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OBJECTIVE: To test the hypothesis that nitric oxide inhalation facilitates CO2 elimination by decreasing alveolar deadspace in an ovine model of acute lung injury. DESIGN: Prospective, placebo-controlled, randomized, crossover model. SETTING: University research laboratory. SUBJECTS: Eleven mixed-breed adult sheep. INTERVENTIONS: To induce acute lung injury, hydrochloric acid was instilled into the tracheas of paralyzed sheep receiving controlled mechanical ventilation. Each sheep breathed 0 ppm, 5 ppm, and 20 ppm nitric oxide in random order. MEASUREMENTS AND MAIN RESULTS: Estimates of alveolar deadspace volumes and arterial-to-end tidal CO2 partial pressure differences were used as indicators of CO2 elimination efficiency. At a constant minute ventilation, nitric oxide inhalation caused dose-independent decreases in Paco2 (p <.05), alveolar deadspace (p <.01), and arterial-to-end tidal CO2 partial pressure differences (p <.01). We found that estimates of arterial-to-end tidal CO2 partial pressure differences may be used to predict alveolar deadspace volume (r2 =.86, p <.05). CONCLUSIONS: Estimates of arterial-to-end tidal CO2 partial pressure differences are reliable indicators of alveolar deadspace. Both values decreased during nitric oxide inhalation in our model of acutely injured lungs. This finding supports the idea that nitric oxide inhalation facilitates CO2 elimination in acutely injured lungs. Future studies are needed to determine whether nitric oxide therapy can be used to reduce the work of breathing in selected patients with cardiopulmonary disorders.

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Tracheal pressure ventilator control (TPVC) is a ventilator mode that relies on tracheal pressure at the carinal end of the endotracheal tube for triggering the ventilator ;;on,'' controlling pressure, and cycling the ventilator ;;off.'' TPVC automatically nullifies imposed resistive work of the breathing apparatus (endotracheal tube plus ventilator) by providing automatic and variable levels of pressure assist. TPVC improves ventilator responsiveness for a spontaneously breathing patient by providing significantly higher peak inspiratory flow rates much closer to that demanded by a patient. TPVC also provides higher assist pressures and flow rates earlier in the breath and thus better-match ventilator-supplied flow to patient-demanded flow than an equivalent level of pressure support ventilation. Matching patient demand for flow to ventilator supply of flow, early in the breath, promotes patient-ventilator synchrony and minimizes work of breathing. We recommend moving the pressure-triggering and control site to the carinal end of the endotracheal tube to provide TPVC.

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The purpose of the present study was to evaluate respiratory system compliance after cardiopulmonary resuscitation (CPR) and subsequent stomach inflation. Further, we calculated peak airway pressure according to the different tidal volume recommendations of the European Resuscitation Council (7.5 ml/kg) and the American Heart Association (15 ml/kg) for ventilation of an unintubated cardiac arrest victim. After 4 min of ventricular fibrillation, and 6 min of CPR, return of spontaneous circulation (ROSC) after defibrillation occurred in seven pigs. Respiratory system compliance was measured at prearrest, after ROSC, and after 2 and 4 l of stomach inflation in the postresuscitation phase; peak airway pressure was subsequently calculated. Before cardiac arrest the mean (+/- S.D.) respiratory system compliance was 30 +/- 3 ml/cm H2O, and decreased significantly (P < 0.05) after ROSC to 24 +/- 5 ml/cm H2O, and further declined significantly to 18 +/- 4 ml/cm H2O after 2 l, and to 13 +/- 3 ml/cm H2O after 4 l of stomach inflation. At prearrest, the mean +/- S.D. calculated peak airway pressure according to European versus American guidelines was 9 +/- 1 versus 18 +/- 3 cm H2O, after ROSC 12 +/- 2 versus 23 +/- 4 cm H2O, and 15 +/- 2 versus 30 +/- 5 cm H2O after 2 l, and 22 +/- 6 versus 44 +/- 12 cm H2O after 4 l of stomach inflation. In conclusion, respiratory system compliance decreased significantly after CPR and subsequent induction of stomach inflation in an animal model with a wide open airway. This may have a significant impact on peak airway pressure and distribution of gas during ventilation of an unintubated patient with cardiac arrest.

