Changes In Pressure Waveform Research Articles

Fault mechanism and dynamic two-phase flow behavior of liquid slugging in reciprocating compressors

Liquid slugging is a fatal fault for large process compressors, leading to transient overpressure, the deformation and fracture of vital pressure-bearing parts, and even gas leakage or explosion. In the study reported here, to reveal the mechanism of overpressure formation, numerical simulations were conducted by means of the volume-of-fluid method to explore the dynamic evolution characteristics of the two-phase flow pattern. Then, high-speed photography was applied to capture the dynamic changes of the liquid boundary in the modified cylinder from different views, thus realizing the validation of the numerical model. This study reveals the significant influence of increased rotational speed on fluid flow patterns, impeding liquid discharge and exacerbating overpressure events. Additionally, changes in pressure waveform and a distinctive waveform feature were identified as effective diagnostic indicators for detecting fluid slugging. Next, a nondestructive pressure monitoring reconstruction method based on measuring bolt strain was proposed. The strain-based pressure showed good agreement with the simulated results, thereby validating its effectiveness and feasibility as an early warning indicator for liquid slugging. This study offers new perspectives on the failure mechanism of liquid slugging in reciprocating compressors by delving into the behavior of two-phase flow, with the potential to enhance the theoretical foundation of compressor condition monitoring and fault diagnosis.

Retraction: Intracranial pressure waveform changes in Alzheimer's disease and mild cognitive impairment.

Background Alzheimer's disease (AD) is known to cause an enormous impairment to the quality of life and impact in the health system; meanwhile, studies show that in the coming years, the number of affected individuals will continue to grow. It is also believed that amnestic mild cognitive impairment (MCI) could represent an early symptomatic form of AD, which precedes dementia. Methods The present study aimed to evaluate the intracranial pressure (ICP) through a noninvasive method in patients with AD and MCI, seeking for differences when compared to healthy elderlies. This is a cross-sectional, correlational, and observational study of a quantitative character, carried out in a Brazilian city, with patients from the ANEC of the UFSCar. Results It was found a statistically significant difference between the ICP morphology when analyzing the results in patients with AD and MCI, compared to healthy volunteers. It is known that dementias means a progressive disorder that leads to the loss of independency and function of the patient, although, it is believed that it can be found early ICP alterations in these patients. Nevertheless, considering this is an unprecedent study, it was not possible to compare results with previous studies and literatures. However, the study has a limitation related to the sample size; an expansion of it could possibility lead to different findings. Conclusion The findings through the ICP measurement could indicate an early diagnosis, which would lead to an early treatment and an improvement in the quality of life of patients with AD. Thus, further investigation and widening studies are encouraged.

Intracranial pressure waveform changes in Alzheimer’s disease and mild cognitive impairment

Background: Alzheimer’s disease (AD) is known to cause an enormous impairment to the quality of life and impact in the health system; meanwhile, studies show that in the coming years, the number of affected individuals will continue to grow. It is also believed that amnestic mild cognitive impairment (MCI) could represent an early symptomatic form of AD, which precedes dementia.Methods: The present study aimed to evaluate the intracranial pressure (ICP) through a noninvasive method in patients with AD and MCI, seeking for differences when compared to healthy elderlies. This is a cross-sectional, correlational, and observational study of a quantitative character, carried out in a Brazilian city, with patients from the ANEC of the UFSCar.Results: It was found a statistically significant difference between the ICP morphology when analyzing the results in patients with AD and MCI, compared to healthy volunteers. It is known that dementias means a progressive disorder that leads to the loss of independency and function of the patient, although, it is believed that it can be found early ICP alterations in these patients. Nevertheless, considering this is an unprecedent study, it was not possible to compare results with previous studies and literatures. However, the study has a limitation related to the sample size; an expansion of it could possibility lead to different findings.Conclusion: The findings through the ICP measurement could indicate an early diagnosis, which would lead to an early treatment and an improvement in the quality of life of patients with AD. Thus, further investigation and widening studies are encouraged.

