Rebreathing Research Articles

Effect of location and type of exhalation valve on carbon dioxide rebreathing during noninvasive positive pressure ventilation: a experimental study

To investigate the influence of exhalation valve location as well as its type on carbon dioxide (CO2) rebreathing during noninvasive positive pressure ventilation (NPPV). With a standardized NPPV experimental model system, the exhalation valve was respectively installed between the ventilator tube and mask (position II), or on the mask (position II). This study included four groups according to the position and type of exhalation valve, namely: single-arch exhalation valve was installed on the position I (A group), and position II (C group, the distal end of single-arch exhalation valve was blocked); plateau exhalation valve was installed on the position I (B group) and position II (D group, the distal end of plateau exhalation valve was blocked). Under standard experimental condition, the pressure of end-tidal carbon dioxide (P(ET)CO2) was monitored in the trachea or the mask through adjusting the expiratory positive airway pressure (EPAP, EPAP was set at 5 cmH2O and 10 cmH2O, 1 cmH2O = 0.098 kPa) and tidal volume (V(T), V(T) was set at 300, 400, 500 mL). Leakage of exhalation (1) Under standard experimental condition, when EPAP was 5 cmH2O, P(ET)CO2 (mmHg, 1 mmHg = 0.133 kPa) in the trachea was 69.6 ± 3.4, 61.4 ± 2.7, 54.8 ± 1.5, 49.8 ± 1.3 in A, B, C, D groups respectively; and it was 24.8 ± 1.9, 21.8 ± 1.6, 2.8 ± 0.8, 1.8 ± 0.8 in the mask, respectively. When EPAP was 10 cmH2O, the P(ET)CO2 in the trachea was 64.2 ± 3.6, 57.2 ± 3.7, 48.8 ± 2.6, 41.8 ± 2.6 in A, B, C, and D groups respectively; and it was 23.0 ± 1.6, 20.2 ± 1.6, 2.2 ± 0.8, 1.2 ± 0.8 in the mask, respectively. For the same exhalation valve type, exhalation valve being installed on position II could induce significantly lower P(ET)CO2 in the trachea and mask than that being installed on position I (all P < 0.05). For the same expiratory valve position, plateau exhalation valve produced significantly lower P(ET)CO2 than single-arch valve (all P < 0.05). (2) As the V(T) increased, the P(ET)CO2 in the trachea of each group was reduced obviously. When V(T) was 500 mL, P(ET)CO2 (mmHg) was significantly lower than V(T), which were 300 mL and 400 mL (A group: 51.4 ± 2.7 vs. 72.8 ± 2.9, 69.6 ± 3.4; B group: 44.8 ± 2.4 vs. 65.4 ± 2.1, 61.4 ± 2.7; C group: 36.8 ± 1.9 vs. 59.0 ± 1.6, 54.8 ± 1.5; D group: 28.8 ± 1.9 vs. 52.6 ± 2.0, 49.8 ± 1.3; all P < 0.05). (3) When exhalation valve type was placed in position I, the air leakage of single-arch exhalation valve was increased to (15.8 ± 1.9), (20.2 ± 1.9), (23.8 ± 2.8), (28.0 ± 1.6) L/min, and the plateau exhalation valve was essentially unchanged to (24.2 ± 1.6), (23.8 ± 1.6), (25.2 ± 1.6), (25.2 ± 1.6) L/min as the IPAP was increased from 5, 10, 15, to 20 cmH2O. Exhalation valve fixing on mask is more appropriate for CO2 discharge than that fixed on tube-mask valve. Plateau exhalation valve as well as moderately increasing V(T) is beneficial for CO2 discharge and CO2 rebreathing prevention.

Ventilatory and waking responses to CO2 in sleeping dogs.

