[Variability of arterial blood pressure: importance, mechanisms and clinical significance].
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Adult↗
Biomedical subjects
G Parati
Publications and source records attributed to G Parati.
Influence of cardiopulmonary receptors on the bradycardic responses to carotid baroreceptor stimulation in man.
Animal studies have shown that arterial baroreflexes are modulated by reflexes originating from the cardiopulmonary volume receptors, and that this modulation consists of a reduction of the inhibitory influence exerted by arterial baroreceptors on the heart and peripheral circulation. This has not been confirmed in man, however, in whom no reduction in the bradycardic response to carotid baroreceptor stimulation has been observed after the mild increase in central venous pressure (right atrial catheter) and cardiopulmonary receptor activity provided by passive leg raising. In seven normotensive subjects carotid baroreceptors were gradedly stimulated by progressively increasing carotid transmural pressure through a neck chamber device, the resulting reflex lengthening in R-R interval being measured in the two-three cardiac cycles immediately after the baroreceptor stimulus. This manoeuvre was performed in control conditions and repeated during a head-out water immersion which increased central venous pressure (right atrial catheter) from 1.5 +/- 0.2 to 12.0 +/- 0.9 mmHg (mean +/- SE), thereby providing a marked increase in the cardiopulmonary receptor stimulus. In the control condition graded stimulation of the baroreceptors caused a progressive lengthening in R-R interval, the maximal effect being + 477.4 +/- 57.2 ms. Immersion increased the R-R interval from 774.2 +/- 3.2 to 961.6 +/- 5.8 ms (P less than 0.01) and reduced mean arterial pressure (cuff measurement) from 96.0 +/- 1.0 to 82.3 +/- 0.9 mmHg. The changes in R-R interval induced by carotid baroreceptor stimulation were virtually identical with those observed in the absence of immersion.
Adult↗
Relationship of 24-hour blood pressure mean and variability to severity of target-organ damage in hypertension.
Casual blood pressure (BP) can predict the development of cardiovascular morbidity and mortality, but the correlations between its values and the subsequent occurrence of such complications are low. This may depend on different individual resistance to the damage produced by hypertension. However, it may also depend on the recognized inability of causal BP to reflect accurately the 24-h mean and profile BP. In order to test the latter hypothesis, 24-h BP was recorded intra-arterially (Oxford method) in 108 hospitalized subjects with essential hypertension ranging from mild to severe. The 24-h means and standard deviations (i.e. variabilities) for systolic, mean and diastolic BP obtained by computer analysis of the BP tracing were related to the rate and severity of target-organ damage (TOD) assessed by clinical examination and quantified according to a predetermined score. The results confirmed that 24-h BP may be variably different from cuff BP among subjects. For nearly any value of cuff BP, subjects in whom the 24-h mean BP was low had a lower prevalence and severity of TOD than those in whom the 24-h mean BP was high (P less than 0.01). Furthermore, for nearly any level of 24-h mean BP, subjects in whom the 24-h BP variability was low had a lower prevalence and severity of TOD than those in whom the 24-h BP variability was high (P less than 0.05). These findings demonstrate that the severity of hypertension is more closely related to 24-h mean BP than to cuff BP values.(ABSTRACT TRUNCATED AT 250 WORDS)
Adolescent↗
Role of heart rate variability in the production of blood pressure variability in man.
In both normotensive and hypertensive subjects blood pressure (BP) and heart rate (HR) show concordant changes over 24 h. This may depend on a central factor exerting influences of the same nature on cardiac and vascular targets. An alternative explanation, however, is that a cause-effect relationship links these variabilities, i.e. that HR variations induce BP changes [presumably via variations in cardiac output (CO)]. Blood pressure was recorded intra-arterially in five supine and five exercising (walking) essential hypertensive subjects during a control period of 1 h and during an additional hour in which atropine, 0.04 mg/kg body weight, was injected intravenously (i.v.). The same recordings were performed in seven other subjects, in which saline rather than atropine was employed. One-hour BP and HR variabilities (variation coefficients, VC) were computer analysed. In both the supine and the exercising subjects atropine caused a marked reduction in HR VC (-65.3 and -48.4%, respectively). In the supine subjects this reduction was accompanied by only a modest reduction in BP VC whereas in the exercising subjects the BP VC increased by 30.4%. In the seven subjects in which saline was injected no change in BP and HR VC occurred. Thus a marked reduction in HR variability is not accompanied by a comparable attenuation in BP variability, which rules out a cause-effect link between these two phenomena. Indeed, during physical exercise HR stabilization is followed by an increase rather than a reduction in BP variation, which supports the conclusion that under some circumstances HR plays an anti-oscillatory role.
