Measures Of Systemic Blood Flow Research Articles

A Parameter Identification Approach towards Hemodynamics based on Capnography

Research question Pulse detection decisions during cardiopulmonary resuscitation (CPR) are commonly augmented by end-tidal CO2-concentration (etCO2) levels and trend as etCO2 is a surrogate measure of systemic blood flow during (CPR)1. However, ventilatory and circulatory parameters influence the interpretability of etCO2 heavily. Recently developed methods of continuous cardiac output measurement based on capnography are not applicable during CPR due to the required controlled ventilation settings2. In this study, a parameter identification for a model of CO2 transport during resuscitation is used to estimate cardiac output based on capnography and tidal flow. Methodology After development of a compartmental ordinary differential equation (ODE) model to represent CO2 transport during CPR, parameters such as airway dead space and the level of systemic perfusion are estimated by a multishooting parameter identification approach3. To evaluate the method, tests are conducted on experimental data from a porcine model (approved by an ethics committee vote of the Austrian Federal Ministry of Education, Science and Research (GZ: 2021-0.895.386)). The estimated level of systemic perfusion is compared visually to invasively measured mean arterial pressure due to a lack of continuous cardiac output measurements as a ground truth. Results For exemplary data from a female pig (weight 50.4 kg), airway resistance was estimated to 20.8 hPa s /L, compliance: 25.2 mL/hPa, and dead space: 109 mL. Changes in cardiac output can be identified qualitatively as shown in Fig. 1. Conclusion A validated, simple ODE model for CO2 extraction during CPR could contribute quantifying the impact of ventilatory parameters on etCO2 and elucidate CO2 production, storage and transport during cardiac arrest. Assumptions on CO2 production during cardiac arrest and redistribution in the body, and the lacking cardiac output measurements complicate the analysis. Conflicts of Interest All authors have no conflict of interest to declare.

Assessment of superior vena cava flow and cardiac output in different patterns of patent ductus arteriosus shunt

Despite the widespread use of superior vena cava (SVC) flow as a marker of systemic blood flow from the upper body, no previous studies have systematically evaluated the correlation between SVC flow and other echocardiography measures of systemic blood flow in the context of different patterns of patent ductus arteriosus (PDA) shunt direction METHODS: A retrospective cohort study of preterm infants (<30weeks,<21 days of life) who underwent comprehensive targeted neonatal echocardiography (TnECHO) was performed. Patients were categorized as follows: (i) Hemodynamically significant left-to-right shunt; (ii): Bidirectional shunt; (iii) No PDA or insignificant shunt. SVC flow, as measured by two distinct methods, was compared to left and right ventricular outputs (LVO and RVO). Intra- and inter-observer reliability testing was performed RESULTS: In total, 45 patients were included (15 in each group) with a median [IQR] weight of 720 [539, 917] grams at the time of assessment. SVC dimensions and flow measurements were not different between the groups, although patients with left-to-right shunt had higher LVO/RVO ratio. SVC flow, as estimated using the modified method, had a strong correlation with LVO (r=.63, p=0.012) and RVO (r=.635, p=0.011) in patients with no PDA. Inter- and intra-observer reliability were both stronger for LVO and RVO when compared to SVC flow measurements CONCLUSION: SVC flow was comparable across all three groups irrespective of higher LVO and LVO/RVO ratio in patients with left-to-right shunts. This may reflect poor measurement reliability or compensation for left-to-right ductal shunt by increased LVO to maintain systemic perfusion.

Associations of measures of systemic blood flow used in a randomized trial of delayed cord clamping in preterm infants.