We examined ventilatory and waking responses to hyperoxic hypercapnia in 3 dogs during natural sleep. Progressive hypercapnia was induced by a rebreathing technique, and sleep was determined by electroencephalographic and behavioral criteria. In non-rapid eye movement sleep (high-voltage, slow-frequency electroencephalography) rebreathing continued for 0.99 +/- 0.05 min (mean +/- SE) before arousal occurred, and the alveolar PCO2, at arousal was 54.2 +/- 3.4 mm Hg. In contrast, during rapid eye movement sleep, rebreathing lasted for 1.71 +/- 0.27 min (P less than 0.05) before arousal occurred and the alveolar PCO2 at arousal was 60.3 +/- 4.2 mm Hg (P less than 0.05). Linear regression analysis of breath-by-breath instantaneous minute volume of ventilation, tidal volume, and respiratory frequency against alveolar PCO2 revealed regression coefficients in rapid eye movements sleep that were 14 to 33 per cent of those found in non-rapid eye movement sleep, and correlation coefficients of 0.26 to 0.46, compared to 0.71 to 0.91 in non-rapid eye movement sleep. Thus, the link between CO2 and ventilation appeared to be strong in non-rapid eye movement sleep but considerably disrupted during rapid eye movement sleep. We conclude that centers involved in both waking and ventilatory responses to hypercapnia behave as if they are less aware of or responsive to CO2 in rapid eye movement sleep than in non-rapid eye movement sleep.

Measurement of the total lung capacity by helium dilution in a constant volume system.

A method for measuring the total lung capacity by helium dilution in a constant volume, closed circuit, rebreathing system is described. The description includes details of apparatus, methods of procedure and calculation, variations encountered, and sources of error and their correction. A simple means of determining the time lag for achieving a stable reading of helium concentration in the system is also described so that the helium mixing time can be standardized among laboratories as a measure of intrapulmonary gas distribution. Evidence is provided that changes as large as 1,200 ml in the volume of the system during the rebreathing period result in insignificant changes in the measurement of total lung capacity by this method.

Diffference between mouth and esophageal occlusion pressure during CO2 rebreathing in chronic obstructive pulmonary disease.

During CO2 rebreathing, we measured the pressures generated at the mouth and in the esophagus during the first 0.1 sec of inspiratory effort against a closed airway in 6 normal subjects and 6 patients with chronic obstructive lung disease. Normal subjects showed similar reponses to CO2 in terms of both mouth pressure and esophageal pressure. Patients' responses at the mouth to CO2 were decreased compared to those of normal subjects, but the responses in the esophagus were not significantly different. The patients demonstrated a greater response of occlusion pressure measured in the esophagus than at the mouth. In patients with altered mechanical properties of the lung, the change in mouth occlusion pressure might be influenced by problems of equalization of pressure within the airways due to unequal time constants, by problems of regional differences in pressure gradients over the pleural surface, or both. Esophageal pressure during airway occlusion 100 msec after the onset of inspiration may be better measure of respiratory drive than mouth pressure in patients with intrinsic increase of airway resistance.

Time course of end-tidal desflurane concentration during delivery and elimination according to the type and location of filters in a semi-closed circuit system.

BackgroundThe aim of this study was to determine whether the end-tidal concentration of desflurane would be affected by a breathing circuit system filter attached at two different positions in anesthetic breathing circuit systems.MethodsAn artificial lung was ventilated under five different conditions. The first group was without any filter or desflurane (n = 5, sham), the second was with desflurane but without any filter (n = 10, control), the third group had a bacterial filter on the expiratory limb (n = 10), and the fourth and fifth groups had a viral/bacterial filter added on the expiratory limb (n = 10) or at the Y-piece of the breathing circuit (n = 10), respectively. In all groups except the sham, administration of 10% desflurane was performed for 5 minutes and then stopped for 5 minutes.ResultsThe mean (SD) end-tidal concentration of desflurane for the groups described above peaked at 0 (0), 9.8 (0.1), 9.8 (0.1), 8.5 (0.1), and 6.7% (0.1) (P < 0.001), respectively. There was no difference in the desflurane concentrations and the expired tidal volume over time between the control and bacterial group, but there was a significant difference between the control and the fourth and fifth groups (P < 0.001).ConclusionsFilters can affect the expiratory desflurane concentration during anesthesia.

