Clinical and experimental hypertension : CHE
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Clin. Exp. Hypertens. · Jan 2011
Controlled Clinical TrialBlood pressure changes after automatic and fixed CPAP in obstructive sleep apnea: relationship with nocturnal sympathetic activity.
Treatment of obstructive sleep apnea (OSA) by continuous positive airway pressure (CPAP) usually causes a reduction in blood pressure (BP), but several factors may interfere with its effects. In addition, although a high sympathetic activity is considered a major contributor to increased BP in OSA, a relationship between changes in BP and in sympathetic nervous system activity after OSA treatment is uncertain. This study was undertaken to assess if, in OSA subjects under no pharmacologic treatment, treatment by CPAP applied at variable levels by an automatic device (APAP) may be followed by a BP reduction, and if that treatment is associated with parallel changes in BP and catecholamine excretion during the sleep hours. ⋯ Nocturnal DBP changes were correlated with norepinephrine (in the whole sample: r = .61, p < 0.02) and normetanephrine (r = .71, p < 0.01) changes. In OSA subjects under no pharmacologic treatment, APAP reduces BP during wakefulness and sleep, similarly to CPAP. A reduction in nocturnal sympathetic activity could contribute to the reduction in DBP during sleep following OSA treatment.
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Clin. Exp. Hypertens. · Jan 2011
Assessment of sympathovagal imbalance by spectral analysis of heart rate variability in prehypertensive and hypertensive patients in Indian population.
Though the incidence of hypertension has increased considerably in recent years, the pathophysiologic mechanism that causes progression from stage of prehypertension to hypertension has not been fully elucidated. Therefore, the present study was conducted to assess the sympathovagal imbalance in prehypertensives and hypertensives by spectral analysis of heart rate variability (HRV) to understand the nature of change in autonomic balance in this common dysfunction of mankind. Body mass index (BMI), basal heart rate (BHR), blood pressure (BP), and spectral indices of HRV such as total power (TP), normalized low frequency power (LFnu), normalized high frequency power (HFnu), ratio of low frequency power to high frequency power (LF-HF ratio), mean heart rate (mean RR), square root of the mean squared differences of successive normal to normal intervals (RMSSD), the number of interval differences of successive NN intervals greater than 50 ms (NN50), and the proportion derived by dividing NN50 by the total number of NN intervals (pNN50) were assessed in three groups of subjects: normotensives (n = 32), prehypertensives (n = 28), and hypertensives (n = 31). ⋯ It was observed that autonomic imbalance in prehypertensives was due to proportionate increased sympathetic activity and vagal inhibition, whereas in hypertensives, vagal withdrawal was more prominent than sympathetic overactivity. The LF-HF ratio, the sensitive indicator of sympathovagal balance, was significantly correlated with BMI, BHR, and BP. It was concluded that vagal inhibition plays an important role in the critical alteration of sympathovagal balance in the development of clinical hypertension in prehypertensive subjects.