Use of an inspiratory impedance threshold valve during cardiopulmonary resuscitation: a progress report

Building upon studies on the mechanism of active compression-decompression (ACD) cardiopulmonary resuscitation, a new inspiratory impedance threshold valve has been developed to enhance the return of blood to the thorax during the decompression phase of CPR. Use of this device results in a greater negative intrathoracic pressure during chest wall decompression. This leads to improved vital organ perfusion during both standard and ACD CPR. Animal and human studies suggest that this simple device increases cardiopulmonary circulation by harnessing more efficiently the kinetic energy of the outward movement of the chest wall during standard CPR or active chest wall decompression. When used in conjunction with ACD CPR during clinical evaluation, addition of the impedance valve resulted in sustained systolic pressures of greater than 100 mmHg and diastolic pressures of greater than 55 mmHg. The new valve may be beneficial in patients in asystole or shock refractory ventricular fibrillation, when enhanced return of blood flow to the chest is needed to 'prime the pump'. The potential long-term benefits of this new valve remain under investigation.     

Influence of an impedance threshold valve on ventilation with supraglottic airway devices during cardiopulmonary resuscitation in a manikin

Aim This study investigates if a n impedance threshold valve (ITV) might improve survival after cardiac arrest by increasing vital organ blood flow. The combination of ITV and supraglottic airway devices (SADs) has not been previously studied. This simulation study in a manikin aimed at analysing differences in ventilation with different SADs without and with an ITV.

Methods

In a resuscitation manikin, cardiopulmonary resuscitation (CPR) was performed with interrupted (30:2) and continuous chest compressions using facemask, tracheal tube and 10 SADs (six different laryngeal masks, LT-D, LTS-D, Combitube^® and Easy Tube^®). Ventilation was performed with and without an ITV. A total of 550 CPR cycles of 3-min duration were performed with chest compressions and ventilation standardised by use of a mechanical thumper device and an emergency ventilator.

Results

Sufficient ventilation was possible with all devices tested. For ventilation during continuous chest compressions, there were significantly reduced tidal volumes for all airway devices with ITV use. By contrast, during interrupted chest compressions, no differences in tidal volumes with the ITV occurred in the majority of devices. The maximum reduction of tidal volume for any device was 7.8% of the volume reached without the ITV.

Conclusion

Based on the findings of this manikin trial, the use of an ITV for ventilation during CPR is possible in combination with supraglottic airway devices. Merging these two strategies warrants further clinical evaluation to judge the relevance of tidal volume reduction found in this trial.     

Effect of an inspiratory impedance threshold device on hemodynamics during conventional manual cardiopulmonary resuscitation

BACKGROUND: In animals in cardiac arrest, an inspiratory impedance threshold device (ITD) has been shown to improve hemodynamics and neurologically intact survival. The objective of this study was to determine whether an ITD would improve blood pressure (BP) in patients receiving CPR for out-of-hospital cardiac arrest. METHODS: This prospective, randomized, double-blind, intention-to-treat study was conducted in the Milwaukee, WI, emergency medical services (EMS) system. EMS personnel used an active (functional) or sham (non-functional) ITD on a tracheal tube on adults in cardiac arrest of presumed cardiac etiology. Care between groups was similar except for ITD type. Low dose epinephrine (1mg) was used per American Heart Association Guidelines. Femoral arterial BP (mmHg) was measured invasively during CPR. RESULTS: Mean+/-S.D. time from ITD placement to first invasive BP recording was approximately 14 min. Twelve patients were treated with a sham ITD versus 10 patients with an active ITD. Systolic BPs (mean+/-S.D.) [number of patients treated at given time point] at T = 0 (time of first arterial BP measurement), and T=2, 5 and 7 min were 85+/-29 [10], 85+/-23 [10], 85+/-16 [9] and 69+/-22 [8] in the group receiving an active ITD compared with 43+/-15 [12], 47+/-16 [12], 47+/-20 [9], and 52+/-23 [9] in subjects treated with a sham ITD, respectively (p < 0.01 for all times). Diastolic BPs at T = 0, 2, 5 and 7 min were 20+/-12, 21+/-13, 23+/-15 and 25+/-14 in the group receiving an active ITD compared with 15+/-9, 17+/-8, 17+/-9 and 19+/-8 in subjects treated with a sham ITD, respectively (p = NS for all times). No significant adverse device events were reported. CONCLUSIONS: Use of the active ITD was found to increase systolic pressures safely and significantly in patients in cardiac arrest compared with sham controls.     

