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Fractal biological structures are pervasive throughout the plant and animal kingdoms, with the mammalian lung being a quintessential example. The lung airway and vascular trees are generated during embryogenesis from a small set of building codes similar to Turing mechanisms that create robust trees ideally suited to their functions. Whereas the blood flow pattern generated by these fractal trees has been shown to be genetically determined, the geometry of the trees has not. We explored a newly established repository providing high-resolution bronchial trees from the four most commonly studied laboratory mice (B6C3F1, BALB/c, C57BL/6 and CD-1). The data fit a fractal model well for all animals with the fractal dimensions ranging from 1.54 to 1.67, indicating that the conducting airway of mice can be considered a self-similar and space-filling structure. We determined that the fractal dimensions of these airway trees differed by strain but not sex, reinforcing the concept that airway branching patterns are encoded within the DNA. The observations also highlight that future study design and interpretations may need to consider differences in airway geometry between mouse strains. NEW & NOTEWORTHY Similar to larger mammals such as humans, the geometries of the bronchial tree in mice are fractal structures that have repeating patterns from the trachea to the terminal branches. The airway geometries of the four most commonly studied mice are different and need to be considered when comparing results that employ different mouse strains. This variability in mouse airway geometries should be incorporated into computer models exploring toxicology and aerosol deposition in mouse models.

To facilitate computational toxicology, we developed an approach for generating high-resolution lung-anatomy and particle-deposition mouse models. Major processing steps of our method include mouse preparation, serial block-face cryomicrotome imaging, and highly automated image analysis for generating three-dimensional (3D) mesh-based models and volume-based models of lung anatomy (airways, lobes, sublobes, and near-acini structures) that are linked to local particle-deposition measurements. Analysis resulted in 34 mouse models covering 4 different mouse strains (B6C3F1: 8, BALB/C: 11, C57Bl/6: 8, and CD-1: 7) as well as both sexes (16 male and 18 female) and different particle sizes [2 μm ( n = 15), 1 μm ( n = 16), and 0.5 μm ( n = 3)]. On average, resulting mouse airway models had 1,616.9 ± 298.1 segments, a centerline length of 597.6 ± 59.8 mm, and 1,968.9 ± 296.3 outlet regions. In addition to 3D geometric lung models, matching detailed relative particle-deposition measurements are provided. All data sets are available online in the lapdMouse archive for download. The presented approach enables linking relative particle deposition to anatomical structures like airways. This will in turn improve the understanding of site-specific airflows and how they affect drug, environmental, or biological aerosol deposition. NEW & NOTEWORTHY Computer simulations of particle deposition in mouse lungs play an important role in computational toxicology. Until now, a limiting factor was the lack of high-resolution mouse lung models and measured local particle-deposition information, which are required for developing accurate modeling approaches (e.g., computational fluid dynamics). With the developed imaging and analysis approach, we address this issue and provide all of the raw and processed data in a publicly accessible repository.

Most physician leaders assume their administrative role based on past achievements but with very little leadership training. In this article, leaders of the Association of Pulmonary, Critical Care, and Sleep Division Directors describe two leadership skills that are often required to effectively lead in a clinical division at an academic or community hospital setting: leading change and negotiation strategy. We adopted our discussion from the business sector and refined the approaches through our own experiences to help division leaders in leading a successful team, whether as a division chief, residency or fellowship program director, or a clinical service director. Leading any change project may include an eight-step process, starting with creating a sense of urgency and completing with anchoring the change to the organizational culture. We then review negotiation strategies, comparing positional bargaining vs principled negotiation, to create more changes and continuing growth for the division. Finally, we discuss the importance of emotional intelligence, exemplary leadership practices, and self-development that the division leader should embrace.

An academic medical career traditionally revolves around patient care, teaching, and scholarly projects. Thus, when an opportunity for a leadership role arises, such as division chief, the new leader is often unprepared with little or no formal leadership training. In this focused review, academic leaders of the Association of Pulmonary, Critical Care, and Sleep Division Directors describe several leadership concepts adapted from the business sector and apply their years of experience to aid new division chiefs with their first day on the job. The first 90 days are highlighted to include achieving early wins; performing a division-wide Strengths, Weaknesses, Opportunities, Threats analysis; establishing division rapport; redefining the division infrastructure; avoiding conflicts; and managing the relationship with the department chair. The five levels of leadership applicable to academic medicine are discussed: position, permission, production, people, and pinnacle. Finally, emotional intelligence and behavior styles crucial to leadership success are reviewed.

Purpose The purpose of this study was to evaluate quality of life (QOL), psychological function, and self-efficacy outcomes in the Anti-Arrhythmic Effects of Exercise After an ICD Trial. Methods In the Anti-Arrhythmic Effects of Exercise After an ICD Trial, 160 patients (124 men and 36 women) who had an implantable cardioverter defibrillator for primary (43%) or secondary (57%) prevention were randomized to exercise (EX, n = 84) or usual care (UC, n = 76). The EX consisted of 8 wk of home walking 1 hr/d 5 d/wk, followed by 16 wk of maintenance home walking for 150 min/wk. Adherence was determined from exercise logs, ambulatory HR recordings, and phone calls. Assessments were conducted at baseline, 8, and 24 wk for QOL: Patient Concerns Assessment and Short Form-36; anxiety: State Trait Anxiety Inventory; depression: Physician Health Questionnaire-Depression; and self-efficacy: Self-Efficacy for Walking Scale. Results Participants averaged 55 ± 12 yr of age with ejection fraction = 40.6 ± 15.7%. The EX significantly decreased depression severity (EX: 1.33 ± 0.64; UC: 1.51 ± 0.86, P = .05) and improved self-efficacy (EX: 7.65 ± 1.97; UC: 6.85 ± 2.40, P = .05) at 8 wk. There were no significant effects at 24 wk. Adherent exercisers had significant improvements in QOL, psychological, and self-efficacy outcomes at 8 and 24 wk compared with those who were nonadherent. There were no implantable cardioverter defibrillator shocks associated with exercise. Conclusions The EX conferred significant effects on depression and self-efficacy at 8 wk, without effects on QOL. Adherent exercisers experienced significant improvements in outcomes over those who were nonadherent or received UC.

