Biomedical subjects

E H Austin

Publications and source records attributed to E H Austin.

At least 37 records · Page 2Linked to original sources

PubMed1996

Inotropes in the hypoplastic left heart syndrome: effects in an animal model.

BACKGROUND: Despite substantial changes in the surgical treatment of children born with the hypoplastic left heart syndrome, overall mortality remains high. Although further improvements in outcomes appear to depend on more effective perioperative care, few experimental data exist to guide appropriate pharmacologic therapy in these infants. Because different inotropic agents may have different effects on the ratio of pulmonary to systemic flow (Qp/Qs), we hypothesize that they may not be equally effective at increasing oxygen delivery. METHODS: In neonatal piglets (n = 6; 3.5 to 6.5 kg), we placed an innominate artery-to-pulmonary artery shunt, created an atrial septal defect, and then occluded right ventricular outflow. We examined the effects of a number of commonly used inotropic agents, administering high and low concentrations of dopamine (5 and 15 micrograms.kg-1 .min-1), dobutamine (5 and 15 micrograms.kg-1.min-1), and epinephrine (0.05 and 0.1 microgram /min). RESULTS: Dobutamine at 15 micrograms.kg-1.min-1 increased the Qp/Qs ratio from 1.03 +/- 0.6 at baseline to 2.52 +/- 0.55 (p < 0.05) and decreased oxygen delivery from 50 +/- 4.3 to 36 +/- 1.7 mL/min (p < 0.1). The arterial-venous oxygen difference increased as oxygen delivery went down, going from 44% +/- 1% to 48% +/- 2% (p < 0.1). Epinephrine at 0.1 microgram.kg-1.min-1 decreased the Qp/Qs ratio from 1.23 +/- 0.21 to 0.82 +/- 0.08 (p < 0.05) and increased oxygen delivery from 40 +/- 9.7 to 56 +/- 1.7 mL/min (p < 0.05). Systemic venous oxygen saturation increased from 36% +/- 4.8% to 50% +/- 8.6% (p < 0.05). Although dopamine decreased the Qp/Qs ratio and increased oxygen delivery, these changes were not statistically significant. CONCLUSIONS: Dopamine, dobutamine, and epinephrine all increased cardiac output but had substantially different effects on the Qp/Qs ratio and on oxygen delivery, possibly due to differential effects on systemic and pulmonary vascular resistances. This suggests that inotropic agents may not be equally beneficial in the clinical setting. Systemic venous oxygen saturation and the arteriovenous oxygen difference may help determine if a given inotrope improves oxygen delivery.

Animals↗

PubMed1996

Effects of oxygen, positive end-expiratory pressure, and carbon dioxide on oxygen delivery in an animal model of the univentricular heart.

OBJECTIVE: Respiratory manipulations are a mainstay of therapy for infants with a univentricular heart, but until recently little experimental information has been available to guide their use. We used an animal model of a univentricular heart to characterize the physiologic effects of a number of commonly used ventilatory treatments, including altering inspired oxygen tension, adding positive end-expiratory pressure, and adding supplemental carbon dioxide to the ventilator circuit. RESULTS: Lowering inspired oxygen tension decreased the ratio of pulmonary to systemic flow. This ratio was 1.29 +/- 0.08 at an inspired oxygen tension of 100%, 0.61 +/- 0.09 at an inspired oxygen tension of 21%, and 0.42 +/- 0.09 at an inspired oxygen tension of 15% (p < 0.05 compared with an inspired oxygen tension of 100% and a positive end-expiratory pressure of 0 cm H2O). High-concentration supplemental carbon dioxide (carbon dioxide tension of 80 to 90 mm Hg) added to the ventilator circuit decreased inspired oxygen tension from 1.29 +/- 0.11 to 0.42 +/- 0.12 (p < 0.05 compared with baseline). A mixture of 95% oxygen and 5% carbon dioxide (carbon dioxide tension of 50 to 60 mm Hg) did not decrease the pulmonary/systemic flow ratio significantly. All three types of interventions influenced systemic oxygen delivery, which was a function of the pulmonary/systemic flow ratio. As the pulmonary/systemic flow ratio decreased from initially high levels (greater than 1), oxygen delivery first increased and reached an optimum at a flow ratio slightly less than 1. As the pulmonary/systemic flow ratio decreased further, below 0.7, oxygen delivery decreased. The ability of systemic arterial and venous oxygen saturations to predict the pulmonary/systemic flow ratio was examined. Venous oxygen saturation correlated well with both pulmonary/systemic flow ratio and systemic oxygen delivery, whereas arterial oxygen saturation did not accurately predict either pulmonary/systemic flow ratio or oxygen delivery. CONCLUSION: This model demonstrated the value of estimating the pulmonary/systemic flow ratio before initiating therapy. When the initial ratio was greater than about 0.7, interventions that decreased the ratio increased oxygen delivery and were beneficial. When the initial pulmonary/systemic flow ratio was below 0.7, interventions that decreased the ratio decreased oxygen delivery and were detrimental. We conclude by presenting a framework to guide therapy based on the combination of arterial and venous oxygen saturations and the estimate of the pulmonary/systemic flow ratio that they provide.

