Changes In Lung Compliance Research Articles

Ultrasound assessment of ex vivo lung tissue properties using a fluid-filled negative pressure bath.

A relationship between tendon stress and strain and ultrasonic echo intensity has previously been defined in tendons, demonstrating a correlation between tissue stiffness and echo intensity. An analogous relationship between volume-dependent pressure changes and echo intensity changes in inflating lungs would indicate a correlation between lung compliance and echo intensity. Lung compliance is an important metric to diagnose pathologies which affect lung tissue mechanics, such as emphysema and cystic fibrosis. The goal of this study is to demonstrate a correlation between ultrasound echo intensity and lung tissue mechanics in an ex vivo model using a fluid-filled negative pressure bath design which provides a controlled environment for ultrasonic and mechanical measurements. Lungs from 4 male Sprague-Dawley rats were removed and mechanically tested via inflation and deflation in a negative pressure chamber filled with hetastarch. Specific volumes (1, 2, 3, and 4 mL) were removed from the chamber using a syringe to create negative pressure, which resulted in lung inflation. A pressure transducer recorded the pressure around the lungs. From these data, lung compliance was calculated. Ultrasound images were captured through the chamber wall to determine echo intensity (grayscale brightness in the ultrasound image), which was then related to mechanical parameters. Ultrasound images of the lung were successfully captured through the chamber wall with sufficient resolution to deduce echo intensity changes in the lung tissue. Echo intensity (0-255 scale) increased with volumetric changes (18.4 ± 5.5, 22.6 ± 5.1, 26.1 ± 7.5, and 42.9 ± 19.5 for volumetric changes of 1, 2, 3, and 4 mL) in a pattern similar to pressure (-6.8 ± 1.7, -6.8 ± 1.4, -9.4 ± 0.7, and -16.9 ± 6.8 cm H2O for 1, 2, 3, and 4 mL), reflecting changes in lung compliance. Measured rat lung tissue compliance was comparable to reported values from ex vivo lungs (0.178 ± 0.067, 0.378 ± 0.051, 0.427 ± 0.062, and 0.350 ± 0.160 mL/cm H20 for 1, 2, 3, and 4 mL), supporting proof of concept for the experimental method. Changes in echo intensity reflected changes in lung compliance in this ex vivo model, thus, supporting our hypothesis that the stiffness-related changes in echo intensity originally seen in tendon can be similarly detected in lung tissue. The presented ultrasound-based methods allowed measurement of local lung tissue compliance in a controlled environment, however, the methods could be expanded to facilitate both ex vivo and in vivo studies.

Maternal tobacco smoke exposure programs increased lung static compliance in female rat offspring (715.5)

Background: Intrauterine growth restriction (IUGR) increases the risk for postnatal lung disease, in part, through programmed alterations in gene expression patterns. A consequence of altered gene expression programs in the developing lung is changes in lung compliance and resistance. In a rat model of surgically‐induced IUGR (sIUGR), male rat pups have increased compliance and decreased resistance, while female rat pups are unaffected. Maternal tobacco smoke (MTS) exposure also results in IUGR. However, the effects of MTS‐induced IUGR on lung compliance and resistance are unknown.Objective: We hypothesized that MTS exposure alters lung compliance and resistance in rat offspring.Design/Methods: Maternal rats received tobacco smoke exposure from gestational day 11 to term. Pups were delivered at term and cross‐fostered to a control dam until they were weaned at postnatal day 21 (d21). At d21, rats were anesthetized and paralyzed, and closed chest, lung static compliance and lung resistance mechanics were measured using the FlexiVent System.Results: MTS significantly increased lung compliance in female (118 ± 4%, p=0.02), but not male rat offspring. Lung resistance was not affected by MTS in either male or female rat offspring.Conclusion: MTS‐induced IUGR leads to a long‐term increase in lung compliance in female rats. We previously showed that increased compliance in male sIUGR rat pups is accompanied by decreased elastin mRNA variant expression. We therefore speculate that MTS‐induced increased compliance in female rat pups will be accompanied by decreased elastin mRNA variant expression.Grant Funding Source: Supported by the APS STRIDE Fellowship Award

