Estimation of blood pressure variability from 24-hour ambulatory finger blood pressure

Blood Pressure Variability as a Risk Factor for Cardiovascular Disease: Which Antihypertensive Agents Are More Effective?

Blood pressure oscillations during different time scales, known as blood pressure variability (BPV), have become a focus of growing scientific interest. BPV can be measured at long-term (seasonal variability or visit-to-visit), at mid-term (differences in consecutive days or weeks) or at short-term (day-night differences or changes induced by other daily activities and conditions). An increased BPV, either at long, mid or short-term is associated with a poor cardiovascular prognosis independently of the amount of blood pressure elevation. There is scarce evidence on the effect of different antihypertensive treatments on BPV, but some observational and interventional studies suggest that calcium channel blockers in general, and particularly amlodipine, either in monotherapy or combined with renin-angiotensin system blockers, can reduce BPV more efficiently than other antihypertensive drugs or combinations. Nevertheless, there are several aspects of the relationship between BPV, antihypertensive treatment, and clinical outcomes that are still unknown, and more work should be performed before considering BPV as a therapeutical target in clinical practice.

Blood pressure variability: methodological aspects, clinical relevance and practical indications for management - a European Society of Hypertension position paper ∗

Blood pressure is not a static parameter, but rather undergoes continuous fluctuations over time, as a result of the interaction between environmental and behavioural factors on one side and intrinsic cardiovascular regulatory mechanisms on the other side. Increased blood pressure variability (BPV) may indicate an impaired cardiovascular regulation and may represent a cardiovascular risk factor itself, having been associated with increased all-cause and cardiovascular mortality, stroke, coronary artery disease, heart failure, end-stage renal disease, and dementia incidence. Nonetheless, BPV was considered only a research issue in previous hypertension management guidelines, because the available evidence on its clinical relevance presents several gaps and is based on heterogeneous studies with limited standardization of methods for BPV assessment. The aim of this position paper, with contributions from members of the European Society of Hypertension Working Group on Blood Pressure Monitoring and Cardiovascular Variability and from a number of international experts, is to summarize the available evidence in the field of BPV assessment methodology and clinical applications and to provide practical indications on how to measure and interpret BPV in research and clinical settings based on currently available data. Pending issues and clinical and methodological recommendations supported by available evidence are also reported. The information provided by this paper should contribute to a better standardization of future studies on BPV, but should also provide clinicians with some indications on how BPV can be managed based on currently available data.

Beat-to-beat blood pressure variability: an early predictor of disease and cardiovascular risk

Blood pressure (BP) varies on the long, short and very-short term. Owing to the hidden physiological and pathological information present in BP time-series, increasing interest has been given to the study of continuous, beat-to-beat BP variability (BPV) using invasive and noninvasive methods. Different linear and nonlinear parameters of variability are employed in the characterization of BP signals in health and disease. Although linear parameters of beat-to-beat BPV are mainly measures of dispersion, such as standard deviation (SD), nonlinear parameters of BPV quantify the degree of complexity/irregularity- using measures of entropy or self-similarity/correlation. In this review, we summarize the value of linear and nonlinear parameters in reflecting different information about the pathophysiology of changes in beat-to-beat BPV independent of or superior to mean BP. We then provide a comparison of the relative power of linear and nonlinear parameters of beat-to-beat BPV in detecting early and subtle differences in various states. The practical advantage and utility of beat-to-beat BPV monitoring support its incorporation into routine clinical practices.

Analysis of Pulse Arrival Time as an Indicator of Blood Pressure in a Large Surgical Biosignal Database: Recommendations for Developing Ubiquitous Blood Pressure Monitoring Methods

As non-invasive continuous blood pressure monitoring (NCBPM) has gained wide attraction in the recent decades, many pulse arrival time (PAT) or pulse transit time (PTT) based blood pressure (BP) estimation studies have been conducted. However, most of the studies have used small homogeneous subject pools to generate models of BP based on particular interventions for induced hemodynamic change. In this study, a large open biosignal database from a diverse group of 2309 surgical patients was analyzed to assess the efficacy of PAT, PTT, and confounding factors on the estimation of BP. After pre-processing the dataset, a total of 6,777,308 data pairs of BP and temporal features between electrocardiogram (ECG) and photoplethysmogram (PPG) were extracted and analyzed. Correlation analysis revealed that PAT or PTT extracted from the intersecting-tangent (IT) point of PPG showed the highest mean correlation to BP. The mean correlation between PAT and systolic blood pressure (SBP) was -0.37 and the mean correlation between PAT and diastolic blood pressure (DBP) was -0.30, outperforming the correlation between BP and PTT at -0.12 for SBP and -0.11 for DBP. A linear model of BP with a simple calibration method using PAT as a predictor was developed which satisfied international standards for automatic oscillometric BP monitors in the case of DBP, however, SBP could not be predicted to a satisfactory level due to higher errors. Furthermore, multivariate regression analyses showed that many confounding factors considered in previous studies had inconsistent effects on the degree of correlation between PAT and BP.