Monitoring of Pulse Pressure and Arterial Pressure Waveform Changes during the Valsalva Maneuver by a Portable Ultrasound System.

This work presents non-invasive evaluation of the arterial blood pressure (ABP) waveform during the Valsalva maneuver. Ultrasound scanning is conducted to acquire blood flow and arterial distension signals. Motion-tolerant ultrasound measurement schemes are employed by using two wide rectangular transducers. Pulse pressure (PP) estimated at the common carotid artery is compared to that of a finger waveform measured by a volume clamping device. The changes of PP are correlated between the two measurements. A more depressed dicrotic notch during the Valsalva strain is observed, and beat-to-beat variations of PP and a pulse rate caused by respiration and baroreflex is observed during the control. This validation suggests novel opportunities to investigate the pathophysiology of cardiovascular diseases through the noninvasive ABP waveform monitoring during the stress test.

Sheath placement in femoral artery during cardiac catheterization in children can influence pressure waveform

IntroductionIt is reported that pressure wave reflection is enhanced by external compression of the femoral artery. Therefore, it is possible that cardiac catheterization itself can influence the aortic pressure waveform. AimThe purpose of this study is to clarify the influence of sheath placement in a femoral artery on the pressure waveform. MethodsThis study enrolled 21 pediatric patients (5.1±4.0years) who underwent cardiac catheterization. A sheath was placed in the femoral arteries of all patients. The change in the pressure waveform induced by the placement of the sheath was investigated using the b/a and d/a ratio of second derivative of a fingertip photoplethysmogram. A high b/a ratio means a stiff aorta and a low d/a ratio represents an enhancement of the aortic pressure wave reflection. ResultsBy the placement of the sheath in their femoral arteries, the b/a ratio was not influenced (sheath (−): −0.556±0.081 vs. sheath (+): −0.558±0.072; p=0.896). However, the d/a ratio was significantly decreased (−0.150±0.074 vs. −0.185±0.084; p=0.0003). ConclusionsThe placement of the femoral arterial sheath enhances the pressure wave reflection and would lead to a change in the central aortic pressure waveform.

The mathematical model of the radial artery blood pressure waveform through monitoring of the age-related changes

Age-related changes in blood vessels affect the pulse wave propagation. These changes may cause an increase in wave reflection which leads to amplification of pulse pressure. The pulse pressure changes are associated with certain vascular diseases. Here we present a mathematical model of blood pressure for different age groups. The model is based on one-dimensional wave propagation theory and assumes that the pressure waveform is a superposition of forward propagating wave and backward waves from many reflection sites. The model is based on experimental data obtained by direct measurement of radial artery blood flow. The model clearly shows age-related changes in blood pressure waveform. The results of mathematical model correlate with the radial pressure waveform data. The model can be used in cases where it is not possible to measure the pressure due to movement of subject. Application of model to the direct blood flow measurements data allows the real-time pressure waveform monitoring. Furthermore, this approach enables monitoring of changes in pressure waveform due to the effects of medications.

Cryoballoon pressure waveform change during balloon inflation is not a reliable predictor of adequate pulmonary vein occlusion.

Cryoballoon ablation of pulmonary veins (PVs) is widely used to treat atrial fibrillation (AF). Successful ablation requires occluding the PVs by cryoballoon. Angiography is a standard method of assessing PV occlusion. To decrease contrast doses and overcome potential contraindications (e.g., allergy to contrast, renal disease), alternative methods have been tested, including intracardiac echocardiography, transesophageal echocardiography-color flow Doppler, and distal cryoballoon pressure monitoring. We evaluated pressure monitoring’s accuracy in detecting PV occlusion during cryoballoon ablation. We studied 72 PVs in 18 nonconsecutive patients (mean age 68 ± 8 years; 13 male) who underwent cryoballoon ablation for paroxysmal AF. In 67 PVs, we documented the point at which the recorded pressure waveform at the distal tip of the inflated cryoballoon transformed from a left atrial into a pulmonary arterial pressure waveform. PV occlusion was confirmed by concurrent PV angiography through the distal balloon channel. Occlusion was rated on a I–IV scale in which I indicated poor occlusion with major leakage and IV indicated complete occlusion without leakage. In 43 of 67 PVs (64%), the change in the pressure waveform from left atrial to pulmonary arterial was associated with complete PV occlusion (grade IV), confirmed by angiography. In the other 24 PVs, complete occlusion was achieved by further movement of the cryoballoon under intracardiac echocardiographic guidance and angiographic confirmation. All 67 PVs were electrically isolated with cryoballoon. The change in pressure waveforms at the distal tip of inflated cryoballoon is not a reliable predictor of complete PV occlusion during cryoballoon ablation.