Intersystem Relationships of Respiration and Hemodynamics in the Initial Period of Postural Effects

We studied the dependence of parameters of lung volumes and the elastic properties of the lungs on changes in the central hemodynamics occurring in the initial period of passive postural changes in cats. It was found that transition from the horizontal to head-up and head-down tilting was accompanied by opposite hemodynamic changes in the cranial and caudal parts of the body. Changes in lung compliance and functional residual capacity of the lungs were opposite and linearly depended on the intensity of hemodynamic shifts, which indicates passive character of the primary disorders primarily determined by a physical factor, gravity-dependent redistribution of body fluids.

Dynamic and Volumetric Variables Reliably Predict Fluid Responsiveness in a Porcine Model with Pleural Effusion

BackgroundThe ability of stroke volume variation (SVV), pulse pressure variation (PPV) and global end-diastolic volume (GEDV) for prediction of fluid responsiveness in presence of pleural effusion is unknown. The aim of the present study was to challenge the ability of SVV, PPV and GEDV to predict fluid responsiveness in a porcine model with pleural effusions.MethodsPigs were studied at baseline and after fluid loading with 8 ml kg−1 6% hydroxyethyl starch. After withdrawal of 8 ml kg−1 blood and induction of pleural effusion up to 50 ml kg−1 on either side, measurements at baseline and after fluid loading were repeated. Cardiac output, stroke volume, central venous pressure (CVP) and pulmonary occlusion pressure (PAOP) were obtained by pulmonary thermodilution, whereas GEDV was determined by transpulmonary thermodilution. SVV and PPV were monitored continuously by pulse contour analysis.ResultsPleural effusion was associated with significant changes in lung compliance, peak airway pressure and stroke volume in both responders and non-responders. At baseline, SVV, PPV and GEDV reliably predicted fluid responsiveness (area under the curve 0.85 (p<0.001), 0.88 (p<0.001), 0.77 (p = 0.007). After induction of pleural effusion the ability of SVV, PPV and GEDV to predict fluid responsiveness was well preserved and also PAOP was predictive. Threshold values for SVV and PPV increased in presence of pleural effusion.ConclusionsIn this porcine model, bilateral pleural effusion did not affect the ability of SVV, PPV and GEDV to predict fluid responsiveness.

Respiratory and hemodynamic effects of a stepwise lung recruitment maneuver in pediatric ARDS: A feasibility study

Little is known about the efficacy and safety of recruitment maneuvers (RMs) in pediatric patients with acute respiratory distress syndrome (ARDS). We therefore assessed the effects on gas exchange and lung mechanics and the possible detrimental effects of a sequential lung RMs and decremental positive end-expiratory pressure (PEEP) titration in pediatric ARDS patients. We enrolled patients <15 years of age with ARDS, progressive hypoxemia, <72 hr of mechanical ventilation, and hemodynamic stability. A step-wise RM and decremental PEEP trial were performed. Safety was evaluated as the occurrence of hypotension and low pulse oxymeter oxygen saturation during the maneuver and development of airleaks after. Efficacy was evaluated as changes in lung compliance (Cdyn ) and gas exchange 1, 12, and 24 hr after the RM. We included 25 patients, of median age 5 (1-16) months, median weight 7.0 (4.1-9.2) kg, median PaO2 /FIO2 117 (96-139), and median Cdyn 0.48 (0.41-0.68) ml/cmH2 O/kg at baseline. Thirty RM were performed, with all completed successfully. No airleaks developed. Mild hypotension was detected during four procedures. Following RM, Cdyn , and PaO2 /FIO2 increased significantly (P < 0.01 each), without changes in PaCO2 (P = 0.4). A >25% improvement in lung function (Cdyn or PaO2 /FIO2 ) was observed after 90% of the RM procedures. Gas exchange worsening over the next 24 hr resulted in HFOV use in 36% of patients, while the remaining subjects sustained improvements in oxygenation at 12 and 24 hr. The 28-day mortality rate was 16%. Sequential RMs were safe and well tolerated in hemodynamically stable children with ARDS. RMs and a decremental PEEP trial may improve lung function in pediatric patients with ARDS and severe hypoxemia.