The speed of blood pressure fluctuations in patients with chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) has been associated with increased risk for cardiovascular disease but mechanisms underlying this association are incompletely understood. The speed of beat-to-beat changes in systolic blood pressure (vSBP) was found to be pronounced in patients with elevated cardiovascular risk. Although increased vSBP may thus be a contributing mechanism to cardiovascular morbidity, no data exist on vSBP in patients with COPD. Therefore, the purpose of this study was to evaluate whether there is an association between severity of COPD and vSBP.

METHODS

Resting beat-to-beat blood pressure was recorded during 5 min. vSBP was assessed by calculating the slopes of oscillatory fluctuations in SBP for different inter-beat intervals (IBI). Univariate and multivariate analyses were performed to evaluate the association between forced expiratory volume in 1 s (FEV1) and vSBP.

RESULTS

This study comprised 60 patients with COPD (24 females) with a mean [SD] FEV1 of 45.4 [22.7] %predicted and 34 healthy controls. Short-term fluctuations in SBP were more pronounced in patients with COPD compared to healthy controls. There was a significant inverse correlation between FEV1 and vSBP (r=-0.41, p=0.001). Even after adjustment for covariates in multivariate analysis, FEV1 was found to be independently associated with vSBP.

CONCLUSIONS

Patients with COPD are characterised by steeper blood pressure changes than healthy controls. The speed of fluctuations in SBP is associated with the severity of airflow limitation. Increased vSBP may be a mechanism underpinning the association between COPD and cardiovascular disease.

Blood Pressure Variability: Prognostic Value and Therapeutic Implications

Blood pressure variability (BPV) is considered nowadays a novel risk factor for cardiovascular disease. Early findings in sinoaortic denervated rats have clearly shown that enhanced fluctuation of blood pressure induced left ventricular hypertrophy, vascular stiffness, and renal lesion. A large number of clinical trials confirm that short-term and long-term blood pressure variability independently contributes to target organ damage, cardiovascular events, and mortality not only in hypertensive patients but also in subjects with diabetes mellitus and chronic kidney disease. Therefore, amelioration of BPV has been suggested as an additional target of the treatment of cardiovascular diseases. Preliminary evidence obtained from meta-analysis and controlled clinical trials has shown that antihypertensive classes differ in their ability to control excessive BP fluctuations with an impact in the prevention of cardiovascular events. Calcium channel blockers seem to be more effective than other blood pressure lowering drugs for the reduction of short-term and long-term BPV. In order to increase actual knowledge regarding the prognostic value and therapeutic significance of BPV in cardiovascular disease, there is a need for additional clinical studies specifically designed for the study of the relevance of short-term and long-term BPV control by antihypertensive drugs.

Quantifying the speed of fluctuations in systolic blood pressure

Increased blood pressure variability (BPV), even in the absence of hypertension, has been identified as an important independent cardiovascular risk factor (CVRF). However, the role of the speed of changes in systolic blood pressure (SBP; vSBP) on cardiovascular risk needs to be investigated. The objective of this study was to investigate whether subjects with a high cardiovascular risk profile have an increased degree and speed of changes in SBP compared with subjects with low or no risk. Resting beat-to-beat blood pressure (BP) was recorded for 5 min. Standard BPV measures in both time and frequency domains were conducted. The s.d. of SBP (s.d.-SBP) values was used to quantify the degree of BPV. vSBP was assessed by calculating the slopes of oscillatory fluctuations in SBP for different interbeat intervals (IBI). Subjects were allocated to one of four groups according to the number of CVRFs (0, 1, 2, ≥ 3 CVRF). Of 122 subjects, 19.7% had 0 CVRF, 27.0% had 1, 32.0% had 2 and 21.3% had ≥ 3 CVRFs. There was an increase in vSBP across the four risk groups. The vSBP in patients without CVRF was 3.12 (1.09), 1 CVRF 3.23 (1.07), 2 CVRF 4.16 (2.26) and ≥ 3 CVRF 4.22 (1.66; P = 0.015). The s.d.-SBP was not significantly different between the cardiovascular risk groups. The speed of fluctuations in SBP rather than the degree of BPV is pronounced in patients with elevated cardiovascular risk. Increased speed of BP fluctuations may thus be a contributing mechanism to cardiovascular morbidity.

