Biomedical subjects

P Laguna

Publications and source records attributed to P Laguna.

At least 19 recordsLinked to original sources

PubMed2003

Detection of body position changes using the surface electrocardiogram.

A method for detecting body position changes that uses the surface vectorcardiogram (VCG) is presented. Such changes are often manifested as sudden shifts in the electrical axis of the heart and can erroneously be interpreted as acute ischaemic events. Axis shifts were detected by analysing the rotation angles obtained from the alignment of successive VCG loops to a reference loop. Following the rejection of angles originating from noise events, the detection of body position changes was performed on the angle series using a Bayesian approach. On a database of ECG recordings from normal subjects performing a predefined sequence of body position changes, a detection rate of 92% and a false alarm rate of 7% was achieved.

Adult↗

PubMed2003

Estimation of the respiratory frequency using spatial information in the VCG.

A new method for extracting respiratory signals from the ECG/VCG is presented. The method is based on the alignment of an observed VCG loop to a reference loop with respect to the transformations of rotation and time synchronisation. The resulting series of estimated rotation angles reflects respiratory-induced changes in the electrical axis of the heart. The respiratory frequency is estimated by power spectral analysis of the derived respiration signal. The value of respiratory modulation of the heart rate is considered by analysing the cross power spectrum of the signals related to rotation angles and heart rate. For comparison, a respiratory signal derived from the QRS area of two different leads is implemented. The performance of the methods is validated on a database with simultaneously recorded VCG and respiratory signals acquired from 20 healthy subjects. The agreement between the respiratory frequencies obtained from the derived and the respiratory signals is presented. The angle-based respiratory signal is found to produce the best agreement with a gross median error of only 4.2%.

Algorithms↗

PubMed2002

[Control of the endotracheal cuff balloon pressure as a method of preventing laryngotracheal lesions in critically ill intubated patients].

OBJECTIVES: To study the development of tracheal stenosis after endotracheal intubation, percutaneous tracheotomy or both; to assess risk factors for tracheal stenosis and the relation of risk to endotracheal cuff pressure. PATIENTS AND METHODS: A prospective study enrolling patients sustaining endotracheal intubation longer than 8 hours and/or undergoing percutaneous tracheotomy. Cuff pressure was recorded at the moment of intubation and every 8 hours thereafter; a ceiling of 25 mm Hg was targeted. The patients were examined 6 months after discharge. RESULTS: Sixteen percutaneous tracheotomies were performed in the 95 patients enrolled (58 men, 37 women). The mean age was 54.1 +/- 19.7 years. The mean APACHE II score for all patients was 16.3 +/- 7.7 and the mean intubation time was 7.3 +/- 11 days, whereas the respective means for patients undergoing percutaneous tracheotomy were 18.4 +/- 7.6 and 20.5 +/- 19 days. Six months after discharge, 55 patients were examined for laryngotracheal lesions by fiberoptic endoscopy. Twenty-three of the remaining patients had died, 7 were lost to follow-up and 10 were only interviewed by telephone. Fiberoptic laryngotracheal endoscopy revealed minimal scarring and reduction of the endotracheal lumen. Reduction of the lumen was observed only in patients who had undergone percutaneous tracheotomy. CONCLUSIONS: Monitoring cuff pressure three times per day seems to contribute to preventing ischemic lesions and tracheal stenosis.

Adult↗

PubMed2001

Correlation between clinical, radiological and ultrasonographical image of knee joints in children with haemophilia.

The aims of the study were to evaluate the clinical, radiological and ultrasonographical images of knee joints in children with severe haemophilia and von Willebrand's disease, to determine the correlation between these images and to assess the usefulness of ultrasonography (USG) in evaluating the intensity of haemophilic arthropathy. Thirty-nine boys were included in the study, all of them with a past history of knee bleeds. The average age of the children was 10.02 +/- 3.01 years. In patients with slight (1-3 points) and moderate (4-7 points) radiological changes in knee joint bones, an increase in synovial fluid, considerable hypertrophy and inflammation of the synovium were observed in USG. In haemophilic patients with severe (8-13 points) bone changes, the amount of fluid was usually normal and there was slight inflammation but considerable hypertrophy of the synovium. Radiological evaluation of haemophilic arthropathy was made according to the Pettersson classification. A good correlation between the degree of cartilage damage in USG and the progression of bone changes in radiographs was found. Cartilage and bone damage progressed with the increase in the number of intra-articular haemorrhages into the knee joint. In our opinion USG is useful in evaluating the fluid, synovium and cartilage of joints in haemophiliacs.

