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Results for “Measuring algorithm”

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PubMed1991

Noninvasive cerebral optical spectroscopy for monitoring cerebral oxygen delivery and hemodynamics.

OBJECTIVE: To present an algorithm for noninvasive measurement of cerebral oxygen saturation (cerebral oximetry) and cerebral hemodynamics with near infrared spectroscopy. DESIGN: In vitro correlation of oximetry measurements with reference measurements; illustrative cases of hemodynamic and oximetric recordings. SETTING: Tertiary care neuroscience ICU. PATIENTS: Brain-injured patients with a prolonged, decreased level of consciousness chosen as illustrative examples. INTERVENTIONS: Two-channel multiple wavelength diffuse infrared transmission spectroscopy was interfaced with the scalp using adhesive. Transmission data were collected with gross superficial-to-deep spatial resolution. Saturation calculation based on the deep signal was observed longitudinally in the patient. With the same technology, arterial input and cerebral response functions, generated by iv tracer bolus, were deconvoluted to measure mean cerebral transit time. MEASUREMENTS AND MAIN RESULTS: A positive linear regression fit between diffuse transmission oximetry and measured blood oxygen saturation over the range 23% to 99% (r2 = .98, p less than .001) was noted. CONCLUSIONS: The approach used overcomes previously identified difficulties with cerebral oximetry, and demonstrates excellent in vitro correlation. The technique can be performed clinically without difficulty. A simultaneous measure of mean cortical transit time is possible.

Brain↗

PubMed2001

Transthoracic monitoring of the impedance of the right lung in patients with cardiogenic pulmonary edema.

OBJECTIVE: To evaluate the suitability of the new electrical impedance monitor RS-205 for monitoring of cardiogenic pulmonary edema (CPE). DESIGN: Prospective, controlled study. SETTING: A department of internal medicine in a 1,200-bed university-affiliated, teaching hospital. PATIENTS: Sixty patients, aged 52-80 yrs, 30 without CPE (controls) and 30 with or at high risk for CPE. INTERVENTIONS: Internal thoracic impedance (ITI) was monitored by the RS-205. The RS-205 is approximately three times more sensitive than the Kubicek monitor, and it eliminates the effect of the drift of skin-to-electrode impedance. This is achieved by eliminating skin electrode impedance by a special algorithm, thus allowing measurement of ITI rather than total transthoracic impedance. Measuring ITI, the main component of which is lung impedance, is a noninvasive and safe method. CPE was diagnosed in accordance with well-accepted clinical and roentgenological criteria. MEASUREMENTS AND MAIN RESULTS: The controls' initial ITI was 68.3 +/- 12.38 ohms. During 6 hrs of monitoring, the ITI attained a minimum average value of -1.3 +/- 2.08% and a maximum average value of 4.6 +/- 3.56% relative to baseline. In all patients entering CPE, ITI decreased by 14.4 +/- 5.42% on the average (p <.001) 1 hr before the appearance of clinical symptoms. In patients with evolving CPE, ITI decreased significantly compared with controls (22.25 +/- 9.82%, p <.001). In patients at the peak of pulmonary edema, ITI was 2.1 times lower than in the control group (33.1 +/- 10.90 ohms, p <.001). In the last hour before the resolution of CPE, ITI increased in all patients by 17.7 +/- 19.74% compared with the peak of disease (p <.05). After the resolution of pulmonary edema, ITI increased in all patients by 44.14 +/- 26.90% compared with the peak of disease (p <.001). Importantly, the trend in ITI in all patients changed in accordance with the dynamics of CPE. A mixed general linear model shows that ITI values correlated well with the degree of crepitation, a direct characteristics of CPE. CONCLUSIONS: The RS-205 is suitable for monitoring patients at high risk of CPE development. It enables detection of CPE and the monitoring of patients at all stages of CPE.

Aged↗

PubMed1998

Assessment of prevalence of left ventricular hypertrophy in hypertension.

