[Pathophysiology of capnoperitoneum. Implications for ventilation and hemodynamics]

Laparoscopic surgery was introduced into clinical practice in the early 1950s by gynaecologists. Technical improvements allowed its use for more complex and longer lasting procedures. Reduction of postoperative pain, more favourable cosmetic results, quicker recovery and reduced length of hospital stay proved to be advantageous when compared to open surgery. As a result progressively older patients with corresponding pulmonary and cardiovascular comorbidities and morbidly obese patients are now undergoing advanced laparoscopic surgery. Detailed knowledge of the respiratory and hemodynamic pathophysiology induced by capnoperitoneum is necessary to administer safe anaesthesia to such patients. This review addresses the most important effects of capnoperitoneum and recent research as well as the possible implications for clinical practice.

Neurally adjusted ventilatory assist decreases ventilator-induced lung injury and non-pulmonary organ dysfunction in rabbits with acute lung injury

OBJECTIVE: To determine if neurally adjusted ventilatory assist (NAVA) that delivers pressure in proportion to diaphragm electrical activity is as protective to acutely injured lungs (ALI) and non-pulmonary organs as volume controlled (VC), low tidal volume (Vt), high positive end-expiratory pressure (PEEP) ventilation. DESIGN: Prospective, randomized, laboratory animal study. SUBJECTS: Twenty-seven male New Zealand white rabbits. INTERVENTIONS: Anesthetized rabbits with hydrochloric acid-induced ALI were randomized (n = 9 per group) to 5.5 h NAVA (non-paralyzed), VC (paralyzed; Vt 6-ml/kg), or VC (paralyzed; Vt 15-ml/kg). PEEP was adjusted to hemodynamic goals in NAVA and VC6-ml/kg, and was 1 cmH2O in VC15-ml/kg. MEASUREMENTS AND MAIN RESULTS: PaO2/FiO2; lung wet-to-dry ratio; lung histology; interleukin-8 (IL-8) concentrations in broncho-alveolar-lavage (BAL) fluid, plasma, and non-pulmonary organs; plasminogen activator inhibitor type-1 and tissue factor in BAL fluid and plasma; non-pulmonary organ apoptosis rate; creatinine clearance; echocardiography. PEEP was similar in NAVA and VC6-ml/kg. During NAVA, Vt was lower (3.1 +/- 0.9 ml/kg), whereas PaO2/ FiO2, respiratory rate, and PaCO2 were higher compared to VC6-ml/kg (p<0.05 for all). Variables assessing ventilator-induced lung injury (VILI), IL-8 levels, non-pulmonary organ apoptosis rate, and kidney as well as cardiac performance were similar in NAVA compared to VC6-ml/kg. VILI and non-pulmonary organ dysfunction was attenuated in both groups compared to VC15-ml/kg. CONCLUSIONS: In anesthetized rabbits with early experimental ALI, NAVA is as effective as VC6-ml/kg in preventing VILI, in attenuating excessive systemic and remote organ inflammation, and in preserving cardiac and kidney function.

The effects of cardiac output and pulmonary arterial hypertension on volumetric capnography derived-variables during normoxia and hypoxia

The aim of this study was to test the effect of cardiac output (CO) and pulmonary artery hypertension (PHT) on volumetric capnography (VCap) derived-variables. Nine pigs were mechanically ventilated using fixed ventilatory settings. Two steps of PHT were induced by IV infusion of a thromboxane analogue: PHT25 [mean pulmonary arterial pressure (MPAP) of 25 mmHg] and PHT40 (MPAP of 40 mmHg). CO was increased by 50 % from baseline (COup) with an infusion of dobutamine ≥5 μg kg(-1) min(-1) and decreased by 40 % from baseline (COdown) infusing sodium nitroglycerine ≥30 μg kg(-1) min(-1) plus esmolol 500 μg kg(-1) min(-1). Another state of PHT and COdown was induced by severe hypoxemia (FiO2 0.07). Invasive hemodynamic data and VCap were recorded and compared before and after each step using a mixed random effects model. Compared to baseline, the normalized slope of phase III (SnIII) increased by 32 % in PHT25 and by 22 % in PHT40. SnIII decreased non-significantly by 4 % with COdown. A combination of PHT and COdown associated with severe hypoxemia increased SnIII by 28 % compared to baseline. The elimination of CO2 per breath decreased by 7 % in PHT40 and by 12 % in COdown but increased only slightly with COup. Dead space variables did not change significantly along the protocol. At constant ventilation and body metabolism, pulmonary artery hypertension and decreases in CO had the biggest effects on the SnIII of the volumetric capnogram and on the elimination of CO2.

