Biomedical subjects

P Ask

Publications and source records attributed to P Ask.

At least 19 recordsLinked to original sources

PubMed2006

Pulse wave transit time for monitoring respiration rate.

In this study, we investigate the beat-to-beat respiratory fluctuations in pulse wave transit time (PTT) and its subcomponents, the cardiac pre-ejection period (PEP) and the vessel transit time (VTT) in ten healthy subjects. The three transit times were found to fluctuate in pace with respiration. When applying a simple breath detecting algorithm, 88% of the breaths seen in a respiration air-flow reference could be detected correctly in PTT. Corresponding numbers for PEP and VTT were 76 and 81%, respectively. The performance during hypo- and hypertension was investigated by invoking blood pressure changes. In these situations, the error rates in breath detection were significantly higher. PTT can be derived from signals already present in most standard monitoring set-ups. The transit time technology thus has prospects to become an interesting alternative for respiration rate monitoring.

Adult↗

PubMed2005

Detection of the third heart sound using a tailored wavelet approach: method verification.

Heart sounds can be considered as mechanical fingerprints of myocardial function. The third heart sound normally occurs in children but disappears with maturation. The sound can also appear in patients with heart failure. The sound is characterised by its low-amplitude and low-frequency content, which makes it difficult to identify by the traditional use of the stethoscope. A wavelet-based method has recently been developed for detection of the third heart sound. This study investigated if the third heart sound could be identified in patients with heart failure using this detection method. The method was also compared with auscultation using conventional phonocardiography and with characterisation of the patients with echocardiography. In the first study, 87% of the third heart sounds were detected using the wavelet method, 12% were missed, and 6% were false positive. In study 2, the wavelet-detection method identified 87% of the patients using the third heart sound, and regular phonocardiography identified two (25%) of the subjects.

Adult↗

PubMed2004

Detection of the third heart sound using a tailored wavelet approach.

The third heart sound is normally heard during auscultation of younger individuals but disappears with increasing age. However, this sound can appear in patients with heart failure and is thus of potential diagnostic use in these patients. Auscultation of the heart involves a high degree of subjectivity. Furthermore, the third heart sound has low amplitude and a low-frequency content compared with the first and second heart sounds, which makes it difficult for the human ear to detect this sound. It is our belief that it would be of great help to the physician to receive computer-based support through an intelligent stethoscope, to determine whether a third heart sound is present or not. A precise, accurate and low-cost instrument of this kind would potentially provide objective means for the detection of early heart failure, and could even be used in primary health care. In the first step, phonocardiograms from ten children, all known to have a third heart sound, were analysed, to provide knowledge about the sound features without interference from pathological sounds. Using this knowledge, a tailored wavelet analysis procedure was developed to identify the third heart sound automatically, a technique that was shown to be superior to Fourier transform techniques. In the second step, the method was applied to phonocardiograms from heart patients known to have heart failure. The features of the third heart sound in children and of that in patients were shown to be similar. This resulted in a method for the automatic detection of third heart sounds. The method was able to detect third heart sounds effectively (90%), with a low false detection rate (3.7%), which supports its clinical use. The detection rate was almost equal in both the children and patient groups. The method is therefore capable of detecting, not only distinct and clearly visible/audible third heart sounds found in children, but also third heart sounds in phonocardiograms from patients suffering from heart failure.

Adolescent↗

PubMed2004

An improved bioacoustic method for monitoring of respiration.

Reliable monitoring of respiration plays an important role in a broad spectrum of applications. Today, there are several methods for monitoring respiration, but none of them has proved to be satisfactory in all respects. We have recently developed a bioacoustic method that can accurately time respiration from tracheal sounds. The aim of this study is to tailor this bioacoustic method for monitoring purposes by introducing dedicated signal processing. The method was developed on a material of ten patients and then tested in another ten patients treated in an intensive care unit. By studying the differences in the variation of the spectral content between the different phases of respiration, the described method can distinguish between inspiration and expiration and can extract respiration frequency, and respiration pause periods. The system detected 98% of the inspirations and 99% of the expirations. This method for respiration monitoring has the advantage of being simple, robust and the sensor does not need to be placed closed to the face. A commercial heart microphone was used and we anticipate that further improvement in performance can be achieved trough optimization of sensor design.

Acoustics↗

PubMed2002

Force to restore the shape of an asymmetric extracorporeal tube as the basis for non-invasive pressure measurements.

