Cardiovascular Engineering (dordrecht, Netherlands)最新文献

To investigate patterns of cardiovascular control, a protocol of head up tilt (HUT) followed by lower body negative pressure (LBNP), which represents a significant cardiovascular control challenge, was employed. Linear regression of beat-to-beat heart rate (HR) and mean blood pressure (MBP) data collected over repeated tests was used to analyze control response during the LBNP phase of the combined HUT + LBNP protocol. Four runs for each of 10 healthy young males reaching presyncope were analyzed. Subjects were classified into 2 groups based on the consistency of MBP regulation in response to central hypovolemia induced by LBNP. The consistent group tended to exhibit consistent HR slope (rate of change of HR over time as calculated by linear regression) whereas subjects in the inconsistent group could not be easily classified. Subjects with consistent MBP maintenance exhibited patterns suggesting a consistency of response in cardiovascular control whereas subjects less successful in maintaining MBP exhibited less clearly defined patterns over four runs.

Reversible left ventricular failure was produced in conscious dogs by compromise of the coronary circulation. In animals with prior left anterior descending coronary artery occlusion, mean left atrial pressure (LAP) was incorporated into an automatic feedback control system used to inflate a balloon cuff on the circumflex (Cfx) coronary artery. The system could produce stable increases in LAP to 15-20 mm Hg. The dominating system transfer function was the ratio of LAP to balloon volume (BV), which was characterized by a fixed delay (5 s), with LAP/BV = (8e(-jomegatau ))/(0.02 + jomega). The system was stabilized by a phase lead network to reduce oscillations of LAP. A total of seven experiments were conducted in three dogs, and testing of inotropic agents was possible in three experiments under stable conditions with the pump off after an hour or more of operation. Problems encountered were 0.003-0.008 Hz oscillations in LAP in three experiments, which could usually be controlled by reducing the system gain. Late stage ventricular fibrillation occurred in all three animals, but defibrillation was easily accomplished after deflating the Cfx balloon. This system produces reversible left ventricular failure solely due to ischemia, thus closely simulating clinical heart failure due to coronary insufficiency.

A new method to predict acute hypotensive episodes (AHE) is proposed in this paper. The AHE is defined as any period of 30 min or more during which at least 90% of mean arterial pressure (MAP) measurements are below 60 mmHg. Since arterial pressure has a direct correlation with heart rate through heart rate (HR) baroreflex and cardiovascular systems, any changes in MAP, directly affect HR and vice versa. Predicting HR using our developed model, the periods in which HR drops to the values less than 40 beat/min are detected. The demonstrated AHE data for twenty patients are picked to validate the proposed algorithm. Results show that the proposed method could truly predict occurrence of the AHE in 17 out of 20 cases analyzed. Results show reliable accuracy in predicting AHE in these patients.

Right ventricular (RV) afterload is a key determinant of RV function and is increased in many cardiopulmonary pathologies. Pulmonary circulation input impedance has been used to quantify afterload previously but due to its complexity has not been widely applied. This study examines the effect of a subset of the impedance spectrum, the zeroth and first harmonic impedance moduli (Z (0), Z (1)), on RV performance in large animals. An artificial circuit with adjustable resistance and compliance (C) was implanted into the pulmonary circulation of five sheep. Resistance was varied to increase Z (0) in increments of 2 mmHg/(L/min) until Z (0) was 8 mmHg/(L/min) above baseline. At each Z (0), C was adjusted between 0, 0.5 and 2 mL/mmHg or 0, 1, and 5 mL/mmHg. Fourier transforms of the pulmonary artery pressure and flow in each situation were used to calculate the pulmonary impedance. Results show that the percent change in cardiac output (%DeltaCO) is linearly related to the change in Z (0) (DeltaZ (0)). Increases in Z (1) (DeltaZ (1)) decreased %DeltaCO but to a much smaller degree, with the effect of DeltaZ (1) increasing with DeltaZ (0). Regression of these results produce the equation: %DeltaCO = (-0.0829DeltaZ (1) - 3.65)DeltaZ (0) - 9.02 (R (2) = 0.69). Blood flow and pressure moduli are small at harmonics higher than the first and are unlikely to affect RV function. Therefore, during acute, high afterload states, Z (0) is the primary determinant of CO, while the effect of Z (1) is minor.

