Research on nitrogen-oxygen saturation diving with repetitive excursions.
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For some tasks of underwater operation the need for longer dive duration and more working divers necessitates the use of saturation diving techniques with excursions. Saturation diving with excursion has high working efficiency. A collaborative experiment with Chinese Underwater Technology Institute, American National Office of Research Undersea Program and Hamilton Research Ltd. was conducted at our Institute in Shanghai. The main experiment objectives were to assess the longer, deeper repetitive excursions during nitrogen-oxygen saturation situation, oxygen exposure management, nitrox saturation decompression after excursions and performance aspects. Four Chinese professional experienced divers were saturated at 25 msw for 5 days at the hyperbaric facility, where they did 15 air excursions to depths between 50 and 75 msw, for duration up to 240 min. Decompression from excursions to the storage were mostly no-stops, but 5 required stops for 3 to 116 min. Saturation decompression began with the "precursory" ascent following a brief return to 25 msw. Doppler bubble detection showed some bubbles of Spencer Grade II and occasionally III, following excursions and during saturation decompression, especially after muscle flexing. No symptoms of decompression sickness were reported: one diver was more of fatigued on one occasion than other times. Oxygen exposure reached its peak of 3103 Oxygen Toxicity Units on Day 6. The only subjective symptom of oxygen toxicity was mild and transient numb fingertips. No significant change was seen in vital capacity. (+info)
Prevention of spinal cord injuries caused by diving: evaluation of the distribution and usage of a diving safety video in high schools.
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OBJECTIVE: To determine and assess the distribution and use of Sudden Impact, a video designed by Think First and SportsSmart Canada, to help prevent spinal cord injury caused by careless shallow water diving among teenagers in the high risk group (15-24 years old). DESIGN: Survey of 92 public secondary schools in Toronto, Canada. SUBJECTS: The heads of the physical and health education departments of the 92 secondary public schools in the Metropolitan Toronto region. RESULTS: The response rate was 64% (59 schools), of which 76% (45) had actually received the video. Forty one schools (91%) of those that received the video reported using it. Eighty per cent of responding schools showed it to grade 11 students. Eighty per cent of schools with swimming pools used the video compared with only 42% of schools without swimming pools. CONCLUSIONS: There is a need for improvements in the system of distribution to ensure greater use of material such as this video. These may include direct distribution to principals, continuing contact with the schools, or mandatory inclusion of diving safety into the school curriculum. (+info)
Relationship between the clinical features of neurological decompression illness and its causes.
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There is dispute as to whether paradoxical gas embolism is an important aetiological factor in neurological decompression illness, particularly when the spinal cord is affected. We performed a blind case-controlled study to determine the relationship between manifestations of neurological decompression illness and causes in 100 consecutive divers with neurological decompression illness and 123 unaffected historical control divers. The clinical effects of neurological decompression illness (including the sites of lesions and latency of onset) were correlated with the presence of right-to-left shunts, lung disease and a provocative dive profile. The prevalence and size of shunts determined by contrast echocardiography were compared in affected divers and controls. Right-to-left shunts, particularly those which were large and present without a Valsalva manoeuvre, were significantly more common in divers who had neurological decompression illness than in controls (P<0.001). Shunts graded as large or medium in size were present in 52% of affected divers and 12.2% of controls (P<0.001). Spinal decompression illness occurred in 26 out of 52 divers with large or medium shunts and in 12 out of 48 without (P<0.02). The distribution of latencies of symptoms differed markedly in the 52 divers with a large or medium shunt and in the 30 divers who had lung disease or a provocative dive profile. In most cases of neurological decompression illness the cause can be determined by taking a history of the dive profile and latency of onset, and by performing investigations to detect a right-to-left shunt and lung disease. Using this information it is possible to advise divers on the risk of returning to diving and on ways of reducing the risk if diving is resumed. Most cases of spinal decompression illness are associated with a right-to-left shunt. (+info)
Humboldt penguins outmanoeuvring El Nino.
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We satellite-tracked five Humboldt penguins during the strong 1997/98 El Nino Southern Oscillation (ENSO) from their breeding island Pan de Azucar (26 degrees 09'S, 70 degrees 40'W) in Northern Chile and related their activities at sea to satellite-derived information on sea surface temperature (SST), sea surface temperature anomaly (SSTA), wind direction and speed, chlorophyll a concentrations and statistical data on fishery landings. We found that Humboldt penguins migrated by up to 895 km as marine productivity decreased. The total daily dive duration was highly correlated with SSTA, ranging from 3.1 to 12.5 h when the water was at its warmest (+4 degrees C). Birds travelled between 2 and 116 km every day, travelling further when SSTA was highest. Diving depths (maximum 54 m), however, were not increased with respect to previous years. Two penguins migrated south and, independently of each other, located an area of high chlorophyll a concentration 150 km off the coast. Humboldt penguins seem to use day length, temperature gradients, wind direction and olfaction to adapt to changing environmental conditions and to find suitable feeding grounds. This makes Humboldt penguins biological in situ detectors of highly productive marine areas, with a potential use in the verification of trends detected by remote sensors on board satellites. (+info)
Seasonal changes in buoyancy and diving behaviour of adult grey seals.