A zero-balance principle is described where intraluminal pressure is estimated from the counter force needed to restore the tube shape of an elastic extra corporeal tube. The aim was to optimise cross-sectional tube geometry for tube expansion due to pressure and to reduce the sensitivity to variation in mechanical tube characteristics using an experimental statistical and factorial design. The main application is pressure monitoring in blood and dialysate tubes during hemodialysis. Improving the monitoring of the dialysis process will reduce complications, such as sudden decreases in systemic blood pressure or occlusion at the artero-venous fistula. The factorial design indicated strong influence from the geometrical characteristics of the tube as well from the geometrical design parameters of the pressure transducer. We found a consistent relationship between the intraluminal pressure and the applied force needed to restore the tube shape. The modified cross-sectional tube geometry enhances measurement sensitivity and facilitates the desired behavior of tubes during pressure applications.

Biophysical Phenomena↗

PubMed2001

Assessment of effective orifice area of prosthetic aortic valves with Doppler echocardiography: an in vivo and in vitro study.

OBJECTIVES: We sought to evaluate the Doppler assessment of effective orifice area in aortic prosthetic valves. The effective orifice area is a less flow-dependent parameter than Doppler gradients that is used to assess prosthetic valve function. However, in vivo reference values show a pronounced spread of effective orifice area and smaller orifices than expected compared with the geometric area. METHODS: Using Doppler echocardiography, we studied patients who received a bileaflet St Jude Medical valve (n = 75; St Jude Medical, Inc, St Paul, Minn) or a tilting disc Omnicarbon valve (n = 46; MedicalCV, Incorporated, Inver Grove Heights, Minn). The prosthetic valves were also investigated in vitro in a steady-flow model with Doppler and catheter measurements in the different orifices. The effective orifice area was calculated according to the continuity equation. RESULTS: In vivo, there was a wide distribution with the coefficient of variation (SD/mean x 100%) for different valve sizes ranging from 21% to 39% in the St Jude Medical valve and from 25% to 33% in the Omnicarbon valve. The differences between geometric orifice area and effective orifice area in vitro were 1.26 +/- 0.41 cm(2) for St Jude Medical and 1.17 +/- 0.38 cm(2) for Omnicarbon valves. The overall effective orifice areas and peak catheter gradients were similar: 1.35 +/- 0.37 cm(2) and 25.9 +/- 16.1 mm Hg for St Jude Medical and 1.46 +/- 0.49 cm(2) and 24.6 +/- 17.7 mm Hg for Omnicarbon. However, in St Jude Medical valves, more pressure was recovered downstream, 11.6 +/- 6.3 mm Hg versus 3.4 +/- 1.6 mm Hg in Omnicarbon valves (P =.0001). CONCLUSIONS: In the patients, we found a pronounced spread of effective orifice areas, which can be explained by measurement errors or true biologic variations. The in vitro effective orifice area was small compared with the geometric orifice area, and we suspect that nonuniformity in the spatial velocity profile causes underestimation. The St Jude Medical and Omnicarbon valves showed similar peak catheter gradients and effective orifice areas in vitro, but more pressure was recovered in the St Jude Medical valve. The effective orifice area can therefore be misleading in the assessment of prosthetic valve performance when bileaflet and tilting disc valves are compared.

Aortic Valve↗

PubMed2001

An asymmetric dialysis tube as an integrated part of a pressure-monitoring sensor.

A sensor has been designed consisting of a tube holder with a force transducer and a tube with a modified cross-section. The holder has a lid that encloses the tube. By having a stiff holder and a compliant tube, the idea is that the intraluminal pressure in the tube can be obtained from the measured force. The method is intended for non-invasive pressure measurements in blood or dialysate tubes. We have used a tube cross-sectional geometry where the outer surface is elliptic and the inner surface is circular with a relation of 2:1 between the thinnest and thickest tube sides. The pressure transducer system shows a linear relationship between the applied pressure and the sensor output (r=0.999). Within the temperature range, 32 degrees --36 degrees C, which corresponds to the blood and dialysate temperatures, the sensor accuracy is within +/- 0.8 kPa (+/- 6 mm Hg). This indicates that the sensor should be clinically useful during dialysis and similar applications.

Blood Pressure Monitors↗

PubMed2000

Doppler flow measurement using surface integration of velocity vectors (SIVV): in vitro validation.