To determine associations of low superior vena cava (SVC) flow (≤55 ml/kg/min) and low right ventricular output (RVO) (≤150 ml/kg/min) in preterm infants. An observational study in infants <30 weeks gestation randomized to receive immediate (<10 s) or delayed cord clamping (DCC) (≥60 s). The study enrolled 265 infants with a mean (SD) gestation 28 (2) weeks. Eighty-six (33%) infants had low SVC flow and 81 (31%) infants had low RVO. In multivariate analysis, low SVC flow was associated with gestation; low RVO was associated with DCC, gender and 5-minute Apgar; whereas mean RVO was negatively associated with both FiO2 and mean airway pressure (MAP) at 9 h and 24 h. Low SVC flow was associated with ductus arteriosus (DA) treatment. Infants with low RVO had higher mortality on univariate analysis, but this was not significant after adjusting for gestation. SVC flow was associated with gestation, whilst RVO was associated with placental transfusion, gender, condition at birth, and early respiratory adaptation. Compared to infants with normal values, more infants with low SVC flow were treated for DA, but infants with low RVO had no significant difference in mortality or morbidity.

Chronic Cardiac Output measurements in unrestrained rats: Surgical description

Measurement of systemic blood flow and cardiac output in awake but restrained rats has previously been possible via complicated tether and electrical commutator systems that are no longer widely available. A new, fully implantable telemetry system with modified transit-time volume flow probes, allows ascending aorta flow (cardiac output minus coronary flow) measurements in unrestrained rats over extended periods of time. A surgical protocol (adapted from Thomas L. Smith, PhD. Dept. of Orthopaedic Surgery, Wake Forest Baptist Health) was developed for the chronic implantation of the flow probe around the rat ascending aorta, with subcutaneous tunneling of the flowprobe cable to the implant site and securing of the telemetry unit in the abdominal cavity. Animals may be deeply anesthetized with 5% isoflurane and directly intubated transpharyngeally to avoid use of long lasting injectable anesthetics. The pectoral muscles are bisected to expose the transversus costarium crossing the 3rd intercostal space (surgical approach to the aorta) to insert on the 4th rib. The thoracic cavity is opened ~ 3 mm lateral to the sternum to avoid the internal mammary artery and extended dorsally ~ 1 cm. The 3rd intercostal space is expanded with a lacrimal sac retractor to permit reflection of the lung and thymus allowing exposure of the superior vena cava and ascending aorta. A 5 mm section of the aorta is isolated from the vena cava and pulmonary artery and sutures are placed around the aorta. The flow probe is placed in midsternal position and sutures are used to position the aorta into the probe lumen. The intercostal space is closed with 3 sutures and the probe cable secured with the telemetry implant located in the abdomen. The chest is evacuated and surgical incisions are closed. This technique permits long term internal battery or inductively powered assessment of cardiac output along with ECG and/or arterial pressure measurements. This is particularly important for vascular resistance determinations and also other applications that require simultaneous measurements of flow, pressure and ECG in small animals. Telemetry data from rat at day 6 post implantation. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Interobserver agreement and image quality of functional cardiac ultrasound measures used in a randomised trial of delayed cord clamping in preterm infants

ObjectiveFunctional cardiac ultrasound measures are used clinically and in trials for assessing the haemodynamic status of newborn infants. Superior vena cava (SVC) flow and right ventricular output (RVO) are established...

Does umbilical cord milking result in higher measures of systemic blood flow in preterm infants?

