|Year : 2012 | Volume
| Issue : 3 | Page : 159-162
A study of the sympathetic nervous system in bronchial asthma
Th Pricila Devi, W Kanan, Th Shantikumar Singh, W Asoka, L Benjamin
Department of Physiology, Respiratory Medicine, RIMS, Imphal, Manipur, India
|Date of Web Publication||10-Jun-2013|
Th Pricila Devi
Department of Physiology, RIMS, Imphal, Manipur
Source of Support: Director, RIMS, Imphal, Manipur, Conflict of Interest: None
DOI: 10.4103/0972-4958 .113227
Objective: To test sympathetic division of autonomic nervous system and observe any dysfunction in patients of bronchial asthma. Materials and Methods: Fifty four patients, 18 males, 36 females, and 30 healthy control subjects attending Respiratory Medicine out-patient department Regional Institute of Medical Sciences, Imphal were included in the study. Age ranging from 15 to 60 years were recruited for the study. Spirometry values of forced vital capacity (FVC), forced expiratory volume in first second (FEV 1 ) , FEV 1 /FVC, peak expiratory flow rate (PEFR), forced expiratory flow (FEF 25-75% ) recorded by using HELIOS 702 (Recorders and Medicare System, Chandigarh). Predicted values were taken as values for normal subjects. Sympathetic nervous system tested by measuring diastolic blood pressure response to sustained hand-grip for 2 min and from supine to standing for 3 min. Results: FVC, FEV 1 , PEFR, FEF 25-75% were significantly lower in asthmatics as compared to controls. Diastolic blood pressure response to sustained hand-grip for 2 min and from supine to standing for 3 min was higher in asthmatics as compared to controls. Conclusion: Sympathetic nervous function assessment of the patients shows that sympathetic abnormalities occur in patients of bronchial asthma.
Keywords: Bronchial asthma, Sympathetic nervous system, Spirometry
|How to cite this article:|
Devi T, Kanan W, Singh T, Asoka W, Benjamin L. A study of the sympathetic nervous system in bronchial asthma. J Med Soc 2012;26:159-62
| Introduction|| |
Asthma is a common clinical disorder and is characterized by reversible obstruction of the bronchial airways leading to symptoms such as shortness of breath, wheezing, and coughing. The obstruction of the bronchial airways can be produced by one or more of the following: Contraction of bronchial smooth muscle, hypertrophy of the bronchial wall, dilatation of bronchial mucosa, and secretions in the bronchial lumina. Airway hyper responsiveness and accompanying bronchospasm are the principal hallmarks of asthma. 
The bronchoconstricting and bronchodilating divisions of the autonomic nervous system control airway caliber of lungs. Parasympathetic hyperactivity in asthmatics eventuates in bronchoconstriction. Sympathetic activity increases to combat this but, fails to control bronchoconstriction due to negligible innervations of the airway smooth muscles although; it causes vasoconstriction of blood vessels. The cholinergic nervous system is more important in the regulation of airway tone as it has direct innervations of airway smooth muscle, while adrenergic system is important in regulation of airway blood flow and glandular secretion but it does not innervate airway smooth muscle. It may be that the inhibitory non-adrenergic non-cholinergic mechanism is the only neural bronchodilator pathway present in human airways. However, β2 -adrenergic receptors are abundantly expressed on human airway smooth muscle. Activation of these receptors causes bronchodilation. 
Autonomic function tests are standardized, non-invasive, and easily reproducible tests that can detect altered respiratory autonomic status and hence, assess autonomic abnormality in asthmatic patients. 
Airflow limitation is highly reversible either spontaneously or with therapy in asthma. Moreover, use of spirometry in patients at risk for the development of both diseases or with respiratory symptoms help in detecting cases at an early stage when intervention may prevent further deterioration. Because of reversible component of asthma, the use of peak flow meters to determine airflow on a continued basis is practical and results in improved outcomes. Therefore, frequent flow determination is recommended in the routine management of asthma. 
Not many studies have established significant autonomic dysfunction in asthma. This study was undertaken to explore further and see the impact of sympathetic nervous system activity on different grades of functional lung impairment.
| Materials and Methods|| |
The present study was carried out in the Department of Physiology, Regional Institute of Medical Sciences (RIMS), Imphal, Manipur during the period of July, 2011 to July, 2012.
A total of 54 patients, 18 males, 36 females, and 30 healthy control subjects attending Respiratory Medicine out-patient department RIMS, Imphal were included in the study. Age ranging from 15 to 60 years was recruited for the study.
