A metabolic simulator for unmanned testing of breathing apparatuses in hyperbaric conditions.

BACKGROUND: A major part of testing of rebreather apparatuses for underwater diving focuses on the oxygen dosage system. METHODS: A metabolic simulator for testing breathing apparatuses was built and evaluated. Oxygen consumption was achieved through catalytic combustion of propene. With an admixture of carbon dioxide in the propene fuel, the system allowed the respiratory exchange ratio to be set freely within human variability and also made it possible to increase test pressures above the condensation pressure of propene. The system was tested by breathing ambient air in a pressure chamber with oxygen uptake (Vo2) ranging from 1-4 L · min(-1), tidal volume (VT) from 1-3 L, breathing frequency (f) of 20 and 25 breaths/min, and chamber pressures from 100 to 670 kPa. RESULTS: The measured end-tidal oxygen concentration (Fo2) was compared to calculated end-tidal Fo2. The largest average difference in end-tidal Fo2during atmospheric pressure conditions was 0.63%-points with a 0.28%-point average difference during the whole test. During hyperbaric conditions with pressures ranging from 100 to 670 kPa, the largest average difference in Fo2was 1.68%-points seen during compression from 100 kPa to 400 kPa and the average difference in Fo2during the whole test was 0.29%-points. CONCLUSION: In combination with a breathing simulator simulating tidal breathing, the system can be used for dynamic continuous testing of breathing equipment with changes in VT, f, Vo2, and pressure.

[Fewer cases of decompression sickness in Västra Götaland. Eight years of statistics show a reduced number of consultations and treatments]. / Färre fall av dykarsjuka i Västra Götaland. Åtta års statistik visar minskat antal konsultationer och behandlingar.

During the period 2005 to 2012, a total of 340 consultations (phone calls and/or visits) regarding possible decompression illness were recorded at the two hospitals with recompression chambers in the Västra Götaland region, Sweden. An analysis of the data showed a trend towards fewer consultations and recompression treatments. A similar trend has been observed in many other countries. Possible reasons for this reduction in the number of cases are discussed. Most of the patients only present relatively mild signs and symptoms at the time of consultation. This, together with the fact that the number of patients is low, involves a risk that awareness and knowledge regarding correct handling and care in diving accidents might be lost. Since rapid and correct care of decompression illness is important to avoid later sequeale it is important that competence in diving medicine is maintained at hospitals Nationwide.

Swedish recommendations on recreational diving and diabetes mellitus.

Divers from many countries travel to explore various diving sites worldwide. In 2005, the Divers Alert Network (DAN) wrote guidelines for recreational diving and diabetes mellitus, but there is no up-to-date consensus or adoption of international guidelines on diabetes and diving. There are also large differences between the regulations in different countries. This is potentially both a medical and an insurance problem for a diver with diabetes. We present the current Swedish recommendations for recreational divers with Type 1 diabetes mellitus.

Continuous glucose monitoring--a study of the Enlite sensor during hypo- and hyperbaric conditions.

BACKGROUND: The performance and accuracy of the Enlite(™) (Medtronic, Inc., Northridge, CA) sensor may be affected by microbubble formation at the electrode surface during hypo- and hyperbaric conditions. The effects of acute pressure changes and of prewetting of sensors were investigated. MATERIALS AND METHODS: On Day 1, 24 sensors were inserted on the right side of the abdomen and back in one healthy individual; 12 were prewetted with saline solution, and 12 were inserted dry. On Day 2, this procedure was repeated on the left side. All sensors were attached to an iPro continuous glucose monitoring (CGM) recorder. Hypobaric and hyperbaric tests were conducted in a pressure chamber, with each test lasting 105 min. Plasma glucose values were obtained at 5-min intervals with a HemoCue(®) (Ängelholm, Sweden) model 201 glucose analyzer for comparison with sensor glucose values. RESULTS: Ninety percent of the CGM systems operated during the tests. The mean absolute relative difference was lower during hyperbaric than hypobaric conditions (6.7% vs. 14.9%, P<0.001). Sensor sensitivity was slightly decreased (P<0.05) during hypobaric but not during hyperbaric conditions. Clarke Error Grid Analysis showed that 100% of the values were found in the A+B region. No differences were found between prewetted and dry sensors. CONCLUSIONS: The Enlite sensor performed adequately during acute pressure changes and was more accurate during hyperbaric than hypobaric conditions. Prewetting the sensors did not improve accuracy. Further studies on type 1 diabetes subjects are needed under various pressure conditions.