Reflecting on posture

Cardiovascular parameters are most often assessed at rest, and in many cases in the supine position. This generally facilitates measurement procedures and obviates the need to account for external and usually complex confounding factors, other than those related to the inherent physiology being investigated. Although the supine resting position may be relevant for some part of circadian living, a large part of human activity is characterized by locomotion and the upright posture. Physiological adaptations to locomotion are studied under controlled conditions and at varying degrees of exercise. However, although primary measures of basic physiological quantities (e.g. stroke volume) can be obtained with some level of confidence at rest in supine position, it becomes extremely difficult to measure them during exercise, and so they are generally derived from other measurable quantities, with the associated errors. Notwithstanding this, the large body of work done so far on the physiological response to exercise has been extremely beneficial in elucidating both underlying and adaptive mechanisms for the function of the circulatory system. On the other hand, assessment of the changes occurring in cardiovascular variables when shifting from supine to standing is the procedure most commonly adopted to explore the response of cardiovascular control mechanisms to gravitational challenges, both when investigating physiological adaptations to the upright posture in healthy individuals and when assessing alterations in cardiovascular regulation in patients with a variety of diseases.

Inadvertent arterial insertion of a central venous catheter: delayed recognition with abrupt changes in pressure waveform during surgery -A case report-

We present a case of inadvertent arterial insertion of a central venous catheter, identified during a pericardiectomy procedure after observing abrupt changes in pressure waveform and confirmed via arterial blood gas analysis and transesophageal echocardiography. Central venous pressure measurement was initially 20 mmHg in supine, and then elevated to 30-40 mmHg in right lateral decubitus, presumably resulting from constrictive physiology of pericarditis. The pressure waveforms, however, abruptly changed from a venous to an arterial waveform during surgery. When visual discrimination between arterial and venous blood regurgitation is unreliable, anesthesiologists should confirm that using all the available methods one has on the scene, especially after at least two unsuccessful attempts or in patients with advanced age or clinical conditions resulting in jugular venous dilation. To prevent arterial catheterization, one should limit the leftward rotation of the head by <40° and consider using ultrasound-guided method after more than two unsuccessful attempts.

Cardiac output by thermodilution and the MostCare system in patients on intra-aortic balloon pump

The intra-aortic balloon pump (IABP) is a device used to help the heart pump. During the IABP assistance, significant changes in arterial pressure waveform occur. The so-called pulse contour methods (PCMs) use proper algorithms to analyse the arterial pressure waveform and obtain the cardiac output (CO) [1]. As a consequence, changes in pressure waveform in patients on IABP may affect the reliability of different PCMs. The aim of this study was to investigated the reliability of a new PCM, the MostCare powered by the pressure recording analytical method (PRAM) (Vytech Health, Laboratoires Pharmaceutiques Vygon, Ecouen, France), by comparing its CO values (PRAM-CO) with those determined by bolus thermodilution (ThD-CO) during aortic counterpulsation.

