Cardiopulmonary effects of methacholine in asthmatic and normal subjects

Phase-contrast MRI for detection of mild systemic hemodynamic response after segmental allergen challenge in asthmatic patients

RATIONALE AND OBJECTIVES

Detection of a systemic hemodynamic response in patients suffering from allergic asthma after segmental endobronchial allergen challenge using phase-contrast magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Nine asthma patients and four healthy volunteers were examined using MRI (1.5T) before (0 hour), 6 hours, and 24 hours after segmental allergen challenge. Two-dimensional phase-contrast MRI measurements were performed in the aorta (AO) and in the pulmonary artery (PA). In addition, short-axis balanced steady state free precession cardiac cine MRI was performed. Maximum systolic flow, maximum flow acceleration, acceleration volume, acceleration time, distensibility, ejection fraction, stroke volume, end-systolic/diastolic volume, cardiac mass, heart rate (HR), and cardiac output (CO) were determined. Spirometry and bronchoalveolar lavage were also performed.

RESULTS

In patients with asthma, maximal systolic flow and maximal flow acceleration increased 6 hours after provocation in the AO (112.3% and 118.9%, respectively) and PA (113.9% and 116.0%, respectively) compared to baseline (100%, P < .05). HR and CO increased significantly at 6 hours (115% and 118%, respectively) compared to baseline (100%, P = .003). In healthy subjects, almost all MRI-derived hemodynamic parameters did not significantly change at 6 hours and were significantly lower than baseline values at 24 hours (P < .02). Twenty-four hours after allergen challenge, all MRI-derived flow parameters were significantly lower in the control group compared to the asthma group (P < .05). HR, CO, and cardiac function parameters measured at 24 hours showed no significant difference comparing the two groups (P > .05).

CONCLUSIONS

In asthmatic patients, MRI-derived hemodynamic parameters using phase-contrast MRI are slightly altered after segmental allergen provocation compared to normal controls indicating a mild systemic reaction to local allergen challenge.

Chronic homeostatic vagal efferent activity turndown: a theory of asthma

There is an abundance of evidence of an autonomic nervous system (ANS) imbalance in asthma, and most theories have suggested that a defect in the ANS is the fundamental pathology in asthma. This paper proposes that there is no ANS defect in asthma. It assumes that the normal homeostatic response to bronchial obstruction is a reduction in the vagally mediated, normal bronchoconstricting tonus of the airways. It then discusses how many of the pathological features of asthma may be shown to result from chronic vagal efferent activity turndown which itself results from protracted intense and continuous bronchial obstruction.

Bronchial histamine reactivity: its relationship to the reactivity of the bronchi to allergens

The aim of this study was to examine the proposal that the magnitude of the response of the bronchi to an immediate allergic reaction depends not only on the degree of sensitization of the bronchi by allergen specific IgE antibody but also on the reactivity of the bronchi to the vasoactive mediators which are released during immediate allergic reactions. This was done by determining the bronchial reactivity to Dermatophagoides pteronyssinus and to histamine of both symptomatic and asymptomatic groups of atopic subjects who had comparable serum levels of D. pteronyssinus specific IgE. Positive bronchial responses to the D. pteronyssinus extract were recorded with both the symptomatic and asymptomatic subjects, the mean bronchial threshold dose of allergen being significantly higher in the asymptomatic than in the asthmatic patients. There was a highly significant correlation between the serum level of allergen specific IgE and the bronchial threshold dose of allergen extract and also between the bronchial threshold dose of allergen extract and of histamine in all groups of subjects. The ability to predict bronchial reactivity to the allergen from the serum level of allergen specific IgE within each group was significantly better if the bronchial reactivity to histamine was included in the correlation analysis. This supports the hypothesis that whether a particular subject who is producing specific IgE antibody will develop symptoms on the inhalation of that allergen depends not only on the amount of allergen which he inhales and on the degree of sensitization of his bronchi but also on the reactivity of his bronchi to the vasoactive mediators which are released by allergen-IgE interaction.