Using Lempel-Ziv Complexity to Assess ECG Signal Quality.

The poor quality of wireless electrocardiography (ECG) recordings can lead to misdiagnosis and waste of medical resources. This study presents an interpretation of Lempel-Ziv (LZ) complexity in terms of ECG quality assessment, and verifies its performance on real ECG signals. Firstly, LZ complexities for typical signals, namely high-frequency (HF) noise, low-frequency (LF) noise, power-line (PL) noise, impulse (IM) noise, clean artificial ECG signals, and ECG signals with various types of noise added (ECG plus HF, LF, PL, and IM noise, respectively) were analyzed. Then, the effects of noise, signal length, and signal-to-noise ratio (SNR) on the LZ complexity of ECG signals were analyzed. The simulation results show that LZ complexity for HF noise was obviously different from those for PL and LF noise. The LZ value can be used to determine the presence of HF noise. ECG plus HF noise had the highest LZ values. Other types of noise had low LZ values. Signal lengths of over 40 s had only a small effect on LZ values. The LZ values for ECG plus all types of noise increased monotonically with decreasing SNR except for LF and PL noise. For the test of real ECG signals plus three types of noise, namely muscle artefacts (MAs), baseline wander (BW), and electrode motion (EM) artefacts, LZ complexity varied obviously with increasing MA but not for BW and EM noise. This study demonstrates that LZ complexity is sensitive to noise level (especially for HF noise) and can thus be a valuable reference index for the assessment of ECG signal quality.

Novel photoplethysmography cardiovascular assessments in patients with Raynaud's phenomenon and systemic sclerosis: a pilot study.

OBJECTIVE: Multisite photoplethysmography (PPG) cardiovascular assessments can evaluate endothelial, peripheral autonomic and arterial dysfunction. The aim of this pilot study was to investigate the potential clinical utility of the technology in assessing patients with SSc and primary RP (PRP). METHODS: Multisite PPG pulse measurements, a reference ankle brachial pressure index (ABPI) and a full clinical assessment were undertaken for three subject groups: SSc, PRP and controls. Endothelial and autonomic function and arterial disease measures were obtained using pulse wave analysis. RESULTS: Nineteen SSc, 19 PRP and 23 control subjects were assessed and compared. Endothelial function was significantly impaired in SSc (P < 0.02), but with no difference between controls and PRP. Receiver operating characteristic-based classification accuracy was 81% (sensitivity 90%, specificity 74%) for separating SSc from controls and 82% (sensitivity 84%, specificity 79%) for separating SSc from PRP. SSc patients with digital ulcers had significantly lower endothelial function compared with those without ulcers (P < 0.05). Autonomic dysfunction was suggested in both SSc and PRP and was most exaggerated in patients with diffuse SSc. All groups had overall normal ABPI and arterial stiffness timing measures. Bilateral timing differences at the toes, which represents peripheral occlusive arterial disease, did show increased asymmetry in SSc (P < 0.02). CONCLUSION: Multisite PPG pulse technology showed potential diagnostic ability. By using measures of endothelial function, it differentiated SSc from control and PRP subjects with an accuracy of at least 81%. Objective pulse-derived measures of autonomic function and arterial disease in SSc have also been reported in this pilot study.

Novel assessment of microvascular changes in idiopathic restless legs syndrome (Willis-Ekbom disease).

Many patients with restless legs syndrome (Willis-Ekbom disease) complain of burning sensations in their feet associated with the desire to move, such that they seek cooler environments. This pilot study aimed to characterise the microvascular skin changes in 12 patients with restless legs syndrome compared with 12 age- and sex-matched controls. Patients with moderate or severe restless legs syndrome and controls underwent detailed thermovascular assessment in a controlled temperature room at three different stages (normothermic phase 23 °C, hot phase 30 °C, cold phase 18 °C). Microvascular activity was recorded during all phases by bilateral great toe laser-Doppler flowmetry and also by whole-body thermography. Patient and control measurements were compared. The study protocol was well tolerated. Parameters extracted from the laser-Doppler flowmetry measurements were used to model a logistic function using binary logistic regression. This demonstrated a statistically significant difference between patients with restless legs syndrome and healthy controls (P < 0.001). Visual inspection of the body thermography image sequences showed increased lower limb movement in patients with restless legs syndrome patients compared with controls. Thermography analysis also showed significant differences between foot temperatures in patients with restless legs syndrome compared with controls during the hot phase (P = 0.011). Notably, patients with restless legs syndrome had more uniform foot temperatures, whereas controls had a wider variability in surface temperature across the feet. This novel study demonstrates impaired microvascular circulation in patients with restless legs syndrome in comparison to matched controls and a potential mechanism for the sensation of burning feet. The protocol also provides an experimental paradigm to test therapeutic interventions for the future.