The reported prevalence of left ventricular hypertrophy (LVH) in human hypertension is much lower than that among animals with experimental hypertension. With current methods of determining left ventricular mass by M-mode echocardiography, the standard error of a single estimate is high and consequently so is the SD of the population distribution. This accounts for the large overlap in individual values of left ventricular mass index (LVMI) between hypertensive and normotensive groups. The high SD is due to the use of the cube algorithm for relating measurements made in a single plane to the whole left ventricle, and to the difference between actual and assumed left ventricular geometries. These are not problems with nuclear magnetic resonance imaging, which provides information about the entire left ventricle without assumptions about geometry. M-mode echocardiography is well suited for estimating differences between mean LVMI values for groups of subjects but it underestimates the prevalence of LVH. In most series only about 30% of hypertensives have been reported to have LVH. The estimated prevalence of structural remodelling is increased to 50-60% of the same group of subjects when 'low-SD' measurements such as wall thickness and the wall thickness: internal radius ratio are employed. The estimated prevalence of LVH and remodelling is still greater with multivariate discriminant function analysis, with which it is found in about 70% of hypertensives. Overall, the data suggest that prevalence of LVH in established hypertension is high. The 30% of subjects reported to have LVH on the basis of LVMI measurements that are beyond the limits of the control group probably have the most severe changes. The inability to detect lesser grades of left ventricular remodelling reliably is due to the way LVMI is derived by echocardiography, rather than to intrinsic inaccuracies. It suggests that existing approaches should be supplemented by greater use of 'low-SD' variables and discriminant functions. Detecting the full spectrum of left ventricular structural changes in individuals with hypertension is needed for risk assessment and, increasingly, for management aimed at minimizing irreversible myocardial damage. Nuclear magnetic resonance imaging provides 'global' and more accurate information about left chamber structure than does M-mode echocardiography but its cost at present is much greater. Nevertheless, the information provided by echocardiography may be adequate for the above applications, but the high SD of LVMI is a weakness. Greater use of 'low-SD' variables and multivariate discriminant functions may help overcome this problem.

Animals↗

PubMed1994

Distinguishing panic disorder and agoraphobia from social phobia.

An attempt was made to differentially diagnose panic disorder with agoraphobia from social phobia on the basis of self-reported phobic situations, panic attack symptomatology, and feared outcomes. Sixty-nine patients with panic disorder (with and without agoraphobia) were compared with 69 patients with social phobia. Subjects completed a modified self-report version of the panic and phobia sections from the Composite International Diagnostic Interview to assess phobic situations, panic symptomatology, and feared outcomes. The two groups were distinguishable on all three measures. A diagnostic algorithm was developed that predicted the primary diagnosis allocated by a clinician for subjects who meet DSM-III-R criteria for panic disorder (with or without agoraphobia) rather than social phobia on the basis of self-reported phobic avoidance, panic symptomatology, and feared outcomes.

Adult↗

PubMed2003

Risk adjustment using automated ambulatory pharmacy data: the RxRisk model.

OBJECTIVES: Develop and estimate the RxRisk model, a risk assessment instrument that uses automated ambulatory pharmacy data to identify chronic conditions and predict future health care cost. The RxRisk model's performance in predicting cost is compared with a demographic-only model, the Ambulatory Clinical Groups (ACG), and Hierarchical Coexisting Conditions (HCC) ICD-9-CM diagnosis-based risk assessment instruments. Each model's power to forecast health care resource use is assessed. DATA SOURCES: Health services utilization and cost data for approximately 1.5 million individuals enrolled in five mixed-model Health Maintenance Organizations (HMOs) from different regions in the United States. STUDY DESIGN: Retrospective cohort study using automated managed care data. SUBJECTS All persons enrolled during 1995 and 1996 in Group Health Cooperative of Puget Sound, HealthPartners of Minnesota and the Colorado, Ohio and Northeast Regions of Kaiser-Permanente. MEASURES RxRisk, an algorithm that classifies prescription drug fills into chronic disease classes for adults and children. RESULTS: HCCs produce the most accurate forecasts of total costs than either RxRisk or ACGs but RxRisk performs similarly to ACGs. Using the R(2) criteria HCCs explain 15.4% of the prospective variance in cost, whereas RxRisk explains 8.7% and ACGs explain 10.2%. However, for key segments of the cost distribution the differences in forecasting power among HCCs, RxRisk, and ACGs are less obvious, with all three models generating similar predictions for the middle 60% of the cost distribution. CONCLUSIONS: HCCs produce more accurate forecasts of total cost, but the pharmacy-based RxRisk is an alternative risk assessment instrument to several diagnostic based models and depending on the nature of the application may be a more appropriate option for medical risk analysis.

