Nonpulsatile Flow Research Articles

Uterine Arteriovenous Malformation

We aimed to report a case of uterine arteriovenous malformation (UAVM) which was successfully treated by uterine artery embolization.A multiparous 23-year-old woman referred to our clinic for 7 weeks scar pregnancy. On ultrasound, incisional 32×37 mm gestational sac surrounded with non-pulsatile high flow vessels was demonstrated. Uterine artery embolization was performed with Gelfoam by interventional radiology. The post-embolization arteriogram showed complete embolization of the UAVM with slow flow of contrast in both uterine arteries.In clinical suspicion, UAVM can be diagnosed with Doppler ultrasonography and can be treated successfully with either uterine artery embolization or uterine surgery. UAVM is commonly diagnosed in women of childbearing age, angiographic embolization should be the firstly preferred treatment.

Vascular Contributions to Intracranial Hemodynamic Pulsatility and Pulsatile Dampening in Adults

The brain is a high‐flow organ that requires continuous, non‐pulsatile blood flow. Intracranial blood flow pulsatility depends on the ability of the large elastic arteries and cerebrovasculature to dampen pulsatile hemodynamics transmitted from the heart. Aging is accompanied by large artery stiffening and reductions in cerebrovascular dampening, ultimately increasing intracranial pulsatility. It is unclear what hemodynamic forces may be responsible for these age‐related changes in the transmission and dampening of intracranial pulsatility across the lifespan. The purpose of this study was to explore hemodynamic contributors to intracranial pulsatility and pulsatile dampening in 244 adults between 35–85 yr (49% female, 56±12 yr, 27±4.2 kg/m2). Intracranial pulsatile dampening was calculated as the ratio between common carotid and middle cerebral artery (MCA) blood velocity pulsatility index (PI) measured via Doppler. Carotid ultrasound and wave intensity analysis were used to measure carotid diameter, forward compression wave energy (W1), wave reflection index (RIx), and forward traveling expansion wave (W2). Aortic (carotid‐femoral) and carotid pulse wave velocity (PWV) were assessed via tonometry and carotid ultrasound, respectively, and expressed as a ratio (aortic:carotid PWV). Carotid pulse pressure (PP) was measured via tonometry. Multiple regression was used to examine the contributions of 1) age, sex, BMI, aortic:carotid PWV, carotid diameter, PP, and W1 to intracranial pulsatility (MCA PI); and 2) age, sex, BMI, aortic:carotid PWV, carotid diameter, RIx, and W2 to intracranial pulsatile dampening. After entering all variables, significant predictors of MCA PI included age (β,0.44), aortic:carotid PWV (β,0.16), PP (β,0.29), and W1 (β,0.20; R2=0.50, p<0.01). Significant predictors of intracranial pulsatile dampening included age (β,−0.47), sex (β,−0.43), and RIx (β,0.26; R2=0.53, p<0.01). Our data confirms recent literature linking age, exaggerated stiffening of the aorta compared to carotid artery, and extracranial hemodynamics to intracranial pulsatility in the MCA. Moreover, our findings indicate age, sex, and wave reflections in the carotid artery impact the ability of the cerebrovasculature to dampen transmission of pulsatile hemodynamics. These data highlight the potential utility of the large extracranial arteries as therapeutic targets to reduce intracranial pulsatility and importance of carotid wave reflections in dampening intracranial pulsatility.Support or Funding InformationFunded in part by an ACSM Foundation Research Grant (WKL), AHA Predoctoral Fellowship (WKL), and Dairy Research Institute/Dairy management Inc. Grant 1154 (KSH).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Strokes in LVADS. Insights from Modelling Flow in the Circle of Willis

