Pathogenesis of Asthma: A Review

Calcium channel blockers for lung function improvement in asthma: A systematic review and meta-analysis

BACKGROUND

For decades, calcium channel blockers (CCBs) have been believed to play a role in asthma treatment. However, the clinical efficacy of CCBs for lung function improvement in patients with asthma has not been qualitatively evaluated.

OBJECTIVE

To assess the effect of CCBs vs placebo on lung function test results in adults with asthma.

METHODS

Various databases were systematically searched to identify all randomized clinical trials with adults with asthma. We aimed to assess the influence of CCBs on forced expiratory volume in 1 second (FEV₁), forced vital capacity (FVC), peak expiratory flow rate (PEFR), and provocative concentration of bronchoconstrictive agents causing a 20% decrease in FEV₁ (PC₂₀) compared with a placebo. All effect estimates were pooled by the generic inverse variance method with random-effects meta-analysis. Subgroup analysis, sensitivity analysis, and heterogeneity investigation were performed.

RESULTS

Thirty eligible articles with 301 patients were included in this meta-analysis. Our results revealed that in a standard exercise test CCBs could produce a mean maximal percentage decrease in FEV₁ of 11.56% (95% confidence interval, 8.97%-14.16%; P < .001) and an increase in postdose FEV₁ by 80 mL (95% confidence interval, 0.02-0.15 mL; P = .01). However, there was no statistical significance for CCBs in postdose FVC, PEFR, or PC₂₀ of histamine and methacholine.

CONCLUSION

CCBs may be beneficial for lung function improvement in asthma, especially in exercise-induced asthma. However, there is a lack of evidence for CCBs protecting asthma patients from chemical irritation.

Anti-allergic effects of herbal product from Allium cepa (bulb)

Allium cepa (Family Liliaceae) is a reputed Indian medicinal herb that is prescribed as an effective remedy for several ailments in the Ayurvedic system of medicine. The aim of this study was to evaluate its efficacy against various events responsible for Type I allergic reactions. A herbal fraction (ALC-02) from A. cepa (bulb) inhibited histamine release and attenuated intracellular calcium levels in Compound 48/80-induced rat peritoneal mast cells. It also prevented Compound 48/80-mediated systemic anaphylaxis while lowering histamine levels in plasma. ALC-02 suppressed carrageenan-induced rat paw edema. It inhibited eosinophil peroxidase activity and protein content in bronchoalveolar lavage fluid (BALF) of ovalbumin-challenged mice. In this experiment ALC-02 also caused a substantial reduction in lipid peroxidation in BALF/lung tissue and augmented superoxide dismutase activity in lung tissue. ALC-02 suppressed erythrocytic lysis caused by Triton X-100. A significant quenching of 1,1-diphenyl-2-picrylhydrazyl radical by ALC-02 was observed. The results have shown a promising anti-allergic profile of ALC-02 that could be attributed to its potential antihistaminic, anti-inflammatory, and antioxidant activities.

Reflex heart rate control in asthma. Evidence of parasympathetic overactivity

The bronchial hyperreactivity characteristic of asthma may be related to enhanced parasympathetic nervous activity. We postulated that an abnormality in the autonomic control of airway caliber might be reflected by a parallel change in the reflex control of heart rate. We examined the heart-rate variations induced by deep breathing (respiratory sinus arrhythmia), the Valsalva maneuver, and standing up from the recumbent position in asthmatic subjects and nonasthmatic control subjects. The asthmatic patients had evidence of enhanced parasympathetic neural drive to the sinoatrial node, as manifested by a significantly greater magnitude of respiratory sinus arrhythmia, than the controls (p less than 0.0005). We were unable to induce a similar change in normal subjects by resistance breathing. A statistical analysis suggested the presence of a relationship between the magnitude of respiratory sinus arrhythmia and the degree of bronchial hyperreactivity in a group of asthmatic patients. Our results support the hypothesis that enhanced parasympathetic activity is an important factor in the pathogenesis of bronchial asthma.