Blood flow measurement using an improved surface integration of velocity vectors (SIVV) technique was tested in in vitro phantoms. SIVV was compared with true flow (12-116 mL/s) in a steady-state model using two angles of insonation (45 degrees and 60 degrees ) and two vessel sizes (internal diameter = 11 and 19 mm). Repeatability of the method was tested at various flow rates for each angle of insonation and vessel. In a univentricular pulsatile model, SIVV flow measured at the mitral inlet was compared to true flow (29-61 mL/s). Correlation was excellent for the 19-mm vessel (r(2)= 0.99). There was a systematic bias but close limits of agreement (mean +/- 2 SD = -24.1% +/- 7.6% at 45 degrees; +16.4% +/- 11.0% at 60 degrees ). Using the 11-mm vessel, a quadratic relationship was demonstrated between between SIVV and true flow (r(2) = 0.98-0.99), regardless of the angle of insonation. In the pulsatile system, good agreement and correlation were shown (r(2) = 0.94, mean +/- 2 SD = -4.7 +/- 10.1%). The coefficients of variation for repeated SIVV measurements ranged from 0.9% to 10.3%. This method demonstrates precision and repeatability, and is potentially useful for clinical measurements.

Blood Flow Velocity↗

PubMed2000

A bioacoustic method for timing of the different phases of the breathing cycle and monitoring of breathing frequency.

It is well known that the flow of air through the trachea during respiration causes vibrations in the tissue near the trachea, which propagate to the surface of the body and can be picked up by a microphone placed on the throat over the trachea. Since the vibrations are a direct result of the airflow, accurate timing of inspiration and expiration is possible. This paper presents a signal analysis solution for automated monitoring of breathing and calculation of the breathing frequency. The signal analysis approach uses tracheal sound variables in the time and frequency domains, as well as the characteristics of the disturbances that can be used to discriminate tracheal sound from noise. One problem associated with the bioacoustic method is its sensitivity for acoustic disturbances, because the microphone tends to pick up all vibrations, independent of their origin. A signal processing method was developed that makes the bioacoustic method clinically useful in a broad variety of situations, for example in intensive care and during certain heart examinations, where information about both the precise timing and the phases of breathing is crucial.

Acoustics↗

PubMed2000

Pediatric cardiac output measurement using surface integration of velocity vectors: an in vivo validation study.

OBJECTIVE: To test the accuracy and reproducibility of systemic cardiac output (CO) measurements using surface integration of velocity vectors (SIVV) in a pediatric animal model with hemodynamic instability and to compare SIVV with traditional pulsed-wave Doppler measurements. DESIGN: Prospective, comparative study. SETTING: Animal research laboratory at a university medical center. SUBJECTS: Eight piglets weighing 10-15 kg. INTERVENTIONS: Hemodynamic instability was induced by using inhalation of isoflurane and infusions of colloid and dobutamine. MEASUREMENTS: SIVV CO was measured at the left ventricular outflow tract, the aortic valve, and ascending aorta. Transit time CO was used as the reference standard. RESULTS: There was good agreement between SIVV and transit time CO. At high frame rates, the mean difference +/- 2 SD between the two methods was 0.01+/-0.27 L/min for measurements at the left ventricular outflow tract, 0.08+/-0.26 L/min for the ascending aorta, and 0.06+/-0.25 L/min for the aortic valve. At low frame rates, measurements were 0.06+/-0.25, 0.19+/-0.32, and 0.14+/-0.30 L/min for the left ventricular outflow tract, ascending aorta, and aortic valve, respectively. There were no differences between the three sites at high frame rates. Agreement between pulsed-wave Doppler and transit time CO was poorer, with a mean difference +/- 2 SD of 0.09+/-0.93 L/min. Repeated SIVV measurements taken at a period of relative hemodynamic stability differed by a mean difference +/-2 SD of 0.01+/-0.22 L/min, with a coefficient of variation = 7.6%. Intraobserver coefficients of variation were 5.7%, 4.9%, and 4.1% at the left ventricular outflow tract, ascending aorta, and aortic valve, respectively. Interobserver variability was also small, with a coefficient of variation = 8.5%. CONCLUSIONS: SIVV is an accurate and reproducible flow measurement technique. It is a considerable improvement over currently used methods and is applicable to pediatric critical care.

Animals↗

PubMed2000

Aortic prosthetic valve design and size: relation to Doppler echocardiographic findings and pressure recovery- an in vitro study.

