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PubMed1977

Inhibition of gas vesicle production in Microcyclus aquaticus by L-lysine.

The timing and degree of gas vesicle production in Microcyclus aquaticus was affected by nutritional conditions. If 50 microng L-lysine/ml was added to a glucose-mineral salts medium (DM), the organism did not form gas vesicles. This effect was specific for L-lysine, as neither D-lysine nor meso-diaminopimelic acid prevented gas vesicle production. Cells grown in the presence of L-lysine did not contain any immunologically detectable gas vesicle protein, which indicates that L-lysine affects expression of the structural gene for the gas vesicle protein rather than assembly of the protein into gas vesicles. The addition of L-lysine to cultures in DM did not immediately decrease the rate of gas vesicle assembly, nor did the removal of cells from DM plus L-lysine to DM result in immediate gas vesicle production. Gas vesicle production was also affected by the addition of L-threonine or L-cysteine to culture media or by an increase in the medium's ionic strength. These results are discussed in relation to the aspartic acid pathway of amino acid biosynthesis and effects upon the intracellular L-lysine concentration.

Amino Acids↗
PubMedDate not supplied

Portomesenteric vein gas: pathologic mechanisms, CT findings, and prognosis.

Portomesenteric vein gas is a rare condition whose pathogenesis is not fully understood. Portomesenteric vein gas is most commonly caused by mesenteric ischemia but may have a variety of other causes. The primary factors that favor the development of this pathologic entity are intestinal wall alterations, bowel distention, and sepsis. Portomesenteric vein gas is idiopathic in approximately 15% of cases. Advanced imaging techniques such as computed tomography (CT) have increased the sensitivity for detection of portomesenteric vein gas. At CT, portal vein gas appears as tubular areas of decreased attenuation in the liver, predominantly in the left lobe. Gas in the great mesenteric veins can easily be demonstrated with contrast material-enhanced CT, whereas gas in the small mesenteric veins appears as tubular or branched areas of decreased attenuation in the mesenteric border of the bowel. Findings of portomesenteric vein gas at CT should be carefully evaluated in the context of clinical findings. In the majority of cases, the prognosis is favorable and surgery is not required. However, when CT demonstrates portomesenteric vein gas and clinical findings suggest the presence of mesenteric ischemia, surgery is mandatory.

Diagnosis, Differential↗
PubMed1979

Effects of common dead space on inert gas exchange in mathematical models of the lung.

Theoretical gas exchange is compared in lung models having two different types of dead space. In one, the dead space of a lung unit is "personal" and contains gas equivalent in composition to its own alveolar gas; in the other, the dead space is "common" and contains mixed gas from all gas-exchanging units. Formal algebraic analysis of tracer inert gas exchange in two-compartment models shows that values of compartmental ventilation and perfusion can be found that establish one and only one personal dead-space model equivalent for every common dead-space model. When the total dead space and distribution of blood flow and ventilation in the two models are the same, common dead space will always result in improved inert gas elimination. Under these conditions, the amount of improvement is usually greatest when the partition coefficient of the inert gas is between 0.1 and 1.0 and when there is greatest disparity in the ventilation-perfusion ratios (VA/Q). In the inert gas elimination technique that analyzes all dead space as personal, the presence of common dead space consistently causes the recovered VA/Q distributions to be narrower than the actual distributions, but the resultant error is small.

Humans↗
PubMed1981

Measurement of respiratory gas exchange during artificial respiration.

This paper reports a new system for the continuous measurements of respiratory gas exchange in ventilated subjects. It involves mixing some of the inspired gas with all of the expired gas and withdrawing the mixture at a constant rate through a dry gas meter that measures the flow. The inspired gas and expired gas mixtures are sampled and O2 and CO2 concentrations measured with a paramagnetic gas analyzer and a capnograph, respectively, to an accuracy of 0.01%. Evidence is presented to confirm the necessary stability and sensitivity of these instruments. It is possible to use the system with high inspired O2 concentrations, with ventilators where there is incomplete separation of inspired and expired gas, and in the presence of intermittent mandatory ventilation, positive end-expiratory pressure, and continuous airway pressure. The system was compared with the N2-dilution method and with the collection of expired gas in a Douglas bag in dog experiments and with patients in the intensive therapy unit. Excellent correlation between these methods was found in all circumstances.