Measuring heart rate variability (HRV) is widely used to assess autonomic nervous system function. It requires accurate measurement of the interval between successive heartbeats. This can be achieved from recording the electrocardiogram (ECG), which is non-invasive and widely available. However, methodological problems inherent in recording and analyzing ECG traces have motivated a search for alternative means of measuring the interval between successive heartbeats. Recording blood oxygenation pulsations (photoplethysmography-PPG) is also convenient, non-invasive and widely available, and has been suggested as an effective alternative to ECG to derive HRV. Moreover, it has been claimed that the pulse waveforms produced by oximetry may be more practicable than R-R intervals measured from the by ECG, especially for ambulatory recordings. We have therefore compared PPG with ECG recordings to measure HRV applying the same signal analysis techniques to PPG and ECG recordings made simultaneously. Comparison of 5 min recording epochs demonstrated a very high degree of correlation, in temporal, frequency domains and non-linear analysis, between HRV measures derived from the PPG and ECG. However, we found that the PPG signal is especially vulnerable to motion artifacts when compared to the ECG, preventing any HRV analysis at all in a significant minority of PPG recordings. Our results demonstrate that even though PPG provides accurate interpulse intervals to measure heart rate variability under ideal conditions, it is less reliable due to its vulnerability to motion artifacts. Therefore it is unlikely to prove a practical alternative to the ECG in ambulatory recordings or recordings made during other activities.

The aim of the present study was to investigate, whether pulse transit time (PTT), a popular index of arterial stiffness at rest, can be also used as such, during steady state exercise. For this purpose, twelve male volunteers exercised on a cycle ergometer for 70 min on three separate occasions whereas, cycling cadence and workload were manipulated in order to produce diverse cardiorespiratory responses. PTT, blood pressure, cardiac output and respiratory frequency were measured during exercise. Resistance to systole and total peripheral resistance were calculated by the ratio of systolic pressure, and mean arterial pressure over cardiac output, respectively. All subjects across all conditions, showed a negative linear correlation (P < 0.01) between changes in PTT and systolic pressure (SP) (r = -0.66), changes in cardiac output (r = -0.76), and respiratory frequency (r = -0.40), whereas PTT was positively correlated (P < 0.05) with total peripheral resistance (r = 0.31), the SP to cardiac output ratio (r = 0.30) and plasma volume changes (r = 0.29). However, forward stepwise multiple regression analysis revealed that 71% (P < 0.001) of PTT changes from rest (DeltaPTT) variability was attributed to changes in cardiac output, SP and SP to cardiac output ratio. In the same model, total peripheral resistance did not exert significant influence on DeltaPTT variability. In conclusion, PTT is a reflection not only of SP but also of cardiac output changes per se and in combination with cardiac output (SP to cardiac output ratio) and should not be used as a pure marker of arterial stiffness under marked exercise cardiovascular and respiratory perturbations.

A powerful alternative means to studying hemodynamics in diseased or healthy coronary arteries can be achieved by providing a numerical model in which blood flow can be virtually simulated, for instance, using the computational fluid dynamics (CFD) method. In fact, it is well documented that CFD allows reliable physiological blood flow simulation and measurements of flow parameters. A requisite for obtaining reliable results from coronary CFD is to use exact anatomical models and realistic boundary conditions. To date, in almost all of the modeling studies on hemodynamics of stenosed coronary arteries, a velocity based boundary conditions has been assigned. The objective of this study is to show that inlet velocity actually depends on the degree of stenosis and thus for severe constriction in coronary artery, a velocity based boundary conditions cannot be realistic. We then prove that regardless of severity of stenosis in coronary arteries, the upstream pressure, systemic pressure, is always constant, thus, should be used as boundary conditions instead. The two sets of boundary conditions are implemented to demonstrate the robustness of each in modeling of stenosed coronary artery in a CFD study. These boundary conditions are applied in a stenosed cylindrical pipe including three categories of symmetrical stenosis (mild, moderate and severe stenosis starting from 15 to 95% diameter reduction) for steady state and pulsatile flow. Results strongly indicate that inlet velocity boundary conditions are no longer valid when effective diameter in stenosis goes below approximately 2.8 mm (a healthy diameter is considered 3.2 mm) which corresponds to 10-15% diameter reduction. Further work will determine the effect of flow reduction on the oxygen tension in blood to better define conditions for clinical symptoms such as angina.

