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Biomedical subjects

A E Aubert

Publications and source records attributed to A E Aubert.

At least 19 recordsLinked to original sources
PubMed2005

Influence of supplemental magnesium, tryptophan, vitamin C, and vitamin E on stress responses of pigs to vibration.

Our objectives were to investigate and compare the effects of supplemental Mg, Trp, vitamin E (vit E), and vitamin C (vit C) on stress responses of pigs undergoing transport simulation. In this study, 126 pigs (25.1 +/- 4.4 kg BW) were allocated to one of the six following treatments: 1) negative control (no supplementation); 2) positive control (i.m. injection with 0.5 mg of carazolol/20 kg BW 12 h before vibration, beta-blocker); 3) Trp (additional amount of 6 g/kg of feed for 5 d, as-fed basis); 4) Mg (3 g/L drinking water for 2 d); 5) vit E (additional amount of 150 mg/kg of feed for 21 d, as-fed basis); 6) or vit C (additional amount of 300 mg/kg of feed for 21 d, as-fed basis). Pigs were treated in groups of three, and each treatment was replicated seven times. Feed and water intake were not different among treatments. Heart rate variables (mean, peak, and minimum heart rate, ventricular ectopic beats, and ST elevation of Channels A and B) and heart rate variability were registered from the night before vibration. Pigs were subjected to vibration in a transport simulator (8 Hz, 3 m/s) for 2 h and allowed to recover for 2 h. Generally, the positive control pigs had the lowest heart rate values (mean, peak, minimum heart rate, ST elevation of Channel A; P < 0.05), whereas Mg and Trp decreased ventricular ectopic beats and ST elevation of Channel B, respectively. The effect of vit C and E as vagal stimulators was clearly visible, whereas carazolol and Mg clearly blocked the sympathetic pathways of the autonomic nervous system. During vibration, the negative control pigs lay the least, and Mg pigs the most (P < 0.05). Salivary cortisol concentrations (taken before and after vibration and after recovery) showed that vit E pigs produced the least cortisol during stress periods. Intermediary metabolites (glucose, lactate, creatine kinase, and NEFA) were analyzed in plasma from blood taken before and after vibration. At the two sampling points, the vit E and Mg pigs had the lowest NEFA concentrations (P < 0.05), and the vit E pigs also had the lowest lactate concentrations before vibration. Urine samples were collected before and after vibration to determine catecholamine concentrations; only negative control pigs had an increase (P = 0.04) in epinephrine concentration, despite large individual variation. In general, these results indicate that the supplementation of Trp, Mg, vit E, or vit C improved coping ability of pigs during vibration comparison with the negative control treatment. A muscular injection of carazolol influenced only the heart rate variables.

Adaptation, Psychological↗
PubMed2003

Parasympathetic heart rate modulation during parabolic flights.

During parabolic flight short periods of microgravity and hypergravity are created. These changes influence cardiovascular function differently according to posture. During the 29th parabolic flight campaign of the European Space Agency (ESA), the electrocardiogram (ECG) was recorded continuously in seven healthy volunteers in two positions (standing and supine). Five different phases were differentiated: 1 g (1 g=9.81 m/s(2)) before and after each parabola, 1.8 g at the ascending leg of the parabola (hypergravity), 0 g at the apex, 1.6 g at the descending leg (hypergravity). We assessed heart rate variability (HRV) by indices of temporal analysis [mean RR interval (meanRR), the standard deviation of the intervals (SDRR), and the square root of the mean squared differences of successive intervals (rMSSD) and coefficient of variation (CV)]. In the supine position no significant differences were shown between different gravity phases for all HRV indices. In the standing position the 0 g phase showed a tendency towards higher values of meanRR compared to the control and to the other phases ( p=NS). SDRR, rMSSD and CV were significantly higher compared to control ( p<0.05). Significantly higher values for meanRR in the supine position at 1 g and hypergravity ( p<0.05) were found when compared to standing. SDRR was significantly higher at 0 g in the standing position compared to supine [95 (44) ms vs. 50 (15) ms; p<0.05] and lower in other phases. rMSSD and CV showed the same trend ( p=NS). We confirm that, during parabolic flights, position matters for cardiovascular measurements. Time domain indices of HRV during different gravity phases showed: (1) higher vagal modulation of the autonomic nervous system in microgravity, when compared with normo- or hypergravity in standing subjects; and (2) no differences in supine subjects between different g phases.

Adaptation, Physiological↗
PubMed2002

Effects of melanocortins on cardiovascular regulation in rats.

