Assessing hemodynamics from the photoplethysmogram to gain insights into vascular age: a review from VascAgeNet.

The photoplethysmogram (PPG) signal is widely measured by clinical and consumer devices, and it is emerging as a potential tool for assessing vascular age. The shape and timing of the PPG pulse wave are both influenced by normal vascular aging, changes in arterial stiffness and blood pressure, and atherosclerosis. This review summarizes research into assessing vascular age from the PPG. Three categories of approaches are described: 1) those which use a single PPG signal (based on pulse wave analysis), 2) those which use multiple PPG signals (such as pulse transit time measurement), and 3) those which use PPG and other signals (such as pulse arrival time measurement). Evidence is then presented on the performance, repeatability and reproducibility, and clinical utility of PPG-derived parameters of vascular age. Finally, the review outlines key directions for future research to realize the full potential of photoplethysmography for assessing vascular age.

Wave propagation through a viscous fluid-filled elastic tube under initial pressure: theoretical and biophysical model.

The velocity of propagation of pulse waves through the arteries is one of the indicators of the health of the cardiovascular system. By measuring the pulse wave velocity, cardiologists estimate the elasticity of the blood vessel walls and the changes that occur with aging. When the Moens-Korteweg equation is used in analysis, it leads to an erroneous assessment. This paper presents the solution of Navier-Stokes equations for propagation of pulse waves through an elastic tube filled with viscous fluid under initial pressure. The equation for pulse wave velocity depending on viscosity, density and initial fluid pressure, density and elasticity of the wall and geometry of the tube is derived. The results of the equation were compared with experimental results measured using a biophysical model of the cardiovascular system.

Biophysical modeling of wave propagation phenomena: experimental determination of pulse wave velocity in viscous fluid-filled elastic tubes in a gravitation field.

Biophysical understanding of arterial hemodynamics plays an important role in proper medical diagnosis and investigation of cardiovascular disease pathogens. One of the major cardiovascular parameters is pulse wave velocity (PWV), which depends on the mechanical properties of the arterial wall. The PWV contains information on the condition of the cardiovascular system as well as its physiological age. In humans and most animals, blood flow through the blood vessels is affected by several internal and external forces. The most influencing external force on blood flow is gravity. In the upright position of the body, blood moves from heart to head, opposite to gravity, and from the heart to the legs, in direction of the gravitational force. To investigate how gravity affects PWV, we have developed a biophysical model of cardiovascular system that simulates blood flow in the upright position of the body. The paper presents the results of measurement of PWV in an elastic tube filled with fluids of different viscosities in the gravitational field.

An improved design of optical sensor for long-term measurement of arterial blood flow waveform.

We present here the improved design and development of optical sensor for non-invasive measurements of arterial blood flow waveform. The sensor is based on a physical principle of reflective photoplethysmography (PPG). As the light source we used serially connected infrared diodes whereas NPN silicon phototransistors were used as light detectors. The electronic components were molded into square package and poured with silicone. Such preparation produced an elastic superficies that allowed excellent attachment of the sensor on the skin's surface. Moreover, a serial connection of infrared diodes and phototransistors completely eliminated signal artifacts caused by minor muscle contractions. The sensor recording performances were examined at the photoplethysmographic sites on three different arteries; the commune carotid, femoral and radial and, on each site the sensor demonstrated remarkable capability to make a consistent, reproducible measurements. Because of the advantageous physical and electrical properties, the new sensor is suitable for various cardiovascular diagnostics procedures, especially when long-term measurements of arterial blood flow waveform are required, for monitoring of different parameters in cardiovascular units and for research.

A mathematical model of pressure and flow waveforms in the aortic root.

The differences in the pressure and flow waveforms in the aortic root have not been explained so far in a satisfactory mathematical way. It is a generally accepted idea that the existence of the reflected wave causes the differences in shapes of pressure and flow. In this paper, a mathematical model is proposed that explains the blood pressure and flow waveforms based on changes in left ventricular volume during blood ejection into the aorta. According to the model, a change in volume of the left ventricle during contraction can be mathematically presented with solutions of differential equations that describe the behavior of a second-order system. The proposed mathematical equations of pressure and flow waveforms are derived from left ventricular volume change and basic equations of fluid dynamics. The position of the reflected wave depends on the age and elasticity of arteries, and has an effect on the flow and pressure waveforms. The model is in acceptable agreement with the experimental data available.

