Surfactants: physicochemical interactions with biological macromolecules.

Macromolecules are essential cellular components in biological systems responsible for performing a large number of functions that are necessary for growth and perseverance of living organisms. Proteins, lipids and carbohydrates are three major classes of biological macromolecules. To predict the structure, function, and behaviour of any cluster of macromolecules, it is necessary to understand the interaction between them and other components through basic principles of chemistry and physics. An important number of macromolecules are present in mixtures with surfactants, where a combination of hydrophobic and electrostatic interactions is responsible for the specific properties of any solution. It has been demonstrated that surfactants can help the formation of helices in some proteins thereby promoting protein structure formation. On the other hand, there is extensive research towards the use of surfactants to solubilize drugs and pharmaceuticals; therefore, it is evident that the interaction between surfactants with macromolecules is important for many applications which includes environmental processes and the pharmaceutical industry. In this review, we describe the properties of different types of surfactants that are relevant for their physicochemical interactions with biological macromolecules, from macromolecules-surfactant complexes to hydrophobic and electrostatic interactions.

Pseudomonas aeruginosa biofilm disruption using microbial surfactants.

AIMS: To establish the ability of the rhamnolipids biosurfactants from Pseudomonas aeruginosa, in the presence and absence of caprylic acid and ascorbic acid, to disrupt bacterial biofilms, compared with the anionic alkyl sulphate surfactant Sodium dodecyl sulphate (SDS). METHODS AND RESULTS: Pseudomonas aeruginosa ATCC 15442 biofilms were disrupted by rhamnolipids at concentrations between 0·5 and 0·4 g l(-1) and with SDS at 0·8 g l(-1) . The combination of rhamnolipids 0·4 g l(-1) and caprylic acid at 0·1 g l(-1) showed a remarkable effect on biofilm disruption and cell killing. After 30 min of treatment most of the biofilm was disrupted and cell viability was significantly reduced. Neither caprylic acid nor ascorbic acid has any effect on biofilm disruption at 0·1 g l(-1) . SDS is an effective antimicrobial agent; however, in the presence of caprylic acid its effect was neutralized. CONCLUSIONS: The results show that rhamnolipids at low concentration in the presence of caprylic acid are promising molecules for inhibition/disruption of biofilms formed by Ps. aeruginosa ATCC 15442. SIGNIFICANCE AND IMPACT OF THE STUDY: The disruption of biofilms has major significance in many industrial and domestic cleaning applications and in medical situations.

Effect of biosurfactants on Pseudomonas aeruginosa and Staphylococcus aureus biofilms in a BioFlux channel.

Recent studies have indicated that biosurfactants play a role both in maintaining channels between multicellular structures in biofilms and in dispersal of cells from biofilms. A combination of caprylic acid (0.01 % v/v) together with rhamnolipids (0.04 % v/v) was applied to biofilms of Pseudomonas aeruginosa ATCC 15442, Staphylococcus aureus ATCC 9144 and a mixed culture under BioFlux flowthrough conditions and caused disruption of the biofilms. The biofilms were also treated with a combination of rhamnolipids (0.04 % v/v) and sophorolipids (0.01 %). Control treatments with PBS 1× had no apparent effect on biofilm disruption. The Gram-positive bacterium (S. aureus ATCC 9144) was more sensitive than P. aeruginosa ATCC 15442 in terms of disruption and viability as shown by Live/Dead staining. Disruption of biofilms of P. aeruginosa ATCC 15442 was minimal. Oxygen consumption by biofilms, after different treatments with biosurfactants, confirms that sophorolipid on its own is unable to kill/inhibit cells of P. aeruginosa ATCC 15442, and even when used in combination with rhamnolipids, under static conditions, no decrease in the cell viability was observed. Cells in biofilms exposed to mono-rhamnolipids (0.04 % v/v) showed behaviour typical of exposure to bacteriostatic compounds, but when exposed to di-rhamnolipids (0.04 % v/v), they displayed a pattern characteristic of bactericidal compounds.

The effect of sophorolipids against microbial biofilms on medical-grade silicone.

