In-field use of I-VED electrical impedance sensor for assessing post-dive decompression stress in humans

Purpose

Ultrasound imaging is commonly used in decompression research to assess venous gas emboli (VGE) post-dive, with higher loads associated with increased decompression sickness risk. This work examines, for the first time in humans, the performance of a novel electrical impedance spectroscopy technology (I-VED), on possible detection of post-dive bubbles presence and arterial endothelial dysfunction that may be used as markers of decompression stress.

Methods

I-VED signals were recorded in scuba divers who performed standardized pool dives before and at set time points after their dives at 35-minute intervals for about two hours. Two distinct frequency components of the obtained signals, Low-Pass Frequency-LPF: 0-0.5 Hz and Band-Pass Frequency-BPF: 0.5-10 Hz, are extracted and respectively compared to VGE presence and known flow-mediated dilation trends for the same dive profile for endothelial dysfunction.

Results

Subjects with VGE counts above the median for all subjects were found to have an elevated average LPF compared to subjects with lower VGE counts, although this was not statistically significant (p=0.06), as well as significantly decreased BPF standard deviation post-dive compared to pre-dive (p=0.008).

Conclusions

I-VED was used for the first time in humans and operated to provide qualitative in-vivo electrical impedance measurements that may contribute to the assessment of decompression stress. Compared to ultrasound imaging, the proposed method is less expensive, not operator-dependent and compatible with continuous monitoring and application of multiple probes. This study provided preliminary insights; further calibration and validation are necessary to determine I-VED sensitivity and specificity.

Acclimatization to diving: a systematic review

Multiday hyperbaric exposure has been shown to reduce the incidence of decompression sickness (DCS) of compressed-air workers. This effect, termed acclimatization, has been addressed in a number of studies, but no comprehensive review has been published. This systematic review reports the findings of a literature search. PubMed, Ovid Embase, The Cochrane Library and Rubicon Research Repository were searched for studies reporting DCS incidence, venous gas embolism (VGE) or subjective health reports after multiday hyperbaric exposure in man and experimental animals. Twenty-nine studies fulfilled inclusion criteria. Three epidemiological studies reported statistically significant acclimatization to DCS in compressed-air workers after multiday hyperbaric exposure. One experimental study observed less itching after standardized simulated dives. Two human experimental studies reported lower DCS incidence after multiday immersed diving. Acclimatization to DCS has been observed in six animal species. Multiday diving had less consistent effect on VGE after hyperbaric exposure in man. Four studies observed acclimatization while no statistically significant acclimatization was reported in the remaining eight studies. A questionnaire study did not report any change in self-perceived health after multiday diving. This systematic review has not identified any study suggesting a sensitizing effect of multiday diving, and there is a lack of data supporting benefit of a day off diving after a certain number of consecutive diving days. The results suggest that multiday hyperbaric exposure probably will have an acclimatizing effect and protects from DCS. The mechanisms causing acclimatization, extent of protection and optimal procedure for acclimatization has been insufficiently investigated.

Acclimatization to diving: a systematic review

Multiday hyperbaric exposure has been shown to reduce the incidence of decompression sickness (DCS) of compressed-air workers. This effect, termed acclimatization, has been addressed in a number of studies, but no comprehensive review has been published. This systematic review reports the findings of a literature search. PubMed, Ovid Embase, The Cochrane Library and Rubicon Research Repository were searched for studies reporting DCS incidence, venous gas embolism (VGE) or subjective health reports after multiday hyperbaric exposure in man and experimental animals. Twenty-nine studies fulfilled inclusion criteria. Three epidemiological studies reported statistically significant acclimatization to DCS in compressed-air workers after multiday hyperbaric exposure. One experimental study observed less itching after standardized simulated dives. Two human experimental studies reported lower DCS incidence after multiday immersed diving. Acclimatization to DCS has been observed in six animal species. Multiday diving had less consistent effect on VGE after hyperbaric exposure in man. Four studies observed acclimatization while no statistically significant acclimatization was reported in the remaining eight studies. A questionnaire study did not report any change in self-perceived health after multiday diving. This systematic review has not identified any study suggesting a sensitizing effect of multiday diving, and there is a lack of data supporting benefit of a day off diving after a certain number of consecutive diving days. The results suggest that multiday hyperbaric exposure probably will have an acclimatizing effect and protects from DCS. The mechanisms causing acclimatization, extent of protection and optimal procedure for acclimatization has been insufficiently investigated.