Advances in photoplethysmography: beyond arterial oxygen saturation

Signal completion using generative adversarial networks for enhanced photoplethysmography measurement accuracy

Despite the growing adoption of wearable photoplethysmography (PPG) devices in personal health management, their measurement accuracy remains limited due to susceptibility to noise. This paper proposes a novel signal completion technique using generative adversarial networks that ensures both global and local consistency. Our approach innovatively addresses both short- and long-term PPG variations to restore waveforms while maintaining waveform consistency within and between pulses. We evaluated our model by removing up to 50 % of segments from segmented PPG waveforms and comparing the original and reconstructed waveforms, including systolic peak information. The results demonstrate that our method accurately reconstructs waveforms with high fidelity, producing natural and seamless transitions without discontinuities at reconstructed boundaries. Additionally, the reconstructed waveforms preserve typical PPG shapes with minimal distortion, underscoring the effectiveness and novelty of our technique.

Consumer wearables and personal devices for tracking the fertile window

The market for technology that tracks ovulation to promote conception is rapidly expanding in the United States, targeting the growing audience of technologically proficient, reproductive-age female consumers. In this narrative review, 23 different, nonprescription wearables and devices designed to help women track their fertile window were identified as currently, commercially available in the United States. The majority of these utilize measurements of basal body temperature or combinations of various urinary hormones. This clinical opinion characterizes the scant available research validating the accuracy of these technologies. It further examines research oversight, discusses the utility of these wearables and devices to consumers, and considers these technologies through an equity lens. The discussion concludes with a call for innovation, describing promising new technologies that not only harness unique physiologic parameters to predict ovulation, but also focus on cost-effectiveness with the hope of increasing access to these currently costly devices and wearables.

Comparing the compensatory reserve metric obtained from invasive arterial measurements and photoplethysmographic volume-clamp during simulated hemorrhage

PURPOSE

The compensatory reserve metric (CRM) is a novel tool to predict cardiovascular decompensation during hemorrhage. The CRM is traditionally computed using waveforms obtained from photoplethysmographic volume-clamp (PPGVC), yet invasive arterial pressures may be uniquely available. We aimed to examine the level of agreement of CRM values computed from invasive arterial-derived waveforms and values computed from PPGVC-derived waveforms.

METHODS

Sixty-nine participants underwent graded lower body negative pressure to simulate hemorrhage. Waveform measurements from a brachial arterial catheter and PPGVC finger-cuff were collected. A PPGVC brachial waveform was reconstructed from the PPGVC finger waveform. Thereafter, CRM values were computed using a deep one-dimensional convolutional neural network for each of the following source waveforms; (1) invasive arterial, (2) PPGVC brachial, and (3) PPGVC finger. Bland-Altman analyses were used to determine the level of agreement between invasive arterial CRM values and PPGVC CRM values, with results presented as the Mean Bias [95% Limits of Agreement].

RESULTS

The mean bias between invasive arterial- and PPGVC brachial CRM values at rest, an applied pressure of -45mmHg, and at tolerance was 6% [-17%, 29%], 1% [-28%, 30%], and 0% [-25%, 25%], respectively. Additionally, the mean bias between invasive arterial- and PPGVC finger CRM values at rest, applied pressure of -45mmHg, and tolerance was 2% [-22%, 26%], 8% [-19%, 35%], and 5% [-15%, 25%], respectively.

CONCLUSION

There is generally good agreement between CRM values obtained from invasive arterial waveforms and values obtained from PPGVC waveforms. Invasive arterial waveforms may serve as an alternative for computation of the CRM.

Arch watch: current approaches and opportunities for improvement

Coarctation of the aorta (CoA) is a ductus arteriosus (DA)-dependent form of congenital heart disease (CHD) characterized by narrowing in the region of the aortic isthmus. CoA is a challenging diagnosis to make prenatally and is the critical cardiac lesion most likely to go undetected on the pulse oximetry-based newborn critical CHD screen. When undetected CoA causes obstruction to blood flow, life-threatening cardiovascular collapse may result, with a high burden of morbidity and mortality. Hemodynamic monitoring practices during DA closure (known as an "arch watch") vary across institutions and existing tools are often insensitive to developing arch obstruction. Novel measures of tissue oxygenation and oxygen deprivation may improve sensitivity and specificity for identifying evolving hemodynamic compromise in the newborn with CoA. We explore the benefits and limitations of existing and new tools to monitor the physiological changes of the aorta as the DA closes in infants at risk of CoA.