The extent to which Doppler echocardiography information can be used in the assessment of prosthesis hemodynamic performance is still controversial. The goals of our study were to assess the importance of valve design and size both on Doppler echocardiography findings and on pressure recovery in a fluid mechanics model. We performed Doppler and catheter measurements in the different orifices of the bileaflet St Jude (central and side orifices), the monoleaflet Omnicarbon (major and minor orifices), and the stented Biocor porcine prosthesis. Net pressure gradients were predicted from Doppler flow velocities, assuming either independence or dependence of valve size. The peak Doppler estimated gradients (mean +/- SD for sizes 21 to 27) were 21 +/- 10.3 mm Hg for St Jude, 18 +/- 9.3 mm Hg for Omnicarbon, and 37 +/- 14.5 mm Hg for Biocor (P <.05 for St Jude and Omnicarbon vs Biocor). The pressure recovery (proportion of peak catheter pressure) was 53% +/- 8.6% for central-St Jude, 29% +/- 8. 9% for side-St Jude, 20% +/- 5.6% for major-Omnicarbon, 23% +/- 7.4% for minor-Omnicarbon, and 18% +/- 3.6% for Biocor (P <.05 for central-St Jude and side-St Jude vs Omnicarbon and Biocor). Valve sizes (x) significantly influenced pressure recovery (y in percentage) (central-St Jude: y = 3.7x - 35.9, r = 0.88, P =.0001; major-Omnicarbon: y = 2.1x - 30.3, r = 0.85, P =.0001). By assuming dependence of valve size, Doppler was able to predict net pressure gradients in St Jude with a mean difference between net catheter and Doppler-predicted gradient of -3.8 +/- 2.5 mm Hg. In conclusion, prosthetic valve design and size influence the degree of pressure recovery, making Doppler gradients potentially misleading in both the assessment of hemodynamic performance and the comparison of one design with another. The preliminary results indicate that net gradient can be predicted from Doppler gradients.

Aortic Valve↗

PubMed1999

[To use the stethoscope correctly is not easy. The intricate art of auscultation should receive more attention in medical education].

Although the stethoscope is used daily by almost every physician, the full potential of the art of stethoscopy is seldom tapped. It has been replaced by newer and more costly techniques. In the article it is argued that more time in medical education should be allocated to stethoscopy, so that it can be used in selecting patients who will benefit most from examination with modern diagnostic tools. The medical technological background of stethoscopy is also reviewed, as are the reasons why it is difficult to give sound advice on the choice of stethoscope.

Acoustics↗

PubMed1999

Validation and characterization of the computerized laryngeal analyzer (CLA) technique.

The aim of this study was to investigate the response characteristics of the Computerized Laryngeal Analyzer (CLA) and the validity of the noninvasive CLA method to detect swallowing-induced laryngeal elevation correctly. Two healthy adults and two experimental models were used in the study. The CLA technique identified all swallowing events but was unable to discriminate between swallowing and other movements of the tongue or the neck. The computer program produced a derivated response to a square wave signal. Stepwise bending increments of the sensor displayed a linear amplitude response. The degree of laryngeal elevation could not be estimated with the CLA technique, and it was not possible to draw any reliable conclusions from the recordings as to whether the larynx was moving upward or downward.

Adult↗

PubMed1999

Increased accuracy of echocardiographic measurement of flow using automated spherical integration of multiple plane velocity vectors.

The calculation of blood flow in the heart by surface integration of velocity vectors (SIVV) using Doppler ultrasound is independent of the angle. Flow is normally calculated from velocity in a spherical thick shell with its center located at the ultrasound transducer. In a numerical simulation, we have shown that the ratio between minor and major axes of an elliptic flow area substantially influences the accuracy of the estimation of flow in a single scan plane. The accuracy of flow measurements by SIVV can be improved by calculating the mean of the values from more than one scan plane. We have produced an automated computer program that includes an antialiasing procedure. We confirmed an improvement of flow measurements in a pulsatile hydraulic flow model, the 95% confidence interval for single estimations being reduced from 20% to 10% (p < 0.05) using the newly developed software. We think that the SIVV method has important implications for clinical transthoracic echocardiography.

Algorithms↗

PubMed1997

[Overestimation of regurgitation velocities of intact mechanical heart valve prostheses and other small orifices with 10 mm2 Doppler echocardiography].