Air Pressure↗
PubMed1982

Influence of Bohr-Haldane effect on steady-state gas exchange.

The influence of the Bohr-Haldane effect (BH) on steady-state gas exchange has previously been described by its effect of gas transfer from the blood when arterial and venous blood gas tensions were held constant. This report quantifies by computer analysis the effects of BH when either or both arterial and venous blood gas tensions are subject to change. When mixed venous blood gas composition is held constant, elimination of BH from a single lung unit typically reduces CO2 output by 6.5% and O2 uptake by 0.5%. Similar effects occur in a two-compartment lung model whether alveolar ventilation-perfusion (VA/Q) mismatch occurs in a parallel or series ventilatory arrangement. When arterial blood gas composition is held constant, elimination of BH increases systemic venous CO2 partial pressure, but O2 partial pressure is hardly affected in the absence of metabolic acidosis. When both mixed venous and arterial blood gas tensions vary and gas exchange is stressed by VA/Q inequality, altitude, anemia, or exercise, elimination of BH predominantly affects mixed venous rather than arterial blood gas tensions. it is concluded that BH may act primarily to reduce tissue acidosis.

Acidosis↗
PubMed2001

Iatrogenic pneumothorax: marker gas technique for predicting outcome of manual aspiration.

BACKGROUND: Although manual aspiration is used for treating pneumothorax, the post-aspiration radiograph may not be a reliable indicator of whether the pleural leak remains. We have previously shown that marker gas can identify an air leak in patients with spontaneous pneumothoraces. OBJECTIVE: This study examines whether a marker gas technique can be safely used to manage patients with iatrogenic pneumothoraces. METHODS: 10 patients with iatrogenic pneumothorax were identified among a cohort referred for manual aspiration of pneumothorax, using a marker gas technique, in which inspired metered-dose inhaler propellant gas is detectable in pneumothorax aspirate using a portable flame ioniser. The presence of marker gas was taken to imply a persistent air leak. RESULTS: Marker gas was detected in the aspirate from 3 out of 10 pneumothoraces. 2 required intercostal tube drainage because of lung collapse following initial aspiration and 1 was treated conservatively. Marker gas was not detected in 7 cases (2 post-pacemaker insertion, 5 pleural aspiration +/- biopsy), and in all these cases, manual aspiration resulted in sustained re-expansion of the lung. There was a trend towards a significant relationship between the presence or absence of marker gas and the need for a further intervention (p = 0.055). CONCLUSION: The presence or absence of a pleural leak during manual aspiration of iatrogenic pneumothorax can be demonstrated by this technique. The absence of marker gas in the aspirate implies that manual aspiration will be successful, whereas its presence, in most cases, predicts either failure of manual aspiration to expand the lung or early re-collapse of the lung.

Aged↗
PubMed2005

Role of Gas-6 in adipogenesis and nutritionally induced adipose tissue development in mice.

OBJECTIVE: A potential role of growth arrest-specific gene 6 (Gas-6) in energy storage in adipose tissue was investigated in murine models of obesity. Gas-6 is a ligand for the Axl, C-Mer, and Sky family of tyrosine kinase receptors. METHODS AND RESULTS: Whereas Gas-6, C-Mer, and Sky were expressed in mature murine adipocytes, the expression of Axl was restricted to the stromal-vascular fraction, which includes pre-adipocytes. During the in vitro conversion of adipogenic 3T3-F442A cells into mature adipocytes, the expression of Gas-6 increased in undifferentiated confluent pre-adipocytes during a transient phase of growth arrest. On treatment of these cells with an adipogenic medium, Gas-6 expression decreased sharply, coinciding with expression of early adipocytes markers. This modulation was not observed in the nonadipogenic 3T3-C2 cells. The Gas-6 mRNA level was transiently downregulated during nutritionally induced expansion of adipose tissues in vivo. When kept on a standard diet, no significant difference in either total body weight or weight of gonadal or subcutaneous fat pads was observed between Gas-6 deficient and wild-type mice. On exposure to a high-fat diet, however, Gas-6-deficient mice had significantly less fat mass than their wild-type counterparts. CONCLUSIONS: Gas-6 enhances the accumulation of adipose tissue in diet-induced obese mice.

