Page 9 - JCTR-10-5

Schirato et al. | Journal of Clinical and Translational Research 2024; 10(5): 269-282 271
2. Methods Table 1. Study population characteristics
Parameter Value
2.1. Study participants
Age (years) 44.18±6.77
The present study was undertaken in healthy individuals, Weight (kg) 87.82±13.47
all trained divers, experienced in the experimental profiles Height (cm) 180.32±8.27
utilized. The volunteers provided written informed consent. The Body mass index 27.03±3.90
ethical committee of the Biosciences Institute of the University Note: Data are presented as the mean±standard deviation.
of Sao Paulo approved the experimental protocol (CAAE
#91231618.6.0000.5464), and all experiments were performed Table 2. Simulated dive profiles
in accordance with relevant guidelines and regulations. Decompression Depth Time Breathing loop,
Briefly, a total of 23 male divers participated in this study. profile (msw) (min) PO (ATA)
2
Female volunteers were not accepted to avoid the potential Deep 53 15 1.2
effects of neurovegetative changes due to the menstrual 27 1 1.2
cycle [23]. Two volunteers participated in only one experiment 24 1 1.2
and were released from the second due to medical conditions not 21 2 1.2
related to diving. No decompression sickness symptoms were 18 2 1.2
observed during the experimental dives. Table 1 summarizes the 15 3 1.2
anthropometric data of the study population. 12 4 1.2

2.2. Simulated dives 9 5 1.2
6 22 1.4
Experiments involving exposure compression and subsequent Shallow 53 15 1.2
decompression were conducted at the Centro Hiperbárico 21 2 1.2
Paulista (São Paulo Hyperbaric Center), Indaiatuba, São Paulo, 18 2 1.2
Brazil, under the supervision of a trained physician. Each 15 3 1.2
volunteer underwent two different trials, each one with the same 12 4 1.2
maximum depth and bottom time. Decompression schedules 9 6 1.2
were created to simulate different decompression profiles with 6 26 1.4
similar total decompression times. Each trial was performed in
the morning, at the same time of the day. Divers were requested Abbreviation: msw: Meters of seawater; PO : Partial pressure of oxygen.
2
to rest for at least 30 min before the start of the experiment, There were two phases of continuous data collection: (i)
and the interval between the experiments was at least 7 days a 30-min pre-dive period to establish the baseline condition
for each volunteer to minimize any carry-over effect [24]. The for each volunteer; and (ii) a 30-min post-dive reading that
experiments executed were performed using electronically was initiated 30 min after the end of the dive. This protocol
controlled closed-circuit rebreathers. was adopted due to previous observations that the magnitude
nd
2.3. Simulated dive profiles of HRV changes tends to be higher in the 2 half-hour post-
decompression. Interestingly, it is well-documented that venous
The diluent gas mix consisted of 18% oxygen, 45% helium, and gas bubble counts tend to take approximately the same amount
37% nitrogen. Rebreathers were set to keep the oxygen pressure at of time to reach a peak [24].
121 kPa (1.2 ATA; total pressure: Gauge plus 0.93 atm of surface ECG recordings were converted into R-R intervals. The R-R
pressure) throughout the dive, raising the oxygen pressure to 141 time series was then subdivided into non-overlapping windows
kPa (1.4 ATA) at 162 kPa (6 meters of seawater [msw]). The bottom of 256 consecutive R-R intervals. Subsequently, the following
pressure was 638 kPa (53 msw) and the time required to reach this estimators of HRV were obtained from each window (as detailed
pressure was 20 min. The divers were kept at the simulated bottom by the task force of the European Society of Cardiology and the
for an additional 15 min. Subjects were decompressed at a rate of 9 North American Society of Pacing and Electrophysiology [20]):
msw/min until the first decompression stop was reached. The dive (i) Time domain:
profiles are detailed in Table 2. - R–R interval
2.4. Electrocardiographic (ECG) data - Standard deviation of the normal-to-normal R-R interval
(SDNN)
ECG records were obtained using superficial electrodes - The square root of the mean squared differences of
in a modified CM5 thoracic positioning. Data were collected successive R-R intervals (RMSSD).
while the subjects were seated in a comfortable position using (ii) Frequency domain:
the MP36 system (BIOPAC Systems, Inc., United States of - Fast Fourier transform, to obtain the power spectrum
America [USA]), set up at AHA configuration, with 0.05 and density [20], which was subsequently divided into:
100 Hz as low and high pass filters, respectively, and a sampling 1. Ultra-LF: 0.01 – 0.04 Hz (not relevant to this study
rate of 1000 Hz. due to the relatively short ECG recording intervals)

DOI: https://doi.org/10.36922/jctr.24.00021