A novel laboratory approach for the demonstration of hemodynamic principles: the arterial blood flow reflection.

In the frame of a laboratory training course for medicine students, a new approach for laboratory exercises has been applied to teach the phenomena of circulation. The exercise program included measurements of radial artery blood flow waveform for different age groups using a noninvasive optical sensor. Arterial wave reflection was identified by measurements of blood flow waveforms before and after arterial branching. Students were able to distinguish between different waveforms of blood flow within different age groups. Furthermore, students were given the opportunity to explore the effect of aging on the elasticity of blood vessels. This exercise is an introduction to the fundamental physical laws of hemodynamics that can facilitate the learning and understanding of cardiovascular physiology to students of medicine.

Using the photoplethysmography method to monitor age-related changes in the cardiovascular system.

Introduction: Aging is a physiological process characterized by progressive changes in all organ systems. In the last few decades, the elderly population has been growing, so the scientific community is focusing on the investigation of the aging process, all in order to improve the quality of life in elderly. One of the biggest challenges in studying the impact of the aging on the human body represents the monitoring of the changes that inevitably occur in arterial blood vessels. Therefore, the medical community has invested a great deal of effort in studying and discovering new methods and tools that could be used to monitor the changes in arterial blood vessels caused by the aging process. The goal of our research was to develop a new diagnostic method using a photoplethysmographic sensor and to examine the impact of the aging process on the cardiovascular system in adults. Long-term recorded arterial blood flow waveforms were analyzed using detrended fluctuation analysis. Materials and Methods: The study included 117 respondents, aged 20-70 years. The waveform of the arterial blood flow was recorded for 5 min, with an optical sensor placed above the left common carotid artery, simultaneously with a single-channel ECG. For each cardiac cycle, the blood flow amplitude was determined, and a new time series was formed, which was analyzed non-linearly (DFA method). The values of the scalar coefficients α 1 and α 2, particularly their ratio (α 1/α 2) were obtained, which were then monitored in relation to the age of the subjects. Result: The values of the scalar ratio (α 1/α 2) were significantly different between the subjects older and younger than 50 years. The value of the α 1/α 2 decreased exponentially with the aging. In the population of middle-aged adults, this ratio had a value around 1, in young adults the value was exclusively higher than 1 and in older adults the value was exclusively lower than 1. Conclusion: The results of this study indicated that the aging led to a decrease in the α 1/α 2 in the population of healthy subjects. With this non-invasive method, changes in the cardiovascular system due to aging can be detected and monitored.

Effect of viscosity on the wave propagation: Experimental determination of compression and expansion pulse wave velocity in fluid-fill elastic tube.

The velocity by which the disturbance travels through the medium is the wave velocity. Pulse wave velocity is one of the main parameters in hemodynamics. The study of wave propagation through the fluid-fill elastic tube is of great importance for the proper biophysical understanding of the nature of blood flow through of cardiovascular system. The effect of viscosity on the pulse wave velocity is generally ignored. In this paper we present the results of experimental measurements of pulse wave velocity (PWV) of compression and expansion waves in elastic tube. The solutions with different density and viscosity were used in the experiment. Biophysical model of the circulatory flow is designed to perform measurements. Experimental results show that the PWV of the expansion waves is higher than the compression waves during the same experimental conditions. It was found that the change in viscosity causes a change of PWV for both waves. We found a relationship between PWV, fluid density and viscosity.

Sport-specific influences on respiratory patterns in elite athletes.

OBJECTIVE: To examine differences in lung function among sports that are of a similar nature and to determine which anthropometric/demographic characteristics correlate with lung volumes and flows. METHODS: This was a cross-sectional study involving elite male athletes (N = 150; mean age, 21  4 years) engaging in one of four different sports, classified according to the type and intensity of exercise involved. All athletes underwent full anthropometric assessment and pulmonary function testing (spirometry). RESULTS: Across all age groups and sport types, the elite athletes showed spirometric values that were significantly higher than the reference values. We found that the values for FVC, FEV1, vital capacity, and maximal voluntary ventilation were higher in water polo players than in players of the other sports evaluated (p < 0.001). In addition, PEF was significantly higher in basketball players than in handball players (p < 0.001). Most anthropometric/demographic parameters correlated significantly with the spirometric parameters evaluated. We found that BMI correlated positively with all of the spirometric parameters evaluated (p < 0.001), the strongest of those correlations being between BMI and maximal voluntary ventilation (r = 0.46; p < 0.001). Conversely, the percentage of body fat correlated negatively with all of the spirometric parameters evaluated, correlating most significantly with FEV1 (r = -0.386; p < 0.001). CONCLUSIONS: Our results suggest that the type of sport played has a significant impact on the physiological adaptation of the respiratory system. That knowledge is particularly important when athletes present with respiratory symptoms such as dyspnea, cough, and wheezing. Because sports medicine physicians use predicted (reference) values for spirometric parameters, the risk that the severity of restrictive disease or airway obstruction will be underestimated might be greater for athletes.