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OBJECTIVE: Infusing nitric oxide at a constant rate into a breathing circuit with intermittent mainstream flow causes formation of nitric oxide pools between successive breaths. We hypothesized that incomplete mixing of these pools can confound estimates of delivered nitric oxide concentrations. METHODS: Nitric oxide flowed at a constant rate into the upstream end of a standard adult breathing circuit connected to a lung model. One-milliliter gas samples were obtained from various sites within the breathing system and during various phases of the breathing cycle. These samples were aspirated periodically by a microprocessor controlled apparatus and analyzed using an electrochemical sensor. RESULTS: The pools of nitric oxide distorted into hollow parabolic cone shapes and remained unmixed during their propagation into the lungs. In our preparation, time-averaged nitric oxide concentrations were minimal 60 cm downstream of the infusion site (18 ppm) and maximal 15 cm upstream of the Y-piece (36 ppm). The concentrations were mid-range within the lung (23 ppm), yet were substantially less than predicted by assuming homogeneity of the gases (31 ppm). Generally, nitric oxide concentrations within the lung were different from all other sites tested. CONCLUSION: Incomplete mixing of nitric oxide confounds estimates of delivered nitric oxide concentrations. When nitric oxide is infused at a constant rate into a breathing circuit, we doubt that any sampling site outside the patient's lungs can reliably predict delivered nitric oxide concentrations. Strategies to ensure complete mixing and representative sampling of nitric oxide should be considered carefully when designing nitric oxide delivery systems.

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OBJECTIVES: To review the operational characteristics of commercial devices used to detect endotracheal intubation; and to identify an ideal device for detecting endotracheal intubation in emergency situations, especially in the prehospital setting during cardiac arrest. DATA SOURCES: Relevant articles from the medical literature are referenced. STUDY SELECTION: The authors identified the need for understanding the basic operation principles of portable devices used to detect endotracheal intubation and to correctly use them in unpredictable clinical situations. DATA EXTRACTION: Data from published literature. DATA SYNTHESIS: Recently, a number of new portable devices have been marketed for detecting endotracheal intubation, each having advantages and disadvantages, especially when used during emergency situations. The devices are classified based on their principle of operation. Some rely on CO2 detection (STATCAP, Easy Cap, and Pedi-Cap), others utilize the transmission of light (Trachlight, SURCH-LITE), one operates based on reflection of sound energy (SCOTI), and some depend on aspiration of air (TubeChek and TubeChek-B). A brief description of each device and its operational characteristics are reviewed. A comparative analysis among the devices is made based on size, portability, cost, ease of operation, need for calibration or regular maintenance, reliability for patients with and without cardiac arrest, and the possibility of use for adult and pediatric patients. False-negative and false-positive results for each device are also discussed. False-negative results mean that although the endotracheal tube is in the trachea, the device indicates it is not. False-positive results mean that although the endotracheal tube is in the esophagus, the device indicates it is in the trachea. CONCLUSIONS: Although no clinical comparative study of commercial devices to detect endotracheal intubation exists, the syringe device (TubeChek) has most of the characteristics necessary for a device to be considered ideal in emergency situations in the prehospital setting. It is simple, inexpensive, easy to handle and operate, disposable, does not require maintenance, gives reliable results for patients with and without cardiac arrest, and can be used for almost all age groups. The device may yield false-negative results, most commonly in the presence of copious secretions and in cases of accidental endobronchial intubation. Regardless of the device used, clinical judgment and direct visualization of the endotracheal tube in the trachea are required to unequivocally confirm proper endotracheal tube placement.

