| 1. |
- Mulder, Eric, et al.
(författare)
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Case Studies in Physiology : Is blackout in breath-hold diving related to cardiac arrhythmias?
- 2023
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Ingår i: Journal of applied physiology. - : American Physiological Society. - 8750-7587 .- 1522-1601. ; 134:4, s. 951-956
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Tidskriftsartikel (refereegranskat)abstract
- Syncope or "blackout" (BO) in breath-hold diving (freediving) is generally considered to be caused by hypoxia. However, it has been suggested that cardiac arrhythmias affecting the pumping effectivity could contribute to BO. BO is fairly common in competitive freediving, where athletes aim for maximal performance. We recorded heart rate (HR) during a static apnea (STA) competition, to reveal if arrhythmias occur. Four male freedivers with STA personal best (PB) of 349 ± 43 s, volunteered during national championships, where they performed STA floating face down in a shallow indoor pool. A non-coded Polar T31 chest strap recorded R-R intervals and a water- and pressure-proof pulse oximeter arterial oxygen saturation. Three divers produced STA near their PB without problems, whereas one diver ended with BO at 5 min 17s, which was 12 s beyond his PB. He was immediately brought up by safety divers and resumed breathing within 10 s. All divers attained similar lowest diving HR (47 ± 4 beats/min), but HR recordings displayed a different pattern for the diver ending with BO. After a short tachycardia, the three successful divers developed bradycardia, which became more pronounced during the second half of the apnea. The fourth diver developed pronounced bradycardia earlier, and at 2.5 min into the apnea, HR started alternating between approximately 50 and 140 beats/min, until the diver lost consciousness. At resumed breathing, HR returned to baseline. Nadir oxygen saturation was similar for all divers. We speculate that arrhythmia could have contributed to BO, by lowering stroke volume leading to a systolic blood pressure drop, affecting brain perfusion.NEW & NOTEWORTHY Heart rate during prolonged breath-holding until the point of loss of consciousness has not previously been published. The recordings show that blackout was preceded by a period of persistent alterations in R-R intervals, whereby an ectopic beat followed every normal heartbeat. Explanations for this deviating heart rate pattern could be either premature atrial contractions or premature ventricular contractions following every atrial beat, i.e., bigeminy, which could have compromised cardiac pumping function and caused/contributed to blackout.
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| 2. |
- Mulder, Eric, et al.
(författare)
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First Evaluation of a Newly Constructed Underwater Pulse Oximeter for Use in Breath-Holding Activities
- 2021
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Ingår i: Frontiers in Physiology. - : Frontiers Media SA. - 1664-042X. ; 12
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Tidskriftsartikel (refereegranskat)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 (SpO(2)) and heart rate (HR) were recorded, while breathing room air (21% O-2) and subsequently a hypoxic gas (10.7% O-2) at rest in dry conditions. Bland-Altman analysis was used to evaluate bias and precision of SUB relative to SpO(2) 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), SpO(2) 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, SpO(2) 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 SpO(2) was approximately 15 and 12 s shorter in SUB compared to TPULS, respectively. Lowest SpO(2) 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 SpO(2) 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.
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| 3. |
- Mulder, Eric, et al.
(författare)
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New scientific methods in breath-hold diving research
- 2021
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Ingår i: Freiberg Online Geoscience (FOG). - 1434-7512. ; 58, s. 115-125
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Tidskriftsartikel (refereegranskat)abstract
- Physiological field research on breath-hold divers (freedivers) is challenging as divers are exposed to hyperbaric environments hostile to classical physiological measurement methods. Two main challenges are; I) The need of developing methods allowing measurements of physiological variables underwater at depth, II) To accompany the studied freediver in the water. The rapid vertical descent and ascent makes it impossible for researchers to use SCUBA to follow the participants to depth. We present new approaches in scientific diving to meet these demands. Our methods development of underwater technology has included water- and pressure-proof dataloggers to record and store data from a 12 lead ECG (250Hz) and photoplethysmograms from two SpO2 probes using red- and infrared signals (30Hz), combined with ambient pressure and temperature loggers. We previously used SCUBA to enable real-time blood pressure and ECG measurements on freedivers, by waiting for them at the bottom of their pre-determined depth. A breath-hold diving approach for the researcher was found to be superior due to enhanced flexibility in contrast to a heavy, static SCUBA setup. A method was developed in order to perform such scientific freediving safely, the basis being diving in e.g., the professional Japanese Ama divers. Combining the use of novel wearable water- and pressureproof physiological measurement methods with “scientific freediving”, seems to provide optimal work flexibility for both our study participants and the researcher, and may be the preferred approach for our future research.