Activity Cycles↗
Calcium antagonists and neural control of circulation in essential hypertension.
Data from animals and from man suggest that calcium antagonists interfere with alpha-adrenergic receptors and that this mechanism may be responsible for some of the vasodilation induced by these drugs. However, alpha-adrenergic receptors play a primary role in baroreceptor regulation of the cardiovascular system and blood pressure homeostasis, which might therefore be adversely affected by calcium antagonist treatment. We addressed this question in 14 essential hypertensives studied before treatment, 1 h after 20 mg oral nitrendipine and 5-7 days after daily administration of 20 mg oral nitrendipine. Blood pressure was measured by an intra-arterial catheter, heart rate by an electrocardiogram, cardiac output by thermodilution and forearm blood flow by venous occlusion plethysmography. Total peripheral and forearm vascular resistances were calculated by dividing mean blood pressure by blood flow values. Plasma norepinephrine was also measured (high performance liquid chromatography) in blood taken from the right atrium. Compared with the pretreatment values, acute nitrendipine administration caused a fall in resting blood pressure, an increase in the resting heart rate and cardiac output, and a fall in resting peripheral and forearm vascular resistance. The resting hypotension and vasodilation were also evident during the prolonged nitrendipine administration, which was, however, accompanied by much less resting cardiac stimulation than that observed in the acute condition. Baroreceptor control of the heart rate (vasoactive drug method) was similar before and after acute and prolonged nitrendipine treatment. This was also the case for carotid baroreceptor control of blood pressure (neck chamber technique) and for control of forearm vascular resistance as exerted by receptors in the cardiopulmonary region (lower-body negative-pressure and passive leg-raising techniques).(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Antihypertensive effect of a new formulation of slow release oxprenolol in essential hypertension.
To test whether a new formulation of a slow release oxprenolol (SLOx) can produce a steady 24-h antihypertensive effect, we recorded 24-h intraarterial blood pressure (Oxford technique) in eight ambulant inpatients (age 44.5 +/- 3.0 years, mean +/- SE) with a mild or moderate hypertension who were untreated since three weeks. The study was started seven days after hospitalization and was conducted according to a randomized doubleblind cross-over design. Blood pressure recordings were made after (a) a 7-day administration of SLOx in a single evening dose, and (b) a 7-day administration of placebo. This design allowed to determine the effect of SLOx without interference from nonspecific blood pressure lowering factors. Blood pressure effects of handgrip, submaximal cyclette exercise, and cold pressor test 20-24 h after the administration of SLOx and placebo were also evaluated. The blood pressure tracing was analyzed beat-to-beat by a computer which provided also the analysis of the heart rate data. The 24-h mean systolic and diastolic blood pressure measured during placebo were 144.6 +/- 6.4 and 81.1 +/- 3.9 mm Hg, the corresponding heart rate being 76.9 +/- 3.5 beats/min. SLOx reduced these values by 6.2, 10.6, and 4.8%, respectively, all effects being similarly evident throughout the blood pressure recording. The pressor responses to handgrip, cyclette exercise, and cold pressor test were not affected by SLOx. By contrast, the small tachycardic response to handgrip and the large tachycardic response to submaximal cyclette exercise were significantly reduced by the drug.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Alerting reaction and rise in blood pressure during measurement by physician and nurse.
Blood pressure was monitored by a continuous intra-arterial recording in 46 subjects to investigate whether the alarm reaction and the blood pressure and heart rate increases that occur during cuff blood pressure measurement made by a physician 1) attenuate when the physician's visit is repeated several times and 2) are less pronounced if a nurse measures the blood pressure. In 16 subjects the peak mean blood pressure and heart rate rises that occurred in the early part of the physician's first visit (22.6 +/- 1.8 mm Hg and 17.7 +/- 1.7 beats/min) were virtually identical to those occurring during three subsequent visits by the same physician throughout a 2-day intra-arterial blood pressure monitoring. The less pronounced pressor and tachycardic responses observed in the last part of the physician's visit also were virtually identical among the four visits. In contrast, in 30 other subjects the blood pressure and heart rate rises that occurred during the nurse's visit were 46.7% and 42.1% less (p less than 0.01) than those occurring during the physician's visit. The late and less pronounced pressor and tachycardic responses to the visit were also significantly less (p less than 0.01) in the former than in the latter condition. These results indicate that the error of overestimation of blood pressure inherent in cuff blood pressure measurement by a physician cannot be avoided by repeated visits by the physician over a short time span. It clearly can be reduced, however, if blood pressure measurements are performed by a nurse.
