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Biomedical subjects

S Martina

Publications and source records attributed to S Martina.

14 recordsLinked to original sources
PubMed2004

Multichannel surface EMG for the non-invasive assessment of the anal sphincter muscle.

BACKGROUND/AIMS: This work focuses on recording, processing and interpretation of multichannel surface EMG detected from the external anal sphincter muscle. The aim is to describe the information that can be extracted from signals recorded with such a technique. METHODS: The recording of many signals from different locations on a muscle allows the extraction of additional information on muscle physiology and anatomy with respect to that obtained by classic bipolar recordings. Multichannel EMG methods have been recently developed for the assessment of the external anal sphincter. An anal probe was used in this study to record signals at different depths within the anal canal during contractions at different effort levels. The plug is 150 mm in length and 14 mm in diameter, holding a circumferential array of 16 equally spaced silver bar electrodes, located at a distance of 20 mm from the probe tip and aligned with the probe axis. RESULTS: Information about localization of the innervation zone, fiber length, EMG amplitude, muscle fiber conduction velocity and single motor unit analysis can be obtained from the signals recorded with the circumferential array by means of innovative signal processing techniques. CONCLUSIONS: The type of information extracted from multichannel surface EMG signals cannot be obtained with other currently available techniques. The technological innovation described in this work is promising for a further insight into the investigation of pelvic floor pathologies and rehabilitation treatments.

Anal Canal↗
PubMed2004

Innervation zones of the external anal sphincter in healthy male and female subjects. Preliminary results.

OBJECTIVES: The objective of this work was to investigate the distribution of the innervation zones of the motor units that make up the external anal sphincter (EAS) in healthy males and females. METHODS: A cylindrical probe carrying a circumferential array of 16 electrodes was used to detect the generation, propagation and extinction of individual motor unit action potentials (MUAPs) at 1, 2, and 3 cm depth from the orifice of the anal canal during maximal voluntary contractions of the EAS. Fifteen healthy males and 37 healthy nulliparous females were investigated. RESULTS: IZs could be detected in all males and in 34 out of 37 females. In the males, the IZs are scattered in the right and left hemisphincter at each of the three levels and their distribution is not affected by depth. In the females, the distribution is also concentrated in the right and left hemisphincter at depth 1 cm but is more uniform at depth 2 cm and more concentrated in the dorsal and ventral regions at depth 3 cm. ANOVA shows a statistically significant dependence of the IZ distribution on depth only in females and not in males. CONCLUSIONS: It is concluded that (a) IZs of the EAS can indeed be detected with a circumferential array placed at different depths along the anal canal; (b) large individual variability is observed, and (c) IZs show similar distribution at the three depth levels in males and different distributions in females.

Adult↗
PubMed2004

Advances in surface electromyographic signal simulation with analytical and numerical descriptions of the volume conductor.

Surface electromyographic (EMG) signal modelling is important for signal interpretation, testing of processing algorithms, detection system design and didactic purposes. Various surface EMG signal models have been proposed in the literature. This study focuses on the proposal of a method for modelling surface EMG signals, using either analytical or numerical descriptions of the volume conductor for space-invariant systems, and on the development of advanced models of the volume conductor by numerical approaches, accurately describing the volume conductor geometry and the conductivity, as mainly done in the past, but also the conductivity tensor of the muscle tissue. For volume conductors that are space-invariant in the direction of source propagation, the surface potentials generated by any source can be computed by one-dimensional convolutions, once the volume conductor transfer function has been derived (analytically or numerically). Conversely, more complex volume conductors require a complete numerical approach. In a numerical approach, the conductivity tensor of the muscle tissue should be matched with the fibre orientation. In some cases (e.g. multi-pinnate muscles), accurate description of the conductivity tensor can be very complex. A method for relating the conductivity tensor of the muscle tissue, to be used in a numerical approach, to the curve describing the muscle fibres is presented and applied to investigate representatively a bi-pinnate muscle with rectilinear and curvilinear fibres. The study thus proposes an approach for surface EMG signal simulation in space invariant systems, as well as new models of the volume conductor using numerical methods.

Action Potentials↗
PubMed2004

Comparison of spatial filter selectivity in surface myoelectric signal detection: influence of the volume conductor model.

Spatial filters are used for increasing selectivity in surface EMG signal detection. The study investigated the importance of the description of the volume conductor to the inference of conclusions on comparing filter selectivity from simulation analyses. A cylindrical multi-layer description of the volume conductor was used for the simulation analysis. Different anatomies were analysed with this model, and results on filter selectivity were compared. The longitudinal single (LSD), double (LDD) and normal double differential (Laplacian, NDD) filters were investigated. Largely different conclusions could be drawn when comparing filter selectivity resulting from simulations with different volume conductor models. A filter that performed best with a particular anatomy could be the poorest with another anatomy. With a bone-muscle model and superficial fibres, the ratio between peak-to-peak values of the propagating and non-propagating signal components was approximately 220% for LDD and LSD and lower than for NDD (approximately 290%). With a bone-muscle-fat-skin model, LSD performed significantly worse (150%) than both LDD and NDD, which showed similar performances (approximately 300%). Similarly, if the lateral distance of the recording was increased by 10 degrees, the signal amplitude was reduced to 2% with LSD and LDD and to 4% with NDD. With another anatomy, LSD and LDD reduced signal amplitude to 20-25%, and NDD reduced it to 4%. Similar considerations could be drawn for other selectivity indexes. Thus, modelling should be used carefully to infer conclusions on spatial selectivity and to indicate particular choices of spatial filters.