Animals↗

PubMed1996

An unusually long ligamentum arteriosum.

During routine laboratory dissections an unusually long ligamentum arteriosum, measuring 40 mm, was observed. Apparently, such a length for an otherwise normal ligamentum has not been reported previously. Forty-three other ligamenta in adults and three in newborn or stillborn infants were also measured having a range of 8 mm to 24 mm (mean 15.47 mm) and 7.5 mm to 11 mm (mean 9.5 mm) respectively. Since short and long ligaments have been reported previously, both in the newborn as well as in the adult, the variability in length of this structure appears normal and without any functional significance.

Aorta, Thoracic↗

PubMed1996

The role of neuromonitoring in cardiovascular surgery.

This review describes the techniques currently used for quantitative neurophysiologic measurement during cardiac surgery and their potential impact on clinical outcome. Electroencephalography (EEG) characterizes cerebrocortical neuronal electrical activity and was part of some of the earliest cardiopulmonary bypass procedures, yet today it is not widespread use. Each of the common misunderstandings regarding a supposed limitation of this technology is explained. Its major genuine shortcoming, a lack of selectivity, may now be overcome with the combined use of additional monitoring modalities. The influence of intracranial hemodynamics on observed EEG changes may be determined continuously and noninvasively with transcranial Doppler (TCD) ultrasound. TCD provides an indication of sudden change in either blood flow or vascular resistance as well as the detection of emboli. In addition, the metabolic status of cortical neurons can be monitored by regional cerebral venous oxygen saturation (rCVOS) using noninvasive transcranial near-infrared spectroscopy. The % rCVOS tends to remain remarkably stable over a wide range of temperatures, perfusion pressures, and anesthetic states. Marked change in either direction signifies a serious imbalance between oxygen delivery and consumption. Measurement of rCVOS does not require blood flow, pulsatile or otherwise, so that it offers the only means of monitoring during circulatory arrest. By characterizing the dynamic interplay among cerebral hemodynamics, metabolism, and electrogenesis, these technologies permit the rapid detection and correction of potentially hazardous conditions.

Brain↗

PubMed1995

Postbypass effects of delayed rewarming on cerebral blood flow velocities in infants after total circulatory arrest.

Cerebral perfusion is reduced after prolonged periods of total circulatory arrest in infants. Methods of rewarming after arrest may modify the flow pattern of recovery, and a single report has suggested that using cold reperfusion to delay rewarming could mitigate abnormalities in cerebral blood flow. Cerebral perfusion was evaluated by transcranial Doppler sonography in 16 infants who required periods of total circulatory arrest of 35 minutes or more. In group A (n = 9) rewarming was begun immediately on reperfusion, whereas in group B (n = 7) a 10-minute period of cold reperfusion was instituted before rewarming was begun. The mean and end-diastolic flow velocities were measured before incision (baseline) and at 20, 45, and 90 minutes after conclusion of cardiopulmonary bypass. Mean arterial pressure, hematocrit value, and arterial carbon dioxide tension were controlled, with no significant differences between the two groups (p > 0.05). In group A, the mean cerebral blood flow velocity was below the baseline level at all three postbypass measurements (p < 0.001). In group B, however, mean velocity did not differ significantly from the baseline value (p > 0.05). Twenty minutes after bypass, 89% of the patients in group A had no diastolic Doppler signal, indicating absence of perfusion during diastole, compared with only 28% in group B (p = 0.02). These preliminary results suggest that a delay in rewarming on reperfusion may be beneficial in infants after circulatory arrest.

