Heart rate variability changes as an indicator of decompression-related physiological stress

Abstract

Many aspects of the physiological stress related to the exposure to the hyperbaric environment have been studied, but no research has been made to evaluate the impacts of scuba diving on heart rate variability (HRV). We investigated the effects of a simulated dive to 557 KPa (45 meters of salt water) for a 30-minute bottom time on the frequency and time domains estimators of HRV. Electrocardiogram records were obtained with superficial electrodes for 30 minutes before the simulated dive and, subsequently, for one hour after the dive. Each of these time-series was then subdivided into non-overlapping windows of 256 consecutive R-R in- tervals. A control group was submitted to the same proto- col, breathing the same gases used in the simulated dive, while not being exposed to the hyperbaric environment. In the control group we observed a significant increase in SDNN (the square root of the variance of the R–R intervals), RMSSD (the square root of the mean squared differences of successive R-R intervals), and in two bands (high and low) of the power spectrum of frequencies. The subjects in the simulated dive presented only an increase in the low frequency estimator without any further relevant changes in other estimators of HRV. This study suggests that the low frequency increase without concomitant high frequency increase might be an indicator of the physiological stress caused by decom- pression and that such a dissimilarity in responses might be correlated to the dive-related impairment of the endothelial function.

Association Between Heart Rate Variability and Decompression-Induced Physiological Stress

“…We observed in a control group in our previous study that the exposure to high fractions of oxygen, even in the absence of changes in the ambient pressure, is associated with increased Heart Rate Variability measured, given by SDNN in the time domain and in the HF in the frequency domain (Schirato et al, 2018). It is plausible that general post dive increased values in these HRV indicators observed in this (and in other previously published studies) is related to the hyperoxia almost inherently linked to the exposure to hyperbaric environments.…”

“…There were two phases of continuous data collection: a 30-min pre-dive period used to establish the baseline condition for each volunteer and a 30-minutes post dive reading that was initiated 30 min after the end of the dive. This protocol was adopted due to previous observations that the magnitude of the changes in HRV tends to be higher in the second half-hour post decompression (Schirato et al, 2018). Interestingly, it is well documented that venous gas bubbles counts tend to take approximately the same amount of time to reach a peak (Cialoni et al, 2017).…”

“…Besides the well documented appearance of bubbles, alterations in the endothelial function and biochemical markers found in the blood stream, recently published studies also reported changes in the Heart Rate Variability (HRV) after exposure to hyperbaric environments (Noh et al, 2018;Schirato et al, 2018).…”

Diving Responses in Experienced Rebreather Divers: Short-Term Heart Rate Variability in Cold Water Diving

“…Immersion in cold water stimulates both the parasympathetic (PNS) and sympathetic (SNS) branches of the ANS ( Doubt, 1996 ; Mourot et al, 2007 ). Submersion causes physiological and psychological stress which activates the SNS ( Doubt, 1996 ; Schirato et al, 2018 , 2020 ). The human diving responses mainly cause an increase in PNS activity and can be divided into separate physiological responses to immersion and submersion.…”

Investigação da utilização da Variabilidade Cardíaca como indicador de estresse fisiológico induzido por exposição a ambientes hiperbáricos e subsequente descompressão

“…There were two phases of continuous data collection: a 30-minutes pre-dive period used to establish the baseline condition for each volunteer and a 30-minutes post dive reading that was initiated 30 minutes after the end of the dive. This protocol was adopted due to previous observations that the magnitude of the changes in HRV tends to be higher in the second half-hour post decompression 36 . Interestingly, it is well documented that venous gas bubbles counts tend to take approximately the same amount of time to reach a peak.…”