Despite substantial development of sophisticated subject-specific computational models of aerosol transport and deposition in human lungs, experimental validation of predictions from these new models is sparse. We collected aerosol retention and exhalation profiles in seven healthy volunteers and six subjects with mild-to-moderate COPD (FEV1=50–80%predicted) in the supine posture. Total deposition was measured during continuous breathing of 1 and 2.9 µm-diameter particles (tidal volume of 1 L, flow rate of 0.3 L/s and 0.75 L/s). Bolus inhalations of 1 µm particles were performed to penetration volumes of 200, 500 and 800 mL (flow rate of 0.5 L/s). Aerosol bolus dispersion (H), deposition, and mode shift (MS) were calculated from these data. There was no significant difference in total deposition between healthy subjects and those with COPD. Total deposition increased with increasing particle size and also with increasing flow rate. Similarly, there was no significant difference in aerosol bolus deposition between subject groups. Yet, the rate of increase in dispersion and of decrease in MS with increasing penetration volume was higher in subjects with COPD than in healthy volunteers (H: 0.798±0.205 vs. 0.527±0.122 mL/mL, p=0.01; MS: −0.271±0.129 vs. −0.145 ±0.076 mL/mL, p=0.05) indicating larger ventilation inhomogeneities (based on H) and increased flow sequencing (based on MS) in the COPD than in the healthy group. In conclusion, in the supine posture, deposition appears to lack sensitivity for assessing the effect of lung morphology and/or ventilation distribution alteration induced by mild-to-moderate lung disease on the fate of inhaled aerosols. However, other parameters such as aerosol bolus dispersion and mode shift may be more sensitive parameters for evaluating models of lungs with moderate disease.

Of the 300 billion capillaries in the human lung, a small fraction meet normal oxygen requirements at rest, with the remainder forming a large reserve. The maximum oxygen demands of the acute stress response require that the reserve capillaries are rapidly recruited. To remain primed for emergencies, the normal cardiac output must be parceled throughout the capillary bed to maintain low opening pressures. The flow-distributing system requires complex switching. Because the pulmonary microcirculation contains contractile machinery, one hypothesis posits an active switching system. The opposing hypothesis is based on passive switching that requires no regulation. Both hypotheses were tested ex vivo in canine lung lobes. The lobes were perfused first with autologous blood, and capillary switching patterns were recorded by videomicroscopy. Next, the vasculature of the lobes was saline flushed, fixed by glutaraldehyde perfusion, flushed again, and then reperfused with the original, unfixed blood. Flow patterns through the same capillaries were recorded again. The 16-min-long videos were divided into 4-s increments. Each capillary segment was recorded as being perfused if at least one red blood cell crossed the entire segment. Otherwise it was recorded as unperfused. These binary measurements were made manually for each segment during every 4 s throughout the 16-min recordings of the fresh and fixed capillaries (>60,000 measurements). Unexpectedly, the switching patterns did not change after fixation. We conclude that the pulmonary capillaries can remain primed for emergencies without requiring regulation: no detectors, no feedback loops, and no effectors—a rare system in biology. NEW & NOTEWORTHY The fluctuating flow patterns of red blood cells within the pulmonary capillary networks have been assumed to be actively controlled within the pulmonary microcirculation. Here we show that the capillary flow switching patterns in the same network are the same whether the lungs are fresh or fixed. This unexpected observation can be successfully explained by a new model of pulmonary capillary flow based on chaos theory and fractal mathematics.

Background— Despite its salutary effects on health, aerobic exercise is often avoided after receipt of an implantable cardioverter defibrillator (ICD) because of fears that exercise may provoke acute arrhythmias. We prospectively evaluated the effects of a home aerobic exercise training and maintenance program (EX) on aerobic performance, ICD shocks, and hospitalizations exclusively in ICD recipients. Methods and Results— A total of 160 patients (124 men and 36 women) were randomly assigned who had an ICD for primary (43%) or secondary (57%) prevention to EX or usual care (UC). The primary outcome was peak oxygen consumption, measured with cardiopulmonary exercise testing at baseline and 8 and 24 weeks. EX consisted of 8 weeks of home walking for 1 h/d, 5 d/wk at 60% to 80% of heart rate reserve, followed by 16 weeks of maintenance home walking for 150 min/wk. Adherence to EX was determined from exercise logs, ambulatory heart rate recordings of exercise, and weekly telephone contacts. Patients assigned to UC received no exercise directives and were monitored by monthly telephone contact. Adverse events were identified by ICD interrogations, patient reports, and medical charts. ICD recipients averaged 55±12 years and mean ejection fraction of 40.6±15.7; all were taking β-blocker medications. EX significantly increased peak oxygen consumption (EX, 26.7±7.0 mL/kg per minute; UC, 23.9±6.6 mL/kg per minute; P =0.002) at 8 weeks, which persisted during maintenance exercise at 24 weeks (EX, 26.9±7.7 mL/kg per minute; UC, 23.4±6.0 mL/kg per minute; P Conclusions— Prescribed home exercise is safe and significantly improves cardiovascular performance in ICD recipients without causing shocks or hospitalizations. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT00522340.