The impact of aging on cerebral vasomotor reactivity to carbon dioxide (1069.5)

The objective of this study was to determine the age‐related differences in cerebral vasomotor reactivity (CVMR) to carbon dioxide. Methods: 92 healthy adults aged 23‐77 underwent measurements of cerebral blood flow velocity (CBFV) using transcranial Doppler, mean arterial pressure, and end‐tidal CO2 (EtCO2) during baseline, hyperventilation (HVT), and modified rebreathing (RB). CVMR was determined by the maximal gain between changes in normalized CBFV (CBFV%) and EtCO2 using a 3rd order polynomial model and its derivative. Results: Lower CBFV and EtCO2 were related to increasing age at baseline. HVT decreased EtCO2 by 21±4 mmHg while RB increased by 19±3 mmHg. Increasing age was related to smaller hypocapnic but larger hypercapnic changes in CBFV% at the end of HVT and RB, respectively. The maximal gain between CBFV% and EtCO2 did not differ by age. Advanced age was associated with greater differences in EtCO2 between the baseline and the level at which the maximum gain in CBFV% occurred. Conclusions: These findings suggest that age‐related reductions in baseline CBFV and EtCO2 may lead to a decrease in hypocapnic but an increase in hypercapnic CBFV response. The larger differences in EtCO2 between baseline and the maximal gain of CBFV% with aging may lead to blunted response of CBF to given changes in arterial CO2 at levels close to baseline.Grant Funding Source: Supported by National Institute on Aging

Assessment of neural respiratory drive in humans

Assessment of neural respiratory drive is useful for diagnosis of dyspnea and respiratory failure with unknown causes. The purpose of the study was to compare the sensitivity of trandiaphragmatic pressure (Pdi) and diaphragm electromyogram (EMGdi) in assessment of neural respiratory drive. A combined catheter with 10 electrodes and 2 balloons was used to record EMGdi and Pdi during CO2 rebreathing. Three different inspiratory maneuvers-inspiration from functional residual capacity to total lung capacity (TLC), deep inspiration from functional residual capacity against closed airway (MIP), and short sharp inspiration through the nose (Sniff) were performed. Ten healthy subjects [male 4 and female 6; age (26 ± 4) years] were studied. Linear relationship between EMGdi and end-tidal CO2 (r = 0.83-0.98, all P < 0.01) was better than that between Pdi and end-tidal CO2 (r = 0.48-0.96, all P < 0.01) during CO2 rebreathing, Z = -2.731, P < 0.05. The slope of linear relation between EMGdi and end-tidal CO2 (16.3-32.5) was significantly higher than that between Pdi and end-tidal CO2 (0.4-11.1), Z = -3.780, P < 0.01. The maximal EMGdi derived from TLC maneuver (211 ± 48) µV was larger than those from the MIP maneuver (161 ± 48) µV and the Sniff maneuver (145 ± 37) µV, F = 5.931, P < 0.05, whereas the maximal Pdi derived from TLC maneuver (58 ± 27) cm H2O (1 cm H2O = 0.098 kPa) was significantly lower than those from the MIP maneuver (92 ± 32) cm H2O and the Sniff maneuver (95 ± 27) cm H2O, F = 5.155, P < 0.05. EMGdi is more sensitive than Pdi in the assessment of neural respiratory drive.

Cases of carbon dioxide rebreathing without significant color change in the appearance of the carbon dioxide absorbent canisters

To the Editor: Three cases of carbon dioxide rebreathing without a significant color change in the appearance of the canisters were experienced during general anesthesia with the same model anesthesia machines; Aestiva/5 (Datex Ohmeda, Wisconsin, USA) with a fresh gas flow of 1–2 l/min. Carbon dioxide rebreathing was recognized because the inspiratory carbon dioxide baseline of the capnogram trace gradually rose. The inhalational carbon dioxide concentration decreased immediately after increasing the fresh gas flow, and rose again with decreasing the fresh gas flow. This indicates that carbon dioxide rebreathing was due to carbon dioxide accumulation in the semi-closed circuit system of the anesthesia machines. A color change in the appearance of the carbon dioxide absorbent was recognized only in the upper part of the canister (Fig. 1a). The top surface of the canister showed a significant color change limited to the middle part of it (Fig. 1b). The section image of the canister showed a significant columnar color change of the carbon dioxide absorbent along the full length of the center part of it (Fig. 1c). The observation of the canister bottom of Aestiva/5 revealed that only the center part of it had the mesh part for the exhaled gas, and the color change of the carbon dioxide absorbent seemed to accord with the mesh part of the bottom (Fig. 1d). As an experiment, when a transparent plastic partition wall was settled in the canister before filling with carbon dioxide absorbent, the columnar color change was no longer visible. This indicated that the flow of the exhaled gas was influenced by the wall in the canister. Considering these results, it is supposed that the structural characteristic of the canister bottom of the anesthesia machine; Aestiva/5, caused channeling and the inhomogeneity of the current of inhaled gas in the canister led to the columnar color change of the carbon dioxide absorbent. The role of the carbon dioxide absorbent canister becomes more important as the fresh gas flow quantity decreases. A technique of using a fresh gas flow of 1 l/min was reported first in 1952 [1]. The technique with the fresh gas flow less than 1 l/min subsequently became known as ‘‘low-flow anesthesia’’. Afterwards, a technique using a fresh gas flow of 500 ml/min was reported as ‘‘minimal flow anesthesia’’ [2]. These cases of carbon dioxide rebreathing without significant color change in the appearance of the canisters provide very important information not only for anesthesiologists, but also for all persons using anesthesia machines. When carbon dioxide rebreathing is recognized, carbon dioxide accumulation in the circuit system of the anesthesia machines should be suspected and exhaustion of the carbon dioxide absorbent should be immediately T. Yamamoto (&) Department of Pediatric Anesthesiology and Critical Care Medicine, Children’s Hospital Asklepios Klinik Sankt Augustin, Arnold-Janssen-Str. 29, 53757 Sankt Augustin, Germany e-mail: yamatomo270@hotmail.com; t.yamamoto@asklepios.com