1. Of the melanocortin peptides, gamma(2)-melanocyte-stimulating hormone (MSH) has been attributed a cardiovascular effect, inducing an increase in blood pressure and heart rate. Although still controversial, this effect, based on pharmacological blockade experiments, is supposed to be mediated through sympathetic activation. 2. The aims of the present study were to identify the N-terminal pro-opiomelanocortin (N-POMC) fragments and melanocortins that influence blood pressure and heart rate and to investigate the real-time changes in baroreflex sensitivity and in sympathetic and vagal modulation underlying cardiovascular effects in conscious rats without the use of pharmacological blockade. 3. Intracerebroventricular administration of different melanocortins and N-POMC induced a long-lasting dose- dependent pressor response from 1 nmol onwards, with only a small initial bradycardic response with the highest dose. 4. Coinciding with this pressor response, an elicitation of the low-frequency (LF) component was observed in spectral analysis of both blood pressure variability (BPV) and heart rate variability (HRV), followed by the high-frequency (HF) component in at least BPV. Baroreflex sensitivity remained unchanged. 5. After intravenous administration, gamma(2)-MSH produced a short-lasting dose-dependent pressor and cardioaccelerator response with very rapid onset with concentrations from 1 nmol onwards. 6. Continuous infusion of gamma(2)-MSH depressed baroreflex sensitivity and simultaneously increased both components of BPV, with a radical reduction of the LF component and a preserved vagal HF component in HRV. 7. Of all the intravenously administered melanocortins, only gamma(2)-MSH was active. The central effect is likely to depend on an increase of (alpha-)sympathetic outflow. 8. For the peripheral effect, gamma(2)-MSH appeared to act as a baroreceptor reflex-blocking agent, being compatible with a role in the acute stress response.

Animals↗
PubMed2002

Heart rate variability during gravity transitions.

During parabolic flight short periods of microgravity and hypergravity are created. During standing position time domain analysis showed higher vagal modulation of the autonomic nervous system in microgravity compared to hypergravity. We hypothesised that this behaviour could better be unravelled by analysis of frequency domain heart rate variability (HRV) techniques. During parabolic flights a subject is exposed to 20-25 sec periods of microgravity (at the top of the parabola), preceded and followed by 20 sec duration episodes of hypergravity. No significant differences were found in the frequency parameters in supine position for each of the phases. In standing position higher values for Total Power, high frequency (HF), low frequency (LF), LF/HF and HF% in 0 g phase were found in comparison with the 3 other phases. LF% was significant lower in standing position at 0 g compared with 1.8 g. These results show that despite the time window limitations, frequency analysis is still possible on ultra short data segments.

Adult↗
PubMed2002

Head out of water immersion as simulation study: an heart rate variability study.

During head out of water immersion (HOI), the hydrostatic pressure on the tissues of the lower limbs causes an increase in thoracic blood volume and a high vascular perfusion. This blood shift results in changes in autonomic balance. The aim of this study was to evaluate the activity of the autonomic nervous system, as obtained from the analysis of heart rate variability (HRV), during HOI at 2 different temperatures and compare these results with data obtained during parabolic flight. In HOI, two different positions (sitting and standing) were compared. Results showed a shift to vagal activity as well during HOI as in microgravity during parabolic flight.

Comparative Study↗
PubMed2001

Analysis of heart rate variability with correlation dimension method in a normal population and in heart transplant patients.

INTRODUCTION: The correlation dimension (CD) method is related to chaos theory and is used to quantify heart rate variability (HRV). The CD is a measure for the amount of correlations present in the signal. METHODS: The algorithm used to calculate the CD is based on the method of Grassberger and Proccacia. The method was first validated on signals with known CD and then applied to HRV-signals of heart transplants and an age-matched control group of healthy subjects. The CD of the corresponding surrogate time series was calculated to investigate non-linear correlations in the HRV-signal. Circadian variations of the CD were studied in 20 healthy subjects, including men and women. RESULTS: The value of the CD for healthy subjects ranged from 2.12 to 5.53 with a mean value of 4.32. For heart transplants, only a few time series showed a finite value of the CD that varied between 2.10 and 5.60. Also, a significant difference was found between the CD of the original and the surrogate time series in healthy subjects. The CD of women is higher than the CD of men, and this difference was more pronounced during the night than during the day. CONCLUSIONS: This limited study shows that the CD alone cannot be used to make a distinction between HRV-signals of healthy subjects and of heart transplants. However, there is evidence that there are non-linear correlations present in the HRV-signal and that there are significant gender and circadian differences in the CD.

Algorithms↗
PubMed2001

Wavelet decomposition analysis of heart rate variability in aerobic athletes.