The prone posture is known to have numerous effects on gas exchange, both under normal conditions and in patients with ARDS. Clinical studies have consistently demonstrated improvements in oxygenation, and a multi-center randomized trial found that, when implemented within 48 h of moderate-to-severe ARDS, placing subjects in the prone posture decreased mortality. Improvements in gas exchange occur via several mechanisms: alterations in the distribution of alveolar ventilation, redistribution of blood flow, improved matching of local ventilation and perfusion, and reduction in regions of low ventilation/perfusion ratios. Ventilation heterogeneity is reduced in the prone posture due to more uniform alveolar size secondary to a more uniform vertical pleural pressure gradient. The prone posture results in more uniform pulmonary blood flow when compared with the supine posture, due to an anatomical bias for greater blood flow to dorsal lung regions. Because both ventilation and perfusion heterogeneity decrease in the prone posture, gas exchange improves. Other benefits include a more uniform distribution of alveolar stress, relief of left-lower-lobe lung compression by the heart, enhanced secretion clearance, and favorable right-ventricular and systemic hemodynamics.

Computer models for inhalation toxicology and drug-aerosol delivery studies rely on ventilation pattern inputs for predictions of particle deposition and vapor uptake. However, changes in lung mechanics due to disease can impact airflow dynamics and model results. It has been demonstrated that non-invasive, in vivo, 4DCT imaging (3D imaging at multiple time points in the breathing cycle) can be used to map heterogeneities in ventilation patterns under healthy and disease conditions. The purpose of this study was to validate ventilation patterns measured from CT imaging by exposing the same rats to an aerosol of fluorescent microspheres (FMS) and examining particle deposition patterns using cryomicrotome imaging.Six male Sprague-Dawley rats were intratracheally instilled with elastase to a single lobe to induce a heterogeneous disease. After four weeks, rats were imaged over the breathing cycle by CT then immediately exposed to an aerosol of ∼ 1 μm FMS for ∼ 5 minutes. After the exposure, the lungs were excised and prepared for cryomicrotome imaging, where a 3D image of FMS deposition was acquired using serial sectioning. Cryomicrotome images were spatially registered to match the live CT images to facilitate direct quantitative comparisons of FMS signal intensity with the CT-based ventilation maps.Comparisons of fractional ventilation in contiguous, non-overlapping, 3D regions between CT-based ventilation maps and FMS images showed strong correlations in fractional ventilation (r = 0.888, p0.0001).We conclude that ventilation maps derived from CT imaging are predictive of the 1 μm aerosol deposition used in ventilation-perfusion heterogeneity inhalation studies.

This review provides an overview of the relationship between ventilation/perfusion ratios and gas exchange in the lung, emphasising basic concepts and relating them to clinical scenarios. For each gas exchanging unit, the alveolar and effluent blood partial pressures of oxygen and carbon dioxide (PO2andPCO2) are determined by the ratio of alveolar ventilation to blood flow (V′A/Q′) for each unit. Shunt and lowV′A/Q′ regions are two examples ofV′A/Q′ mismatch and are the most frequent causes of hypoxaemia. Diffusion limitation, hypoventilation and low inspiredPO2cause hypoxaemia, even in the absence ofV′A/Q′ mismatch. In contrast to other causes, hypoxaemia due to shunt responds poorly to supplemental oxygen. Gas exchanging units with little or no blood flow (highV′A/Q′ regions) result in alveolar dead space and increased wasted ventilation,i.e.less efficient carbon dioxide removal. Because of the respiratory drive to maintain a normal arterialPCO2, the most frequent result of wasted ventilation is increased minute ventilation and work of breathing, not hypercapnia. Calculations of alveolar–arterial oxygen tension difference, venous admixture and wasted ventilation provide quantitative estimates of the effect ofV′A/Q′ mismatch on gas exchange. The types ofV′A/Q′ mismatch causing impaired gas exchange vary characteristically with different lung diseases.

A highly automated method for the segmentation of airways in the serial block-face cryomicrotome images of rat lungs is presented. First, a point inside of the trachea is manually specified. Then, a set of candidate airway centerline points is automatically identified. By utilizing a novel path extraction method, a centerline path between the root of the airway tree and each point in the set of candidate centerline points is obtained. Local disturbances are robustly handled by a novel path extraction approach, which avoids the shortcut problem of standard minimum cost path algorithms. The union of all centerline paths is utilized to generate an initial airway tree structure, and a pruning algorithm is applied to automatically remove erroneous subtrees or branches. Finally, a surface segmentation method is used to obtain the airway lumen. The method was validated on five image volumes of Sprague-Dawley rats. Based on an expert-generated independent standard, an assessment of airway identification and lumen segmentation performance was conducted. The average of airway detection sensitivity was 87.4% with a 95% confidence interval (CI) of (84.9, 88.6)%. A plot of sensitivity as a function of airway radius is provided. The combined estimate of airway detection specificity was 100% with a 95% CI of (99.4, 100)%. The average number and diameter of terminal airway branches was 1179 and 159 μm, respectively. Segmentation results include airways up to 31 generations. The regression intercept and slope of airway radius measurements derived from final segmentations were estimated to be 7.22 μm and 1.005, respectively. The developed approach enables the quantitative studies of physiology and lung diseases in rats, requiring detailed geometric airway models.