Purpose Strokes are a serious complication of LVADs and are especially known to occur with hypertension. Hypoperfusion of the innominate artery has been described in LVADS, especially in smaller diameter outflow grafts. (1) The normal circle of Willis is often incomplete and Hypoplasia of the posterior communicating artery is a common variant. Modelling flow in the circle of Willis may shed light on strokes in LVADS ( 1) Effect of Outflow Graft Size on Flow in the Aortic Arch and Cerebral Blood Flow in Continuous Flow Pumps: Possible Relevance to Strokes.ASAIO 63:2,144-149 Methods The arterial pulse wave propagation model was used to compare pressure and flow in the circle of Willis for 1.Normal pulsatile and nonpulsatile flow at 5 litres per minute 2. varying degrees of pulsatility in LVADS 3.Flow in the right and left cerebral arteries when the right carotid artery is having no flow, with and without a patent right posterior communicating artery Results The mean pressure in all the vessels is significantly higher for a non pulsatile compared to a pulsatile flow . Mean pressures are lower with increasing pulsatility. Absence of Posterior communicating AND Right common carotid artery flow lowered the pressure and flow drastically in the all the Right sided cerebral arteries but not the left. Conclusion Nonpulsatile flow increases the mean pressure in all the vessels including cerebral vessels . Increasing pulsatility attenuates this effect. Anatomical variations in the circle of willis may increase the vulnerability to strokes. Identifying these factors may help in lowering the risk of of strokes and diminition of cognitive function in long term LVAD therapy.

Early Gastrointestinal Complications From Ventricular Assist Devices is Increased by Non-Pulsatile Flow

Measurements of organ flow and perfusion during cardiopulmonary bypass suggest that perfusion of the splanchnic bed can be impaired by non-pulsatile flow. We postulated that non-pulsatile flow from centrifugal ventricular assist devices might also compromise splanchnic blood flow and cause bowel ischaemia especially in the period of circulatory instability early post-implant. The aim of the present studies was to compare the incidence of gastrointestinal (GI) complications in patients having a non-pulsatile device with the incidence in those having a pulsatile device. In a pilot study, the initial 12 patients who received the Ventrassist (Ventracor, Sydney, NSW, Australia) centrifugal, non-pulsatile device during the period from June 2003 to September 2005 at the Alfred Hospital, Melbourne were compared with 11 patients who received a Thoratec (Thoratec, Pleasanton, CA, USA), pulsatile, positive displacement device and the incidence was recorded of GI complications requiring an intervention either surgical, endoscopic or by interventional radiology. This was followed by a larger (full) study of a second cohort of similar ventricular assist device (VAD) patients from January 1992 until December 2012 comparing 53 patients having non-pulsatile devices and 110 having pulsatile devices. In the pilot study, the overall incidence of complications in the non-pulsatile group (67%) was almost double that in the pulsatile group (36%) but the difference was not statistically significant (p = 0.15) because of the small number (n = 23) of participants. In the full study, all GI complications with either device occurred within the first 3 weeks post-implant. In the non-pulsatile patients, there was a higher incidence of GI bleeding, 23% vs 4% (p = 0.002), endoscopies, 24% vs 12% (p = 0.049). More patients with a non-pulsatile flow device had delayed absorption of nasogastric feeds than their pulsatile counterparts, 35% vs 7% (p < 0.0001). Patients with a non-pulsatile flow device had a higher overall rate of gastrointestinal complications than patients had with a pulsatile flow device, 56% vs 20% (p < 0.0001). After correcting for the other predictors, the odds of developing a gastrointestinal complication in the pulsatile group was significantly lower (odds ratio 0.07) than in the non-pulsatile device group (p < 0.0001). We conclude that the use of non-pulsatile centrifugal VADs compared with pulsatile positive displacement VADs is associated with a higher incidence of both haemorrhagic and ischaemic complications in the gastro-intestinal system especially in the very early post-implant period. Whether these complications could be reduced in centrifugal devices by increasing their pulsatility is not clear and merits further research.

Postoperative Cognitive Dysfunction after Coronary Artery Bypass Grafting.

Postoperative cognitive dysfunction is a common complication following cardiac surgery. The incidence of cognitive dysfunction is more pronounced in patients receiving a cardiac operation than in those undergoing a non-cardiac operation. Clinical observations demonstrated that pulsatile flow was superior to nonpulsatile flow, and membrane oxygenator was superior to bubble oxygenator in terms of postoperative cognitive status. Nevertheless, cognitive assessments in patients receiving an on-pump and off-pump coronary artery bypass surgery have yielded inconsistent results. The exact mechanisms of postoperative cognitive dysfunction following coronary artery bypass grafting remain uncertain. The dual effects, neuroprotective and neurotoxic, of anesthetics should be thoroughly investigated. The diagnosis should be based on a comprehensive cognitive evaluation with neuropsychiatric tests, cerebral biomarker inspections, and electroencephalographic examination. The management strategies for cognitive dysfunction can be preventive or therapeutic. The preventive strategies of modifying surgical facilities and techniques can be effective for preventing the development of postoperative cognitive dysfunction. Investigational therapies may offer novel strategies of treatments. Anesthetic preconditioning might be helpful for the improvement of this dysfunction.