The purpose of the study was to asses the potential use of pulse wave velocity (PWV) and digital volume pulse (DVP) as estimators of systolic (SBP) and diastolic (DPB) blood pressure. Single and multiple correlation studies were conducted, including biometric parameters and risk factors. Brachial-ankle PWV (baPWV) and DVP signals were obtained from a Pulse Trace PWV and Pulse Trace PCA (pulse contour analysis), respectively. The DVP (obtained by photoplethysmography), allowed stiffness (SI) and reflection indexes (RI) to be derived. The first study on 47 healthy volunteers showed that both SBP and DPB correlated significantly both with baPWV and SI. Multiple regression models of the baPWV and the waist-to-hip ratio (WHR) allowed SBP and DBP to be modeled with r = 0.838 and r = 0.673, respectively. SI results also employed WHR and modeled SBP and DBP with r = 0.852 and r = 0.663, respectively. RI did not correlate either with SBP or DBP. In order to avoid the use of ultrasound techniques to measure PWV, we then developed a custom-built system to measure PWV by photoplethysmography and validated it against the Pulse Trace. With the same equipment we conducted a second pilot study with ten healthy volunteers. The best SBP multiple regression model for SBP achieved r = 0.997 by considering the heart-finger PWV (hfPWV measured between R-wave and index finger), WHR and heart rate. Only WHR was significant in the DBP model. Our findings suggest that the hfPWV photoplethysmography signal could be a reliable estimator of approximate SBP and could be used, for example, to monitor cardiac patients during physical exercise sessions in cardiac rehabilitation.

Coronary perfusion pressure (CPP) is a major indicator of the effectiveness of cardiopulmonary resuscitation in human and animal research studies, however, methods for calculating CPP differ among research groups. Here we compare the 6 published methods for calculating CPP using the same data set of aortic (Ao) and right atrial (RA) blood pressures. CPP was computed using each of the 6 calculation methods in an anesthetized pig model, instrumented with catheters with Cobe pressure transducers. Aortic and right atrial pressures were recorded continuously during electrically induced ventricular fibrillation and standard AHA CPR. CPP calculated from the same raw data set by the 6 calculation methods ranged from -1 (signifying retrograde blood flow) to 26 mmHg (mean +/- SD of 15 +/- 11 mmHg). The CPP achieved by standard closed chest CPR is typically reported as 10-20 mmHg. Within a single study the CPP values may be comparable; however, the CPP values for different studies may not be a reliable indicator of the efficacy of a given CPR method. Electronically derived true mean coronary perfusion pressure is arguably the gold standard method for representing coronary perfusion pressure.

In this study, an analysis of the effects of cuff looseness on mean blood pressure readings was performed. Using a standard adult blood pressure cuff, pressure readings were taken on each arm at a cuff looseness of 0, 2, 4, and 6 cm beyond patient arm circumference. The cuff was then switched to the opposite arm and the procedure repeated. Blood pressure readings taken from the left arm with the cuff at an appropriately snug fit served as the reference. Increasing cuff looseness simulates the possibly incorrect blood pressure cuff placement by health care workers in the clinical setting. Data from 24 subjects support the claims that mean blood pressure increases with respect to increasing cuff looseness. It was shown that measurements taken on left and right arms will result in significantly different blood pressure readings (p < 0.001). It is therefore crucial to properly place the cuff at a snug fit on the patient's arm for each measurement procedure, to prevent false readings. Lack of consistent cuff size and snugness procedures can lead to misdiagnosis of hypertension, acute patient discomfort, and inconvenient costs to the patient and health care provider.