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| 4. |
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| 5. |
- Mulder, Eric, et al.
(författare)
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Underwater pulse oximetry reveals increased rate of arterial oxygen desaturation across repeated freedives to 11 metres of freshwater
- 2023
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Ingår i: Diving and Hyperbaric Medicine. - : Diving and Hyperbaric Medicine Journal. - 1833-3516 .- 2209-1491. ; 53:1, s. 16-23
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Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: Recreational freedivers typically perform repeated dives to moderate depths with short recovery intervals. According to freediving standards, these recovery intervals should be twice the dive duration; however, this has yet to be supported by scientific evidence. METHODS: Six recreational freedivers performed three freedives to 11 metres of freshwater (mfw), separated by 2 min 30 s recovery intervals, while an underwater pulse oximeter measured peripheral oxygen saturation (SpO2) and heart rate (HR). RESULTS: Median dive durations were 54.0 s, 103.0 s and 75.5 s (all dives median 81.5 s). Median baseline HR was 76.0 beats per minute (bpm), which decreased during dives to 48.0 bpm in dive one, 40.5 bpm in dive two and 48.5 bpm in dive three (all P < 0.05 from baseline). Median pre-dive baseline SpO2 was 99.5%. SpO2 remained similar to baseline for the first half of the dives, after which the rate of desaturation increased during the second half of the dives with each subsequent dive. Lowest median SpO2 after dive one was 97.0%, after dive two 83.5% (P < 0.05 from baseline) and after dive three 82.5% (P < 0.01 from baseline). SpO2 had returned to baseline within 20 s after all dives. CONCLUSIONS: We speculate that the enhanced rate of arterial oxygen desaturation across the serial dives may be attributed to a remaining 'oxygen debt', leading to progressively increased oxygen extraction by desaturated muscles. Despite being twice the dive duration, the recovery period may be too short to allow full recovery and to sustain prolonged serial diving, thus does not guarantee safe diving. Copyright: This article is the copyright of the authors who grant Diving and Hyperbaric Medicine a non-exclusive licence to publish the article in electronic and other forms.
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| 6. |
- Mulder, Eric, et al.
(författare)
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Unlocking the depths : multiple factors contribute to risk for hypoxic blackout during deep freediving
- 2023
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Ingår i: European Journal of Applied Physiology. - : Springer. - 1439-6319 .- 1439-6327. ; 123:11, s. 2483-2493
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To examine the effect of freediving depth on risk for hypoxic blackout by recording arterial oxygen saturation (SpO2) and heart rate (HR) during deep and shallow dives in the sea. Methods: Fourteen competitive freedivers conducted open-water training dives wearing a water-/pressure proof pulse oximeter continuously recording HR and SpO2. Dives were divided into deep (> 35 m) and shallow (10–25 m) post-hoc and data from one deep and one shallow dive from 10 divers were compared. Results: Mean ± SD depth was 53 ± 14 m for deep and 17 ± 4 m for shallow dives. Respective dive durations (120 ± 18 s and 116 ± 43 s) did not differ. Deep dives resulted in lower minimum SpO2 (58 ± 17%) compared with shallow dives (74 ± 17%; P = 0.029). Overall diving HR was 7 bpm higher in deep dives (P = 0.002) although minimum HR was similar in both types of dives (39 bpm). Three divers desaturated early at depth, of which two exhibited severe hypoxia (SpO2 ≤ 65%) upon resurfacing. Additionally, four divers developed severe hypoxia after dives. Conclusions: Despite similar dive durations, oxygen desaturation was greater during deep dives, confirming increased risk of hypoxic blackout with increased depth. In addition to the rapid drop in alveolar pressure and oxygen uptake during ascent, several other risk factors associated with deep freediving were identified, including higher swimming effort and oxygen consumption, a compromised diving response, an autonomic conflict possibly causing arrhythmias, and compromised oxygen uptake at depth by lung compression possibly leading to atelectasis or pulmonary edema in some individuals. Individuals with elevated risk could likely be identified using wearable technology.
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| 7. |
- Mulder, Eric, et al.
