Spectral analysis of heart rate variability in bronchial asthma patients

The study was carried in the Departments of Physiology and Medicine at S.M.S. Medical College, Jaipur. Thirty patients of bronchial asthma, aged 20-30 years attending outpatient clinics of S.M.S. Hospital and thirty healthy volunteers were recruited in the present study for spectral analysis of Heart Rate Variability (HRV) using impedance peripheral pulse in the right forearm. Two spectral components were recorded namely high frequency (HF) component (0.15-0.4 Hz), an indicator of vagal efferent activity and low frequency (LF) component (0.04-0.15 Hz), replicator of composite sympatho-vagal interplay. These components were analyzed as LF nu (Low Frequency normalized unit), HF nu (High Frequency normalized unit) and LF/HF ratio. Low frequency component in absolute units of the asthmatic patients differed insignificantly (P > 0.05) from LF of the subjects, whereas the same calculated as normalized units was found to be significantly low in the patient group (P < 0.01), as compared to that of the control group. The High Frequency (in absolute units) index of HRV was significantly high in asthmatics (P < 0.01) as compared to the HF (absolute units) of controls. Similar trend was observed in the normalized units of HF (P<0.01). LF/HF ratio was not significantly different in patient and control groups (P > 0.05). It was concluded that a significantly raised central vagal outflow and a concomitant significantly low central sympathetic efferent could be appreciated in asymptomatic asthmatic patients as compared to that in the control group. This deranged sympathovagal interplay with parasympathetic dominance could be a plausible pathophysiological mechanism leading to airway obstruction, the hallmark of bronchial asthma.