Detection of venous gas emboli after repetitive breath-hold dives: case report

INTRODUCTION

Neurological symptoms after breathhold (BH) diving are often referred to as "Taravana" and considered a form of decompression sickness. However, the presence of "high" gas embolism after BH diving has never been clearly shown. This study showed high bubble formation after BH diving.

MATERIALS AND METHODS

We performed transthoracic echocardiography on a 53-year-old male spearfishing diver (180 cm; 80 kg; BMI 24.7) 15 minutes before diving and at 15-minute intervals for 90 minutes after diving in a 42-meter-deep pool. Number of dives, bottom time and surface intervals were freely determined by the diver. Dive profiles were digitally recorded for depth, time and surface interval, using a freediving computer. Relative surface interval (surface interval/diving time) and gradient factor were calculated.

REULTS

High bubble grades were found in all the recorded echocardiograms. From the first to third recording (45 minutes), Grade 4 Eftedal-Brubakk (EB) bubbles were observed. The 60-, 75- and 90-minute recordings showed a reduction to Grades 3, 2 and 1 EB. Mean calculated GF for every BH dive was 0.22; maximum GF after the last dive was 0.33.

CONCLUSIONS

High bubble grades can occur in BH diving, as confirmed by echocardiographic investigation. Ordinary methods to predict inert gas supersaturation may not able to predict Taravana cases.

Nitric oxide-related endothelial changes in breath-hold and scuba divers

OBJECTIVE

Scuba and breath-hold divers are compared to investigate whether endothelial response changes are similar despite different exposure(s) to hyperoxia.

DESIGN

14 divers (nine scuba and five breath-holding) performed either one scuba dive (25m/25 minutes) or successive breath-hold dives at a depth of 20 meters, adding up to 25 minutes of immersion time in a diving pool. Flow-mediated dilation (FMD) was measured using echography. Peripheral post-occlusion reactive hyperemia (PORH) was assessed by digital plethysmography and plasmatic nitric oxide (NO) concentration using a nitrate/nitrite colorimetric assay kit.

RESULTS

The FMD decreased in both groups. PORH was reduced in scuba divers but increased in breath-hold divers. No difference in circulating NO was observed for the scuba group. Opposingly, an increase in circulating NO was observed for the breath-hold group.

CONCLUSION

Some cardiovascular effects can be explained by interaction between NO and superoxide anion during both types of diving ending to less NO availability and reducing FMD. The increased circulating NO in the breath-hold group can be caused by physical exercise. The opposite effects found between FMD and PORH in the breath-hold group can be assimilated to a greater responsiveness to circulating NO in small arteries than in large arteries.

Effect of varying deep stop times and shallow stop times on precordial bubbles after dives to 25 msw (82 fsw)

In our previous research, a deep 5-min stop at 15 msw (50 fsw), in addition to the typical 3-5 min shallow stop, significantly reduced precordial Doppler detectable bubbles (PDDB) and "fast" tissue compartment gas tensions during decompression from a 25 msw (82 fsw) dive; the optimal ascent rate was 10 msw (30 fsw/min). Since publication of these results, several recreational diving agencies have recommended empirical stop times shorter than the 5 min stops that we used, stops of as little as 1 min (deep) and 2 min (shallow). In our present study, we clarified the optimal time for stops by measuring PDDB with several combinations of deep and shallow stop times following single and repetitive open-water dives to 25 msw (82 fsw) for 25 mins and 20 minutes respectively; ascent rate was 10 msw/min (33 fsw). Among 15 profiles, stop time ranged from 1 to 10 min for both the deep stops (15 msw/50 fsw) and the shallow stops (6 msw/20 fsw). Dives with 2 1/2 min deep stops yielded the lowest PDDB scores--shorter or longer deep stops were less effective in reducing PDDB. The results confirm that a deep stop of 1 min is too short--it produced the highest PDDB scores of all the dives. We also evaluated shallow stop times of 5, 4, 3, 2 and 1 min while keeping a fixed time of 2.5 min for the deep stop; increased times up to 10 min at the shallow stop did not further reduce PDDB. While our findings cannot be extrapolated beyond these dive profiles without further study, we recommend a deep stop of at least 2 1/2 mins at 15 msw (50 fsw) in addition to the customary 6 msw (20 fsw) for 3-5 mins for 25 meter dives of 20 to 25 minutes to reduce PDDB.