3T3 Cells↗
PubMed1998

Disconnect alarm failure in detection of common gas outlet disconnection.

This laboratory study was prompted by two paediatric cases where low pressure alarms and capnography failed to detect common gas outlet disconnection when using a T-piece pump ventilator. A carbon dioxide producing model lung was ventilated using the Clare ventilator (a T-piece pump type ventilator) via an Ayres T-piece. The T-piece used has 3 mm diameter fresh gas tubing. Common gas outlet disconnects were carried out using varying fresh gas flows and ventilatory patterns. At fresh gas flows of less than 8 l/min, the low pressure alarm of the Clare ventilator failed to sound following common gas outlet disconnection. Oxygraphy showed a rapid rise in inspired oxygen. End-tidal CO2 rose, whilst inspired CO2 remained at zero. This experiment demonstrates that the Clare ventilator's low pressure alarm detects common gas outlet disconnection poorly when used with an Ayres T-piece with narrow fresh gas tubing. Graphical representation of airway oxygen content has merit as an alerting monitor for common gas outlet disconnection.

Anesthesiology↗
PubMed2006

Characterization of a mid-infrared hollow waveguide gas cell for the analysis of carbon monoxide and nitric oxide.

Infrared spectroscopy is commonly applied to the analysis of small gas-phase molecules. One of the limitations of using Fourier transform infrared (FT-IR) spectroscopy for these applications is the time response of long path length gas cells. Hollow waveguides (HW) that transmit in the mid-infrared spectral range have higher optical efficiencies compared to long path length cells due to smaller cell volumes. This study characterizes a silver coated, 2 mm inner diameter HW for the analysis of carbon monoxide (CO) and nitric oxide (NO) and compares the performance to a 3 m gas cell and traditional gas analyzers. The HW was found to have a CO response time less than the NDIR analyzer and approximately one-tenth of the response time on the FT-IR system equipped with a 3 m gas cell. The utility of the increased response time was demonstrated by measuring CO concentrations in sidestream cigarette smoke at the same temporal resolution as an NDIR analyzer. A 10 to 60% increase in sensitivity using various frequencies for both CO and NO was observed using the HW compared to the 3 m multipass gas cell. However, cost savings for gas-sensing applications can be achieved on a per analyte basis by using FT-IR spectroscopy, especially in combination with a HW gas-sensing module, which is significantly less expensive than a multipass gas cell.

Air Pollutants↗
PubMed2005

Effects of gas leak on triggering function, humidification, and inspiratory oxygen fraction during noninvasive positive airway pressure ventilation.

