First Evaluation of a Newly Constructed Underwater Pulse Oximeter for Use in Breath-Holding Activities

Abstract

Studying risk factors in freediving, such as hypoxic blackout, requires development of new methods to enable remote underwater monitoring of physiological variables. We aimed to construct and evaluate a new water- and pressure proof pulse oximeter for use in freediving research. The study consisted of three parts: (I) A submersible pulse oximeter (SUB) was developed on a ruggedized platform for recording of physiological parameters in challenging environments. Two MAX30102 sensors were used to record plethysmograms, and included red and infra-red emitters, diode drivers, photodiode, photodiode amplifier, analog to digital converter, and controller. (II) We equipped 20 volunteers with two transmission pulse oximeters (TPULS) and SUB to the fingers. Arterial oxygen saturation (SpO2) and heart rate (HR) were recorded, while breathing room air (21% O2) and subsequently a hypoxic gas (10.7% O2) at rest in dry conditions. Bland-Altman analysis was used to evaluate bias and precision of SUB relative to SpO2 values from TPULS. (III) Six freedivers were monitored with one TPULS and SUB placed at the forehead, during a maximal effort immersed static apnea. For dry baseline measurements (n = 20), SpO2 bias ranged between −0.8 and −0.6%, precision between 1.0 and 1.5%; HR bias ranged between 1.1 and 1.0 bpm, precision between 1.4 and 1.9 bpm. For the hypoxic episode, SpO2 bias ranged between −2.5 and −3.6%, precision between 3.6 and 3.7%; HR bias ranged between 1.4 and 1.9 bpm, precision between 2.0 and 2.1 bpm. Freedivers (n = 6) performed an apnea of 184 ± 53 s. Desaturation- and resaturation response time of SpO2 was approximately 15 and 12 s shorter in SUB compared to TPULS, respectively. Lowest SpO2 values were 76 ± 10% for TPULS and 74 ± 13% for SUB. HR traces for both pulse oximeters showed similar patterns. For static apneas, dropout rate was larger for SUB (18%) than for TPULS (<1%). SUB produced similar SpO2 and HR values as TPULS, both during normoxic and hypoxic breathing (n = 20), and submersed static apneas (n = 6). SUB responds more quickly to changes in oxygen saturation when sensors were placed at the forehead. Further development of SUB is needed to limit signal loss, and its function should be tested at greater depth and lower saturation.

Unlocking the depths: multiple factors contribute to risk for hypoxic blackout during deep freediving

“…A fit-for-purpose submersible pulse oximeter, consisting of two identical reflective sensor heads which were placed on the temples and connected by cables to a data logger, was used to record SpO 2 and HR during dives. The model of the prototype used was previously described and evaluated in detail (Mulder et al 2021b ); it is based on a prototype previously employed to shallow depths (Kuch et al 2010 ; Kiviniemi et al 2012 ). Prior to the dives, the sensors’ placement and function was confirmed through visual inspection of the live plethysmograph signals on a laptop.…”

“…Wearable measurement devices can make this possible. In a pilot study using a novel underwater pulse oximeter (Mulder et al 2021b ), a rapid decrease in SpO 2 during the ascent phase from freedives to depth was observed (Mulder et al 2021a ). The oxygen desaturation was less pronounced in shorter, shallow dives by the same individuals, but whether this was due to pressure change, apnea duration or other factors is unclear.…”

Understanding and supporting wearable technologies for freedivers

“…Only studies that had already been carried out with special hardware were used in some cases in order to be able to carry out further investigations by improving the previously developed devices [172], [229]. At the same time, the commercially available dive computers are only very limited for collecting scientific data, due to the lack of open interfaces, proprietary sensors, data formats, or they are simply too expensive for large studies.…”