Clinical evaluation of an inspiratory impedance threshold device during standard cardiopulmonary resuscitation in patients with out-of-hospital cardiac arrest

OBJECTIVE: To determine whether an impedance threshold device, designed to enhance circulation, would increase acute resuscitation rates for patients in cardiac arrest receiving conventional manual cardiopulmonary resuscitation. DESIGN: Prospective, randomized, double-blind, intention-to-treat. SETTING: Out-of-hospital trial conducted in the Milwaukee, WI, emergency medical services system. PATIENTS: Adults in cardiac arrest of presumed cardiac etiology. INTERVENTIONS: On arrival of advanced life support, patients were treated with standard cardiopulmonary resuscitation combined with either an active or a sham impedance threshold device. MEASUREMENTS AND MAIN RESULTS: We measured safety and efficacy of the impedance threshold device; the primary end point was intensive care unit admission. Statistical analyses performed included the chi-square test and multivariate regression analysis. One hundred sixteen patients were treated with a sham impedance threshold device, and 114 patients were treated with an active impedance threshold device. Overall intensive care unit admission rates were 17% with the sham device vs. 25% in the active impedance threshold device (p = .13; odds ratio, 1.64; 95% confidence interval, 0.87, 3.10). Patients in the subgroup presenting with pulseless electrical activity had intensive care unit admission and 24-hr survival rates of 20% and 12% in sham (n = 25) vs. 52% and 30% in active impedance threshold device groups (n = 27) (p = .018, odds ratio, 4.31; 95% confidence interval, 1.28, 14.5, and p = .12, odds ratio, 3.09; 95% confidence interval, 0.74, 13.0, respectively). A post hoc analysis of patients with pulseless electrical activity at any time during the cardiac arrest revealed that intensive care unit and 24-hr survival rates were 20% and 11% in the sham (n = 56) vs. 41% and 27% in the active impedance threshold device groups (n = 49) (p = .018, odds ratio, 2.82; 95% confidence interval, 1.19, 6.67, and p = .037, odds ratio, 3.01; 95% confidence interval, 1.07, 8.96, respectively). There were no statistically significant differences in outcomes for patients presenting in ventricular fibrillation and asystole. Adverse event and complication rates were also similar. CONCLUSIONS: During this first clinical trial of the impedance threshold device during standard cardiopulmonary resuscitation, use of the new device more than doubled short-term survival rates in patients presenting with pulseless electrical activity. A larger clinical trial is underway to determine the potential longer term benefits of the impedance threshold device in cardiac arrest.     

Evaluation of a prototypic inspiratory impedance threshold valve designed to enhance the efficiency of cardiopulmonary resuscitation

OBJECTIVE: Assess a prototype inspiratory impedance threshold valve (ITV) designed to enhance vital organ circulation during standard and active compression/decompression cardiopulmonary resuscitation (CPR). BACKGROUND: The ITV attaches to commonly used airway assist devices and decreases intrathoracic pressure during the decompression (chest recoil) phase of CPR by creating a vacuum within the thorax, which increases venous blood flow to the heart and thus increases coronary perfusion pressure and blood flow to the brain. METHODS: The evaluation included laboratory bench testing, according to American Society for Testing and Materials (ASTM) and International Standards Organization (ISO) guidelines, and performance testing with pigs in cardiac arrest. A vacuum pull test was developed to determine the inspiratory impedance under various inspiratory flow conditions. RESULTS: The valve passed all minimum ASTM and ISO performance tests. During cardiac arrest in pigs the ITV decreased intrathoracic pressures by 6-8 mm Hg during the decompression phase. The vacuum pull test demonstrated that the prototype ITV functioned as intended. CONCLUSIONS: The prototype ITV passed all performance testing recommended by international guidelines and functioned effectively as intended for use. The animal study results, when combined with recent clinical data, suggest that an ITV inspiratory cracking pressure of 12 cm H(2)O should be sufficient to decrease intrathoracic pressure during the decompression phase of standard CPR. Clinical studies are now underway.     