A deep stop during decompression from 82 fsw (25 m) significantly reduces bubbles and fast tissue gas tensions

In spite of many modifications to decompression algorithms, the incidence of decompression sickness (DCS) in scuba divers has changed very little. The success of stage, compared to linear ascents, is well described yet theoretical changes in decompression ratios have diminished the importance of fast tissue gas tensions as critical for bubble generation. The most serious signs and symptoms of DCS involve the spinal cord, with a tissue half time of only 12.5 minutes. It is proposed that present decompression schedules do not permit sufficient gas elimination from such fast tissues, resulting in bubble formation. Further, it is hypothesized that introduction of a deep stop will significantly reduce fast tissue bubble formation and neurological DCS risk. A total of 181 dives were made to 82 fsw (25 m) by 22 volunteers. Two dives of 25 min and 20 min were made, with a 3 hr 30 min surface interval and according to 8 different ascent protocols. Ascent rates of 10, 33 or 60 fsw/min (3, 10, 18 m/min) were combined with no stops or a shallow stop at 20 fsw (6 m) or a deep stop at 50 fsw (15 m) and a shallow at 20 fsw (6 m). The highest bubbles scores (8.78/9.97), using the Spencer Scale (SS) and Extended Spencer Scale (ESS) respectively, were with the slowest ascent rate. This also showed the highest 5 min and 10 min tissue loads of 48% and 75%. The lowest bubble scores (1.79/2.50) were with an ascent rate of 33 fsw (10 m/min) and stops for 5 min at 50 fsw (15 m) and 20 fsw (6 m). This also showed the lowest 5 and 10 min tissue loads at 25% and 52% respectively. Thus, introduction of a deep stop significantly reduced Doppler detected bubbles together with tissue gas tensions in the 5 and 10 min tissues, which has implications for reducing the incidence of neurological DCS in divers.

Intrathoracic pressure changes after Valsalva strain and other maneuvers: implications for divers with patent foramen ovale

Scuba divers with patent foramen ovale (PFO) may be at risk for paradoxical nitrogen gas emboli when performing maneuvers that cause a rebound blood loading to the right atrium. We measured the rise and fall in intrathoracic pressure (ITP) during various maneuvers in 15 divers. The tests were standard isometric exercises (control), forceful coughing, knee bend (with and without respiration blocked), and Valsalva maneuver (maximal, gradually increased to reach control ITP, and as performed by divers to equalize middle ear pressure). All the maneuvers, as well as the downward slope of ITP at the release phase, were related to the control value. ITP levels were significantly higher than the standard isometric effort during a breath-hold knee bend (172%, P < 0.001), cough (133%, P < 0.05), and maximal Valsalva (136%, P < 0.05) whereas "usual" Valsalva maneuvers produced ITPs significantly lower than the standard (28%, P < 0.001). The downward slope of the pressure release curve was not significantly different among the different maneuvers (P < 0.1447). We conclude that maneuvers other than the usual divers' Valsalva are more likely to cause post-release central blood shift, both by the levels of ITP reached and by the time during which these ITPs are sustained. Divers (especially with PFO) should be advised to refrain from strenuous leg, arm, or abdominal exercise after decompression dives.

[Physiopathologic changes and morbidity in divers in saturation. Epidemiologic evaluation of 9 years' activities (1973-1982)]

An epidemiological study was made of 315 man-saturations over a period of 4508 days worked in saturation. The results were compared with those from 541 drillers working on a high-isolation site for periods of 30 days per shift making a total of 16,230 working days. Saturation was asymptomatic in 15,9%. The average length of conditions not interfering with diving or work was 3 days in the sample and 4 days in the controls. There were only two instances of type I decompression sickness in the divers (0,6%). These were both resolved without complications. Two subjects had to give up for health reasons (one case of parotitis and one anxiety-depression syndrome). It is felt that saturation is a very safe procedure as far as immediate pathological consequences are concerned, and that its minor pathological forms are of a significantly different type from those of the control series, especially with regard to ORL forms, upper airway conditions, sleep disturbances, and sensations of malaise and poor adaptation.

[Bacteriological and clinical notes on otitis externa in saturation. Double-blind study on the efficacy of prophylactic and therapeutic preparations]

Microbiological analysis of the variation in the bacterial flora of the external auditory canal was carried out during 39 immersion in saturated solutions. A double blind test on the usefulness of prophylactic and therapeutic preparations was also carried out. Prophylactics. - 5% Al acetate in H2O (P1), Boric alcohol (P2), lactic acid in H2O (P3, Domeboro (P4), no prophylactic (P0). After the immersions, a significant increase in Pseudomonas Aeruginosa and Candida Albicans (p less than 0,01) was noted in the auricular bacterial flora. Gram positive bacteria in general were considerably reduced (p less than 0,01). Gram negative bacteria other than pseudomonas. A (p less than 0,3) and coagulase negative straphylococci (p less than 0,03) did not vary significantly. Prophylactic preparations P1 and P2 were shown to be significantly more effective than P3, P4 and P0 in preventing the symptomatology (p less than 0,01). The most effective therapeutic preparation was found to be a locally applied gentamycinpolymixin association.