Emotions↗
Evaluation of a new non-invasive semiautomatic blood pressure monitoring device.
The accuracy of a new device for indirect blood pressure measurement was evaluated by comparison with the intra-arterial pressure measurement. The device is based on the Korotkoff's method using a cuff and a microphone, but is characterized by a two-channel recorder to monitor the cuff pressure and the events picked up by the microphone. The blood pressure is determined automatically by a computer program which analyzes the microphone signal during a cuff deflation, and manually by the same criteria to confirm the result. The comparison was carried out on 29 subjects undergoing catheterization of the brachial artery for clinical examination. The difference between the direct and indirect reading ranged from -14 to +9 mmHg (-0.55 +/- 0.91, mean +/- SE) for the systolic pressure and from -5 to +14 mmHg (3.78 +/- 0.95) for the diastolic pressure. It was found advantageous that blood-pressure reading can be confirmed repeatedly on the recorded chart after the measurement.
Adult↗
Evaluation of the antihypertensive effect of TTS clonidine by multiple 24-hour automatic blood pressure monitoring.
Transdermal clonidine (TTSC) has been proposed as a means to improve compliance to treatment of hypertensive patients because of the reported 7-day duration of its antihypertensive effect. However, no detailed information is available on the onset, the time course, and the day and night distribution of this effect throughout the 7 days of the drug skin application. In 12 hospital in-patients with mild or moderate untreated essential hypertension, 24-h blood pressure (BP) was measured at 10-20 min intervals via a noninvasive automatic device (Spacelabs 5300 M) in a no-drug condition, on the 2nd, 4th, and 7th day of the arm application of a 7.0 or 10.5 cm2 patch of TTS clonidine, and on the 2nd and 4th day after substitution of the TTS clonidine patch with an identical patch containing an inert substance (placebo). In nine out of 12 patients, TTS clonidine reduced 24-h systolic and diastolic blood pressure at the 2nd day and even more so on the 4th and 7th day of its application. The reduced blood pressure values observed on the 7th day increased progressively on the 2nd and 4th day after TTS clonidine removal with no rebound over the pre-drug values. The hypotensive effects observed during TTS clonidine were evident throughout the day and night. Thus TTS clonidine exerts a hypotensive effect that starts early and is maintained throughout the 7 days and nights of its application. The discontinuation of this treatment is associated with a smooth return of blood pressure values towards the pre-treatment levels.
Administration, Cutaneous↗
Effects of celiprolol on reflex control of the cardiovascular system in essential hypertension.
We have previously shown that baroreceptor control of the cardiovascular system and the cardiopulmonary receptor control of peripheral circulation are preserved or only moderately reduced during antihypertensive treatment with acebutolol or nadolol, which indicates that treatment with beta blockers with or without intrinsic sympathomimetic activity does not impair fundamental neural mechanisms involved in circulatory homeostasis. In the present study we have investigated the reflex control of circulation before and during antihypertensive treatment with celiprolol, which, in addition to its beta-blocking action, has vasodilator properties that may stem from interference with neural cardiovascular control. In six essential hypertensive subjects we measured blood pressure (intraarterial catheter), heart rate (ECG recording), central venous pressure (right atrial catheter), and forearm blood flow and resistance (plethysmography) before and during alterations in the activity of the arterial baroreceptors obtained by means of lower body suction and passive leg raising. The study was performed before and after 5-7 days of oral administration of celiprolol at 200-400 mg once a day. Compared to the values obtained in the control, condition celiprolol caused a reduction in blood pressure, a slight change in heart rate, and an increase in forearm blood flow, which indicated the occurrence of a clear-cut forearm vasodilatation. The heart rate responses to arterial baroreceptor manipulation were unchanged by celiprolol which reset the carotid baroreflex so that its tonic restraint on blood pressure increased despite the hypotension induced by the drug. The inhibitory restraint tonically exerted by the cardiopulmonary receptors on peripheral circulation was also increased by celiprolol.(ABSTRACT TRUNCATED AT 250 WORDS)
Acebutolol↗
Control of circulation by arterial baroreceptors and cardiopulmonary receptors in hypertension.