Twenty-four hour non-invasive ambulatory blood pressure and heart rate monitoring in Parkinson's disease

Non-motor symptoms are now commonly recognized in Parkinson's disease (PD) and can include dysautonomia. Impairment of cardiovascular autonomic function can occur at any stage of PD but is typically prevalent in advanced stages or related to (anti-Parkinsonian) drugs and can result in atypical blood pressure (BP) readings and related symptoms such as orthostatic hypotension (OH) and supine hypertension. OH is usually diagnosed with a head-up-tilt test (HUT) or an (active) standing test (also known as Schellong test) in the laboratory, but 24 h ambulatory blood pressure monitoring (ABPM) in a home setting may have several advantages, such as providing an overview of symptoms in daily life alongside pathophysiology as well as assessment of treatment interventions. This, however, is only possible if ABPM is administrated correctly and an autonomic protocol (including a diary) is followed which will be discussed in this review. A 24-h ABPM does not only allow the detection of OH, if it is present, but also the assessment of cardiovascular autonomic dysfunction during and after various daily stimuli, such as postprandial and alcohol dependent hypotension, as well as exercise and drug induced hypotension. Furthermore, information about the circadian rhythm of BP and heart rate (HR) can be obtained and establish whether or not a patient has a fall of BP at night (i.e., "dipper" vs. non-"dipper"). The information about nocturnal BP may also allow the investigation or detection of disorders such as sleep dysfunction, nocturnal movement disorders, and obstructive sleep apnea, which are common in PD. Additionally, a 24-h ABPM should be conducted to examine the effectiveness of OH therapy. This review will outline the methodology of 24 h ABPM in PD, summarize findings of such studies in PD, and briefly consider common daily stimuli that might affect 24 h ABPM.

Sleep bruxism is associated with a rise in arterial blood pressure

STUDY OBJECTIVES

Sleep bruxism (SB) is a movement disorder identified by grinding of teeth and rhythmic masticatory muscle activity (RMMA). RMMA is associated with body movements and cortical arousals. Increases in autonomic sympathetic activities that characterize sleep cortical arousal precede RMMA/SB. Based on these findings, this study examined whether RMMA/SB episodes are also associated with significant changes in arterial blood pressure (BP).

DESIGN

Participants underwent 3 nights of full polysomnography that included noninvasive beat-to-beat BP recording. Single RMMA/SB episodes and arousal episodes were analyzed in stage 2 sleep and categorized as: (i) RMMA/SB + arousal; (ii) RMMA/SB + body movement; (iii) RMMA/SB + arousal + body movement; or (iv) arousal alone. Sleep and RMMA/SB data were compared to a Non SB group. RMMA/SB clusters (RMMA/SB episodes ≤ 30 sec apart) were also analyzed.

SETTING

Sleep Laboratory at l'Hôpital du Sacré-Coeur de Montréal.

PARTICIPANTS

Ten young, healthy participants with SB (mean age = 26 ± 1.8 years) and 9 without SB (mean age = 29 ± 1.2 years).

INTERVENTIONS

N/A MEASUREMENTS AND RESULTS: BP increased with all RMMA/SB and arousal episodes (P ≤ 0.05). The average maximum BP surges (systolic/diastolic ± SE mm Hg) were: 25.6 ± 3.3/12.6 ± 2.0 for RMMA/SB + arousal; 30.1 ± 1.7/19.1 ± 1.9 for RMMA/SB + body movement; 26.0 ± 2.8/15.1 ± 2.0 for RMMA/SB + arousal + body movement; 19.4 ± 2.3/8.9 ± 1.2 for arousal alone; and for RMMA/SB clusters: Episode: 1: 26.2 ± 8.7/16.4 ± 5.7; Episode 2: 21.1 ± 7.9/12.6 ± 6.4.

CONCLUSION

Rhythmic masticatory muscle activity/sleep bruxism (RMMA/SB) is associated with blood pressure fluctuations during sleep. Arousals and body movements often occur with RMMA/SB and can impact the magnitude of this BP surge.

Managing hypertension in obstructive sleep apnea: the interplay of continuous positive airway pressure, medication and chronotherapy

Hypertension is highly prevalent and usually uncontrolled among patients with obstructive sleep apnea despite multiple interventions, namely lifestyle modifications, use of antihypertensive drugs and continuous positive airway pressure application. Main prognosticators of the blood pressure (BP) reduction with continuous positive airway pressure therapy are high levels of BP, severity of apnea and daytime sleepiness. The long-term effect of continuous positive airway pressure on BP is still inconclusive, and compliance issues constitute a major limitation. There is no clear evidence for preference for a specific type of antihypertensive drug, and selection should primarily be guided by the patient's cardiometabolic profile and associated clinical conditions. Furthermore, as hypertensive patients with obstructive sleep apnea frequently exhibit a disturbed circadian BP pattern, chronotherapy emerges as a possible therapeutic supplement.

Reproducibility of blood pressure variability, white‐coat effect and dipping pattern in untreated, uncomplicated and newly diagnosed essential hypertension

OBJECTIVE

To investigate the reproducibility of blood pressure (BP) variability, white-coat effect (WCE) and nocturnal dipping pattern in untreated patients with uncomplicated essential hypertension using 24-hour ambulatory BP monitoring (ABPM).