Adolescent↗

PubMed2004

The facial nerve canal: an important cochlear conduction path revealed by Clarion electrical field imaging.

HYPOTHESIS: Electrical properties of the implanted scala tympani could be accurately modeled by means of a simple resistive ladder network model. The subject-specific model parameters can be obtained from electrical field imaging (EFI) recordings. It is a powerful tool for analysis of the cochlear current spread. BACKGROUND: In EFI mode, the telemetry systems of contemporary cochlear implants can measure the intracochlear potential distribution. At present, the clinical use of EFI is typically limited to checking the implant's proper functioning. METHODS: Accurate EFI measurements and estimation algorithms have been developed to fit a small, yet physically relevant electrical model of the conductivity of the intracochlear structures. RESULTS: The model can attain up to 95% agreement with in vivo EFI data. A first discovery is that in a majority of the tested subjects, a substantial fraction of the monopolar current leaves the scala along the facial nerve canal. The role of the facial nerve canal has been confirmed by a temporal bone study and a high-resolution computed tomography (HRCT) scan in two of the implanted subjects. CONCLUSIONS: The clinical use of EFI is not limited to checking the implant's status. For the Clarion II implant, a purely resistive model is able to match in vivo EFI recordings. The model indicates that the facial nerve canal is an important conduction path to the reference electrode. EFI can provide clinically relevant information, especially in problematic cases of cochlear malformations, postoperative fibrosis/ossification, implanted otosclerotic cochleae, postoperative facial nerve stimulation, increased stimulation thresholds, and so on.

Algorithms↗

PubMed1989

Estimating lung mechanics of dogs with unilateral lung injury.

Extended least-squares algorithms using transpulmonary pressure and airway flow data from ventilatory waveforms were studied for their ability to track parameters of one- and two-compartment models of lung mechanics. A recursive extended least-squares algorithm with discounted measures estimated parameters of discrete-time models during synchronized intermittent mandatory ventilation. In tests on seven dogs developing oleic acid-induced unilateral hemorrhagic pulmonary edema, the one-compartment estimator responded rapidly and appropriately to changes in mechanics: compliance fell to 0.55 +/- 0.15 of its initial value and resistance rose by a factor of 1.8 +/- 0.5 in 3 h following injection of oleic acid. One-compartment parameter estimates revealed a difference between the airway resistance of inspiration and expiration. Two-compartment estimates were seldom physiologically plausible. The difference between inspiratory and expiratory resistance may have caused the two-compartment estimator to fail when applied to data from the entire respiratory cycle; when only expiratory data were used for estimation, the two-compartment estimates were meaningful. These estimates demonstrated increasing lung inhomogeneity after oleic acid was injected; at the end of 3 h, the ratio of the time constants of the two compartments ranged from 5 to 20 in six of the seven dogs. We conclude that the one- and two-compartment estimates may be combined to provide a meaningful assessment of lung mechanics.

Animals↗

PubMed1995

The application of cepstral coefficients and maximum likelihood method in EMG pattern recognition.