Hemodynamic energy during pulsatile extracorporeal circulation using flexible and rigid arterial tubing: a reassessment

Pulsatile extracorporeal circulation may improve organ perfusion during cardiac surgery. Some minimally invasive extracorporeal circulation (MiECC) systems allow pulsatile perfusion. The present study investigated the influence of arterial tubing compliance on hemodynamic energy transfer into the patient. Aortic models with adult human geometry were perfused in a mock circulation. A MiECC system was connected using either high-compliance silicone tubing or standard kit tubing. Energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE) were computed from flow and pressure data. Aortic models with physiological and sub-physiological compliance were tested to assess the influence of the pseudo-patient. Non-pulsatile flow did not generate SHE. SHE during pulsatile flow in the compliant aortic model was significantly higher with kit tubing compared to silicone tubing. Maximum SHE was achieved at 1.6 L/min with kit tubing (7.7% of mean arterial pressure) and with silicone tubing (4.9%). Using the low-compliance aortic model, SHE with kit tubing reached a higher maximum of 14.2% at 1.8 L/min compared to silicone tubing (11.8% at 1.5 L/min). Flexible arterial tubing did not preserve more hemodynamic energy from a pulsatile pump compared to standard kit tubing in a model of adult extracorporeal circulation. The pseudo-patient's compliance significantly affected the properties of the mock circulation.

Posthypoxic encephalopathy in patients after cardiac surgery: etiological, pathogenetic, and clinical aspects (a literature review)

Post-hypoxic encephalopathy is a brain damage manifested by neurological, neuropsychiatric, and mental disorders, which is caused by a reduction in cerebral blood flow and by a resultant effect of an episode of hypoxia of various etiology and duration. This complication is most characteristic of patients who have undergone cardiac surgery in view of the high prevalence and severity of clinical manifestations, worse quality of life, the longer length of hospital stay, and the higher cost of treatment and rehabilitation. To determine the individual management tactics for such patients, combining both successful surgical treatment, by reducing perioperative stress, and prevention of cerebral complications, it is necessary to analyze the patterns of their development. The role of pathophysiological risk factors, including preoperative, perioperative and postoperative ones, for posthypoxic encephalopathy, is considered. Its preoperative risk factors include age, gender, concomitant diseases, education level, and cognitive functions before surgery, cardiac morphofunctional changes, and depressive disorders. There are surgery-related (type and duration of anesthesia, operating-suite temperatures, and hyperglycemia) and postoperative (pain syndrome after surgical intervention, sleep disorders, and the environment) risk factors. Emphasis is placed on the technical characteristics of on-pump operations, among which there are cerebral hypoperfusion, microembolism, non-pulsatile flow, and duration of extracorporeal circulation. Classifications of cerebral complications are presented. Different types of brain dysfunction are analyzed to assess their incidence rates, clinical features, and dynamics in the postoperative period.

Early Detection of Cerebral Infarction With Middle Cerebral Artery Occlusion With Functional Near-Infrared Spectroscopy: A Pilot Study.

Background: NIRSIT, a functional near-infrared spectroscopy (fNIRS) device with 204 channels, can measure oxyhemoglobin (HbO2) and deoxyhemoglobin (HbR) in non-pulsatile blood flow non-invasively using the absorption difference between HbO2 and HbR at a wavelength of 700–1,000 nm and can display the perfusion status in real time.Objective: We applied NIRSIT to patients with stroke to evaluate the usefulness of NIRSIT as an fNIRS device for the early detection of stroke.Methods: We performed a prospective pilot study in an emergency department (ED). Adult patients who had suspected symptoms and signs of stroke within 12 h of the first abnormal time and who underwent intravenous thrombolysis (IVT) or intra-arterial thrombectomy with acute middle cerebral artery (MCA) or internal carotid artery (ICA) infarction were enrolled. NIRSIT was applied to the patients before the imaging study, and the perfusion status of the brain was displayed in real time at the bedside. We compared the NIRSIT results with the mean transit time (MTT) map from perfusion computed tomography (PCT) and the time-to-peak (TTP) map from perfusion-weighted magnetic resonance imaging (PWI).Results: Six male and three female patients were enrolled, and the median age was 74 years. The most common symptom was unilateral extremity weakness (77.8%), followed by dysarthria (33.3%) and aphasia (11.1%). The median National Institutes of Health Stroke Scale (NIHSS) score was 17. All cases of MCA infarction showed different cerebral oxygen saturation values between bilateral lobes of the brain in fNIRS imaging, and these values matched the PCT and PWI results.Conclusions: The brain hemisphere with low oxygen saturation on fNIRS showed hypoperfusion on PCT or PWI. The fNIRS device could be useful in assessing the perfusion status of the brain and detecting MCA or ICA infarction in real time at the bedside.