Spontaneous shutoff of desflurane vaporizer

To the Editor: We would like to report the intraoperative failure of a desflurane vaporizer. The incident occurred as a 57-yearold man underwent parathyroid surgery. After induction and intubation, anesthesia was maintained with 5 % inhaled desflurane, using a Tec 6 Plus vaporizer (GE Healthcare Japan Co., Tokyo, Japan), via a semiclosed circuit with a 3 l/min fresh gas flow. Approximately 7 min into the case, the ‘‘no output’’ vaporizer alarm sounded and the desflurane concentration in the anesthesia circuit began to fall. We immediately turned off the vaporizer. After several seconds, the vaporizer automatically reset but within several minutes, the ‘‘no output’’ error occurred again. The surgery was then completed using sevoflurane, without assessing the depth of anesthesia. The patient emerged from anesthesia uneventfully, with no recollection of the intraoperative events. We purchased the vaporizer 2 months prior to the incident; it was used almost every day for 2 months. Although clinical engineers and anesthesiologists maintain anesthetic machines and circuits, vaporizers are not inspected usually in our operating rooms. According to the manufacturer’s technical department, 10 incidences of initial failure have been confirmed in 431 products since the vaporizer’s 2011 release in Japan. The vaporizer was exchanged at no charge following this initial failure. Afterward, the manufacturer reported to us that the failure of an electronic pressure transducer caused this incident. They recommended the immediate use of alternative anesthetics if the ‘‘no output’’ error recurred. Reports of spontaneous shutoff during surgery of a correctly mounted desflurane vaporizer have not previously been published [1–3]. Unlike conventional mechanical vaporizers, the desflurane vaporizer has sophisticated electronic components. As a fail-safe, it completely halts agent output if an electronic failure occurs. Since the washout for desflurane is more rapid than that for other inhalation agents, patients emerge from anesthesia soon after shutoff of the vaporizer. The incidence of initial failure reported by the manufacturer seems relatively high. This case serves to emphasize the importance of fully understanding the features of equipment that is in frequent use [4].

Transcriptomic and cellular response to bacterial challenge (pathogenic Vibrio parahaemolyticus) in farmed juvenile Haliotis rufescens fed with or without probiotic diet

The abalone production in Chile has increased considerably in recent years with no sign of tapering off. Open and semi-closed circuits in the marine water zones in the north and south of Chile are the preferred areas of culture. Coastal ecosystems are subjected to a wide variety of contaminants that generate stress that affects populations via their impacts to individuals at both physiological and genetic levels. This work investigated the genomic and cellular response of post-weaning juvenile Haliotis rufescens abalone under hatchery conditions, fed with probiotic diets, and subsequently challenged with Vibrio parahaemolyticus. The expression patterns of 16 selected genes associated with different metabolic pathways were analyzed using Real-Time PCR. Gene expression was then compared to immunological response parameters in the abalone and quantification of V. parahaemolyticus during the experimental period. Both transcriptomic and immunological analyses indicated significant alteration of physiological processes in H. rufescens correlated to exposure to the pathogenic bacteria, as well as to probiotic nutrition.