Action Potentials↗
PubMed1992

Ventricular ectopic activity in physically trained hypertensive subjects.

Exercise training is currently recommended in the management of mild hypertension, but the relationship between training and ventricular arrhythmias has never been investigated in hypertensive subjects. Forty hypertensive sportsmen were studied by means of 24-h ECG Holter monitoring and the results were compared with those obtained in 40 sedentary hypertensives, 40 normotensive sportsmen and 40 normotensive sedentary subjects. Among the hypertensive sportsmen 82.5% exhibited at least one ventricular extrasystole and 32.5% complex forms of ectopy, a prevalence higher than that observed in the sedentary hypertensives (50% and 17.5%; P = 0.002). In the normotensive sportsmen the prevalence of ventricular arrhythmias (62.5% and 22.5%) was lower than that in the hypertensive sportsmen, but the difference was not statistically significant. During a training session the prevalence of ventricular ectopy was similar in the two groups of trained individuals. Among the hypertensive sportsmen no correlation was found between the severity of ventricular arrhythmias and the degree of left ventricular hypertrophy and performance. The results of the present study suggest that exercise training may enhance left ventricular vulnerability in hypertensive subjects. Whether subjects who manifest complex ventricular arrhythmias should continue to train remains a matter for individual judgement.

Adolescent↗
PubMed1992

[Clinical significance of blood pressure response to posture].

To assess the clinical significance of the blood pressure reaction to orthostatic posture, 55 normotensives and 369 subjects with different degrees of hypertension were studied with non-invasive 24-hour blood pressure monitoring. During the recordings blood pressure response to standing was evaluated at 8 a.m., and at 2, 4 and 7 p.m. All subjects were attributed a target organ damage score on the basis of ECG, chest x-ray and fundoscopic findings. To assess whether the orthostatic reaction may represent a marker for the severity of hypertension, subjects were divided into 4 classes of increasing blood pressure levels, and each class was further subdivided into two groups of subjects with orthostatic reaction above and below the mean value. On average, blood pressure rose by 2.7 +/- 9/7.2 +/- 7 mmHg while standing up, an increase which was inversely correlated to that of heart rate (p < 0.05). The orthostatic response was substantially constant throughout daytime hours. The systolic orthostatic change from lying to standing was directly correlated with age (p < 0.02) and average daytime blood pressure (p < 0.01), and inversely correlated with lying blood pressure immediately before standing up (p < 0.001). Both systolic (p < 0.05) and diastolic (p < 0.01) pressure responses to standing were related to the day-night blood pressure difference and to the standard deviation from mean daytime blood pressure. The degree of target organ damage was not significantly greater in the 4 groups of subjects with high orthostatic response compared to those with low response. The present results show that the pressure reaction to orthostatic stress is constant throughout daytime, even though a large intraindividual variability in the extent of the response is present. Orthostatic pressure change seems to be an important determinant of diurnal pressure rhythm, while it is not a marker for the severity of hypertension.

Adolescent↗
PubMed1991

[Left ventricular filling studied by echo-Doppler in hypertensive and normotensive subjects].

Purpose of the study was to evaluate the influence of different clinical and echocardiographic parameters on left ventricular diastolic filling in a group of 66 mild to moderate hypertensive subjects (mean age = 45.9 +/- 13.9 yrs) and in 49 normotensive controls (mean age = 44.2 +/- 15.9 yrs). All subjects underwent an echocardiographic study with pulsed Doppler evaluation of left ventricular filling. In the hypertensives, a noninvasive 24-hour blood pressure monitoring was performed. The ratio of early to atrial peak diastolic filling velocity (VmaxE/VmaxA) and the ratio between the respective velocity flow integral (Earea/Aarea) were significantly lower in the hypertensives compared to the normotensives (p less than 0.001). As within the hypertensives, office systolic blood pressure, average 24-hour mean blood pressure (24MBP), left atrial dimensions, and left ventricular mass index (MAXIND) were related both to age and diastolic filling. To study the relation between these parameters and diastolic filling a partial correlation test was used. The only variable related to diastolic filling, independently of age, was 24MBP (VmaxE/VmaxA vs 24MBP: r = -0.307, p less than 0.05, Earea/Aarea vs 24MBP: r = -0.261, p less than 0.05). Linear multivariate analysis using the method of stepwise regression established that age, 24MBP and heart rate were responsible for 75% of the VmaxE/VmaxA variance in the hypertensive group. To evaluate if the difference between the indexes of diastolic filling in the normotensives and the hypertensives varied according to age, we divided each group into two classes of subjects older and younger than 40 yrs. Under the age of 40 only VmaxE/VmaxA was significantly different in the two groups (p less than 0.05), while in the subjects older than 40 yrs both VmaxE/VmaxA and Earea/Aarea differed to a great level of statistical significance (p less than 0.001). The results of the present study allow the following conclusions: 1) age has the greatest influence on diastolic filling in both hypertensive and normotensive individuals. Diastolic filling is impaired in mild to moderate hypertension, when systolic function is still normal; 2) the worsening of diastolic filling determined by hypertension is more evident in the subjects greater than 40 yrs; 3) the only clinical variable that influences diastolic filling, independently of age, is 24MBP, while office blood pressure, MAXIND and left ventricular ejection fraction do not seem to be related to this clinical entity.