Neuromuscular Blockade and Lung Function during Resuscitation of Infants with Congenital Diaphragmatic Hernia

Background: There is no consensus or evidence as to whether a neuromuscular blocking agent should be used during the initial resuscitation of infants with congenital diaphragmatic hernia (CDH) in the labour ward. Objective: To determine if administration of a neuromuscular blocking agent affected the lung function of infants with CDH during their initial resuscitation in the labour ward. Methods: Fifteen infants with CDH were studied (median gestational age 38 weeks, range 34–41; birth weight 2,790 g, range 1,780–3,976). Six infants had undergone feto-endotracheal occlusion (FETO). Flow, airway pressure, tidal volume and dynamic lung compliance changes were recorded using a respiratory function monitor (NM3, Respironics). Twenty inflations immediately before, immediately after and 5 min after administration of a neuromuscular blocking agent (pancuronium bromide) were analysed. Results: The median dynamic lung compliance of the 15 infants was 0.22 ml/cm H₂O/kg (range 0.1–0.4) before and 0.16 ml/cm H₂O/kg (range 0.1–0.3) immediately after pancuronium bromide administration (p < 0.001) and remained at a similar low level 5 min after pancuronium bromide administration. The FETO compared to the non-FETO infants had a lower median dynamic compliance both before (p < 0.0001) and 5 min after pancuronium administration (p < 0.001) and required significantly longer durations of ventilation (p = 0.004), supplementary oxygen (p = 0.003) and hospitalisation (p = 0.007). Conclusions: Infants with CDH, particularly those who have undergone FETO, have a low lung compliance at birth, and this is further reduced by administration of a neuromuscular blocking agent.

Evaluation of Cytokine Levels and Pulmonary Function in Patients Undergoing Coronary Artery Bypass Graft

Systemic inflammatory response syndrome is commonly observed in coronary artery bypass grafts (CABG) with cardiopulmonary bypass (CB). The objective of this study was to evaluate the systemic and pulmonary levels of cytokines and their correlation with lung function in patients undergoing myocardial revascularization (MR) with CB. This study was approved by the Institutional Ethics Committee, and 13 patients undergoing MR with CB were evaluated. After anesthetic induction and at the end of CB, plasma and bronchoalveolar lavage levels of IL-1β, IL-6, IL-8, IL-10, and TNF-α were determined. The duration of CB and surgery, PaO(2)/FiO(2) ratio, alveolar-arterial oxygen gradient (A-a gradient), shunt, and lung compliance were evaluated. Results were submitted to analysis of variance for repeated measurements (*p < 0.05) and Spearman's correlation coefficient. We observed increased levels of cytokines in plasma and bronchoalveolar lavage after CB and a direct relationship between the increase in IL-1β and decrease in lung compliance (p = 0.0439), as well as the inverse relationship between the increase in IL-10 and a decrease in compliance (p = 0.0325). The increase in IL-6 was directly related to the duration of CB (p = 0.012), while the increase in IL-8 was directly related to the duration of surgery (p < 0.0001). Levels of interleukin-1β, IL-8, and TNF-α in bronchoalveolar lavage were higher than in plasma. There is an increase in cytokine levels in plasma and bronchoalveolar lavage after CB, as well as a correlation between increased cytokine levels and CB duration and surgery and changes in lung compliance.