OBJECTIVES: During noninvasive positive pressure ventilation (NPPV), the gas leak that commonly occurs around the mask can render NPPV ineffective. We evaluated the effects of gas leak on inspiratory trigger function during NPPV with bilevel pressure and ICU ventilators. In addition, we evaluated the effects of gas leak on fraction of inspired oxygen (Fio(2)) and humidification. METHODS: Air leak was created at the airway opening of a model lung by establishing several different-size holes in the circuit. During simulated spontaneous breathing, we evaluated inspiratory trigger performance of two bilevel pressure ventilators (BiPAP Vision and BiPAP S/T-D; Respironics; Murrysville, PA) and two ICU ventilators (Puritan-Bennett 7200ae and Puritan-Bennett 840; Tyco Healthcare; Mansfield, MA). Inspiratory delay time and inspiratory trigger pressure were analyzed. Fio(2) at the airway opening and inside the model lung were evaluated during BiPAP S/T-D ventilation at supplemental oxygen flows of 3, 6, 9, 12 and 15 L/min. Measured oxygen concentration was compared to mathematically predicted levels. Finally, using two heated humidifiers, we evaluated the effect of gas leak on humidification. RESULTS: The bilevel pressure ventilators triggered properly at all levels of gas leak, and inspiratory triggering was more effective than with the ICU ventilators. Delivered Fio(2) with the BiPAP S/T-D ventilator was affected by gas leak and could be predicted mathematically unless the gas leak was large. With large gas leaks, although relative humidity was maintained, absolute humidity decreased. CONCLUSION: Gas leak affected triggering of ICU ventilators, Fio(2) of the BiPAP S/T-D ventilator, and humidity with both types of humidifiers.

Equipment Design↗
PubMed1999

Gas in the sternoclavicular joints of patients with blunt chest trauma: significance and frequency of CT findings.

OBJECTIVE: In trauma patients, gas (vacuum phenomenon) in the sternoclavicular joints could represent sequelae of significant distraction forces and thus serve as a potential marker for severe intrathoracic injury. We evaluated the significance and frequency of the finding of gas in the sternoclavicular joints on chest CT of patients with blunt trauma. SUBJECTS AND METHODS: We prospectively studied all chest CT examinations performed at our institution over a 14-week period for the finding of gas in the sternoclavicular joints. Chest CT examinations (n = 267) were performed in 234 patients. We excluded data from follow-up CT examinations (n = 33), limiting our evaluation to the initial CT examination for each patient. Of the study population, 103 patients (83 men and 20 women) who ranged in age from 14 to 79 years (mean, 40 years) had sustained blunt chest trauma. For all trauma patients, we recorded the mechanism of injury and the associated thoracic injuries. RESULTS: CT revealed gas in the sternoclavicular joints in 47 patients (21%). Gas was unilateral in 27 patients and bilateral in 20 patients. Sternoclavicular joint gas was seen in 39 (38%) of the 103 trauma patients but was found in only eight (6%) of the 131 nontrauma patients (p < .0001). In the 39 trauma patients with sternoclavicular joint gas, associated thoracic injuries were seen in 17 patients (44%); either a sternal fracture or a retrosternal hematoma was seen in three patients. Radiographically evident thoracic injury was revealed in 20 (31%) of the 64 trauma patients who had no gas in the sternoclavicular joint; however, 10 of these 20 patients had either a sternal fracture or a mediastinal hematoma. CONCLUSION: Although gas in the sternoclavicular joints is more frequently seen in patients with blunt chest trauma than in patients undergoing chest CT for other indications, this finding does not indicate a greater risk of significant mediastinal or thoracic injury.

Adolescent↗
PubMed2005

Wheat pasture bloat dynamics, in vitro ruminal gas production, and potential bloat mitigation with condensed tannins.