Patients with associated diseases like diabetes mellitus, hypertension, cardiac problems, pulmonary fibrosis, neuromuscular diseases, and ascites were excluded.
Spirometric studies were conducted by means of HELIOS 702 (Recorders and Medicare System, Chandigarh) in the Respiratory Physiology Laboratory of Department of Physiology, RIMS, Imphal. The results were compared with the predicted values for the same age, sex, height, and weight. Spirometric studies were conducted to grade the severity of functional lung impairment. Severity of asthma is graded, based on FEV 1 % of predicted value according to guidelines given by the global initiative for asthma (GINA) updated 2008. FEV 1 ≤ 60% is graded as severe, FEV 1 60-80% as moderate and FEV 1 ≥ 80% is graded as mild asthma.
Sympathetic division of the autonomic nervous system was tested by performing the following tests:
- Blood pressure response to sustained hand-grip;
The subjects were asked to grip the dynamometer (Model India Medico Instrument 2095, Delhi-6) with their dominant hand at one third of maximal voluntary contraction and maintain the pressure on dynamometer for 2 min and the blood pressure were recorded from the non-exercising arm before the test, 1 min after onset of hand-grip and just prior to release of hand-grip at 2 min. The results were recorded.
- Blood pressure response to standing from the supine posture:
The subjects were asked to stand-up quickly from supine posture and keep standing quietly for 3 min. The blood pressure was recorded at 0 min (in lying position) and 0.5 th , 1 st , 2 nd , and 3 rd min of standing up. The difference in systolic and diastolic pressure at half, 1 st , 2 nd , and 3 rd min of standing from that of supine (baseline; 0 min) posture were calculated. The results were recorded.
For analytical purposes, statistical techniques like mean, standard deviation, t-test, and correlation co-efficient are used whenever found suitable and necessary through SPSS software and accordingly interpretations are made. Statistical significance is taken to be at P < 0.05.
| Results|| |
[Table 1] show the demographic profile of 54 patients who were selected for the study. Eighteen males (33.3%) and 36 females (66.7%) were recruited for the study. The highest percentage of the patients has their age range of 25-34 years with 33.3%, followed by 35-44 with 26%. Age group between 15-24 and 55-60 contributes 14.8% of patients each with age group 45-54 contributing the least. The average age is found to be 36.09.
[Table 2] shows comparison of FVC, FEV 1 , FEV 1 /FVC, PEFR, FEF 25-75% of asthmatics against their predicted values. It is seen that all values are significantly less in asthmatics except FEV 1 /FVC which is more in asthmatics.
|Table 2: Mean±SD of FVC, FEV1, FEV1/FVC, PEFR, FEF25-75% of asthmatics as compared with the predicted values|
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[Table 3] shows the distribution of patients according to the severity of asthma, which was graded based on FEV 1 (according to the guidelines given by GINA). Highest percentages of patients belong to mild asthma accounting 59.3%. 18.5% of the patients have severe asthma with 22.2% of the patients having moderate asthma.
|Table 3: Percentage-wise distribution of cases according to grading of severity of asthma|
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[Table 4] demonstrates the sympathetic function tests results in asthmatics as compared to controls. It is observed that there is significant rise in diastolic blood pressure (DBP) 2 min after hand-grip test in asthmatics as compared to control subjects, but rise in DBP 1 min, 2 min and 3 min after supine to standing test is not significant.
[Table 5] shows sympathetic function tests results in relation to severity of asthma. DBP rise 2 min after hand-grip test is found to be highest in cases of severe asthma, which is significant. Rise in DBP 1 min after supine to standing test is highest in mild asthma though, statistically not significant, rise in DBP after 2 min and 3 min are insignificantly highest in moderate asthma.
|Table 5: Comparison of sympathetic function tests in different groups of asthma severity with control subjects|
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[Table 6] shows correlation between FEV 1 % Predicted and DBP rise 2 min after hand-grip test in different asthmatic groups. It is found that there is an insignificant negative correlation in cases of mild asthma which indicates that with the fall in FEV 1 % predicted there is more rise in DBP after hand-grip test in mild asthma.
|Table 6: Correlation between FEV1 % predicted and DBP rise 2 min after hand-grip test in different asthmatic groups|
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| Discussion|| |
In our study, we have taken 54 cases of diagnosed bronchial asthma whose spirometry and sympathetic function tests were done and relevant observations made. There were 33.3% males against 66.7% females. The highest percentage of patients has their age range of 25-34 years contributing 33.3% of total with average age of 36.09.
