Closed-circuit Breathing Apparatus Research Articles

Role of NMDA Receptor in High-Pressure Neurological Syndrome and Hyperbaric Oxygen Toxicity.

Professional divers exposed to pressures greater than 11 ATA (1.1 MPa) may suffer from high-pressure neurological syndrome (HPNS). Divers who use closed-circuit breathing apparatus and patients and medical attendants undergoing hyperbaric oxygen therapy (HBOT) face the risk of CNS hyperbaric oxygen toxicity (HBOTx) at oxygen pressure above 2 ATA (0.2 MPa). Both syndromes are characterized by reversible CNS hyperexcitability, accompanied by cognitive and motor deficits, and N-methyl-D-aspartate receptor (NMDAR) plays a crucial role in provoking them. Various NMDAR subtypes respond differently under hyperbaric conditions. The augmented currents observed only in NMDAR containing GluN2A subunit increase glutamatergic synaptic activity and cause dendritic hyperexcitability and abnormal neuronal activity. Removal of the resting Zn2+ voltage-independent inhibition exerted by GluN2A present in the NMDAR is the major candidate for the mechanism underlying the increase in receptor conductance. Therefore, this process should be the main target for future research aiming at developing neuroprotection against HPNS and HBOTx.

VERIFICATION OF TACTICAL AND TECHNICAL DATA OF THE BREATHING APPARATUS

The function of the breathing apparatus is to protect the health of firefighters in a harmful and non-respirable environment. Closed-circuit breathing apparatus provides members of the Fire and Rescue Service with respiratory protection in the elimination of adverse events in tunnels and underground spaces. The MSA 4h Air Elite is a four-hour self-contained breathing apparatus that operates on the principle of generating oxygen by an exothermic reaction of potassium hyperoxide. Each breathing apparatus has its tactical technical parameters. We verified the tactical and technical data of the MSA AIRE ELITE by the experiment they participated in the firefighter. Each firefighter was equally coupled. An MSA Air Elite was used during the experiment. Tactical-technical data reported by the manufacturer varies in some points with the practical results that we have managed to obtain. The manufacturer's largest deviations in tactical and technical data and practical results are mainly in the length of work activity, temperature in use in intervention, and air consumption. According to our experiment, the MSA 4h Air Elite breathing apparatus does not last in the working activity 240 minutes as it discloses a manufacturer, but on the other hand, this time-inconsistency may be caused by the intensity of training and demanding of the training track.

The Mechanism of NMDA Receptor Hyperexcitation in High Pressure Helium and Hyperbaric Oxygen.

Professional divers exposed to pressures greater than 1.1 MPa may suffer from the high pressure neurological syndrome (HPNS). Divers who use closed-circuit breathing apparatus face the risk of CNS hyperbaric oxygen toxicity (HBOTox). Both syndromes are characterized by reversible CNS hyperexcitability, accompanied by cognitive and motor deficits. Previous studies have demonstrated that the hyperexcitability of HPNS is induced mainly by NMDA receptors (NMDARs). In our recent studies, we demonstrated that the response of NMDARs containing GluN1 + GluN2A subunits was increased by up to 50% at high pressure (HP) He, whereas GluN1 + GluN2B NMDARs response was not affected under similar conditions. Our aim was to compare the responses of both types of NMDARs under HBOTox conditions to those of HP He and to reveal their possible underlying molecular mechanism(s). The two combinations of NMDARs were expressed in Xenopus laevis oocytes, placed in a pressure chamber, voltage-clamped, and their currents were tested at 0.1 (control) −0.54 MPa 100% O2 or 0.1–5.1 MPa He pressures. We show, for the first time, that NMDARs containing the GluN2A subunit exhibit increased responses in 100% O2 at a pressure of 0.54 MPa, similar to those observed in 5.1 MPa He. In contrast, the GluN1 + GluN2B response is not sensitive to either condition. We discovered that neither condition produced statistically significant changes in the voltage-dependent Mg2+ inhibition of the response. The averaged IC50 remained the same, but a higher [Mg2+]o was required to restore the current to its control value. The application of TPEN, a Zn2+ chelator, in control, HP He and HBOTox conditions, revealed that the increase in GluN1 + GluN2A current is associated with the removal of the high-affinity voltage-independent Zn2+ inhibition of the receptor. We propose that HPNS and HBOTox may share a common mechanism, namely removal of Zn2+ from its specific binding site on the N-terminal domain of the GluN2A subunit, which increases the pore input-conductance and produces larger currents and consequently a hyperexcitation.

Exploring virtual mental practice in maintenance task training.

- This paper aims to contribute to a general understanding of mental practice by investigating the utility of and participant reaction to a virtual reality maintenance training among underground coal mine first responders. - Researchers at the National Institute for Occupational Safety and Health's Office of Mine Safety and Health Research (OMSHR) developed software to provide opportunities for mine rescue team members to learn to inspect, assemble and test their closed-circuit breathing apparatus and to practice those skills. In total, 31 mine rescue team members utilized OMSHR's BG 4 Benching Trainer software and provided feedback to the development team. After training, participants completed a brief post-training questionnaire, which included demographics, perceived training climate and general training evaluation items. - The results overall indicate a generally positive reaction to and high perceived utility of the BG 4 benching software. In addition, the perceived training climate appears to have an effect on the perceived utility of the mental practice virtual reality game, with benchmen from mines with more positive training climates reporting greater perceived efficacy in the training's ability to prepare trainees for real emergencies. - This paper helps to broaden current applications of mental practice and is one of the few empirical investigations into a non-rehabilitation virtual reality extension of mental practice. This paper also contributes to the growing literature advocating for greater usage of accurate and well-informed mental practice techniques, tools and methodologies, especially for occupational populations with limitations on exposure to hands-on training.