Heart rate variability (HRV) can be quantified, among others, in the frequency domain using digital signal processing (DSP) techniques. The wavelet transform is an alternative tool for the analysis of non-stationary signals. The implementation of perfect reconstruction digital filter banks leads to multi resolution wavelet analysis. Software was developed in LabVIEW. In this study, the average power was compared at each decomposition level of a tachogram, containing the consecutive RR-intervals of two groups of subjects: aerobic athletes and a control group. Compared to the controls, the aerobic athletes showed an increased power in all frequency bands. These results are in accordance with values obtained by spectral analysis using the Fourier transform, suggesting that wavelet analysis could be an appropriate tool to evaluate oscillating components in HRV, but in addition to classic methods, it also gives a time resolution.

Adolescent↗
PubMed2001

Short-term heart rate variability in young athletes.

OBJECTIVES: The purpose of this study was to determine whether the type of training in a young population differentiates heart rate variability parameters between athlete groups and sedentary subjects. METHODS: The effect of different types of physical training on heart rate variability was evaluated in 10 aerobic trained athletes, in 7 anaerobic trained athletes, in 7 rugby players (mixed type training) and in 10 sedentary control subjects. All groups were age matched (18-34 years). Electrocardiogram tracings were recorded digitally in the supine position and standing position. Measures of heart rate variability were obtained, from both time- and frequency analysis of 10 min resting heart rate. After these tests, blood pressure was measured using an automatic inflation cuff. RESULTS: Resting heart rate was lower in aerobic and mixed type athletes compared to controls. Only aerobic athletes had evidence of increased vagal activity in the time domain compared with control subjects (increased SDNN supine, increased rMSSD supine and standing and pNN50 standing). In the frequency domain, aerobic athletes presented with both higher low-frequency and high-frequency power in the standing position and low-frequency power in the supine position compared to controls. CONCLUSIONS: It can be concluded that heart rate variability is affected by chronic exercise, especially in endurance trained athletes. This infers that especially aerobic exercising can have beneficial effects on the cardiovascular risk profile.

Adolescent↗
PubMed1999

The analysis of heart rate variability in unrestrained rats. Validation of method and results.

An experimental setting and software were developed to evaluate cardiac autonomic function in unrestrained rats. Subcutaneously implanted ECG electrodes and an indwelling venous catheter were tunneled to a tail cuff in five rats. The ECG was A/D converted at 1000 Hz. After peak detection, a time series of RR intervals was obtained. Programs for the analysis of heart rate variability (HRV) were implemented in LabVIEW. Statistical properties were determined in the time domain. After cubic spline function curve fitting, resampling at 0.1 s and test for stationarity, power spectral analysis was performed on sampled records of 30 min duration after applying a sliding Hanning window (Welch method: 256 points (duration 25.6 s), 50% overlap and 0.039 Hz resolution). Algorithms were tested with simulated signals consisting of isolated frequency components, which were retrieved at their exact locations. Physiological validation of the system was performed by, beta-adrenergic and cholinergic blockade and by forced breathing at a fixed rate. Measurements were performed on five unrestrained rats under basal conditions. Mean RR was 174.2 +/- 3.6 ms; S.D., 13.3 +/- 4.6 ms; rMSSD, 5.2 + /- 1.2 ms; pNN10, 3.5 +/- 1.9% and pNN5, 18.7 +/- 6.4%. Low (0.19-0.74 Hz) and high frequency (0.78-2.5 Hz) power were determined (and also percent of low to total and high to total): 18.42 +/- 10.74 ms2 (22.9 +/- 6.5%) and 15.66 +/- 5.56 ms2 (19.9 +/- 2.7%), and the ratio low/high: 1.16 +/- 0.39. In conclusion, HRV analysis programs were developed and thoroughly tested through simulations and in vivo, under basal conditions and after pharmacological blockades. Using this software, HRV data from unrestrained rats were obtained.

Animals↗
PubMed1999

Neurocardiology: the benefits of irregularity. The basics of methodology, physiology and current clinical applications.

Cardiovascular variability in heart rate and blood pressure can be used to quantify the autonomic modulation of cardiovascular function. Although the first studies were only published 10 to 20 years ago, there is presently a vast amount of knowledge from numerous publications that allows a better insight into the neural control mechanisms of the heart. The development of methods such as heart rate variability and baroreflex sensitivity prompted a multidisciplinary approach since many aspects were involved: mathematics, signal processing, physiology and cardiology. Therefore, it is obvious that an adequate understanding of certain basic principles is necessary before its clinical potential can be fully exploited. This current review outlines the physiological background and the fundamental methodology used in the field of neurocardiology by presenting the newer insights and developments from both fundamental and clinical sides. Recent publications indicate that neurocardiological applications in (risk stratification of) myocardial infarction, congestive heart failure and heart transplant patients can be expected to enter daily clinical practice in the next millennium.