A new technique for classifying patterns of movement via electromyographic (EMG) signals is presented. Two methods (conventional autoregressive (AR) coefficients and cepstral coefficients) for extracting features from EMG signals and three classification algorithms (Euclidean Distance Measure (EDM), Weighted Distance Measure (WDM), and Maximum Likelihood Method (MLM)) for discriminating signals representative of broad classes of movements are described and compared. These three classifiers are derived from Bayes classifier with some assumptions, the relationship among them is discussed. The conventional MLM is modified to avoid heavy matrix inversion. Six able-bodied subjects with two pairs of surface electrodes located on bilateral sternocleidomastoid and upper trapezius muscles were studied in the experiment. The EMG signals of 20 repetitions of 10 motions were analyzed for each subject. Experimental results showed that mean recognition rate of the cepstral coefficients was at least 5% superior to that of the AR coefficients. The improvement achieved by the cepstral method was statistically significant for all the three classifiers. Reasons for the superiority of cepstral features were investigated from the feature space and frequency domain, respectively. The cepstral coefficients owned better cluster separability in feature space and they emphasized the more informative part in the frequency domain. The discrimination rate of the MLM was the highest among three classifiers. Incorporation of the cepstral features with the MLM could reduce the misclassification rate by 10.6% when compared with the combination of AR coefficients and EDM. Proper choice of five of ten motions could further raise the recognition rate to more than 95%.

Adult↗

PubMed2006

Multigrid tomographic inversion with variable resolution data and image spaces.

A multigrid inversion approach that uses variable resolutions of both the data space and the image space is proposed. Since the computational complexity of inverse problems typically increases with a larger number of unknown image pixels and a larger number of measurements, the proposed algorithm further reduces the computation relative to conventional multigrid approaches, which change only the image space resolution at coarse scales. The advantage is particularly important for data-rich applications, where data resolutions may differ for different scales. Applications of the approach to Bayesian reconstruction algorithms in transmission and emission tomography with a generalized Gaussian Markov random field image prior are presented, both with a Poisson noise model and with a quadratic data term. Simulation results indicate that the proposed multigrid approach results in significant improvement in convergence speed compared to the fixed-grid iterative coordinate descent method and a multigrid method with fixed-data resolution.

Algorithms↗

PubMed2006

Determination of density distribution in ferrous powder compacts using ultrasonic tomography.

Laser-induced ultrasonic bulk wave tomography is used for density variation determination of powder metal compacts. A laser beam is used to excite ultrasonic energy, and the signals passing through the specimen are received by an air-coupled transducer. The density variations of powder metal compacts can be determined directly by the cross-sectional tomographic images of slowness obtained by using a filtered, backprojection algorithm based on measured time of flights. Interpolations with respect to sample and projection angles are used to generate the input data required for displaying a well-balanced, reconstructed image to reduce the aliasing distortions caused by insufficient input data. Results of presintered cylindrical ferrous powdered samples show that this novel approach makes the reconstruction process more cost effective than the very tedious, time-consuming, and inaccurate metallographic methods, thus making it a potentially powerful tool for studying manufacturing processes through significant parameters to obtain a more uniform density distribution.

Journal Article↗

PubMed1994

Effects of follicular phase exercise on luteinizing hormone pulse characteristics in sedentary eumenorrhoeic women.

OBJECTIVE: Current studies reveal little regarding the inception of exercise-induced LH changes during physical training. This study aimed to assess the susceptibility of the hypothalamic-pituitary axis to the acute physical stress of exercise in untrained, physically inactive women. The acute effects of submaximal endurance exercise upon the pulsatile LH secretion in the follicular phase were compared with those accompanying leisurely strolling for a similar time period. SUBJECTS: All subjects were eumenorrhoeic, as determined by biphasic temperature patterns, detection of the urinary LH surge, and mid-luteal serum progesterone levels. Subjects were not physically active and had little history of strenuous exercise (VO2max = 38.0 +/- 1.8) (mean +/- SEM) ml/kg/min). DESIGN: All women completed a 13.5-hour pulsatility test which included three consecutive 20-minute runs on a treadmill at 50, 60 and 70% of the subjects' maximum oxygen uptake (n = 16). Six of these same subjects completed a separate test on another occasion in which one hour of leisurely strolling was substituted for exercise. Blood was sampled every 10 minutes via an indwelling cannula for 4.5 hours before and 8 hours after one hour of exercise and or strolling. MEASUREMENTS: A pulse algorithm (Pulsar) was used to quantify LH pulse characteristics. RESULTS: Exercise produced no significant effects upon LH pulse frequency or mean serum LH concentration. However, exercise of moderate intensity caused a significant increase in LH pulse amplitude (P < 0.05). Strolling produced no significant changes in LH secretion. CONCLUSION: Acute exercise of moderate intensity in the follicular phase of untrained women is an insufficient stimulus to inhibit the GnRH pulse generator in the post-exercise period, yet may produce a slight stimulatory effect on the amount of LH released per pulse.

