Probability Of Decompression Sickness Research Articles

Validation of algorithms used in commercial off-the-shelf dive computers.

Whilst the US Navy has been very systematic about validating Navy dive computer algorithms, there has been little documented or published evidence of rigorous testing of the algorithms in commercial off-the-shelf dive computers. This paper reports the evaluation of four algorithms used in these - Bühlmann ZHL-16C; VPM-B; Suunto-RGBM; EMC-20H - by comparison with US Navy experimental dives with known decompression sickness outcomes. Three specific tests were developed to test the algorithms' ability to mitigate decompression sickness: Total decompression time; no stop times and first stop depth. Output of commercial decompression algorithms were compared to either the probability of decompression sickness (PDCS) results from US Navy man-trials or statistical models derived from PDCS data. The algorithms were first tested with default conservative factors, then these factors were adjusted if the tests were not initially passed. The last verification step was to compare the output of the wrist computer with that of the full desktop algorithm. This testing indicated that, whilst none of the four passed all of the proposed tests with factory-default conservatism, ZHL-16C and Suunto-RGBM could be made to pass by adjusting user-defined settings. Man-trial data on PDCS is available to the non-US Navy scientific community for testing of commercial decompression algorithms. This type of validation testing can be very informative on how to best use available commercial dive computers to improve diver safety.

A Systematic Review and Meta-Analysis of Decompression Sickness in Altitude Physiological Training.

INTRODUCTION: A review of decompression sickness (DCS) cases associated with the NASA altitude physiological training (APT) program at the Johnson Space Center (JSC) motivated us to place our findings into the larger context of DCS prevalence from other APT centers.METHODS: We reviewed JSC records from 1999 to 2016 and 14 publications from 1968 to 2004 about DCS prevalence in other APT programs. We performed a meta-analysis of 15 APT profiles (488 cases / 385,116 exposures). We used meta-regression to evaluate the relation between estimated exposures and probability of DCS in a test group, accounting for the heterogeneity between studies.RESULTS: Our in-house review identified 6 Type I DCS (1 from an inside observer) and 1 Type II DCS. There were 6 cases in 9560 student hypobaric exposures from 3 NASA training flights; a student pooled prevalence rate of 0.44 cases / 1000 exposures compared to 1.44 cases / 1000 from 12 published APT profiles. The overall pooled DCS prevalence rate was 1.16 cases / 1000 exposures. There was substantial heterogeneity in DCS prevalence across studies. Denitrogenation time, exposure pressure, and exposure time were associated with probability of DCS in the meta-regression model.CONCLUSIONS: While the overall DCS prevalence rate is relatively low, there is marked heterogeneity among profiles. The pooled DCS prevalence rate estimate for the NASA profiles was lower than the overall rate. Variability in APT profile DCS prevalence could be further explained given student level and additional test-level covariates.Conkin J, Sanders RW, Koslovsky MD, Wear ML, Kozminski AG, Abercromby AFJ. A systematic review and meta-analysis of decompression sickness in altitude physiological training. Aerosp Med Hum Perform. 2018; 89(11):941-951.

Decompressing recompression chamber attendants during Australian submarine rescue operations.

Inside chamber attendants rescuing survivors from a pressurised, distressed submarine may themselves accumulate a decompression obligation which may exceed the limits of Defense and Civil Institute of Environmental Medicine tables presently used by the Royal Australian Navy. This study assessed the probability of decompression sickness (PDCS) for medical attendants supervising survivors undergoing oxygen-accelerated saturation decompression according to the National Oceanic and Atmospheric Administration (NOAA) 17.11 table. Estimated probability of decompression sickness (PDCS), the units pulmonary oxygen toxicity dose (UPTD) and the volume of oxygen required were calculated for attendants breathing air during the NOAA table compared with the introduction of various periods of oxygen breathing. The PDCS in medical attendants breathing air whilst supervising survivors receiving NOAA decompression is up to 4.5%. For the longest predicted profile (830 minutes at 253 kPa) oxygen breathing at 30, 60 and 90 minutes at 132 kPa partial pressure of oxygen reduced the air-breathing-associated PDCS to less than 3.1 %, 2.1% and 1.4% respectively. The probability of at least one incident of DCS among attendants, with consequent strain on resources, is high if attendants breathe air throughout their exposure. The introduction of 90 minutes of oxygen breathing greatly reduces the probability of this interruption to rescue operations.