METHODS

Seventy-five newly diagnosed, untreated essential hypertensive subjects (54 men, 21 women 47.6 +/- 9.3 years) were recruited for the study based on conventional measured BP from a total of 180 patients referred for ABPM. Of these, 65 patients underwent repeated ABPM after 4 weeks observation without treatment. Reproducibility of BP, nocturnal dipping pattern, WCE and BP variability were assessed using different methods.

RESULTS

The average 24-hour BP (140.8 +/- 11.9/91.8 +/- 6.4 vs. 140.5 +/- 14.5/90.7 +/- 7.6 mmHg, ns) or PP (49.6 +/- 10.8 vs. 49.8 +/- 9.8 mmHg, ns) did not change, nor did daytime BP or PP. The WCE diminished significantly during the observation period (reduction in SBP WCE delta8.2 +/- 12.5 mmHg, p < 0.0001, in DBP WCE, delta3.3 +/- 9.2 mmHg, p = 0.008 and in PP WCE delta4.8 +/- 11.2 mmHg, p = 0.002). Variability in SBP, DBP and PP decreased consistently and significantly during the observation period. The nocturnal dipping pattern was unchanged in 82% of the patients. In 12% non-dipping pattern was converted to dipping pattern after repeated measurement.

CONCLUSION

Average ABPs are highly reproducible in patients with uncomplicated essential hypertension of limited duration. Similarly, nocturnal dipping pattern reproduced satisfactorily. These measures have important clinical applicability. The white-coat effect as well as variability are greatly attenuated during repeated measurements, and these measures may thus be of less utility in clinical practice.

Continuous blood pressure monitoring using ECG and finger photoplethysmogram

Pulse arrival time and the amplitude of the finger photoplethysmogram were used to track blood pressure continuously over 10-minute intervals. The measures were recorded with a holter-oximeter from a sample of 8 young, healthy human subjects in the supine and standing positions. Results indicate that, with individual calibration, systolic and diastolic blood pressure can be estimated with an average error of +/-6 and +/-4 mmHg respectively. Using pulse arrival time in combination with the amplitude of the finger photoplethysmogram gave better results than using any one alone, with PPG amplitude appearing to be more robust.

Effect of aging on baroreflex function in humans

Arterial blood pressure (BP) is regulated via the interaction of various local, humoral, and neural factors. In humans, the major neural pathway for acute BP regulation involves the baroreflexes. In response to baroreceptor activation/deactivation, as occurs during transient changes in BP, key determinants of BP, such as cardiac period/heart rate (via the sympathetic and parasympathetic nervous system) and vascular resistance (via the sympathetic nervous system), are modified to maintain BP homeostasis. In this review, the effects of aging on both the parasympathetic and sympathetic arms of the baroreflex are discussed. Aging is associated with decreased cardiovagal baroreflex sensitivity (i.e., blunted reflex changes in R-R interval in response to a change in BP). Mechanisms underlying this decrease may involve factors such as increased levels of oxidative stress, vascular stiffening, and decreased cardiac cholinergic responsiveness with age. Consequences of cardiovagal baroreflex impairment may include increased levels of BP variability, an impaired ability to respond to acute challenges to the maintenance of BP, and increased risk of sudden cardiac death. In contrast, baroreflex control of sympathetic outflow is not impaired with age. Collectively, changes in baroreflex function with age are associated with an impaired ability of the organism to buffer changes in BP. This is evidenced by the reduced potentiation of the pressor response to bolus infusion of a pressor drug after compared to before systemic ganglionic blockade in older compared with young adults.

Automation of analysis of cardiovascular autonomic function from chronic measurements of arterial pressure in conscious rats

At present, there is no single software package that provides a comprehensive power spectral analysis of pulse interval (PI) and arterial blood pressure (BP), spontaneous cardiac baroreceptor reflex gain (sBRG) and respiratory rate. Furthermore, scientific validation of the software that is currently commercially available and employed has not been published. We introduce 'Hey-Presto' software, which fully evaluates cardiovascular autonomic function from the BP signal obtained from rats. The program performs power spectral analysis of HR and BP variability, respiratory rate and, based on a time-series method, spontaneous cardiac baroreceptor (sBRG). We have validated Hey-Presto with conventional pharmacological agents to block cardiac vagal and cardiac sympathetic transmission in conscious rats fitted with a radio-telemetery BP transducer. Following administration of atropine (1 mg kg(-1), I.V.), high-frequency (HF) power of the PI decreased (P < 0.01) and was associated with the expected increase in HR. Subsequent cardiac sympathetic blockade (atenolol, 1 mg kg(-1), I.V.) reduced the low frequency (LF) to HF ratio (LF:HF) of the PI (P < 0.01), which was consistent with the observed reduction in HR. We also found that alterations in sBRG after blockade of cardiac autonomic transmission were highly comparable to values computed manually using vasoactive drugs administered intravenously. The software also detected circadian rhythms in sBRG, HF component of the PI, LF:HF of the PI and LF component of the BP as well as BP and HR during continuous 24 h recording. By demonstrating its application to humans, we found appropriate changes in the power of PI and the LF power of the BP during postural changes. These results demonstrate that Hey-Presto allows a fully automated, reliable, fast and comprehensive evaluation of cardiovascular autonomic function based on chronic measurements of BP in rats. Moreover, we have confirmed its versatility by demonstrating its application to man.