Response to CO2 in novice closed-circuit apparatus divers and after 1 year of active oxygen diving at shallow depths

Elevated arterial Pco(2) (hypercapnia) has a major effect on central nervous system oxygen toxicity in diving with a closed-circuit breathing apparatus. The purpose of the present study was to follow up the ability of divers to detect CO(2) and to determine the CO(2) retention trait after 1 year of active oxygen diving with closed-circuit apparatus. Ventilatory and perceptual responses to variations in inspired CO(2) (range: 0-5.6 kPa, 0-42 Torr) during moderate exercise were assessed in Israeli Navy combat divers on active duty. Tests were carried out on 40 divers during the novice oxygen diving phase (ND) and the experienced oxygen diving phase. No significant changes were found between the two phases for the minimal mean inspired Pco(2) that could be detected. The mean (with SD in parentheses) end-tidal Pco(2) during exposure to an inspired Pco(2) of 5.6 kPa (42 Torr) was significantly higher in the novice diving phase than in the experienced diving phase [8.1 kPa (SD 0.7), 62 Torr (SD 5) and 7.8 kPa (SD 0.6), 59 Torr (SD 4), respectively; P < or = 0.001]. One year of shallow oxygen diving activity with a closed-circuit apparatus does not affect the ability to detect CO(2) nor does it lead to increased CO(2) retention; rather, it may even bring about a decrease in this trait. This finding suggests that acquiring experience in oxygen diving with a closed-circuit apparatus at shallow depths does not place the diver at a greater risk of central nervous system oxygen toxicity due to CO(2) retention.

Ventilatory Response to Carbon Dioxide during Moderate Exercise

Ventilatory Response to Carbon Dioxide during Moderate Exercise: Masayoshi Takahashi, et al. National Institute for Resources and Environment—Elevated carbon dioxide (CO2) concentration is one of the most important physiological stressors with closed‐circuit breathing‐apparatus (CCBA). We determined the ventilatory response to CO2 during moderate exercise by measuring the relationship between VE and PETCO2. Based on our findings, it is recommended that the permissible inhaled CO2 limit for CCBA in the Japan Industrial Standard (JIS) be lowered from 3% to 2%, and that the members of a rescue or fire fighter team who use CCBA be selected on the basis of their ventilatory sensitivity to CO2.

Heated diver decompression shelter: The “womb concept”

A hybrid thermal protection method using waste heat from a surface-mounted outboard motor is shown to create a warm “micro-climate” environment for divers. The effects of surface heater capacities, water flow rates, shelter volume and shelter insulation on micro-climate temperatures are characterized. During long, cold-water decompression stops this method offers a reliable, low-cost alternative to surface-supplied hot water suits or diver-carried heating systems. An added bonus for divers using closed-circuit breathing apparatus is prolonged durations of their carbon dioxide scrubbers when surrounded by the warm water “micro-climate”. Closed-circuit and open-circuit options of this diver decompression shelter concept are evaluated.

Ventilatory responses to elastic loading at constant PACO2 hypercapnic hyperpnea.

Elastic loads of 9 cmH2O/1 were suddenly applied to the external airways of four normal human subjects during hypercapnic hyperpnea of 20-32 1/min using a closed-circuit breathing apparatus that permitted alveolar carbon dioxide pressure (PACO2) to be held nearly constant in spite of loading induced changes in ventilation. Transient depression of minute ventilation (V) and mean inspiratory flow (VT/TI) was observed immediately on loading; both these variables increased progressively to steady levels less than control without significant changes in alveolar chemistry. Two subjects increased VT (volume compensators) whereas the other two chose to increase f (frequency compensators). The net result in V and VT/TI compensation was not different between these groups. Load removal always resulted in an overshooting response of V lasting for several breaths and due entirely to an overshoot in VT because f transiently fell to or below control at once. Elastic loading always resulted in a steeper plot of V-VT in the steady state; in three of the subjects, the transition to this steeper line was immediate. The steady-state responses were qualitatively though not quantitatively consistent with pattern adaptation appropriate to minimize the work-rate of breathing.

Suggested methods of testing and standards of resistance for respiratory protective devices.

There is need to establish a method of bench testing and standards of allowable resistance for respiratory protective devices. It is suggested that a technique for recording pressure-volume diagrams using a sine-wave pump is satisfactory. Standards of resistance are proposed which are expressed as total rate of respiratory work done on the apparatus, and the percentage of this which is done in expiration. It is suggested that apparatus should be tested at minute volumes up to 100 l/min. Other information derivable by this technique is discussed. Fundamental principles of aerodynamics are also considered in relation to closed-circuit breathing apparatus. It is shown that under conditions of practical use of such systems, flow is only laminar in rare instances. Useful information can be gained about the frictional resistance of a respiratory circuit from simple bench tests at various constant rates of flow of air, and from the results of such experiments theoretical calculations can be made of the rate of work done. They are shown to correspond well with the measured rates of work done by human volunteers when breathing against the same resistance at all levels of exertion on a treadmill. Submitted on March 7,1960