49 research outputs found
Beat-to-beat blood pressure estimation by photoplethysmography and its interpretation
Blood pressure (BP) is among the most important vital signals. Estimation of absolute BP solely using photoplethysmography (PPG) has gained immense attention over the last years. Available works differ in terms of used features as well as classifiers and bear large differences in their results. This work aims to provide a machine learning method for absolute BP estimation, its interpretation using computational methods and its critical appraisal in face of the current literature. We used data from three different sources including 273 subjects and 259,986 single beats. We extracted multiple features from PPG signals and its derivatives. BP was estimated by xgboost regression. For interpretation we used Shapley additive values (SHAP). Absolute systolic BP estimation using a strict separation of subjects yielded a mean absolute error of 9.456mmHg and correlation of 0.730. The results markedly improve if data separation is changed (MAE: 6.366mmHg, r: 0.874). Interpretation by means of SHAP revealed four features from PPG, its derivation and its decomposition to be most relevant. The presented approach depicts a general way to interpret multivariate prediction algorithms and reveals certain features to be valuable for absolute BP estimation. Our work underlines the considerable impact of data selection and of training/testing separation, which must be considered in detail when algorithms are to be compared. In order to make our work traceable, we have made all methods available to the public
In-ear photoplethysmography for central pulse waveform analysis in non-invasive hemodynamic monitoring
In recent years, the analysis of the photoplethys-mographic (PPG) pulse waveforms has attracted much research focus. However, the considered signals are primarily recorded at the fingertips, which suffer from reduced peripheral perfusion in situations like hypovolemia or sepsis, rendering waveform analysis infeasible. The ear canal is not affected by cardiovascular centralization and could thus prove to be an ideal alternate measurement site for pulse waveform analysis. Therefore, we developed a novel system that allows for highly accurate photoplethysmographic measurements in the ear canal. We conducted a measurement study in order to assess the signal-to-noise ratio of our developed system Hereby, we achieved a mean SNR of 40.65 dB. Hence, we could show that our system allows for highly accurate PPG recordings in the ear canal facilitating sophisticated pulse waveform analysis. Furthermore, we demonstrated that the pulse decomposition analysis is also applicable to in-ear PPG recordings
A substudy of a randomized controlled trial
Data on early markers for acute kidney injury (AKI) after noncardiovascular
surgery are still limited. This study aimed to determine the diagnostic value
of plasma neutrophil-gelatinase-associated lipocalin (pNGAL) and
intraoperative diuresis for AKI in patients undergoing major abdominal surgery
treated within a goal-directed hemodynamic algorithm. This study is a post-hoc
analysis of a randomized controlled pilot trial comparing intravenous
solutions within a hemodynamic goal-directed algorithm based on the esophageal
Doppler in patients undergoing epithelial ovarian cancer surgery. The
diagnostic value of plasma NGAL obtained at ICU admission and intraoperative
diuresis was determined with respect to patients already meeting AKI criteria
6 hours after surgery (AKI6h) and to all patients meeting AKI criteria at
least once during the postoperative course (AKItotal). AKI was diagnosed by
the definition of the Kidney Disease Improving Global Outcome (KDIGO) group
creatinine criteria and was screened up to postoperative day 3. Receiver
operating characteristic curves including a gray zone approach were performed.
A total of 48 patients were analyzed. None of the patients had increased
creatinine levels before surgery and 14 patients (29.2%) developed AKI after
surgery. Plasma NGAL was predictive for AKI6h (AUCAKI6h 0.832 (95% confidence
interval [CI], 0.629–0.976), P = .001) and AKItotal (AUCAKItotal 0.710 (CI
0.511–0.878), P = .023). The gray zones of pNGAL calculated for AKI6h and
AKItotal were 210 to 245 and 207 to 274 ng mL−1, respectively. The lower
cutoffs of the gray zone at 207 and 210 ng mL−1 had a negative predictive
value (NPV) (i.e., no AKI during the postoperative course) of 96.8% (CI
90–100) and 87.1% (CI 78–97), respectively. Intraoperative diuresis was also
predictive for AKI6h (AUCAKI6h 0.742 (CI 0.581–0.871), P = .019) with a gray
zone of 0.5 to 2.0 mL kg−1 h−1. At the lower cutoff of the gray zone at 0.5 mL
kg−1 h−1, corresponding to the oliguric threshold, the NPV was 84.2% (78–92).