This article reviews observations made on reflex control of circulation in essential hypertension and in a few models of experimental hypertension. It is emphasized that a wide consensus exists on the fact that baroreceptor control of heart rate is impaired in essential hypertension and that this occurs not only in severe but also in mild and borderline hypertensive conditions. On the other hand, baroreceptor control of blood pressure is much less affected by chronic elevations in arterial blood pressure due to central or peripheral factors that differentially affect cardiac and vascular responses to the vagus and the sympathetic drive, respectively. Cardiopulmonary receptor control of peripheral circulation and renin release is also little affected by hypertension, and the suggestion has been made that its sensitivity may even be enhanced in early hypertensive stages and then undergoes a subsequent reduction as cardiac hypertrophy develops. Finally, the possible consequences of preservation of reflex control of circulation in hypertension are discussed. It is speculated that this phenomenon may be in part responsible for the similar percentage of blood pressure oscillations that can be observed in normotensive and borderline, moderate, and severe hypertensive subjects.
Animals↗
24-hour blood pressure measurements: methodological and clinical problems.
Awareness that sphygmomanometry is encompassed with serious limitations has led to the development of techniques that allow blood pressure (BP) to be monitored intraarterially or noninvasively during the day or over a 24-hour period. Although intraarterial BP monitoring allows an accurate evaluation of 24-hour BP mean and variability, its invasiveness prevents routine use in the clinical practice. This use can be more easily foreseen for noninvasive ambulatory BP monitoring, provided that the questions posed by this approach are answered. In the present study we show that the intermittent cuff inflations which allow BP to be measured noninvasively do not induce an alerting reaction and a BP rise in the patients, which means that this approach does not disrupt the daily BP profile. We also show that noninvasive BP monitoring does not alter the nocturnal hypotension, thus, preserving the day and night BP rhythm. Finally, we present evidence from a cross-sectional study that 24-hour BP monitoring reflects more closely the hypertension-related target organ damage than sphygmomanometric BP measurement and that target organ damage is related not only to average BP regimens but also to the degree of BP variability. Although support from prospective studies is necessary, this suggests that the diagnosis of hypertension and the prediction of its risk may be improved by ambulatory BP monitoring.
Blood Pressure↗
Arterial baroreflexes and blood pressure and heart rate variabilities in humans.
The factors responsible for 24-hour blood pressure and heart rate variabilities have never been clarified; however, studies performed in unanesthetized animals have shown an increase in blood pressure variability after sinoaortic denervation, and a negative relationship has been reported occasionally between blood pressure variability and baroreflex control of heart rate in humans. We have systematically investigated this issue in 82 ambulant hypertensive subjects using 24-hour intraarterial blood pressure recording (Oxford method) in which blood pressure and heart rate variabilities were measured by calculating the standard deviations of the values obtained throughout the 24 hours or during separate daytime and nighttime periods. Baroreflex sensitivity was assessed by the bradycardic or tachycardic responses to intravenous injections of phenylephrine or nitroglycerin and by the blood pressure response to changes in carotid transmural pressure obtained with a neck chamber. The sensitivity of the baroreceptor-heart rate reflex as assessed by the vasoactive drug technique showed a negative relationship with 24-hour blood pressure variability as well as with daytime and nighttime blood pressure variabilities measured separately (r = -0.28 to -0.50, p less than 0.05). These variabilities also correlated negatively with the sensitivity of the baroreceptor-blood pressure reflex as assessed by the neck chamber technique. By contrast, baroreflex sensitivity showed a positive correlation with heart rate variabilities (r = 0.32 to 0.47, p less than 0.05). The relationship between baroreflex sensitivity and blood pressure and heart rate variabilities was confirmed when the data were analyzed by multiple regression to adjust for blood pressure and age differences among the 82 subjects.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
[Significance of continuous monitoring of arterial blood pressure in the diagnosis of hypertension].
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Adolescent↗
Variability of the haemodynamic responses to laboratory tests employed in assessment of neural cardiovascular regulation in man.
