https://digitalrepository.unm.edu/cgi/viewcontent.cgi?article=1334&context=nm_composer_archive

To Be Human

Blood pressure monitoring based on pulse transit or arrival time has been the focus of much research in order to design ambulatory blood pressure monitors. The accuracy of these monitors is limited by several challenges, such as acquisition and processing of physiological signals as well as changes in vascular tone and the pre-ejection period. In this work, a literature survey covering recent developments is presented in order to identify gaps in the literature. The findings of the literature are classified according to three aspects. These are the calibration of pulse transit/arrival times to blood pressure, acquisition and processing of physiological signals and finally, the design of fully integrated blood pressure measurement systems. Alternative technologies as well as locations for the measurement of the pulse wave signal should be investigated in order to improve the accuracy during calibration. Furthermore, the integration and validation of monitoring systems needs to be improved in current ambulatory blood pressure monitors.

http://iopscience.iop.org/article/10.1088/0967-3334/36/3/R1/pdf

A survey on signals and systems in ambulatory blood pressure monitoring using pulse transit time

Optimizing risk assessment may reduce use of advanced diagnostic testing in patients with symptoms suggestive of stable coronary artery disease (CAD). Detection of diastolic murmurs from post-stenotic coronary turbulence with an acoustic sensor placed on the chest wall can serve as an easy, safe, and low-cost supplement to assist in the diagnosis of CAD. The aim of this study was to evaluate the diagnostic accuracy of an acoustic test (CAD-score) to detect CAD and compare it to clinical risk stratification and coronary artery calcium score (CACS). We prospectively enrolled patients with symptoms of CAD referred to either coronary computed tomography or invasive coronary angiography (ICA). All patients were tested with the CAD-score system. Obstructive CAD was defined as more than 50 % diameter stenosis diagnosed by quantitative analysis of the ICA. In total, 255 patients were included and obstructive CAD was diagnosed in 63 patients (28 %). Diagnostic accuracy evaluated by receiver operating characteristic curves was 72 % for the CAD-score, which was similar to the Diamond–Forrester clinical risk stratification score, 79 % (p = 0.12), but lower than CACS, 86 % (p < 0.01). Combining the CAD-score and Diamond–Forrester score, AUC increased to 82 %, which was significantly higher than the standalone CAD-score (p < 0.01) and Diamond–Forrester score (p < 0.05). Addition of the CAD-score to the Diamond–Forrester score increased correct reclassification, categorical net-reclassification index = 0.31 (p < 0.01). This study demonstrates the potential use of an acoustic system to identify CAD. The combination of clinical risk scores and an acoustic test seems to optimize patient selection for diagnostic investigation.

/pdf/diagnosing-coronary-artery-disease-by-sound-analysis-from-jd2d0d0kdj.pdf

Diagnosing coronary artery disease by sound analysis from coronary stenosis induced turbulent blood flow: diagnostic performance in patients with stable angina pectoris.

This paper presents the idea of a non invasive screening system for identifying Coronary Artery Disease (CAD) patients from fingertip Photoplethysmogram (PPG) signal. A combined feature set, related to heart rate variability (HRV) as well as shapes of PPG waveform has been defined for distinguishing CAD and non CAD subjects. Support Vector Machine (SVM) is used for classification. Our methodology yields sensitivity and specificity scores of 0.82 and 0.88 respectively in identifying CAD patients on a corpus of 112 subjects, selected from MIMIC II dataset. Further, we achieved sensitivity and specificity scores of of 0.73 and 0.87 on another dataset of 30 subjects, collected from an urban hospital using commercial oximeter device.

Identifying coronary artery disease from photoplethysmogram

Objective Diagnosing coronary artery disease (CAD) continues to require substantial healthcare resources. Acoustic analysis of transcutaneous heart sounds of cardiac movement and intracoronary turbulence due to obstructive coronary disease could potentially change this. The aim of this study was thus to test the diagnostic accuracy of a new portable acoustic device for detection of CAD. Methods We included 1675 patients consecutively with low to intermediate likelihood of CAD who had been referred for cardiac CT angiography. If significant obstruction was suspected in any coronary segment, patients were referred to invasive angiography and fractional flow reserve (FFR) assessment. Heart sound analysis was performed in all patients. A predefined acoustic CAD-score algorithm was evaluated; subsequently, we developed and validated an updated CAD-score algorithm that included both acoustic features and clinical risk factors. Low risk is indicated by a CAD-score value ≤20. Results Haemodynamically significant CAD assessed from FFR was present in 145 (10.0%) patients. In the entire cohort, the predefined CAD-score had a sensitivity of 63% and a specificity of 44%. In total, 50% had an updated CAD-score value ≤20. At this cut-off, sensitivity was 81% (95% CI 73% to 87%), specificity 53% (95% CI 50% to 56%), positive predictive value 16% (95% CI 13% to 18%) and negative predictive value 96% (95% CI 95% to 98%) for diagnosing haemodynamically significant CAD. Conclusion Sound-based detection of CAD enables risk stratification superior to clinical risk scores. With a negative predictive value of 96%, this new acoustic rule-out system could potentially supplement clinical assessment to guide decisions on the need for further diagnostic investigation. Trial registration number ClinicalTrials.gov identifier NCT02264717; Results.