This study indicates that pNGAL can be used as an early marker to rule out AKI
occurring within 3 days after major abdominal surgery. Intraoperative diuresis
can be used to rule out AKI occurring up to 6 hours after surgery
Correlation of arterial blood pressure to synchronous piezo, impedance and photoplethysmographic signal features : Investigating pulse wave features and transit times
In this paper we investigate which pulse wave pick-up technologies are well suited for blood pressure trend estimation. We use custom built hardware to acquire electrocardiographic, applanation-tonometric, photo- and impedance-plethysmographic signals during low intensity workouts. Beat-to-beat features and pulse wave runtimes are correlated to the reference arterial blood pressure. Temporal lag adjustment is performed to determine the latency of feature response. Best results are obtained for systolic arterial blood pressure. These suggest that every subject has a range of well-performing features, but it is not consistent among all. Spearman Rho values reach in excess of 0.8, with their significance being validated by p-values lower than 0.01
A Prospective Substudy of a Randomized Controlled Trial
Malignant ascites (MA) is most commonly observed in patients scheduled for
epithelial ovarian cancer (EOC) surgery and is supposed as a major risk factor
promoting perioperative hemodynamic deterioration. We aimed to assess the
hemodynamic consequences of MA on systemic circulation in patients undergoing
cytoreductive EOC surgery. This study is a predefined post-hoc analysis of a
randomized controlled pilot trial comparing intravenous solutions within a
goal-directed algorithm to optimize hemodynamic therapy in patients undergoing
cytoreductive EOC surgery. Ascites was used to stratify the EOC patients prior
to randomization in the main study. We analyzed 2 groups according to the
amount of ascites (NLAS: none or low ascites [<500 mL] vs HAS: high ascites
group [>500 mL]). Differences in hemodynamic variables with respect to time
were analyzed using nonparametric analysis for longitudinal data and
multivariate generalized estimating equation adjusting the analysis for the
randomized study groups of the main study. A total of 31 patients in the NLAS
and 16 patients in the HAS group were analyzed. Although cardiac output was
not different between groups suggesting a similar circulatory blood flow, the
HAS group revealed higher heart rates and lower stroke volumes during surgery.
There were no differences in pressure-based hemodynamic variables. In the HAS
group, fluid demands, reflected by the time to reindication of a fluid
challenge after preload optimization, increased steadily, whereas stroke
volume could not be maintained at baseline resulting in hemodynamic
instability after 1.5 h of surgery. In contrast, in the NLAS group fluid
demands were stable and stroke volume could be maintained during surgery.