[Lack of association between blood pressure variability and left ventricular hypertrophy in essential hypertension]

BACKGROUND AND OBJECTIVE

Blood pressure (BP) fluctuations may contribute to the development of target organ damage in essential hypertension. However, a possible relationship with left ventricular hypertrophy (LVH) is controversial. The aim of the present study was to analyze the association between BP variability, defined through different instrument measures, and LVH in a group of essential hypertensive patients.

PATIENTS AND METHOD

Forty-three untreated hypertensive patients were studied. BP variability was evaluated by using both non-invasive, beat-to-beat finger 24-hour monitoring (Portapres) and discontinuous oscillometric ambulatory blood pressure monitoring (ABPM). All patients underwent echocardiography in order to detect the presence or absence of LVH.

RESULTS

Thirty out of 43 patients studied (70%) exhibited LVH. Office [167.7 (19.5) versus 156.7 (14.9) mmHg; p = 0.032], 24-hour ambulatory [146.6 (15.7) versus 131.9 (15.1) mmHg; p = 0.003] and 24-hour continuous finger [147.5 (21.3) versus 135.7 (14.2) mmHg; p = 0.046] systolic BP were significantly higher in patients with LVH with respect to those without cardiac hypertrophy. No differences were observed in terms of nocturnal BP fall, ABPM 24-h standard deviation of BP or continuous finger BP variability estimates.

CONCLUSION

Left ventricular hypertrophy is mainly correlated with the severity of systolic BP elevation, but not with BP variability, neither long-term nor short-term.

The role of blood pressure variability in end-organ damage

The ultimate goal when treating high blood pressure is to reduce the incidence of end-organ damage and prevent cardiovascular disease, and thus reduce the incidence of premature death. Cuff blood pressure measurements have some prognostic value and have traditionally been used to predict the risk of end-organ damage. Such measurements, however, do not reflect accurately the 24-h mean blood pressure and hourly variations. For any value of cuff blood pressure, a lower 24-h mean blood pressure was associated with a lower prevalence and severity of end-organ damage. In the Pressioni Arteriose Monitorate E Loro Associazioni (PAMELA) study, data from 24-h ambulatory blood pressure monitoring (ABPM) were more strongly associated with prognosis than other blood pressure data. Longitudinal evidence of the clinical relevance of 24-h ABPM data in predicting cardiovascular risk is less extensive. However, results from the Study on Ambulatory Monitoring of Pressure and Lisinopril Evaluation (SAMPLE) trial show the superiority of mean 24-h, daytime and night-time blood pressures over clinic readings in predicting the regression of left ventricular mass index in treated hypertensive patients. Furthermore, a direct, positive relationship has been established between 24-h blood pressure variability and the severity and rate of progression of end-organ damage. In addition, ABPM data demonstrate that hypertensive patients who do not exhibit a nocturnal reduction in blood pressure have a higher incidence of end-organ damage. Future directions for research and treatment of hypertension will need to consider the circadian cycle of blood pressure, the effect of treatment on blood pressure variability, and the magnitude of blood pressure changes in daily life.

Combination of lisinopril and nifedipine GITS increases blood pressure control compared with single drugs in essential hypertensive patients

The present study was designed to evaluate the effect of combination therapy using the angiotensin-converting enzyme-inhibitor lisinopril and the dihydropyridine calcium antagonist nifedipine GITS on the degree and homogeneity of 24-hour blood pressure reduction in essential hypertensive patients. After a 4-week placebo run-in period, 51 patients (mean age, 54.4 +/- 9.4 years) with essential hypertension and clinic diastolic blood pressure between 105 and 115 mm Hg were randomized to 4-week treatment with lisinopril (20 mg), nifedipine GITS (30 mg), or their combination according to a multicenter, randomized, double-blind, crossover study. Trough clinic blood pressure and 24-hour ambulatory blood pressure were measured at the end of the run-in period and after 4 weeks of treatment. In addition to clinic and 24-hour average blood pressure reduction, the trough-to-peak ratio and the smoothness index, a new measure for the homogeneity of blood pressure reduction, were also calculated. Although both lisinopril and nifedipine GITS produced a significant reduction in clinic and 24-hour average blood pressure values, the reduction obtained with the combination was significantly (P < 0.001) greater. Moreover, the combination therapy increased (P < 0.01) the smoothness index as compared with each single drug for both systolic (lisinopril, 1.02; nifedipine GITS, 1.1; combination, 1.76) and diastolic (lisinopril, 0.98; nifedipine GITS, 0.87; combination, 1.54) blood pressure values, whereas trough-to-peak ratio values (expressed as median) for systolic (lisinopril, 0.41; nifedipine GITS, 0.52; combination, 0.55) and diastolic (lisinopril, 0.35; nifedipine GITS, 0.40; combination, 0.49) blood pressure values were not significantly increased by the combination therapy. Thus, antihypertensive treatment with the combination of lisinopril and nifedipine GITS is more effective and balanced over the 24 hours than the combination components administered alone, confirming that the smoothness index is superior to the trough-to-peak ratio in assessing homogeneity of pharmacologic blood pressure reduction.