Novel optical assessments of tissue composition and viability using fluorescence spectroscopy and tissue oxygenation spectrophotometry in patients with systemic sclerosis: a pilot study.

OBJECTIVE: Patients with systemic sclerosis (SSc) experience significant morbidity and mortality, therefore, the development of tests to aid its early diagnosis are very important. The aim of this pilot study was to assess the diagnostic value of novel optical non-invasive skin fluorescence spectroscopy (FS) and tissue oxygen saturation (TOS) viability measurements in patients with established SSc. APPROACH: Two groups were studied, comprising 14 SSc patients and nine healthy controls (93% and 73% females, respectively). FS and TOS measurements were collected from three body sites: the forearm, chest, and calf. Fluorescence intensities at wavelengths attributed to collagen, elastin, and L-tryptophan were computed, with adjustment for melanin, and a normalised combined fluorescence score (NCFS) was determined. MAIN RESULTS: The NCFS was significantly higher (p < 0.001) and the combined TOS significantly lower (p < 0.001) in the SSc group. TOS measurements alone showed good classification accuracy (95.7%) at separating SSc from healthy control participants, with some clustering of values close to the 50% oxygenation level in both groups. When the composition and viability measures were combined and modelled using binary logistic regression, excellent results for the sample were obtained following leave one out cross validation (100%). SIGNIFICANCE: The results of this pilot study demonstrate the potential diagnostic utility of FS and TOS assessments in SSc patients and further work is now needed to validate these techniques prospectively in a larger group of SSc patients across the spectrum of the disease, and also patients with other types of vasculopathy and conditions that can cause skin fibrosis.

Innovative multi-site photoplethysmography measurement and analysis demonstrating increased arterial stiffness in paediatric heart transplant recipients.

OBJECTIVE: It has been documented that heart transplantation in children is often complicated by arterial hypertension and increased arterial stiffness. We use innovative multi-site photoplethysmography (MPPG) pulse measurement and analysis technology to assess changes in arterial stiffness in paediatric heart transplant recipients (HTRs) in comparison with healthy control (HC) children. APPROACH: A group of 20 HTRs (median age 13.5 years, eight male) were compared to an overall age- and gender-matched group of 161 HCs (median age 11.6 years, 74 male). Peripheral pulse was recorded bilaterally using MPPG at the ear lobe, index finger and great toe sites, along with an electrocardiogram cardiac timing reference. Segmental pulse arrival times between peripheral sites (finger-ear, PATf-e; toe-finger, PATt-f; and toe-ear PATt-e) were calculated as arterial stiffness measures, and differences between subject groups were tested using multivariate analysis. Normalised ear, finger and toe pulse shapes were also studied and compared between groups. MAIN RESULTS: After correction for heart rate and diastolic and mean arterial blood pressures, the HTR group was found to have significantly lower segmental PATt-e and PATt-f measurements, with median values of 150 ms versus 172 ms in the HC group (p = 0.02), and 104 ms versus 118 ms in the HC group (p = 0.01), respectively, consistent with increased arterial stiffness in the patient group. The normalised ear, finger and toe sites showed only a mild elongation in each pulse rise time for the transplant group. SIGNIFICANCE: This study shows that innovative and easy-to-do MPPG gives further evidence for increased arterial stiffness in children who have undergone successful cardiac transplantation.

Quantifying the correlation between photoplethysmography and laser Doppler flowmetry microvascular low-frequency oscillations.

Photoplethysmography (PPG) and laser Doppler flowmetry (LDF) are two recognized optical techniques that can track low-frequency perfusion changes in microcirculation. The aim of this study was to determine, in healthy subjects, the correlation between the techniques for specific low-frequency bands previously defined for microcirculation. Twelve healthy male subjects (age range 18 to 50 years) were studied, with PPG and LDF signals recorded for 20 min from their right and left index (PPG) and middle (LDF) fingers. Wavelet analysis comprised dividing the low-frequency integral wavelet spectrum (IWS) into five established physiological bands relating to cardiac, respiratory, myogenic, neurogenic, and endothelial activities. The correlation between PPG and LDF was quantified using wavelet correlation analysis and Spearman correlation analysis of the median IWS amplitude. The median wavelet correlation between signals (right-left side average) was 0.45 (cardiac), 0.49 (respiratory), 0.86 (myogenic), 0.91 (neurogenic), and 0.91 (endothelial). The correlation of IWS amplitude values (right-left side average) was statistically significant for the cardiac (ρ = 0.64, p < 0.05) and endothelial (ρ = 0.62, p < 0.05) bands. This pilot study has shown good correlation between PPG and LDF for specific physiological frequency bands. In particular, the results suggest that PPG has the potential to be a low-cost replacement for LDF for endothelial activity assessments.