Commentary on: Katheria AC, Truong G, Cousins L, Oshiro B, Finer NN. Umbilical cord milking versus delayed cord clamping in preterm infants. Pediatrics. 2015 July;136(1):61–69; doi:10.1542/peds.2015-0368. The American Congress of Obstetricians and Gynecologists recommends a 30–60 s delay in umbilical cord clamping for all preterm deliveries, though limited data regarding outcomes by mode of delivery exists 1. Umbilical cord milking (UCM) is a method to auto-infuse blood into the neonate in a shorter amount of time. A 2011 study comparing UCM with delayed cord clamping (DCC) in infants <33 weeks’ gestation found no major clinical differences between the groups, though the trial did not stratify outcomes by mode of delivery 2. The reviewed study (Katheria et al.) is the first trial to compare UCM and DCC at Caesarean delivery and to evaluate DCC for more than 30 seconds in preterm infants. The authors hypothesised that UCM after Caesarean delivery would improve systemic blood flow and be associated with decreased morbidities compared with DCC. The study was unique in its use of delayed consent, in which parents were informed and consented after delivery. Delayed consent was used because antenatal consent requirements would exclude a subset of newborns, and because UCM and DCC are both standard practices at these institutions. This method of consent may raise ethical concerns; however, others have praised it as a strategy to increase enrolment of high risk infants 3. The study was adequately blinded and used advanced techniques to measure neonatal hemodynamics. The primary outcome of superior vena cava flow was chosen as a marker of neonatal transition that is not affected by foetal shunts. Right ventricular output was lower in the DCC group, which previous studies have shown to be associated with increased oxygen requirement, severe intraventricular haemorrhage (IVH) and death 4. There was no difference in left ventricular output (LVO), but LVO may be confounded by a left to right shunt across a patent ductus arteriosus and thereby overestimate systemic blood flow. The authors argue that given the markers suggestive of improved organ perfusion, UCM may stabilise fluctuations in systemic blood flow and therefore prevent IVH, although the study did not have adequate power to assess this outcome. Despite not being statistically significant, the different rates of IVH appear to be clinically relevant. With an absolute risk difference of 6/100, it is difficult to dismiss the potential decreased risk of IVH associated with UCM. Another limitation of the study is the lack of a control group to undergo immediate cord clamping (ICC). Given improved clinical outcomes associated with placental transfusion, the authors state that they did not have clinical equipoise to assign ICC. Lastly, the study was limited by only including 94/197 infants who were <29 weeks’ gestational age. It remains uncertain if and how the present study will influence clinical practice. Larger trials involving smaller, more premature neonates are needed in addition to long-term assessment of neurodevelopmental outcomes. The authors confidently state that ‘UCM should no longer be considered experimental…[but] a beneficial option for preterm infants delivered by Caesarean delivery’. With the growing body of evidence supporting the safety of UCM, we concur with the authors in advocating for this intervention. https://ebneo.org/2015/12/does-umbilical-cord-milking-result-in-higher-measures-of-systemic-blood-flow-in-preterm-infants/ None. None.

Umbilical Cord Milking Versus Delayed Cord Clamping in Preterm Infants.

Delayed cord clamping (DCC) is recommended for premature infants to improve blood volume. Most preterm infants are born by cesarean delivery (CD), and placental transfusion may be less effective than in vaginal delivery (VD). We sought to determine whether infants <32 weeks born by CD who undergo umbilical cord milking (UCM) have higher measures of systemic blood flow than infants who undergo DCC. This was a 2-center trial. Infants delivered by CD were randomly assigned to undergo UCM or DCC. Infants delivered by VD were also randomly assigned separately. UCM (4 strippings) or DCC (45-60 seconds) were performed. Continuous hemodynamic measurements and echocardiography were done at site 1. A total of 197 infants were enrolled (mean gestational age 28 ± 2 weeks). Of the 154 infants delivered by CD, 75 were assigned to UCM and 79 to DCC. Of the infants delivered by CD, neonates randomly assigned to UCM had higher superior vena cava flow and right ventricular output in the first 12 hours of life. Neonates undergoing UCM also had higher hemoglobin, delivery room temperature, blood pressure over the first 15 hours, and urine output in the first 24 hours of life. There were no differences for the 43 infants delivered by VD. This is the first randomized controlled trial demonstrating higher systemic blood flow with UCM in preterm neonates compared with DCC. UCM may be a more efficient technique to improve blood volume in premature infants delivered by CD.

Postnatal systemic blood flow in neonates with abnormal fetal umbilical artery Doppler.

Objective. Abnormal umbilical artery Doppler (UAD) studies are associated with poor neonatal outcomes. We sought to determine if postnatal measures of systemic blood flow (SBF), as measured by functional echocardiography (fECHO), could identify which fetuses with abnormal UAD were at the highest risk of adverse outcomes. Study Design. This is a retrospective review of fetuses with abnormal UAD who received fECHO in the first 72 hours of life. Measures of SBF (right ventricular output (RVO) and superior vena cava (SVC) flow) were performed and compared with prenatal variables and postnatal outcomes. Result. 63 subjects had abnormal UAD, 20 of which also had fECHO. Six subjects had abnormal flow. Gestational age at delivery was similar between the two groups. Those with abnormal SBF had fewer days of abnormal UAD prior to delivery and developed RDS (P < 0.001). Conclusion. Postnatal measures of SBF were associated with poor postnatal outcomes in fetuses with abnormal UAD. Future studies incorporating antenatal measures of SBF may help obstetricians determine which pregnancies complicated by UAD are likely to have postnatal morbidity.

