Blood pressure and heart rate variabilities in normotensive and hypertensive human beings

Long-lasting cardiovascular depression induced by acupuncture-like stimulation of the sciatic nerve in unanaesthetized rats. Effects of arousal and type of hypertension

Prolonged low frequency stimulation of the sciatic nerve in conscious spontaneously hypertensive rats (SHR), is reported to induce a naloxone-reversible long-lasting depressor response (Yao et al. 1982a). In the present study this depressor response was compared during daytime and night-time conditions to determine whether different degrees of arousal affect this response. In addition, the effect of sciatic nerve stimulation was examined in one-clip, two-kidney renal hypertensive rats (RHR); a type of secondary hypertension which lacks the central autonomic hyper-reactivity which characterizes the SHR variant of primary hypertension. A maximal fall in blood pressure of 20 mm Hg was observed 1 h after sciatic nerve stimulation in SHR examined in daytime. We also found a significant bradycardia that lasted for 2.5 h. Neither poststimulatory depression nor bradycardia were observed in RHR examined at daytime. A short-lasting, non-significant decrease in blood pressure and heart rate was found following sciatic stimulation in SHR examined at night.

Blood pressure variability and hemodynamic response to stress in patients with paroxysmal elevation of blood pressure

Blood pressure variability during 24 hours and hemodynamic response to stress were studied in essential hypertensive patients, displaying paroxysmal hypertension and pheochromocytoma-type symptoms (PH). Hemodynamics at rest, in response to mental arithmetic, bicycle ergometer exercise or the cold together with baroreflex sensitivity were not different between these patients and other essential hypertensives (EH). Average waking systolic blood pressure was lower but variabilities of both systolic and diastolic blood pressure were greater in PH than in EH. During sleep, these differences disappeared. Thus, the greater variability in blood pressure seen only in waking PH patients cannot be estimated from the hemodynamic patterns at rest and is not likely to be related to an excessive response to stress or impaired baroreflex.

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.

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.

Twenty-four-hour blood pressure profile and blood pressure variability in untreated hypertension and during antihypertensive treatment by once-a-day nadolol

First, blood pressure and heart rate variability was studied in 89 normotensive and hypertensive ambulatory subjects with the use of an intra-arterial monitoring device. Short- and long-term variabilities were analyzed by computer. Absolute variabilities (standard deviations) were greatest in patients with hypertension, but relative variabilities (variation coefficients, i.e., standard deviations as percent of means) were slightly lower in the subjects with more severe hypertension. Second, the effect of nadolol on 24-hour blood pressure and heart rate values and on their variability was assessed in seven ambulatory patients with essential hypertension by means of the same intra-arterial device and computer analysis. Two recording sessions were performed (1) without treatment and (2) after 10 days' administration of nadolol once a day (dose range, 80 to 320 mg). Nadolol, given once a day, was shown to reduce blood pressure uniformly throughout the 24-hour period without loss of activity in the hours farthest from administration. The lack of alteration in relative blood pressure variability suggests that nadolol lowers blood pressure without interfering with the mechanisms involved in cardiovascular homeostasis. Reduction in heart rate variability after nadolol suggests less chance of tachycardia episodes in patients with angina and/or arrhythmias receiving nadolol.

Arterial baroreceptor control of blood pressure in man

Information on arterial baroreceptor control of circulation is much more restricted in man than in animals, largely because of the limitations in the techniques available in humans for this type of study. However, recent utilization of the neck chamber technique that addresses the primary function of an arterial baroreflex, i.e. blood pressure control, has provided a significant amount of information. This paper describes baroreceptor control of blood pressure as derived from neck chamber studies in normal people and discusses its modifications by exercise and ageing, and its participation in a phenomenon such as spontaneous blood pressure variability. The description given here is focused on aspects of this baroreceptor control that have changed the concept of the overall arterial baroreceptor function developed by means of techniques for studying only baroreceptor influences on heart rate.

Concern about gain: is this the best measure of performance of cardiovascular reflexes?

Open-loop gain is commonly used as a measure of the effectiveness of cardiovascular reflex control systems. There is no evidence that directly measured baroreflex gain for heart rate gives useful information about blood pressure control in human or experimental hypertension. Calculation of open-loop gain for blood pressure from closed-loop observations requires many assumptions to be made. Calculation of the independent and interactive effects of reflex inputs by factorial analysis may be more versatile, and give a more useful expression of the actions and interactions of cardiovascular reflexes in response to physiological disturbances, than does the calculation of gain.