Recent medical strategies rely on the search for effective antimicrobials as surface coatings to prevent and treat infections in humans and animals. Biosurfactants have recently been shown to have properties as antiadhesive and antibiofilm agents. Sophorolipids in particular are biosurfactant molecules known to act as therapeutic agents. This study aimed to evaluate antimicrobial properties of sophorolipids in medical-grade silicone discs using strains of clinical relevance. Sophorolipids were produced under fed batch conditions, ESI-MS analyses were carried out to confirm the congeners present in each formulation. Three different products were obtained SLA (acidic congeners), SL18 (lactonic congeners) and SLV (mixture of acidic and lactonic congeners) and were tested against Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 10145 and Candida albicans IHEM 2894. All three congener mixtures showed a biofilms disruption effect (> 0.1 % w/v) of 70 %, 75 % and 80 % for S. aureus, P. aeruginosa and C. albicans, respectively. On pre-coated silicone discs, biofilm formation of S. aureus was reduced by 75 % using SLA 0.8 % w/v. After 1.5 h the inhibition of C. albicans attachment was between 45-56 % whilst after 24 h incubation the percentage of inhibition for the cell attachment increased to 68-70 % when using SLA 0.8 % w/v. Finally, in co-incubation experiments SLA 0.05 % w/v significantly reduced the ability of S. aureus and C. albicans to form biofilms and to adhere to surfaces by 90-95 % at concentrations between 0.025-0.1 % w/v. In conclusion sophorolipids significantly reduced the cell attachment of both tested strains which suggests that these molecules could have a potential role as coating agents on medical grade silicone devices for the preventions of Gram positive bacteria and yeast infections.

Autophagy induction in atrophic muscle cells requires ULK1 activation by TRIM32 through unanchored K63-linked polyubiquitin chains.

Optimal autophagic activity is crucial to maintain muscle integrity, with either reduced or excessive levels leading to specific myopathies. LGMD2H is a muscle dystrophy caused by mutations in the ubiquitin ligase TRIM32, whose function in muscles remains not fully understood. Here, we show that TRIM32 is required for the induction of muscle autophagy in atrophic conditions using both in vitro and in vivo mouse models. Trim32 inhibition results in a defective autophagy response to muscle atrophy, associated with increased ROS and MuRF1 levels. The proautophagic function of TRIM32 relies on its ability to bind the autophagy proteins AMBRA1 and ULK1 and stimulate ULK1 activity via unanchored K63-linked polyubiquitin. LGMD2H-causative mutations impair TRIM32's ability to bind ULK1 and induce autophagy. Collectively, our study revealed a role for TRIM32 in the regulation of muscle autophagy in response to atrophic stimuli, uncovering a previously unidentified mechanism by which ubiquitin ligases activate autophagy regulators.

Dynamic adaptation of cardiac baroreflex sensitivity to prolonged exposure to microgravity: data from a 16-day spaceflight.

This study explored the process of arterial baroreflex adaptation to microgravity, starting from the first day of flight, during the 16-day STS-107 Columbia Space Shuttle mission. Continuous blood pressure (BP), ECG, and respiratory frequency were collected in four astronauts on ground (baseline) and during flight at days 0-1, 6-7, and 12-13, both at rest and during moderate exercise (75 W) on a cycle ergometer. Sensitivity of the baroreflex heart rate control (BRS) was assessed by sequence and spectral alpha methods. Baroreflex effectiveness index (BEI); low-frequency (LF) power and high-frequency (HF) power of systolic BP (SBP), diastolic BP (DBP), and R-R interval (RRI); the RRI LF/HF ratio; and the RRI root mean square of successive differences (RMSSD) index were also estimated. We found that, at rest, BRS increased in early flight phase, compared with baseline (means +/- SE: 18.3 +/- 3.4 vs. 10.4 +/- 1.2 ms/mmHg; P < 0.05), and it tended to return to baseline in subsequent days. During exercise, BRS was lower than at rest, without differences between preflight and in-flight values. At rest, in the early flight phase, RMSSD and RRI HF power increased (P < 0.05) compared with baseline, whereas LF powers of SBP and DBP decreased. No statistical difference was found in these parameters during exercise before vs. during flight. These findings demonstrate that heart rate baroreflex sensitivity and markers of cardiac vagal modulation are enhanced during early exposure to microgravity, likely because of the blood centralization, and return to baseline values in subsequent flight phases, possibly because of the fluid loss. No deconditioning seems to occur in the baroreflex control of the heart.

Upgraded diagnostic value of Gen-Probe PACE 2 assay for detection of Chlamydia trachomatis infection.