Ventilación mecánica en el paciente con lesión cerebral aguda

In about 20% of patients admitted to an Intensive Care Unit (ICU) the indication of mechanical ventilation (MV) is a neurological disease. These patients have a prolonged MV stay and high mortality. The appropriate use of MV in patients with acute brain injury (ABI) is critical considering that MV by itself is able to induce or worsen an underlying lung injury. Patients with ABI have a higher risk to develop pulmonary complications. During endotracheal intubation the activation of airway reflexes should be prevented, because they may increase intracranial pressure. Tracheostomy is indicated to improve airway management and it is performed in about 33% of these patients. Indications for MV are loss of spontaneous respiratory effort, changes in lung compliance, gas exchange impairment and ventilatory failure due to muscle fatigue or neuromuscular junction dysfunction. During MV, hypoxemia should be avoided. The pC0(2) level has a critical role in cerebral blood flow regulation; therefore a normal pCO must be maintained in order to guarantee an optimal cerebral blood flow. Despite that, hypocapnia has been used in patients with increased intracranial pressure, at the present it is not recommended. Its use should be limited to the emergency management of intracranial hypertension, while the underlying cause is being treated. Non-conventional ventilatory modes as prone position ventilation, high-frequency oscillatory ventilation and extracorporeal C02 removal can be used in patients with ABI. All of them have specific risks and should be employed cautiously This paper reviews upper airway management and MV in patients with acute brain injury.

Mechanical ventilation in patients with acute brain injury

In about 20% of patients admitted to an Intensive Care Unit (ICU) the indication of mechanical ventilation (MV) is a neurological disease. These patients have a prolonged MV stay and high mortality. The appropriate use of MV in patients with acute brain injury (ABI) is critical considering that MV by itself is able to induce or worsen an underlying lung injury. Patients with ABI have a higher risk to develop pulmonary complications. During endotracheal intubation the activation of airway reflexes should be prevented, because they may increase intracranial pressure. Tracheostomy is indicated to improve airway management and it is performed in about 33% of these patients. Indications for MV are loss of spontaneous respiratory effort, changes in lung compliance, gas exchange impairment and ventilatory failure due to muscle fatigue or neuromuscular junction dysfunction. During MV, hypoxemia should be avoided. The pC0(2) level has a critical role in cerebral blood flow regulation; therefore a normal pCO must be maintained in order to guarantee an optimal cerebral blood flow. Despite that, hypocapnia has been used in patients with increased intracranial pressure, at the present it is not recommended. Its use should be limited to the emergency management of intracranial hypertension, while the underlying cause is being treated. Non-conventional ventilatory modes as prone position ventilation, high-frequency oscillatory ventilation and extracorporeal C02 removal can be used in patients with ABI. All of them have specific risks and should be employed cautiously This paper reviews upper airway management and MV in patients with acute brain injury.

Part 15: Neonatal Resuscitation

The following guidelines are an interpretation of the evidence presented in the 2010 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations 1 ). They apply primarily to newly born infants undergoing transition from intrauterine to extrauterine life, but the recommendations are also applicable to neonates who have completed perinatal transition and require resuscitation during the first few weeks to months following birth. Practitioners who resuscitate infants at birth or at any time during the initial hospital admission should consider following these guidelines. For the purposes of these guidelines, the terms newborn and neonate are intended to apply to any infant during the initial hospitalization. The term newly born is intended to apply specifically to an infant at the time of birth. Approximately 10% of newborns require some assistance to begin breathing at birth. Less than 1% require extensive resuscitative measures. 2,3 Although the vast majority of newly born infants do not require intervention to make the transition from intrauterine to extrauterine life, because of the large total number of births, a sizable number will require some degree of resuscitation. Those newly born infants who do not require resuscitation can generally be identified by a rapid assessment of the following 3 characteristics: ● Term gestation? ● Crying or breathing? ● Good muscle tone? If the answer to all 3 of these questions is “yes,” the baby does not need resuscitation and should not be separated from the mother. The baby should be dried, placed skin-to-skin with the mother, and covered with dry linen to maintain temperature. Observation of breathing, activity, and color should be ongoing. If the answer to any of these assessment questions is “no,” the infant should receive one or more of the following 4 categories of action in sequence:

