Blood Pressure and Sleep

On the Physiology of Blood Pressure Decrease During Nocturnal Sleep in Healthy Humans

Friedhelm Sayk; Christoph Becker; Christina Teckentrup; Horst-Lorenz Fehm; Jan Struck; Jens Peter Wellhoener; Christoph Dodt
From the Clinic for Internal Medicine I, University Hospital of Schleswig-Holstein, Luebeck, Germany

That sleep is accompanied by a blood pressure decrease is well known; however, the underlying physiology deserves further investigation.

The present study examines in healthy subjects 2 main questions: is this dipping actively evoked? and what are the consequences of nondipping for daytime blood pressure?

Nocturnal blood pressure was extrinsically elevated in 12 sleeping subjects to mean daytime values by continuously infused phenylephrine.

This nondipping significantly lowered morning blood pressure during rest and 3 hours after resuming physical activity compared with a control condition (isotonic saline).

Neither muscle sympathetic nerve activity nor sensitivity of -adrenoceptors was reduced. However, the set point for initiation of regulatory responses through the baroreflex was clearly shifted toward lower blood pressure levels.

Our results support the hypothesis of an actively regulated central mechanism for blood pressure resetting and set point consolidation of the baroreflex during nighttime sleep.

This is suggested by the fact that extrinsically induced nondipping induces sustained decrease in blood pressure during the following morning through an actively lowered baroreflex set point.

Keywords: dipping • baroreflex • microneurography • MSNA • sympathovagal balance

Hypertension. 2007;49:1070.

© 2007 American Heart Association, Inc.

Mild and Moderate Hypertension: Cerebral Hemodynamics

Cerebral Hemodynamics After Short- and Long-Term Reduction in Blood Pressure in Mild and Moderate Hypertension

Rong Zhang; Sarah Witkowski; Qi Fu; Jurgen A.H.R. Claassen; Benjamin D. Levine
From the Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas and the University of Texas Southwestern Medical Center at Dallas

This study tested the hypothesis that acute reduction in blood pressure (BP) at the initial stage of antihypertensive therapy compromises brain perfusion and dynamic cerebral autoregulation in patients with hypertension.

Cerebral blood flow velocity and BP were measured in patients with mild and moderate hypertension and in healthy volunteers at baseline upon reduction of BP within 1 to 2 weeks of administration of losartan/hydrochlorothiazide and after 3 to 4 months of treatment.

The transfer function between beat-to-beat changes in BP and cerebral blood flow velocity was estimated to assess dynamic autoregulation.

After 1 to 2 weeks of treatment, BP was reduced in mild (143±7/88±4 versus 126±12/77±6 mm Hg) and moderate hypertension (163±11/101±9 versus 134±17/84±9 mm Hg; P<0.05).>

These reductions in BP were well maintained over the 3 to 4 month period. Cerebral blood flow velocity did not change, whereas cerebrovascular resistance index was reduced by 17% (P<0.05)>

Baseline transfer function gain at the low frequencies (0.07 to 0.20 Hz) was reduced in moderate hypertension, consistent with cerebral vasoconstriction and/or enhanced dynamic autoregulation.

However, this reduced transfer function gain was restored to the level of control subjects after reduction in BP.

These findings, contrary to our hypothesis, demonstrate that there is a rapid adaptation of the cerebral vasculature to protect the brain from hypoperfusion even at the initial stage of antihypertensive therapy in patients with mild and moderate hypertension.

Keywords: hemodynamics • brain • hypertension • cerebral blood flow • angiotensin AT1 receptor • transcranial Doppler

Hypertension. 2007;49:1149.

© 2007 American Heart Association, Inc

Children: Blood pressure and Microcirculation

Blood Pressure and Retinal Arteriolar Narrowing in Children

Paul Mitchell; Ning Cheung; Kristin de Haseth; Bronwen Taylor; Elena Rochtchina; F. M. Amirul Islam; Jie Jin Wang; Seang Mei Saw; Tien Y. Wong
From the Centre for Vision Research (P.M., B.T., E.R., J.J.W.), Department of Ophthalmology, University of Sydney, New South Wales, Australia; Centre for Eye Research Australia (N.C., K.d.H., F.M.A.I., J.J.W., T.Y.W.), University of Melbourne, Victoria, Australia; Royal Melbourne Hospital (N.C.), Victoria, Australia; Medical University Leiden (K.d.H.), Leiden, The Netherlands; and Singapore Eye Research Institute (S.M.S., T.Y.W.) and the Department of Community, Occupational and Family Medicine (S.M.S.), Yong Loo Lin School of Medicine, National University of Singapore, Singapore.

Retinal arteriolar narrowing is a known response of hypertension and independently predicts cardiovascular mortality in adults. Whether elevated blood pressure leads to retinal arteriolar narrowing in young children is unknown.

We examined the relationship of retinal vascular caliber and blood pressure levels in 2 population-based cohorts among children aged 6 to 8 years in Sydney, Australia (1572 children) and Singapore (380 children). Participants had digital retinal photographs and measurement of retinal arteriolar (or small artery) and venular (or small vein) caliber.