Background Estimation of myocardial blood flow (MBF) with cardiac PET is often performed with conventional compartmental models. In this study, we developed and evaluated a physiologically and anatomically realistic axially distributed model. Unlike compartmental models, this axially distributed approach models both the temporal and the spatial gradients in uptake and retention along the capillary.

Transbronchial biopsy of peripheral lung nodules is hindered by the inability to access lesions endoluminally due to the large diameter of conventional bronchoscopes. An ultrathin scanning fiber bronchoscope has recently been developed to advance image-guided biopsy several branching generations deeper into the peripheral airways. However, navigating a potentially complex 3-D path to the region of interest presents a challenge to the bronchoscopist. An accompanying guidance system has also been developed to track the bronchoscope through the airways, and display its position and intended path on a virtual display. Intraoperative localization of the bronchoscope was achieved by combining electromagnetic tracking (EMT) and image-based tracking (IBT). An error-state Kalman filter was used to model the disagreement between the two tracking sources. The positional tracking error was reduced from 14.22 and 14.92 mm by independent EMT and IBT, respectively, to 6.74 mm using the hybrid approach. Hybrid tracking of the scope orientation and respiratory motion compensation further improved tracking accuracy and stability, resulting in an average tracking error of 3.33 mm and 10.01 degrees.

The principles of ventilation and perfusion distribution in the lung form the foundation of pulmonary physiology and remain cornerstones in caring for critically ill patients. Due to improved imaging technologies with greater spatial resolution, our understanding of the determinants of local ventilation and blood flow have evolved over the past five decades. This review provides a brief history of how the concepts governing regional ventilation and perfusion have developed and presents the most recent studies that are shaping new perspectives on the determinants of ventilation and perfusion. How these new principles apply to acute lung injury and gas exchange in the intensive care unit (ICU) are reviewed.

Long-term survival after lung transplantation is limited by acute and chronic graft rejection. Induction of immune tolerance by first establishing mixed hematopoietic chimerism (MC) is a promising strategy to improve outcomes. In a preclinical canine model, stable MC was established in recipients after reduced-intensity conditioning and hematopoietic cell transplantation from a DLA-identical donor. Delayed lung transplantation was performed from the stem cell donor without pharmacological immunosuppression. Lung graft survival without loss of function was prolonged in chimeric (n = 5) vs. nonchimeric (n = 7) recipients (por = 0.05, Fisher's test). There were histological changes consistent with low-grade rejection in 3/5 of the lung grafts in chimeric recipients ator =1 year. Chimeric recipients after lung transplantation had a normal immune response to a T-dependent antigen. Compared to normal dogs, there were significant increases of CD4+INFgamma+, CD4+IL-4+ and CD8+ INFgamma+ T-cell subsets in the blood (p0.0001 for each of the three T-cell subsets). Markers for regulatory T-cell subsets including foxP3, IL10 and TGFbeta were also increased in CD3+ T cells from the blood and peripheral tissues of chimeric recipients after lung transplantation. Establishing MC is immunomodulatory and observed changes were consistent with activation of both the effector and regulatory immune response.

We used quantitative Single Photon Emission Computed Tomography (SPECT) to study the effect of the upright posture on regional lung blood flow and ventilation. Nine (upright) plus seven (prone and supine) healthy volunteers were studied awake, breathing spontaneously. Regional blood flow and ventilation were marked in sitting upright, supine and prone postures using (113m)In-labeled macroaggregates and inhaled Technegas ((99m)Tc); both remain fixed in the lung after administration. All images were obtained while supine. In comparison with horizontal postures, both blood flow and ventilation were greater in caudal regions when upright. The redistribution was greater for blood flow than for ventilation, resulting in decreasing ventilation-to-perfusion ratios down the lung when upright. We conclude that gravity redistributes regional blood flow and ventilation in the upright posture, while the influence is much less in the supine and prone postures.

Lethal ventricular arrhythmias responsible for sudden cardiac arrest (SCA) have been attributed to multiple causes. Evidence points to the important role of the autonomic nervous system (ANS) in producing susceptibility to ventricular fibrillation in subsets of patients with heart disease. Findings demonstrate that patients at risk for cardiac arrest exhibit a reduction in parasympathetic nervous system activity. Protection against SCA may be achieved through mechanisms that increase parasympathetic tone,1 exercise being one of these therapies.2 Exercise interventions in cardiac arrest survivors who have an implantable cardioverter defibrillator (ICD) have not been well studied. Health care providers are often reluctant to prescribe exercise for this group because of the belief that it will provoke ventricular arrhythmias and cardiac arrest. Patients are often afraid to exercise because of concern for receiving an ICD shock. It has been unclear if the amount of exercise required to improve cardiopulmonary function and parasympathetic nervous system activity can be achieved in this group. However, exercise offers the potential benefit of stabilization of autonomic function and protection against future arrhythmic occurrences, in a population of cardiac patients who could potentially benefit the most.3 Exercise training is an inexpensive, non-pharmacological intervention that is essentially available to everyone. Therefore the purpose of this study was to determine the impact of 8 weeks of aerobic exercise on: 1) cardiopulmonary fitness and activity, 2) heart rate variability (HRV), 3) health outcomes, and 4) high sensitivity C-reactive protein (hsCRP) in persons who have an ICD for the secondary prevention of cardiac arrest. Follow-up at 6 months after completing the exercise program was done to determine if early effects of aerobic training were sustained.