Determination of respiratory gas flow by electrical impedance tomography in an animal model of mechanical ventilation

Background A recent method determines regional gas flow of the lung by electrical impedance tomography (EIT). The aim of this study is to show the applicability of this method in a porcine model of mechanical ventilation in healthy and diseased lungs. Our primary hypothesis is that global gas flow measured by EIT can be correlated with spirometry. Our secondary hypothesis is that regional analysis of respiratory gas flow delivers physiologically meaningful results. Methods In two sets of experiments n = 7 healthy pigs and n = 6 pigs before and after induction of lavage lung injury were investigated. EIT of the lung and spirometry were registered synchronously during ongoing mechanical ventilation. In-vivo aeration of the lung was analysed in four regions-of-interest (ROI) by EIT: 1) global, 2) ventral (non-dependent), 3) middle and 4) dorsal (dependent) ROI. Respiratory gas flow was calculated by the first derivative of the regional aeration curve. Four phases of the respiratory cycle were discriminated. They delivered peak and late inspiratory and expiratory gas flow (PIF, LIF, PEF, LEF) characterizing early or late inspiration or expiration. Results Linear regression analysis of EIT and spirometry in healthy pigs revealed a very good correlation measuring peak flow and a good correlation detecting late flow. PIFEIT = 0.702 · PIFspiro + 117.4, r2 = 0.809; PEFEIT = 0.690 · PEFspiro-124.2, r2 = 0.760; LIFEIT = 0.909 · LIFspiro + 27.32, r2 = 0.572 and LEFEIT = 0.858 · LEFspiro-10.94, r2 = 0.647. EIT derived absolute gas flow was generally smaller than data from spirometry. Regional gas flow was distributed heterogeneously during different phases of the respiratory cycle. But, the regional distribution of gas flow stayed stable during different ventilator settings. Moderate lung injury changed the regional pattern of gas flow. Conclusions We conclude that the presented method is able to determine global respiratory gas flow of the lung in different phases of the respiratory cycle. Additionally, it delivers meaningful insight into regional pulmonary characteristics, i.e. the regional ability of the lung to take up and to release air.

Lung Volume Reduction in Pulmonary Emphysema from the Radiologist's Perspective

Pulmonary emphysema causes decrease in lung function due to irreversible dilatation of intrapulmonary air spaces, which is linked to high morbidity and mortality. Lung volume reduction (LVR) is an invasive therapeutical option for pulmonary emphysema in order to improve ventilation mechanics. LVR can be carried out by lung resection surgery or different minimally invasive endoscopical procedures. All LVR-options require mandatory preinterventional evaluation to detect hyperinflated dysfunctional lung areas as target structures for treatment. Quantitative computed tomography can determine the volume percentage of emphysematous lung and its topographical distribution based on the lung's radiodensity. Modern techniques allow for lobebased quantification that facilitates treatment planning. Clinical tests still play the most important role in post-interventional therapy monitoring, but CT is crucial in the detection of postoperative complications and foreshadows the method's high potential in sophisticated experimental studies. Within the last ten years, LVR with endobronchial valves has become an extensively researched minimally-invasive treatment option. However, this therapy is considerably complicated by the frequent occurrence of functional interlobar shunts. The presence of "collateral ventilation" has to be ruled out prior to valve implantations, as the presence of these extraanatomical connections between different lobes may jeopardize the success of therapy. Recent experimental studies evaluated the automatic detection of incomplete lobar fissures from CT scans, because they are considered to be a predictor for the existence of shunts. To date, these methods are yet to show acceptable results. KEY POINTS Today, surgical and various minimal invasive methods of lung volume reduction are in use. Radiological and nuclear medical examinations are helpful in the evaluation of an appropriate lung area. Imaging can detect periinterventional complications. Reduction of lung volume has not yet been conclusively proven to be effective and is a therapeutical option with little scientific evidence.

S-nitrosothiol repletion by an inhaled gas regulates pulmonary function

NO synthases are widely distributed in the lung and are extensively involved in the control of airway and vascular homeostasis. It is recognized, however, that the O2-rich environment of the lung may predispose NO toward toxicity. These Janus faces of NO are manifest in recent clinical trials with inhaled NO gas, which has shown therapeutic benefit in some patient populations but increased morbidity in others. In the airways and circulation of humans, most NO bioactivity is packaged in the form of S-nitrosothiols (SNOs), which are relatively resistant to toxic reactions with O2/O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{-}}}\end{equation*}\end{document}. This finding has led to the proposition that channeling of NO into SNOs may provide a natural defense against lung toxicity. The means to selectively manipulate the SNO pool, however, has not been previously possible. Here we report on a gas, O-nitrosoethanol (ENO), which does not react with O2 or release NO and which markedly increases the concentration of indigenous species of SNO within airway lining fluid. Inhalation of ENO provided immediate relief from hypoxic pulmonary vasoconstriction without affecting systemic hemodynamics. Further, in a porcine model of lung injury, there was no rebound in cardiopulmonary hemodynamics or fall in oxygenation on stopping the drug (as seen with NO gas), and additionally ENO protected against a decline in cardiac output. Our data suggest that SNOs within the lung serve in matching ventilation to perfusion, and can be manipulated for therapeutic gain. Thus, ENO may be of particular benefit to patients with pulmonary hypertension, hypoxemia, and/or right heart failure, and may offer a new therapeutic approach in disorders such as asthma and cystic fibrosis, where the airways may be depleted of SNOs.

