13 research outputs found
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Photoplethysmography: Towards a non-invasive pressure measurement technique
There is a need for a non-invasive and continuous blood pressure monitor. Photoplethysmography (PPG) is one of the techniques that were investigated for this purpose in an in vitro model where the relationship between the PPG and pressure-volume (P-V) changes was investigated. Pressure and red (R) infrared (IR) PPG signals were recorded continuously in an arterial model that simulates fluid flow utilizing a pulsatile pump. Flow rates were controlled through three set-points of pumping frequencies at low and high stroke volumes. Normalized Pulse Volume (NPV) is defined as the light intensity ratio at each wavelength, R (NPVR) and IR (NPVIR). Adjusted Pulse Volume (APV) was determined for both wavelengths. It was found that the optimum method for estimation of the pulsatile volume is through APV, which has a remarkable correlation (r2=0.99, p<0.001) with the assumed exponential P-V model. APV obtained significantly better fit when compared to NPVIR (r2=0.73, z=25.85, p<0.001) and NPVR (r2=0.95, z=12.26, p<0.001). Our preliminary findings emphasize the potential of APV as a non-invasive continuous method of blood pressure measurement
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In vitro validation of measurement of volume elastic modulus using photoplethysmography
Arterial stiffness (AS) is one of the earliest detectable symptoms of cardiovascular diseases and their progression. Current AS measurement methods provide an indirect and qualitative estimation of AS. The purpose of this study is to explore the utilisation of Photoplethysmography (PPG) as a measure of volumetric strain in providing a direct quantification of the Volume Elastic modulus (Ev). An in vitro experimental setup was designed using an arterial model to simulate the human circulation in health (Model 2) and disease (Model 1). Flow, pressure, and PPG signals were recorded continuously under varied conditions of flow dynamics. The obtained Ev values were validated with the gold standard mechanical testing techniques. Values obtained from both methods had no significant difference for both models with a percent error of 0.26% and 1.9% for Model 1 and Model 2, respectively. This study shows that PPG and pressure signals can provide a direct measure of AS in an in vitro setup. With emerging noninvasive pressure measurement methods, this research paves the way for the direct quantification of AS in vivo
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Investigations of photoplethysmography in the assessment of haemodynamics, vascular mechanics and haemorheology
Realâtime cardiovascular assessment is vital for monitoring patients at an early stage of cardiovascular diseases (CVDs), at risk of reoccurrence of heart attacks and strokes and during pharmacological and nonâpharmacological treatments. Blood Pressure (BP), Arterial Stiffness (AS) and Blood Viscosity (BV) are three essential parameters that can provide a reliable assessment of hypertension, atherosclerosis, and hyperviscosity associated with the development and progression of cardiovascular pathologies to complex stages. The currently available methods designed for evaluation of such parameters incur limitations and challenges that stand as an obstacle to the development of nonâinvasive, portable and reliable allâinâone device intended for personal use. This project engaged in novel fundamental and rigorous in vivo and in vitro investigations in an effort to shed more light on the photoplethysmographic signals (AC and DC) during induced changes of BP, AS, and BV. The underlying hypothesis is to show for the first time that Photoplethysmography (PPG) has the potential to nonâinvasively assess, in a qualifying and quantifying manner, the above parameters. Positives outcomes from such approach will establish the potential of the PPG as a preferential monitoring (screening and possible diagnosis) technique for the assessment of CVDs.
Novel miniature PPG sensors were developed along with a state of the art PPG processing unit, a data acquisition system and a customised manuscript for offline signal analyses. ECG and temperature processing systems were also designed and developed for use in the in vivo investigations. State of the art in vitro experimental rig was developed to mimic the human circulation under a wide range of flow conditions. A pilot volunteer investigation highlighted the effect of a cold pressor test in one hand on the PPG signals from both hands. The results indicated that there are changes in flow regulation mechanisms and hemodynamics besides the expected vasoconstriction effects of local cooling. These findings led to the controlled in vitro experiments. The in vitro investigations were completed in four stages where the potential of the PPG to provide a measure of blood pressure values, volume elastic modulus (Ev) and to detect fluid viscosity and haemorheological changes.