This brief review is meant to serve as a refresher for faculty teaching respiratory physiology to medical students. The concepts of ventilation and perfusion matching are some of the most challenging ideas to learn and teach. Some strategies to consider in teaching these concepts are, first, to build from simple to more complex by starting with a single lung unit and then adding additional units representing shunting, mismatch, and deadspace. Second, use simplified analogies, such as a bathtub, to help students conceptualize new ideas. Third, introduce the concept of alveolar to arterial O2 differences and the mechanisms for increasing differences as additional lung units are added. Fourth, use the consistent thread of causes of hypoxemia through the lecture to maintain continuity and provide clinical relevance. Finally, use clinically relevant examples at each step and solidify new concepts by discussing differential diagnoses at the end of the lecture(s).

Repeated high-resolution measurements of both regional pulmonary ventilation and regional blood flow (r) have revealed that ∼6 to 10% of the summed spatial and temporal heterogeneity can be attributed to spontaneous temporal variability. To test the hypothesis that the spontaneous temporal shifts of r and r are coordinated, 12 anaesthetized juvenile pigs had pairs of colours of aerosol and intravenous fluorescent microspheres (FMS) administered simultaneously at 20 min intervals to mark r and r. The animals were killed, the lungs inflated, air-dried and cut into ∼2 cm3 cubes. The concentrations of FMS colours from each cube, representing r and r at every 20 min interval, were measured with a fluorescence spectrophotometer. The correlation between per-piece temporal shifts in r and r, calculated as the mean within-piece covariance, was positive (P < 0.001) for every temporally adjacent pair of measurements in every animal, although there were large differences in the magnitude of the mean temporal covariance among animals. The individual cubes with the most positive temporal covariance across all measurement periods usually demonstrated a large single-interval coordinated shift of r and r, with average temporal covariance observed at the other intervals. The largest between-interval shifts in r and r included equal proportions of coordinated increases and coordinated decreases. High-resolution measurements of r and r acquired over 20 min intervals reveal that the overall positive correlation between temporal changes in r and r is driven by relatively infrequent large-magnitude changes within small regions of the lung.

We thank Dr Ayoub for his questions about our recently published trial.1 In response to the first point, the difference between the usual care (UC) and exercise training and maintenance (EX) groups in their receipt of implantable cardioverter-defibrillator shocks was not statistically different during the study period. However, there were few implantable cardioverter-defibrillator shocks in both groups, limiting the power for this comparison. A slightly higher proportion of patients in …

Computational fluid dynamics (CFD) modeling is well suited for addressing species-specific anatomy and physiology in calculating respiratory tissue exposures to inhaled materials. In this study, we overcame prior CFD model limitations to demonstrate the importance of realistic, transient breathing patterns for predicting site-specific tissue dose. Specifically, extended airway CFD models of the rat and human were coupled with airway region-specific physiologically based pharmacokinetic (PBPK) tissue models to describe the kinetics of 3 reactive constituents of cigarette smoke: acrolein, acetaldehyde and formaldehyde. Simulations of aldehyde no-observed-adverse-effect levels for nasal toxicity in the rat were conducted until breath-by-breath tissue concentration profiles reached steady state. Human oral breathing simulations were conducted using representative aldehyde yields from cigarette smoke, measured puff ventilation profiles and numbers of cigarettes smoked per day. As with prior steady-state CFD/PBPK simulations, the anterior respiratory nasal epithelial tissues received the greatest initial uptake rates for each aldehyde in the rat. However, integrated time- and tissue depth-dependent area under the curve (AUC) concentrations were typically greater in the anterior dorsal olfactory epithelium using the more realistic transient breathing profiles. For human simulations, oral and laryngeal tissues received the highest local tissue dose with greater penetration to pulmonary tissues than predicted in the rat. Based upon lifetime average daily dose comparisons of tissue hot-spot AUCs (top 2.5% of surface area-normalized AUCs in each region) and numbers of cigarettes smoked/day, the order of concern for human exposures was acrolein > formaldehyde > acetaldehyde even though acetaldehyde yields were 10-fold greater than formaldehyde and acrolein.

Mechanical ventilation (MV) is frequently employed for the management of critically ill patients with respiratory failure. A major complication of mechanical ventilation (MV) is the development of ventilator-associated pneumonia (VAP), in which Staphylococcus aureus is a prominent pathogen. Moreover, previous studies suggest that MV may be an important cofactor in the development of acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS). S. aureus pulmonary infection was induced in spontaneously breathing mice (C57Bl/6) or mechanically ventilated mice to determine whether MV contributes to the development of ALI and/or systemic inflammation. The combination of MV and bacteria significantly increased the influx of neutrophils into bronchoalveolar lavage fluid (BALF), augmented pulmonary production of the proinflammatory cytokines KC, MIP-2, TNF-alpha, and IL-6, and increased alveolar-capillary permeability to proteins. MV also induced proinflammatory cytokine expression in peripheral blood, associated with extrapulmonary hepatic and renal dysfunction. Surprisingly, bacterial clearance in the lungs and extrapulmonary bacterial dissemination was not affected by MV. These data indicate that MV exacerbates both pulmonary and systemic inflammation in response to bacteria and contributes to the pathogenesis of both ALI and the multiple organ dysfunction syndrome, without necessarily affecting bacterial clearance or extra-pulmonary bacterial dissemination.