Current status and training requirements for retraining program of general practitioner

The current status and training requirements for general practitioner (GP) were surveyed with questionnaires in 84 trainees from the first Beijing GP retraining program. Results showed that three most demanded skills of health service in community were electrocardiogram (98.8%), clinical lab results reading (96.4%), dressing change (90.5%). The services not provided but should be provided in community were aerosol rebreathing method (23.8%), resection of small superficial lumps (22.6%) and reading X-ray films (20.2%). The reasons for services not provided were insufficient resources (41.7%), lack of skilled personnel (35.7%) and staffing shortage (20.2%). The most required training skills were reading X-ray films (64.3%), electrocardiogram (54.8%) and laboratory results reading (51.2%). There were some skills inadequately trained including cricothyroid membrane puncture, suprapubic bladder puncture and resection of superficial small lumps. The results indicate that the required skills in community health service and individual demands of general practitioners should be the priority of the future training programs. Key words: Inservice training; Questionnaires; General practitioners

Spontaneous Breathing of Heliox Using a Semi-Closed Circuit: A Bench Study

The use of helium-oxygen mixture (heliox) for ventilation has an advantage in patients with obstruction of the airways. The physical properties of helium enable an easier gas flow through the airways; this enables easier breathing for the patient when compared to standard ventilation of air. A high cost of heliox falls within the factors that limit the use of heliox in clinical practice. At present, heliox is administered by use of an open circuit. The aim of this study is to propose a way of heliox administration that reduces heliox consumption but does not affect the positive heliox effects upon the airway resistance. To minimize consumption of heliox, a semi-closed circuit has been designed. The circuit is a modification of an anesthetic circuit composed of parts with the lowest possible resistances. As any circuit has its own resistance, the evaluation of its possible negative effect upon the work of breathing of patients with exacerbation of chronic obstructive pulmonary disease (COPD) has been conducted. A semi-closed circuit for heliox administration has been constructed and evaluated. The intrinsic resistance of both the inspiratory and expiratory limbs of the circuit is less than 140 Pa.s/l. This resistance does not represent a significant workload for a patient with COPD exacerbation whose airway resistance is 10 to 20 fold higher. The designed semi-closed circuit offers a potential benefit of heliox in patients with COPD exacerbation.

Anesthetic management of a neonate with congenital laryngeal cyst

Anesthetic management of a neonate with congenital laryngeal cyst

Effect of Charcoal Filter on the Emergence from Sevoflurane Anesthesia in a Semi-Closed Rebreathing Circuit

PurposeA charcoal filter attached within the anesthetic circuit has been shown to efficiently adsorb halothane or isoflurane, thus hastening anesthetic recovery in low or minimal flow system. This study was intended to demonstrate whether the charcoal filter enhances the recovery time from sevoflurane anesthesia using a semi-closed circuit system.Materials and MethodsThirty healthy patients scheduled for elective surgery under sevoflurane anesthesia were randomly assigned to the charcoal filter or control group. Upon completion of surgery, the end-tidal concentration of sevoflurane was maintained at 2.0 vol%. A charcoal filter was attached to the expiratory limb of the breathing circuit of charcoal filter group subjects. After sevoflurane was discontinued, ventilation was controlled with the same minute volume as the intra-operative period at a fresh gas flow rate of 5 L·min-1 with 100% O2. The elimination kinetics of sevoflurane from end-tidal concentration, Bispectral index and times of eye opening and extubation were obtained.ResultsThe exponential time constant (τ) of alveolar sevoflurane concentration in the charcoal filter group was significantly shorter than that in the control group (1.7±0.5 vs. 2.5±1.1 min, p=0.008). The charcoal filter hastened rapid eye opening (11.1±3.8 vs. 14.8±3.0 min, p=0.007) and extubation (11.9±3.9 vs. 15.3±3.2 min, p=0.014), compared to the control group.ConclusionA charcoal filter enhances the recovery from sevoflurane anesthesia with a semi-closed rebreathing circuit.