Blood Flow Velocity↗

PubMed1995

Auditory evoked responses in children during hypothermic cardiopulmonary bypass: report of cases.

Variations in core temperature and cerebral blood flow during open heart surgery may affect auditory brainstem responses (ABRs) and middle latency responses (MLRs) in both adults and children. We documented the changes in ABRs of two infants (ages 3 and 11 weeks, respectively) with variations in core temperature during hypothermic cardiopulmonary bypass and total circulatory arrest and compared them with those of a 19-year-old adult. Changes in MLRs that occurred in association with reductions in cerebral blood flow as monitored by transcranial Doppler are also reported in a 6-year-old child. With the reductions in temperature in both infants and the young adult, ABR latencies increased and amplitudes decreased. Effects of hypothermia on ABR latencies were completely reversed by rewarming. MLR amplitudes were transiently reduced during periods of normothermic hypoperfusion. Hypothermia partially prevented these changes, and normoperfusion after rewarming recovered MLRs. Monitoring ABRs and MLRs may be a useful technique for assessment of brain function during hypothermic cardiopulmonary bypass in children and infants.

Adult↗

PubMed1994

Balancing the circulation: theoretic optimization of pulmonary/systemic flow ratio in hypoplastic left heart syndrome.

OBJECTIVES: This study examined the effects of the pulmonary (QP)/systemic (QS) blood flow ratio (QP/QS) on systemic oxygen availability in neonates with hypoplastic left heart syndrome. BACKGROUND: The management of neonates with hypoplastic left heart syndrome is complex and controversial. Both before and after surgical palliation and before heart transplantation, a univentricle with parallel pulmonary and systemic circulations exists. It is generally assumed that balancing pulmonary and systemic blood flow is best to stabilize the circulation. METHODS: We developed a mathematical model that was based on the simple flow of oxygen uptake in the lungs and whole-body oxygen consumption to study the effect of varying the QP/QS ratio. An equation was derived that related the key variables of cardiac output, pulmonary venous oxygen saturation and the QP/QS ratio to systemic oxygen availability. RESULTS: The key findings are 1) as the QP/QS ratio increases, systemic oxygen availability increases initially, reaches a maximum and then decreases; 2) for maximal systemic oxygen availability, the optimal QP/QS ratio is < or = 1; 3) the optimal QP/QS ratio decreases as cardiac output or percent pulmonary venous oxygen saturation, or both, increase; 4) the critical range of QP/QS, where oxygen supply exceeds basal oxygen consumption, decreases as cardiac output and percent pulmonary venous oxygen saturation decrease; 5) the relation between oxygen availability and QP/QS is very steep when QP/QS approaches this critical value; and 6) the percent oxygen saturation of systemic venous blood is very low outside the critical range of QP/QS and high within the critical range. CONCLUSIONS: This analysis provides a theoretic basis for balancing both the pulmonary and systemic circulation and suggests that evaluating both systemic arterial and venous oxygen saturation may be a useful way to determine the relative pulmonary and systemic flows. When high systemic arterial and low systemic venous oxygen saturation are present, pulmonary blood flow should be decreased; conversely, when both low systemic arterial and venous oxygen saturation are present, more flow should be directed to the pulmonary circulation.

Cardiac Output↗

PubMed1994

Balancing the circulation in hypoplastic left heart syndrome.

A mathematical model based on oxygen flow was developed to study the effects of pulmonary to systemic flow ratios (QP/QS) on systemic oxygen availability. The model suggests that QP/QS = 1 is the safest ratio that would provide the largest safety margin in either low cardiac output or low pulmonary oxygenation conditions. The optimal value of QP/QS that will result in maximum oxygen availability is smaller than unity and depends on several circulatory parameters such as cardiac output, maximal oxygen capacity, level of pulmonary oxygenation, and oxygen consumption. The values of these parameters also dictate the permissible range of QP/QS beyond which abrupt oxygen deficiency ensues. Decreased pulmonary resistance resulting in increased pulmonary flow may eventually result in QP/QS that is beyond the vital range.