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OBJECTIVES: When ventilating a nonintubated patient in cardiac arrest, the European Resuscitation Council has recently recommended a decrease in the tidal volume from 0.8 to 1.2 L to 0.5 L, partly in an effort to decrease peak flow rate, and therefore, to minimize stomach inflation. The purpose of the present study was to examine the validity of the European Resuscitation Council's recommendation in terms of gas distribution between lungs and stomach in a bench model that simulates ventilation of a nonintubated patient with a self-inflatable bag representing tidal volumes of 0.5 and 0.75 L. DESIGN: A bench model of a patient with a nonintubated airway was used consisting of face mask, manikin head, training lung (lung compliance, 50 mL/cm H2O; airway resistance, 5 cm H2O/L/sec), adjustable lower esophageal sphincter pressure (LESP) and simulated stomach. SETTING: University hospital laboratory. SUBJECTS: Thirty healthcare professionals. INTERVENTIONS: Healthcare professionals performed 1-min bag-mask ventilation at each LESP level of 5, 10, and 15 cm H2O at a rate of 12 breaths/min, using an adult and pediatric self-inflating bag, respectively. Volunteers were blinded to the LESP, which was randomly varied. MEASUREMENTS AND MAIN RESULTS: Both types of self-inflating bags induced stomach inflation, with higher stomach and lower lung tidal volumes when the LESP was decreased. Lung tidal volume with the pediatric bag was significantly (p < .05) lower at all LESP levels when compared with the adult bag, and ranged between 240 mL at an LESP of 15 cm H2O and 120 mL at an LESP of 5 cm H2O. Stomach tidal volume with the adult bag ranged between 250 mL at an LESP of 15 cm H2O and increased to 550 mL at an LESP of 5 cm H2O. Stomach tidal volume with the pediatric bag was significantly lower (p < .05) at all LESP levels when compared with the adult bag and ranged between 70 mL at an LESP of 15 cm H2O and 300 mL at an LESP of 5 cm H2O. CONCLUSIONS: Our data support the recommendation of the European Resuscitation Council to decrease tidal volumes to 0.5 L when ventilating a cardiac arrest victim with an unprotected airway. A small tidal volume may be a better trade-off in the basic life support phase, as this may provide reasonable ventilation while avoiding massive stomach inflation.

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OBJECTIVES: This study was designed to test the hypothesis that the practice of infusing nitric oxide at constant flow rates directly into breathing circuits with intermittent (pulsatile) flow can lead to streaming and tidal pooling of the nitric oxide. This study was also designed to show the extent to which streaming and tidal pooling of nitric oxide affect nitric oxide delivery. DESIGN: A series of five in vitro experiments was performed. For each experiment, either one or two features of the nitric oxide delivery/sampling system were varied, and the effects of these variations were evaluated with regard to measured nitric oxide concentration changes. The results from each experiment were analyzed using either one- or two-factor analysis of variance. SETTING: University research laboratory. SUBJECTS: Breaths were provided by a mechanical ventilator that was connected to a lung model. A standard, corrugated, adult breathing circuit was used. Gas samples were obtained from either the lung model's bellows or selected sites within the breathing circuit. Nitric oxide concentrations were measured, using an electrochemical gas analyzer. INTERVENTIONS: The system features that were varied included the cross-sectional position of the sampling site within the breathing circuit, the distance between the infusion port and the sampling site, the breathing frequency, the distance between the Y-piece and the infusion port, and the airway (deadspace) volume. MEASUREMENTS AND MAIN RESULTS: Streaming of nitric oxide within the breathing circuit was detected as far as 25 cm downstream of the infusion site (p < .0001). Pooling of nitric oxide was detected both near and downstream of the infusion site (p < .0001). Increasing the breathing frequency from 5 to 30 breaths/min increased mixing thoroughness (p < .005). Increasing the distance between the Y-piece and the infusion port from 15 to 180 cm decreased nitric oxide delivery to our lung model (p < .0001). Interestingly, increasing airway (deadspace) volume from 150 to 450 mL decreased nitric oxide delivery to our lung model (p < .0001). CONCLUSIONS: Estimates of nitric oxide delivery using a constant flow rate of nitric oxide infused directly into a breathing circuit during controlled mechanical ventilation can be confounded by streaming and tidal propagation of nitric oxide pools. Improved reproducibility of reported dose-response relationships is likely to be achieved through further study of nitric oxide behavior within the breathing circuits. Reduced toxicity associated with nitric oxide inhalation may also be achieved through a better understanding of this nitric oxide behavior.