Baroreflex↗
PubMed1998

Heart rate variability and heart rate in healthy volunteers. Is the female autonomic nervous system cardioprotective?

AIMS: Heart rate variability has been proposed as an indicator of cardiovascular health. Since women have a lower cardiovascular risk, we hypothesized that there are gender differences in autonomic modulation. METHODS AND RESULTS: In 276 healthy subjects (135 women, 141 men) between 18 and 71 years of age, 24 h heart rate and heart rate variability were determined. All heart rate variability parameters, except for pNN50 and high frequency power, were higher in men. After adjustment for heart rate, we obtained gender differences for: the standard deviation (P=0.049), the standard deviation of the 5 min average (P=0.047), low frequency power (absolute values, P=0.002; normalized units, P<0.001) and ratio low frequency/high frequency (P<0.001). There were no significant gender differences in heart rate variability parameters denoting vagal modulation. Gender differences were confined to age categories of less than 40 years of age. The majority of heart rate variability parameters decreased with age. Only in men, was a higher body mass index associated with a higher heart rate and with lower heart rate variability parameters (P<0.001). CONCLUSION: Cardiac autonomic modulation as determined by heart rate variability, is significantly lower in healthy women compared to healthy men. We hypothesize that this apparently paradoxical finding may be explained by lower sympathetic activity (low frequency power) in women. This may provide protection against arrhythmias and against the development of coronary heart disease.

Adolescent↗
PubMed1995

In vivo comparison between two tip pressure transducer systems.

Experimental findings are presented of an in vivo comparison between a Sentron catheter and another tip transducer manometer: a Millar microtip catheter. Both catheters have been used simultaneously in the left ventricle of dogs. Pressure variations were elicited by drug infusion. Pressure values and derivatives obtained from both systems were compared. A cross correlation between episodes of the two pressures was computed. Results from this study showed good correlation between left ventricular systolic pressure measured with both manometers (R = 0.992, p < 0.0001), end-diastolic pressure (R = 0.809, p < 0.0001) and between first derivatives: positive derivative (R = 0.993, p < 0.0001) and negative (R = 0.634, p < 0.0001). The mean cross correlation between both pressure signals was 0.61 +/- 0.04. In the frequency domain no statistical difference was found between the location of the maxima of the peaks. It is concluded that a Sentron manometer can be a valid alternative, at a reasonable price, to a cheaper, though less accurate fluid filled catheter and a more expensive 'golden standard' microtip catheter.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1995

Determinants of transmitral inflow pattern 10-14 days after acute myocardial infarction.

AIM: The administration of thrombolytic therapy after an acute myocardial infarction can reduce the size of the infarct and improve left ventricular function. We used pulsed Doppler to assess left ventricular diastolic function after an acute myocardial infarction in patients treated with recombinant tissue plasminogen activator (rTPA). PATIENTS AND METHODS: We studied 104 patients after an acute myocardial infarction, 48 treated with a placebo and 56 with rTPA. They were compared with 36 age-matched controls. The Doppler parameters measured included the early peak in diastolic flow velocity, the peak during atrial contraction, the atrial: early ratio, mean deceleration, deceleration time, and half-filling fraction. Doppler parameters for large and small infarct sizes were compared. RESULTS: The Doppler parameters did not differ between treatment groups. Compared with the normal controls, significant differences were observed in both treatment groups for the early peak (placebo P < 0.05; rTPA P < 0.001), the atrial: early ratio (placebo P < 0.05; rTPA P < 0.01), and the half-filling fraction (P < 0.001 for both). In patients with large infarcts, the atrial peak was depressed (P = 0.008). Multivariate analysis showed that end-diastolic pressure, age, end-systolic volume, and regional wall motion parameters were major predictors of Doppler parameters.

Adult↗
PubMed1994

Automatic detection of ventricular tachycardia and fibrillation using ECG processing and intramyocardial pressure measurement.