Mechanical ventilation (MV) with tidal volumes of 10–12 ml/kg is considered safe in the absence of acute lung injury (ALI). However, recent studies show that, when lung injury is already present, tidal volumes of this magnitude increase inflammation and injury in the lungs. We hypothesized that MV with tidal volumes of 10-ml/kg can also function as a cofactor in the initiation of ALI by modulating the transcriptional response to bacterial products. To test this hypothesis, we developed a mouse model in which MV did not independently cause inflammation or injury but augmented the inflammatory response to low-dose aspirated LPS and promoted development of ALI. We analyzed gene expression in lungs from 24 mice assigned to four different groups: control, MV only, intratracheal LPS only, and MV + LPS. There were twice as many differentially regulated genes in the MV + LPS group compared with the LPS-only group and 10 times as many differentially regulated genes compared with the MV-only group. For genes up-regulated by LPS treatment alone, the addition of MV further augmented expression. Cytokine concentrations in bronchoalveolar lavage fluid and tissue distribution of an intracellular protein, GADD45-γ, correlated with mRNA levels. We conclude that MV with conventional tidal volumes enhanced the transcriptional response to LPS and promoted development of ALI.

Hypoxic pulmonary vasoconstriction (HPV) is known to affect regional pulmonary blood flow distribution. It is unknown whether lungs with well-matched ventilation (V̇)/perfusion (Q̇) have regional differences in the HPV response. Five prone pigs were anesthetized and mechanically ventilated (positive end-expiratory pressure = 2 cmH2O). Two hypoxic preconditions [inspired oxygen fraction (FiO2) = 0.13] were completed to stabilize the animal's hypoxic response. Regional pulmonary blood Q̇ and V̇ distribution was determined at various FiO2 (0.21, 0.15, 0.13, 0.11, 0.09) using the fluorescent microsphere technique. Q̇ and V̇ in the lungs were quantified within 2-cm3 lung pieces. Pieces were grouped, or clustered, based on the changes in blood flow when subjected to increasing hypoxia. Unique patterns of Q̇ response to hypoxia were seen within and across animals. The three main patterns (clusters) showed little initial difference in V̇/Q̇ matching at room air where the mean V̇/Q̇ range was 0.92–1.06. The clusters were spatially located in cranial, central, and caudal portions of the lung. With decreasing FiO2, blood flow shifted from the cranial to caudal regions. We determined that pulmonary blood flow changes, caused by HPV, produced distinct response patterns that were seen in similar regions across our prone porcine model.

Hypoxic pulmonary vasoconstriction (HPV) is thought to protect gas exchange by decreasing perfusion to hypoxic regions. However, with global hypoxia, non-uniformity in HPV may cause over-perfusion to some regions, leading to high-altitude pulmonary edema. To quantify the spatial distribution of HPV and regional P O 2 ( P R O 2 ) among small lung regions (∼2.0 cm3), five prone beagles (∼8.3 kg) were anesthetized and ventilated (PEEP ∼ 2 cm H2O) with an F I O 2 of 0.21, then 0.50, 0.18, 0.15, and 0.12 in random order. Regional blood perfusion (Q), ventilation (VA) and calculated P R O 2 were obtained using iv infusion of 15 μm and inhalation of 1 μm fluorescent microspheres. Lung pieces were clustered by their relative blood flow response to each F I O 2 . Clusters were shown to be spatially grouped within animals and across animals. Lung piece resistance increased as P R O 2 decreased to 60–70 mmHg but dropped at P R O 2 ’ s 60 mmHg. Regional ventilation changed little with hypoxia. HPV varied more in strength of response, rather than P R O 2 response threshold. In initially homogeneous VA/Q lungs, we conclude that HPV response is heterogeneous and spatially clustered.

Hypoxic pulmonary vasoconstriction (HPV) serves to maintain optimal gas exchange by decreasing perfusion to hypoxic regions. However, global hypoxia and nonuniform HPV may result in overperfusion of poorly constricted regions leading to local edema seen in high-altitude pulmonary edema. To quantify the spatial distribution of HPV and its response to regional Po2 (PrO2) among small lung regions, five pigs were anesthetized and mechanically ventilated in the supine posture. The animals were ventilated with an inspired O2 fraction (FiO2) of 0.50 and 0.21 and then (in random order) 0.15, 0.12, and 0.09. Regional blood flow (Q̇) and alveolar ventilation (V̇a) were measured by using intravenous infusion of 15 μm and inhalation of 1-μm fluorescent microspheres, respectively. PrO2 was calculated for each piece at each FiO2. Lung pieces differed in their Q̇ response to hypoxia in a manner related to their initial V̇a/Q̇ with FiO2 = 0.21. Reducing FiO2 < 0.15 decreased Q̇ to the initially high V̇a/Q̇ (higher PrO2) regions and forced Q̇ into the low V̇a/Q̇ (dorsal-caudal) regions. Resistance increased in most lung pieces as PrO2 decreased, reaching a maximum resistance when PrO2 is between 40 and 50 Torr. Local resistance decreased at Pro2 < 40 Torr. Pieces were statistically clustered with respect to their relative Q̇ response pattern to each FiO2. Some clusters were shown to be spatially organized. We conclude that HPV is spatially heterogeneous. The heterogeneity of Q̇ response may be related, in part, to the heterogeneity of baseline V̇a/Q̇.