Adolescent↗

PubMed2001

Control group and maintenance treatment with bacillus Calmette-Guerin for carcinoma in situ and/or high grade bladder tumors.

PURPOSE: Intravesical instillations of bacillus Calmette-Guerin have demonstrated satisfactory results in the treatment of vesical carcinoma in situ and high grade superficial bladder tumors. We designed a protocol to evaluate the decrease in tumor recurrence with maintenance therapy. MATERIALS AND METHODS: Between June 1989 and May 1995 an initial course of 6 intravesical instillations of Connaught strain bacillus Calmette-Guerin was administered in patients with carcinoma in situ and/or high grade superficial bladder tumors. Six months later 131 disease-free patients were randomly assigned to a control group or a maintenance therapy group that received 6 instillations every 6 months (6 x 6) for a 2-year period. RESULTS: Of the 126 evaluable patients at a mean followup of 79 months there were no significant differences in recurrence nor progression. A total of 16 patients (26.2%) in the control and 10 (15.1%) in the maintenance group had superficial relapse at a mean of 24 and 20 months, respectively (p = 0.07). Eight patients underwent radical cystectomy due to bladder contraction in 1, high grade superficial recurrence in 4 and disease progression in 3. Of the 65 patients on maintenance therapy 22 (33.85%) completed the planned 2-year treatment. CONCLUSIONS: Six-month maintenance therapy in patients treated initially for carcinoma in situ and/or high grade superficial bladder tumors who are disease-free at 6 months did not significantly decrease recurrence or progression.

Adult↗

PubMed2000

Grazing collisions of black holes via the excision of singularities.

We present the first simulations of non-head-on (grazing) collisions of binary black holes in which the singularities are excised from the simulation. Initially equal mass m black holes (spinning or not) are separated by approximately 10m and with impact parameter approximately 2m. Evolutions to t approximately 35m are obtained where two separate horizons are present for t approximately 3.8m; then a single enveloping horizon forms indicating that the holes merged. Apparent horizon area estimates suggest gravitational radiation of about 2%-3% of the total mass. The evolutions end after a moderate amount of time because of instabilities.

Journal Article↗

PubMed2000

Sampling rate and the estimation of ensemble variability for repetitive signals.

The measurement of ensemble variability in time-aligned event signals is studied in relation to sampling rate requirements. The theoretical analysis is based on statistical modelling of time misalignment in which the time resolution is limited by the length of the sampling interval. For different signal-to-noise ratios (SNRs), the sampling rate is derived which limits the misalignment effect to less than 10% of the noise effect. Each signal is assumed to be corrupted by additive noise. Using a normal QRS complex with a high SNR (approximately equal to 30 dB), a sampling rate of approximately 3 kHz is needed for accurate ensemble variability measurements. This result is surprising since it implies that the Nyquist rate is far too low for accurate variability measurements. The theoretical results are supplemented with results obtained from an ECG database of 94 subjects for which the ensemble variability is computed at different sampling rates using signal interpolation. The ensemble variability is substantially reduced (40%) when increasing the rate from 1 to 3 kHz, thus corroborating the results suggested by the theoretical analysis.

Electrocardiography↗

PubMed2000

Temporal evolution of traditional versus transformed ECG-based indexes in patients with induced myocardial ischemia.

The time course of changes in the electrocardiogram as a result of myocardial ischemia induced during prolonged coronary angioplasty has been studied. We have analyzed the electrocardiogram evolution during the occlusion in terms of the Ischemic Changes Sensor, which is a parameter that describes the capacity of different indexes to detect induced changes. Traditional indexes at specific time locations (ST level, T wave amplitude and position, and durations of QT interval and QRS complex) and global indexes (based on the Karhunen-Loève transform as applied to the QRS complex, ST-T complex, ST segment and T wave) have been considered. The global indexes better detected ischemic changes than the traditional indexes. The most sensitive were the index for the ST-T complex (89%) in the Karhunen-Loève transform-derived group and for the ST level (61%) in the traditional group. Changes in the ventricular repolarization period usually appeared earlier (77% of patients) than changes in the depolarization period (23% of patients). A similar percentage of patients exhibited the earliest ischemic changes in the T wave (41%) and in the ST segment (36%). The evolution of the Ischemic Changes Sensor parameters showed that the majority (60%) of the total changes occurred during the first minute of occlusion. The results suggest that the use of global electrocardiogram indexes better reflect ischemic changes than do traditional indexes, such as the ST segment deviation.

