Heart rate variability during static and dynamic breath-hold dives in elite divers.

The purpose of this study was to assess the differences in cardiac autonomic modulation during maximal static (SA) and dynamic (DA) underwater apneas. Arterial oxygen saturation (SpO(2)), heart rate (HR) and HR variability (SD1 from Poincaré plot and short-term fractal-like scaling exponent, α(1)) were analyzed at the immersed baseline (3 min) and initial, mid- and end-phases (each 30s) of SA and DA in nine elite breath-hold divers. DA and SA lasted 78 ± 8 and 225 ± 20s (mean ± SEM), respectively, and resulted in similar decrements in end-stage SpO(2) (78 ± 3 and 75 ± 3%, p=0.352). During DA, initial increase in HR (from 80 ± 5 to 122 ± 5 bpm, p<0.001) was followed by gradual decrease towards the baseline at mid-apnea and end-apnea phase (101 ± 6 and 80 ± 8 bpm, respectively). During SA, HR decreased at mid-apnea (from 78 ± 4 to 66 ± 3 bpm, p=0.004) but did not decrease further at end-apnea phase (66 ± 4b pm). Decreased SD1 was observed at the initial phase of DA (from 28 ± 5 to 10 ± 4 ms, p=0.005) being lower compared with SA (24 ± 4 ms, p=0.005). At the end of DA and SA, SD1 tended to increase above the baseline (62 ± 16 and 66 ± 10 ms, p=0.128 and p=0.093, respectively, p=0.602 DA vs. SA). α(1) tended to be higher at the end of DA compared with SA (1.17 ± 0.10 vs. 0.79 ± 0.10, p=0.059). We concluded that apnea blunts the effects of exercise on cardiac vagal activity at the end of DA. However, higher HR during DA compared with SA indicates larger cardiac sympathetic activity during DA, as suggested also by slightly higher α(1).

Cardiovascular changes during underwater static and dynamic breath-hold dives in trained divers.

Limited information exists concerning arterial blood pressure (BP) changes in underwater breath-hold diving. Simulated chamber dives to 50 m of freshwater (mfw) reported very high levels of invasive BP in two divers during static apnea (SA), whereas a recent study using a noninvasive subaquatic sphygmomanometer reported unchanged or mildly increased values at 10 m SA dive. In this study we investigated underwater BP changes during not only SA but, for the first time, dynamic apnea (DA) and shortened (SHT) DA in 16 trained breath-hold divers. Measurements included BP (subaquatic sphygmomanometer), ECG, and pulse oxymetry (arterial oxygen saturation, SpO2, and heart rate). BP was measured during dry conditions, at surface fully immersed (SA), and at 2 mfw (DA and SHT DA), whereas ECG and pulse oxymetry were measured continuously. We have found significantly higher mean arterial pressure (MAP) values in SA (∼40%) vs. SHT DA (∼30%). Postapneic recovery of BP was slightly slower after SHT DA. Significantly higher BP gain (mmHg/duration of apnea in s) was found in SHT DA vs. SA. Furthermore, DA attempts resulted in faster desaturation vs. SA. In conclusion, we have found moderate increases in BP during SA, DA, and SHT DA. These cardiovascular changes during immersed SA and DA are in agreement with those reported for dry SA and DA.

Advanced instrumentation for research in diving and hyperbaric medicine.

Improving the safety of diving and increasing knowledge about the adaptation of the human body to underwater and hyperbaric environment require specifically developed underwater instrumentation for physiological measurements. In fact, none of the routine clinical devices for health control is suitable for in-water and/or under-pressure operation. The present paper addresses novel technological acquisitions and the development of three dedicated devices: * an underwater data logger for recording O2 saturation (reflective pulsoxymetry), two-channel ECG, depth and temperature; * an underwater blood pressure meter based on the oscillometric method; and * an underwater echography system. Moreover, examples of recordings are presented and discussed.

A novel wearable apnea dive computer for continuous plethysmographic monitoring of oxygen saturation and heart rate.

We describe the development of a novel wrist-mounted apnea dive computer. The device is able to measure and display transcutaneous oxygen saturation, heart rate, plethysmographic pulse waveform, depth, time and temperature during breath-hold dives. All measurements are stored in an external memory chip. The data-processing software reads from the chip and writes the processed data into a comma-separated values file which can be analysed by applications such as Microsoft Excel™ or Open Office™. The housing is waterproof and pressure-resistant to more than 20 bar (2.026 MPa) (breath-hold divers have already exceeded 200 metres' sea water depth). It is compact, lightweight, has low power requirements and is easy to use.

An underwater blood pressure measuring device.

Measurement of arterial blood pressure is an important vital sign for monitoring the circulation. However, up to now no instrument has been available that enables the measurement of blood pressure underwater. The present paper details a novel, oscillometric, automatic digital blood pressure (BP) measurement device especially designed for this purpose. It consists mainly of analogue and digital electronics in a lexan housing that is rated to a depth of up to 200 metres' sea water, a cuff and a solenoid for inflation of the cuff with air supplied from a scuba tank. An integrated differential pressure sensor, exposed to the same ambient pressure as the cuff, allows accurate BP measurement. Calculation of systolic and diastolic pressures is based on the analysis of pressure oscillations recorded during the deflation. In hyperbaric chamber tests to pressures up to 405 kPa, BP measurements taken with the prototype were comparable to those obtained with established manual and automated methods. Swimming pool tests confirmed the correct functioning of the system underwater. The quality of the recorded pressure oscillations was very good even at 10 metres' fresh water, and allowed determination of diastolic and systolic pressure values. Based on these results we envisage that this device will lead to a better understanding of human cardiovascular physiology in underwater and hyperbaric environments.