Importance of the aortic reservoir in determining the shape of the arterial pressure waveform – The forgotten lessons of Frank

Summary It has been recognised for nearly 200 years that the human pressure waveform changes in shape with ageing and disease. The shape of the pressure waveform has been explained in terms of two fundamental models: the Windkessel (reservoir) and wave theory. In its simplest form the Windkessel model satisfactorily explains the pressure waveform in diastole but cannot model pressure changes in systole. Wave theory satisfactorily models the pressure waveform but predicts the existence of ‘self-cancelling’ forward and backward waves in diastole which are difficult to explain in biological terms. We propose that a hybrid reservoire wave model better describes the pressure waveform and may enable assessment of aortic function from pressure measurements made at any large systemic artery. a 2007 Published by Elsevier B.V. on behalf of Association for Research into Arterial Structure and Physiology.

Analysis of the arterial blood pressure waveform during left ventricular nonpulsatile assistance in animal models.

When the rotary blood pump is used as a left ventricular assist device (LVAD), the arterial blood pressure waveform changes with the LVAD condition. Based on evidence from an in vitro study, the change of the arterial blood pressure waveform during left ventricular assistance was evaluated using animal models. After the left pleural cavity was opened through the fifth intercostal space under general anesthesia, a rotary blood pump was implanted as an LVAD into 6 healthy calves. The direct left carotid arterial blood pressure waveform was measured and recorded by an oscilloscope. The Fast Fourier Transform technique was utilized to analyze the arterial blood pressure waveform and calculate the pulsatility index (PI) and the pulse power index (PPI). Similar to the in vitro study, the PI and PPI decreased exponentially with the increase of the LVAD assist ratio. By using this analysis methodology, a physiologically effective ventricular assistance might be achieved.

Ventriculo-atrial shunt insertion: pressure monitoring as an aid to accurate placement

The objective of this paper is to describe a new method to ensure accurate placement of a ventriculo-atrial shunt distal catheter. A technique is described using pressure waveform changes within the right side of the heart. Pressure monitoring is a new method of placing atrial catheters and is easy to perform.

Effects of reconstructive surgery for left ventricular anterior aneurysm on ventriculoarterial coupling

ObjectiveTo investigate left ventricular elastance (Emax) and effective arterial elastance (Ea) in postinfarction left ventricular aneurysm and evaluate their role in left ventricular function improvement after endoventricular circular patch plasty...

Thermoregulatory vasoconstriction increases the difference between femoral and radial arterial pressures.

Thermoregulatory vasoconstriction locally increases arterial wall tension and arteriolar resistance, thereby altering physical properties of the arteries. The arterial pressure waveform is an oscillatory phenomenon related to those physical characteristics; accordingly, we studied the effects of thermoregulatory vasomotion on central and distal arterial pressures, using three hydraulic coupling systems having different dynamic responses. We studied 7 healthy volunteers. Central arterial pressure was measured from the femoral artery and distal pressure was measured from the radial artery, using 10.8-cm long, 20-gauge catheters. Three hydraulic coupling systems were used: (1) a 10-cm-long, 2-mm internal diameter connector; (2) a 150-cm-long, 1-mm internal diameter connector (Combidyn 520-5689, B. Braun, Melsungen, Germany); (3) a 180-cm long, 2-mm internal diameter connector (Medex MX564 and MX562, Medex Inc., Hillard, OH). Brachial artery pressure was measured oscillometrically. Core temperature was measured at the tympanic membrane. The vasomotor index, defined as finger temperature minus room temperature, divided by core temperature minus room temperature, was used to estimate the degree of vasoconstriction. Constriction was considered near maximal when the index was less than 0.1, and minimal when it exceeded 0.75. Measurements were taken every 3 min. Baseline readings were obtained when subjects were warm. They then were cooled by exposure to 20 degrees C to 22 degrees C room air and a circulating-water mattress set at 4 degrees C until index was less than 0.1. They then were rewarmed by increasing water temperature to 42 degrees C and adding a forced-air warmer until the vasomotor index exceeded 0.75. Data were analyzed by ANOVA and linear regression. Thermoregulatory vasoconstriction was associated with marked arterial pressure waveform changes. Radial pressure showed, in lieu of a dicrotic notch, large oscillations of decreasing amplitude. Femoral pressure showed a single diastolic oscillation of smaller amplitude. The waveforms appeared different, depending on the hydraulic coupling system used, artifact being more marked with the longer connectors. On the average, radial systolic pressure exceeded femoral systolic pressure during vasoconstriction; however, during vasodilatation, femoral systolic pressure exceeded radial systolic pressure (p < 0.05). Oscillometric measurements underestimated systolic pressure, and did so more markedly during vasoconstriction. There were no differences in the values of mean and diastolic pressures. Thermoregulatory vasoconstriction alters radial arterial pressure waveform, artifactually increasing its peak systolic pressure compared with the femoral artery. Poor dynamic responses of recording systems further distort the waveforms. Consequently, radial artery pressure may be misleading in vasoconstricted patients.