In this study, we evaluate the performance of a nucleic acid amplification assay, COBAS AMPLICOR (Roche Molecular systems) (PCR), compared to non-amplified DNA probe assay PACE2 (Gen-Probe Inc.) for the detection of C. trachomatis in a total of 2,916 samples (2,114 females and 802 males) consecutively collected in two different clinical pathology laboratories, over a period of three years. In the females, the endocervical swabs showed a similar range of detection when using the two different methods: out of 1,581 females processed with PACE 2, 1.4% (2005), 0.9% (2006), 0.5% (2007), resulted positive for C. trachomatis; out of 533 females processed with PCR, 1.3% (2005), 1.5% (2006) and 1.2% (2007), resulted positive. However, in the male subjects we found an increased positivity of Chlamydia detection on urethral swabs by using PACE 2: 4.8% (2005), 1.9% (2006) and 2.9% (2007), compared to urine specimen processed by PCR: 1% (2005), 1.4% (2006) and 0% (2007). Even if PCR should be considered a most promising tool for routine diagnosis of Chlamydia infection, Gen Probe allowed us to better identify Chlamydia trachomatis (in 4.8% of urethral swabs compared to urine) leading to a hypothesis that extracellular EB forms of Chlamydia could be absent in urine in persistent infectious.

Human PRDM2: Structure, function and pathophysiology.

PRDM2/RIZ is a member of a superfamily of histone/protein methyltransferases (PRDMs), which are characterized by the conserved N-terminal PR domain, with methyltransferase activity and zinc finger arrays at the C-terminus. Similar to other family members, two main protein types, known as RIZ1 and RIZ2, are produced from the PRDM2 locus differing by the presence or absence of the PR domain. The imbalance in their respective amounts may be an important cause of malignancy, with the PR-positive isoform commonly lost or downregulated and the PR-negative isoform always being present at higher levels in cancer cells. Interestingly, the RIZ1 isoform also represents an important target of estradiol action downstream of the interaction with hormone receptor. Furthermore, the imbalance between the two products could also be a molecular basis for other human diseases. Thus, understanding the molecular mechanisms underlying PRDM2 function could be useful in the pathophysiological context, with a potential to exploit this information in clinical practice.

Effect of gestational hypercholesterolaemia on omental vasoreactivity, placental enzyme activity and transplacental passage of normal and oxidised fatty acids.

OBJECTIVE: Maternal hypercholesterolaemia during pregnancy increases lipid peroxidation in mothers and fetuses and programs increased susceptibility to atherosclerosis later in life. The objective of this study was to elucidate the role of the placenta in mediating oxidative stress from mother to offspring. DESIGN: Comparison between normo- and hypercholesterolaemic mothers (n = 36 each) and their children. SETTING: Obstetric wards, hospitals of the University of Naples and Regione Campania. POPULATION: Healthy primiparas delivering by caesarean section. METHODS: Biochemical measurements of oxidative stress and serum leptin in cord plasma and placenta, immunochemistry of placenta microvessels, and vasoreactivity studies were performed. MAIN OUTCOME MEASURES: Oxidative status (i.e. lipid composition and content of oxidised fatty acids, activity of pro- and antioxidant enzymes, immunohistochemical presence of oxidation-specific epitopes) in maternal and cord blood and in placental tissue, as well as vascular reactivity in omental arteries. RESULTS: Hypercholesterolaemia during pregnancy was associated with extensive changes in fatty acid composition of both maternal and cord blood lipids, sufficient to alter vasoreactivity of omental vessels. Results also indicated that the placenta is not only subject to substantial oxidative stress, but that it may further increase fetal oxidative stress through changes of pro- and antioxidant enzyme activities. CONCLUSIONS: The placenta plays an important role in both transmitting and enhancing pathogenic effects of gestational hypercholesterolaemia.

[B-mode sonography visualizing microemboli flow in the main cerebral arteries]. / Visualisation du passage de micro-emboles cérébraux par ultrasonographie en mode B-Flow.

In a patient with a mechanical prosthetic aortic valve admitted for transient amnesia, transcranial duplex Doppler and B-mode sonography visualized the transit of microemboli along the main cerebral arteries. Gaseous microemboli resulting from a cavitation phenomenon at valve closure were seen as high-intensity transient signals (HITS). To our knowledge, this is the first report of microemboli flow visualized in B-mode.

Blood pressure changes after high- and low-salt diets: are intermittent arm measures and beat-by-beat finger measures equivalent?