Children with higher quartiles of blood pressure had significantly narrower retinal arterioles than those with lower blood pressure (retinal arteriolar caliber 162.8, 161.0, 157.8, and 157.1 µm (P for trend<0.001), trend="0.0024">

After controlling for age, sex, race, body mass index, refraction, and birth parameters, each 10-mm Hg increase in systolic blood pressure was associated with narrowing of the retinal arterioles by 2.08 µm (95% confidence interval: 1.38 to 2.79; P<0.0001) p="0.016)">

These associations were consistent across age, sex, body mass index, and birth parameters.

Retinal venules were not affected by blood pressure.

We conclude that higher childhood blood pressure is associated with retinal arteriolar narrowing.

Our data provide evidence that the effects of elevated blood pressure may manifest early in life.

Keywords: retinal arteriolar narrowing • blood pressure • children • microcirculation • hypertension

Hypertension. 2007;49:1156.

© 2007 American Heart Association, Inc.

Pregnancy and Previous Hypertensive Disease

Previous Hypertensive Disease of Pregnancy Is Associated With Alterations of Markers of Insulin Resistance

Joël Girouard; Yves Giguère; Jean-Marie Moutquin; Jean-Claude Forest
From the CHUQ (J.G., Y.G., J-C.F.), Hôpital St-François d’Assise, Faculté de Médecine, Université Laval, Québec City, Québec, Canada; and Centre hospitalier universitaire de Sherbrooke (J-M.M.), Pavillon Fleurimont, Sherbrooke, Québec, Canada

Insulin resistance syndrome has been observed in women with hypertensive disease of pregnancy, but few studies evaluated the presence of the syndrome a few years after delivery.

The objective of this study was to evaluate the presence of insulin resistance and its metabolic alterations in these women compared with those who had a normal pregnancy.

We performed an observational study in 168 women with previous hypertensive disease of pregnancy and 168 control subjects with normal pregnancy contacted, on average, 7.8 years after their first delivery (mean age: 34.8 years).

Complete blood lipid profile, insulin, glucose, homocysteine, adipokins, and markers of inflammation were measured.

Also, an oral glucose tolerance test was performed in 146 case and 135 control subjects. Case subjects were more overweight compared with control subjects.

We found significantly lower high-density lipoprotein cholesterol and adiponectin levels and higher apolipoprotein (apo) apoB/apoA1 ratio, homocysteine, leptin, and insulin levels among case subjects compared with control subjects (P 0.004).

Also, case subjects were more insulin resistant in the basal state estimated by homeostasis assessment model 2, as well as in the nonbasal state as estimated by insulin sensitivity indices calculated from the oral glucose tolerance test.

Finally, in a multivariate regression model, leptin, apoB/apoA1 ratio, waist circumference, adiponectin, and free fatty acids explained 40% of homeostasis assessment model 2 variance.

Young women with previous hypertensive disease of pregnancy show signs of insulin resistance within the first decade after delivery.

These findings suggest that insulin resistance may be the link between hypertensive disease of pregnancy and increased cardiovascular risk later in life.

Keywords: hypertension • insulin resistance • obesity • preeclampsia • gestational hypertension • cardiovascular diseases • dyslipidemia

Hypertension. 2007;49:1056.

© 2007 American Heart Association, Inc.

Pressor Effect of Salt

What Initiates the Pressor Effect of Salt in Salt-Sensitive Humans?
Observations in Normotensive Blacks

Olga Schmidlin; Alex Forman Anthony Sebastian; R. Curtis Morris, Jr
From the Division of Nephrology, Department of Medicine, University of California San Francisco.

We tested the traditional hypothesis that an abnormally enhanced renal reclamation of dietary NaCl alone initiates its pressor effect ("salt sensitivity").

Under metabolically controlled conditions, we grouped 23 normotensive blacks as either salt-sensitive (SS) or salt-resistant (SR), depending on whether or not dietary NaCl loading did or did not increase mean arterial blood pressure (MAP) by 5 mm Hg.

We determined whether dietary NaCl loading induces greater increases in external Na+ balance, plasma volume, and cardiac output in SS, compared with any in SR subjects, and differential changes in systemic vascular resistance (SVR) that could account for the pressor differences between SS and SR subjects.

Using impedance cardiography, we measured cardiac output and SVR daily at 4-hour intervals throughout the last 3 days of a 7-day period of low NaCl intake (30 mmol per day) and throughout a subsequent 7-day period of NaCl loading (250 mmol per day).

In the 11 SS subjects, compared with the 12 SR subjects, NaCl loading induced no greater increases in Na+ balance, body weight, plasma volume, and cardiac output. Yet, from days 2 to 7 of NaCl loading, changes of MAP in SS diverged progressively from those in SR.

From days 2 to 4, progressive increases of MAP in SS subjects reflected importantly impaired decreases of SVR, as judged from "normal" decreases of SVR in SR subjects.

In SS and SR subjects combined, changes in both MAP and SVR on day 2 strongly predicted changes in MAP on day 7.

In many normotensive blacks, vascular dysfunction is critical to the initiation of a pressor response to dietary NaCl.

Keywords: blood pressure • sodium chloride • electrolyte balance • vascular resistance • cardiac output

Hypertension. 2007;49:1032.

© 2007 American Heart Association, Inc.