Angioplasty, Balloon, Coronary↗

PubMed2000

Prostate specific antigen and benign prostatic hyperplasia.

Benign prostatic hyperplasia is a common condition in males over 50 years, but prostate cancer can develop in the same population. Prostate specific antigen, the best marker for prostate cancer, is also produced by benign epithelial cells, and there is an overlapping phenomenon between both conditions. The better we understand the relationships between benign prostatic hyperplasia and prostate specific antigen, the higher will be the discrimination power of prostate specific antigen measurement as a marker for prostate cancer. Our scope includes a review of the latest published material to date on this subject.

Age Factors↗

PubMed2000

Vectorcardiographic loop alignment and the measurement of morphologic beat-to-beat variability in noisy signals.

The measurement of subtle morphologic beat-to-beat variability in the electrocardiogram (ECG)/vectorcardiogram (VCG) is complicated by the presence of noise which is caused by, e.g., respiration and muscular activity. A method was recently presented which reduces the influence of such noise by performing spatial and temporal alignment of VCG loops. The alignment is performed in terms of scaling, rotation and time synchronization of the loops. Using an ECG simulation model based on propagation of action potentials in cardiac tissue, the ability of the method to separate morphologic variability of physiological origin from respiratory activity was studied. Morphologic variability was created by introducing a random variation in action potential propagation between different compartments. The results indicate that the separation of these two activities can be done accurately at low to moderate noise levels (less than 10 microV). At high noise levels, the estimation of the rotation angles was found to break down in an abrupt manner. It was also shown that the breakdown noise level is strongly dependent on loop morphology; a planar loop corresponds to a lower breakdown noise level than does a nonplanar loop.

Action Potentials↗

PubMed2000

Improved heart rate variability signal analysis from the beat occurrence times according to the IPFM model.

The heart rate variability (HRV) is an extended tool to analyze the mechanisms controlling the cardiovascular system. In this paper, the integral pulse frequency modulation model (IPFM) is assumed. It generates the beat occurrence times from a modulating signal. This signal is thought to represent the autonomic nervous system action, mostly studied in its frequency components. Different spectral estimation methods try to infer the modulating signal characteristics from the available beat timing on the electrocardiogram signal. These methods estimate the spectrum through the heart period (HP) or the heart rate (HR) signal. We introduce a new time domain HRV signal, the Heart Timing (HT) signal. We demonstrate that this HT signal, in contrast with the HR or HP, makes it possible to recover an unbiased estimation of the modulating signal spectra. In this estimation we avoid the spurious components and the low-pass filtering effect generated when analyzing HR or HP.

Analysis of Variance↗

PubMed2000

Automatic detection of ST-T complex changes on the ECG using filtered RMS difference series: application to ambulatory ischemia monitoring.

A new detector is presented which finds changes in the repolarization phase (ST-T complex) of the cardiac cycle. It operates by applying a detection algorithm to the filtered root mean square (rms) series of differences between the beat segment (ST segment or ST-T complex) and an average pattern segment. The detector has been validated using the European ST-T database, which contains ST-T complex episodes manually annotated by cardiologists, resulting in sensitivity/positive predictivity of 85/86%, and 85/76%, for ST segment deviations and ST-T complex changes, respectively. The proposed detector has a performance similar to those which have a more complicated structure. The detector has the advantage of finding both ST segment deviations and entire ST-T complex changes thereby providing a wider characterization of the potential ischemic events. A post-processing stage, based on a cross-correlation analysis for the episodes in the rms series, is presented. With this stage subclinical events with repetitive pattern were found in around 20% of the recordings and improved the performance to 90/85%, and 89/76%, for ST segment and ST-T complex changes, respectively.

Algorithms↗

PubMed1999

Identification of the occluded artery in patients with myocardial ischemia induced by prolonged percutaneous transluminal coronary angioplasty using traditional vs transformed ECG-based indexes.

