An investigation on the influence of yogic methods on heart rate variability.

BACKGROUND: The role of underlying mechanisms of yogic strategies which exert beneficiary effects on cardiac autonomic control is poorly understood. We have performed heart rate variability (HRV) analysis on subjects performing yogic methods and control subjects who mimic them through paced breathing and focused attention tasks using external cues. METHODS: Heart rate (HR) time series is generated from electrocardiogram measured from subjects of yogic group (YG); performing yogic practices (n = 15), paced breathing group (PBG); involved in breathing exercises cued at breathing rates (BR) from 3 to 15 cycles per minute (cpm) (n = 23), normal breathing group (NBG) under regular breathing (n = 15), and subjects performing three different cognitive tasks designated as focused attention group (FAG), (n = 24). HRV is analyzed using coherence plots, spectrograms, HRV parameters, and instantaneous frequency recurrence plots (IFRP). RESULTS: HRV is similar among YG and PBG (at BR <12 cpm) and significantly different for YG vs. NBG (p < 0.001) and PBG vs. NBG (p < 0.001). Regularity of breathing oscillations observed in HR is quantified using IFRP and is identical among FAG, PBG, and YG and significantly different for YG vs. NBG (p < 0.01), PBG vs. NBG (p < 0.01), and FAG vs. NBG (p < 0.05). CONCLUSIONS: Low-frequency breathing (BR <12 cpm) plays a primary role in eliciting physiologically significant changes in HRV. By identifying a similarity in breathing oscillations of HR of FAG, YG, and PBG, the results recognize the coexistence of attention and breathing strategies and postulate their joint role in sustaining autonomic benefits, while effects induced by breathing alone on HRV could be attained even intermittently.

Noninvasive Determination of HV Interval Using Magnetocardiography.

BACKGROUND: The His-ventricular (HV) interval is an important index of atrioventricular conduction, but at present can be reliably measured only during an invasive electrophysiology (EP) study. Magnetocardiography (MCG) is a noninvasive measurement of weak magnetic fields generated by the heart. We compared HV interval noninvasively assessed using MCG with the corresponding values measured directly in an EP study. METHODS: MCG was measured using a 37-channel system inside a magnetically shielded room in patients who had previously undergone an EP study. His-bundle potential was identified in the PR segment after signal averaging. Magnetic field maps representing the spatial distribution of ramp-like signals in the PR segment generated at various instants of time were used to identify His-bundle signals in cases where the deflection representing the His was ambiguous. RESULTS: The study included 23 patients (14 male, nine female) with a wide range of HV intervals measured during EP study (49 ± 17 ms, range 35-120 ms). In 21 (91%) subjects, discernible His-bundle signals are observed in the PR segment of MCG traces. HV intervals measured between the two methods showed a correlation (r2 = 0.87, P < 0.0001) with a mean difference of 5.4 ± 3.2 ms. CONCLUSION: With the use of new criteria to identify the His-bundle deflection in signal-averaged MCG signals, we report a high success rate in noninvasive HV interval measurement and a good agreement with those from EP study. The results encourage the use of MCG as a noninvasive method for measurement of the HV interval.