Results from the in vitro investigations highlighted that Adjusted Pulse Volume (APV) was found to be the optimum method for measuring BP values using Red (R) and Infrared (IR) wavelengths as validated under a range of BP values simulating hypotensive to hypertensive scenarios. The correlation was significant with Rsquare ranging between 0.96 and 0.99 for different arterial models and circulating fluids. Moreover, a proposed mathematical derivation allowed the PPG to provide a direct measure of AS using Ev. The method showed strong agreement with the gold standard measurement of material testings, the Instron device, with a percent error of 0.26% and 1.9% for different arterial models. Furthermore, the PPG signals also responded to changes in rheological characteristics in relation to fluid viscosities, the presence of the red blood cells, changes in shear rates and blood clotting.
These results strongly suggest that PPG has the potential to be used as a nonâinvasive and continuous method for the assessment of cardiovascular disease markers such as blood pressure, arterial stiffness and blood viscosity
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Investigation of pulse transit times using multi-site reflectance photoplethysmography under conditions of artificially induced peripheral vasoconstriction
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Investigation of finger reflectance photoplethysmography in volunteers undergoing a local sympathetic stimulation
Optical sensors used in clinical applications have gained great popularity over the last few decades, especially the photoplethysmographic (PPG) technique used in estimating arterial blood oxygen saturation in the well-known medical devices called pulse oximeters. In this study we investigate the photoplethysmogram further in an effort to understand its origin better, as there is a significant void in the current knowledge on the PPG quantitative measurement. The photoplethysmographic signal provides a heart rhythm pulsating AC component, and a non-pulsating DC component. The signal is commonly believed to originate from tissue volume changes only and hasn't been investigated intensively. This in vivo study examines the source of the PPG signal in relation to pulse amplitude and pulse rhythm while volunteers undergo a right hand ice immersion. It was found that the PPG signal is sensitive in detecting the sympathetic stimulation which corresponds to volumetric and heart rate changes. During the immersion, AC pulse amplitudes (PA) from both hands decreased significantly, while DC levels increased significantly in the right hand and non-significantly in the left hand. Also, a significant decrease in the pulse repetition time (PRT) was observed. Using blood pressure-flow theories, these results suggest that there are possibly other factors in the blood flow regulation that alter the blood optical density which contributes to the detected signal. Further studies need to investigate PPGs in relation to blood optical density and the dynamics of the pulsatile flow effects besides volumetric changes. Such investigations might explore further applications of the PPG in medicine
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Photoplethysmography for the Assessment of Haemorheology
Haemorheology has been long identified as an early biomarker of a wide range of diseases, especially cardiovascular diseases. This study investigates for the first time the suitability of Photoplethysmography (PPG) as a non-invasive diagnostic method for haemorheological changes. The sensitivity of both PPG components (AC and DC) to changes in haemorheology were rigorously investigated in an in vitro experimental setup that mimics the human circulation. A custom-made reflectance PPG sensor, a pressure transducer and an ultrasonic Doppler flowmeter were used to map changes in flow dynamics and optical responses in an arterial model. The study investigated the effect of shear rates by varying fluid pumping frequencies using 4 set-points and the effect of clot formation using a chemical trigger. Both PPGAC amplitudes and PPGDC levels showed significant (pâ<â0.001) changes during the increase in shear rates and an immediate change after thromboplastin activation. The findings highlight that PPG has the potential to be used as a simple non-invasive method for the detection of blood characteristics, including disaggregation, radial migration and cross-linking fibrin formations. Such capability will enable the assessment of the effects of clotting-activators and anticoagulants (including non-pharmacological methods) and might aid in the early non-invasive assessment of cardiovascular pathologies
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Photoplethysmography for blood volumes and oxygenation changes during intermittent vascular occlusions
