Kohara K, Nishida W, Maguchi M, Hiwada K
Autonomic nervous function in non-dipper essential
(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
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Sympathetic nervous system
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