Evaluation of Two Femoral Arterial Cannulae With Conventional Non-Pulsatile and Alternative Pulsatile Flow in a Simulated Adult ECLS Circuit.

The objective of this study is to evaluate the hemodynamic characteristics of two femoral arterial cannulae in terms of circuit pressure, pressure drop, and hemodynamic energy transmission under non-pulsatile and pulsatile modes in a simulated adult extracorporeal life support (ECLS) system. The ECLS circuit consisted of i-cor diagonal pump and console (Xenios AG, Heilbronn, Germany), an iLA membrane ventilator (Xenios AG), an 18 Fr or 16 Fr femoral arterial cannula (Xenios AG), and a 23/25 Fr Estech remote access perfusion (RAP) femoral venous cannula (San Ramon, CA, USA). The circuit was primed with lactated Ringer's solution and packed red blood cells to achieve a hematocrit of 35%. All trials were conducted at room temperature with flow rates of 1-4 L/min (1 L/min increments). The pulsatile flow settings were set at pulsatile frequency of 75 bpm and pulsatile amplitudes of 1000-4000 rpm (1000 rpm increments). Flow and pressure data were collected using a custom data acquisition system. Total hemodynamic energy (THE) is calculated by multiplying the ratio between the area under the hemodynamic power curve (∫flow×pressure dt) and the area under the pump flow curve (∫flow dt) by 1332. The pressure drop across the arterial cannula increased with increasing flow rate and decreasing cannula size. The pressure drops of 18 Fr and 16 Fr cannulae were 19.4-24.5 and 38.4-45.3 mmHg at 1 L/min, 55.2-56.8 and 110.9-118.3 mmHg at 2 L/min, 94.1-105.1 and 209.7-215.1 mmHg at 3 L/min, and 169.2-172.6 and 376.4 mmHg at 4 L/min, respectively. Pulsatile flow created more hemodynamic energy than non-pulsatile flow, especially at lower flow rates. The percentages of THE loss across 18 Fr and 16 Fr cannula were 16.0-18.7 and 27.5-30.8% at 1 L/min, 35.1-35.7 and 52.3-53.8% at 2 L/min, 48.3-50.3 and 67.3-68.4% at 3 L/min and 62.9-63.1 and 79.0% at 4 L/min. The hemodynamic performance of the arterial cannula should be evaluated before use in clinical practice. The pressure drops and percentages of THE loss across two cannulae tested using human blood were higher compared to the manufacturer's data tested using water. The cannula size should be chosen to match the expected flow rate. In addition, this novel i-cor ECLS system can provide non-pulsatile and ECG-synchronized pulsatile flow without significantly increasing the cannula pressure drop and hemodynamic energy loss.

Surveying the Literature

Surveying the Literature

Gastrointestinal Hemorrhage Associated BacteremiaExtracorporeal Membrane Oxygenation (ECMO): Temporal Trends and Outcomes