Adverse childhood experiences are associated with altered cardiovascular reactivity to head-up tilt in young adults

Adverse childhood experiences (ACEs) are associated with greater prevalence of cardiovascular disease and altered acute stress reactivity. The current study investigated the effect of ACEs on hemodynamic and autonomic responses to orthostatic stress imposed by 60° head-up tilt (HUT) in young adults. Two-hundred twenty-six healthy young adults (age = 22.6 ± 1.5 yr; n = 116 females) without cardiovascular disease participated and had complete data. Participants underwent supine blood pressure (BP), R-R interval (RRI), cardiac output (CO), total peripheral resistance (TPR), and cardiovagal baroreflex sensitivity (cvBRS) testing followed by a transition to 60° HUT where measures were reassessed. Childhood adversity exposures were assessed based on categorical exposure and nonexposure to childhood household dysfunction and maltreatment, and <4 and ≥4 types of ACEs. Significantly greater increases in SBP (P < 0.05), DBP, MAP, and TPR (P < 0.01; all) following 60° HUT were observed in individuals with ≥4 compared with those with <4 types of ACEs. Attenuated decreases in RRI and cvBRS were observed in those with ≥4 types of ACEs (P < 0.05). Experiencing ≥4 types of ACEs was associated with augmented BP and TPR reactivity and a blunted decrease in cvBRS in response to 60° HUT in young adults. Results suggest that a reduced vagal response to orthostatic stress is present in those who have experienced ≥4 types of ACEs that may promote autonomic dysfunction. Future research examining the sympathetic and vagal baroreflex branches is warranted.

BIOMARKERS: CAN THEY REALLY GUIDE OUR DAILY PRACTICE?

ABSTRACT

Optimal management of septic patients requires accurate assessment of both current severity status and prognosis. Since the 1990s, substantial advances have been made in the use of circulating biomarkers for such assessments. This summary of the session on "Biomarkers: can they really use guide our daily practice?" presented at the 2021 WEB-CONFERENCE OF THE EUROPEAN SHOCK SOCIETY, 6 November 2021. These biomarkers include ultrasensitive detection of bacteremia, circulating soluble urokina-type plasminogen activator receptor (suPAR), C-reactive protein (CRP) and ferritin and procalcitonin. In addition, the potential application of novel multiwavelength optical biosensor technology allows noninvasive monitoring of multiple metabolites that can be used to assess severity and prognosis in septic patients. The application these biomarkers and improved technologies provide the potential for improved personalized management of septic patients.

Oxygen saturation in intraosseous sternal blood measured by CO-oximetry and evaluated non-invasively during hypovolaemia and hypoxia - a porcine experimental study

PURPOSE

This study intended to determine, and non-invasively evaluate, sternal intraosseous oxygen saturation (SsO₂) and study its variation during provoked hypoxia or hypovolaemia. Furthermore, the relation between SsO₂ and arterial (SaO₂) or mixed venous oxygen saturation (SvO₂) was investigated.

METHODS

Sixteen anaesthetised male pigs underwent exsanguination to a mean arterial pressure of 50 mmHg. After resuscitation and stabilisation, hypoxia was induced with hypoxic gas mixtures (air/N₂). Repeated blood samples from sternal intraosseous cannulation were compared to arterial and pulmonary artery blood samples. Reflection spectrophotometry measurements by a non-invasive sternal probe were performed continuously.

RESULTS

At baseline SaO₂ was 97.0% (IQR 0.2), SsO₂ 73.2% (IQR 19.6) and SvO₂ 52.3% (IQR 12.4). During hypovolaemia, SsO₂ and SvO₂ decreased to 58.9% (IQR 16.9) and 38.1% (IQR 12.5), respectively, p < 0.05 for both, whereas SaO₂ remained unaltered (p = 0.44). During hypoxia all saturations decreased; SaO₂ 71.5% (IQR 5.2), SsO₂ 39.0% (IQR 6.9) and SvO₂ 22.6% (IQR 11.4) (p < 0.01), respectively. For hypovolaemia, the sternal probe red/infrared absorption ratio (SQV) increased significantly from baseline (indicating a reduction in oxygen saturation) + 5.1% (IQR 7.4), p < 0.001 and for hypoxia + 19.9% (IQR 14.8), p = 0.001, respectively.

CONCLUSION

Sternal blood has an oxygen saturation suggesting a mixture of venous and arterial blood. Changes in SsO₂ relate well with changes in SvO₂ during hypovolaemia or hypoxia. Further studies on the feasibility of using non-invasive measurement of changes in SsO₂ to estimate changes in SvO₂ are warranted.