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OBJECTIVES: Triggering a ventilator "ON" at the carinal end of the endotracheal tube decreases imposed work of breathing by bypassing the resistance imposed by the breathing circuit and the endotracheal tube. We compared work of breathing during spontaneous ventilation between three methods of triggering the ventilator "ON": a) conventional pressure triggering from inside the ventilator; b) flow-by triggering; or c) tracheal pressure triggering at the carinal end of the endotracheal tube. We hypothesized that the work of breathing would be substantially decreased with tracheal pressure triggering compared with conventional pressure and flow-by methods in patients receiving continuous positive airway pressure. DESIGN: Clinical, prospective study. SETTING: University teaching hospital. PATIENTS: Fourteen adults diagnosed with acute respiratory failure. INTERVENTIONS: All patients were breathing spontaneously at an FIO2 of 0.30 to 0.40 and received 5 cm H2O of continuous positive airway pressure. Three different methods of triggering the ventilator while set in the continuous positive airway pressure mode were administered in random order. MEASUREMENTS AND MAIN RESULTS: Real-time measurements of esophageal pressure and tidal volume were integrated with a respiratory monitor (CP-100, Bicore, Riverside, CA) that uses the Campbell diagram to calculate total work of breathing. Imposed work of breathing was calculated by integrating tidal volume with the pressure at the carinal end of the endotracheal tube. Physiologic work of breathing was calculated by subtracting imposed work of breathing from the total work of breathing. Breathing frequency, the index of rapid shallow breathing (breathing frequency/tidal volume), peak inspiratory flow rate demand, exhaled minute ventilation, and the duration of respiratory muscle contraction assessed by the ratio of inspiratory time to total cycle time were also measured. Data were analyzed by Friedman's repeated-measures analysis of variance on ranks. Alpha was set at .05 for statistical significance. Imposed work of breathing decreased to approximately zero during tracheal pressure triggering. As a result, total work of breathing decreased by approximately 40% compared with the flow-by and conventional methods. During tracheal pressure triggering only, airway pressure increased above baseline pressure to approximately 11 cm H2O, which resembled pressure-support ventilation. Also, during tracheal pressure triggering, tidal volume and peak inspiratory flow rate were significantly increased, while the pressure-time product and the index of rapid shallow breathing were significantly decreased. Hemodynamic status and oxygen saturation were not clinically affected. CONCLUSIONS: The tracheal pressure triggering of a demand-flow continuous positive airway pressure system creates an effect similar to pressure-support ventilation that significantly decreases imposed work of breathing and, thus, total work of breathing. We recommend moving the triggering site of the ventilator to the carinal end of the endotracheal tube.

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OBJECTIVE: To document the effect of administering artificial surfactant into the trachea, either by instillation or aerosolization, on acute lung injury experimentally induced with kerosene in sheep. DESIGN: Randomized, prospective, controlled study. SETTING: Research laboratory. SUBJECTS: Sheep (n = 24), weighing 8.5 to 25.2 kg (average 16.6). INTERVENTIONS: In anesthetized, tracheally intubated sheep with pulmonary and femoral artery catheters inserted, lung injury was induced by instilling kerosene (0.3 mL/kg) into the trachea. After 15 mins of spontaneous breathing, mechanical ventilation was instituted with a uniform F10(2) and a tidal volume of 10 mL/kg. Sheep were then assigned randomly to one of four regimens as follows: exogenous surfactant or saline (5 mL/kg each) was administered as a bolus intratracheally or by aerosolization for 6 hrs. MEASUREMENTS AND MAIN RESULTS: Arterial and mixed venous blood gases, pH, airway pressure, and static respiratory system compliance were measured and compared between aerosol saline and aerosol surfactant and between bolus saline and bolus surfactant. For all variables except static respiratory system compliance, the hourly rate of change from 15 mins, 1 hr, and 6 hrs after kerosene instillation was determined for each animal, and group rank sums of hourly rates of change were compared. For static respiratory system compliance, the slope of the pressure-volume curve with volumes of 100, 200, 300, 400, and 500 mL was computed for each animal at baseline and at 3 and 6 hrs after kerosene instillation. Group rank sums for static respiratory system compliance at 3 and 6 hrs were compared. Also, the 3- and 6-hr static respiratory system compliance values at each of the volumes were compared. With saline, six of eight sheep died; with surfactant, no sheep died (p = .001). When compared with saline at 15 mins, 1 hr, and 6 hrs after kerosene instillation, surfactant, regardless of whether administered by aerosol or bolus, significantly increased rate of change of arterial oxygen saturation, mixed venous oxygen saturation, and PO2. CONCLUSIONS: In the present animal study, artificial surfactant was an effective treatment for hydrocarbon aspiration. Aerosolized surfactant achieved results similar to instilled surfactant but at a lower total dose.