Sport-specific influences on respiratory patterns in elite athletes / Influências específicas do esporte nos padrões respiratórios em atletas de elite

ABSTRACT OBJECTIVE: To examine differences in lung function among sports that are of a similar nature and to determine which anthropometric/demographic characteristics correlate with lung volumes and flows. METHODS: This was a cross-sectional study involving elite male athletes (N = 150; mean age, 21  4 years) engaging in one of four different sports, classified according to the type and intensity of exercise involved. All athletes underwent full anthropometric assessment and pulmonary function testing (spirometry). RESULTS: Across all age groups and sport types, the elite athletes showed spirometric values that were significantly higher than the reference values. We found that the values for FVC, FEV1, vital capacity, and maximal voluntary ventilation were higher in water polo players than in players of the other sports evaluated (p < 0.001). In addition, PEF was significantly higher in basketball players than in handball players (p < 0.001). Most anthropometric/demographic parameters correlated significantly with the spirometric parameters evaluated. We found that BMI correlated positively with all of the spirometric parameters evaluated (p < 0.001), the strongest of those correlations being between BMI and maximal voluntary ventilation (r = 0.46; p < 0.001). Conversely, the percentage of body fat correlated negatively with all of the spirometric parameters evaluated, correlating most significantly with FEV1 (r = −0.386; p < 0.001). CONCLUSIONS: Our results suggest that the type of sport played has a significant impact on the physiological adaptation of the respiratory system. That knowledge is particularly important when athletes present with respiratory symptoms such as dyspnea, cough, and wheezing. Because sports medicine physicians use predicted (reference) values for spirometric parameters, the risk that the severity of restrictive disease or airway obstruction will be underestimated might be greater for athletes.

RESUMO OBJETIVO: Analisar as diferenças na função pulmonar em atletas praticantes de esportes de natureza semelhante e determinar quais características antropométricas/demográficas se correlacionam com os fluxos e volumes pulmonares. MÉTODOS: Estudo transversal com atletas de elite do sexo masculino (N = 150; média de idade de 21  4 anos), praticantes de um dos quatro esportes investigados. Os atletas foram classificados de acordo com o tipo e a intensidade de exercício relacionado ao esporte. Todos os atletas foram submetidos a antropometria completa e testes de função pulmonar (espirometria). RESULTADOS: Em todas as faixas etárias e tipos de esporte, os atletas de elite apresentaram valores espirométricos significativamente maiores que os valores de referência. Os valores de CVF, VEF1, capacidade vital e ventilação voluntária máxima foram maiores nos praticantes de polo aquático que nos praticantes dos outros esportes avaliados (p < 0,001). Além disso, o PFE foi significativamente maior em jogadores de basquete do que em jogadores de handebol (p < 0,001). A maioria dos parâmetros antropométricos/demográficos apresentou correlações positivas com os parâmetros espirométricos avaliados. O IMC se correlacionou positivamente com todos os parâmetros espirométricos avaliados (p < 0,001), sendo a correlação mais forte entre o IMC e a ventilação voluntária máxima (r = 0,46; p < 0,001). De forma contrária, o percentual de gordura corporal se correlacionou negativamente com todos os parâmetros espirométricos, mais significativamente com VEF1 (r = −0,386; p < 0,001). CONCLUSÕES: Nossos resultados sugerem que o tipo de esporte praticado tem um impacto significativo na adaptação fisiológica do sistema respiratório. Esse conhecimento é particularmente importante quando os atletas apresentam sintomas respiratórios tais como dispneia, tosse e sibilância. Visto que os especialistas em medicina do esporte utilizam valores previstos (de referência) para os parâmetros espirométricos, o risco de se subestimar a gravidade de doença restritiva ou obstrução de vias aéreas pode ser maior nos atletas.