A systematic evaluation of the accuracy of continuous wave echo Doppler measurements across prosthetic valve leakages and regurgitant lesions has not been performed. Continuous echo Doppler velocity measurements in an in vitro, steady flow model, across the leaks of 12 intact mechanical prostheses and across six circular nozzles (area, 0.5-20 mm2) at pressure drops between 30 and 105 mm Hg were analyzed and compared to the velocities predicted by the modified Bernoulli equation. Laser Doppler anemometry of flow velocities through the nozzles was performed in addition. Despite excellent correlation, there was substantial overestimation of "Bernoulli predicted"-velocities by echo Doppler in the prosthetic leaks (mean +12.3 +/- 9.4%; range, 90.3-143.4%). Also in nozzles < or = 10 mm2, but not in those > 20 mm2, an overestimation of the "Bernoulli predicted"-velocities was observed (mean +6.2 +/- 2%). Laser Doppler anemometry of flow velocities through the nozzles showed slightly lower values than predicted by the Bernoulli equation. This effect apparently is due to transit time effects leading to spectral broadening and should be taken into account when using echo Doppler measurements in very small (< 10 mm2) orifices, such as mild to moderate regurgitant lesions and prosthetic valve leakage.

Artifacts↗

PubMed1997

Flow characteristics of the Hemopump: an experimental in vitro study.

BACKGROUND: The Hemopump (DLP/Medtronic) has been in clinical use for about 7 years. There is still no adequate way of determining actual output from the three available pump systems in the clinical situation. If the pump is completely stopped during weaning from the device, there is a possibility of back-leakage through the pump, endangering the patient from regurgitation into the left ventricle. It can also make it more difficult to judge the recovery of heart function because of a volume load of the left ventricle. The aim of this study was to evaluate in a standardized, experimental in vitro model the output from three different-sized Hemopump catheters at various pressure levels and to quantify the back-flow through the pumps. METHODS: The Hemopump models were tested in an in vitro study regarding total outflow at various speeds at three pressure levels. The back-flow through the pumps was also measured with the pumps at a complete stop. RESULTS: The outflow from the Hemopumps ranged from 0.4 to 4.5 L/min, depending on which pump and speed were used. Variations in total output, depending on speed and various pressure settings, could be up to 0.4 L/min. Back-flow through the pump into the left ventricle may be as great as 1.6 L/min. CONCLUSIONS: The flow outputs from the different Hemopump models were reproducible over time and were closely related to the resistance of the model. The Hemopump, if not running, can induce substantial regurgitation through the pump into the left ventricle.

Blood Flow Velocity↗

PubMed1996

Heat transfer evaluation of the nasal thermistor technique.

When analyzing transvalvular and venous flow velocity patterns, it is important to relate them to respiration. An accurate recording of respiratory phase can be carried out with different methods. One of these methods is the use of a thermistor, which reacts to the variation in air temperature, placed in the noise of the patient. The thermistor used has a diameter for 1.0 mm and is of standard bead type. Although small, it has a considerable long time-constant and a long time-delay. The high time-constant gives a low cutoff frequency, well below the respiratory frequency and thereby causing a large phase difference. The thermistor was analyzed with the lumped heat capacity method, where it was easy to study the influence from design parameters, time-dependent air temperature, and velocity. The analysis was extended using the finite element method and the temperature field in the thermistor and the probe was calculated as a function of space and time. These calculations confirmed the result from the lumped model. The result showed that timing of respiration was not accurately obtained with the thermistor analyzed. To improve the timing, it was necessary either to change the measuring method or to use signal processing in order to achieve faster response.

Blood Flow Velocity↗

PubMed1995

New method to quantify the urodynamic improvement when treating bladder outlet obstruction: the efficacy of transurethral resection in benign prostatic hypertrophy.

A method to measure the urodynamic improvement when treating urethral obstruction is introduced and applied to patients with benign prostatic hypertrophy. The patients performed pressure-flow studies before and 3-6 months after TUR-p. The urethral resistance relation was estimated by curve fitting in the pressure flow plot. The new method quantifies the improvement in urethral resistance as the distance between the urethral resistance relation before and after treatment expressed in pressure units. The distance is measured at the flow rate equal to 75% of the maximum flow rate for the micturition with the lowest maximum flow rate and this distance is called delta-URA. The median improvement after TUR-p was 71 cm H2O (range 2-119). The improvement was strongly correlated to the resistance before treatment and the regression line indicates that the operation normalizes the resistance irrespective of its preoperative value. On the average a lowering of the urethral resistance relation with 8 cm H2O improved the maximum flow rate with 1 ml/s. The greatest advantage with the new method is that it has a high validity and is almost completely insensitive to changes in contractility.

Humans↗