Blood Circulation↗

PubMed1993

Pulmonary arteriovenous malformation in the neonate.

Pulmonary arteriovenous malformation (AVM) is a congenital condition, but because the symptoms usually do not occur until middle age, the diagnosis is often delayed. The authors report on a neonate, diagnosed at 2 weeks of age, who was treated by lobectomy at 35 months of age. This prompted a review of the diagnosis, pathophysiology, and treatment of pulmonary AVM. In the literature there are approximately 500 cases of pulmonary AVM. Special attention is given to the reports involving children. Eight cases have been reported in which the diagnosis was made in the first year of life. In two series, a chest roentgenogram showed abnormalities in all affected patients. Because of the strong association of pulmonary AVM with hereditary telangiectasia (Rendu-Osler-Weber syndrome), it is recommended that family members of affected patients be screened by chest roentgenograms for pulmonary AVM.

Arteriovenous Malformations↗

PubMed1993

The pulmonary autograft for aortic valve replacement in the young.

Until recently, a mechanical prosthesis has been the substitute valve of choice for children and young adults who require aortic valve replacement. The preference for using mechanical valves in this group resulted from the discovery that porcine valves experienced accelerated structural degeneration in the young. Unfortunately, mechanical valves impose a constant risk of thromboembolism, resulting in a lifelong requirement for anticoagulant therapy. Thus, young patients with the potential for longer survival face a higher likelihood of having a thromboembolic or hemorrhagic event. To provide young patients with a durable replacement aortic valve that is not thrombogenic and does not require anticoagulation, some cardiac surgeons are transferring the patient's own pulmonary valve to the aortic position and replacing the pulmonary valve with a cryopreserved valve (a homograft) from a cadaveric donor. Long-term follow-up of the experience of Mr Donald Ross of London, England, who introduced this operation in 1967, indicates that the pulmonary autograft has the best event-free survival of any form of aortic valve replacement. The technical demands of this operation are greater than those for routine aortic valve replacement with a mechanical prosthesis; however, the pulmonary autograft can be performed at an acceptably low risk. As more experience is acquired with this technique, it may become the preferred procedure for aortic valve replacement in the young.

Adult↗

PubMed1991

Feasibility of intraoperative aortic root angiography in the identification of critical coronary lesions.

Early revascularization is critical for the treatment of acute myocardial infarction (AMI) because the ischemic myocardium begins to suffer irreversible damage after 4 h from the onset of symptoms. However, to make a diagnosis, perform coronary angiography, and prepare for operative revascularization usually takes longer than 4 h. Also, once a patient develops severe cardiogenic shock, coronary angiography is often impossible. Without angiography, the patient is no longer a candidate for surgical repair. To circumvent this problem, we designed this experiment to determine whether intraoperative aortic root angiography after cardiopulmonary bypass and cardioplegic arrest could satisfactorily substitute for angiographic examination in the identification of critical coronary lesions. The feasibility of this approach was tested in dog hearts in which one or tow of the major coronary arteries were ligated. The ascending aorta was then clamped, contrast material was injected, and continuous real-time fluoroscopic images were obtained and recorded on videotape. The videotape was then analyzed by three physicians independently, each without prior knowledge of the lesion locations. Lesions of the left anterior descending artery, the circumflex coronary artery, and the right coronary artery were identified with 94, 91, and 94% accuracy, respectively, for an overall identification rate of 92%. We conclude that aortic root angiography reliably demonstrates coronary artery lesions, and refinements in this technique may allow certain patients to undergo coronary operations without preoperative catheterization.

Angiocardiography↗

PubMed1990

Transfemoral balloon aortic occlusion during open cardiopulmonary resuscitation improves myocardial and cerebral blood flow.