External factors that affect the photoplethysmography waveforms

Photoplethysmography (PPG) is a simple and inexpensive technology used in many smart devices to monitor cardiovascular health. The PPG sensors use LED lights to penetrate into the bloodstream to detect the different blood volume changes in the tissue through skin contact by sensing the amount of light that hits the sensor. Typically, the data are displayed on a graph and it forms the pulse waveform. The information from the produced pulse waveform can be useful in calculating measurements that help monitor cardiovascular health, such as blood pressure. With many more people beginning to monitor their health status on their smart devices, it is extremely important that the PPG signal is accurate. Designing a simple experiment with standard laboratory equipment and commercial sensors, we wanted to find how external factors influence the results. In this study, it was found that external factors, touch force and temperature, can have a large impact on the resulting waveform, so the effects of those factors need to be considered in order for the information to become more reliable.

Digital health care and arrhythmia: a case of WPW syndrome in South Korea, 2020

Background

The digital health care field is expanding from the daily monitoring of chronic diseases to the detection of acute diseases, such as arrhythmia. Wolff-Parkinson-White (WPW) syndrome, a congenital cardiac disorder due to accessory pathways, causes tachycardia, syncope, and even sudden death.

Case presentation

We presented a 26-year-old female office worker with WPW syndrome managing the disease with a wearable device and discussed its significance in occupational medicine. After reviewing the worker's electrocardiogram results, symptoms, and pulse rate records extracted from the wearable device, we referred the worker to a cardiologist for further evaluations such as electrophysiology study. The worker monitors her symptom recurrence with the wearable device following successful radiofrequency catheter ablation of the bypass tract.

Conclusions

A case of an office worker with WPW syndrome managing the disease using a smart watch is presented. Further research is required to ensure its scientific validity, and we suggest policymakers promptly introduce digital health care to occupational environments.

Study of cuffless blood pressure estimation method based on multiple physiological parameters

Objective.Noninvasive blood pressure (BP) measurement technologies have been widely studied, but they still have the disadvantages of low accuracy, the requirement for frequent calibration and limited subjects. This work considers the regulation of vascular activity by the sympathetic nervous system and proposes a method for estimating BP using multiple physiological parameters.Approach.The parameters used in the model consist of heart rate variability (HRV), pulse transit time (PTT) and pulse wave morphology features extracted from electrocardiogram (ECG) and photoplethysmogram (PPG) signals. Through four classic machine learning algorithms, a hybrid data set of 3337 subjects from two databases is evaluated to verify the ability of cross-database migration. We also recommend an individual calibration procedure to further improve the accuracy of the method.Main results.The mean absolute error (MAE) and the root mean square error (RMSE) of the proposed algorithm is 10.03 and 14.55 mmHg for systolic BP (SBP), and 5.42 and 8.19 mmHg for diastolic BP (DBP). With individual calibration, the MAE and standard deviation (SD) is -0.16 ± 7.96 (SBP) and -0.13 ± 4.50 (DBP) mmHg, which satisfied the Advancement of Medical Instrumentation (AAMI) standard. In addition, the models are used to test single databases to evaluate their performance on different data sources. The overall performance of the Adaboost algorithm is better on the Multi-parameter Intelligent Monitoring in Intensive Care Unit (MIMIC) database; the MAE between its predicted value and true value reaches 6.6mmHg (SBP) and 3.12mmHg (DBP), respectively.Significance.The proposed method considers the regulation of blood vessels and the heart by the autonomic nervous system, and verifies its effectiveness and robustness across data sources, which is promising for improving the accuracy of continuous and cuffless BP estimation.

Using pulse oximetry waveforms to detect coarctation of the aorta

Background

Coarctation of the aorta is a common form of critical congenital heart disease that remains challenging to diagnose prior to clinical deterioration. Despite current screening methods, infants with coarctation may present with life-threatening cardiogenic shock requiring urgent hospitalization and intervention. We sought to improve critical congenital heart disease screening by using a novel pulse oximetry waveform analysis, specifically focused on detection of coarctation of the aorta.