Baroreflex and chemoreflex function after bilateral carotid body tumor resection

OBJECTIVE

To investigate whether bilateral carotid body tumor resection invariably and chronically affects arterial baroreflex or peripheral chemoreflex function.

METHODS

We studied eight consecutive patients (two men and six women; ages 48.1 +/- 11.8 years), a median time of 3.4 years (range 1.3-20.6 years) after bilateral carotid body tumor resection, and 12 healthy control individuals (eight men and four women; ages 53.7 +/- 10.1 years). Baroreflex sensitivity (phenylephrine), blood pressure and its variability (24 h Spacelabs and 5 h Portapres recordings), responses to standard cardiovascular reflex tests and the ventilatory responses to normocapnic and hypercapnic hypoxia were assessed.

RESULTS

Baroreflex sensitivity was lower in patients (6.4 +/- 7.2 ms/mmHg) than in controls (14.7 +/- 6.6 ms/mmHg; P +/- 0.011). Mean office blood pressure and heart rate were normal in patients (123.3 +/- 11.9/79.0 +/- 7.3 mmHg and 67.5 +/- 9.4 beats/min, respectively) and controls (117.8 +/- 10.6/74.0 +/- 6.8 mmHg and 61.1 +/- 9.2 beats/min, respectively). Blood pressure variability was increased during ambulatory measurements. Three patients exhibited orthostatic hypotension. The Valsalva ratio, an index of baroreflex-mediated cardiovagal innervation, was lower in patients (1.4 +/- 0.2) than in controls (1.8 +/- 0.5; P +/- 0.008). The normocapnic ventilatory response to hypoxia was absent in all patients, whereas a small residual response to hypoxia was observed under hypercapnic conditions in two patients.

CONCLUSIONS

Bilateral carotid body tumor resection results in heterogeneous expression of arterial baroreflex dysfunction, whereas the normocapnic hypoxic drive is invariably abolished as a result of peripheral chemoreflex failure.

Non-invasive beat-to-beat blood pressure monitoring: new developments

Continuous blood pressure monitoring is an essential prerequisite for any study on blood pressure variability. Invasive procedures are no longer acceptable for research projects in a clinical setting, and recently developed devices able to record blood pressure on a beat-by-beat basis in a non-invasive fashion may represent valuable alternative tools. This article will briefly review the available information on the most recent advances in this field. It will focus on further developments of the original technology for finger blood pressure monitoring introduced by Penáz, as well as on newer devices that have been proposed over the last few years for non-invasive cardiovascular monitoring both in research and in clinical studies.

Arterial baroreflex and peripheral chemoreflex function after radiotherapy for laryngeal or pharyngeal cancer

PURPOSE

Denervation of the carotid sinus causes baroreflex and chemoreflex failure, resulting in labile hypertension and loss of hypoxic responsiveness. We investigated whether radiation therapy for laryngeal or pharyngeal cancer affects baroreflex and chemoreflex function.

METHODS AND MATERIALS

Twelve patients were studied after radiation therapy for locally advanced laryngeal or pharyngeal cancer (11 male, 1 female, age: 56.0 +/- 7.9 years), 3.3 years (median; range 1.0-4.7) after radiotherapy and 15 healthy controls (11 male, 4 female, 53.4 +/- 9.2 years). We measured baroreflex sensitivity (phenylephrine), blood pressure level and variability (24-h Spacelabs and 5-h Portapres recordings), responses to cardiovascular reflex tests, and the ventilatory responses to normocapnic and hypercapnic hypoxia.

RESULTS

Baroreflex sensitivity was lower in patients (9.7 +/- 7.8 ms/mm Hg) than in controls (17.5 +/- 10.3 ms/mm Hg, p = 0.011). Mean office blood pressure was significantly higher in patients (141.5 +/- 27.8/89.2 +/- 10.6 mm Hg, 63.3 +/- 12.3 bpm) than in controls (117.3 +/- 10.1/75.1 +/- 6.8 mm Hg, 61.8 +/- 10.8 bpm). Blood pressure variability was not different between groups, nor were the responses to reflex tests. The normo/hypercapnic ventilatory response to hypoxia was similar in patients (0.21 +/- 0.10/1.37 +/- 0.60 L/min/%) and controls (0.22 +/- 0.16/1.19 +/- 0.78 L/min/%).