These experiments were designed to determine whether the limited cardiac output during open cardiac massage could be preferentially directed to the coronary and cerebral vessels by balloon occlusion of the descending thoracic aorta. Sixteen dogs were instrumented to monitor cardiac output and left atrial, right atrial, right ventricular, left ventricular, and arterial blood pressures. Measurements of myocardial and cerebral blood flow distribution during massage were made using the radioactive microsphere technique. Each animal underwent two episodes of fibrillation and resuscitation. In one episode the arrest was managed by open massage alone, and in the other, open massage was accompanied by balloon occlusion, with the order randomized. When compared to control, open cardiac massage was associated with a significant decrease in mean arterial pressure; however, the addition of balloon occlusion produced a 130% increase in the mean arterial pressure that was obtained during open CPR (control, 93 +/- 5 mm Hg; massage alone, 35 +/- 2 mm Hg; massage + balloon, 76 +/- 2 mm Hg, P less than 0.01). In a similar fashion, although the absolute blood flow was reduced by 50% when compared to control, the blood flow (ml/min/g) to the brain and heart during massage was 100% better when balloon occlusion was employed (brain: control, 0.41 +/- 0.03; massage only, 0.05 +/- 0.01; massage + balloon, 0.25 +/- 0.02, P less than 0.01; heart: control, 1.46 +/- 0.11; massage alone, 0.35 +/- 0.05; massage + balloon, 0.71 +/- 0.05, P less than 0.01). These results suggest that aortic occlusion significantly increased myocardial and cerebral perfusion patterns during ventricular fibrillation and open cardiac massage.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Reappraisal of the mechanism for cerebrospinal fluid hypertension during aortic surgery.

Cerebrospinal fluid (CSF) hypertension during aortic surgery is a poorly understood, multifactorial event that may increase the risk of spinal cord injury. To assess the factors that may contribute to changes in CSF pressure during aortic surgery, measurements of ascending arterial and CSF pressures were made in 17 anesthetized mongrel dogs. Changes in CSF patterns were monitored under several conditions tested in random sequence. These included systemic hypertension produced by an infusion of phenylephrine, cross-clamping of the descending thoracic aorta, and manual, superior displacement of the transverse aortic arch (arch elevation), either alone or in conjunction with the cross-clamp. Hypertension, cross-clamping, and cross-clamping combined with arch elevation all produced significant increases in ascending mean arterial pressure (204 +/- 20, 170 +/- 8, and 158 +/- 11 mm Hg, respectively, vs. 117 +/- 8 mm Hg [control]; (p less than 0.01). Small, nonsignificant increases in CSF pressure were detected in the cross-clamp group, but none were detected with hypertension alone, despite significant increases in ascending arterial blood pressure in both groups. Thus, neither arterial hypertension nor cross-clamping alone could be demonstrated directly to cause significant CSF hypertension. However, when aortic elevation (displacement) was combined with cross-clamping, the rise in CSF pressure increased to significant levels, even though the ascending arterial hypertension was least severe in this group. In contrast, arch elevation alone did not produce any significant increase in ascending arterial pressure but did produce an approximately 114% increase in CSF pressure (15.2 +/- mm Hg vs. 7.7 +/- 1 mm Hg [control]; p less than 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Improvement in thoracic aortic pressure after proximal aortic cross-clamping by balloon occlusion of the distal aorta.

Spinal cord hypoperfusion injury is a devastating complication of cross-clamping the proximal thoracic aorta. The collateral circulation around the cross-clamp is generally poorly developed, and the run-off is immense, resulting in extremely low thoracic aortic and spinal cord perfusion pressures. The authors postulated that balloon occlusion of the abdominal aorta might confine this reduced collateral flow around the cross-clamp to the thoracic aorta. In 8 of 16 dogs subjected to aortic cross-clamping of the aorta just beyond the arch vessels, the abdominal aorta was also occluded by a balloon. Thoracic aortic pressure and spinal cord perfusion pressure were significantly higher in the animals with aortic balloon occlusion than in those without balloon occlusion (77 +/- 8 mm Hg versus 26 +/- 1 mm Hg, p less than 0.01, and 67 +/- 8 mm Hg versus 18 +/- 2 mm Hg, p less than 0.01, at 10 minutes after cross-clamping). Abdominal aortic balloon occlusion increases thoracic aortic pressure after the aorta is cross-clamped proximally. Further studies are necessary in primates to assess the effect of this procedure in spinal cord perfusion and the rate of paraplegia.