Adult↗

PubMed1993

Evaluation of mechanisms behind elevated energy expenditure in cancer patients with solid tumours.

The aim of this study was to demonstrate significant factors behind elevated resting energy expenditure in weight-losing cancer patients. Therefore, weight-losing cancer patients (n = 60), with normal liver and kidney function tests, were randomized to receive one of four drug treatments for 5 days: (a) Propranolol 80 mg x 2 (beta-adrenoceptor blockade); (b) Indomethacin 50 mg x 2 (prostaglandin synthesis inhibition); (c) Morphine 5 mg x 3 (pain relief) or (d) Placebo x 2. A reference group of healthy well-nourished individuals were examined outside the formal randomization protocol and they received Propranolol 80 mg x 2. The cancer patients were randomized by a computer based algorithm stratifying for measured resting energy expenditure (REE), body composition, biochemical tests, previous therapy, tumour type and tumour stage. Resting energy expenditure was measured by indirect calorimetry in the morning after an overnight fast before and after drug treatment. beta-blockade reduced REE significantly in cancer patients from 1416 +/- 95 kcal day-1 to 1160 +/- 63 kcal day-1 (P < 0.02) and from 1472 +/- 69 vs, 1398 +/- 63 kcal day-1 (P < 0.01) in the well-nourished reference individuals. The reduction found in cancer patients (10%) was significantly larger than that in the group of reference patients (5%), (P < 0.01). Indomethacin, morphine or placebo did not induce any significant alteration in energy expenditure in our cancer patients. Propranolol treatment was associated with a significant reduction in plasma concentrations of free fatty acids (FFA), but not in plasma glycerol.(ABSTRACT TRUNCATED AT 250 WORDS)

Basal Metabolism↗

PubMed2005

An evaluation of an intervention to assist primary care physicians in screening and educating older patients who use alcohol.

OBJECTIVES: To evaluate whether providing physicians and older patients with personalized reports of drinking risks and benefits and patient education reduces alcohol-related risks and problems. DESIGN: Prospective comparison study. SETTING: Community primary care. PARTICIPANTS: Twenty-three physicians and 665 patients aged 65 and older. INTERVENTION: Combined report, in which six physicians and 198 [corrected] patients received reports of patients' drinking classifications and patients also received education; patient report, in which 245 patients received reports and education, but their five physicians did not receive reports; and usual care. MEASUREMENTS: Assessments at baseline and 12 months later to determine patients' nonhazardous (no known risks), hazardous (risks for problems), or harmful (presence of problems) classifications using the Computerized Alcohol-Related Problems Survey (CARPS). The CARPS contains a scanned screening measure and scoring algorithms and automatically produces patient and physician reports and patient education. RESULTS: At baseline, 21% were harmful drinkers, and 26% were hazardous drinkers. The patient report and combined report interventions were each associated with greater odds of lower-risk drinking at follow-up than usual care (odds ratio=1.59 and 1.23, respectively, P<.05 for each). The patient report intervention significantly reduced harmful drinking at follow-up from an expected 21% in usual care to 16% and increased nonhazardous drinking from 52% expected in usual care to 58%. Patients in the combined report intervention experienced a significantly greater average decrease in quantity and frequency. CONCLUSION: Older primary care patients can effectively reduce their alcohol consumption and other drinking risks when given personalized information about their drinking and health.