Ventricular electrograms and intramyocardial pressure signals were recorded in 11 dogs during sinus rhythm, during paced ventricular tachycardia, and at the onset of and during ventricular fibrillation. The autocorrelation function and the probability density function of short episodes of the electrograms were analyzed off-line on a digital computer. Peak-to-peak values of the intramyocardial pressure were calculated during sinus rhythm and during ventricular tachycardia and fibrillation. An algorithm was developed to recognize tachycardia and fibrillation using the autocorrelation function, the probability density function, and the intramyocardial pressure as input signals. Results show that in case of sinus rhythm all detection methods are reliable (recognition rate of 100%). In case of ventricular tachycardia with hemodynamic impairment the autocorrelation function is slightly better (66.6%) than the probability density function (44.4%). The onset of ventricular fibrillation is sensed in 81.8% of all episodes with the autocorrelation function and in 63.6% with the probability density function. During ventricular fibrillation this improves, respectively, to 92.3 and 69.2%. In all previous cases the intramyocardial pressure signal was 100% reliable. It is concluded that in this arrhythmia model, the sensitivity of an automatic ventricular tachycardia/fibrillation detection system was increased by combining ECG processing with analysis of an hemodynamic parameter.

Algorithms↗
PubMed1994

Relaxation within the left ventricular myocardial wall.

To evaluate relaxation mechanics in the wall of the left ventricle needle mounted miniature pressure transducers were inserted at the subendocardial (ENDO) and subepicardial (EPI) level of the anterior wall of the left ventricle during acute open-chest experiments in 10 mongrel dogs. Pressures were recorded during control, volume load and after verapamil administration. The relaxation time constant (tau) was determined by fitting a monoexponential with offset to the isovolumic relaxation period of the ENDO, EPI and left ventricular pressure (LVP) tracings: p = p0e-t/tau + p1. Mean tau-values for LVP, ENDO and EPI during control were (mean +/- 1 SD, ms): 38 +/- 5, 60 +/- 12, 83 +/- 5; during volume overload: 55 +/- 10, 72 +/- 20, 85 +/- 31 and after verapamil administration: 58 +/- 13, 60 +/- 17 and 73 +/- 15, respectively. Relaxation time constants of ENDO and EPI were significantly longer than those of LVP during control and volume loading but not after verapamil when only EPI was significantly different from LVP. These results demonstrate that relaxation indices obtained from LVP may not always reflect intramyocardial mechanics.

Animals↗
PubMed1993

Clinical aspects during long-term follow-up after DC shock ablation of the atrioventricular junction. A Belgian experience.

Ninety-three patients, who underwent DC shock ablation were reviewed over a mean follow-up period of 54 months (range 3 to 84 months). These patients (46 male and 47 female, mean age: 58 years) had failed an average of 3 drugs, and the duration of symptoms was more than 2 years. Paroxysmal atrial fibrillation or flutter was treated in 75 patients (80.6%); the remainder had supraventricular tachycardia or reciprocating tachycardia using an accessory pathway. One shock of 200 J was effective in producing third degree AV block in 40 patients (43%), while 2 or more shocks were used in another 53 patients (57%). Chronic complete heart block (CHB) was obtained in 85 patients (91%), modification of conduction was seen in 2 patients (2.1%), and failure to achieve an improvement in 6 patients (6.4). All the patients of the last group had received more than 4 shocks (200 to 400 J). However no significant difference between the amplitude of atrial and His electrograms could be shown between the CHB patients and those in whom conduction persisted. Over a mean follow-up of 54 months, 66 patients (72%) with successful ablation during the first 48 hours after the procedure remained in CHB. In 18 patients AV conduction resumed but they were all asymptomatic: 10 patients (10.8%) without antiarrhythmic therapy and 8 patients (8.6%) with medication. In conclusion, ablation of the AV junction is effective in more than 82% of patients. Most of the time long-term success can be predicted within 48 hours. However, due to the invasive character of DC shocks, this technique has been supplanted by the less aggressive radiofrequency method.

Adult↗
PubMed1992

Influence of short atrioventricular delay on late diastolic transmitral flow and stroke volume.

Atrial transport function and the corresponding transmitral flow and stroke volume depend on the timing of atrial contraction. To study the influence of short atrioventricular delay (AVD) on these hemodynamic parameters, transmitral flow velocity (by pulsed wave Doppler) and aortic flow (by electromagnetic technique) were studied and compared (paired t test) during normal and short AVD at fixed rate DDD pacing (80 bpm) in AV-blocked, open-chest canine preparations (n:16). The short AVD resulted in a shorter acceleration (difference 4.1 +/- 4.9 msec, mean +/- SD, p less than 0.05), a lower peak velocity (difference: 7.1 +/- 3.2 cm/sec, p less than 0.001), a shorter (difference: 26.9 +/- 16.2 msec, p less than 0.001) and more rapid deceleration (difference: 220.7 +/- 291.7 cm/sec2, p less than 0.005) of the late diastolic transmitral flow elicited by atrial systole. Stroke volume decreased (7.8 +/- 5.2%, p less than 0.001) during short AVD as a consequence of a reduced left ventricular filling due to the interruption of the active atrial transport by the onset of the ventricular contraction.

Animals↗