Effect of airway blood flow on airflow

Surgical Repair of Mitral Valve Disease in Children: Perioperative Changes in Respiratory Function

OBJECTIVE

To assess the profile of changes in airway and respiratory tissue mechanics within a follow-up study performed in children with mitral valve disease, before and after surgical valve repair.

DESIGN

Perioperative measurements in a prospective, consecutive cross-sectional study.

SETTING

University hospital, tertiary care teaching hospital

PARTICIPANTS

The study comprised 24 children with congenital or post-rheumatic mitral valve insufficiency.

INTERVENTIONS

Input impedance of the respiratory system during spontaneous breathing was measured before and 5 days and 3 weeks after mitral valve surgery. In addition, airway and respiratory tissue mechanics and pulmonary arterial pressure were assessed with the patient under general anesthesia preoperatively and immediately postoperatively. Respiratory tissue elastance and changes in airway measurements were estimated from forced oscillatory impedance data by fitting an appropriate model.

MEASUREMENT AND MAIN RESULTS

Relating airway and respiratory tissue mechanics to previously established reference values obtained in age-matched healthy control patients revealed abnormal respiratory function (135±6.2% and 148±13% in respiratory elastance and resistance, respectively; p<0.001). Improvement in the airway properties was observed immediately after surgery (-15.2±3.4%; p<0.005) and lasted for the study period (-19±4.1%; p<0.001). Respiratory tissue elastance, which correlated preoperatively to the diastolic pulmonary arterial pressure, decreased only 5 days postoperatively (-20.6±4.1%; p<0.005). However, there was no evidence of a clear, immediate effect of surgery on the tissue mechanical parameters measured intraoperatively despite a decrease in diastolic pulmonary pressure.

CONCLUSIONS

Mitral valve disease in children leads to abnormal airway and respiratory tissue mechanics. Even though surgical repair of mitral insufficiency alleviates abnormal airway function, residual lung tissue stiffening may persist even weeks after the surgery, contributing to a sustained impairment in lung function.

Influence of bronchial blood flow and conductance on pulmonary function in stable systolic heart failure

BACKGROUND

The aim of this study was to determine the relationship between airway blood flow (Q(aw)), airway conductance (G(f-aw)) and pulmonary function in patients with stable HF.

METHODS

12 controls (CTRL: age=63±9 years, FVC=98±15%pred, LVEF=61±6%) (all data presented as mean±SD), 16 patients with mild HF (HF-A, NYHA I-II: age=64±9 years, FVC=90±17%pred, LVEF=28±6%), and 14 patients with moderate/severe HF (HF-B, NYHA III-IV: age=65±6 years, FVC=84±12%pred, LVEF=26±6%) were studied. Q(aw) was assessed using soluble gas measurements; perfusion pressure across airway bed (ΔP(aw)) was estimated from systemic and pulmonary pressure measurements; G(f-aw) was calculated as Q(aw)/ΔP(aw); PF was assessed by spirometry.

RESULTS

While Q˙(aw) was not significantly different between CTRL (61.3±17.9 μL min(-1)mL(-1)), HF-A (70.1±26.9 μL min(-1)mL(-1)) and HF-B (56.2±14.9 μL min(-1)mL(-1)) groups, G(f-aw), was elevated in HF-A (1.1±0.4 μL min(-1)mL(-1)mm Hg(-1), p<0.03) and tended to be elevated in HF-B (1.2±0.6 μL min(-1)mL(-1)mm Hg(-1), p=0.07) when compared to CTRL (0.8±0.3 μL min(-1)mL(-1)mm Hg(-1)). Significant positive correlations were found between G(f-aw) and RV/TLC for HF-A (r=0.63, p<0.02) and HF-B (r=0.58, p<0.05).

CONCLUSIONS

These results support the hypothesis that increased bronchial conductance and bronchial congestion may be related to greater small airway obstruction and as such may play a role in the PF abnormalities and symptoms of congestion commonly observed in HF patients.

