الفهرس 
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Abstract
Bronchial asthma (BA) is a chronic inflammatory disorder of the airways in which many cells and cellular elements play a role. It is associated with airway hyperresponsiveness that leads to recurrent episodes of wheezing, breathlessness, chest tightness and coughing (GINA, 2006).
It is likely that this hyperresponsiveness is associated with abnormal autonomic nervous system (ANS) control. In particular, the parasympathetic (vagal) component of the ANS appears to be implicated in the pathogenesis of asthma (Lewis et al., 2006).
The present work was done to assess heart rate variability (HRV) in asthmatic patients free from acute asthmatic attacks, as a reflection of the status of the ANS. Thirty children with asthma were recruited from the Chest clinic, the Children’s hospital, Ain Shams University. They were 17 males and 13 females. Their ages ranged from 6 to 13 years. Ten apparently healthy age and sex matched children served as controls.
All patients were assessed by history taking, clinical examination, spirometry, 12 lead surface electrocardiogram, non invasive cardiovascular reflex tests and ambulatory E.C.G. (Holter monitoring) with measurement of time domain HRV indices (SDNN, SDANN, RMSSD and PNN50).
Assessment of ANS using non invasive cardiovascular reflex tests revealed that there was an autonomic nervous system dysfunction in the form of parasympathetic hyperresponsiveness. Analysis of HRV indices revealed that significantly more patients demonstrated decreased SDNN values than controls. This implies that the overall function of autonomic nervous system as expressed by SDNN, is decreased in patients. On the other hand we found that RMSSD and PNN50 was significantly increased in asthmatics compared to controls which indicates parasympathetic hyperresponsiveness.
In our study we found no difference of statistical significance between group І (mild intermittent)and group П (persistent asthma) in all non invasive cardiovascular reflex tests and all HRV except PNN50 that showed a significant increase in patients with mild intermittent asthma compared to patients with persistent asthma. Patients with mild intermittent asthma also demonstrated lower FEF25-75 values even though this was not statistically significant. This finding may suggest that changes in HRV precede changes in spirometric functions in detecting potentially poor control of asthma. This suggests a novel role for HRV testing in the evaluation of the degree of asthma control.
In our study we found no difference of statistical significance in SDNN and SDANN between patients on β2 agonists or steroids and controls. However, they had lower values for RMSSD and PNN50 compared to patients not on β2 agonists or steroids. RMSSD and PNN50 values in patients on β2 agonists or steroids were closer to controls than those of patients not on either medication. Therefore, β2 agonists and steroids can alter the function of the ANS in asthmatics to become closer to normal, suggesting that treatment of asthma reduces parasympathetic tone.
from the results of this study we can conclude that:
- Even in normal conditions when patients are free of asthmatic attack, autonomic nervous function of asthmatics differs from that of normal children.
- There is high vagal tone in asthma which suggests that the parasympathetic component of the ANS is strongly implicated in the pathogenesis of asthma.
- Drug therapy used in treatment of asthma had an important role in correction of the ANS imbalance which existed in asthmatics towards normal.