[Evaluations of 169 cases of decompression sickness treated in Italian hyperbaric centers 1980-1981]

An assessment was made of 169 cases of decompression sickness occurring during the period 1980-81. Nearly all (95,6%) were attributable to superficial planning and execution of the immersion and reascent to the surface marker as the result of panic. Breakdown in the diving apparatus was only responsible in 4.4% of cases. Irrispective of the intermediate decompression stages, the rate of reascent was more than 10 metres a minute in 71.6% of cases. Full recovery as a result of hyperbaric management was obtained in 78,2% type I sickness and 61.9% type II, with improvements in 17.3% and 35.1% respectively. The interval between emersion and treatment ranged from 1 to 72 hr, though the results of treatment were not significantly related to the rapidity of intervention (p greater than 0.05). Good results were dependent on the type of treatment employed, with a significantly better outcome (p less than 0.01) from U.S. Navy tables 2-2A, 3-3A, 4, 5 and 6 and the 2 + 6 recompression protocol, than from tables 5A and 6A.

[Changes in the health status in occupational under-water activities]

For the past 10 years of so, Italian professional divers have had obligatory medical check-ups once a year. These check-ups are based on International standards and are particularly important for divers going to work abroad or in the open sea. The present report is based on clinical data about 100 professional divers aged 20-50. The subjects had worked 1-30 years accumulating a total of 200-5000 shallow dives. 41% had also done deep work using intervention and saturation techniques. No significant incidence of common was encountered. Radiology revealed bone alterations in 52 subjects (to the joints in 17 cases). Hearing problems were encountered in 47 divers, mostly slight and often totally or partially cured during the observation period. 5 subjects were found to be unsuitable for saturation work. The aetiopathogenetic significance of the alterations encountered is discussed in terms of the type and duration of diving practised.

[Comparative analysis of radiographic data of "structural changes" in the bones of divers and non-divers]

The Authors examine one thousand lone bone X-rays of professional divers and non-diving controls. The goal is to look for a correlation between hyperbaric exposure and bone alteration images type "dense bony islet" and "translucent cystic area" according to McCallum, Walder and Davidson. The results show a statistically non significant difference between divers and controls: Hip: Divers 31%, Controls 30%; Knee: Divers 17%, Controls 23%; Shoulder: Divers 22%, Controls 22.5%. The types of bone structural alterations studied never seemed to originate forms of aseptic bone necrosis but had a tendency to evolve favourably and independently from diving activity. These structural alterations are therefore deemed as non significant with regard to the bone risk of professional diving. The Authors suggest that until the real significance of these bone X-ray images is cleared by further research only the bone structural alteration which are within one centimeter from the articular surface should be considered for possible negative evolution.

[Considerations on 209 cases of decompression sickness treated in Italian hyperbaric centers in 1978 and 1979]

Results of an epidemiological study on the incidence and aethiology of the cases of Decompression Sickness treated in eleven Italian Hyperbaric facilities during 1978 and 1979 are reported 209 cases were treated; 186 recovered completely, 92 improved, 5 had no advantage from treatment, 2 died. The majority of cases were in the age-range 25-29 years (15-55) and in the depth-range 40-50 msw (12-100). Decompression was mandatory in 207 cases and was not respected, mainly because the divers ascended at a wrong rate (20 msw/min in the majority, 10 cass "ballooned" to the surface, 2 cases surfaced at 1-2 msw/min). In a significant number of times decompression was aborted due to exhaustion of compressed air in the bottles. 55% of the 1979 cases referred to repetitive diving (2nd or 3rd dive of the day). The Authors conclude that human error in by far the most recurring aethiological agent in this study and point out the coincidence of the high incidence of D.S. cases south of Rome with the relative lack of diving schools in that area.

[Effects of variations in the ascending speed on the production of circulating gas bubbles after compressed-air diving]

Ninety-seven compressed air divers at depths of 20 to 52 msw were done. Every dive reached a tissue nitrogen saturation level greater than or equal to M value according to U.S. Navy decompression schedules and respected all prescribed decompression stop. Dives were divided in two groups according to the speed of ascent:--1st group: 33 dives (18 simulated, 15 open water) with ascent at 18 msw/min. for the first half of the distance and 10 msw/min. for the second half. No work on the bottom. Average ascent rate 14 msw/min. This profile was due to the flow limits of the outlet of our chamber during the second part of the ascent, and it was repeated in open water diving.--2nd group: 64 dives (4 simulated, 60 open water) with linear ascent at 10 msw/min. Half the open water dives were repetitive within 4 hours from the first one. Medium to heavy work on the bottom. Ultrasound Doppler bubble detection at rest and after exercise was performed at five minutes intervals and during 40 minutes after surfacing.