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OBJECTIVE: To evaluate the relationships between directly measured work of breathing (WOB) and variables of the breathing pattern commonly used at the bedside to infer WOB for intubated, spontaneously breathing patients treated with pressure support ventilation (PSV). DESIGN: In vivo measurements of the WOB were obtained on a consecutive series of adults. Breathing frequency (f), tidal volume (VT), the index of rapid, shallow breathing (f/V T), the duration of respiratory muscle contraction expressed as the ratio of inspiratory time over total respiratory cycle time (TI/TTOT), and a breathing pattern score (applied to approximately 50% of the patients) which ranks f, VT, sternocleidomastoid muscle activity, substernal retraction, and abdominal paradox on a scale were variables of the breathing pattern were also measured. The greater the breathing pattern score, the lower the WOB and vice versa. SETTING: Surgical ICUs in two university teaching hospitals. PATIENTS: Sixty-seven adults (42 men and 25 women, aged 20 to 78 years) who had acute respiratory failure from various etiologies were studied. All patients were breathing spontaneously receiving continuous positive airway pressure and PSV. INTERVENTIONS: Intraesophageal pressure (indirect measurement of intrapleural pressure) was measured with an esophageal balloon integrated into a nasogastric tube. VT was obtained by positioning a flow sensor between the "Y" piece of breathing circuit and the endotracheal tube. Data from these measurements were directed to a bedside respiratory monitor (Bicore; Allied Healthcare Products; Riverside, Calif) that calculates WOB using the Campbell diagram. Patients received PSV at levels deemed reasonable to unload the respiratory muscles. All measurements were obtained after 15 to 20 min at each level of PSV, averaged over 1 min, and then variables of the breathing pattern were regressed with directly measured values for WOB. RESULTS: All breathing pattern variables poorly predicted WOB as evidenced by the low values for the coefficients of determination (r2). Breathing frequency correlated positively with WOB (r = 0.47, p < 0.001) and predicted or explained only 22% (r2 = .22) of the variance in WOB. VT correlated negatively and f/VT and TI/TTOT each correlated positively with WOB. However, these variables predicted only 20 to 27% of the variance in WOB. The breathing pattern score correlated negatively with WOB and predicted only 43% of the variance in WOB. A prediction model taking all variables into consideration using multiple regression analysis predicted only 50% of the variance in WOB; thus, it too was a poor to moderate predictor of WOB. CONCLUSION: Our data reveal that WOB should be measured directly because variables of the breathing pattern commonly used at the bedside appear to be inaccurate and misleading inferences of the WOB. The clinical implication of these findings involves the traditional and empirical practice of titrating PSV based on the breathing pattern. We do not imply that the patient's breathing pattern should be ignored, nor undermine its importance, for it provides useful diagnostic information. It appears, however, that relying primarily on the breathing pattern alone does not provide enough information to accurately assess the respiratory muscle workload. Using the breathing pattern as the primary guideline for selecting a level of PSV may result in inappropriate respiratory muscle workloads. A more comprehensive strategy is to employ WOB measurements and the breathing pattern in a complementary manner when titrating PSV in critically ill patients.

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STUDY OBJECTIVE: We evaluated the difference in work of breathing (WOB) during spontaneous ventilation with continuous positive airway pressure (CPAP) among three methods of triggering the ventilator: conventional pressure triggering, tracheal pressure triggering, and flow-by triggering. METHODS: In an in vitro model of the respiratory system consisting of a bellows (lungs) in a plastic canister (chest wall), spontaneous ventilation was simulated with a piston-driven pump (respiratory muscles). Data were recorded during CPAP of 5 cm H2O (model 7200ae ventilator, Puritan-Bennett, Overland Park, Kan) at peak sinusoidal inspiratory flow rate demands of 60 and 80 L/min and airway resistances of 5 and 20 cm H2O/L/s, with the demand flow system triggered by conventional pressure, tracheal pressure, or flow. Under each condition, tidal volume, pressure-time product (PTP), WOB, and changes in intrapleural pressure (Ppl) and airway pressure were recorded in real time by means of a computerized portable respiratory monitor (model CP-100, Bicore, Irvine, Calif). The Ppl was measured from within the canister, tidal volume by positioning a flow sensor between the Y-piece of the breathing circuit and the endotracheal tube (ETT), and airway pressure from a catheter attached to the flow sensor. The WOB was calculated by the monitor in real time. RESULTS: Changes in Ppl were greatest with conventional pressure triggering, less with flow-by triggering, and least with tracheal pressure triggering. The WOB was significantly lower (approximately 50%) with tracheal pressure triggering than with the other two methods. With tracheal pressure triggering only, an effect similar to that of pressure support ventilation (PSV) occurred, which accounted in part for the significant decrease in WOB. The PTP/breath ratio correlated strongly and was a good predictor of WOB (r2 = 0.95). CONCLUSIONS: Compared with conventional pressure and flow-by methods, triggering with tracheal pressure decreased WOB significantly. This method of triggering may improve patient-ventilator interaction.