In-vitro performance of the Enlite Sensor in various glucose concentrations during hypobaric and hyperbaric conditions.

BACKGROUND: There is a need for reliable methods of glucose measurement in different environmental conditions. The objective of this in vitro study was to evaluate the performance of the Enlite® Sensor when connected to either the iPro™ Continuous Glucose Monitor recording device or the Guardian® REAL-Time transmitting device, in hypobaric and hyperbaric conditions. METHODS: Sixteen sensors connected to eight iPro devices and eight Guardian REAL-Time devices were immersed in three beakers containing separate glucose concentrations: 52, 88, and 207 mg/dl (2.9, 4.9, and 11.3 mmol/liter). Two different pressure tests were conducted: a hypobaric test, corresponding to maximum 18000 ft/5500 m height, and a hyperbaric test, corresponding to maximum 100 ft/30 m depth. The linearity of the sensor signals in the different conditions was evaluated. RESULTS: The sensors worked continuously, and the sensor signals were collected without interruption at all pressures tested. When comparing the input signals for glucose (ISIGs) and the different glucose concentrations during altered pressure, linearity (R(2)) of 0.98 was found. During the hypobaric test, significant differences (p < .005) were seen when comparing the ISIGs during varying pressure at two of the glucose concentrations (52 and 207 mg/dl), whereas no difference was seen at the 88 mg/dl glucose concentration. During the hyperbaric test, no differences were found. CONCLUSIONS: The Enlite Sensors connected to either the iPro or the Guardian REAL-Time device provided values continuously. In hyperbaric conditions, no significant differences were seen during changes in ambient pressure; however, during hypobaric conditions, the ISIG was significantly different in the low and high glucose concentrations.

Accuracy and reliability of continuous glucose monitoring in individuals with type 1 diabetes during recreational diving.

BACKGROUND: This study evaluated the accuracy and function of the Continuous Glucose Monitoring System (CGMS, Minneapolis, MN) during recreational scuba diving in individuals with type 1 diabetes. METHODS: Twenty-four adults, 12 with type 1 diabetes and 12 healthy controls, were studied during five recreational scuba dives performed on three consecutive days. All the participants used the CGMS on all the days and during all the dives. Comparisons were made between plasma glucose at specific time intervals and the CGMS. RESULTS: The recording by the CGMS was robust, with few sensor problems. The mean sensor survival time was >48 h. Eighty-five percent of the individuals used one sensor during the entire length of the trial. The overall mean absolute difference (MAD) within the group with diabetes was 14.4 +/- 6%, and the corresponding daily figures were 23.2 +/- 19.3% on day 1, 11.6 +/- 4.5% on day 2, and 11.2 +/- 5.7% on day 3. A significant improvement regarding MAD when day 1 was compared with day 2 and 3 (P < 0.05). With a limit set at 70 mg/dL, hypoglycemia pre- and post-dive was detected with a positive predictive value of 0.39, negative predictive value of 0.98, sensitivity of 0.64, and specificity of 0.94. CONCLUSIONS: We demonstrate that the CGMS was used with accuracy in such difficult conditions as scuba diving and provided robust information on glucose variations.

The benefits of continuous glucose monitoring and a glucose monitoring schedule in individuals with type 1 diabetes during recreational diving.