The aim of this study was to determine the effect of winter wheat (Triticum aestivum L.) forage growth stage, forage allowance, time of day, and commercial condensed tannins (CT) on steer bloat dynamics and in vitro ruminal gas production. Twenty-six crossbreed steers (Angus x Hereford x Salers; average initial BW = 194 +/- 26 kg) were used. Wheat forage allowances were either 18 kg (high forage allowance) and 6 kg (low forage allowance) of DM/(100 kg BW.d). In each bloat observation period, fresh wheat forage samples were hand-clipped to ground level in all study pastures for nutrient and in vitro ruminal gas production analyses. In vitro ruminal gas accumulation was measured at 0, 1, 2, 3, 4, 5, 6, and 12 h. Commercial CT was added at 0, 10, 15, and 20 mg of CT/g of DM. Bloat was scored once per week on two consecutive days at 0800 and 1500 during the vegetative stage and once every 2 wk during the reproductive stage of wheat development. Mean bloat score was calculated for each steer by time of day, stage of plant growth, and forage allowance. Bloat was detected in 65.8% of the observation periods. Average bloat scores were four and 2.5 times greater (P < 0.05) in cattle grazing at a high forage allowance than at a low forage allowance in the vegetative and reproductive growth phases of wheat, respectively. Rate of gas production was greater (P < 0.001) in the vegetative stage than in the reproductive stage. Steer bloat score was positively correlated with forage CP (r = 0.22; P < 0.05) and IVDMD (r = 0.32; P < 0.05). Rate of ruminal gas production was positively correlated (P < 0.01) to forage CP (r = 0.48), NPN (r = 0.40), soluble protein (r = 0.32), and IVDMD (r = 0.47). Conversely, negative correlations were found for forage DM (r = -0.20; P < 0.05), insoluble protein (r = -0.40), NDF (r = -0.69), and forage height (r = -0.49; P < 0.01) on the rate of ruminal gas production. Addition of CT at levels greater than 10 mg of CT/g of DM decreased (P < 0.05) the rate of in vitro ruminal gas and methane gas production after 5 h of incubation. Wheat pasture bloat is a complex disorder that varies across an array of forage and environmental conditions. Condensed tannins have the potential to decrease bloat by altering ruminal gas production and soluble protein digestibility from wheat forage.

Animal Nutritional Physiological Phenomena↗
PubMed1997

New approaches to toxicity: a seven-gas predictive model and toxicant suppressants.

Two new research approaches in combustion toxicology are: 1. the prediction of smoke toxicity from mathematical equations, which are empirically derived from, experiments on the toxicological interactions of complex fire gas mixtures and 2. the use of toxicant suppressants in materials or products to prevent the formation of toxic combustion products. The predictive approach consists of burning materials using a bench-scale method that simulates realistic fire conditions, measuring the concentrations of the primary fire gases--CO, CO2, low O2, HCN, HCl, HBr, and NO2--and predicting the toxicity of the smoke using either the 6- or 7-gas N-Gas Model. These models are based on the results of toxicological studies of these primary gases as individual gases and as complex mixtures. The predicted toxic potency is checked with a small number of animal (Fischer 344 male rats) tests to assure that an unanticipated toxic gas is not generated or an unexpected synergistic or antagonistic effect has not occurred. The results indicate if the smoke from a material or product is extremely toxic (based on mass consumed at the predicted toxic level) or unusually toxic (based on the gases deemed responsible). The predictions based on bench-scale laboratory tests have been validated with full-scale room burns of a limited number of materials of widely differing characteristics chosen to challenge the system. The advantages of this new approach are 1. the number of test animals is minimized by predicting the toxic potency from the chemical analysis of the smoke, 2. smoke may be produced under conditions that simulate the fire scenario of concern, 3. fewer tests are needed, thereby reducing the overall cost of the testing and 4, information is obtained on both the toxic potency of the smoke and the responsible gases. The N-Gas Models have been developed into the N-Gas Method (described in this paper) and these results have been used in computations of fire hazard. The 6-Gas Model is now part of the international standard ISO 13344 approved by 16 member countries of the International Standards Organization (ISO) and is also included in the U.S. national standard ASTM E1678 approved by the American Society for Testing and Materials (ASTM). In addition, the 6-Gas Model is used in the American National Standard--NFPA 269--approved by the National Fire Protection Association (Quincy, MA). The second new research approach, toxicant suppressants, examines the potential of chemical compounds, which when added to a material, to inhibit or reduce the concentration of a specific toxic gas normally generated during the material's thermal decomposition. The effectiveness of this approach was demonstrated at the National Institute of Standards and Technology (NIST) when HCN generation was reduced by 90% and the resultant toxicity of the combustion products was lowered by 50% when a flexible polyurethane foam (FPU) was treated with 0.1% (by weight) cuprous oxide (Cu2O). Copper and cupric oxide (CuO) also reduced the HCN generation but were not as efficient as Cu2O. Although melamine-treated FPU foams are being promoted as more fire safe than standard foams, a melamine-treated foam generated 10 times more HCN than a foam without melamine. The addition of Cu2O to this melamine foam also reduced the HCN generation by 90%.