The relationship between BNP, NTproBNP and echocardiographic measurements of systemic blood flow in very preterm infants

Preterm infants are at risk of circulatory compromise following birth. Functional neonatal echocardiography including superior vena cava (SVC) flow is increasingly used in neonatal medicine, and low SVC flow has been associated with adverse outcome. However, echocardiography is not readily available in many neonatal units and B-type natriuretic peptides (BNPs) may be useful in guiding further cardiovascular assessment. This study investigated the relationship between BNP, N-terminal pro-BNP (NTproBNP) and echocardiographic measurements of systemic blood flow in very preterm infants. This is a prospective observational study. Sixty preterm infants <32 weeks gestational age were included after the treating neonatologist had requested an echocardiogram for suspected cardiovascular compromise. BNP and NTproBNP were sampled just before the echocardiogram. Echocardiographic examination included fractional shortening (FS), SVC flow, left and right ventricular output (LVO and RVO). Statistical analysis included simple linear regression of BNP and NTproBNP with echocardiographic measures and multiple regression including potential confounding variables. Mean (s.d.) gestational age at birth was 27(5) (2(1)) weeks, median (interquartile range, IQR) birth weight was 995 (845 to 1175) grams. Neither BNP nor NTproBNP correlated with SVC flow (BNP 95% confidence interval (CI) -0.0014 to 0.013, P=0.12; NTproBNP 95% CI -0.00069 to 0.01, P=0.085); LVO (BNP 95% CI -0.00078 to 0.0072, P=0.11; NTproBNP 95% CI -0.0034 to 0.0034, P=0.99); RVO (BNP 95% CI -0.00066 to 0.0058, P=0.12; NTproBNP 95% CI -0.0012 to 0.0044, P=0.25); or FS (BNP 95% CI -0.053 to 0.051, P=0.96; NTproBNP 95% CI -0.061 to 0.019, P=0.3). Multivariate linear regression did not significantly alter results. In this cohort of very preterm infants, BNP and NTproBNP did not correlate with echocardiographic measurements of systemic blood flow within the first 72 h of life.

Changes in hemodynamics after rescue surfactant administration

To evaluate the hemodynamic changes occurring after rescue surfactant dosing in relation to the clinical respiratory response in preterm infants with respiratory distress syndrome. We studied 20 infants who received surfactant (poractant alfa) after failing continuous positive airway pressure (CPAP) beyond 2 h of life. Consecutive echocardiograms were performed before the surfactant dose, 10 min after and 1 h after the surfactant dose. Superior vena cava flow, right ventricular output, atrial and patent ductus arteriosus diameter and direction of shunting were measured. A surfactant responder (SR) was defined as an infant whose inspired fraction of oxygen was reduced to air (0.21) by 3 h after surfactant administration. A surfactant non-responder (SNR) was defined as an infant who remained on more than 0.21 at 3 h postsurfactant administration. Concurrent physiological parameters (heart rate, transcutaneous CO2, mean arterial blood pressure, mean airway pressure) were also recorded. Subject characteristics were compared relative to noted hemodynamic effects. Of the 20 infants enrolled in the study, 12 were SR. These infants received surfactant earlier and had increased measures of systemic blood flow after receipt of surfactant compared with baseline. SNR did not have changes in systemic blood flow from baseline after surfactant dosing. There was no change in ductal shunting or atrial shunting between the two groups. A good clinical response to rescue surfactant is seen in infants who received surfactant earlier and is associated with increase in systemic blood flow. Timing of rescue surfactant administration needs to be further evaluated in larger prospective studies.

