Effect of hyperbaric pressure during scuba diving on autonomic modulation of the cardiac response: application of the continuous wavelet transform to the analysis of heart rate variability.

This study sought to determine the effects of hyperbaric pressure on heart rate modulation, by analyzing potential changes in heart rate variability (HRV). Ten divers were exposed to pressures of 1, 2, 3, and 4 atmospheres absolute (ATA). The test was performed in a hyperbaric chamber. Heart rate (HR) was recorded in supine subjects for 10 minutes per atmosphere. HRV was analyzed in the frequency mode (fast-Fourier transform and continuous wavelet transform). Results confirmed bradycardia as pressure increased. The drop in HR attained statistical significance after 2, 3, and 4 ATA. Signal energy (normalized TP values) rose progressively, becoming significant at 2 ATA. High frequency and low frequency displayed similar behavior in both cases. Although frequency band peaks did not yield clear results, continuous wave transform analysis showed that the frequency spectrum tended to shift into the high-frequency range as pressure increased. In summary, increased pressure prompted increased bradycardia, and HRV shifted into high-frequency range.

Heart rate dynamics in different levels of Zen meditation.

The dynamic interactions among physiological rhythms imbedded in the heart rate signal can give valuable insights into autonomic modulation in conditions of reduced outward attention. Therefore, in this study we analyzed the heart rate variability (HRV) in different levels of practice in Zen meditation (Zazen). Nineteen subjects with variable experience took part in this study. In four special cases we collected both HRV and respiration data. The time series were analyzed in frequency domain and also using the Continuous Wavelet Transform, which detects changes in the time domain and in the frequency domain simultaneously. The shifts in the respiratory modulation of heart rate, or respiratory sinus arrhythmia (RSA), reflect the different levels of practice among practitioners with variable experience in Zazen; in turn the modulation of the RSA may reflect changes in the breathing pattern as in the parasympathetic outflow related to the quality and focus of attention in each stage.

Middle and long distance athletics races viewed from the perspective of complexity.

Middle and long distance athletics races behave as power-laws when time (or average speed) and distance are related, thus suggesting the presence of critical phenomena. Power-laws as a function of the athlete's position in the all-time world ranking allows us to define a Performance Index that reveals the existence of possible multifractal structures associated to the natural barriers to that the athletes tend in their evolution towards better results and in pursuit of world records. The new theories of self-organized critical phenomena provide an explanation for the power-law and fractal structures in systems at, or near, their critical points. In this paper we analyse the athletic races using these theories and as a result of this study a new variety of interpretations are posited.