Use of impedance threshold device in conjunction with our novel adhesive glove device for ACD-CPR does not result in additional chest decompression

Objective

To evaluate the hemodynamic effects of using an adhesive glove device (AGD) to perform active compression–decompression CPR (AGD-CPR) in conjunction with an impedance threshold device (ITD) in a pediatric cardiac arrest model.

Design

Controlled, randomized animal study.

Methods

In this study, 18 piglets were anesthetized, ventilated, and continuously monitored. After 3 min of untreated ventricular fibrillation, animals were randomized (6/group) to receive either standard CPR (S-CPR), active compression–decompression CPR via adhesive glove device (AGD-CPR) or AGD-CPR along with an ITD (AGD-CPR + ITD) for 2 min at 100–120 compressions/min. AGD is delivered using a fingerless leather glove with a Velcro patch on the palmer aspect and the counter Velcro patch adhered to the pig's chest. Data (mean ± SD) were analyzed using one-way ANOVA with pair wise multiple comparisons to assess differences between groups. p-Value ≤ 0.05 was considered significant.

Results

Both AGD-CPR and AGD-CPR + ITD groups produced lower intrathoracic pressure (IttP, mmHg) during decompression phase (−13.4 ± 6.7, p = 0.01 and −11.9 ± 6.5, p = 0.01, respectively) in comparison to S-CPR (−0.3 ± 4.2). Carotid blood flow (CBF, % of baseline mL/min) was higher in AGD-CPR and AGD-CPR + ITD (respectively 64.3 ± 47.3%, p = 0.03 and 67.5 ± 33.1%, p = 0.04) as compared with S-CPR (29.1 ± 12.5%). Coronary perfusion pressure (CPP, mmHg) was higher in AGD-CPR and AGD-CPR + ITD (respectively 19.7 ± 4.6, p = 0.04 and 25.6 ± 12.1, p = 0.02) when compared to S-CPR (9.6 ± 9.1). There was no statistically significant difference between AGD-CPR and AGD-CPR + ITD groups with reference to intra-thoracic pressure, carotid blood flow and coronary perfusion pressure.

Conclusion

Active compression decompression delivered by this simple and inexpensive adhesive glove device resulted in improved cerebral blood flow and coronary perfusion pressure. There was no statistically significant added effect of ITD use along with AGD-CPR on the decompression of the chest.     

Treatment of hypotension in pigs with an inspiratory impedance threshold device: a feasibility study