We have studied the spatial properties of ischemic changes as induced by prolonged angioplasty and how the changes are related to different ECG indexes. Indexes based on measurements at specific points in time (ST level at J + 60 ms point, maximal T wave amplitude and position, QT interval, and QRS duration) and global indexes (based on the Karhunen-Loève transform and applied to the QRS complex, ST-T complex, ST segment, and T wave), considering both repolarization and depolarization information, were analyzed. The changes during the occlusion period of the different indexes were used as variables in a multivariate discriminant analysis to determine which indexes showed the best discrimination of the three major occlusion sites (corresponding to LAD, RCA, and LCX coronary arteries). Occlusions in LCX artery were the most difficult to classify. With three local indexes (ST60 level measured in lead V3, T wave amplitude in I, and ST60 in III) it was possible to correctly classify 76% of patients by the occlusion site, and with three KLT-derived indexes (first-order KLT index for ST-T complex in I and for QRS in leads V3 and I) 83% of correct classification was obtained. Using six indexes for local and KLT-derived indexes the correct classification was increased to 85 and 90% of patients, respectively. The use of different ECG indexes (from different intervals) on quasiorthogonal leads permitted the identification of the occluded artery in patients undergoing PTCA and may be extended to more general use.

Angioplasty, Balloon, Coronary↗

PubMed1999

Analysis of the ST-T complex of the electrocardiogram using the Karhunen--Loève transform: adaptive monitoring and alternans detection.

The Karhunen-Loève transform (KLT) is applied to study the ventricular repolarisation period as reflected in the ST-T complex of the surface ECG. The KLT coefficients provide a sensitive means of quantitating ST-T shapes. A training set of ST-T complexes is used to derive a set of KLT basis vectors that permits representation of 90% of the signal energy using four KLT coefficients. As a truncated KLT expansion tends to favor representation of the signal over any additive noise, a time series of KLT coefficients obtained from successive ST-T complexes is better suited for representation of both medium-term variations (such as ischemic changes) and short-term variations (such as ST-T alternans) than discrete parameters such as the ST level or other local indices. For analysis of ischemic changes, an adaptive filter is described that can be used to estimate the KLT coefficient, yielding an increase in the signal-to-noise ratio of 10 dB (u = 0.1), with a convergence time of about three beats. A beat spectrum of the unfiltered KLT coefficient series is used for detection of ST-T alterans. These methods are illustrated with examples from the European ST-T Database. About 20% of records revealed quasi-periodic salvos of ischemic ST-T change episodes and another 20% exhibit repetitive, but not clearly periodic patterns of ST-T change episodes. About 5% of ischemic episodes were associated with ST-T alterans.

Electrocardiography↗

PubMed1998

[Detection of human herpesvirus 8 in patients with Kaposi's sarcoma or Castleman's disease associated with AIDS].

A new herpesvirus provisionally termed as KSHV or HHV-8 has been detected in lesions from AIDS-based Kaposi's sarcoma (KS) and from other KS clinical forms, and also in other tumors such as body cavity-based lymphomas or Castleman's disease (CD). We have assessed the presence of this novel herpesvirus in specimens from patients diagnosed with either AIDS and KS or AIDS and CD. DNA samples from skin lesions and peripheral blood obtained from 8 patients diagnosed with AIDS, seven with KS and one with multicentric CD were analyzed; skin specimens and peripheral blood samples from volunteer blood donors or from KS and CD free HIV seronegative patients were used as controls. Detection of the virus was done by PCR amplification of KS330 region, one of the HHV-8 sequences first reported. All skin lesions analysed tested positive for KS330; peripheral blood samples from 5 of the patients, including the one diagnosed with CD, showed also the virus sequence. All skin specimens and peripheral blood samples from controls were negative. From our results it can be concluded that the novel herpesvirus HHV-8 can also be detected in patients with AIDS-associated KS and AIDS-associated CD in Spain.

Acquired Immunodeficiency Syndrome↗

PubMed1998

Comparative study of local and Karhunen-Loève-based ST-T indexes in recordings from human subjects with induced myocardial ischemia.