BACKGROUND: Our objective is to evaluate the Medtronic CGMS continuous glucose monitoring system and plasma glucose (PG) measurement performed in a monitoring schedule as tools to identify individuals with type 1 diabetes at risk when diving. METHODS: We studied 24 adults, 12 type 1 diabetes subjects and 12 controls, during 5 recreational scuba dives performed on 3 consecutive days. The CGMS was used by all participants on all the days and all the dives. Comparisons were made between PG performed in a monitoring schedule during the days of diving, self-monitored blood glucose (SMBG) performed 2 weeks prior to diving, and the CGMS during the study. RESULTS: One hundred seventeen dives were performed. Hypoglycemia (<70 mg/dl) was found in six individuals and on nine occasions. However, no symptoms of hypoglycemia were present during or immediately postdiving. In one case, repetitive hypoglycemia prediving gave rise to a decision not to dive. None of the dives were aborted. The number of hypoglycemic episodes, 10 min prediving or immediately postdiving, were related to the duration of diabetes, r = 0.83 and p =0.01, and the percentage of SMBG values below target (<72 mg/dl), r = 0.65 and p =0.02. Moreover, the number of hypoglycemic episodes was also related to the total duration below low limit (<70 mg/dl), measured by the CGMS, r =0.74 and p =0.006. CONCLUSION: Safe dives are possible to achieve by well-informed, well-controlled individuals with type 1 diabetes. Using downloaded SMBG, CGMS, and repetitive PG in a monitoring schedule, it is possible to identify those subjects who are suitable for diving.

[Recreational diving accidents in Sweden]. / Olycksfallsskador vid sportdykning i Sverige.

Even if recreational diving is gradually becoming safer, the 2-6 fatalities each year is the most serious problem in recreational diving. Human factors are behind 75% of the fatalities and medical problems seldom cause fatalities. On average 40 recreational divers are treated with recompression each year. Signs and symptoms are in general mild and only few sequelas are seen. The number of traumas to ear/balance organs, sinuses, lungs etc are difficult to estimate but these are most likely not a large part of all patients in the health care. It is currently difficult to estimate the risks in recreational diving since there is no exact information on the number of dives that are performed each year.

[Health fitness assessment for recreational diving requires special medical competence]. / Hälsobedömning för sportdykning kräver medicinska specialkunskaper.

Recreational diving has become increasingly popular in Sweden over the last years and about half a million dives are made each year. During the same time the health requirements for diving have changed and today we allow asthmatics and diabetics to dive under certain conditions. Chest X-ray, that earlier was compulsory, is not required in the fitness to dive examination, and in the future Europe the minimal requirements will be a health declaration rather than a FTD examination by a doctor. Despite this there will be a need for doctors with competence in diving medicine to handle medical problems in connection to diving and to evaluate all the questions generated by the divers' answers in the health declarations.

Atmospheric changes and physiological responses during a 6-day "disabled submarine" exercise.

BACKGROUND: Survival time within a disabled submarine (SUBSUNK) is dependant on atmospheric composition and proper design and use of emergency atmospheric control systems. The objective of this study was to investigate atmospheric changes and physiological responses during a SUBSUNK trial. METHODS: There were 18 volunteers who were restrained within a 250 m3 front compartment of an Ula-class submarine submerged in 8 degrees C seawater for 6 d, 18 h. Atmospheric control was maintained according to emergency procedures using non-electrically powered chemical CO2 absorption, and O2 was replenished using chlorate candles. Atmospheric parameters, skin and body temperatures, weight, urine, and drinking volume were measured. Subjective responses to cold were measured on a visual analog scale (VAS), and symptoms were logged on the environmental symptoms questionnaire (ESQ). RESULTS: Atmospheric temperature gradually decreased to a minimum of 14.1 degrees C. Toe, heel, and finger temperatures decreased significantly. Subjects reported inferior subjective thermal comfort on the VAS and increased cold stress on the ESQ. Except for CO2, no inorganic or volatile organic compounds exceeded occupational exposure limits. The PO2 and PCO2 ranged from 17.4-20.3 and 1.9-2.8 kPa, respectively, during the first 5 d. During the last 2 d, PO2 and PCO2 were deliberately maintained at about 15.8 and 3.1 kPa, respectively. Mean oxygen consumption and CO2 production were 23.8 and 19.8 L standard temperature and pressure (STP) x man(-1) x h(-1), respectively. Soda lime and lithium hydroxide CO2 absorption capacities were 126 and 405 L STP x kg(-1) respectively. CONCLUSIONS: Atmospheric conditions can be controlled acceptably for 6 d, 18 h within the front compartment of an Ula-class submarine operating according to emergency SUBSUNK procedures.