio of physiological dead space to tidal volume (V(D,phys)/V(T)) were measured. Electrocardiogram was recorded, and the amplitude of R-R interval variability in the high-frequency component (RRIHF) was utilized as an index of RSA magnitude. These parameters of pulmonary function were measured before and after administration of atropine (0.02 mg kg(-1)). Decreased RRIHF (P < 0.01) was accompanied by decreases in P(aO(2)) and S(pO(2)) (P < 0.05 and P < 0.01, respectively) and an increase in D(A-aO(2)) (P < 0.05). Anatomical dead space, V(D,alv) and V(D,phys)/V(T) increased (P < 0.01, P < 0.05 and P < 0.01, respectively) after atropine administration. The blockade of the vagal nerve with atropine resulted in an increase in V(D,an) and V(D,alv) and a deterioration of pulmonary oxygenation, accompanied by attenuation of RSA. Our findings suggest that both phasic cardiac and tonic pulmonary vagal nerve activity contribute to improve the efficiency of pulmonary gas exchange in hypoxic conscious humans.

Effects of Pulse-Synchronized Massage With Air Cuffs on Peripheral Blood Flow and Autonomic Nervous System

There are almost no reports on the physiological effects of the various electric massage devices available on the market. This report describes the effects on peripheral vascular circulation and autonomic-nervous system activity of a pulse-synchronized air-massage (PS-AM) device in which cuffs apply air pressure cyclically to the lower limbs only during the cardiac diastolic phase. The PS-AM device consists of a main unit with a pulse-wave detector that uses the pulse-wave to activate an air pump only during the cardiac diastolic phase. Pressure is applied sequentially from the feet to the thighs by 4 pairs of cuffs attached to the main unit. The study was carried out on 55 volunteers (19 males, 36 females). A laser Doppler flow-meter attached to the subjects' toes was used to measure blood flow (BF), while ECG, blood pressure and cardiac autonomic nerve activity [parasympathetic nerve activity (high-frequency component (HF))] were measured by a multibiomedical recorder (TM2425). The measurements were made for a total of 45 min consisting of three 15-min periods: before massage, during PS-AM, and after massage. BF increased 139+/-33 (SD) % in males and 154+/-44% in females during PS-AM, with a significant correlation being observed between BF and HF during PS-AM (p<0.01). PS-AM significantly increased peripheral vascular BF in the lower extremities, a change that may affect venous return and cardiac parasympathetic nerve activity.

Disruption of inhibitory G-proteins mediates a reduction in atrial β-adrenergic signaling by enhancing eNOS expression

Cardiac parasympathetic nerve activity is reduced in most cardiovascular disease states, and this may contribute to enhanced cardiac sympathetic responsiveness. Disruption of inhibitory G-proteins (Gi) ablates the cholinergic pathway and increases cardiac endothelial nitric oxide (NO) synthase (eNOS) expression, suggesting that NO may offset the impaired attenuation of beta-adrenergic regulation of supraventricular excitability. To test this, we investigated the role of endogenous NO production on beta-adrenergic regulation of rate (HR), contraction (CR) and calcium (Ca2+) handling in atria following blockade of Gi-coupled muscarinic receptors. Mice were administered pertussis toxin (PTx, n=105) or saline (C, n=100) intraperitoneally. After 3 days, we measured CR, HR, and NOS protein levels in isolated atria. Intracellular calcium (Ca2+) transients and Ca2+ current density (I(Ca)) were also measured in atrial myocytes. PTx treatment increased atrial myocyte eNOS protein levels compared to C (P<0.05). This did not affect basal atrial function but was associated with a significant reduction in the CR and HR response to isoprenaline (ISO) compared with C. NOS inhibition normalized responses in PTx atria with respect to responses in C atria (P<0.05), which were unaffected. Furthermore, PTx did not affect ISO-stimulated HR and CR in eNOS gene knockout mice (n=40). In agreement with these findings, the ISO-mediated increase in Ca2+ transient was suppressed in PTx-treated myocytes (P<0.05), whereas I(Ca) did not differ between groups. eNOS-derived NO inhibits beta-adrenergic responses following disruption of Gi signaling. This suggests that increased eNOS expression may be a compensatory mechanism which reduces beta-adrenergic regulation of heart rate when cardiac parasympathetic control is impaired.

Low-frequency oscillation of sympathetic nerve activity decreases during development of tilt-induced syncope preceding sympathetic withdrawal and bradycardia

Sympathetic activation during orthostatic stress is accompanied by a marked increase in low-frequency (LF, approximately 0.1-Hz) oscillation of sympathetic nerve activity (SNA) when arterial pressure (AP) is well maintained. However, LF oscillation of SNA during development of orthostatic neurally mediated syncope remains unknown. Ten healthy subjects who developed head-up tilt (HUT)-induced syncope and 10 age-matched nonsyncopal controls were studied. Nonstationary time-dependent changes in calf muscle SNA (MSNA, microneurography), R-R interval, and AP (finger photoplethysmography) variability during a 15-min 60 degrees HUT test were assessed using complex demodulation. In both groups, HUT during the first 5 min increased heart rate, magnitude of MSNA, LF and respiratory high-frequency (HF) amplitudes of MSNA variability, and LF and HF amplitudes of AP variability but decreased HF amplitude of R-R interval variability (index of cardiac vagal nerve activity). In the nonsyncopal group, these changes were sustained throughout HUT. In the syncopal group, systolic AP decreased from 100 to 60 s before onset of syncope; LF amplitude of MSNA variability decreased, whereas magnitude of MSNA and LF amplitude of AP variability remained elevated. From 60 s before onset of syncope, MSNA and heart rate decreased, index of cardiac vagal nerve activity increased, and AP further decreased to the level at syncope. LF oscillation of MSNA variability decreased during development of orthostatic neurally mediated syncope, preceding sympathetic withdrawal, bradycardia, and severe hypotension, to the level at syncope.

The Effect of Animal Assisted Therapy with a Dog on the Autonomic Nervous System

Background & Aims : Animal assisted therapy (AAT) and its therapeutic benefits have gained much attention in recent years. In this study we attempted to evaluate the effects of AAT on the autonomic nervous system. Methods : Ten, normal, healthy adults were recruited for the study. The investigation involved two sessions : an experimental session with a dog, and a control session without a dog. We chose to evaluate the effects of the control and experimental sessions by examining heart rate variability using power spectrum analysis. Results : Cardiac parasympathetic nerve activities in the experimental sessions were significantly higher than in the control sessions. Conclusions : Animal Assisted Therapy with a dog activates the effect of cardiac parasympathetic nerve activities in the heart.