Effect of smoke inhalation on viscoelastic properties and ventilation distribution in sheep

Smoke inhalation injuries are the leading cause of mortality from burn injury. Airway obstruction due to mucus plugging and bronchoconstriction can cause severe ventilation inhomogeneity and worsen hypoxia. Studies describing changes of viscoelastic characteristics of the lung after smoke inhalation are missing. We present results of a new smoke inhalation device in sheep and describe pathophysiological changes after smoke exposure. Fifteen female Merino ewes were anesthetized and intubated. Baseline data using electrical impedance tomography and multiple-breath inert-gas washout were obtained by measuring ventilation distribution, functional residual capacity, lung clearance index, dynamic compliance, and stress index. Ten sheep were exposed to standardized cotton smoke insufflations and five sheep to sham smoke insufflations. Measured carboxyhemoglobin before inhalation was 3.87 +/- 0.28% and 5 min after smoke was 61.5 +/- 2.1%, range 50-69.4% ( P < 0.001). Two hours after smoke functional residual capacity decreased from 1,773 +/- 226 to 1,006 +/- 129 ml and lung clearance index increased from 10.4 +/- 0.4 to 14.2 +/- 0.9. Dynamic compliance decreased from 56.6 +/- 5.5 to 32.8 +/- 3.2 ml/ cmH(2)O. Stress index increased from 0.994 +/- 0.009 to 1.081 +/- 0.011 ( P < 0.01) ( all means +/- SE, P < 0.05). Electrical impedance tomography showed a shift of ventilation from the dependent to the independent lung after smoke exposure. No significant change was seen in the sham group. Smoke inhalation caused immediate onset in pulmonary dysfunction and significant ventilation inhomogeneity. The smoke inhalation device as presented may be useful for interventional studies.

STRUCTURAL AND FUNCTIONAL CORRELATES OF EXERCISE VENTILATORY INEFFICIENCY IN CHRONIC OBSTRUCTIVE PULMONARY DISEASE PATIENTS WITH MILD-TO-MODERATE SPIROMETRIC ABNORMALITIES

Background: Individuals with chronic obstructive pulmonary disease (COPD) have higher than normal ventilatory equivalents for carbon dioxide (VE/VCO2) during exercise. There is growing evidence that emphysema on thoracic computed tomography (CT) scans is associated with poor exercise capacity in COPD patients with only mild-to-moderate airflow obstruction. We hypothesized that emphysema is an underlying cause of microvascular dysfunction and ventilatory inefficiency, which in turn contributes to reduced exercise capacity. We expected ventilatory inefficiency to be associated with a) the extent of emphysema; b) lower diffusing capacity for carbon monoxide; c) a reduced pulmonary blood flow response to exercise; and d) reduced exercise capacity. Methods: In a cross-sectional study, 19 subjects with mild-to-moderate COPD (mean ± SD FEV1= 82 ± 13% predicted, 12 GOLD grade 1) and 26 age-, sex-, and activity-matched controls underwent a ramp-incremental symptom-limited exercise test on a cycle ergometer. Ventilatory inefficiency was assessed by the minimum VE/VCO2 value (nadir). A subset of subjects also completed repeated constant work rate exercise bouts with non-invasive measurements of pulmonary blood flow. Emphysema was quantified as the percentage of attenuation areas below -950 Housefield Units on CT scans. An electronic scoresheet was used to keep track of emphysema sub-types. Results: COPD subjects typically had centrilobular emphysema (76.8 ± 10.1% of total emphysema) in the upper lobes (upper/lower lobe ratio= 0.82 ± 0.04). They had lower peak oxygen uptake (VO2), higher VE/VCO2 nadir and greater dyspnea scores than controls (p<0.05). Lower peak O2 and worse dyspnea were found in COPD subjects with VE/VCO2 nadirs ≥ 30. COPD subjects had blunted increases in pulmonary blood flow from rest to iso-VO2 exercise (p<0.05). Higher VE/VCO2 nadir in COPD subjects correlated with emphysema severity (r= 0.63), which in turn correlated with reduced lung diffusing capacity (r= -0.72) and blunted changes in pulmonary blood flow from rest to exercise (r= -0.69) (p<0.01). Conclusions: Ventilation “wasted” in emphysematous areas is associated with reduced exercise ventilatory efficiency in mild-to-moderate COPD. Exercise ventilatory inefficiency links structure (emphysema) and function (gas transfer) to a key clinical outcome (reduced exercise capacity) in COPD patients with modest spirometric abnormalities.

