Claus Holst-Hansen

Segmentation of heart sound recordings by a duration-dependent hidden Markov model

Digital stethoscopes offer new opportunities for computerized analysis of heart sounds. Segmentation of heart sound recordings into periods related to the first and second heart sound (S1 and S2) is fundamental in the analysis process. However, segmentation of heart sounds recorded with handheld stethoscopes in clinical environments is often complicated by background noise. A duration-dependent hidden Markov model (DHMM) is proposed for robust segmentation of heart sounds. The DHMM identifies the most likely sequence of physiological heart sounds, based on duration of the events, the amplitude of the signal envelope and a predefined model structure. The DHMM model was developed and tested with heart sounds recorded bedside with a commercially available handheld stethoscope from a population of patients referred for coronary arterioangiography. The DHMM identified 890 S1 and S2 sounds out of 901 which corresponds to 98.8% (CI: 97.8-99.3%) sensitivity in 73 test patients and 13 misplaced sounds out of 903 identified sounds which corresponds to 98.6% (CI: 97.6-99.1%) positive predictivity. These results indicate that the DHMM is an appropriate model of the heart cycle and suitable for segmentation of clinically recorded heart sounds.

Comparison of human adipose-derived stem cells and bone marrow-derived stem cells in a myocardial infarction model.

Treatment of myocardial infarction (MI) with bone marrow-derived mesenchymal stem cells and recently also adipose-derived stem cells has shown promising results. In contrast to clinical trials and their use of autologous bone marrow-derived cells from the ischemic patient, the animal MI models are often using young donors and young, often immune-compromised, recipient animals. Our objective was to compare bone marrow-derived mesenchymal stem cells with adipose-derived stem cells from an elderly ischemic patient in the treatment of MI using a fully grown non-immune-compromised rat model. Mesenchymal stem cells were isolated from adipose tissue and bone marrow and compared with respect to surface markers and proliferative capability. To compare the regenerative potential of the two stem cell populations, male Sprague–Dawley rats were randomized to receive intramyocardial injections of adipose-derived stem cells, bone marrow-derived mesenchymal stem cells, or phosphate-buffered saline 1 week following induction of MI. After 4 weeks, left ventricular ejection fraction (LVEF) was improved in the adipose-derived stem cell group, and scar wall thickness was greater compared with the saline group. Adipose-derived as well as bone marrow-derived mesenchymal stem cells prevented left ventricular end diastolic dilation. Neither of the cell groups displayed increased angiogenesis in the myocardium compared with the saline group. Adipose-derived stem cells from a human ischemic patient preserved cardiac function following MI, whereas this could not be demonstrated for bone marrow-derived mesenchymal stem cells, with only adipose-derived stem cells leading to an improvement in LVEF. Neither of the stem cell types induced myocardial angiogenesis, raising the question whether donor age and health have an effect on the efficacy of stem cells used in the treatment of MI.

Segmentation of heart sound recordings from an electronic stethoscope by a duration dependent Hidden-Markov Model

Digital stethoscopes offer new opportunities for computerized analysis of heart sounds. Segmentation of hearts sounds is a fundamental step in the analyzing process. However segmentation of heart sounds recorded with handheld stethoscopes in clinical environments is often complicated by recording and background noise. A duration-dependent hidden Markov model (DHMM) is proposed for robust segmentation of heart sounds. The DHMM model was developed and tested with heart sounds recorded at bedside with a commercially available handheld stethoscope. In a population of 60 patients, the DHMM identified 739 S1 and S2 sounds out of 744 which corresponded to a 99.3% sensitivity. There were seven incorrectly classified sounds which corresponded to a 99.1% positive predictive value. Our results suggest that DHMM could be a suitable method for segmentation of clinically recorded heart sounds.

Detection of coronary artery disease with an electronic stethoscope

A noninvasive method for detection of coronary artery disease (CAD) with an electronic stethoscope is proposed. Heart sounds recorded in clinical settings are often contaminated with background noise and noise caused by friction between the skin and the stethoscope. A method was developed to reduce the influence of the noise artifacts. The diastolic parts of the heart sounds were divided into multiple sub-segments, where noisy sub-segments were indentified as sub-segments with a low degree of stationarity or with a high energy level. The sub-segments not identified as noisy were analyzed with an autoregressive (AR) model, where the pole-magnitude of the 1st pole was used as a discriminating parameter. A test on 50 subjects showed that removal of the noisy sub-segments before analyses improved the diagnostic performance of the AR-model considerably, thereby reducing the influence of noise related to the use of a handhold stethoscope.

Acoustic Features for the Identification of Coronary Artery Disease

Goal: Earlier studies have documented that coronary artery disease (CAD) produces weak murmurs, which might be detected through analysis of heart sounds. An electronic stethoscope with a digital signal processing unit could be a low cost and easily applied method for diagnosis of CAD. The current study is a search for heart sound features which might identify CAD. Methods: Nine different types of features from five overlapping frequency bands were obtained and analyzed using 435 recordings from 133 subjects. Results: New features describing an increase in low-frequency power in CAD patients were identified. The features of the different types were relatively strongly correlated. Using a quadratic discriminant function, multiple features were combined into a CAD-score. The area under the receiving operating characteristic for the CAD score was 0.73 (95% CI: 0.69-0.78). Conclusion: The result confirms that there is a potential in heart sounds for the diagnosis of CAD, but that further improvements are necessary to gain clinical relevance.