OBJECTIVE: An inspiratory impedance threshold device was evaluated in spontaneously breathing animals with hypotension to determine whether it could help improve systemic arterial pressures when fluid replacement was not immediately available. DESIGN: Prospective, randomized. SETTING: Animal laboratory. SUBJECTS: Thirty-nine female farm pigs (weight, 28-33 kg). INTERVENTIONS: A total of 39 anesthetized spontaneously breathing pigs were treated with an impedance threshold device, with cracking pressures from 0 to -20 cm H2O. Four separate experimental protocols were performed: protocol A, in which the hemodynamics of seven pigs were examined during application of an impedance threshold device at various levels of inspiratory impedance (-5, -10, -15, and -20 cm H(2)O), both before and after a severe, controlled hemorrhage to a systolic blood pressure of 50 - 55 mm Hg; protocol B, in which nine pigs bled to systolic blood pressure of 50 -55 mm Hg were treated with an impedance threshold device set at -12 cm H2O and were compared with nine others treated with a sham device; protocol C, in which the effects of the impedance threshold device on mixed venous gases were measured in seven hemorrhaged pigs; and protocol D, in which the effects of the impedance threshold device on cardiac output in seven hemorrhaged pigs were measured. METHODS AND MAIN RESULTS: During initial studies with both normovolemic and hypovolemic pigs, sequential increases in inspiratory impedance resulted in a significant increase in systolic blood pressure, whereas diastolic left ventricular and right atrial pressures decreased significantly and proportionally to the level of impedance. When comparing the sham vs. active impedance threshold device (-12 cm H(2)O) in hypotensive pigs, systolic blood pressure (mean +/- sem) with active impedance threshold device treatment increased from 70 +/- 2 mm Hg to 105 +/- 4 mm Hg (p <.01). Pressures in the control group remained at 70 +/- 4 mm Hg (p <.01). Cardiac output increased by nearly 25% (p <.01) with the active impedance threshold device when calculated using the mixed gas equation and when determined by thermodilution. CONCLUSIONS: These studies demonstrate that it is feasible to use a device that creates inspiratory impedance in spontaneously breathing normotensive and hypotensive pigs to increase blood pressure and enhance cardiopulmonary circulation in the absence of immediate fluid resuscitation. Further studies are needed to evaluate the potential long-term effects and limitations of this new approach to treat hypovolemic hypotension.     

Use of an inspiratory impedance threshold device on a facemask and endotracheal tube to reduce intrathoracic pressures during the decompression phase of active compression-decompression cardiopulmonary resuscitation

INTRODUCTION: Use of an inspiratory impedance threshold device (ITD) significantly increases coronary perfusion pressures and survival in patients ventilated with an endotracheal tube (ETT) during active compression-decompression cardiopulmonary resuscitation. We tested the hypothesis that the ITD could lower intratracheal pressures when attached to either a facemask or ETT. METHODS: An active and sham ITD were randomly applied first to a facemask and then to an ETT during active compression-decompression cardiopulmonary resuscitation in 13 out-of-hospital cardiac arrest patients in a randomized, double-blinded, prospective clinical trial. The compression-to-bag-valve ventilation ratio was 15:2. Airway pressures (surrogate for intrathoracic pressure) were measured with a pressure transducer. A sham and an active ITD were used for 1 min each in a randomized order, first on a facemask and then on an ETT. Statistical analyses were made using Friedman's and Wilcoxon's rank-sum tests. RESULTS: For the primary end point, mean +/- sd maximum negative intrathoracic pressures (mm Hg) during the decompression phase of cardiopulmonary resuscitation were -1.0 +/- 0.73 mm Hg with a sham vs. -4.6 +/- 3.7 mm Hg with an active ITD on the facemask (p = .003) and -1.3 +/- 1.3 mm Hg with a sham ITD vs. -7.3 +/- 4.5 mm Hg with an active ITD on an ETT (p = .0009). Decompression phase airway pressures with the facemask and ETT were not statistically different. CONCLUSIONS: Use of an active ITD attached to a facemask or an ETT resulted in a significantly lower negative intratracheal pressure during the decompression phase of active compression-decompression cardiopulmonary resuscitation when compared with controls. Airway pressures with an ITD on either a facemask or ETT were similar. The ITD-facemask combination was practical and enables rapid deployment of this life-saving technology.     

Utilization of a model lung system to assess the effects of an inspiratory impedance threshold valve on the relationship between active decompression and intra-thoracic pressure

Use of an inspiratory impedance valve has recently been shown to increase the efficacy of standard and active compression-decompression cardiopulmonary resuscitation. We evaluated the effects of a prototypic impedance valve on the relationship between the active decompression and intra-thoracic pressure using a mechanical model lung system. Intermittent impedance to inspiratory flow of respiratory gases during the decompression phase of active compression-decompression cardiopulmonary resuscitation significantly decreased the intra-thoracic pressure, while the pressure was almost zero cm H2O during the cardiopulmonary resuscitation cycle when the impedance threshold valve was not functioning. Thus, this mechanical model will help in evaluating the valve as well as in optimizing its function by simulating various forms of lung disease.     