Mechanisms of airway hyper-responsiveness after coronary ischemia

We explored the consequences of myocardial ischemia (MI) on the lung responsiveness and identified the pathophysiological mechanisms involved. Airway resistance (R(aw)) was identified from the respiratory system input impedance (Z(rs)) in rats. Z(rs) was determined under baseline conditions, and following iv boluses of 20 and 30 microg/kg serotonin. MI was then induced in the animals in Group I by ligating the left-interventricular coronary artery, while rats in Group C underwent sham surgery. Four weeks later, baseline Z(rs) and its changes following serotonin administration were reassessed. Lung morphological changes were assessed by histology, and alpha smooth muscle actin cells (alpha-SMA) were identified. MI induced no changes in baseline R(aw) but led to bronchial hyper-reactivity (BHR) with 2.7+/-0.5-times (p<0.05) greater responses in R(aw) to 30 microg/kg serotonin. Perivascular edema and alpha-SMA cell proliferation were observed after MI. The development of BHR following MI is a consequence of the expression of alpha-SMA, while the geometrical alterations caused by the pulmonary vascular engorgement have smaller impact.

Airway vascular remodeling in asthma

Several characteristic changes occur in the bronchial wall in asthma, including specific changes to the vasculature. These result in an increase in vessel numbers per unit area, as well as increased vessel activity suggested by vasodilatation, vessel leakage, and cellular margination with transmigration to target tissues. This combined action in asthma leads to airway-wall thickening and reduced airflow. Each component of the vascular response has been shown to be controlled by a range of inflammatory mediators and growth factors. These factors are themselves regulated by a complex process initially involving gene expression, transcription, and translation at the molecular level, then subsequent protein release, binding to matrix elements, endothelial cell activation, and a proliferative endothelial response. Many commonly used airway medications are capable of modulating the vascular response to inflammatory stimuli. New therapies might improve airflow through better regulation of vessel growth, dilatation, and leakage in the airway wall.

Angiogenesis in paediatric airway disease

A number of characteristic changes occur in the bronchial wall in paediatric airway diseases. The process of remodelling is usually associated with specific changes to the vasculature, resulting in an increase in vessel numbers, vasodilatation, vessel leakage and cellular margination with transmigration to target tissues. This combined action in conditions such as asthma, cystic fibrosis and bronchiolitis lead to airway wall thickening and reduced airflow. Each component of the vascular response has been shown to be controlled by a range of inflammatory mediators and growth factors. These factors are regulated by a complex process involving gene expression, transcription and translation at the molecular level, protein release, binding to matrix elements and receptors on endothelial cells, then the endothelial response itself. A number of commonly used airway medications are potentially capable of modulating the vascular response to inflammatory stimuli. New therapies may be able to improve airflow through better regulation of vessel growth, dilatation and leakage in the airway wall.

Experimental rhinovirus 16 infection causes variable airway obstruction in subjects with atopic asthma

Exacerbations of asthma are often associated with rhinovirus infections. However, it has not been investigated whether rhinovirus infection can induce variable airway obstruction in asthma. We examined the effect of experimental rhinovirus 16 (RV16) infection on daily home recordings of FEV(1) in 27 subjects (nonsmoking, atopic, mildly asthmatic) who participated in a parallel placebo-controlled study. The subjects used a microspirometer to record FEV(1) three times daily from 4 d before until 10 d after RV16 (n = 19) or placebo (n = 8) inoculation. In addition, symptoms of asthma and symptoms of common cold were scored. Airway hyperresponsiveness to histamine was measured 3 d before and on Days 4 and 11 after RV16/placebo administration. Home recordings of FEV(1) decreased significantly after RV16 infection, reaching a minimum 2 d after inoculation (ANOVA, p </= 0.005), which was significantly different from placebo (p </= 0.004). In the RV16 group the lowest FEV(1) (expressed as a percentage of personal best) during Days 0-3 after infection (mean +/- SEM: 78.7 +/- 2.6% versus baseline: 85.6 +/- 1.2%, p = 0.008) correlated significantly with the cold score (r = -0.47, p = 0.04), asthma score (r = -0.47, p = 0.04), and with the decrease in airway hyperresponsiveness on Day 4 as compared with baseline (r = 0.50, p = 0.03). We conclude that experimental RV16 infection augments variable airway obstruction in subjects with asthma. This favors a causative role for rhinovirus colds in asthma exacerbations, and is in keeping with rhinovirus-induced worsening of airway inflammation.