Animal Testing Alternatives↗
PubMed2003

Experimental use of a gas sensor-based instrument for differentiation of Escherichia coli O157:H7 from non-O157:H7 Escherichia coli field isolates.

The rapid and economical detection of human pathogens in animal and food production systems would enhance food safety efforts. An instrument based on gas sensors coupled with an artificial neural network (ANN) was developed for the detection of and differentiation between laboratory isolates of Escherichia coli O157:H7 and non-O157:H7 E. coli. The purpose of this study was to use field isolates of E. coli to further evaluate the sensor system. This gas sensor-based, computer-controlled detection system was used to monitor gas emissions from 12 isolates of E. coli O157:H7 and 8 non-O157:H7 E. coli isolates. A standard concentration of each isolate was grown in 10 ml of nutrient broth at 37 degrees C for 16 h, and gas sampling was carried out every 5 min. Readings were continuously plotted to generate gas signatures. A back-propagation ANN algorithm was used to interpret the gas patterns. By analysis of the response of the ANN, the sensitivity and specificity of the instrument were calculated. Detectable differences between the gas signatures of the E. coli O157:H7 isolates and the non-O157:H7 isolates were observed. The instruments degree of sensitivity was high for E. coli O157:H7 isolates, but a lower degree of accuracy was observed for non-O157:H7 isolates because of increased strain variation. The sensitivity of the detection system was improved by the normalization of the data generated from the gas sensors. Because of its ability to detect differences in gas patterns, this instrument has a broad range of potential food safety applications.

Animals↗
PubMed1992

Pathophysiology and treatment of decompression sickness and gas embolism.

Decompression sickness and cerebral gas embolism can present as dramatic and profound sudden onset injuries in patients engaged in tunnel work and compressed gas diving, including scuba. The history and management of these illnesses span centuries. The pathophysiology relates to occurrence of gas bubbles in extrapulmonic sites. Decompression sickness is due to supersaturation of the tissue with dissolved gas and subsequent evolution of gas bubbles. Gas embolism results from the direct transit of molecular gas from a pulmonary or intravascular origin into the arterial circulation causing occlusion of a distal locus. Treatment relates to increasing hydrostatic pressure, thus maximizing the gradient for gas reabsorption and dissolution and subsequently gas excretion via the lungs.

Decompression Sickness↗
PubMedDate not supplied

Heated, humidified CO2 gas is unsatisfactory for awake laparoscopy.

BACKGROUND: The necessity for general anesthesia represents an impediment to using a laparoscopic approach for some procedures that are otherwise performed with the patient under local anesthesia using a conventional open technique. Heating and humidifying the insufflation gas reportedly reduces perioperative pain associated with a CO2 pneumoperitoneum, thus enabling awake laparoscopy. METHODS: Two cases are reported herein of laparoscopy performed with the patient under local anesthesia using heated, humidified CO2 gas for the pneumoperitoneum. RESULTS: Both patients experienced pain with insufflation of heated, humidified CO2 gas of sufficient magnitude that the procedure could not be performed. The CO2 gas was washed out and replaced with helium gas insufflation with complete resolution of pain. The laparoscopic procedures were accomplished without further discomfort with local anesthesia and using a helium gas pneumoperitoneum. CONCLUSIONS: Heated, humidified CO2 gas insufflation does not reduce pain sufficiently to permit satisfactory performance of laparoscopy with local anesthesia, especially when full volume insufflation is required. Cold, dry helium gas produces no pain. The theory that cold, dry insufflation gas is a source of peritoneal pain during laparoscopy needs to be reassessed.

Adult↗
PubMed1989

Effect of peripheral temperature on the formation of venous gas bubbles.