Partial oral treatment of endocarditis.

BACKGROUND Guidelines for the treatment of left-sided infective endocarditis (IE) recommend 4 to 6 weeks of intravenous antibiotics. Conversion from intravenous to oral antibiotics in clinically stabilized patients could reduce the side effects associated with intravenous treatment and shorten the length of hospital stay. Evidence supporting partial oral therapy as an alternative to the routinely recommended continued parenteral therapy is scarce, although observational data suggest that this strategy may be safe and effective. STUDY DESIGN This is a noninferiority, multicenter, prospective, randomized, open-label study of partial oral treatment with antibiotics compared with full parenteral treatment in left-sided IE. Stable patients (n = 400) with streptococci, staphylococci, or enterococci infecting the mitral valve or the aortic valve will be included. After a minimum of 10 days of parenteral treatment, stable patients are randomized to oral therapy or unchanged parenteral therapy. Recommendations for oral treatment have been developed based on minimum inhibitory concentrations and pharmacokinetic calculations. Patients will be followed up for 6 months after completion of antibiotic therapy. The primary end point is a composition of all-cause mortality, unplanned cardiac surgery, embolic events, and relapse of positive blood cultures with the primary pathogen. CONCLUSION The Partial Oral Treatment of Endocarditis study tests the hypothesis that partial oral antibiotic treatment is as efficient and safe as parenteral therapy in left-sided IE. The trial is justified by a review of the literature, by pharmacokinetic calculations, and by our own experience.

Noise and the detection of coronary artery disease with an electronic stethoscope

Recent studies demonstrated that diastolic heart sounds, recorded with an electronic stethoscope, contain markers of coronary artery disease (CAD). A difficult is that the CAD-related sound is very weak and recordings are often contaminated by noise. The current study analyses the noise contamination of 633 stethoscope recordings from a clinical environment. Respiration noise, ambient noise, recording noise and abdominal noise were identified in the recordings and were classified according to duration and intensity. To monitor how noise influences the classification performance AR-pole magnitudes were extracted from both the 25–250 Hz frequency band and the 250–1000 Hz frequency band. The classification performance was quantified by the Area Under the receiver operating Characteristic (AUC). Ambient noise was present in 39.9% of the recordings and was the most common noise source. Abdominal noise was the least common noise source, present in 10.8% of the recordings. The best pole, with respect to detection of CAD, extracted from the 250–1000 Hz frequency band was sensitive to noise, since the AUC dropped from 0.70 in to 0.57 when noisy recordings were included. Contrary the best pole from the 25–250 Hz frequency band was relatively robust against noise, since the AUC dropped from 0.73 to only 0.70 when noisy recordings were included. The study demonstrated that noise contamination is a frequent problem and that features from lower frequency bands are more robust against noise than features from higher frequency bands.

Can new pulmonary gas exchange parameters contribute to evaluation of pulmonary congestion in left-sided heart failure?

BACKGROUND Assessment of pulmonary congestion in left-sided heart failure is necessary for guiding anticongestive therapy. Clinical examination and chest x-ray are semiquantitative methods with poor diagnostic accuracy and reproducibility. OBJECTIVES To establish reference values, describe reproducibility, and investigate the diagnostic and monitoring properties in relation to pulmonary congestion of new pulmonary gas exchange parameters describing ventilation/perfusion mismatch (variable fraction of ventilation [fA2] or the drop in oxygen pressure from the mixed alveolar air of the two ventilated compartments to the nonshunted end-capillary blood [DeltaPO(2)]) and pulmonary shunt. METHODS Sixty healthy volunteers and 69 patients requiring an acute chest x-ray in a cardiac care unit were included. The gas exchange parameters were estimated by analyzing standard bedside respiratory and circulatory measurements obtained during short-term exposure to different levels of inspired oxygen. Nine patients were classified as having pulmonary congestion using a reference diagnosis and were followed during 30 days of anticongestive therapy. Diagnostic and monitoring properties were compared with chest x-ray, N-terminal probrain natriuretic peptide (NT-proBNP), spirometry values, arterial oxygen tension, alveolar-arterial oxygen difference and venous admixture. RESULTS The 95% reference intervals for healthy subjects were narrow (ie, fA2 [0.75 to 0.90], DeltaPO(2) [0.0 kPa to 0.5 kPa] and pulmonary shunt [0.0% to 8.2%]). Reproducibility was relatively good with small within subject coefficients of variation (ie, fA2 [0.05], DeltaPO(2) [0.4 kPa] and pulmonary shunt [2.0%]). fA2, DeltaPO(2) and NT-proBNP had significantly better diagnostic properties, with high sensitivities (100%) but low specificities (30% to 40%). During successful anticongestive therapy, fA2, DeltaPO(2), NT-proBNP and spirometry values showed significant improvements. CONCLUSIONS The gas exchange parameter for ventilation/perfusion mismatch but not pulmonary shunt can have a possible role in rejecting the diagnosis of pulmonary congestion and in monitoring anticongestive therapy.