Airway reactivity to bronchoconstrictor and bronchodilator: assessment using thin-section and volumetric three-dimensional CT

The bronchodilator response of in vivo specific airway compliance in adults with asthma

A new technique has been developed to determine in vivo airway compliance in humans that is specific to airway size and transpulmonary pressure, and can be represented as a three-dimensional surface. As yet, the ability of this technique to detect changes in specific airway compliance with disease status has not been demonstrated. The aim of this study was to assess whether this technique could determine changes in airway compliance which are thought to occur with altered smooth muscle tone in adults with asthma. Airway compliance was measured and displayed as a surface in adults with asthma before and after a reduction in smooth muscle tone by bronchodilator administration. Compliance, with respect to airway size, was calculated at three specific lung volumes; functional residual capacity (FRC), total lung capacity (TLC), and midway between FRC and TLC (MID). After bronchodilator, airway compliance increased at FRC and MID in the smaller airways (<3 mm). Furthermore, airway compliance under both conditions was greater in the smaller airways compared to the larger airways. In conclusion, our method may have future utility in assessing changes in airway compliance in respiratory diseases such as asthma.

Investigation of hyperpolarized 3He magnetic resonance imaging utility in examining human airway diameter behavior in asthma through comparison with high-resolution computed tomography

RATIONALE AND OBJECTIVES

Application of a previously developed model-based algorithm on hyperpolarized (HP) (3)He magnetic resonance (MR) dynamic projection images of phantoms was extended to investigate the utility of HP (3)He MR imaging (MRI) in quantifying airway caliber changes associated with asthma.

MATERIALS AND METHODS

Airways of seven volunteers were imaged and measured using HP (3)He MRI and multidetector-row computed tomography (MDCT) before and after a methacholine (MCh) challenge. MDCT data were obtained at functional residual capacity and 1 L above functional residual capacity.

RESULTS

Comparison of the resultant data showed that HP (3)He MRI did not match MDCT in measuring the ratios of airway calibers before and after the MCh challenge in 37% to 43% of the airways from the first six generations at the two lung volumes tested. However, MDCT did yield the observation that 49% to 69% of these airways displayed bronchodilation following MCh challenge.

CONCLUSION

The current implementation of HP (3)He MRI did not match the MCh-induced postchallenge-to-prechallenge airway caliber ratios as measured with MDCT. Elevated parenchymal tethering due to bronchoconstriction-induced hyperinflation was proposed as a possible explanation for this airway dilation.

Characterisation of the acute and reversible airway inflammation induced by cadmium chloride inhalation in healthy dogs and evaluation of the effects of salbutamol and prednisolone

The aims of this study were firstly to characterise a model of subclinical and reversible bronchial inflammation induced by cadmium chloride inhalation in healthy dogs and then to examine the effect of prednisolone or salbutamol treatment on the resulting bronchitis. The model characterisation and the effects of treatment were studied using clinical symptoms, haematology, thoracic radiography, bronchoscopy and bronchoalveolar lavage, barometric whole-body plethysmography and histamine broncho-provocation tests. In addition, the activity of matrix metalloproteinases (MMP)-2 and -9 were determined in serum and bronchoalveolar lavage fluid (BALF). Cadmium inhalation induced: (1) a transient bronchial inflammation, dominated by neutrophils; (2) a neutrophilia of the blood that persisted for up to 4 weeks; (3) a transient increased bronchial reactivity, and (4) a significant increase in MMP-9 activity in the BALF. Prednisolone treatment reduced the influx of inflammatory cells into the BALF, but not significantly, had no effect on pulmonary function, and did not reduce of airway hypersensitivity. Salbutamol had almost no effect on any of the parameters investigated.

Functional imaging of airway narrowing

The report will focus on studies that illustrate how high resolution computed tomography can be used to provide new insights into airway and lung function, that cannot be obtained with any other methodology in humans or animal models. In one series of experiments, we have clearly demonstrated that even large cartilaginous airways are capable of complete closure in vivo. These unequivocal in vivo results invalidate the ubiquitous concept that there is a limit to airway narrowing in normal subjects. In another series of experiments, we have investigated potential reasons why asthmatic subjects might show airway constriction following deep inspiration instead of the normal dilation. Experimental results show that a constrictor response to deep inspiration can be generated in normal airways simply by minimizing tidal stresses. The absence of these normal rhythmic stresses alters the smooth muscle throughout the airway tree, such that subsequent large stresses lead to a further constriction. These results also offer a possible mechanism by which the response to deep inspiration is altered in asthmatic subjects. By allowing accurate measurement of the size of individual airways, computed tomography with modern commercially available scanners thus provides a unique opportunity to evaluate specific hypotheses regarding mechanisms underlying lung disease.