Temperature of the tissue affects the many components involved in the formation of tissue gas phase formation: diffusion, perfusion, and inert gas solubility. Since the effects of perfusion and inert gas solubility may be counteracting in terms of enhancing growth of gas bubbles, the optimal thermal status of divers throughout a dive remains unresolved. To elucidate the role of peripheral body temperature on gas phase formation, four subjects were exposed to a 10 degree and 40 degree C environment for 3 h on two separate occasions, after a no-stop decompression from a 12-h dive to 9.14 m (30 fsw) on air. The 3-hour exposures to either a cold or warm air environment resulted in a significant difference in mean skin temperature (P less than or equal to 0.01) with no alteration in rectal temperature. Total peripheral resistance during the 10 degree C exposure was 13.8 +/- 1.9 mmHg.liter-1.min-1 and significantly higher than that observed during the 40 degree C exposure (10.4 +/- 3.5 mmHg.liter-1.min-1). Gas bubbles in the venous return were monitored with a Doppler ultrasonic transducer placed in the precordial region, both at rest and after a deep knee bend. Venous bubbles were only detected in 1 subject following the warm air exposure, whereas 3 of the 4 subjects developed Doppler-detectable bubbles during the cold air exposure. Although both the cold and warm air exposures (3 h postdecompression) were uneventful, a hot shower taken by the subjects on completion of the cold air exposure (6 h postdecompression) precipitated mild type I symptoms of decompression sickness. These symptoms were not present after a hot shower following the warm air exposure. The present results indicate that despite the assumed greater inert gas solubility of tissues expected during cold air exposure, the decrease in the perfusion may have played a more significant role in the observed levels of detectable venous gas bubbles. Development of type I symptoms following a 12-h saturation, a 3-h cold exposure, and a subsequent hot shower suggests that a rapid rise in peripheral temperature may cause a significant rise in tissue gas tension. This increase in tension does not seem to be sufficiently reduced by increased perfusion to the tissues to prevent bubble formation.

Adult↗
PubMed1994

[Analysis of middle ear cavity gas composition by mass spectrometry].

Gas compositions in the middle ear cavities of patients with a perforated tympanic membrane, and in normal subjects, were analyzed by mass spectrometry. The results showed that the gas in normal subjects consisted of nitrogen (83.7%), oxygen (9.2%) and carbon dioxide (6.2%). (The volume concentration of the various gases was expressed as a percentage of 713 mm Hg.) Thus, the concentrations of the various gases in the middle ear cavity differed greatly from those in the atmosphere. The low concentration of oxygen is suitable for microaerophilic bacteria and acts as a physiological barrier against bacterial infection. It was also found that the gas in patients with exudative otitis media consisted of nitrogen (77.9%), oxygen (15.6%) and carbon dioxide (5.5%), and in patients with chronic perforated otitis media, of nitrogen (77.8%), oxygen (16.9%) and carbon dioxide (4.4%). The concentration of oxygen in the middle ear cavity with perforated tympanic membrane is higher than that in the normal state because of diffusion of atmospheric gas into the middle ear cavity. In other words, perforation of the tympanic membrane exposes the middle ear cavity to a nonphysiological gaseous condition. The diffusion of atmospheric gas was simulated using small cylinders. Simulated results revealed that the atmospheric gas diffused rapidly. The change in the gas concentration during diffusion was approximated by an exponential function and a constant, and reproduced by a mathematical model. The change in the gas concentration in the middle ear cavity was usually approximated by two exponential functions and a constant. The constant represents the estimated final value of the gas concentration from which the effect of the diffusion is excluded. The final values were estimated for normal subjects and patients with perforated tympanic membrane. The final values in the normal subjects were almost equal to the measured values. The final value of carbon dioxide in the patients was greater than the measured value and nearly equal to the final value in the normal subjects. The final oxygen value in the patients was smaller than the measured value, but still greater than the final value in the normal subjects. The high oxygen concentration in the patients suggests enhanced oxygen metabolism.

Adult↗