Shock: A Common Consequence of Neonatal Asphyxia

Neonatal asphyxia is associated with multi-organ hypoxia-ischemia and subsequent dysfunction. The cardiovascular system is frequently affected, causing signs of shock and complicating the neonatal circulatory transition. Hypothermia therapy can improve outcome from neonatal asphyxia without adversely affecting cardiovascular stability. Therapy directed at the cardiovascular system can improve short-term measures of systemic blood flow, but to date has not been demonstrated to improve long-term outcome.

Superior vena cava flow: feasibility and reliability of the off-line analyses

BackgroundSuperior vena cava (SVC) flow has become a surrogate measure of systemic blood flow in neonates.ObjectiveThe aim of this study was to establish normal SVC flow values in healthy term...

Support of the preterm circulation: keynote address to the Fifth Evidence vs Experience Conference, Chicago, June 2008.

Hemodynamics is an area of neonatology that is marked more by what we do not know than what we do. What is clear is that it is much more complex than just measuring blood pressure (BP). Early postnatal preterm hemodynamic pathophysiology is characterized by low systemic blood flow (SBF), possibly relating to a mix of afterload compromise, left-to-right shunting through the unconstricted ductus and to the circulatory effects of ventilation. After approximately 24 h of age, vasodilatation seems to be the dominant pathology. In the face of this complexity, a one-size-fits-all approach to treatment that will be applicable in a large clinical trial may prove elusive. The possibility of using a measure of both BP and SBF to target an appropriate treatment needs to be explored.

Treating hypotension in the preterm infant: when and with what: a critical and systematic review

A very large proportion of extremely preterm infants receive treatments for hypotension. There are, however, marked variations in indications for treatment, and in the interventions used, between neonatal intensive care units and between neonatologists. We performed systematic reviews of the literature in order to determine which preterm infants may benefit from treatment with interventions to elevate blood pressure (BP), and which interventions improve clinically important outcomes. Our review was not able to define a threshold BP that was significantly predictive of a poor outcome, nor whether any interventions for hypotensive infants improved outcomes, nor which interventions were more likely to be beneficial. There is a distinct lack of prospective research of this issue, which prevents good clinical care. It is possible that a simple BP threshold that indicates the need for therapy does not exist, and other factors, such as the clinical status or systemic blood flow measurements, may be much more informative. Such a paradigm shift will also require careful prospective study.

Lower Cardiac Output Is Associated with Greater White Matter Hyperintensities in Older Adults with Cardiovascular Disease

To preliminarily examine the association between cardiac output, a measure of systemic blood flow, and structural brain magnetic resonance imaging indices of white matter hyperintensities (WMHs). Cross-sectional. University medical setting. Thirty-six older adults without dementia with prevalent cardiovascular disease (aged 56-85). Cardiac output, WMHs. Partial correlations, adjusting for age and history of hypertension, yielded an inverse relationship between WMHs adjacent to subcortical nuclei and cardiac output (correlation coefficient=-0.48, P=.03); as cardiac output decreased, WMHs increased significantly. No significant associations were found between cardiac output and total WMHs or periventricular WMHs. These preliminary data suggest that systemic blood flow, measured according to cardiac output, is inversely associated with WMHs adjacent to the subcortical nuclei. Cerebrovascular degeneration and the chronicity of hypoperfusion may exacerbate the susceptibility of white matter integrity to alterations in blood flow in older adults.

Left Ventricular Contractility in Extremely Premature Infants in the First Day and Response to Inotropes

The aim was to assess myocardial contractility in infants born <30 wk gestation developing low systemic blood flow (SBF) in the first day, and the effect of dobutamine versus dopamine. Superior vena cava (SVC) flow was used as a measure of SBF at 3, 10, and 24 h (n = 106). Infants with low SVC flow randomized to dopamine or dobutamine. Myocardial contractility was determined by the relationship between left ventricular (LV) mean velocity of circumferential fiber shortening (mVcfs) and wall stress. Infants who developed low SVC flow had significantly worse myocardial contractility at 3 h, but not 10 h. At 24 h, low-flow infants had lower than expected mVcfs for any given LV stress. In 37 infants randomized to inotrope, there was no significant difference in contractility at 10 microg/kg/min. At 20 microg/kg/min (n = 21), dopamine increased whereas dobutamine decreased LV stress. Infants on dobutamine had significantly lower than expected mVcfs for any given LV stress compared with infants on dopamine. Contractility was not improved by either inotrope at either dose. In conclusion, infants developing low SVC flow in the first day have worse myocardial contractility at 3 h. Neither inotrope increased contractility, but dopamine increased LV stress at 20 microg/kg/min.