CONCLUSIONS

Radiation therapy for laryngeal or pharyngeal carcinoma does not affect chemoreflex function, but results in an attenuated baroreflex sensitivity. Clinically relevant blood pressure lability is absent however.

Comparison of Portapres with standard sphygmomanometry in pregnancy

BACKGROUND

Continuous beat-to-beat noninvasive blood pressure (BP) measurement is possible with Portapres. It constructs finger arterial waveforms beat-to-beat. Dedicated software is used to analyze the arterial waveforms. A new technique has been developed to reconstruct brachial intra-arterial pressure that uses return to flow (RTF). This method has been validated against invasive intra-arterial measurements in nonpregnant individuals.

OBJECTIVES

To validate Portapres in normal and preeclamptic pregnant women against standard aneroid sphygmomanometry according to Riva-Rocci-Korotkoff (RRK).

METHODS

In 30 normotensive (10 in each trimester) and 20 preeclamptic women, two trained observers blinded from each other's results took BP measurements with a standard sphygmomanometer. These measurements were compared with sequential same-arm averaged measurements obtained during 30 sec by Portapres, following protocols from the Association for the Advancement of Medical Instrumentation (AAMI, mean accepted difference < or = 5 mmHg, SD < or = 8) and British Hypertension Society (BHS, gradings A down to D).

RESULTS

A total of 150 measurement pairs were analyzed. Cumulative percentages of absolute pressure differences for all women (BHS) and mean pressure differences (SD) for different trimesters and preeclampsia (AAMI) between sphygmomanometry and Portapres were calculated. Overall, mean difference (SD) for systolic BP was 5 (SD 8) and for diastolic BP was -3 (SD 8), although analysis of variance revealed a significant effect for preeclampsia on diastolic differences between the two methods of BP measurement ( p<0.001).

CONCLUSIONS

Portapres with RTF, developed to equal intra-arterial brachial pressure, compares reasonably well to RRK and overall meets the criteria set by the AAMI. According to the BHS, Portapres receives a B-grading for diastolic BP and a C-grading for systolic BP. As Portapres measures BP and calculates cardiac output continuously and noninvasively, it would appear worthwhile to further evaluate this device in pathological pregnancies.

Dynamic modulation of baroreflex sensitivity in health and disease

Assessment of arterial baroreflex function in humans through laboratory tests has provided a great deal of information of pathophysiological and clinical relevance. Indeed, the sensitivity of the baroreceptor-heart rate reflex quantified through these laboratory methods was shown to predict the risk of cardiovascular events and death from myocardial infarction, heart failure, and in diabetic patients. This traditional approach, however, does not provide information on daily life baroreflex cardiovascular control. Modern techniques, based on computer analysis of spontaneous blood pressure and heart rate fluctuations, are now available and allow baroreflex sensitivity to be assessed under real-life conditions with no need for external stimulation. In particular, these methods offer the possibility of investigating the dynamic modulation of baroreflex sensitivity occurring either on a minute-to-minute basis or over 24 hours.

Mechanisms and clinical implications of blood pressure variability

Several studies have unequivocally shown that the target-organ damage associated with the hypertensive condition is more closely related to 24 h average blood pressure values than to clinic blood pressure. Blood pressure, however, is highly variable over the daytime and night-time period, and of major interest is whether average 24 h blood pressure values, as well as 24 h blood pressure variability, correlate with, and are possibly responsible for, the hypertension-related alterations of the target-organ structure and function. This paper will address this issue by discussing the main features of blood pressure variability in hypertension. It will also examine the mechanisms involved in this phenomenon, with particular emphasis on the pathogenetic role of sympathetic neural factors. The clinical relevance of blood pressure variability in promoting target-organ damage, as well as its therapeutic implications, will finally be highlighted.

Spontaneous fluctuations in cerebral blood flow: insights from extended-duration recordings in humans