The assessment of sodium sensitivity requires to measure the difference in mean arterial pressure (MAP) at the end of sodium-loading (SLoad) and sodium-depletion (SDepl) maneuvers with an arm-cuff manometer. Aim of this study is to evaluate whether MAP measuring devices based on the volume-clamp method at the finger can also be used for assessing sodium sensitivity. Sixty-eight normotensive volunteers underwent SLoad and SDepl diets in random order. MAP was simultaneously measured at the end of each diet with arm (Spacelabs 90207) and finger (Portapres model-2) cuff devices. The sodium sensitivity was assessed as the difference in MAP at the end of SLoad and SDepl diets (ΔMAP), and as salt-sensitivity index (SSI; SSI = ΔMAP divided by the difference in urinary-sodium-excretion rate at the end of the diets). Discrepancies between finger and arm-cuff devices in ΔMAP or SSI were evaluated by Bland and Altman analysis. Even if discrepancies between devices had null-fixed bias, results showed a significant proportional bias and large limits of agreement (between -25 and 25 mm Hg for ΔMAP, between -196 and 180 mm Hg mol(-1) per day for SSI). The SSI distribution over the group was larger, flatter and less symmetric if derived from finger-cuff rather than arm-cuff devices, and this influenced substantially the identification of salt-sensitive individuals. Therefore, the response of MAP to SLoad/SDepl diets and consequently the assessment of the salt-sensitivity condition depends importantly on the measurement site, and brachial measures should be preferred for consistency with literature and normative data.

ICF-based approach to evaluating functionality in cardiac rehabilitation patients after heart surgery.

BACKGROUND: Heart surgery is a frequent reason for admission to in-patient cardiac rehabilitation programmes. ICF approach has never been used to evaluate cardiac patients after major heart surgery. AIM: The aim was to evaluate and measure functionality in cardiac patients who have undergone heart surgery, using for the first time the ICF-based approach and to assess whether such approach can be feasible and useful in cardiac rehabilitation. DESIGN: Observational study. SETTING: In-patients cardiac Rehabilitation Unit in Milan. POPULATION: Fifty consecutively admitted patients who had undergone heart surgery (34 males, 16 females; mean age 65.7±12.5 years). METHODS: We prepared a ICF-core set short enough to be feasible and practical. Patients were individually interviewed by different healthcare professionals (randomly selected from a group of two physicians, two physiotherapists and two psychologists) at the beginning (T1) and end of cardiac rehabilitation (T2) RESULTS: The sum of the scores of each ICF body function, body structure, activity and participation code significantly decreased between T1 and T2 (P<0.001). The environmental code scores significantly decreased in the case of facilitators between T1 and T2 (P=0.0051), but not in the case of barriers. There were significant correlations between the ICF body function scores and Barthel's index (ρ=0.381; P=0.006), NYHA class (ρ=0.404; P=0.004) and plasma Cr-P levels (r=0.31; P=0.03), between the ICF body structure codes and the Conley scale (ρ=0.306; P=0.02), and between the activity/participation codes and SpO2 (ρ=0.319; P=0.04). There were no correlations between the ICF environmental codes and clinical parameters. CONCLUSION: The ICF-based data provided functional information that was consistent with the patients' clinical course. CLINICAL REHABILITATION IMPACT: The core set used allowed to quantify important body functions and activities, including some areas that are generally insufficiently considered by healthcare professionals during cardiac rehabilitation, and document their improvement.

Comparison of finger and intra-arterial blood pressure monitoring at rest and during laboratory testing.

The accuracy of blood pressure values obtained by continuous noninvasive finger blood pressure recording via the FINAPRES device was evaluated by comparison with simultaneous intraarterial monitoring both at rest and during performance of tests known to induce fast and often marked changes in blood pressure. The comparison was performed in 24 normotensive or essential hypertensive subjects. The average discrepancy between finger and intra-arterial blood pressure recorded over a 30-minute rest period was 6.5 +/- 2.6 mm Hg and 5.4 +/- 2.9 mm Hg for systolic and diastolic blood pressure, respectively; a close between-method correspondence was also demonstrated by linear regression analysis. The beat-to-beat changes in finger systolic and diastolic blood pressure were on average similar to those measured intra-arterially during tests that induced a pressor or depressor response (hand-grip, cold pressor test, diving test, Valsalva maneuver, intravenous injections of phenylephrine and trinitroglycerine) as well as during tests that caused vasomotor changes without major variations in blood pressure (application of lower body negative pressure, passive leg raising). The average between-method discrepancy in the evaluation of blood pressure changes was never greater than 4.3 and 2.0 mm Hg for systolic and diastolic blood pressure, respectively; the corresponding standard deviations ranged between 4.6 and 1.6 mm Hg. Beat-to-beat computer analysis of blood pressure variability over the 30-minute rest period provided standard deviations almost identical when calculated by separate consideration of intra-arterial and finger blood pressure tracings (3.7 and 3.8 mm Hg, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Broadband spectral analysis of blood pressure and heart rate variability in very elderly subjects.