Novel thermal imaging analysis technique for detecting inflammation in thyroid eye disease.

CONTEXT: The disease phase in thyroid eye disease (TED) is commonly assessed by clinical investigation of cardinal signs of inflammation and using the clinical activity score (CAS). Although CAS is the current gold standard, the clinical assessment would benefit if a more objective tool were available. OBJECTIVE: The aim of this work was to explore the clinical value of a novel thermal imaging analysis technique to objectively quantify the thermal characteristics of the eye and peri-orbital region and determine the disease phase in TED. DESIGN: This was a cross-sectional study comparing consecutive patients with active TED (CAS ≥ 3/7) attending a tertiary center, with a group of consecutive patients with inactive TED (CAS <3). PATIENTS: Thermal images were acquired from 30 TED patients, 17 with active disease and 13 with inactive disease. INTERVENTIONS: Patients underwent standard ophthalmological clinical assessments and thermal imaging. MAIN OUTCOME MEASURES: Five novel thermal eye parameters (TEP) were developed to quantify the thermal characteristics of the eyes in terms of the highest level of inflammation (TEP1), overall level of inflammation (TEP2), right-left asymmetry in the level of inflammation (TEP3), maximum temperature variability across the eyes (TEP4), and right-left asymmetry in the temperature variability (TEP5). RESULTS: All five TEP were increased in active TED. TEP1 gave the largest accuracy (77%) at separating the two groups, with 65% sensitivity and 92% specificity. A statistical model combining all five parameters increased the overall accuracy, compared to using only one parameter, to 93% (94% sensitivity and 92% specificity). All five of the parameters were also found to be increased in patients with chemosis compared to those without. CONCLUSIONS: The potential diagnostic value of this novel thermal imaging analysis technique has been demonstrated. Further investigation on a larger group of patients is necessary to confirm these results.

Extracting fetal heart beats from maternal abdominal recordings: selection of the optimal principal components.

This study presents a systematic comparison of different approaches to the automated selection of the principal components (PC) which optimise the detection of maternal and fetal heart beats from non-invasive maternal abdominal recordings.A public database of 75 4-channel non-invasive maternal abdominal recordings was used for training the algorithm. Four methods were developed and assessed to determine the optimal PC: (1) power spectral distribution, (2) root mean square, (3) sample entropy, and (4) QRS template. The sensitivity of the performance of the algorithm to large-amplitude noise removal (by wavelet de-noising) and maternal beat cancellation methods were also assessed. The accuracy of maternal and fetal beat detection was assessed against reference annotations and quantified using the detection accuracy score F1 [2*PPV*Se / (PPV + Se)], sensitivity (Se), and positive predictive value (PPV). The best performing implementation was assessed on a test dataset of 100 recordings and the agreement between the computed and the reference fetal heart rate (fHR) and fetal RR (fRR) time series quantified.The best performance for detecting maternal beats (F1 99.3%, Se 99.0%, PPV 99.7%) was obtained when using the QRS template method to select the optimal maternal PC and applying wavelet de-noising. The best performance for detecting fetal beats (F1 89.8%, Se 89.3%, PPV 90.5%) was obtained when the optimal fetal PC was selected using the sample entropy method and utilising a fixed-length time window for the cancellation of the maternal beats. The performance on the test dataset was 142.7 beats(2)/min(2) for fHR and 19.9 ms for fRR, ranking respectively 14 and 17 (out of 29) when compared to the other algorithms presented at the Physionet Challenge 2013.

A multi-step method with signal quality assessment and fine-tuning procedure to locate maternal and fetal QRS complexes from abdominal ECG recordings.

Non-invasive monitoring of fetal electrocardiogram (fECG) plays an important role in detecting and diagnosing fetal diseases. This study aimed to develop a multi-step method for locating both maternal and fetal QRS complexes from abdominal ECG (aECG) recordings. The proposed method included four major steps: abdominal ECG pre-processing, maternal QRS complex locating, maternal ECG cancellation and fetal QRS complex locating. Signal quality assessment (SQA) and fine-tuning for maternal ECG (FTM) were implemented in the first and third steps, respectively. The method was then evaluated using 75 non-invasive 4-channel aECG recordings provided by the PhysioNet/Computing in Cardiology Challenge 2013. The F1 measure, which is a new index introduced by Behar et al (2013 Proc. Comput. Cardiol. 40 297-300), was used to assess the locating accuracy. The other two indices, mean squared error of heart rate (MSE_HR) between the fetal HR signals estimated from the reference and our method (MSE_HR in bpm(2)) and root mean squared difference between the corresponding fetal RR intervals (MSE_RR in ms) were also used to assess the locating accuracy. Overall, for the maternal QRS complex, the F1 measure was 98.4% from the method without the implementation of SQA, and it was improved to 99.8% with SQA. For the fetal QRS complex, the F1 measure, MSE_HR and MSE_RR were 84.9%, 185.6 bpm(2) and 19.4 ms for the method without both SQA and FTM procedures. They were improved to 93.9%, 47.5 bpm(2) and 7.6 ms with both SQA and FTM procedures. These improvements were observed from each individual subject. It can be concluded that implementing both SQA and FTM procedures could achieve better performance for locating both maternal and fetal QRS complexes.