Decompressing rescue personnel during Australian submarine rescue operations.

Personnel rescuing survivors from a pressurized, distressed Royal Australian Navy (RAN) submarine may themselves accumulate a decompression obligation, which may exceed the bottom time limits of the Defense and Civil Institute of Environmental Medicine (DCIEM) Air and In-Water Oxygen Decompression tables (DCIEM Table 1 and 2) presently used by the RAN. This study compared DCIEM Table 2 with alternative decompression tables with longer bottom times: United States Navy XVALSS_DISSUB 7, VVAL-18M and Royal Navy 14 Modified tables. Estimated probability of decompression sickness (PDCS), the units pulmonary oxygen toxicity dose (UPTD), the volume of oxygen required and the total decompression time were calculated for hypothetical single and repetitive exposures to 253 kPa air pressure for various bottom times and prescribed decompression schedules. Compared to DCIEM Table 2, XVALSS_DISSUB 7 single and repetitive schedules had lower estimated PDCS, which came at the cost of longer oxygen decompressions. For single exposures, DCIEM schedules had PDCS estimates ranging from 1.8% to 6.4% with 0 to 101 UPTD and XVALSS_DISSUB 7 schedules had PDCS of less than 3.1%, with 36 to 350 UPTD. The XVALSS_DISSUB 7 table was specifically designed for submarine rescue and, unlike DCIEM Table 2, has schedules for the estimated maximum required bottom times at 253 kPa. Adopting these tables may negate the requirement for saturation decompression of rescue personnel exceeding DCIEM limits.

Allometric scaling of decompression sickness risk in terrestrial mammals; cardiac output explains risk of decompression sickness

A probabilistic model was used to predict decompression sickness (DCS) outcome in pig (70 and 20 kg), hamster (100 g), rat (220 g) and mouse (20 g) following air saturation dives. The data set included 179 pig, 200 hamster, 360 rat, and 224 mouse exposures to saturation pressures ranging from 1.9–15.2 ATA and with varying decompression rates (0.9–156 ATA • min−1). Single exponential kinetics described the tissue partial pressures (Ptiss) of N2: Ptiss = ∫(Pamb – Ptiss) • τ−1 dt, where Pamb is ambient N2 pressure and τ is a time constant. The probability of DCS [P(DCS)] was predicted from the risk function: P(DCS) = 1−e−r, where r = ∫(PtissN2 − Thr − Pamb) • Pamb–1 dt, and Thr is a threshold parameter. An equation that scaled τ with body mass included a constant (c) and an allometric scaling parameter (n), and the best model included n, Thr, and two c. The final model provided accurate predictions for 58 out of 61 dive profiles for pig, hamster, rat, and mouse. Thus, body mass helped improve the prediction of DCS risk in four mammalian species over a body mass range covering 3 orders of magnitude.

Age, weight and decompression sickness in rats

Objective: The aim of this study was to determine if, after controlling for weight, age is associated with decompression sickness (DCS) in rats. Methods: Following compression-decompression, male rats aged 11 weeks were observed for DCS. After two weeks recovery, surviving rats were re-dived using the same compression-decompression profile. Results: In this experiment, there was a clear difference between DCS outcome at ages 11 or 13 weeks in matched rats (p = 0.002). Discussion: Even with weight included in the model, age was significantly associated with DCS (p = 0.01), yet after removal of weight the association was much stronger (p = 0.002). Conclusion: We believe that age is likely to be found associated with the probability of DCS in a larger dataset with a wider range of parameters, after accounting for the effect of weight.

Venous gas bubble formation and decompression risk after scuba diving in persons with chronic spinal cord injury and able-bodied controls

Prospective study. To evaluate the formation of venous gas bubbles following open-sea scuba dives in persons with chronic spinal cord injury (SCI) and in able-bodied diving instructors (C) and to assess the risk for decompression sickness (DCS). Field study at the Island of Krk, Croatia. Gas bubbles were monitored with an ultrasound scanner 40 min after surfacing. The probability of DCS (P((DCS))) was estimated from the recorded depth-time profile using a decompression model. Divers completed six dives in 3 days using a modified Bühlmann decompression model, and none developed signs of DCS. Mean P((DCS)) was similar in both groups, SCI (0.51+/-0.2%) and C (0.64+/-0.27%), and was seen to increase with subsequent dives. Number of bubbles (bubbles per cm(2)) was low in both groups on all 3 days of diving. We have used the P((DCS)) as a severity index of diving exposure. Overall, the severity of exposure in SCI subjects was consistent with the range of typical recreational dives, suggesting that the diving profile used is very safe.