Aged↗

PubMed2001

Coding of the fundamental frequency in continuous interleaved sampling processors for cochlear implants.

In this study the perception of the fundamental frequency (F0) of periodic stimuli by cochlear implant users is investigated. A widely used speech processor is the Continuous Interleaved Sampling (CIS) processor, for which the fundamental frequency appears as temporal fluctuations in the envelopes at the output. Three experiments with four users of the LAURA (Registered trade mark of Philips Hearing Implants, now Cochlear Technology Centre Europe) cochlear implant were carried out to examine the influence of the modulation depth of these envelope fluctuations on pitch discrimination. In the first experiment, the subjects were asked to discriminate between two SAM (sinusoidally amplitude modulated) pulse trains on a single electrode channel differing in modulation frequency ( deltaf = 20%). As expected, the results showed a decrease in the performance for smaller modulation depths. Optimal performance was reached for modulation depths between 20% and 99%, depending on subject, electrode channel, and modulation frequency. In the second experiment, the smallest noticeable difference in F0 of synthetic vowels was measured for three algorithms that differed in the obtained modulation depth at the output: the default CIS strategy, the CIS strategy in which the F0 fluctuations in the envelope were removed (FLAT CIS), and a third CIS strategy, which was especially designed to control and increase the depth of these fluctuations (F0 CIS). In general, performance was poorest for the FLAT CIS strategy, where changes in F0 are only apparent as changes of the average amplitude in the channel outputs. This emphasizes the importance of temporal coding of F0 in the speech envelope for pitch perception. No significantly better results were obtained for the F0 CIS strategy compared to the default CIS strategy, although the latter results in envelope modulation depths at which sub-optimal scores were obtained in some cases of the first experiment. This indicates that less modulation is needed if all channels are stimulated with synchronous F0 fluctuations. This hypothesis is confirmed in a third experiment where subjects performed significantly better in a pitch discrimination task with SAM pulse trains, if three channels were stimulated concurrently, as opposed to only one.

Acoustic Stimulation↗

PubMedDate not supplied

Characteristics of exogenous lipid uptake by renal and intestinal brush-border membrane vesicles.

The transfer of radioactive phosphatidylcholine (PC*) from liposomes to rabbit jejunal and renal brush-border membrane vesicles (BBMVs) was measured with a fast-sampling, rapid-filtration apparatus. PC* uptake by jejunal and renal BBMVs was favoured when liposomes were made from soybean phosphatidylcholine (azolectin, AZO), whereas PC* uptake could not be quantitatively assessed from egg yolk phosphatidylcholine (PC) liposomes even after a 22-h period of incubation. The increased turbidity of BBMV dispersion following the addition of CaCl2 or HCl to AZO-treated BBMVs suggested that negatively charged lipids and phosphatidylethanolamine are transferred during the process. These data and the analysis of PC*-uptake time measurements, using an algorithm simulating aggregation phenomena, indicated that the reaction mechanism involved liposome aggregation to BBMVs rather than specific lipid transfer. The constants of the dimerization reaction between AZO liposomes and BBMVs were evaluated to be 0.016 +/- 0.006 min-1 for jejunal and 0.095 +/- 0.02 min-1 for renal preparations. IntraveSICULAR D-ASPartic acid accumulation in the presence of a NA+ gradient indicated that vesicles were still closed after coincubation with liposomes. In contrast, 70-85% of rabbit jejunal and renal Na(+)-D-glucose cotransporter activities were lost after overnight incubation with either AZO liposomes or buffered solution. Further, H(+)-ATPase activity in rabbit renal BBMVs largely decreased after coincubation with AZO liposomes, while brush-border membrane associated enzymes remained stable. These results demonstrate that coincubation of BBMV with liposomes of different composition may represent a useful approach to study the influence of lipidic environment on various membrane protein functions.