Pulse wave analysis to assess systemic blood flow during mechanical biventricular support

Measurement of systemic blood flow is of crucial importance in patients on mechanical circulatory support (MCS). We reported the case of a 65-year-old female patient in severe cardiogenic shock undergoing left (Jarvik 2000 axial flow pump) and right (Levitronix-Centrimag centrifugal pump) ventricular assist device implant. Evaluation of blood flow was obtained by ultrasonic flowmetry, continuous thermodilution technique, and pressure recording analytical method (PRAM). This pulse contour system allows beat-by-beat systemic blood flow assessment from the analysis of radial artery pressure waveform. At a Jarvik pump speed < or = 10000 rotations per minutes (rpm), thermodilution and PRAM showed similar blood flow values. At a Jarvik pump speed > or = 11000 rpm, the aortic valve did not open and PRAM did not provide blood flow values due to nonpulsatile blood flow. The present paper describes the first experience with PRAM in a single patient on MCS. Further studies are required to assess the validity of PRAM as an additional monitoring system in the setting of ventricular assist device support.

Diagnosis and Treatment of Low Systemic Blood Flow in Preterm Infants

After completing this article, readers should be able to: 1. Delineate the short- and long-term adverse outcomes associated with low systemic blood flow. 2. Explain why it is not appropriate to use blood pressure and population criteria for hypotension to determine which infants who have low systemic blood flow need cardiovascular support. 3. Describe the various hemodynamic states in neonates and the assessment that is useful in allowing discrimination between these states. 4. Characterize the hemodynamic effects of dopamine and dobutamine in neonates. 5. Delineate the most common characteristics of infants who fail to maintain superior vena cava flows despite the use of inotropes. Low systemic blood flow (SBF) commonly occurs in preterm infants who have respiratory distress in the first postnatal day. Such low flows are strongly associated with neonatal morbidity, including peri/intraventricular hemorrhage (P/IVH), developmental impairments, and mortality. Diagnosing which infants have low SBF is problematic; use of blood pressure (BP) and signs of poor tissue perfusion, including capillary refill times (CRT), poor renal function, and acidosis, results in substantial delays in the initiation of cardiovascular support and a proportion of affected infants missing treatment. The traditional approach to cardiovascular support of the preterm infant has been to identify infants who have hypotension and to use agents, particularly dopamine, titrated to improve BP. However, this strategy may not be the best for improving SBF, and it is yet to be demonstrated that this approach improves neonatal outcomes. This review focuses on identifying which infants have low SBF or organ blood flow, discusses mechanisms for low flows, and examines potential therapies for treating or preventing low flow. Cardiovascular compromise occurs in a number of clinical scenarios in preterm infants, but it is most common on the first postnatal day. Not all infants who have low SBF will be suspected based on clinical signs, including …

Which to measure, systemic or organ blood flow? Middle cerebral artery and superior vena cava flow in very preterm infants

Aim: To describe, in very preterm babies, postnatal changes in measures of middle cerebral artery (MCA) Doppler variables. To relate these peripheral measures to echocardiographic measures of systemic blood flow...

Low systemic blood flow in the preterm infant

Low systemic blood flow in the first hours after birth of a preterm infant is an often unrecognized complication. Traditional measures of cardiovascular adequacy used in the neonatal intensive care unit such as capillary refill time and blood pressure may not identify this problem. Longitudinal measurement of systemic blood flow demonstrates a falling off of blood flow in the first 6–12h after birth, often to less than half of normal, before a gradual return to normal values by 24–48h of age. Identification and appropriate treatment of this reduction in flow may assist in preventing some of the complications of prematurity.