Cumulative probability of decompression sickness.

Cumulative probability of decompression sickness.

On the likelihood of decompression sickness during H(2) biochemical decompression in pigs.

A probabilistic model was used to predict decompression sickness (DCS) outcome in pigs during exposures to hyperbaric H(2) to quantify the effects of H(2) biochemical decompression, a process in which metabolism of H(2) by intestinal microbes facilitates decompression. The data set included 109 exposures to 22-26 atm, ca. 88% H(2), 9% He, 2% O(2), 1% N(2), for 0.5-24 h. Single exponential kinetics described the tissue partial pressures (Ptis) of H(2) and He at time t: Ptis = integral (Pamb - Ptis). tau(-1) dt, where Pamb is ambient pressure and tau is a time constant. The probability of DCS [P(DCS)] was predicted from the risk function: P(DCS) = 1 - e(-r), where r = integral (Ptis(H(2)) + Ptis(He) - Thr - Pamb). Pamb(-1) dt, and Thr is a threshold parameter. Inclusion of a parameter (A) to estimate the effect of H(2) metabolism on P(DCS): Ptis(H(2)) = integral (Pamb - A - Ptis(H(2))). tau(-1) dt, significantly improved the prediction of P(DCS). Thus lower P(DCS) was predicted by microbial H(2) metabolism during H(2) biochemical decompression.

Effect of N2-He-O2 on decompression outcome in rats after variable time-at-depth dives.

No study of decompression sickness has examined both variable gas mixtures and variable time at depth to the point of statistical significance. This investigation examined the effect of N2-He-O2 on decompression outcome in rats after variable time-at-depth dives. Unanesthetized male albino rats were subjected to one of two series of simulated dives: 1) N2-He-O2 dives (20.9% O2) at 175 feet of seawater fsw) and 2) N2-O2 dives (variable percentage of O2; depths from 141 to 207 fsw). Time at depth ranged from 10 to 120 min; rats were then decompressed within 10 s to surface pressure. The probability of decompression sickness (severe bends symptoms or death) was analyzed with a Hill equation model, with parameters for gas potency and equilibrium time for the three gases and weight of the animal. Relative potencies for the three gases were of similar magnitude for bends and statistically different for death in ascending order: O2 less than He less than N2. Estimated gas uptake rates were different. N2 took three to four times as long as He to reach full effect; the rate of O2 appeared to be considerably shorter than that of N2 or He. The large influence of O2 on decompression outcome questions the simplistic view that O2 cannot contribute to the decompression requirement.

Decompression outcome following saturation dives with multiple inert gases in rats

This investigation examined the question of whether gas mixtures containing multiple inert gases provide a decompression advantage over mixtures containing a single inert gas. Unanesthetized male albino rats, Rattus norvegicus, were subjected to 2-h simulated dives at depths ranging from 145 to 220 fsw. At pressure, the rats breathed various He-N2-Ar-O2 mixtures (79.1% inert gas-20.9% O2); they were then decompressed rapidly (within 10 s) to surface pressures. The probability of decompression sickness (DCS), measured either as severe bends symptoms or death, was related to the experimental variables in a Hill equation model incorporating parameters that account for differences in the potencies of the three gases and the weight of the animal. The relative potencies of the three gases, which affect the total dose of decompression stress, were determined as significantly different in the following ascending order of potency: He less than N2 less than Ar; some of these differences were small in magnitude. With mixtures, the degree of decompression stress diminished as either N2 or Ar was replaced by He. No obvious advantage or disadvantage of mixtures over the least potent pure inert gas (He) was evident, although limits to the expectation of possible advantage or disadvantage of mixtures were defined. Also, model analysis did not support the hypothesis that the outcome of decompression with multiple inert gases in rats under these experimental conditions can be explained totally by the volume of gas accumulated in the body during a dive.