We have developed a new quantitative single-photon-emission computed tomography (SPECT) method that uses113mIn-labeled albumin macroaggregates and Technegas (99mTc) to estimate the distributions of regional ventilation and perfusion for the whole lung. The multiple inert-gas elimination technique (MIGET) and whole lung respiratory gas exchange were used as physiological evaluations of the SPECT method. Regional ventilation and perfusion were estimated by SPECT in nine healthy volunteers during awake, spontaneous breathing. Radiotracers were administered with subjects sitting upright, and SPECT images were acquired with subjects supine. Whole lung gas exchange of MIGET gases and arterial Po2and Pco2gases was predicted from estimates of regional ventilation and perfusion. We found a good agreement between measured and SPECT-predicted exchange of MIGET and respiratory gases. Correlations ( r2) between SPECT-predicted and measured inert-gas excretions and retentions were 0.99. The method offers a new tool for measuring regional ventilation and perfusion in humans.

Respiratory sinus arrhythmia (RSA) may be associated with improved efficiency of pulmonary gas exchange by matching ventilation to perfusion within each respiratory cycle. Respiration rate, tidal volume, minute ventilation (V˙e), exhaled carbon dioxide (V˙co 2), oxygen consumption (V˙o 2), and heart rate were measured in 10 healthy human volunteers during paced breathing to test the hypothesis that RSA contributes to pulmonary gas exchange efficiency. Cross-spectral analysis of heart rate and respiration was computed to calculate RSA and the coherence and phase between these variables. Pulmonary gas exchange efficiency was measured as the average ventilatory equivalent of CO2(V˙e/V˙co 2) and O2(V˙e/V˙o 2). Across subjects and paced breathing periods, RSA was significantly associated with CO2 (partial r = −0.53, P = 0.002) and O2 (partial r = −0.49, P = 0.005) exchange efficiency after controlling for the effects of age, respiration rate, tidal volume, and average heart rate. Phase between heart rate and respiration was significantly associated with CO2 exchange efficiency (partial r = 0.40, P = 0.03). These results are consistent with previous studies and further support the theory that RSA may improve the efficiency of pulmonary gas exchange.

Patients with acute respiratory distress syndrome have increased lung tissue weight and therefore an increased hydrostatic pressure gradient down the lung. Also, they have a better arterial oxygenation in prone (face down) than in supine (face up) posture. We hypothesized that this effect of the direction of gravity also existed in healthy humans, when increased hydrostatic gradients were induced by hypergravity. Ten healthy subjects were studied in a human centrifuge while exposed to 1 or 5 G in anterio-posterior (supine) or posterio-anterior (prone) direction. We measured blood gases using remote-controlled sampling and gas exchange by mass spectrometry. Hypergravity led to marked impairments of arterial oxygenation in both postures and more so in supine posture. At 5 G, the arterial oxygen saturation was 84.6 +/- 1.2 % (mean +/- S.E.M.) in supine and 89.7 +/- 1.4 % in prone posture (P < 0.001 for supine vs. prone). Ventilation and alveolar PO2 were increased at 5 G and did not differ between postures. The alveolar-to-arterial PO2 difference increased at 5 G to 8.0 +/- 0.2 kPa and 6.6 +/- 0.3 kPa in supine and prone postures (P = 0.003). Arterial oxygenation was less impaired in prone during hypergravity due to a better-preserved alveolo-arterial oxygen transport. We speculate that mammals have developed a cardiopulmonary structure that favours function with the gravitational vector in the posterio-anterior direction.

A quantitative dual-isotope single-photon emis- sion tomography (SPET) technique for the assessment of lung ventilation (V) and perfusion (Q) using, respectively, technetium-99m labelled Technegas (140 keV) and indi- um-113m labelled macro-aggregated albumin (392 keV), is presented, validated and clinically tested in a healthy volunteer. In order to assess V, Q and V/Q distributions in quantitative terms, algorithms which correct for down scattering, photon scattering and attenuation, as well as an organ outline algorithm, were implemented. Scatter and down-scatter correction were made in the spatial do- main by pixel-wise image subtraction of projection-de- pendent global scattering factors obtained from the ener- gy domain. The attenuation correction was based on an iterative projection/back-projection method. All studies were made on a three-headed SPET system (Trionix) with medium-energy parallel-hole collimators. The set of input data for quantification was based on SPET acquisi- tion of emission data in four separate energy windows, the associated cumulative energy spectra and transmis- sion data. The attenuation correction routine as well as the edge detection algorithm utilized data from 99m Tc transmission tomography. Attenuation data for 113mIn were obtained by linear scaling of the 99mTc attenuation maps. The correction algorithms were experimentally validated with a stack phantom system and applied on a healthy volunteer. The mean difference between the cor- rected SPET data of the dense stack lung phantom and those obtained from the corresponding scatter- and atten- uation-"free" version was only 1.9% for 99m Tc and 0.9% for 113mIn. The estimated fractional V/Q distribution in the 3-D lung phantom volume had its peak at V/Q=1, with a width (FWHM) of 0.31 due to noise, particularly in the 113m In images, and to partial volume effects. For a healthy volunteer, the corresponding values were 0.9 and 0.35, respectively. This method allows accurate assess- ment of radionuclide distribution on a regional basis. For basic lung physiology and clinical practice, the method allows assessment of the global frequency functions of the V, Q and V/Q distributions.