Unsteady blade pressures on a propfan - Predicted and measured compressibility effects

The effect of compressibility on unsteady blade pressures is studied by solving the 3D Euler equations. The operation of the eight-bladed SR7L propfan at 4.75 deg angle of attack was considered. Euler solutions were obtained for three Mach numbers, 0.6, 0.7, and 0.8 and the predicted blade pressure waveforms were compared with flight data. In general, the effect of Mach number on pressure waveforms are correctly predicted. The change in pressure waveforms are minimal when the Mach number is increased from 0.6 to 0.7. Increasing the Mach number from 0.7 to 0.8 produces significant changes in predicted pressure levels. The predicted amplitudes, however, differ from measurements at some transducer locations. Also the predicted appearance of a shock in the highly loaded portion of the blade revolution is not indicated by the measurements. At all the three Mach numbers, the measured (installed propfan) pressure waveforms show a relative phase lag compared to the computed (propfan alone) waveforms due to installation effects. Measured waveforms in the blade tip region show nonlinear variations which are not captured by the present numerical procedure.

Doppler waveform pulsatility index and resistance, pressure and flow in the umbilical placental circulation: An investigation using a mathematical model

A mathematical model of the umbilical placental circulation was used to examine the effect of different physiological variables on the pulsatility index (PI) of the umbilical artery Doppler waveform. The variables include the umbilical and placental resistances, the volume flow rate and the pressure. In the model the branching structure of the placental villous tree is considered in detail, while each arterial branch is itself represented simply using a resistor and a capacitor. Placental vascular disease is modelled as obliteration of a fraction of the terminal branches of the tree. The model umbilical artery PI depends on the ratio of the placental resistance to the umbilical artery resistance. The PI increases with vascular disease, but the rate of increase is not uniform. Initially, the placental resistance and the PI increase very slowly with vessel obliteration. Once the level of vessel obliteration has reached a large enough value--typically between 60% and 90% obliteration--the PI begins to rise sharply. A larger placental vascular bed can accommodate a greater level of vessel obliteration before this rapid PI rise begins. The umbilical artery PI also depends on the pulsatility of the input (aortic bifurcation) pressure waveform, but blood pressure variations in the physically attainable range cannot account for the very high PI values associated with fetal compromise. Physically attainable pressure waveform changes would, however, enable the fetus with substantial placental vascular disease to maintain umbilical volume flow rate, and at the same time exhibit a raised umbilical artery PI value.

Performance of respirators at fast rates commonly used in neonatal intensive care units.

The effect on tidal volume and airway pressure of increasing ventilator rate (30, 60, and 120/min) was tested in six commonly used neonatal ventilators. In all six ventilators increased flow was necessary to maintain mean airway pressure at the higher rates. Tidal volume decreased at rates of both 60 and 120/min in all six ventilators, associated with a change in pressure waveform. The most marked reduction in tidal volume, however, was associated with increased positive end-expiratory pressure (PEEP). This was only demonstrated in four ventilators, all incorporating nonassisted expiratory valves. These results stress the necessity for appropriately designed ventilators if fast rates are to be used routinely in clinical practice.