Based on FEV 1 % predicted, severity of asthma is graded. FEV 1 % predicted value for grading of severity of asthma is done according to guidelines given by the GINA updated 2008, where for severe asthma FEV 1 is ≤ 60% predicted, for moderate degree of asthma 60-80% predicted and for mild asthma ≥ 80% predicted. The highest percentage of the patients belongs to mild group accounting for 59.3% followed by moderate degree of asthma with 22.2% and severe asthma contributes 18.5%.
In our study, it is seen that the entire lung function parameters namely FVC, FEV 1 , PEFR, FEF 25-75% are all lower in asthmatics as compared with the predicted values. FVC in liters is 1.99 in asthmatics as compared to predicted value of 2.68 L. FEV 1 in liters in asthmatics is 1.77 whereas predicted value is 2.18 L. PEFR in L/s is 4.21 in asthmatics and predicted value is 6.46 L/s. FEF 25-75% in L/s in asthmatics is 2.27 and predicted value is 3.61 L/s which interpret that patients with bronchial asthma do have reduced ventilatory functions. FEV 1 decline occurs in asthmatics and the rate of decline of FEV 1 is increased in subjects with new asthma whereas in subjects with chronic asthma the decline of FEV 1 does not differ significantly from the annual decline in the non-asthmatics. 
Asthma represents an imbalance of the autonomic nervous system. Several types of autonomic defects have been proposed in asthma; enhanced cholinergic, α-adrenergic, excitatory non-adrenergic non-cholinergic mechanisms promoting bronchoconstriction and glandular secretion. , Hyposensitivity at β-adrenergic receptors promote bronchodilation, reduction in bronchial secretions and impairment of IgE-mediated mast cell degranulation. ,
In our study, vascular response after sympathetic function tests in the form of DBP rise in mmHg in asthmatics after hand-grip test is significantly higher as compared to controls. The mean rise was 16.62 ± 6.96 as compared to 10.62 ± 5.29 in control subjects. The rise in diastolic blood pressure in this test is a measure of sympathetic efferent vasoconstrictor function mediated via α-adrenergic receptor and in asthma α-adrenergic hyper responsiveness has been proposed.  Results of this test demonstrate the function of sympathetic efferent on the blood vessels, but the sympathetic system cannot be directly correlated with bronchial hyperactivity as airway α- and β-receptor stimulation is under control of circulating adrenaline and noradrenaline and direct innervations of human airways smooth muscle is negligible.
The increased adrenergic drive to combat parasympathetic hyperactivity causing bronchoconstriction is also supported by the fact that in asthmatics β-receptor blockade causes severe bronchoconstriction, whereas in normal subjects no significant effect on airway caliber occurs.  Rise in DBP after supine to standing test is seen in our study in asthmatics which is more than the control subjects but it is statistically insignificant. This rise is attributed to increased adrenergic drive (sympathetic hyperactivity) in asthmatics to combat parasympathetic hyperactivity.
In our study, there is a linkage between the severity of disease and sympathetic abnormality. Patients with less severe disease tend to have less severe abnormality than patients with severe disease. The insignificant negative correlation between FEV 1 % predicted and DBP rise 2 min after hand-grip test in mild asthma indicates that with the fall in FEV 1 % predicted there is more rise in DBP in mild asthmatics group. This is because patients with severe disease tend to have more severe abnormality than patients with less severe disease. This supports the findings of other authors that sympathetic hyperactivity develops in asthmatics to combat the bronchoconstriction caused parasympathetic hyperactivity.
| Conclusion|| |
Functional lung impairment in patients of bronchial asthma can be identified by computerized spirometry in terms of severity of air obstruction. Sympathetic nervous function assessment of the patients shows that sympathetic abnormalities occur in patients of bronchial asthma. These abnormalities are found to be more in those patients with severe asthma. Mild and moderate asthmatic patients also exhibit sympathetic abnormalities but in lesser degree than the severe group. Patients with mild asthma are found to have an insignificant negative correlation between FEV 1 % Predicted and DBP rise 2 min after hand-grip test indicating that with the fall in FEV 1 % predicted there is more rise in DBP which supports the notion that sympathetic hyperactivity develops in bronchial asthma to combat parasympathetic over activity that develops in the disease process.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]