(författare)
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Using Underwater Pulse Oximetry in Freediving to Extreme Depths to Study Risk of Hypoxic Blackout and Diving Response Phases
- 2021
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Ingår i: Frontiers in Physiology. - : Frontiers Media SA. - 1664-042X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Deep freediving exposes humans to hypoxia and dramatic changes in pressure. The effect of depth on gas exchange may enhance risk of hypoxic blackout (BO) during the last part of the ascent. Our aim was to investigate arterial oxygen saturation (SpO2) and heart rate (HR) in shallow and deep freedives, central variables, which have rarely been studied underwater in deep freediving. Four male elite competitive freedivers volunteered to wear a newly developed underwater pulse oximeter for continuous monitoring of SpO2 and HR during self-initiated training in the sea. Two probes were placed on the temples, connected to a recording unit on the back of the freediver. Divers performed one “shallow” and one “deep” constant weight dive with fins. Plethysmograms were recorded at 30 Hz, and SpO2 and HR were extracted. Mean ± SD depth of shallow dives was 19 ± 3 m, and 73 ± 12 m for deep dives. Duration was 82 ± 36 s in shallow and 150 ± 27 s in deep dives. All divers desaturated more during deeper dives (nadir 55 ± 10%) compared to shallow dives (nadir 80 ± 22%) with a lowest SpO2 of 44% in one deep dive. HR showed a “diving response,” with similar lowest HR of 42 bpm in shallow and deep dives; the lowest value (28 bpm) was observed in one shallow dive. HR increased before dives, followed by a decline, and upon resurfacing a peak after which HR normalized. During deep dives, HR was influenced by the level of exertion across different diving phases; after an initial drop, a second HR decline occurred during the passive “free fall” phase. The underwater pulse oximeter allowed successful SpO2 and HR monitoring in freedives to 82 m depth – deeper than ever recorded before. Divers’ enhanced desaturation during deep dives was likely related to increased exertion and extended duration, but the rapid extreme desaturation to below 50% near surfacing could result from the diminishing pressure, in line with the hypothesis that risk of hypoxic BO may increase during ascent. Recordings also indicated that the diving response is not powerful enough to fully override the exercise-induced tachycardia during active swimming. Pulse oximetry monitoring of essential variables underwater may be an important step to increase freediving safety.
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| 8. |
- Schuster, Andreas, et al.
(författare)
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Function selection among popular dive computer models : A review and proposed improvements
- 2014
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Ingår i: Underwater Technology. - : Society for Underwater Technology. - 1756-0543. ; 32:3, s. 159-165
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Tidskriftsartikel (refereegranskat)abstract
- For optimal safety a dive computer should be easy to use and the displayed information easy to understand. The present study examines the usability of dive computers and potential technologies to enhance safety. It should be noted that even if the ease of use of a dive computer is increased to an extent where it is intuitive to use, this does not release the diver from the recommendation to read the dive computer manual to safely dive with it. For the present work, 47 dive computer models by 14 manufacturers were purchased and the manuals of another three were studied. Function selection was noted for each model. Where selection required a combination of long and short pushes, or more than one button, it was considered necessary to read the instruction manual merely to modify settings in the dive computer. The mean number of buttons, switches or contacts per dive computer was 3.3 (SD 1.1, range 1–7). Twelve models (24%) did not have multiple functions per button, one model (2%) had a single multi-function and 36 models (72%) had multiple multi-functions per button. Accessing these functions required short or long push combinations. In 41 out of 50 (82%) of the dive computer models, the user interface was not intuitive. The majority of popular dive computers employ combinations of long and short pushes to access multiple functions, requiring training and mnemonic effort to operate the device. They are not intuitive, and scope exists to improve the usability and safety of dive computers. Possibilities are described including touch screens, a wheel to replace traditional buttons and near field communications (NFC).
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| 9. |
- Schuster, Andreas, et al.
(författare)
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Underwater monitoring system for body temperature and ECG recordings
- 2017
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Ingår i: Underwater Technology. - : Society for Underwater Technology. - 1756-0543 .- 1756-0551. ; 34:3, s. 135-139
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Tidskriftsartikel (refereegranskat)abstract
- A new device was developed and tested in a series of diving experiments investigating the physiological effects of immersion on military divers for long periods (8 h to 12 h). During these experiments, the body temperature (core and skin) and electrocardiogram (ECG) of the divers were recorded and monitored in real time. The system developed for this purpose comprised a modified VitalSense temperature monitoring device from Philips Respironics and a one-channel ECG housed in a pressure-proof case. Recorded data were transmitted wirelessly to a PC. The recording and visualisation software was developed under National Instruments LabWindows.
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