Systolic blood pressure (SBP) variability is increased and R-R interval variability is reduced in the elderly. Little is known, however, about how SBP and R-R interval variabilities change in the very elderly. More important, however, it is not known which frequency components of SBP and R-R interval variability are affected significantly. We addressed this issue in subjects older than 70 years by broadband spectral analysis, which allows all variability components from the lowest to the highest frequency to be considered. In 20 very elderly normotensive subjects (mean +/- SD age, 78.1 +/- 6.8 years) and 28 normotensive adult subjects (36.1 +/- 7.1 years), noninvasive finger blood pressure and R-R intervals were recorded continuously for 30 minutes in the supine position and 15 minutes in the upright position. SBP and R-R interval power spectral densities were computed over the entire frequency region between 0.005 Hz (0.007 Hz in the upright position) and 0.5 Hz. Overall SBP variability (SD) was greater and overall R-R interval variability was less in very old subjects than in adult subjects. All spectral R-R interval powers were reduced significantly in very elderly individuals. The spectral SBP powers were greater in the very elderly group than in the adult group only in the very-low-frequency range (<0.04 Hz). This was true in the supine and the standing positions. With subjects in the standing position, the shape of the broadband spectra differed in the very old and adult subjects because in the former group the increase in SBP and R-R interval power around 0.1 Hz that was seen in the latter was blunted. Therefore, in very elderly subjects a reduction in overall R-R interval variability is accounted for by a reduction in all of its frequency components. The accompanying increase in overall BP variability, however, results from a nonhomogeneous behavior of its frequency components, which consists of an increase in the very low frequency and a concomitant reduction in the higher frequency powers. The mechanisms responsible for these changes may be complex, but at least they may in part reflect the baroreflex impairment and autonomic dysfunction that characterize aging.

Spectral analysis of blood pressure and heart rate variability in evaluating cardiovascular regulation. A critical appraisal.

Blood pressure variability includes rhythmic and nonrhythmic fluctuations that, with the use of spectral analysis, appear as clear peaks or broadband power, respectively. This review offers a concise and critical description of the spectral methods most commonly used (fast Fourier transform versus autoregressive modeling, time-varying versus broadband spectral analysis) and an evaluation of their advantages and disadvantages. It also provides insight into the problems that still affect the physiological and clinical interpretations of data provided by spectral analysis of blood pressure and heart rate variability. In particular, the assessment of blood pressure and heart rate spectra aimed at providing indexes of autonomic cardiovascular modulation is discussed. Evidence is given that multivariate models--which allow evaluation of the interactions between changes in blood pressure, heart rate, and other biological signals (such as respiratory activity) in the time or frequency domains--offer a more comprehensive approach to the assessment of cardiovascular regulation than that represented by the separate analysis of fluctuations in blood pressure or heart rate only.

Continuous vs intermittent blood pressure measurements in estimating 24-hour average blood pressure.

In the past few years noninvasive automatic blood pressure (BP) recorders have been increasingly used to estimate patients' 24-hour BP more accurately than by one or few isolated measurements. However, these recorders only allow BP to be intermittently measured at intervals between 5 to 30 minutes, which means that the number of values collected over 24 hours (10 to 100) remains a tiny fraction of the thousands of values that occur during the same period. To determine whether this represents a limitation to this approach, BP was recorded intraarterially for 24 hours (Oxford method) in 20 ambulant hypertensive patients. A beat-to-beat analysis of the BP recording was provided by a computer, and the average 24-hour systolic, diastolic, and mean BP values were compared with those obtained by analyzing single BP waves of the same recording at intervals of 5, 10, 15, 30, and 60 minutes. In each subject the average 24-hour BP values obtained by the beat-to-beat analysis closely corresponded to those obtained by the analysis performed at 5-, 10-, 15-, or 30-minute intervals. In most subjects, this was the case also when the analysis was performed at 60-minute intervals. These findings demonstrate that intermittency of measurements does not limit the accurate assessment of true average BP. Indeed, accurate assessment can be achieved at intervals as much as 30 or 60 minutes apart.