Performances of SBR, chemical–DAF and UV disinfection for poultry slaughterhouse wastewater reclamation

Since the poultry slaughter industry is highly water-consuming and wastewater generator, it is essential to take a step towards achieving the sustainability of wastewater reclamation and reuse schemes. This paper evaluates the performance of a lab-scale advanced wastewater treatment system that consists of sequencing batch reactor (SBR), chemical–dissolved-air flotation (DAF) system and ultraviolet (UV) disinfection, used for the reclamation from anaerobically pre-treated poultry slaughterhouse wastewater. Twelve-hour cycles in a fill-aerobic-anoxic-settle-discharge sequence and ethanol addition as carbon source for denitrification at 1.41±0.19C/N ratio were the SBR operating conditions for nitrogen removal. Ferric chloride and cationic polymer as flocculant aid were the chemicals used for phosphorus removal. 4.5–5.5 coagulation pH, 1.32±0.19 Fe/P molar ratio associated with 1.0mgL−1 cationic polymer, 20% recycle rate and 10cmmin−1 flotation velocity were the best chemical–DAF system operating conditions from which resulted >99% phosphorus and 65±25% suspended solids removals. UV radiation dosages ranging from 23 to 32mWscm−2 have effectively inactivated the coliform organisms and Salmonella. Under such operating conditions, organic matter, nutrients, suspended solids and indicator organisms in the final effluent met the quality standards of the legislation for both potable water and effluent discharge to the receiving waters. Zero discharge potentials for the sustainability of the poultry slaughter industry were also explored. The use of all the reclaimed water in closed circuit is expected to reduce the well water input by 60% with no treated effluent discharge to the river during this stage. The use of reclaimed water in semiclosed circuit is expected to reduce the well water input by 46% and the treated effluent discharge to the river by 76%.

Control of the Haemodynamic Response to Surgical Stimuli in Semi-Closed Circuit or Closed Circuit Anaesthesia Using a Multifunctional Anaesthesia System

This study compared the ability of the Zeus multifunctional anaesthesia system to control haemodynamic response to surgical stimulation in semi-closed (SCA) or closed circuit anaesthesia (CCA) modes. Fifty patients undergoing gynaecological surgery were randomly assigned to SCA or CCA. Anaesthesia was induced with 2 mg propofol and 0.9 mg/kg rocuronium, intravenously, and maintained using sevoflurane (minimum alveolar concentration [MAC], 1.0) using 2 l/min oxygen plus 2 l/min nitrous oxide (SCA 4 l/min group) or 50% oxygen plus 50% nitrous oxide (CCA group). An increase in mean arterial pressure (MAP) > 20% above baseline in response to surgical stimulation provoked a stepwise increase in sevoflurane (1.3 MAC and then 1.6 MAC), followed by fentanyl 1 pg/kg intravenously (rescue drug). The time required for MAP to return to within 10% of baseline was significantly shorter in the CCA group (6.4 +/- 3.6 min) compared with the SCA 4 l/min group (10.2 +/- 6.0 min). The percentage of patients requiring fentanyl was significantly greater in the SCA 4 l/min group than in the CCA group. In conclusion, CCA controlled acute haemodynamic responses to surgical stimuli more successfully and rapidly than SCA 4 l/min, using a multifunctional anaesthesia machine.

Fatty diabetic lung: functional impairment in a model of metabolic syndrome

The Zucker diabetic fatty (ZDF fa/fa) rat with genetic leptin insensitivity develops obesity and Type 2 diabetes mellitus (T2DM) with age accompanied by hyperplastic changes in the distal lung (Am J Physiol Lung Cell Mol Physiol 298: L392-L403, 2010). To determine the functional consequences of structural changes, we developed a rebreathing (RB) technique to simultaneously measure lung volume, pulmonary blood flow, lung diffusing capacity (Dl(CO)), membrane diffusing capacity (Dm(CO)), pulmonary capillary blood volume (Vc), and septal tissue volume in anesthetized tracheostomized male ZDF fa/fa and matched lean (+/+) control animals at 4, 8, and 12 mo of age. Results obtained by RB technique were compared with that measured by a single-breath (SB) technique and to that expected in a wide range of species. In fa/fa animals compared with +/+, lung volumes and compliance were 13-35% lower at different ages, and the normal age-related increase in lung compliance was no longer evident. Mean pulmonary blood flow declined with age in fa/fa but not in +/+ animals. Dl(CO) measured at a given pulmonary blood flow was 20-43% lower at different ages due to reductions in both Dm(CO) and Vc. Septal tissue volume was also reduced in older fa/fa rats. We conclude that obese rats with T2DM develop significant restrictive pulmonary defects with diffusion impairment in a pattern similar to that previously reported in obese human subjects with T2DM. Functional impairment became exaggerated with age and duration of T2DM. In both fa/fa and +/+ animals, Dl(CO) measured by RB was systematically higher than by SB technique whereas lung volume was similar, a finding consistent with heterogeneous distribution of ventilation in the rat lung.

