Kohara K, Nishida W, Maguchi M, Hiwada K
Autonomic nervous function in non-dipper essential hypertensive subjects

Hypertension (Nov) 26:808-814 1995

Continuous ambulatory BP monitoring has identified a subpopulation of patients in whom nocturnal systolic BP does not decrease by more than 10%. These so-called "non-dippers" have a higher risk of LVH, cerebrovascular damage, and future cardiovascular events. Non-dipping is also more common in diabetics and patients with renal impairment. Dipping may be related to function of the autonomic nervous system. One way of assessing the latter is by looking at heart rate variability. The latter is quantified by looking at the "power spectrum" of the R-R interval. Variability in the low frequency band (LFB) is an indicator of both sympathetic and parasympathetic function, whereas variability in the high frequency band (HFB) is a measure of parasympathetic activity.

Kohara et al measured 24 hour blood pressures in 62 hospitalized essential hypertensive patients (diabetes, MI, CVA, renal failure excluded) along with heart rate variability. Plasma renin, catecholamines, and urinary catecholamine excretion also were measured. LV mass index was assessed by echo. All were studied at least 1 week off antihypertensive medication. They found that 31/63 patients were "non-dippers" The night/day ratio of mean blood pressure correlated with the low frequency power spectrum of the heart rate (r=0.37), suggesting that non-dipping was due to failure of withdrawal of sympathetic tone at night. Interestingly, the nocturnal heart rate was similar in dippers and non-dippers. Non-dippers had a significantly higher LV mass index by echo.

Comment: LVH has been linked to baroreceptor dysfunction. It is possible that LVH and associated damage to cardiac pressure and volume receptors may cause the alterations in heart rate variability seen in the present study. The alternative explanation is that there is a subpopulation of hypertensive patients with autonomic dysfunction and increased sympathetic tone that have an accelerated degree of end-organ damage. (Daugirdas)

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H: Pathophysiology : Sympathetic nervous system
H: Exam and lab tests : Ambulatory monitoring