Recreational scuba divers' aversion to low-frequency underwater sound.

Increasing use of active low-frequency sonar by submarines and ships raises the risk of accidental exposure of recreational divers to low-frequency underwater sound (LFS). This study aimed to characterize the subjective responses of recreational scuba divers to LFS to ascertain the extent to which LFS may impact their enjoyment, comfort, or time spent underwater. Seventeen male and nine female recreational scuba divers participated. Diving was conducted in an acoustically transparent tank located within a larger anechoic pool. Subjects wore scuba gear and were positioned I m below the surface in a prone position. The sound transducer was located 4 m directly below the diver's head. Sound exposures consisted of three signal types (pure tone, 30 Hz hyperbolic sweep up, and 30 Hz hyperbolic sweep down) each presented at six center frequencies from 100 to 500 Hz and six sound pressure levels(SPL) ranging from 130 to 157 dB re 1 microPa. The duration of each sound exposure was 7 s. Subjects responded via an underwater console to rate aversion to LFS on a category-ratio scale, and to indicate the presence or absence of vibration of any body part. Aversion to LFS and the percent incidence of vibration increased as the SPL increased. The percent incidence of vibration decreased linearly with increasing frequency. At the highest SPL the probability that an aversion rating would exceed Very Severe (7 on the category-ratio scale) was predicted to be 19%. There was no significant difference in aversion among signal types. The 100 Hz frequency was the most aversive frequency (P < 0.05). A plot of aversion vs. frequency showed a U-shaped function with minimum aversion at 250 Hz. In conclusion, diver aversion to LFS is dependent upon SPL and center frequency. The highest aversion rating was given for 100 Hz, this frequency corresponded with the greatest probability of detecting vibration. Factors other than vibration seem to account for aversion to the highest frequencies. Our data suggest that LFS exposures up to 145 dB re 1 microPa at frequencies between 100 and 500 Hz will have minimal impact on the recreational diver.

Treatment of type I decompression sickness using the U.S. Navy treatment algorithm.

The effectiveness of the U.S. Navy (USN) Diving Manual treatment algorithm in treating pain-only decompression sickness (DCS) was analyzed. Treatment logs from the Naval Diving and Salvage Training Center and the Navy Experimental Diving Unit during the decade 1976-1986 were examined. Two hundred and ninety-two cases diagnosed initially as pain-only DCS were identified. Using the treatment algorithm, 208 cases were completed on USN Treatment Table 5 (TT-5), and 84 cases completed on USN Treatment Table 6 (TT-6). Recurrence of symptoms was 4.3% after TT-5, and 3.6% following TT-6. Difference in rate of recurrence was not statistically significant between treatment tables. Overall, the success rate for following the USN treatment algorithm was 95.9%. These data support the use of the shorter TT-5 in accordance with the Navy treatment algorithm.

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.

U.S. Navy saturation diving and diver neuropsychologic status.

The neuropsychologic status of 25 male U.S. Navy saturation divers was assessed before and after saturation dives conducted at the Navy Experimental Diving Unit. Between 1982 and 1986, 5 dives to simulated depths of 198 to 335 msw were accomplished. Eighteen divers completed 1 dive, and 7 divers completed 2 saturation dives during this period. Dive durations ranged from 26 to 31 d, with helium-oxygen used as the breathing medium. On each dive the men engaged in strenuous, meaningful, in-water work on the bottom. Comparison of neuropsychologic assessment battery results pre- and postdives did not reveal permanent changes in neuropsychologic status. Transient alterations in affect, visual focusing, and physical activity level presented upon surfacing but resolved within 10 d.

Visual reaction time performance preceding CNS oxygen toxicity.

The visual reaction time performance of divers experiencing CNS oxygen toxicity was assessed during the development of closed-circuit 100% oxygen breathing diving schedules at the U.S. Navy Experimental Diving Unit. Divers repeatedly performed the visual reaction time test of the Performance Measurement System (PMS) during multiple excursion dives. Each diver wore a Draeger LAR V UBA and performed moderate work on an underwater bicycle ergometer while engaged in the reaction time test. A single subject, repeated measures design was used. Six divers experienced 7 episodes of CNS oxygen toxicity while engaged in the visual reaction time test. Two episodes were preceded by a slowing and increase in variability of reaction time. Five episodes were not preceded by changes in reaction time performance. Other objective and subjective symptoms of toxicity experienced by the divers did not appear to be correlated with reaction time performance. Thus, the PMS visual reaction time test was not reliable method of detecting CNS oxygen toxicity in this study.