A practical rule for optimal flows for xenon anaesthesia in a semi-closed anaesthesia circuit

Stable haemodynamics and its cardioprotective and neuroprotective properties favour xenon as an ideal but expensive anaesthetic agent. The aim of this study was to optimize a semi-closed anaesthesia circuit for xenon anaesthesia with respect to economics and patient safety. A semi-closed nonrebreathing circuit was compared with a closed anaesthesia circuit. In 12 landrace pigs, we compared eight different wash-in procedures affecting xenon consumption. Additionally, the maintenance of anaesthesia was analysed with regard to minimizing xenon consumption. The current study showed that, by optimization of the electronic regulation of the wash-in procedure for xenon anaesthesia, the consumption of the valuable gas can be reduced by up to 75% in a semi-closed circuit. The additional maintenance of anaesthesia under low flow conditions by coupling the xenon flow to the oxygen consumption is the most effective way to technically reduce the amount of xenon needed for anaesthesia.

Effects of theophylline on ventilatory regulation in patients with chronic obstructive pulmonary disease

The effects and the mechanism of single and long-term administration of theophylline on ventilatory regulation were investigated in patients with chronic obstructive pulmonary disease (COPD). The ventilatory and mouth occlusion pressure (P0.1) responses during CO2 rebreathing were measured before and 4 hours after oral, single administration of theophylline in 15 patients with pulmonary emphysema, 15 patients with asthma and 10 healthy subjects. Ventilatory response to CO2 (VE/PCO2) was increased in patients with asthma and P0.1 response to CO2 (P0.1/PaCO2) was increased in patients with pulmonary emphysema after single theophylline administration. In patients with pulmonary emphysema, the increase in P0.1 was more marked than that in maximum inspiratory pressure static (MIPS). The effect of long-term administration of theophylline was studied in 8 patients with COPD and 8 patients with restrictive lung disease. In patients with COPD, P0.1/PaCO2 was significantly increased and the increase was maintained until three months later. These findings suggest that theophylline is effective in improving ventilatory and occlusion pressure responses to CO2 in patients with asthma probably by its bronchodilating effect, and in patients with pulmonary emphysema by its direct effect on the ventilatory control system.

Clinical characteristics and outcome of 508 patients with hyperventilation syndrome

The characteristics of hyperventilation syndrome (HVS) were studied in 508 patients who visited our hospital over 11 years. Information regarding symptoms and laboratory data was collected from the clinical records, and outcome was surveyed with a questionnaire mailed to all patients. Patients with acute HVS ranged in age from 5-85 years, and acute HVS was particularly prevalent among women in their late teens. Triggers of HVS included anxiety, nausea & vomiting, and fever due to the common cold. The primary symptoms were dyspnea and numbness, but these differed from the symptoms that appeared during a provoked attack, Half of the patients had no underlying disorder, but the others were suffering from neurosis, cardiovascular disorders, or other diseases. These characteristics of acute HVS did not differ from those seen in patients in whom the diagnosis of HVS was confirmed with arterial blood gas analysis. Half of the patients recovered without treatment, and the others underwent paper-bag rebreathing or intravenous infusion of sedatives. The prevalence of chronic HVS was 2% and almost all those patients were middle-aged women. In contrast, the questionnaire revealed that half of the patients had repeated HVS attacks. In 10% of the patients, these attacks persisted for more than 3 years. Many of these patients reported that they sighed frequently and felt air hunger while in remission. These findings were compatible with the criteria for chronic HVS. Therefore, it may be possible to diagnose HVS from symptoms alone, without hyperventilation provocation tests. In conclusion, these data underscore the importance of clinical symptoms in the diagnosis of HVS.