Photoplethysmography (PPG) is an optical technique that measures blood volume variations. The main application of dual-wavelength PPG is pulse oximetry, in which the arterial oxygen saturation (SpO[Formula: see text]) is calculated noninvasively. However, the PPG waveform contains other significant physiological information that can be used in conjunction to SpO[Formula: see text] for the assessment of oxygenation and blood volumes changes. This paper investigates the use of near infrared spectroscopy (NIRS) processing techniques for extracting relative concentration changes of oxygenated ([Formula: see text]HbO[Formula: see text]), reduced ([Formula: see text]HHb) and total haemoglobin ([Formula: see text]tHb) from dual-wavelength PPG signals during intermittent pressure-increasing vascular occlusions. A reflectance PPG sensor was attached on the left forearm of nineteen (n = 19) volunteers, along with a reference NIRS sensor positioned on the same forearm, above the left brachioradialis. The investigation protocol consisted of seven intermittent and pressure-increasing vascular occlusions. Relative changes in haemoglobin concentrations were obtained by applying the modified Beer-Lambert law to PPG signals, while oxygenation changes were estimated by the difference between red and infrared attenuations of DC PPGs (A[Formula: see text] = [Formula: see text]A[Formula: see text] - [Formula: see text]A[Formula: see text]) and by the conventional SpO[Formula: see text]. The [Formula: see text]HbO[Formula: see text], [Formula: see text]HHb, [Formula: see text]tHb from the PPG signals indicated significant changes in perfusion induced by either partial and complete occlusions (p < 0.05). The trends in the variables extracted from PPG showed good correlation with the same parameters measured by the reference NIRS monitor. Bland and Altman analysis of agreement between PPG and NIRS showed underestimation of the magnitude of changes by the PPG. A[Formula: see text] indicated significant changes for occlusion pressures exceeding 20 mmHg (p < 0.05) and correlation with tissue oxygenation changes measured by NIRS, while SpO[Formula: see text] had significant changes after 40 mmHg (p < 0.05). Relative changes in haemoglobin concentrations can be estimated from PPG signals and they showed a good level of accuracy in the detection of perfusion and oxygenation changes induced by different degrees of intermittent vascular occlusions. These results can open up to new applications of the PPG waveform in the detection of blood volumes and oxygenation changes
Takotsubo cardiomyopathy prevalence and associated factors in patients presenting with a clinical picture of acute myocardial infarction in Palestine
Abstract Background Takotsubo cardiomyopathy (TC) is a transient cardiac syndrome that manifests with symptoms resembling acute myocardial infarction (MI). It is characterized by temporary wall-motion abnormalities predominantly affecting the apical and mid-portions of the left ventricle, despite the absence of significant obstructive coronary disease. TC poses diagnostic challenges due to its resemblance to ST-segment elevation myocardial infarction. Our study aimed to determine the prevalence of TC and identify the factors associated with its occurrence in patients presenting with acute MI in Palestine. Results A retrospective analysis was conducted on a cohort of patients diagnosed with TC at Al-Makassed hospital. Women accounted for 90.7% of TC cases (95% CI 88.2â93.2%). The mean age of affected individuals ranged from 62 to 76Â years. The most common presenting symptoms were chest pain (83.4%, 95% CI 80.0â86.7%) and dyspnea (20.4%, 95% CI 16.3â24.5%), often following an emotionally or physically stressful event. Electrocardiography (ECG) on admission indicated ST-segment elevations in 71.1% of cases (95% CI 67.2â75.1%), accompanied by mild elevations of Troponins in 85.0% of cases (95% CI 80.8â89.1%). Despite the initial severity, left ventricular ejection fraction (LVEF) improved from 20â49.9 to 59â76% within a mean time of 7â37Â days. The in-hospital mortality rate was 1.7% (95% CI 0.5â2.8%), with complete recovery observed in 95.9% of cases (95% CI 93.8â98.1%) and rare recurrence. The underlying etiology is believed to involve exaggerated sympathetic stimulation. Conclusions TC should be considered as a significant differential diagnosis in acute coronary syndrome (ACS) cases, particularly among postmenopausal women with a preceding stressful event. Our study provides insights into the prevalence and characteristics of TC in the Palestinian population. While stress has been recognized as a potential trigger for TC, further research is needed to explore if there are specific associations between occupation and other unique stressors in the Palestinian context and the prevalence of TC. The studyâs results can raise awareness among healthcare professionals in Palestine about the prevalence and characteristics of TC in their patient population