Application of a valveless anesthesia circuit for deep diving.

The Mapleson E breathing circuit used in anesthesia has no valves or CO2-absorbent canisters and thus entails low resistance to breathing and has low requirements for fresh gas flow (FGF). The authors investigated whether these advantages would make a circuit, modified for hyperbaric use, able to support ventilation during heavy work on the surface and at deep depths with reduced FGF rates. The current recommended FGF for free-flowing diving circuits is 170 liters/min. Six Navy divers participated in 10-min graded exercise sequences, peak workload 220 W. Measurements were made of inspired and end-tidal concentrations of CO2, tidal volume, respiratory rate, and CO2 production at both sea level and 2.7 MPa dry environment. At sea level, all six divers were able to finish their exercises using the modified circuit with all tested rates of FGF. At 2.7 MPa the exercise sequence could be finished by all subjects when FGF was 170 liter/min and by five subjects when FGF was 127.5 liter/min, but high end-tidal CO2 measurements and hypercapnia symptoms were common at 127.5 liter/min. None of the subjects was able or allowed to finish the exercise sequence when FGF was 85 liter/min. Lower work-loads of 75 and 150 W for up to 4 min were completed easily by all subjects at all three rates of FGF. We conclude that this circuit concept warrants further study because it requires lower FGF than is currently used with open-circuit helmets and is valveless; how much of a reduction in FGF could be tolerated with heavy work at depths such as 2.7 MPa requires further study.

Neuropsychologic assessment of cerebral decompression sickness and gas embolism.

A battery of neuropsychologic tests was administered to individuals who had sustained CNS decompression sickness or arterial gas embolism. Testing was intended to assess the presence of residual cognitive impairment. Five clinical cases are presented in which information obtained through this testing played a determining role in the detection and treatment of residual cerebral dysfunction. Recovery of cerebral integrity was documented using the test battery. Even in the absence of clear signs from a standard neurologic examination, sufficient information was gathered by neuropsychologic testing to prompt recompression therapy. Temporary suppression of CNS symptoms by initial recompression was often observed, as documented by follow-up neurologic and neuropsychologic evaluations. Recovery of full cognitive functioning followed repeated hyperbaric treatments, suggesting that CNS insults may be more refractory to therapy than previously thought.

Decompression sickness in women divers.

The comparative incidence of DCS in women has been debated for years. Diving log data from the Naval Diving and Salvage Training Center (NDSTC), Panama City, FL, demonstrate that there is no increased risk of DCS among Navy female divers compared to their male counterparts. Twenty-eight female students were compared to their 487 male classmates on 878 air and helium-oxygen dives between 4.64 and 10.10 ATA (120 to 300 fsw). None of the women experienced DCS while 8 men developed DCS symptoms. The total duration of the dives ranged from 8 min to 2 h and 6 min; bottom times were less than 20 min. Theoretical inert gas supersaturation on these profiles are commensurate with those experienced on 40- to 60-min sport scuba dives.

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Primary Causes of Drowning and Near Drowning in Scuba Diving.

In brief: Two scuba divers who were semiconscious when retrieved from the water of a training pool were found to have different primary injuries that required distinctly different treatments. Near drowning in a swimmer or scuba diver should alert a physician to look beyond the simple immersion accident to discover if an underlying disorder may have been the cause. In a scuba diver, the differential diagnosis must be extended to include decompression sickness, cerebral air embolism, pneumothorax, and carbon monoxide poisoning. Assessment and treatment-perhaps with hyperbaric oxygen therapy-must be carried out at once, both to resuscitate the diver and maximize the chances for a complete recovery.

Spinal Cord Decompression Sickness in a Sport Scuba Diver.

In brief: A 26-year-old diver suffered spinal cord decompression sickness even though he did not exceed the time and depth limits set in standard US Navy diving tables. This case shows that when dives are strenuous and almost reach time and depth limits they may exceed the parameters of the tables. The case also illustrates the importance of rapid diagnosis and hyperbaric oxygen treatment of pressure-related diving casualties. The author says optimum treatment of decompression sickness depends on a high level of suspicion, an accurate diving history, and prompt treatment with hyperbaric oxygen.