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)

Spectral and sequence analysis of finger blood pressure variability. Comparison with analysis of intra-arterial recordings.

The aim of our study was to assess whether the Finapres device is able to accurately monitor not only average blood pressure values but also blood pressure variability. To examine this issue, we analyzed 30-minute recordings of finger and intra-arterial pressure simultaneously obtained at rest in 14 patients. We compared systolic blood pressure, diastolic blood pressure, mean arterial pressure, pulse interval (the reciprocal of heart rate), overall variability (standard deviation), and specific time-domain and frequency-domain components. Systolic blood pressure, diastolic blood pressure, mean arterial pressure, and pulse interval spectral powers were computed by fast Fourier transform over three frequency bands: low frequency (0.025 to 0.07 Hz), midfrequency (0.07 to 0.14 Hz), and high frequency (0.14 to 0.35 Hz). The coherence, ie, the degree of association between blood pressure and pulse interval powers obtained by the two techniques, was also assessed. Standard deviations of diastolic blood pressure, mean arterial pressure, and pulse interval were similar when assessed from the two recordings, whereas standard deviation of systolic blood pressure was overestimated by analysis of finger pressure recordings. All powers of diastolic blood pressure and mean arterial pressure and high-frequency powers of systolic blood pressure estimated from analysis of finger blood pressure tracings were superimposable to those obtained by analyzing invasive recordings. Low-frequency and midfrequency powers of intra-arterial systolic blood pressure were significantly overestimated by the analysis of finger blood pressure tracings (+13.7 +/- 4.4 mm Hg2, P < .01, and +2.3 +/- 0.9 mm Hg2, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Sequential spectral analysis of 24-hour blood pressure and pulse interval in humans.

Blood pressure and pulse interval are characterized not only by erratic variations but also by rhythmic fluctuations at low-, mid-, and high-frequency (0.025-0.07, 0.07-0.14, and 0.14-0.35 Hz, respectively). However, information on these phenomena has largely been derived from analysis of short-term recordings taken in standardized laboratory conditions. In seven normotensive and 10 untreated mild essential hypertensive subjects, power spectrum analysis was performed on the intra-arterial blood pressure and pulse interval signal collected over a 24-hour period using the fast Fourier transform algorithm and splitting the recording into contiguous segments of 256 beats. About 70% of the segments were suitable for the analysis; the segments excluded for a nonstationary signal amounted to only 30%. All powers were characterized by a high segment-to-segment variability, but in each subject the mid- and high-frequency powers of diastolic blood pressure and the mid-frequency power of systolic blood pressure were markedly reduced during the night as compared with the daytime period, whereas the opposite occurred for the low- and high-frequency powers of the pulse interval. Over the 24-hour period, mid- and high-frequency powers of blood pressure were positively correlated to each other, but both accounted for less than 25% of the 24-hour blood pressure variance. No difference between mean normalized power values of normotensive and hypertensive subjects was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenergic blocking treatment and 24-hour baroreflex sensitivity in essential hypertensive patients.

We dynamically evaluated the effects of beta-blockade on the sensitivity of arterial baroreflex control of heart rate in 10 mild or moderate essential hypertensive patients in whom blood pressure was recorded intra-arterially for 24 hours in ambulatory conditions. Twenty-four-hour baroreflex sensitivity was assessed by both (1) a time-domain approach based on the calculation of the slope of the regression line between linearly related progressive increases in systolic blood pressure and pulse interval (+PI/+SBP sequences) and decreases in systolic blood pressure and pulse interval (-PI/-SBP sequences) and (2) a frequency-domain approach, ie, the ratio between the spectral powers of pulse interval and systolic blood pressure around 0.1 Hz (alpha coefficient). Data were obtained before and after 1 month of administration of either acebutolol (n = 5) or labetalol (n = 5). Before treatment, the 24-hour average slopes of the +PI/+SBP and -PI/-SBP sequences were 4.36 +/- 0.32 and 4.05 +/- 0.27 ms/mm Hg, respectively, while the alpha coefficient was 7.78 +/- 0.7 ms/mm Hg. After beta-blockade, these values were increased by 25.3 +/- 6.8%, 25.0 +/- 8.0%, and 32.1 +/- 9.3%, respectively (P < .01 for all values). Thus, beta-blockers potentiate baroreflex sensitivity in daily life. Time-domain and frequency-domain methods yielded superimposable results in dynamically evaluating 24-hour baroreflex sensitivity and its changes after beta-blockade.