Reducing ventilation frequency combined with an inspiratory impedance device improves CPR efficiency in swine model of cardiac arrest

BACKGROUND: The basic premise that frequent ventilations during cardiopulmonary resuscitation (CPR) are a necessity for tissue oxygenation has recently been challenged. An inspiratory impedance threshold device (ITD) recently has also been shown to increase CPR efficiency, principally by augmenting circulation with little impact on ventilation. The optimal compression to ventilation (C/V) is not known for this new device. The purpose of this study was to compare the currently recommended C/V ratio of 5:1 with a 10:1 ratio, +/- the ITD, to optimize circulation and oxygenation during CPR. METHODS: Thirty-two adult pigs weighing 26-31 kg were randomized to CPR with varying C/V ratios +/- the ITD as follows: A = 5:1, B = 5:1+ITD, C = 10:1, D = 10:1+ITD. After 6 min of untreated ventricular fibrillation (VF), closed-chest standard CPR was performed with an automatic piston device that does not impede passive chest wall recoil, at a continuous compression rate of 100 min(-1). Synchronous breaths were given every 5 or 10 compressions during the decompression phase depending on the group. CPR was performed for 6 min and physiological variables were measured throughout the experimental protocol. RESULTS: A reduction in the frequency of ventilation from 5:1 to 10:1 resulted in significantly improved arterial and coronary perfusion pressure in a pig model of cardiac arrest. Addition of an ITD resulted in further increases in arterial and coronary perfusion pressures with both 5:1 and 10:1 C/V ratios, without compromising oxygenation. CONCLUSION: CPR efficiency can be optimized by changing the compression: ventilation ratio from 5:1 to 10:1 and with concurrent use of the inspiratory threshold device.     

Effects of an inspiratory impedance threshold device on blood pressure and short term survival in spontaneously breathing hypovolemic pigs

BACKGROUND: The inspiratory impedance threshold device (ITD) has been shown to improve hemodynamic variables and survival outcomes during cardiopulmonary resuscitation in animals and humans. We hypothesized that use of an ITD, with a resistance of -10 cm H2O, will improve hemodynamics and short-term survival rates during hypovolemic hypotension in spontaneously breathing pigs. METHODS: Female farm pigs ( approximately 26 kg) were intubated and anesthetized with propofol with the dose adjusted to permit spontaneous respirations. They were bled to 50% of calculated blood volume through an arterial catheter and then prospectively randomized to either treatment with an ITD or observation alone. Arterial and intratracheal pressures as well as arterial blood gases were measured. After 90 min the ITD was removed, normal saline was administered to all surviving animals, the anesthetic was discontinued, and animals were allowed to recover. Statistical analysis was performed with one-way repeated ANOVA and survival rates were calculated with Kaplan-Meier analysis. RESULTS: Treatment with the ITD resulted in lower intratracheal inspiratory pressure in the treatment group (-11+/-0.4 mmHg versus -4+/-0.7 mmHg, respectively, P<0.005). Mean arterial pressure after 30 min of treatment with the ITD was higher in the treatment group (61.1+/-5.5 mmHg versus 37.4+/-2.1 mmHg, respectively, P<0.005). All pigs in the control group died within 65 min of the initial bleed, whereas 7/8 (87%) treated with an ITD survived for >90 min (P<0.001). During the recovery phase, 6/8 (75%) in the ITD group survived for >3h and awoke without neurological deficit; one surviving animal in the ITD group never woke up. Arterial oxygenation was not compromised in the ITD group. CONCLUSIONS: Use of an ITD improved blood pressure and short-term survival rates in a spontaneously breathing porcine model of hypovolemic hypotension.     