Capillaries recruit when pulmonary arterial pressure rises. The duration of increased pressure imposed in such experiments is usually on the order of minutes, although recent work shows that the recruitment response can occur in

With the use of a newly developed Imaging Cryomicrotome to determine the spatial location of fluorescent microspheres in organs, we validate and report our processing algorithms for measuring regional blood flow in small laboratory animals. Microspheres (15-μm diameter) of four different fluorescent colors and one radioactive label were simultaneously injected into the left ventricle of a pig. The heart and kidneys were dissected, and the numbers of fluorescent and radioactive microspheres were determined in 10 randomly selected pieces. All microsphere counts fell well within the 95% expected confidence limits as determined from the radioactive counts. Fluorescent microspheres (15-μm diameter) of four different colors were also injected into the tail vein of a rat and the left ventricle of a rabbit. After correction for Poisson noise, correlation coefficients between the colors were 0.99 ± 0.02 (means ± SD) for the rabbit heart and 0.99 ± 0.02 for the rat lung. Mathematical dissection algorithms, statistics to analyze the spatial data, and methods to visualize blood flow distributions in small animal organs are presented.

We assessed the influence of cranial-to-caudal inertial force (+G z ) and the countermeasures of anti-G suit and positive pressure breathing during G (PBG), specifically during +G z , on regional pulmonary blood flow distribution. Unanesthetized swine were exposed randomly to 0 G z (resting), +3 G z , +6 G z , and +9 G z , with and without anti-G suit and PBG with the use of the Air Force Research Laboratory centrifuge at Brooks Air Force Base (the gravitational force of the Earth, that is, the dorsal-to-ventral inertial force, was present for all runs). Fluorescent microspheres were injected into the pulmonary vasculature as a marker of regional pulmonary blood flow. Lungs were excised, dried, and diced into ∼2-cm3 pieces, and the fluorescence of each piece was measured. As +G z was increased from 0 to +3 G z , blood flow shifted from cranial and hilar regions toward caudal and peripheral regions of the lung. This redistribution shifted back toward cranial and hilar regions as anti-G suit inflation pressure increased at +6 and +9 G z . Perfusion heterogeneity increased with +G z stress and decreased at the higher anti-G suit pressures. The distribution of pulmonary blood flow was not affected by PBG. ANOVA indicated anatomic structure as the major determinant of pulmonary blood flow.

The microsphere method has been used extensively to measure regional blood flow in large laboratory animals. A fundamental premise of the method is that microspheres do not alter regional flow or vascular tone. Whereas this assumption is accepted in large animals, it may not be valid in the pulmonary circulation of smaller animals. Three studies were performed to determine the hemodynamic effects of microspheres on the rat pulmonary circulation. Increasing numbers of 15-μm-diameter microspheres were injected into a fully dilated, isolated-lung preparation. Vascular resistance increased 0.8% for every 100,000 microspheres injected. Microspheres were also injected into an isolated-lung preparation in which vascular tone was increased with hypoxia. Microspheres did not induce vasodilatation, as reported in other vascular beds. Fluorescent microspheres were injected via tail veins into awake rats, and the spatial locations of the microspheres were determined. Regional distributions remained highly correlated when microspheres of one color were injected after microspheres of another color. This indicates that the initial injection did not alter regional perfusion. We conclude that, when used in appropriate numbers, 15-μm-diameter microspheres do not alter regional flow or vascular tone in the rat pulmonary circulation.

Endotoxin increases ventilation-to-perfusion ratio (V˙a/Q˙) heterogeneity in the lung, but the precise changes in alveolar ventilation (V˙a) and perfusion that lead toV˙a/Q˙heterogeneity are unknown. The purpose of this study was to determine how endotoxin affects the distributions of ventilation and perfusion and the impact of these changes onV˙a/Q˙heterogeneity. Seven anesthetized, mechanically ventilated juvenile pigs were given E. coli endotoxin intravenously, and regional ventilation and perfusion were measured simultaneously by using aerosolized and injected fluorescent microspheres. Endotoxemia significantly decreased the correlation between regional ventilation and perfusion, increased perfusion heterogeneity, and redistributed perfusion between lung regions. In contrast, ventilation heterogeneity did not change, and redistribution of ventilation was modest. The decrease in correlation between regional ventilation and perfusion was responsible for significantly moreV˙a/Q˙ heterogeneity than were changes in ventilation or perfusion heterogeneity. We conclude that V˙a/Q˙heterogeneity increases during endotoxemia primarily as a result of the decrease in correlation between regional ventilation and perfusion, which is in turn determined primarily by changes in perfusion.

An automated image acquisition and analysis system has been developed that rapidly determines regional blood flow by using the locations of fluorescent microspheres deposited in tissue. A motor-driven microtome removes sections of frozen tissues in steps variable between 10 and 100 μm. Filtered light excites microsphere fluorescence from the exposed surface of the remaining tissue block. A charge coupled device camera records fluorescence images from the tissue block surface after removal of each slice. Approximately 450 images are analyzed from perfused rat hearts providing precise x, y, and z locations of about 10 000 microspheres. Image analysis of fluorescent microspheres is much faster and less labor intensive than traditional indirect microsphere-based flow measurements while providing higher quality data.