The proper tidal volume target using volume guarantee ventilation in the course of neonatal respiratory distress syndrome: A crucial endpoint

Volume guarantee ventilation (VGV) is an optional ventilation mode which has become the most widely and extensively studied in the last 10 years in premature infants. Nonetheless, theoretical expected endpoints are intriguing and even though VGV has not yet become ‘the’ standard ventilation mode, a great deal of information has been acquired and stored.In our experience, VGV during the course of respiratory distress syndrome is useful and can be considered a standard ventilation mode. Weaning occurs in real time as described earlier, and synchronized intermittent positive pressure ventilation and pressure support ventilation (PSV) seem to be the preferred combined modes. Management during the acute phase requires more care since several sudden changes take place in both the lung mechanics and clinical behavior. The software is designed to protect the lung, and subsequently, sudden changes in lung compliance following iatrogenic procedures such as surfactant administration are powerfully counteracted.VGV has been extensively studied and the proposed algorithm has been found to function as planned. Although the ‘superiority’ of one method over another cannot be demonstrated, the use of new technologies require ‘a staff learning curve’ and homogeneity of treatment, while at the same time other factors, such as patient heterogeneity or illness phase, should be taken into due account.

Does the systolic pressure variation change in the prone position?

The Systolic pressure variation (SPV) is known to be a sensitive indicator of hypovolemia. However, the SPV may be elevated due to other reasons, such as changes in lung compliance or tidal volumes. Using the SPV to monitor the hemodynamic status of patients in the prone position may, therefore, be problematic due to possible effects of increased abdominal pressure on both venous return and lung compliance. The purpose of this study is to examine whether or not the SPV changes significantly when placing the patient in the prone position. The arterial pressure waveform was recorded and SPV measured in 25 patients undergoing spine surgery. Patients that were elderly (age>65 years), obese (BMI >30), or had history of lung disease (COPD, Asthma), were excluded. Measurements were taken in the supine and prone position and the results were compared using the Paired Student's t-test. A P<0.05 was considered significant. Values expressed are for mean+/-standard deviation. The SPV was 6.9+/-1.9 and 7.0+/-1.8 mmHg in the supine and prone position respectively. These two results were not statistically significant. This study is important because it shows for the first time that the SPV does not change significantly in the prone position, and may therefore continue to be used as an indicator of the volume status. It also would appear to indicate that our methods for protecting the chest and abdomen in the prone position are effective.

Influence Of Left Ventricular Diastolic Function On Ventilatory Responses During Exercise In Healthy Individuals

Healthy aging is associated with changes in left ventricular (LV) diastolic function, namely a prolongation of LV relaxation and increased filling pressures. This could influence ventilation through afferent cardiac pulmonary receptors sensitive to stretch or pressure and/or to changes in lung compliance. Such cardio-pulmonary interdependence may be accentuated with exercise. PURPOSE: To determine if indices of LV diastolic function influence ventilation, breathing pattern and gas exchange during exercise in healthy adults, and to determine if these associations are age related. METHODS: 103 adults (age: 50±2, range 22-76yr, 42 females, VO2peak: 34.8±0.8 ml/kg/min, FEV1: 105±1 %pred) underwent echocardiography and cardiopulmonary exercise testing. Isovolumic relaxation time (IVRT) and the ratio of peak early mitral inflow velocity to peak early mitral annular velocity (E/E') were used as indices of LV relaxation and filling pressure. Respiratory rate (RR), tidal volume (VT), ventilation (VE), all indexed to individual vital capacities (VC), as well as ventilatory efficiency (VE/VCO2) and VT/TI, an index of VE drive, were obtained during exercise. RESULTS: Age was positively correlated with IVRT and E/E' (r=0.32, 0.58, p<0.001). An increase in LV filling pressure was positively associated with VE/VC at a matched submaximal workload (r=0.21, p<0.05), and with RR/VC and VE/VCO2 at peak exercise (r=0.21, 0.26, p<0.05). Prolonged LV relaxation was associated with VE/VC, VE/VCO2 and VT/TI at the matched workload (r=0.35, 0.26, 0.21, p<0.05), and with RR/VC, VT/VC and VE/VCO2 at peak exercise (r=-0.22, 0.23, 0.22, p<0.05). The relationship between diastolic function and ventilatory function was not independent of age at the submaximal workload. The associations between RR/VC and LV filling pressure and relaxation, as well as the association between VE/VC and filling pressure were independent of age at peak exercise. CONCLUSION: Resting measures of LV diastolic function are associated with breathing pattern, gas exchange and ventilation, however only measures of breathing pattern at peak exercise appeared to be associated with diastolic function independently of age. NIH Grant HL71478.