Recurring patterns in stationary intervals of abdominal uterine electromyograms during gestation.

Abdominal uterine electromyograms (uEMG) studies have focused on uterine contractions to describe the evolution of uterine activity and preterm birth (PTB) prediction. Stationary, non-contracting uEMG has not been studied. The aim of the study was to investigate the recurring patterns in stationary uEMG, their relationship with gestation age and PTB, and PTB predictivity. A public database of 300 (38 PTB) three-channel (S1-S3) uEMG recordings of 30 min, collected between 22 and 35 weeks' gestation, was used. Motion and labour contraction-free intervals in uEMG were identified as 5-min weak-sense stationarity intervals in 268 (34 PTB) recordings. Sample entropy (SampEn), percentage recurrence (PR), percentage determinism (PD), entropy (ER), and maximum length (L MAX) of recurrence were calculated and analysed according to the time to delivery and PTB. Random time series were generated by random shuffle (RS) of actual data. Recurrence was present in actual data (p<0.001) but not RS. In S3, PR (p<0.005), PD (p<0.01), ER (p<0.005), and L MAX (p<0.05) were higher, and SampEn lower (p<0.005) in PTB. Recurrence indices increased (all p<0.001) and SampEn decreased (p<0.01) with decreasing time to delivery, suggesting increasingly regular and recurring patterns with gestation progression. All indices predicted PTB with AUC≥0.62 (p<0.05). Recurring patterns in stationary non-contracting uEMG were associated with time to delivery but were relatively poor predictors of PTB.

Finger microvascular responses to deep inspiratory gasp assessed and quantified using wavelet analysis.

The physiological changes following a deep inspiratory gasp (DIG) manoeuvre have been described in the literature. However, the lack of a reliable signal processing technique to visualize and quantify these physiological changes has so far limited the applicability of the test to the clinical setting. The main aim of this study was to assess the feasibility of using wavelet analysis to quantify the pulse arrival time (PAT) and its changes during the DIG manoeuvre. Vascular responses were extracted from cardiac (electrocardiogram, ECG) and peripheral pulse (photoplethysmography, PPG) waveforms. Wavelet analysis characterized their cardiovascular responses in healthy adult subjects in the time-frequency space, and for the ECG-PPG inter-relationship in terms of the PAT. PAT showed a characteristic biphasic response to gasp, with an increase of 59 ± 59 ms (p = 0.001) compared to the maximum value reached during quiet breathing, and a decrease of -38 ± 55 ms (p < 0.01) compared to the minimum value during quiet breathing. The response measures were repeatable. This pilot study has successfully shown the feasibility of using wavelet analysis to characterize the cardiovascular waveforms and quantify their changes with DIG.

Chronic fatigue syndrome and impaired peripheral pulse characteristics on orthostasis--a new potential diagnostic biomarker.

Autonomic nervous system dysfunction is frequently reported in chronic fatigue syndrome (CFS) with orthostatic intolerance, a common symptom that can be objectively assessed. The frequent finding of autonomic dysfunction and symptoms on standing has the potential to provide a diagnostic biomarker in chronic fatigue. In this study we explored the clinical value of non-invasive optical multi-site photoplethysmography (PPG) technology to assess cardiovascular responses to standing. Multi-site PPG pulses were collected from tissue pads of the ears, fingers and toes of 14 patients with CFS and 14 age-matched sedentary subjects using a measurement protocol of a 10 min baseline (subject supine) followed by 3 min of tilting on a tilt table (head-up to 70°). Percentage change in pulse timing (pulse transit time, PTTf) and pulse amplitude (AMP) at each site were calculated using beat-to-beat pulse wave analysis. A significant reduction in the overall pulse timing response to controlled standing was found for the CFS group (using summed absolute percentage change in PTTf for ear, finger and toe sites, median change of 26% for CFS and 37% for control with p = 0.002). There were no significant differences between subject groups for the AMP measure at any site. Changes in AMP with tilt were, however, weakly significantly and negatively correlated with fatigue severity (p < 0.05). Receiver operating characteristic (ROC) analysis of timing measures produced an area under the curve of 0.81. Experimental linear discriminant classification analysis comparing both timing and amplitude measures produced an overall diagnostic accuracy of 82%. Pulse wave abnormalities have been observed in CFS and represent a potential objective measure to help differentiate between CFS patients and healthy controls.