Use of assisted forced ventilation of the lungs in patients during prolonged respiratory therapy

A total of 338 patients were treated by prolonged forced ventilation of the lungs (AVL). The adult respiratory distress syndrome was detected in 78 patients. Control group consisted of 260 patients in need of prolonged AVL because of respiratory discomfort. Central hemodynamics was assessed by the Swan-Ganz balloon catheter. The advantages of assisted AVL are decreased resistance of the patient to the respirator, no suppression of muscular activity, decreased intrathoracic pressure, a lower probability of respiratory alkalosis or acidosis, and possibility of inspiration end positive pressure during spontaneous respiration. The shortcomings are poor reaction of trigger mechanisms to the beginning of a spontaneous act and rapid exhaustion of respiratory muscles in grave weak patients.     

Quality of chest compressions during 10min of single-rescuer basic life support with different compression: ventilation ratios in a manikin model

INTRODUCTION: Good quality basic life support (BLS) improves outcome during cardiac arrest. As fatigue may reduce BLS performance over time we wanted to examine the quality of chest compressions in a single-rescuer scenario during prolonged BLS with different compression:ventilation ratios (C:V ratios). MATERIAL AND METHODS: Professional paramedics were asked to perform single-rescuer BLS with C:V ratios of 15:2, 30:2 and 50:2 for 10 min each in random order. A Laerdal Medical Resusci Anne Simulator with PC Skillreporting System was used for BLS quality analysis. Total number of chest compressions, compression depth and compression rate were measured and the differences between the C:V ratios were analysed with repeated measures ANOVA. For analysis of fatigue, chest compression variables for each 2-min period were analysed and compared with the first 2-min period using repeated measures ANOVA. RESULTS: Altogether 50 paramedics completed the study. The mean number of chest compressions increased significantly from 604 to 770 and 862 with C:V ratios of 15:2, 30:2 and 50:2, respectively. Chest compression rate was significantly higher with C:V ratio of 15:2 compared to 30:2 and 50:2 but was above 100 per minute for all three ratios. However, the mean chest compression depth did not change significantly between the different C:V ratios. The number of chest compressions did not change significantly with time for any of the three C:V ratios. Compression depth did decline after the first 2-min period for 30:2 and 50:2 as did compression rate for all three ratios. However all were above the guideline limits for the entire test period. CONCLUSION: Increasing the C:V ratio increases the number of chest compressions during 10 min of BLS. Compression depth and compression rate were within guideline recommendations for all three ratios. We found no decline in chest compression quality below guideline recommendations during 10 min of BLS with any of the three different C:V ratios.     

Continuous chest compressions with asynchronous ventilation improve survival in a neonatal swine model of asphyxial cardiac arrest

BackgroundGuidelines for neonatal resuscitation recommend a 3:1 compression to ventilation ratio. However, this recommendation is based on expert opinion and consensus rather than strong scientific evidence. Our primary aim was to assess whether continuous chest compressions with asynchronous ventilations would increase return of spontaneous circulation (ROSC) rate and survival compared to the 3:1 chest compression to ventilation ratio.MethodsThis was a prospective, randomized, laboratory study. Twenty male Landrace-Large White pigs, aged 1–4 days with an average weight 1.650 ± 228.3 g were asphyxiated and left untreated until heart rate was less than 60 bpm or mean arterial pressure was below 15 mmHg. Animals were then randomly assigned to receive either continuous chest compressions with asynchronous ventilations (n = 10), or standard (3:1) chest compression to ventilation ratio (n = 10). Heart rate and arterial pressure were assessed every 30 s during cardiopulmonary resuscitation (CPR) until ROSC or asystole. All animals with ROSC were monitored for 4 h.ResultsCoronary perfusion pressure (CPP) at 30 s of CPR was significantly higher in the experimental group (45.7 ± 16.9 vs. 21.8 ± 6 mmHg, p < 0.001) and remained significantly elevated throughout the experiment. End-tidal carbon dioxide (ETCO₂) was also significantly higher in the experimental group throughout the experiment (23.4 ± 5.6 vs. 14.7 ± 5.9 mmHg, p < 0.001). ROSC was observed in six (60%) animals treated with 3:1 compression to ventilation ratio and nine (90%) animals treated with continuous chest compressions and asynchronous ventilation (p = 0.30). Time to ROSC was significantly lower in the experimental group (30 (30−30) vs. 60 (60–60) sec, p = 0.021). Of note, 7 (77.8%) animals in the experimental group and 1 (16.7%) animal in the control group achieved ROSC after 30 s (0.02). At 4 h, 2 (20%) animals survived in the control group compared to 7 (70%) animals in the experimental group (p = 0.022).ConclusionContinuous chest compressions with asynchronous ventilations significantly improved CPP, ETCO₂, time to ROSC, ROSC at 30 s and survival in a porcine model of neonatal resuscitation.     