In this work we studied ST-T complex changes in the ECG as result of induced ischemia. The principal aim was to determine whether global changes in the ST-T complex were more sensitive markers of ischemic alterations than those based on measurements of changes at specific locations on ST segment or T wave. High-resolution ECGs from patients undergoing percutaneous transluminal coronary angioplasty in one of the major coronary arteries were analyzed to give a description of the period from the end of active depolarization (QRS complex) to the end of active repolarization (T wave). During artery occlusion traditional local measurements of the ST-T complex were compared to global measurements based on the Karhunen-Loève transform. An ischemic change sensor parameter was estimated for each of the studied indexes showing that global measurements detected changes better in the repolarization period in a larger number of leads and with higher sensitivity (more than 85%) than was done using local measurements (sensitivity of 64% with ST level, 33% with T-wave maximum position, and 37% with T-wave maximum amplitude). Using these global indexes it was found that most cases of ST-segment changes were accompanied by T-wave changes (72% of patients). With the use of traditional indexes 23% of patients showed no changes in the repolarization period, whereas with global indexes this percentage decreased to 8%. Thus a global representation of the entire ST-T complex appears to be more suitable than local measurements when studying the initial stages of myocardial ischemia.

Algorithms↗

PubMed1998

Power spectral density of unevenly sampled data by least-square analysis: performance and application to heart rate signals.

This work studies the frequency behavior of a least-square method to estimate the power spectral density of unevenly sampled signals. When the uneven sampling can be modeled as uniform sampling plus a stationary random deviation, this spectrum results in a periodic repetition of the original continuous time spectrum at the mean Nyquist frequency, with a low-pass effect affecting upper frequency bands that depends on the sampling dispersion. If the dispersion is small compared with the mean sampling period, the estimation at the base band is unbiased with practically no dispersion. When uneven sampling is modeled by a deterministic sinusoidal variation respect to the uniform sampling the obtained results are in agreement with those obtained for small random deviation. This approximation is usually well satisfied in signals like heart rate (HR) series. The theoretically predicted performance has been tested and corroborated with simulated and real HR signals. The Lomb method has been compared with the classical power spectral density (PSD) estimators that include resampling to get uniform sampling. We have found that the Lomb method avoids the major problem of classical methods: the low-pass effect of the resampling. Also only frequencies up to the mean Nyquist frequency should be considered (lower than 0.5 Hz if the HR is lower than 60 bpm). We conclude that for PSD estimation of unevenly sampled signals the Lomb method is more suitable than fast Fourier transform or autoregressive estimate with linear or cubic interpolation. In extreme situations (low-HR or high-frequency components) the Lomb estimate still introduces high-frequency contamination that suggest further studies of superior performance interpolators. In the case of HR signals we have also marked the convenience of selecting a stationary heart rate period to carry out a heart rate variability analysis.

Cardiac Pacing, Artificial↗

PubMed1998

[Abscess of the psoas muscle: analysis of 11 cases and review of the literature].

BACKGROUND: Abscess of the psoas muscle (AP) is an infrequent disease of difficult diagnosis, developing spontaneously (primary AP) or by extension of a subjacent infection (secondary AP). In recent years changes have been observed in its etiology, advances in its diagnosis and modifications in the treatment schedules. METHODS: The cases of AP diagnosed from 1983-1996 were retrospectively studied. RESULTS: The cases included 11 AP, 5 (45%) primary and 6 (55%) secondary, of which the source of origin were: spondylitis in four, sacroiliac arthritis in one and intestinal in another. The clinical presentation was characterized by its prolonged course (evolution of symptoms greater than 30 days in 64% of the cases), with the most frequent symptoms being flank/abdominal pain (82%) and hip/inguinal pain (45%), with fever being presented in only 36%. The diagnostic profitability of echography and computerized tomography (CT) were 57% (4/7) and 91% (10/11), respectively. One case was diagnosed with magnetic resonance. The causal microorganisms were: Mycobacterium tuberculosis (36% of the cases), Staphylococcus aureus (18%), polymicrobian flora (18%) and Salmonella enteritidis, Streptococcus intermedius and Escherichia coli in 9% each. Eight cases (73%) underwent percutaneous (5 cases) and surgical (3 cases) drainage, with the evolution being favorable in 10 (91%) and death in one despite adequate medicosurgical treatment. CONCLUSIONS: The clinical presentation of AP is often unspecific, thereby delaying its diagnosis, and thus, CT is the procedure of choice. The tuberculous etiology continues to be frequent in our environment. Ultrasonographic or CT guided percutaneous drainage is a valid therapeutic alternative versus surgery.

Adolescent↗