Introduction: Extracorporeal membrane oxygenation (ECMO) is associated with hemorrhagic complications such as gastrointestinal hemorrhage (GIH), which in turn may result from coagulopathy, systemic inflammation, reduced gastric perfusion and arteriovenous malformation from non-pulsatile blood flow. GIH in patients treated by ECMO is associated with significant morbidity and mortality. Data are limited regarding the burden of this complication in the United States. Methods: We analyzed the National Inpatient Sample (NIS) database years 2007-2011 to identify hospitalizations in which an ECMO procedure was performed (ICD-9 CM code 39.65). Hospitalizations complicated by a GIH in this cohort were then identified. NIS is the largest all-payer inpatient care database in the United States, containing data on more than seven million hospital stays. Its large sample size is ideal for developing national and regional estimates and enables analyses of rare conditions, uncommon treatments, and special populations. Temporal trends of GIH in this cohort, patient demographics, comorbidity measures, cost of care and outcomes during the study period were determined using Cochran-Armitage trend test. Results: Between 2007 and 2011, ECMO hospitalizations increased from 1,869 to 3,799 (p-trend< 0.0001, figure 1A). Proportion of hospitalizations complicated by GIH increased from 2.12% in 2007 to 7.46% in 2011 (p-trend< 0.0001, figure 1B). GIH was more common in men (56.7%) and in Caucasians (57.4%). Some of the common comorbidities in this population were renal failure (71%), anemia (55%), and hypertension (26%) (figure 2). All-cause inpatient mortality showed a numerical but nonsignificant increase from 56.7% to 61.9% (P= 0.49, figure 1C). Cost of hospitalization increased from $132,420 in 2007 to $215,673 in 2011 (adjusted for inflation, p-trend< 0.0001, figure1D). Conclusion: In this contemporary study of ECMO hospitalizations, GIH occurred in small but significantly increasing proportions. Overall mortality rate and costs associated with GIH were substantial and increased significantly during the study period. Further studies are needed to identify predictors of these trends and factors responsible for such outcomes to better elucidate and perhaps support our findings.540_A Figure 1 No Caption available.540_B Figure 2 No Caption available.

Analysis of blood flow energy characteristics of pulsatile and non-pulsatile flow during extracorporeal circulation

Objective: To analyze the magnitude of blood flow energy and characteristics of frequency domain between pulsatile flow and nonpulsatile flow during cardiopulmonary bypass and physiological flow. Methods: From January 2017 to December 2017, 60 cases of patients with mitral valve disease scheduled for mitral valve replacement or repair at Department of Cardiasurgery, Shanghai Chest Hospital, Shanghai Jiaotong University were randomly divided into 2 groups: pulsatile perfusion (PP) and non-pulsatile perfusion (NP). The magnitude of blood flow energy during pulsatile and non-pulsatile was calculated using energy equivalent pressure (EEP) and surplus hemodynamic energy (SHE) while fast Fourier transformation (FFT) was used to perform power spectral density analysis to identify the frequency domain characteristics between artificial and physiological flow (prior to CPB). The data was analyzed by analysis of variance or t test. Results: At the different time-points after occlusion, the EEP and SHE in PP group were respectively 1.52 to 1.62 and 2.03 to 2.22 times higher than NP at the distal of artery filter. The power density analysis revealed that the blood flow energy of physiological pulsatile flow patterns was within 40 Hz and the ratio of low frequency energy was more than 90% before clamp. The spectral energy ratio of low frequency decreased in both group compared with physiological flow was more obvious in NP group at the radial artery. The ratio of estimated value of power density of PP and NP groups analysis showed the corresponding 0 to 5 Hz, 0 to 10 Hz, 0 to 40 Hz frequency range values measured at the radial artery and filter were 9.51, 4.68, 3.59 and 3.87, 2.69, 2.38 respectively after occulusion. In each frequency range, the energy of PP is higher than that of NP, and the lower the frequency, the greater the difference. The ratio of estimated value of power density of PP and NP groups for the three frequencies measured at the radial artery before and after occlusion were 2.86, 2.83, 2.75 and 14.70, 12.74, 9.85 respectively, and decreased significantly in NP group and low frequency energy. The ratio of estimated value of power density of PP and NP groups under the three different frequencies measured at the radial artery and filter were 26.35, 33.15, 37.36 and 37.41, 54.18, 56.64 respectively, in the conduction process from filter to radial artery, energy exhaustion is significant, especially in group NP. Conclusions: The PP provides significantly more energy than the NP whereby the PP is closer to the physiological pulsatile on the energy frequency structure and attenuation characteristics, with mainly low frequency energy of 0 to 5 Hz and weak energy attenuation. The energy loss of non-pulsatile flow is obvious, especially the low frequency energy.

Impact of Heart Rate on Pulsatile Hemodynamic Performance in a Neonatal ECG-Synchronized ECLS System.