Feasibility and effects of transcutaneous phrenic nerve stimulation combined with an inspiratory impedance threshold in a pig model of hemorrhagic shock

OBJECTIVE: Intrathoracic pressure changes are of particular importance under hypovolemic conditions, especially when central venous blood pressure is critically low. Accordingly, the purpose of this study was to assess the feasibility of transcutaneous phrenic nerve stimulation, used in conjunction with an inspiratory impedance threshold, on hemodynamic variables during hemorrhagic shock. DESIGN: Prospective, randomized laboratory investigation using a porcine model for measurement of hemodynamic variables, left and right ventricular diameter, and transmitral, transpulmonary, and transaortic blood flow employing transesophageal echo-Doppler technique. SETTING: University hospital laboratory. SUBJECTS: Thirteen female pigs weighing 28-36 kg. INTERVENTIONS: The anesthetized pigs were subjected to profound hemorrhagic shock by withdrawal of 55% of estimated blood volume over 20 mins. After a 10-min recovery period, the diaphragm was stimulated with a prototype transcutaneous phrenic nerve stimulator at a rate of ten per minute while the airway was intermittently occluded with an inspiratory threshold valve between positive pressure ventilations. Hemodynamic variables were monitored for 30 mins. MEASUREMENTS AND MAIN RESULTS: Phrenic nerve stimulation in combination with the inspiratory threshold valve significantly (p <.001) improved right and left ventricular diameter compared with hypovolemic shock values by 34 +/- 2.5% and 20 +/- 2.5%, respectively. Moreover, phrenic nerve stimulation together with the inspiratory threshold valve also increased transaortic, transpulmonary, and transmitral valve blood flow by 48 +/- 6.6%, 67 +/- 13.3, and 43 +/- 8.2%, respectively (p <.001 for comparisons within group). Mean +/- sem coronary perfusion and systolic aortic blood pressures were also significantly (p <.001) higher compared with values before stimulation (30 +/- 2 vs. 20 +/- 2 mm Hg, and 37 +/- 2 vs. 32 +/- 3 mm Hg, respectively). CONCLUSIONS: This feasibility study suggests that phrenic nerve stimulation with the inspiratory threshold valve may improve cardiac preload and, subsequently, key hemodynamic variables in porcine model of severe hemorrhagic shock.     

Chest compressions during ventilation in out-of-hospital cardiopulmonary resuscitation cause fragmentation of the airflow