Do New Anesthesia Ventilators Deliver Small Tidal Volumes Accurately During Volume-Controlled Ventilation?

During mechanical ventilation of infants and neonates, small changes in tidal volume may lead to hypo- or hyperventilation, barotrauma, or volutrauma. Partly because breathing circuit compliance and fresh gas flow affect tidal volume delivery by traditional anesthesia ventilators in volume-controlled ventilation (VCV) mode, pressure-controlled ventilation (PCV) using a circle breathing system has become a common approach to minimizing the risk of mechanical ventilation for small patients, although delivered tidal volume is not assured during PCV. A new generation of anesthesia machine ventilators addresses the problems of VCV by adjusting for fresh gas flow and for the compliance of the breathing circuit. In this study, we evaluated the accuracy of new anesthesia ventilators to deliver small tidal volumes. Four anesthesia ventilator systems were evaluated to determine the accuracy of volume delivery to the airway during VCV at tidal volume settings of 100, 200, and 500 mL under different conditions of breathing circuit compliance (fully extended and fully contracted circuits) and lung compliance. A mechanical test lung (adult and infant) was used to simulate lung compliances ranging from 0.0025 to 0.03 L/cm H(2)O. Volumes and pressures were measured using a calibrated screen pneumotachograph and custom software. We tested the Smartvent 7900, Avance, and Aisys anesthesia ventilator systems (GE Healthcare, Madison, WI) and the Apollo anesthesia ventilator (Draeger Medical, Telford, PA). The Smartvent 7900 and Avance ventilators use inspiratory flow sensors to control the volume delivered, whereas the Aisys and Apollo ventilators compensate for the compliance of the circuit. We found that the anesthesia ventilators that use compliance compensation (Aisys and Apollo) accurately delivered both large and small tidal volumes to the airway of the test lung under conditions of normal and low lung compliance during VCV (ranging from 95.5% to 106.2% of the set tidal volume). However, the anesthesia ventilators without compliance compensation were less accurate in delivering the set tidal volume during VCV, particularly at lower volumes and lower lung compliances (ranging from 45.6% to 100.3% of the set tidal volume). Newer generation anesthesia machine ventilators that compensate for breathing circuit compliance and for fresh gas flow are able to deliver small tidal volumes accurately to the airway under conditions of normal and low lung compliance during volume-controlled ventilation. Accurate VCV may be a useful alternative to PCV, as volume is guaranteed when lung compliance changes, and new strategies such as small volume/lung protective ventilation become possible in the operating room.