The experimental circuit consisted of an i-cor diagonal pump, a Medos Hilite 800 LT oxygenator, an 8Fr Biomedicus arterial cannula, a 10Fr Biomedicus venous cannula, and six feet of 1/4 in ID tubing for arterial and venous lines. The circuit was primed with lactated Ringer's solution and packed red blood cells (hematocrit 40%). Trials were conducted at various heart rates (90, 120, and 150 bpm) and flow rates (200, 400, and 600mL/min) under nonpulsatile and pulsatile mode with pulsatile amplitudes of 1000-4000rpm (1000 rpm increments). Real-time pressure and flow data were recorded for analysis. The i-cor pump was capable of creating nonpulsatile and electrocardiography (ECG)-synchronized pulsatile flow, and automatically reducing pulsatile frequency by increasing the assist ratio at higher heart rates. Reduced pulsatile frequency led to lower hemodynamic energy generation but did not affect circuit pressure drop. Pulsatile flow delivered more hemodynamic energy to the pseudopatient when compared with nonpulsatile flow. The pump generated more hemodynamic energy with higher pulsatile amplitudes. The i-cor pump can automatically adjust the pulsatile assist ratio to create pulsatile flow at higher heart rates, although this caused some hemodynamic energy loss. Compared with nonpulsatile flow, pulsatile flow generated and transferred more hemodynamic energy to the neonate during ECLS (200-600mL/min), especially at high pulsatile amplitudes and low flow rates.

Neurovascular coupling during cognitive activity in adults with controlled hypertension.

Hypertension, even when controlled, may accelerate arterial stiffening and impair the ability of the cerebrovasculature to increase blood flow to support neural activity, i.e., neurovascular coupling (NVC). Optimal NVC depends on continuous, nonpulsatile flow, which is partially determined by extra- and intracranial vessel function. We sought to compare extra- and intracranial hemodynamics during cognitive activity (Stroop task) in 30 middle-aged, well-controlled medicated hypertensive and 30 age-, sex-, and body mass index (BMI)-matched nonhypertensive adults (56 ± 6 years, 28.2 ± 2.9 kg/m2 BMI; 32 men). Aortic and carotid (single point) pulse wave velocity (PWV) were assessed via tonometry and ultrasound, respectively. Carotid and middle cerebral artery (MCA) blood velocity pulsatility were measured via ultrasound and Doppler. Prefrontal cortex (PFC) oxygenation was measured via tissue saturation index (TSI) using near-infrared spectroscopy. Accuracy and reaction times were computed to assess cognitive performance. Stroop performance was similar between groups ( P > 0.01). Aortic and carotid PWV increased, carotid flow pulsatility decreased ( P < 0.01), and MCA flow pulsatility and PFC TSI were maintained during Stroop ( P > 0.01). Our findings indicate that middle-age adults with medically controlled hypertension and adults without hypertension demonstrate similar intra- and extracranial cerebrovascular reactivity during cognitive engagement. Despite increases in large artery stiffness, middle-aged adults with controlled hypertension and without hypertension exhibit reductions in extracranial flow pulsatility during cognitive engagement that may be part of a concerted cerebrovascular response to support downstream cerebral oxygenation and overall NVC. NEW & NOTEWORTHY Hypertension is associated with accelerated arterial stiffening, which may alter extra- and intracranial vascular reactivity during cognitive activity and impair neurovascular coupling. Middle-aged adults with medicated hypertension exhibit similar neurovascular coupling and extra-/intracranial vascular reactivity during sustained cognitive activity. Extracranial modulation of central hemodynamics may be an important component of optimal neurovascular coupling.

Improved Outcome in an Animal Model of Prolonged Cardiac Arrest Through Pulsatile High Pressure Controlled Automated Reperfusion of the Whole Body.

The reperfusion period after extracorporeal cardiopulmonary resuscitation has been recognized as a key player in improving the outcome after cardiac arrest (CA). Our aim was to evaluate the effects of high mean arterial pressure (MAP) and pulsatile flow during controlled automated reperfusion of the whole body. Following 20 min of normothermic CA, high MAP, and pulsatile blood flow (pulsatile group, n = 10) or low MAP and nonpulsatile flow (nonpulsatile group, n = 6) controlled automated reperfusion of the whole body was commenced through the femoral vessels of German landrace pigs for 60 min. Afterwards, animals were observed for eight days. Blood samples were analyzed throughout the experiment and a species-specific neurologic disability score (NDS) was used for neurologic evaluation. In the pulsatile group, nine animals finished the study protocol, while no animal survived postoperative day four in the nonpulsatile group. NDS were significantly better at any given time in the pulsatile group and reached overall satisfactory outcome values. In addition, blood analyses revealed lower levels of lactate in the pulsatile group compared to the nonpulsatile group. This study demonstrates superior survival and neurologic outcome when using pulsatile high pressure automated reperfusion following 20 min of normothermic CA compared to nonpulsatile flow and low MAP. This study strongly supports regulating the reperfusion period after prolonged periods of CA.