Animals↗

PubMed2003

Coronary artery calcium: accuracy and reproducibility of measurements with multi-detector row CT--assessment of effects of different thresholds and quantification methods.

PURPOSE: To evaluate the effects of different thresholds and quantification methods on the accuracy and reproducibility of coronary calcium measurements with multi-detector row computed tomography (CT). MATERIALS AND METHODS: A cardiac CT phantom containing predetermined calcified cylinders was scanned. Calcium volume and mass were measured at various threshold values ranging from 80 to 230 HU. In 32 patients, two consecutive CT scans were obtained, and the coronary artery calcium score, volume, and mass were measured by one observer at 130- and 90-HU thresholds. Correlation analysis and analysis of variance were performed to evaluate the measurement errors in the phantom study and the interscan variability in the clinical study. RESULTS: In the phantom, mass measurement error varied with threshold and calcium density (P <.01). Mass error was strongly correlated with volume error (r = 0.91, P <.01) but with a much smaller range. In the clinical study, interscan variability of mass measurements was significantly lower than that with other measurement methods for both patients and individual vessels. For the patients, the mean interscan variability of calcium score, volume, and mass at the 130-HU threshold was 20.4%, 13.9%, and 9.3%, respectively. For all methods, interscan variability was not significantly different between the 130- and 90-HU thresholds (P >.05). CONCLUSION: The mass measurement is more accurate, less variable, and more reproducible in coronary calcium quantification than are measurements with other algorithms. Accurate quantification of calcium in each calcified plaque may require that the threshold be set individually, depending on the calcium density.

Algorithms↗

PubMed1984

Absolute left ventricular volume by an iterative build-up factor analysis of gated radionuclide images.

A method for determining absolute left ventricular (LV) volumes from radionuclide gated blood-pool (GBP) images was validated in 34 patients. The technique is nongeometric, corrects for tissue attenuation, and uses an experimentally determined set of build-up factors to account for the effects of scatter. Only four parameters are needed to determine LV volumes: the LV count rates from a left anterior oblique (LAO) and a right posterior oblique (RPO) image (180 degrees opposed to the LAO), a venous blood sample, and a patient thickness measurement. A computer algorithm is used to reach an iterative solution to two simultaneous equations that yield LV volumes. Phantom studies showed less than 4% error for volume determinations at all investigated depths. For the patients studied the correlation between volumes obtained by GBP and contrast ventriculography was 0.97 for diastole and 0.96 for systole.

Adult↗

PubMed2003

The effect of the interval between blood pressure determinations on the delay in the detection of changes: a computer simulation.

UNLABELLED: The frequency of automated noninvasive blood pressure (NIBP) measurements during routine anesthesia is a balance between potentially deleterious effects of frequent cycling and a delay in detecting changes caused by a long cycle time. A computer model generated systolic blood pressures that changed to a new, random value after a period of stability. We sampled these data at intervals between 1 and 10 min to simulate NIBP measurements. A separate algorithm, based on Trigg's Tracking Variable, indicated when a change had been detected. For each set of variables, the simulation was repeated 1000 times, and the average time to detect a change was recorded. The mean time to detect a change was 8.0 min with a 1-min cycle, 8.9 min with a 2-min cycle, 10.8 min with a 5-min cycle, and 13.0 min with a 10-min cycle. As the cycle time increased, the delay in detecting changes increased but only by approximately half the increase in the cycle time. The optimum variables for the trend detection algorithm also changed as the NIBP interval increased. Provided that abrupt changes in blood pressure are not anticipated, a 1- or 2-min cycle time for NIBP offers little advantage over a longer period. IMPLICATIONS: We used a computer model to study the effect of increasing noninvasive blood pressure (NIBP) sampling interval on the detection of blood pressure changes. The detection time increased only 50% of the increase in the sampling interval. This information may help optimize NIBP intervals in different circumstances.

Algorithms↗