Animals↗

PubMed1989

Aortic atresia with normal left ventricle. Single-stage repair in the neonate.

Four to seven percent of infants born with aortic atresia have a normal-sized left ventricle in association with a ventricular septal defect and a normal mitral valve. In contrast to the more common group of infants with aortic atresia whose left ventricle is hypoplastic, this important subgroup has potential for complete operative correction involving both the right and left ventricles. Previous reports of surgical management of these infants have described early palliative procedures to control systemic and pulmonary blood flow. Our approach has been to perform complete repair at one stage in the neonate. Continuity between the proximal main pulmonary artery and aorta is established, a patch on the ventricular septal defect baffles left ventricular blood to the pulmonary valve, and a homograft conduit achieves right ventricular-pulmonary artery continuity. Three of four neonates who underwent single-stage repair were discharged from the hospital in good condition. Achieving a physiologically normal circulation simplifies the postoperative management of this condition and is to be preferred over neonatal palliation.

Aortic Valve↗

PubMed1988

Improved protection of chronically inflow-limited myocardium with retrograde coronary sinus cardioplegia.

The effects of retrograde coronary sinus cardioplegia (CSC) and conventional aortic route cardioplegia (ARC) on reperfusion blood flow patterns were compared in 18 mongrel dogs having ameroid-induced coronary collaterals. Animals were placed on cardiopulmonary bypass and cooled systemically. The aorta was clamped, and the hearts were arrested with a bolus infusion of hypothermic (4 degrees C) hyperkalemic cardioplegic solution delivered either into the aortic root or through a balloon catheter placed in the coronary sinus. After 45 minutes of ischemic arrest, hearts were reperfused, and blood flow patterns were measured at 1, 5, 10, and 60 minutes. In the normal region, a significant hyperemia occurred with both CSC and ARC. However, the peak reactive transmural flow was 120% more with ARC than with CSC (4.55 +/- 0.45 vs. 2.12 +/- 0.19 ml/min/g, respectively; p less than 0.05) and remained elevated after 60 minutes of reperfusion, when CSC flows had returned to control levels. In the collateral-dependent region, a significant hyperemia was observed with ARC that persisted throughout reperfusion. However, with CSC, no significant changes in blood flow were detected at any time during reperfusion. Thus, the decreased hyperemic response after arrest suggests a reduced energetic debt with CSC compared with ARC and may indicate superior myocardial protection with CSC. This is particularly evident in chronically inflow-restricted myocardial regions.

Animals↗

PubMed1987

Management of patients with heparin-associated thrombocytopenia and thrombosis requiring cardiac surgery.

Heparin-associated thrombocytopenia and thrombosis (HATT) is a serious complication of heparin therapy that results in intravascular platelet aggregation with arterial or venous thrombosis. Platelet aggregation to heparin in vitro is used to confirm the diagnosis. Cessation of heparin therapy with avoidance of reexposure to heparin is an important principle in the management of HATT. However, certain patients with HATT may require reexposure to heparin for emergency cardiac operations requiring cardiopulmonary bypass while still demonstrating positive in vitro platelet aggregation with heparin. The present report describes the management of 2 such patients. In each patient aspirin was shown to inhibit platelet aggregation to heparin in vitro; therefore, aspirin and dipyridamole were administered to each patient before heparin reexposure and continued throughout the perioperative period. Cardiopulmonary bypass with full heparinization was achieved without thrombotic or hemorrhagic complications in both patients. Despite the presence of a heparin-dependent platelet-aggregating factor in the plasma of these 2 patients, inhibition of platelet aggregation with aspirin and dipyridamole allowed uneventful reexposure to heparin.

Adult↗

PubMed1987

Bilateral diaphragm paralysis treated with cuirass ventilation.

The therapeutic effects of cuirass ventilation were studied in two patients with bilateral diaphragm paralysis. Negative inspiratory and positive expiratory pressure applied to the cuirass shell was transmitted to the abdominal and thoracic cavities. Diaphragm excursion was enhanced. Nocturnal cuirass ventilation appears to be an ideal treatment for bilateral diaphragm paralysis.

Adult↗