Gastrointestinal Bleeding in Left Ventricular Assist Device: Octreotide and Other Treatment Modalities.

Left ventricular assist devices (LVADs) offer a therapeutic strategy for patients with end-stage heart failure. Increased device utilization has also increased the incidence of device-related complications including gastrointestinal bleeding (GIB). Multiple mechanisms have been proposed in the pathophysiology of continuous-flow LVAD-associated GIB including physiologic changes associated with high shear and nonpulsatile flow such as gastrointestinal arteriovenous malformations and acquired von Willebrand syndrome. Strategies to minimize the morbidity and mortality of LVAD-associated GIB are needed. Octreotide, a somatostatin analogue, has been described as an adjunct to current therapies and interventions. Factors that contribute to LVAD-associated GIB may be targeted by the pharmacologic effects of octreotide, including improved platelet aggregation, increased vascular resistance, and decreased splanchnic circulation. Octreotide has demonstrated clinical benefit in several case series and clinical trials for the treatment of LVAD-associated GIB. The focus of this article will be to review the pathophysiology of LVAD-associated GIB, discuss pharmacologic and nonpharmacologic treatment modalities, and review available literature on the role of octreotide in the management of LVAD-associated GIB.

Living Without a Pulse: The Vascular Implications of Continuous-Flow Left Ventricular Assist Devices.

Pulsatility seems to have a teleological role because evolutionary hierarchy favors higher ordered animals with more complex, multichamber circulatory systems that generate higher pulse pressure compared with lower ordered animals. Yet despite years of such natural selection, the modern generation of continuous-flow left ventricular assist devices (CF-LVADs) that have been increasingly used for the last decade have created a unique physiology characterized by a nonpulsatile, nonlaminar blood flow profile with the absence of the usual large elastic artery Windkessel effect during diastole. Although outcomes and durability have improved with CF-LVADs, patients supported with CF-LVADs have a high rate of complications that were not as frequently observed with older pulsatile devices, including gastrointestinal bleeding from arteriovenous malformations, pump thrombosis, and stroke. Given the apparent fundamental biological role of the pulse, the purpose of this review is to describe the normal physiology of ventricular-arterial coupling from pulsatile flow, the effects of heart failure on this physiology and the vasculature, and to examine the effects of nonpulsatile blood flow on the vascular system and potential role in complications seen with CF-LVAD therapy. Understanding these concomitant vascular changes with CF-LVADs may be a key step in improving patient outcomes as modulation of pulsatility and flow characteristics may serve as a novel, yet simple, therapy for reducing complications.

In Vitro Hemodynamic Evaluation of ECG-Synchronized Pulsatile Flow Using i-Cor Pump as Short-Term Cardiac Assist Device for Neonatal and Pediatric Population.

The objective of this study was to assess the hemodynamic properties of the i-cor ECG-synchronized cardiac assist system for off-label use as a short-term cardiac assist device for neonatal and pediatric patients and compare nonpulsatile to pulsatile flow with different amplitudes. The circuit consisted of the i-cor diagonal pump with 3 feet of ¼ inch arterial and venous tubing and a soft-shell reservoir, primed with lactated Ringer's solution and human packed red blood cells (hematocrit 42%). Trials were conducted with three different sets of cannulas (8-Fr arterial 10-Fr venous, 10-Fr arterial 12 Fr-venous, and 12-Fr arterial 14-Fr venous) with increasing flow rates at varying pseudo-patient pressures (40, 60, 80, and 100 mm Hg) and under nonpulsatile mode and pulsatile mode with pulsatile amplitudes 2000, 2500, and 3000 rpm at 36°C. Pressure and flow waveforms were recorded using a custom-made data acquisition device for each trial. Energy equivalent pressure (EEP) was higher than mean pressure under pulsatile mode, and increased with increasing pseudo-patient's pressure and flow rate while EEP was the same as the mean pressure under nonpulsatile mode. Total hemodynamic energy (THE) levels increased with pressure and pulsatile amplitude and slightly decreased with increasing flow rate. The percent THE lost throughout the circuit increased with flow rate and pulsatile amplitude and decreased with pseudo-patient's pressure. SHE levels also increased with pseudo-patient pressure and pulsatile amplitude and decreased with increasing flow rate. The i-cor diagonal pump can be used as a short term cardiac assist device for neonatal and pediatric patients and is able to provide nonpulsatile as well as pulsatile flow. Compared with nonpulsatile flow, pulsatile flow can generate and deliver more hemodynamic energy to the patients.

