Small intra-individual variability of the preejection period justifies the use of pulse transit time as approximation of the vascular transit

Background Vascular transit time (VTT) is the propagation time of a pulse wave through an artery; it is a measure for arterial stiffness. Because reliable non-invasive VTT measurements are difficult, as an alternative we measure pulse transit time (PTT). PTT is defined as the time between the R-wave on electrocardiogram and arrival of the resulting pulse wave in a distal location measured with photoplethysmography (PPG). The time between electrical activation of the ventricles and the resulting pulse wave after opening of the aortic valve is called the pre-ejection period (PEP), a component of PTT. The aim of this study was to estimate the variability of PEP at rest, to establish how accurate PTT is as approximation of VTT. Methods PTT was measured and PEP was assessed with echocardiography (gold standard) in three groups of 20 volunteers: 1) a control group without cardiovascular disease aged 50 years, and 3) a group with cardiovascular risk factors, defined as arterial hypertension, dyslipidemia, kidney failure and diabetes mellitus. Results Per group, the mean PEP was: 1) 58.5 ± 13.0 ms, 2) 52.4 ± 11.9 ms, and 3) 57.6 ± 11.6 ms. However, per individual the standard deviation was much smaller, i.e. 1) 2.0-5.9 ms, 2) 2.8-5.1 ms, and 3) 1.6-12.0 ms, respectively. There was no significant difference in the mean PEP of the 3 groups (p = 0.236). Conclusion In conclusion, the intra-individual variability of PEP is small. A change in PT

Non-invasive discrimination between diabetic states (HBA1C<8% and HBA1C>10%) using photoplethysmography

Diabetes mellitus is a group of metabolic diseases associated with the production and/or reaction of insulin leading to hyperglycemia. Glycated hemoglobin (HbA1c) level is generally measured for hyperglycemia. The risk of developing complications depends on both the duration of diabetes and hyperglycemia. A trend of increasing arterial stiffness has been identified in type 2 diabetes. Photoplethysmographic (PPG) pulse wave provides a ‘window’ into the properties of small arteries whereas stiffening of these arteries will alter the PPG waveform. In this research, the potential of PPG in discriminating between type 2 diabetic patients at risk of having HbA1c level > 10% has been investigated. To this end, PPG signals recorded from diabetic patients with different levels of HbA1c (HbA1c level 10%) were acquired from the index finger of the right arm of 101 subjects (53 subjects with HbA1c level 10%) at a sampling rate of 275 Hz. The area under the curve of PPG (auc-PPG) was proposed in analyzing the PPG pulse contour. Results of t-test analysis show that auc-PPG is significantly larger in diabetic patients with HbA1c level 10% (p-value 10% (total 56 subjects) show that there is no significant difference in the mean value of auc-PPG between the first measurement and repeated measurement for both groups. Finally, a logistic regression model for estimating the risk of having HbA1c level > 10% among diabetic patients was estimated using data from 51 female diabetic patients. The model shows that the auc-PPG is an independent predictor for estimating the risk of having HbA1c level > 10% (p-value = 0.005) among female diabetic patients

High-Performance Accelerometer Based On Asymmetric Gapped Cantilevers For Physiological Acoustic Sensing

Continuous or mobile monitoring of physiological sounds is expected to play important role in the emerging mobile healthcare field. Because of the miniature size, low cost, and easy installation, accelerometer is an excellent choice for continuous physiological acoustic signal monitoring. However, in order to capture the detailed information in the physiological signals for clinical diagnostic purpose, there are more demanding requirements on the sensitivity/noise performance of accelerometers. In this thesis, a unique piezoelectric accelerometer based on the asymmetric gapped cantilever which exhibits significantly improved sensitivity is extensively studied. A meso-scale prototype is developed for capturing the high quality cardio and respiratory sounds on healthy people as well as on heart failure patients. A cascaded gapped cantilever based accelerometer is also explored for low frequency vibration sensing applications such as ballistocardiogram monitoring. Finally, to address the power issues of wireless sensors such as wireless wearable health monitors, a wide band vibration energy harvester based on a folded gapped cantilever is developed and demonstrated on a ceiling air condition unit

Non-invasive blood pressure estimation based on electro/phonocardiogram

Ingeniero (a) ElectrónicoPregrad

The Speed of Waves : Measuring the velocity of pressure pulse waves traveling through peripheral blood vessels

Worldwide, cardiovascular diseases (CVDs) are the number one cause of death. Therefore, there is a strong and urgent need for an easy and quick prognostic indicator of this disease to support early diagnosis. The gold standard for determining arterial stiffness is measuring the pulse wave velocity (PWV), which is the speed of the pressure pulse traveling through the moving blood. The goal of this Ph.D. study was to develop and validate a non-invasive, photoplethysmography (PPG)-based device for peripheral measurement of the PWV on the finger. To this aim a novel sensor, called “Multi Photodiode Array” (‘MPA’), was designed for peripheral, non-invasive PWV measurements. Next, the MPA was shown to deliver reliable and accurate PWV measurements with a deviation below 3% within clinically relevant ranges. During the course of the research it was observed that the MPA positioning on the finger could strongly affect the quality of the PWV measurements. Therefore, an explorative study was conducted to find the optimal use condition of the MPA. The final clinical study showed that the MPA could be placed easily, rapidly, and consistently, irrespective of the volunteer whose PWV was measured, and delivered reliable and repeatable results. Overall, the results in this thesis suggest that the novel PPG-based MPA allows accurate and reliable PWV measurements within clinically relevant ranges. In the future, the MPA may substantially simplify PWV measurements and enable long-term monitoring of vascular health, which will contribute to improving prevention, diagnosis and treatment of CVD