To determine the dependence of cerebral blood flow (CBF) on arterial pressure over prolonged time periods, we measured beat-to-beat changes in mean CBF velocity in the middle cerebral artery (transcranial Doppler) and mean arterial pressure (Finapres) continuously for 2 h in six healthy subjects (5 men and 1 woman, 18-40 yr old) during supine rest. Fluctuations in velocity and pressure were quantified by the range [(peak - trough)/mean] and coefficients of variation (SD/mean) in the time domain and by spectral analysis in the frequency domain. Mean velocity and pressure over the 2-h recordings were 60 +/- 7 cm/s and 83 +/- 8 mmHg, associated with ranges of 77 +/- 8 and 89 +/- 10% and coefficients of variation of 9.3 +/- 2.2 and 7.9 +/- 2.3%, respectively. Spectral power of the velocity and pressure was predominantly distributed in the frequency range of 0.00014-0.1 Hz and increased inversely with frequency, indicating characteristics of an inverse power law (1/f(alpha)). However, linear regression on a log-log scale revealed that the slope of spectral power of pressure and velocity was steeper in the high-frequency (0.02-0.5 Hz) than in the low-frequency range (0.002-0.02 Hz), suggesting different regulatory mechanisms in these two frequency ranges. Furthermore, the spectral slope of pressure was significantly steeper than that of velocity in the low-frequency range, consistent with the low transfer function gain and low coherence estimated at these frequencies. We conclude that 1) long-term fluctuations in CBF velocity are prominent and similar to those observed in arterial pressure, 2) spectral power of CBF velocity reveals characteristics of 1/f(alpha), and 3) cerebral attenuation of oscillations in CBF velocity in response to changes in pressure may be more effective at low than that at high frequencies, emphasizing the frequency dependence of cerebral autoregulation.

Baroreflex failure following radiation therapy for nasopharyngeal carcinoma

The authors present a 51-year-old man with right-sided nasopharyngeal carcinoma who was treated for regional lymph node involvement by bilateral radiation therapy of the neck. Six years later he presented with episodic complaints of headache, flushing, and palpitations accompanied by elevations of blood pressure. Examination of arterial baroreflex function indicated selective afferent carotid sinus denervation. Cross spectral analysis of spontaneous heart rate and blood pressure variability showed decreased arterial baroreflex sensitivity (6.5 ms/mm Hg). Twenty-four hour measurements of blood pressure and heart rate variability showed labile hypertension during normal daytime activities. Baroreflex failure in this patient probably represents a late complication of bilateral radiation therapy of the neck.

Ambulatory blood pressure monitoring

This paper will briefly summarize the available evidence on the diagnostic and prognostic relevance of a number of parameters derived from the analysis of 24 hour ambulatory blood pressure recordings. These parameters include the 24 h average blood pressure values, the difference between daytime and nighttime blood pressure, the difference between clinic blood pressure and daytime average blood pressure as a surrogate measure of the "white coat effect", and 24 hour blood pressure variability as quantified by the standard deviation of the 24 hour average value.

The smoothness index: a new, reproducible and clinically relevant measure of the homogeneity of the blood pressure reduction with treatment for hypertension

OBJECTIVE

To introduce a new method, the smoothness index, for assessing the homogeneity of 24 h blood pressure reduction by antihypertensive treatment and to compare it with the trough : peak ratio; and to assess the ability of both indices to predict a reduction in the left ventricular mass index induced by treatment.

PATIENTS AND METHODS

In 174 patients with essential hypertension and left ventricular hypertrophy, enrolled in the Study on Ambulatory Monitoring of Pressure and Lisinopril Evaluation (SAMPLE), aged 20-65 years, we measured clinic blood pressure, 24 h ambulatory blood pressure and the left ventricular mass index (echocardiography) before and after treatment with lisinopril at 20 mg with the addition of 12.5 or 25 mg hydrochlorothiazide as needed to reach a sufficient blood pressure reduction. The following parameters were computed for systolic and diastolic ambulatory blood pressure: (1) hourly and 24 h blood pressure averages (+/- SD) at baseline and after 3 and 12 months of treatment; (2) hourly blood pressure changes from baseline after 3 and 12 months of treatment, and their average (+/- SD) over 24 h; (3) the trough : peak ratio after 3 and 12 months of treatment; and (4) the smoothness index after 3 and 12 months of treatment Similar calculations were also performed at the end of a final study month during which active treatment was withdrawn and placebo was substituted (n = 164).

RESULTS

The smoothness index for systolic and diastolic ambulatory blood pressure computed after 3 months of treatment was more closely related to its corresponding values after 12 months of treatment than the trough : peak ratio values computed after the same time periods were (r = 0.68 versus 0.38 for systolic and 0.68 versus 0.42 for diastolic blood pressure, respectively). The smoothness index showed an inverse correlation with the 24 h standard deviation of systolic and diastolic blood pressure (r = -0.25 and -0.16, P < 0.01 and < 0.05, respectively, for 12 months of treatment), while the trough : peak ratio did not (r = -0.01 to -0.12, NS). A treatment-induced reduction in the left ventricular mass index was related to the smoothness index for systolic and diastolic blood pressure (r = -0.35 and -0.32, P< 0.001 with 12 months of treatment), but not to the corresponding trough : peak ratios.

CONCLUSIONS

The smoothness index identifies the occurrence of a balanced 24 h blood pressure reduction with treatment and correlates with the favourable effects of treatment on left ventricular hypertrophy better than the commonly used trough : peak ratio.