Assessment of cerebral hemodynamic parameters using pulsatile versus non-pulsatile cerebral blood outflow models.

Prior methods evaluating the changes in cerebral arterial blood volume (∆CaBV) assumed that brain blood transport distal to big cerebral arteries can be approximated with a non-pulsatile flow (CFF) model. In this study, a modified ∆CaBV calculation that accounts for pulsatile blood flow forward (PFF) from large cerebral arteries to resistive arterioles was investigated. The aim was to assess cerebral hemodynamic indices estimated by both CFF and PFF models while changing arterial blood carbon dioxide concentration (EtCO2) in healthy volunteers. Continuous recordings of non-invasive arterial blood pressure (ABP), transcranial Doppler blood flow velocity (CBFVa), and EtCO2 were performed in 53 young volunteers at baseline and during both hypo- and hypercapnia. The time constant of the cerebral arterial bed (τ) and critical closing pressure (CrCP) were estimated using mathematical transformations of the pulse waveforms of ABP and CBFVa, and with both pulsatile and non-pulsatile models of ∆CaBV estimation. Results are presented as median values ± interquartile range. Both CrCP and τ gave significantly lower values with the PFF model when compared with the CFF model (p ≪ 0.001 for both). In comparison to normocapnia, both CrCP and τ determined with the PFF model increased during hypocapnia [CrCPPFF (mmHg): 5.52 ± 8.78 vs. 14.36 ± 14.47, p = 0.00006; τPFF (ms): 47.4 ± 53.9 vs. 72.8 ± 45.7, p = 0.002] and decreased during hypercapnia [CrCPPFF (mmHg): 5.52 ± 8.78 vs. 2.36 ± 7.05, p = 0.0001; τPFF (ms): 47.4 ± 53.9 vs. 29.0 ± 31.3, p = 0.0003]. When the CFF model was applied, no changes were found for CrCP during hypercapnia or in τ during hypocapnia. Our results suggest that the pulsatile flow forward model better reflects changes in CrCP and in τ induced by controlled alterations in EtCO2.

The intracranial pressure curve correlates to the pulsatile component of cerebral blood flow

Current methods to measure cerebral blood flow (CBF) in the neuro critical care setting cannot monitor the CBF continuously. In contrast, continuous measurement of intracranial pressure (ICP) is readily accomplished, and there is a component of ICP that correlates with arterial inflow of blood into the cranial cavity. This property may have utility in using continuous ICP curve analysis to continuously estimate CBF. We examined the data from 13 patients, monitored with an intraventricular ICP device determining the pulsatile amplitude ICPamp as well as the area under the ICP curve (AUCICP). Using an elastance measurement, the ICP curve was converted to craniospinal volume (AUCΔV). The patients were examined with Phase Contrast Magnetic Resonance Imaging (MRI), measuring flow in the carotid and vertebral arteries. This made it possible to calculate CBF for one cardiac cycle (ccCBFMRtot) and divide it into the pulsatile (ccCBFMRpuls) and non-pulsatile (ccCBFMRconst) flow. ICP derived data and MRI measurements were compared. Linear regression was used to establish wellness of fit and ANOVA was used to calculate the P value. No correlation was found between ICPamp and the ccICPMRpuls (P = 0.067). In contrast there was a correlation between the AUCICP and ccCBFMRpuls (R2 = 0.440 P = 0.013). The AUCΔV correlated more appropriately with the ccCBFMRpuls. (R2 = 0.688 P < 0.001). Our findings suggests that the pulsatile part of the intracranial pressure curve, especially when transformed into a volume curve, correlates to the pulsatile part of the CBF.