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Phocid seals go through dramatic seasonal changes in body mass and composition as a result of the spatial and temporal separation of foraging, reproduction and moulting. These changes in body fat content and body mass result in seasonal changes in buoyancy, which in turn may influence diving behaviour. We examined the longitudinal changes in buoyancy and diving behaviour of 14 adult grey seals (Halichoerus grypus) during two periods that represent maximal contrast in body mass and composition. During both the post-moulting (PM) and pre-breeding (PB) periods, grey seals were negatively buoyant. However, buoyancy increased by 47.9 % between the PM and PB periods. Descent rate was significantly faster during the PM period (1.0+/-0.07 m s(-1)) than during the PB period (0.7+/-0.06 m s(-1)), suggesting that seals were aided by negative buoyancy during the downward portion of dives. Ascent rate was also significantly faster during the PM period (0.8+/-0.06 m s(-1)) than during the PB period (0.6+/-0.05 m s(-1)), contradicting the prediction that more buoyant animals should ascend faster. The effects of drag could not account for this discrepancy. Dive depth and surface interval between dives did not differ significantly between the two periods. Similarly, the distribution of dive shapes used by individuals did not differ between the two periods. However, dive duration was significantly longer during the PB period than during the PM period (5.5+/-0.25 min compared with 4.4+/-0.24 min, respectively) as was time spent at the bottom of the dive (3.1+/-0.22 min compared with 2.5+/-0.15 min, respectively). (+info)
Estimation of the rate of oxygen consumption of the common eider duck (Somateria mollissima), with some measurements of heart rate during voluntary dives.
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The relationship between heart rate (f(H)) and rate of oxygen consumption (V(O2)) was established for a marine diving bird, the common eider duck (Somateria mollissima), during steady-state swimming and running exercise. Both variables increased exponentially with speed during swimming and in a linear fashion during running. Eleven linear regressions of V(O2) (ml kg(-1 )min(-1)) on f(H) (beats min(-1)) were obtained: five by swimming and six by running the birds. The common regression was described by V(O2)=10.1 + 0.15f(H) (r(2)=0.46, N=272, P<0.0001). The accuracy of this relationship for predicting mean V(O2) was determined for a group of six birds by recording f(H) continuously over a 2-day period and comparing estimated V(O2) obtained using the common regression with (i) V(O2) estimated using the doubly labelled water technique (DLW) and (ii) V(O2) measured using respirometry. A two-pool model produced the most accurate estimated V(O2) using DLW. Because of individual variability within mean values of V(O2) estimated using both techniques, there was no significant difference between mean V(O2) estimated using f(H) or DLW and measured V(O2) values (P>0.2), although individual errors were substantially less when f(H) was used rather than DLW to estimate V(O2). Both techniques are, however, only suitable for estimating mean V(O2) for a group of animals, not for individuals. Heart rate and behaviour were monitored during a bout of 63 voluntary dives by one female bird in an indoor tank 1.7 m deep. Tachycardia occurred both in anticipation of and following each dive. Heart rate decreased before submersion but was above resting values for the whole of the dive cycle. Mean f(H) at mean dive duration was significantly greater than f(H) while swimming at maximum sustainable surface speeds. Heart rate was used to estimate mean V(O2) during the dive cycle and to predict aerobic dive limit (ADL) for shallow dives. (+info)
Hearing loss in diving--a study amongst Navy divers.
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Despite the commonly observed condition of middle and inner ear barotrauma among divers, there is little evidence of insidious and permanent development of sensorineural hearing loss associated with diving. An audiometric survey was performed on a group of 120 divers and 166 non divers from the Royal Malaysian Naval Base in Lumut, West Malaysia between July to December 1991. The results of this survey revealed that insidious development of high frequency sensorineural hearing loss may be associated with diving. At frequencies 4000, 6000 and 8000 Hz the divers had higher mean hearing levels than non divers and their hearing at those frequencies seemed to deteriorate faster. The etiology of this insidious hearing loss is multifactorial and may be related to inner ear barotrauma, decompression sickness or noise-induced deafness. (+info)
Decompression illness associated with underwater logging: 6 case reports from Kenyir Lake, Malaysia.
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The formation of Kenyir Lake as part of a hydroelectric project in the 1980s caused much forest area to be submerged. From 1991, underwater divers were employed to log these sunken trees at depths of up to 100 meters. At least 6 mishaps involving underwater logging personnel were recorded from March 1994 to August 1996. We retrospectively reviewed 5 cases who were managed in Hospital Kuala Terengganu. The patients presented with marked cardiorespiratory and neurological disturbances. One diver died in the Hospital while another died at the recompression chamber. Three divers were treated with recompression and improved. Average delay before the start of recompression was 14 hours. Underwater logging has definite dangers and steps must be taken to ensure that both the divers and the equipment are appropriate for the task. Availability of a nearby recompression facility would greatly enhance the management of diving accidents, not only for commercial divers but also for recreational divers who frequent the islands nearby. (+info)