Adolescent↗
PubMed1990

[The normal limits of arterial pressure registered with portable methods: an approach to the problem].

In the present paper the problem of the normalcy limits of whole-day ambulatory blood pressure has been faced by evaluating the difference between casual and ambulatory blood pressure in a population of 522 subjects with blood pressure values covering the whole blood pressure range. On the basis of the casual blood pressure levels, 60 subjects were normotensives, 110 borderline hypertensives, 214 mild, 103 moderate and 35 severe hypertensives. The differences between casual and median 24-hour blood pressure averaged 18.4/9.6 mmHg. The difference between casual and median day-time was 14.2/6.7 mmHg. This difference was independent from the ambulatory blood pressure values and unrelated to the sex or age of subjects. The upper normal limits of ambulatory blood pressure were established by subtracting the above differences from the normal limits established by the WHO for casual blood pressure (140/90 mmHg). For 24-hour blood pressure the upper limits were 121.6/80.4 mmHg and for day-time blood pressure these were 125.8/83.3 mmHg. Contrary to previous studies conducted on normotensive populations with this approach the selection of patients based on casual blood pressure is avoided and the WHO normalcy limits are taken into account.

Adolescent↗
PubMed1990

[Clinical significance of nocturnal blood pressure and blood pressure variability: analysis of 522 cases].

Purpose of the study was to investigate whether and to what extent blood pressure variability and average night-time blood pressure are related to cardiovascular complications in hypertension. To this aim 60 normotensive and 462 hypertensive subjects were studied by means of non-invasive 24 hour blood pressure monitoring, using either the Avionics, or the ICR Spacelabs, or the Takeda system. Each subject was attributed a target organ damage score on the basis of 12-lead electrocardiogram, chest X-ray and fundoscopy, starting from 0 (no damage) up to 5 (maximum degree of damage). The 522 subjects were subsequently subdivided into 5 classes of increasing average daytime diastolic blood pressure. In each class a higher degree of cardiovascular complications was present in the subjects with the higher blood pressure variability and the higher average night-time blood pressure. From these results it may be inferred that both blood pressure variability and night-time blood pressure are related to the degree of target organ damage in hypertension. This stresses the importance of recording blood pressure throughout the 24 hours.

Adult↗
PubMed1989

Blood pressure changes during heavy-resistance exercise.

To study the mechanisms of the blood pressure changes during weight-lifting, three hypertensive and five normotensive body-builders underwent continuous intra-arterial monitoring. In two subjects (one normotensive and one hypertensive), intrathoracic and intra-abdominal pressures were also measured. Extremely high blood pressure elevations of up to 345/245 mmHg were observed during the lifts. Squatting caused the highest pressure rises and single-arm curls the lowest. Both the intrathoracic and the intra-abdominal pressures increased greatly during each lift and closely paralleled the changes in intra-arterial pressure. A close correlation was found between the blood pressure increase during the exercise and during a hand-grip test (r = 0.95, P less than 0.001). These results suggest that a pronounced increase in intra-thoracic and intra-abdominal pressures is a major determinant of the blood pressure elevations occurring during weight-lifting. The pressor reflex which accompanies static contractions and the individual baseline blood pressure levels also seem to affect the height of the pressure peaks.

Adult↗
PubMed1988

[Reproducibility of ambulatory blood pressure monitoring].

Short-term blood pressure variability has been studied extensively with monitoring techniques. To assess whether or not and to what extent average 24-hour blood pressure varies when repeatedly recorded, 12 mild to moderate hypertensive subjects underwent 3 non-invasive blood pressure monitorings at monthly intervals. When the average 24-hour blood pressure of the whole group was evaluated no substantial differences were found between the 3 recordings, even though slightly lower blood pressure values were recorded at the first monitoring. However, when the within-period comparison was studied in the single patients, remarkable discrepancies of up to 20.9/15.8 mmHg were detected. Systolic and diastolic blood pressure variations greater than or equal to 5 mmHg were recorded in 58% of the subjects. These differences were unrelated to the number of faulty readings. Casual blood pressure varied even to a greater extent between the first and the subsequent visits; no correlation was found between casual and 24-hour blood pressure variations. The results of the present study indicate that ambulatory blood pressure may vary even to a great extent when repeatedly recorded. This finding entails important clinical implications, as the evaluation of the hypertensive patient is usually made with a single blood pressure monitoring.

Adult↗