Clinically relevant associations of the type of fluid replacement with
hemodynamic consequences were particularly observed in the HAS group, in which
transfusion of fresh frozen plasma (FFP) was associated to an improved
circulatory flow and reduced vasopressor and fluid demands, whereas the
administration of artificial infusion solutions was related to opposite
effects. Malignant ascites >500 mL implies increased fluid demands and
substantial alterations in circulatory blood flow during cancer surgery. Fresh
frozen plasma transfusion promotes recovering hemodynamic stability in
patients with malignant ascites >500 mL, in whom artificial infusion solutions
could not prevent from hemodynamic deterioration
Wearable Cardiorespiratory Monitoring Employing a Multimodal Digital Patch Stethoscope: Estimation of ECG, PEP, LVET and Respiration Using a 55 mm Single-Lead ECG and Phonocardiogram
Cardiovascular diseases are the main cause of death worldwide, with sleep disordered breathing being a further aggravating factor. Respiratory illnesses are the third leading cause of death amongst the noncommunicable diseases. The current COVID-19 pandemic, however, also highlights the impact of communicable respiratory syndromes. In the clinical routine, prolonged postanesthetic respiratory instability worsens the patient outcome. Even though early and continuous, long-term cardiorespiratory monitoring has been proposed or even proven to be beneficial in several situations, implementations thereof are sparse. We employed our recently presented, multimodal patch stethoscope to estimate Einthoven electrocardiogram (ECG) Lead I and II from a single 55 mm ECG lead. Using the stethoscope and ECG subsystems, the pre-ejection period (PEP) and left ventricular ejection time (LVET) were estimated. ECG-derived respiration techniques were used in conjunction with a novel, phonocardiogram-derived respiration approach to extract respiratory parameters. Medical-grade references were the SOMNOmedics SOMNO HDTM and Osypka ICON-CoreTM. In a study including 10 healthy subjects, we analyzed the performances in the supine, lateral, and prone position. Einthoven I and II estimations yielded correlations exceeding 0.97. LVET and PEP estimation errors were 10% and 21%, respectively. Respiratory rates were estimated with mean absolute errors below 1.2 bpm, and the respiratory signal yielded a correlation of 0.66. We conclude that the estimation of ECG, PEP, LVET, and respiratory parameters is feasible using a wearable, multimodal acquisition device and encourage further research in multimodal signal fusion for respiratory signal estimation.DFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli
Comparison of the non-invasive Nexfin® monitor with conventional methods for the measurement of arterial blood pressure in moderate risk orthopaedic surgery patients
Objective Continuous invasive arterial blood pressure (IBP) monitoring remains
the gold standard for BP measurement, but traditional oscillometric non-
invasive intermittent pressure (NIBP) measurement is used in most low-to-
moderate risk procedures. This study compared non-invasive continuous arterial
BP measurement using a Nexfin® monitor with NIBP and IBP monitors. Methods
This was a single-centre, prospective, pilot study in patients scheduled for
elective orthopaedic surgery. Systolic BP, diastolic BP and mean arterial
blood pressure (MAP) were measured by Nexfin®, IBP and NIBP at five
intraoperative time-points. Pearson correlation coefficients, Bland–Altman
plots and trending ability of Nexfin® measurements were used as criteria for
success in the investigation of measurement reliability. Results A total of 20
patients were enrolled in the study. For MAP, there was a sufficient
correlation between IBP/Nexfin® (Pearson = 0.75), which was better than the
correlation between IBP/NIBP (Pearson = 0.70). Bland–Altman analysis of the
data showed that compared with IBP, there was a higher percentage error for
MAPNIBP (30%) compared with MAPNexfin® (27%). Nexfin® and NIBP underestimated
systolic BP; NIBP also underestimated diastolic BP and MAP. Trending ability
for MAPNexfin® and MAPNIBP were comparable to IBP. Conclusion Non-invasive BP
measurement with Nexfin® was comparable with IBP and tended to be more precise
than NIBP
A Randomised Controlled Trial
Liver surgery is still associated with a high rate of morbidity and mortality.