IntroductionWhen a patient suffers an out-of-hospital cardiac arrest, ventilation and chest compressions are often given simultaneously during cardiopulmonary resuscitation. These simultaneous chest compressions may cause a fragmentation of the airflow, which may lead to an ineffective ventilation. This study focusses on the occurrence and quantification of this fragmentation and its effect on ventilation.Materials and methodsThis study is a single-center observational study, held at Ghent University Hospital. A custom-built bidirectional flow sensor was used to quantify the volumes of ventilation. Adult cardiac arrest patients who were prehospitally intubated and resuscitated by the medical emergency team were eligible for inclusion. Data of the patients who were ventilated and received simultaneous chest compressions, was used to calculate the volumes of ventilation and the amount and volumes of fragmentation. All data in this study is reported as mean (standard deviation; range).ResultsData of 10 patients (7 male) with a mean age of 71 years (14;51–87) was used in this study. The mean ventilation frequency was 12/min (2;9–16), the mean minute volume and tidal volume were respectively 6.21 L (1.51;3.79–8.15) and 514 mL (99;422–682). Fragmentation of the airflow was observed in all patients, with an average of 3 (1;2–5) fragments per inspiration and a mean volume of 214 mL (65;112–341) per fragment.Discussion and conclusionChest compressions during ventilation caused fragmentation of the airflow in all patients. There was wide variation in the number and volume of the fragments between patients. The importance of quantification of airflow volumes and the effect fragmentation of the airflow on the efficacy of ventilation can be essential in improving cardiopulmonary resuscitation techniques and therefore needs further investigation.     

252例电视胸腔镜手术回顾性分析

目的探讨预防电视胸腔手术（VATS）并发症的方法及电视胸腔镜手术在胸外科领域的应用前景。方法回顾分析1997年6月-2006年2月252例行VATS手术患者的临床资料，术式包括肺大疱切除122例，纵隔肿瘤切除4例，食管肿瘤切除12例，肺叶切除或楔形切除65例，胸外伤止血和／或肺叶修补术18例，胸膜疾病活检术8例，手汗症双侧颈胸交神经节切除23例。结果252例VATS手术顺利，3例自发性气胸术后复发，4例术后持续漏气，手术并发症发生率2．8％（7／252）。结论VATS比传统胸外科手术具有诸多无法比拟的优点．在胸心外科有广阔的应用空间．但一次性耗材价格昂贵，限制其临床广泛应用。     

Effects of an impedance threshold valve upon hemodynamics in Standard CPR: studies in a refined computational model

An impedance threshold valve (ITV) is a new airway adjunct for resuscitation that permits generation of a small vacuum in the chest during the recoil phase of chest compression. OBJECTIVES: To explore in detail the expected magnitude and the hemodynamic mechanisms of circulatory augmentation by an ITV in Standard CPR. METHOD: A 14-compartment mathematical model of the human cardiopulmonary system--upgraded to include applied chest compression force, elastic recoil of the chest wall, anatomic details of the heart and lungs, and the biomechanics of mediastinal compression--is exercised to explore the conditions required for circulatory augmentation by an ITV during various modes of CPR. RESULTS: The ITV augments systemic perfusion pressure by about 5 mmHg compared to any particular baseline perfusion pressure without the ITV. When baseline perfusion is low, owing to either diminished chest compression force, the existence of a thoracic pump mechanism of blood flow, or the presence of an effective compression threshold, then the relative improvement produced by an ITV is significant. With an ITV the heart expands into soft pericardiac tissue, which makes the heart easier to compress. CONCLUSIONS: An ITV can augment perfusion during CPR. The observed effectiveness of ITVs in the laboratory and in the clinic suggests a thoracic pump mechanism for Standard CPR, and perhaps also an effective compression threshold that must be exceeded to generate blood flow by external chest compression.     

Influence of an end inspiratory pause on pulmonary ventilation, gas distribution, and lung perfusion during artificial ventilation

Using a constant tidal volume and ventilatory frequency, anesthetized piglets were ventilated with a new tidal volume ventilator. A short inspiratory time without a pause (10% of breathing cycle) was compared with a longer inspiratory time with a pause (33%) both with and without bronchial obstruction. Mechanics of ventilation, pulmonary ventilation, gas exchange, gas distribution, and lung perfusion were measured. The longer inspiratory time with a pause resulted in lower peak airway and end inspiratory pressures and a higher total compliance. Dead space/tidal volume ratio was reduced and the RQ was increased. While the cranial pulmonary fields were less well ventilated, the right caudal field was better ventilated. In the presence of bronchial obstruction, better alveolar ventilation was achieved when an end inspiratory pause was added. The results emphasize the importance of static end inspiratory tracheal conditions although the tidal volumes were kept unchanged.