Passive solar systems for heating, daylighting and ventilation for rooms without an equator-facing facade

Spaces without northerly orientations have an impact on the ‘energy behaviour’ of a building. This paper outlines possible energy savings and better performance achieved by different zenithal solar passive strategies (skylights, roof monitors and clerestory roof windows) and element arrangements across the roof in zones of cold to temperate climates typical of the central and central-southern Argentina. Analyses were undertaken considering daylighting, thermal and ventilation performances of the different strategies. The results indicate that heating,ventilation and lighting loads in spaces without an equator-facing facade can be significantly reduced by implementing solar passive strategies. In the thermal aspect, the solar saving fraction reached for the different strategies were averaged 43.16% for clerestories, 41.4% for roof monitors and 38.86% for skylights for a glass area of 9% to the floor area. The results also indicate average illuminance levels above 500 lux for the different clerestory and monitor arrangements, uniformity ratios of 0.66–0.82 for the most distributed arrangements and day-lighting factors between 11.78 and 20.30% for clear sky conditions, depending on the strategy. In addition, minimum air changes rates of 4 were reached for the most extreme conditions.

Determination of particle concentration in the breathing zone for four different types of office ventilation systems

Many factors affect the airflow patterns, thermal comfort, contaminant removal efficiency and indoor air quality at individual workstations in office buildings. In this study, four ventilation systems were used in a test chamber designed to represent an area of a typical office building floor and reproduce the real characteristics of a modern office space. Measurements of particle concentration and thermal parameters (temperature and velocity) were carried out for each of the following types of ventilation systems: a) conventional air distribution system with ceiling supply and return; b) conventional air distribution system with ceiling supply and return near the floor; c) underfloor air distribution system; and d) split system. The measurements aimed to analyse the particle removal efficiency in the breathing zone and the impact of particle concentration on an individual at the workstation. The efficiency of the ventilation system was analysed by measuring particle size and concentration, ventilation effectiveness and the Indoor/Outdoor ratio. Each ventilation system showed different airflow patterns and the efficiency of each ventilation system in the removal of the particles in the breathing zone showed no correlation with particle size and the various methods of analyses used.

Sustainable subdivisions – ventilation data analysis

This project, as part of a broader Sustainable Sub-divisions research agenda, addresses the role of natural ventilation in reducing the use of energy required to cool dwellings

The role of natural ventilation in building sustainable subdivisions in south east Queensland

The objective of the consultative phase is to examine the role that natural ventilation has and can play in the subdivision planning process in SEQ. The Centre for Subtropical Design at QUT coordinated the consultative phase and has conducted a workshop, and interviews, with stakeholders including developers, land development consultants, land surveyors, urban designers and regulators, to identify current understanding of the impact of urban subdivision on natural ventilation, and the role of natural ventilation in achieving energy efficiency for dwellings. This report details the findings.

Sustainable subdivisions – ventilation monitoring

Australia’s current pattern of residential development is typified by relatively low-density subdivision of land and highlights the necessity for development to be more sustainable to avoid unnecessary demand on natural resources and to prevent environmental degradation and to safeguard the environment for future generations. What role can climatically appropriate sub-division design play in decreasing the use of energy required to cool premises by maximising access to natural ventilation? How can this design be achieved?

When and how to treat pulmonary non-tuberculous mycobacterial diseases

Nontuberculous mycobacteria are ubiquitous environmental organisms that have been recognised as a cause of pulmonary infection for over 50 years. Traditionally patients have had underlying risk factors for development of disease; however the proportion of apparently immunocompetent patients involved appears to be rising. Not all patients culture-positive for mycobacteria will have progressive disease, making the diagnosis difficult, though criteria to aid in this process are available. The two main forms of disease are cavitary disease (usually involving the upper lobes) and fibronodular bronchiectasis (predominantly middle and lingular lobes). For patients with disease, combination antibiotic therapy for 12-24 months is generally required for successful treatment, and this may be accompanied by drug intolerances and side effects. Published success rates range from 30-82%. As the progression of disease is variable, for some patients, attention to pulmonary hygiene and underlying diseases without immediate antimycobacterial therapy may be more appropriate. Surgery can be a useful adjunct, though is associated with risks. Randomised controlled trials in well described patients would provide stronger evidence-based data to guide therapy of NTM lung diseases, and thus are much needed.