We aimed to compare different haemodynamic treatments in liver surgery. In a
prospective, blinded, randomised, controlled pilot trial patients undergoing
liver resection were randomised to receive haemodynamic management guided by
conventional haemodynamic parameters or by oesophageal Doppler monitor (ODM,
CardioQ-ODM) or by pulse power wave analysis (PPA, LiDCOrapid) within a goal-
directed algorithm adapted for liver surgery. The primary endpoint was stroke
volume index before intra-operative start of liver resection. Secondary
endpoints were the haemodynamic course during surgery and postoperative pain
levels. Due to an unbalance in the extension of the surgical procedures with a
high rate of only minor procedures the conventional group was dropped from the
analysis. Eleven patients in the ODM group and 10 patients in the PPA group
were eligible for statistical analysis. Stroke volume index before start of
liver resection was 49 (37; 53) ml/m2 and 48 (41; 56) ml/m2 in the ODM and PPA
group, respectively (p=0.397). The ODM guided group was haemodynamically
stable as shown by ODM and PPA measurements. However, the PPA guided group
showed a significant increase of pulse-pressure-variability (p=0.002) that was
not accompanied by a decline of stroke volume index displayed by the PPA
(p=0.556) but indicated by a decline of stroke volume index by the ODM
(p<0.001). The PPA group had significantly higher postoperative pain levels
than the ODM group (p=0.036). In conclusion, goal-directed optimization by ODM
and PPA showed differences in intraoperative cardiovascular parameters
indicating that haemodynamic optimization is not consistent between the two
monitors
Detection of a stroke volume decrease by machine-learning algorithms based on thoracic bioimpedance in experimental hypovolaemia
Compensated shock and hypovolaemia are frequent conditions that remain clinically undetected and can quickly cause deterioration of perioperative and critically ill patients. Automated, accurate and non-invasive detection methods are needed to avoid such critical situations. In this experimental study, we aimed to create a prediction model for stroke volume index (SVI) decrease based on electrical cardiometry (EC) measurements. Transthoracic echo served as reference for SVI assessment (SVI-TTE). In 30 healthy male volunteers, central hypovolaemia was simulated using a lower body negative pressure (LBNP) chamber. A machine-learning algorithm based on variables of EC was designed. During LBNP, SVI-TTE declined consecutively, whereas the vital signs (arterial pressures and heart rate) remained within normal ranges. Compared to heart rate (AUC: 0.83 (95% CI: 0.73–0.87)) and systolic arterial pressure (AUC: 0.82 (95% CI: 0.74–0.85)), a model integrating EC variables (AUC: 0.91 (0.83–0.94)) showed a superior ability to predict a decrease in SVI-TTE ≥ 20% (p = 0.013 compared to heart rate, and p = 0.002 compared to systolic blood pressure). Simulated central hypovolaemia was related to a substantial decline in SVI-TTE but only minor changes in vital signs. A model of EC variables based on machine-learning algorithms showed high predictive power to detect a relevant decrease in SVI and may provide an automated, non-invasive method to indicate hypovolaemia and compensated shock
A Modified Approach to Induce Predictable Congestive Heart Failure by Volume Overload in Rats
The model of infrarenal aortocaval fistula (ACF) has recently gained new interest in its use to investigate cardiac pathophysiology. Since in previous investigations the development of congestive heart failure (CHF) was inconsistent and started to develop earliest 8-10 weeks after fistula induction using a 18G needle, this project aimed to induce a predictable degree of CHF within a definite time period using a modified approach. An aortocaval fistula was induced in male Wistar rats using a 16G needle as a modification of the former 18G needle-technique described by Garcia and Diebold. Results revealed within 28 +/- 2 days of ACF significantly increased heart and lung weight indices in the ACF group accompanied by elevated filling pressure. All hemodynamic parameters derived from a pressure-volume conductance-catheter in vivo were significantly altered in the ACF consistent with severe systolic and diastolic left ventricular dysfunction. This was accompanied by systemic neurohumoral activation as demonstrated by elevated rBNP-45 plasma concentrations in every rat of the ACF group. Furthermore, the restriction in overall cardiac function was associated with a beta 1- and beta 2-adrenoreceptor mRNA downregulation in the left ventricle. In contrast, beta 3-adrenoreceptor mRNA was upregulated. Finally, electron microscopy of the left ventricle of rats in the ACF group showed signs of progressive subcellular myocardial fragmentation. In conclusion, the morphometric, hemodynamic and neurohumoral characterization of the modified approach revealed predictable and consistent signs of congestive heart failure within 28 +/- 2 days. Therefore, this modified approach might facilitate the examination of various questions specific to CHF and allow for pharmacological interventions to determine pathophysiological pathways