Heart Rate Variability and Asthma Control Test

Abstract

Background HRV is widely accepted to have prognostic significance in patients with cardiovascular diseases especially after acute myocardial infarction. However, recently, interest has grown in relating some pathologies with abnormal autonomic activity based on HRV studies. Although asthmatics are known to have enhanced cholinergic activity, little HRV studies were done on asthma patients. Moreover, the results of these studies are not reproducible, probably due to inter-individual differences of autonomic balance in test group or inadequately designed methods. Objectives 1. To develop an effective spirometric score that can faithfully reflect ventilatory functions of the lungs and efficiently discriminating asthmatics from nonasthmatics 2. To detect reliability and validity of Asthma Control Test (ACT) and National Asthma Education and Prevention Program (NAEPP) in the classification of studied asthmatic patients based on above-mentioned spirometric score. 3. To correlate asthma control (using ACT and NAEPP) and ventilatory function with parameters of autonomic balance. 4. To detect the pattern of autonomic balance in asthmatics using a parameter known to be influenced by sympathetic and parasympathetic e.g. airways narrowing indicated by spirometry, blood pressure and blood glucose concentration. Methods The study involved 56 apparently healthy subjects and gender and an age matched group of 100 asthma patients classified into subgroups according to asthma severity using ACT and NAEPP classifications. Blood pressure, anthropometric, spirometric, HRV measurements together with drug therapy, blood level of glucose, hemoglobin and electrolytes were assessed for every subject. All spirometric measurements were condensed into one representative score (discrimination analysis score (DAS)) using discrimination analysis. Sensitivity and specifity of DAS were tested using conditional ratios and Receiver Operating Characteristic (ROC) curve. Screening of studied variables for significant correlations and mean differences among different groups with adjustment for possible confounding factors was performed using appropriate statistical techniques. XIII Results Spirometry: Correlations between all spirometric measurements and DAS were highly significant (P = 0.000 for all correlations). DAS when compared with FEV1% (at the most accurate cutoff equal to 80%) as a predictive measurement for presence of asthma, is proved to be more sensitive (81.00% for DAS and 71.00% for FEV1%), specific (94.14% for DAS and 92.86% for FEV1%) and accurate (86.54% for DAS and 78.85% for FEV1%). For further verification, accuracy of DAS was compared with the remaining of spirometric measurements using ROC curves. DAS is proved to be the most sensitive measure in diagnosing asthma (area under the curve = 0.933, P = 2.77E-19 and 95% confidence interval 0.897 - 0.971). Of asymptomatic asthma patients, 34.0 % were labeled poorly controlled and 41.5% were labeled uncontrolled. ACT score was higher while NAEPP class was lower in symptoms free compared with symptomatic asthmatic patients (P = 0.000 and 0.005 respectively). DAS correlate significantly, but moderately, with ACT score and NAEPP class (P = 0.000 for both, CC = 0.38 and -0.49 respectively). Heart Rate Variability: Sympathetic tone (LF Norm) of mild asthmatics was significantly lower while parasympathetic tone (HF Norm) was significantly higher compared with apparently healthy subjects (P = 0.016 and 0.017 respectively). This was also true when mild asthmatics are compared with severe asthma patients (P = 0.020 and 0.015 respectively). ACT state of asthmatics correlate significantly, but weakly, with LF Norm (CC = 0.292, P = 0.003) and HF Norm (CC = 0.309, P = 0.002). Blood Pressure and Blood Glucose Concentration: In contrast to systolic and mean arterial blood pressures, diastolic blood pressure was significantly higher in asthmatics compared with non-asthmatics (P = 0.002). Blood pressures correlate positively with sympathetic and negatively with parasympathetic activity in nonasthmatics (P < 0.05 for all). However, these correlations are lost in asthmatics. Blood glucose concentrations in asthmatic patients were significantly higher as compared with healthy subjects (P = 0.000). Blood glucose concentrations correlate positively with parasympathetic and negatively with sympathetic in non-asthmatics (P < 0.05 for all). Nevertheless, these correlations are lost in asthmatic patients. XIV Conclusions 1. DAS is more sensitive, specific and accurate compared with other spirometric measurements, but like other indicators it fails to reach 100% sensitivity and specifity on asthma diagnosis. 2. Presence or absence of symptoms did not correlate with asthma control which draws attention to asthma classification criteria. 3. The autonomic balance of mild asthma (showing high parasympathetic and low sympathetic activities) is different compared to the severe form of the disease (which showed normal parasympathetic and sympathetic activities). 4. Autonomic balance might influence symptomatology but not ventilatory function 5. Many signs of functional impairment (control of blood pressure and blood glucose concentrations) of the autonomic nervous system are noted in asthmatic patients.