In man evaluation of neural cardiovascular regulation makes use of a variety of tests which address the excitatory and reflex inhibitory neural influences that control circulation. Because interpretation of these tests is largely based on the magnitude of the elicited haemodynamic responses, their reproducibility in any given subject is critical. In 39 subjects with continuous blood pressure (intra-arterial catheter) and heart rate monitoring we measured the blood pressure and heart rate rises during hand-grip and cold-pressor test, the heart rate changes occurring during baroreceptor stimulation and deactivation by injection of phenylephrine and trinitroglycerine, and the heart rate and blood pressure changes occurring with alteration in carotid baroreceptor activity by a neck chamber. Each test was carefully standardized and performed at 30 min intervals for a total of six times in each subject. The results showed that the responses to any test were clearly different from one another and that this occurred in all subjects studied. For the group as a whole the average response variability (coefficient of variation) ranged from 10.2% for the blood pressure response to carotid baroreceptor stimulation to 44.2% for the heart rate response to cold-pressor test. The variability of the responses was not related to basal blood pressure or heart rate, nor to the temporal sequence of the test performance. Thus tests employed for studying neural cardiovascular control in man produce responses whose reproducibility is limited. This phenomenon may make it more difficult to define the response magnitude typical of each subject, as well as its comparison in different conditions and diseases.
Adult↗
Blood pressure monitoring over short day and night times cannot predict 24-hour average blood pressure.
Evidence has been produced that average 24-h or day-time blood pressure (BP) values provide a better diagnosis of hypertension and a better prediction of its risk than BP values provided by one or few isolated measurements. This has led to a number of attempts to simplify the time-consuming procedure necessary to obtain this information and to identify short periods during the 24 h when average BP might closely reflect the 24-h or day-time average values. In 40 ambulant subjects BP was recorded intra-arterially for 24 h using the Oxford method. The BP signal was analysed beat-to-beat by a computer to obtain the average 24-h mean BP values. This value was compared with the mean BP average values obtained by beat-to-beat analysis of subperiods of the same recording, ranging from 30 min to 12 h in duration. For each duration the analysis was performed on 48 different subperiods, each shifted by 30 min from the preceding one, so that every time interval within the 24 h was considered. Throughout the 24-h period the average mean BP values obtained by the analysis of the 30-min subperiods showed very marked differences compared to the 24-h mean BP average. The differences between the subperiod and 24-h values showed a progressive reduction as the subperiod duration was increased. Their magnitude, however, was still marked for subperiods of 2 and 4 h, and only showed a clear-cut attenuation when the subperiods encompassed 12 h.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Mechanisms of blood pressure variability in man.
This paper will touch on three points derived from the studies our group has performed by means of continuous 24 hour blood pressure recording in humans. The first point will concern a description of the factors involved in the production of spontaneous blood pressure variability and in particular of our evidence that the magnitude of this phenomenon depends on arterial baroreflexes but also, and perhaps to a larger extent, on central modulation of the cardiovascular system. The second point will deal with the differences in blood pressure variability we have observed in subjects with normal and high blood pressure. Finally, the third point will briefly address the changes in blood pressure variability that take place with ageing.
Aging↗
Absence of alarm reactions with use of non-invasive blood pressure monitoring devices.
We have previously shown that blood pressure measurement by a doctor or a nurse is often accompanied by an alarm reaction and a marked blood pressure rise which leads to an overestimation of patients' daily blood pressure. To determine whether this phenomenon occurs to some extent also during automatic or semiautomatic measurements of blood pressure, we have studied 20 subjects in which blood pressure was recorded invasively for 24 hours by the Oxford method. During the day time of the recording the arm contralateral to the one used for the invasive procedure was equipped with a non-invasive blood pressure recorder (Vita-Stat 901) the blood pressure measurements being performed automatically (2 hours) or semiautomatically (2 hours) at intervals of 10 minutes. The analysis of the intra-arterial blood pressure trace during the periods preceding and following the beginning of the cuff inflations that started the non-invasive measurements showed that these procedures had caused no increment in systolic and diastolic blood pressure. In nearly all subjects this applied not only to the mean data for all automatic or semiautomatic measurements, but also to the individual observations including those made in the first part of each 2 hour period, when the emotional component might have been greater. It can be concluded that non-invasive blood pressure monitoring does not induce an alarm reaction and a blood pressure rise either when performed automatically and semiautomatically. Thus this approach does not overestimate patients' blood pressure, which adds to its reliability for the diagnosis of hypertension.
Adult↗