Methods and results

Over a 2-year period, we obtained pulse oximetry waveform data on 18 neonates with coarctation of the aorta and 18 age-matched controls hospitalized in the cardiac intensive care unit at Children’s Healthcare of Atlanta. Patients with coarctation were receiving prostaglandin E1 and had a patent ductus arteriosus. By analyzing discrete features in the waveforms, we identified statistically significant differences in the maximum rate of fall between patients with and without coarctation. This was accentuated when comparing the difference between the upper and lower extremities, with the lower extremities having a shallow slope angle when a coarctation was present (p-value 0.001). Postoperatively, there were still differences in the maximum rate of fall between the repaired coarctation patients and controls; however, these differences normalized when compared with the same individual’s upper vs. lower extremities. Coarctation patients compared to themselves (preoperatively and postoperatively), demonstrated waveform differences between upper and lower extremities that were significantly reduced after successful surgery (p-value 0.028). This screening algorithm had an accuracy of detection of 72% with 0.61 sensitivity and 0.94 specificity.

Conclusions

We were able to identify specific features in pulse oximetry waveforms that were able to accurately identify patients with coarctation and further demonstrated that these changes normalized after surgical repair. Pulse oximetry screening for congenital heart disease in neonates may thus be improved by including waveform analysis, aiming to identify coarctation of the aorta prior to critical illness. Further large-scale testing is required to validate this screening model among patients in a newborn nursery setting who are low risk for having coarctation.

Photoplethysmography in dogs and cats: a selection of alternative measurement sites for a pet monitor

OBJECTIVE

Photoplethysmography (PPG) is an increasingly popular health and well-being tool for monitoring heart rate and oxygen saturation. Due to the pigmentation and hairiness of dogs and cats, a pulse oximeter is routinely placed solely on the tongue. As this approach is feasible only for pet monitor use during surgical procedures, we investigate PPG signal quality on several other measurement sites that would be better tolerated by conscious animals.

APPROACH

Acquired PPG signals are analyzed by four signal quality indices: mean baseline, signal power, kurtosis, and tolerance score.

MAIN RESULTS

In dogs, the metacarpus and tail can be substituted for oral pulse oximeter placement since both measurement sites exhibited high PPG signal kurtosis and were considered well-tolerated. In cats, the digit could be used with some limitations.

SIGNIFICANCE

Pet monitors with pulse oximeter probes adjusted to promising measurement sites could enable veterinarians and owners to monitor animals when fully awake.

Design of liver functional reserve monitor based on three-wavelength from red light to IR

BACKGROUND

The preoperative evaluation of liver functional reserve is very important to determine the excision of liver lobe for the patients with liver cancer. There already exist many effective evaluation methods, but these ones have many disadvantages such as large trauma, complicated process and so on.

OBJECTIVE

Therefore, it is essential to develop a fast, accurate and simple detection method of liver functional reserve for the practical application in the clinical engineering field.

METHODS

According to the principle of spectrophotometry, this paper proposes a detection method of liver functional reserve based on three-wavelength from red light to infrared light (IR), in which the artery pulse, the vein pulse and the move of tissue are taken into account.

RESULTS

By using photoelectric sensor technology and excreting experiment of indocyanine green, a minimally invasive, fast and simple testing equipment is designed in this paper.

CONCLUSIONS

The testing result shows this equipment can greatly reduce the interference from human body and ambient, realize continuous and real-time detection of arterial degree of blood oxygen saturation and liver functional reserve.

Heated humidified high-flow nasal cannula oxygen after thoracic surgery - A randomized prospective clinical pilot trial

BACKGROUND

Thoracic surgery patients are at high-risk for adverse pulmonary outcomes. Heated humidified high-flow nasal cannula oxygen (HHFNC O₂) may decrease such events. We hypothesized that patients randomized to prophylactic HHFNC O₂ would develop fewer pulmonary complications compared to conventional O₂ therapy.

METHODS AND PATIENTS

Fifty-one patients were randomized to HHFNC O₂ vs. conventional O₂. The primary outcome was a composite of postoperative pulmonary complications. Secondary outcomes included oxygenation and length of stay. Continuous variables were compared with t-test or Mann-Whitney-U test, categorical variables with Fisher's Exact test.

RESULTS

There were no differences in postoperative pulmonary complications based on intention to treat [two in HHFNC O₂ (n=25), two in control (n=26), p=0.680], and after exclusion of patients who discontinued HHFNC O₂ early [one in HHFNC O₂ (n=18), two in control (n=26), p=0.638]. Discomfort from HHFNC O₂ occurred in 11/25 (44%); 7/25 (28%) discontinued treatment.

CONCLUSIONS

Pulmonary complications were rare after thoracic surgery. Although HHFNC O₂ did not convey significant benefits, these results need to be interpreted with caution, as our study was likely underpowered to detect a reduction in pulmonary complications. High rates of patient-reported discomfort with HHFNC O₂ need to be considered in clinical practice and future trials.