Use of Respiratory Inductance Plethysmography to Monitor Changes in Lung Compliance and Resistance in Allergic Asthma

Use of Respiratory Inductance Plethysmography to Monitor Changes in Lung Compliance and Resistance in Allergic Asthma

Proteoglycans and pathophysiology

ventilation-induced lung injury (VILI) is an important clinical entity whose pathophysiology is incompletely understood. The article by Moriondo and coworkers ([14][1]) in the Journal of Applied Physiology offers new insights into potential mechanistic pathways. These authors report that one of the

Hyperoxia-induced Tissue Hypoxia

Hyperoxia-induced Tissue Hypoxia

The neutrophil in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a complex, heterogeneous collection of conditions characterized by irreversible expiratory airflow limitation. The disease involves a multifaceted progressive inflammatory process leading to the development of mucus hypersecretion, tissue destruction, and disruption to the normal repair and defense mechanisms. The result is increased resistance to airflow in small conducting airways, change in lung compliance, and the premature collapse of airways during expiration that leads to air trapping. Neutrophils are necessary in healthy lungs; they are an important component of innate immunity, protecting healthy individuals against infection. However, in COPD, they play a role in the destructive processes that characterize the disease. They can be responsible for significant damage when they accumulate at sites of inflammation and are harmful to healthy tissue. In recent years, increased understanding of the role of neutrophils has led to improved knowledge of the pathogenesis of COPD and allowed new avenues of treatment to be investigated.

Comparison between effects of intravenous and nebulized histamine in guinea pigs: Correlation between changes in respiratory mechanics and exhaled nitric oxide

Nitric oxide (NO) is a marker of airway inflammation in humans, despite not having effects on basal bronchial tone. Inhibition of NO synthesis can lead to enhanced airway reactivity in humans and it is therefore of importance to understand how bronchial provocation can affect endogenous NO. Presently, we have studied the role of exhaled nitric oxide in airway reactivity by measuring changes in pulmonary mechanics in response to histamine in anaesthetized guinea pigs. Two groups were challenged i.v. and four groups were challenged by aerosol at different doses. One of the i.v. and one of the aerosol groups received an inhibitor of NO synthesis, N ω -nitro- l-arginine methyl ester ( l-NAME), to reduce endogenous production of NO before histamine challenge. All animals with intact NO production showed a decrease in exhaled nitric oxide after challenge. There were positive correlations between the peak in exhaled nitric oxide and pulmonary resistance, and between the decrease in exhaled nitric oxide and lung compliance. l-NAME pretreatment increased the reactivity to aerosolized histamine but not to i.v. histamine. We conclude that the different ways of administration elicit different response patterns of exhaled nitric oxide, resistance, and compliance, even when compared at similar insufflation pressure changes. The effects of l-NAME suggest that, although different mechanisms might be responsible for the changes in pulmonary mechanics, inhibition of endogenous NO enhances decrements in pulmonary function when histamine is administered in an aerosol. The close relationship between changes in exhaled nitric oxide and changes in lung compliance and pulmonary resistance merits further studies on the relationship between NO and airway reactivity.

Contributions of vascular flow and pulmonary capillary pressure to ventilator-induced lung injury

To evaluate the influence of vascular flow on ventilator-induced lung injury independent of vascular pressures. Laboratory study. Hospital laboratory. Thirty-two New Zealand White rabbits. Thirty-two isolated perfused rabbit lungs were allocated into four groups: low flow/low pulmonary capillary pressure; high flow/high pulmonary capillary pressure; low flow/high pulmonary capillary pressure, and high flow/low pulmonary capillary pressure. All lungs were ventilated with peak airway pressure 30 cm H2O and positive end-expiratory pressure 5 cm H2O for 30 mins. Outcome measures included frequency of gross structural failure (pulmonary rupture), pulmonary hemorrhage, edema formation, changes in lung compliance, pulmonary vascular resistance, and pulmonary ultrafiltration coefficient. Lungs exposed to high pulmonary vascular flow ruptured more frequently, displayed more hemorrhage, developed more edema, suffered larger decreases in compliance, and had larger increases in vascular resistance than lungs exposed to low vascular flows (p < .05 for each pairwise comparison between groups). These findings suggest that high pulmonary vascular flows might exacerbate ventilator-induced lung injury independent of their effects on pulmonary vascular pressures.