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STUDY OBJECTIVE: In a previous cardiopulmonary resuscitation (CPR) study in swine, ventilation was associated with improved rate of return of spontaneous circulation (ROSC) compared with nonventilated animals, which had greater hypoxia and hypercarbic acidosis. We used the same model to determine the independent effect of hypoxia and hypercarbic acidosis on ROSC after cardiac arrest. DESIGN: Laboratory model of cardiac arrest. SETTING: University teaching hospital laboratory. PARTICIPANTS: Domestic swine (23 to 61 kg). INTERVENTIONS: Twenty-four swine were randomly assigned to three groups receiving ventilation during CPR with 85% O2/15% N2 (control), 95% O2/5% CO2 (hypercarbia), or 10% O2/90% N2 (hypoxia). All animals had ventricular fibrillation for 6 min without CPR, then CPR with one of the ventilation gases for 10 min, then defibrillation. Animals without ROSC received epinephrine, 85% O2, CPR for another 3 min, and defibrillation. MEASUREMENTS AND RESULTS: During the tenth minute of CPR, the hypercarbic group had more mean (SD) arterial hypercarbia than the control group (PCO2, 47 +/- 6, compared with 34 +/- 6; p < 0.01), and greater mixed venous hypercarbia (PCO2, 72 +/- 14, compared with 59 +/- 8; p < 0.05), while mean arterial and mixed venous PO2 was not significantly different. The hypoxic group had significantly less mean arterial (43 +/- 9 compared with 228 +/- 103 mm Hg) and mixed venous (22 +/- 5 compared with 35 +/- 7 mm Hg) PO2 when compared with the control group (p < 0.01), while mean arterial and mixed venous PCO2 were not significantly different. Thus, the model succeeded in producing isolated hypercarbia without hypoxia in the hypercarbic group and isolated hypoxia without hypercarbia in the hypoxic group. The rate of ROSC was 6/8 (75%) for the control group, 1/8 (13%) for the hypercarbic group, and 1/8 (13%) for the hypoxic group (p < 0.02). CONCLUSIONS: Both hypoxia and hypercarbia independently had an adverse effect on resuscitation from cardiac arrest. In this model with a prolonged interval of untreated cardiac arrest, adequate ventilation was important for resuscitation.

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OBJECTIVE: In intubated, mechanically ventilated patients, inspiration is forced by externally applied positive pressure. In contrast, exhalation is passive and depends on the time constant of the total respiratory system. The expiratory time constant is thus an important determinant of mechanical ventilation. The aim of this study was to evaluate a simple method for measuring the expiratory time constant in ventilated subjects. DESIGN: Prospective study using a lung simulator and ten dogs. SETTING: University hospital. SUBJECTS: Commercially available lung simulator and ten greyhound dogs. INTERVENTIONS: Different expiratory time constants were set on the lung simulator. In the dogs, the endotracheal tube was clamped to increase airways resistance by 22.5 cm H2O/(L/sec) and the lungs were injured with hydrochloric acid to decrease total respiratory compliance by 16 mL/cm H2O. This procedure resulted in a wide range of expiratory time constants. MEASUREMENTS AND MAIN RESULTS: Pneumotachography was used to measure flow and volume. The ratio of exhaled volume and peak flow was calculated from these signals, corrected for the limited exhalation time yielding the "calculated expiratory time constant" and compared with the actual expiratory time constant. The typical error was +/- 0.19 sec for the lung simulator and +/- 0.15 sec for the dogs. CONCLUSIONS: The volume and peak flow corrected for limited exhalation time is a good estimate of the total expiratory time constant in passive subjects and may be useful for the titration of mechanical ventilation.

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STUDY OBJECTIVE: To develop an automatic mechanical device capable of performing active compression-decompression (ACD) CPR in laboratory animals. DESIGN: A swine model was used to study standard and ACD CPR. One-minute periods of standard mechanical chest compressions were alternated with mechanical ACD CPR. SETTING: University hospital laboratory. INTERVENTIONS: A commercially available device that provided standard chest compressions only was modified to deliver ACD CPR. RESULTS: The absolute difference in intrapleural pressure and tidal volume almost doubled during ACD CPR compared with that with standard CPR. CONCLUSION: The presence of a greater negative change in intrapleural pressure confirmed that active decompression of the chest had occurred and that the device was capable of performing ACD CPR. The device provides consistent rate, depth, force, and duty cycle.

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