Evaluation of noise within the MK 12 SSDS helmet and its effect on divers' hearing.

The noise inside the U.S. Navy MK 12 SSDS helmet was measured and its effect on the hearing of divers assessed. Seven male divers completed 20 dives while breathing air at simulated depths ranging from 1.8 to 30.5 msw with dive durations ranging from 40 to 120 min. Microphones recorded sound pressure levels inside the helmet while the diver was in the water and exercising. Average corrected sound intensity levels in the helmet ranged from 90.5 dB(A) at 1.8 msw to 97.3 dB(A) at 30.5 msw. Diver hearing threshold level shifts were recorded as a function of helmet noise exposure; moderate threshold shifts were observed at depths of 9.1 msw or deeper after 120-min dives. The hearing of all divers completing dives up to 120 min returned to predive levels within 24 h after noise exposure. However, dive durations in excess of 120 min at 9.1 and 20.1 msw resulted in substantial auditory shifts in 1 diver, which required 2-3 d to recover to predive levels. These results suggest that the impact of helmet noise on diver hearing should be included in planning operations using the MK 12 SSDS.

Cognitive performance during a heat acclimatization regimen.

The cognitive performance of six male Marines undergoing a 10-d heat acclimatization regimen was assessed using repeated acquisition and time estimation tasks. Subjects performed controlled treadmill exercise in a heat acclimatization chamber at 33.3 degrees C dry bulb, 29.4 degrees C wet bulb temperature. Multiple performance assessments were conducted during each daily heat exposure of 155 min. On the first day of heat exposure, time estimates decreased from preacclimatization baseline values recorded at moderate temperatures while performance on the repeated acquisition tasks yielded slight decrements. By the 10th day of heat exposure, all subjects demonstrated significant heat acclimatization. However, mean performance on the repeated acquisition task was still impaired and time estimates were higher than during the first heat exposure. These results suggest that tasks requiring the acquisition of new behaviors may be difficult to perform in a hot environment, even by partially acclimatized individuals.

Operator performance in the one-atmosphere diving system JIM in water at 20 degrees C and 30 degrees C.

Performance and physiology of five operators of the one-atmosphere diving system JIM were assessed when diving JIM in mild (20 degrees C) and warm (30 degrees C) water. Each operator completed a minimum of 3 dives at each water temperature; during each dive 5 walks of 18 m and 3 step maneuvers were accomplished. At the conclusion of 40-min dives in water at 30 degrees C, operator heart rate averaged 151 beats/min, system interior temperature averaged 32.6 degrees C, and the mean respiration rate of operators was 28 breaths/min. Task completion times were faster in warm water. Thermal considerations in the deployment of the JIM system are discussed in relation to these data.

The behavioral toxicity of a tributyltin ester in the rat.

The behavioral toxicity of an organic tin compound under consideration for use in marine antifouling paint was assessed using a Sidman avoidance paradigm. The assessed compound, an organometallic polymer (tributyltin [methacrylic-CO-methylmethacrylate] ester), is from a group of alkyltin compounds of which triethyl and tributyltin are known to be toxic. Rats were tested under a free-operant avoidance procedure for 6 months while ingesting the polymer in their drinking water. At the beginning of the 5th month significant behavioral changes became evident, reflected in increases in shock rate, decreased responding, and a shifting of the interresponse time distribution. Performance improved upon withdrawal of the contaminant suggesting that limited exposure to the polymer may not result in permanent behavioral dysfunction.

Behavioral effects of morphine on free-operant avoidance under hyperbaric pressure.

Morphine sulfate was tested under hyperbaric pressure to assess its effects on behavior. Four male hooded rats were trained to avoid brief electric shocks under a free-operant unsignalled avoidance procedure. Using an individual organism design, we injected each rat subcutaneously with morphine sulfate (2.0, 4.0, 6.0, 8.0 mg/kg body wt.) or saline (0.1 ml/100 g body wt.). Rats were tested at 1.0 and 7.1 atmospheres absolute (ATA) in a dry hyperbaric chamber while breathing a mixture of helium and oxygen. Each session lasted 60 min. Overall, the analgesic effects of morphine at 1.0 and 7.1 ATA were found to be similar. Shock avoidance by a rat was found to be a monotonic function of the drug dose; the fewest shocks were associated with the 2.0 mg/kg dose. Increased pressure did not significantly affect the number of shocks received by a rat across doses. Total responding remained stable throughout the study, but the temporal pattern of responding was differentially influenced by drug dose.