https://heart.bmj.com/content/heartjnl/104/11/928.full.pdf

Diagnostic performance of an acoustic-based system for coronary artery disease risk stratification

The aim of the current study was to study the low-frequency power distribution of diastolic heart sounds in patients with coronary artery disease (CAD). Heart sound recordings were made from the 4th intercostal space in 132 patients referred for elective coronary angiography. CAD patients were defined as subjects with at least one stenosis with a diameter reduction of at least 50% as identified with quantitative coronary angiography. The diastolic heart sounds were analyzed using short-time Fourier transform (STFT) and autoregressive (AR) models. The STFT analyses showed that the energy below 100 Hz was increased approximately 150 ms after the second heart sound in CAD patients. The AR-spectra of the band-pass filtered (20–100 Hz) diastolic heart sound showed that the frequency distribution shifted towards lower frequencies in the case of CAD. The cause of these changes might be due to variations in ventricular filling patterns.

/pdf/coronary-artery-disease-and-low-frequency-heart-sound-4m3lc9if86.pdf

Coronary artery disease and low frequency heart sound signatures

The aim of the study was to design and evaluate a coupler/microphone system for recording weak murmurs from stenoses in the coronar artery. The suggested design is based on the use of a high quality microphone, coupled to the chest through a small air cavity. Since the determination of the exact frequency range of interest related to murmurs is part of the purpose of the study, one of the goals of the design was to achieve a high signal to noise ratio in a broad frequency range. The high cut off frequency of the coupler is determined by the acoustic impedance of the chest and the design of the coupler, while the low frequency behavior was determined by the properties of the microphone, electronic circuits and inadvertent leakages in the acoustical coupling. The requirement for the microphone and pr-amplifier was a low inherent noise level. The setup was used for collection of heart sounds in a clinical trial including 463 patients referred for elective coronary angiography. The preliminary results show, that it was possible to record heart sound in the diastolic period with a sound pressure level approximately 30 dB above the noise floor of the microphone and recording system in the frequency range from 200–700 Hz. The capability of the sensor to record diastolic heart sound in the relevant frequency range indicates that the sensor is suitable for recording of coronary murmurs.

/pdf/acoustic-coupler-for-acquisition-of-coronary-artery-murmurs-1vgy482wy7.pdf

Acoustic coupler for acquisition of coronary artery murmurs

The aim of the present study is to describe the design of an acquisition system for the specific purpose of recording heart murmurs originating from stenosis in the coronary arteries. The design and development of such a system require knowledge in many disciplines: acoustic couplers, microphones, skin adhesives, electronic hardware, software and patient safety. Special considerations are needed in order to record these murmurs since they have a 60 dB lower sound level, than that of the closing heart valves. The system was implemented and successfully used for collection of heart sounds in a clinical trial including 463 patients referred for elective coronary angiography.

/pdf/system-for-acquisition-of-weak-murmurs-related-to-coronary-u3mpb9m7zk.pdf

System for acquisition of weak murmurs related to coronary artery diseases

Separation and characterization of maternal cardiac and vascular sounds in the third trimester of pregnancy.

Non-invasive fetal ECG (NI-FECG) extraction algorithms enable long-term continuous beat-to-beat monitoring of the fetal heart rate (FHR), as opposed to the gold standard in FHR monitoring, cardiotocography (CTG). We investigate how NI-FECG extraction algorithms selected from the CinC 2013 Challenge (CinC13) perform on data with low quality signals and how performance can be evaluated using CTG, when FQRS annotation is not possible.Four-channel NI-FECG was recorded simultaneously with a CTG trace on 22 pregnant women, gestational age 29-41 weeks. Seven algorithms were tested: The winning CinC13 entry from Varanini et al. and six algorithms from the unofficial top-scoring CinC13 entry by Behar et al. Two accuracy measures were used: 1) The RMSE between the FECG-based FHR and CTG traces; 2) The Pearson correlation coefficient r between the FECG-based FHR and CTG trace and its average over all recordings, $\bar r$.The algorithms with the lowest RMSE’s are Behar’s FUSE-SMOOTH, a constant FHR, and Varanini, while the Varanini algorithm delivers the best correlation with the CTG trace $(\bar r = 0.73)$ with 41% of the recordings having r > 0.8, whereas the other algorithms have $\bar r \leq 0.59$ and ≤ 29% of the recordings with r > 0.8. FHR was estimated accurately in some recordings and poorly in others, believed to be due to large differences in signal quality.

/pdf/comparison-of-cardiotocography-and-fetal-heart-rate-1glfj4jhry.pdf

Henrik Zimmermann

Papers

Coronary artery disease and low frequency heart sound signatures

Acoustic coupler for acquisition of coronary artery murmurs

System for acquisition of weak murmurs related to coronary artery diseases

Separation and characterization of maternal cardiac and vascular sounds in the third trimester of pregnancy.

Comparison of Cardiotocography and Fetal Heart Rate Estimators Based on Non-Invasive Fetal ECG