Comparison of the effects of salbutamol and adrenaline on airway smooth muscle contractility in vitro and on bronchial reactivity in vivo

BACKGROUND

The effect of adrenergic agonists in asthma depends on their net effect on microvascular leakage, mucosal oedema, vascular clearance of spasmogens, inhibition of cholinergic neurotransmission, and airway smooth muscle contractility. It has been postulated that adrenaline, by virtue of its alpha effects on the vasculature and cholinergic neurotransmission, may have additional useful properties in asthma compared with selective beta agonists such as salbutamol.

METHODS

The airway effects of adrenaline (a non-selective adrenoreceptor agonist) were compared with the selective beta 2 agonist salbutamol. Their airway smooth muscle relaxant potencies and effect on histamine contraction in human bronchi in vitro were compared with their effects on airway calibre and histamine reactivity in asthmatic subjects in vivo. For the in vitro studies changes in tension were measured in response to these agents in thoracotomy specimens of human airways. In vivo the effects of adrenaline and salbutamol on airway calibre and histamine reactivity were measured in eight subjects with mild to moderate asthma in a randomised crossover study.

RESULTS

Salbutamol and adrenaline had approximately equivalent airway smooth muscle relaxant potencies in vitro and bronchodilator potency in vivo. However, their effects on histamine induced contraction in vitro were significantly different from their effects on histamine reactivity in vivo. Salbutamol was less potent in vitro producing a mean (SE) 2.4 (0.15) doubling dose increase in the histamine EC20 and adrenaline a 5.2 (0.18) doubling dose increase (mean difference between salbutamol and adrenaline 2.8 doubling doses; 95% CI 1.1 to 4.5). Salbutamol had no effect on the maximal response to histamine whereas adrenaline reduced it by 54%. In contrast, salbutamol was more potent in vivo producing a mean (SE) increase in PD20 histamine of 1.84 (0.5) doubling doses whereas adrenaline was without effect increasing PD20 by only 0.06 (0.47) doubling doses (mean difference between adrenaline and salbutamol 1.78, 95% CI 0.26 to 3.29 doubling doses).

CONCLUSIONS

These findings suggest that the alpha adrenergic airway effects of non-selective adrenoreceptor agonists such as adrenaline offer no additional protection against histamine-induced broncho-constriction in vivo than beta 2 selective drugs such as salbutamol, despite adrenaline providing greater protection against histamine-induced contraction in vitro. The differences between the effects of these agents in vitro and in vivo may be related to their opposing vascular effects in vivo.

Studies of human airways in vitro: a review of the methodology

The pathophysiology of human airway narrowing is only partly understood. In order to gain more insight in the mechanisms of human lung diseases and potential beneficial therapeutic agents, adequate models are needed. Animal airway models are of limited value since lung diseases such as asthma and chronic obstructive pulmonary disease (COPD) are unique to humans and because the mechanisms of airway narrowing differ between species. Therefore, it is important to perform studies on human isolated airways. We describe the models that have been developed to study airway function in vitro, emphasizing human airway preparations. The easily prepared airway strip and ring preparations are described first. The potential damage during preparation and the interference with airway structure are important drawbacks in these preparations. Lung parenchymal strips, described next, were designed in order to study responsiveness of small airways. However, parenchymal strips are anatomically complex, and responsiveness is determined by the relative amounts of airway and vascular smooth muscle. The lack of reproducibility between species and even within one animal limits their usefulness. Airway tube preparations, in which luminal and serosal stimulation can be separated, enable us to study the modulatory role of the airways epithelium in vitro. Furthermore, airway compliance can be measured. In the isolated perfused lung preparation, relationships between the airways and the vascular system are preserved and the interaction between these two systems can be studied. Weight gain due to fluid extravasation is a problem in this model which has not been used yet to study human lungs in vitro. Next, methodological aspects such as tissue handling and storage, recording of responses, removal of the epithelium, and electrical field stimulation are discussed in some detail. Although animal airways tissue can be studied immediately after removal, human tissue is often obtained with some delay. However, this seems tenable since electron microscopy of lung tissue obtained at autopsy showed that recovery of the preparation occurs during incubation of carbogenated Krebs-Henseleit (K-H) buffer. Dissected airways can be stored overnight in cooled K-H buffer until up to 55 hr after resection without losing viability. Commonly used physiological salt solutions which bath the tissue contain osmotic molecules, ions important for contractility, glucose as a substrate, and a bicarbonate-carbon dioxide buffer.(ABSTRACT TRUNCATED AT 400 WORDS)