Biomedical subjects

D F Teitel

Publications and source records attributed to D F Teitel.

At least 19 recordsLinked to original sources

PubMed1998

Intramyocardial hematoma causing cardiac tamponade after repair of Ebstein malformation: erroneous echocardiographic diagnosis as intracavitary thrombus.

Intramyocardial hematoma is an uncommon lesion, most often occurring after chest trauma, aortic valve disease, acute myocardial infarction, or coronary artery bypass surgery. We describe a 17-year-old patient who experienced cardiac tamponade after repair of Ebstein malformation. The malformation was caused by an enlarging intramyocardial hematoma that extended from the right atrium to the atrialized right ventricle. The hematoma was incorrectly diagnosed by echocardiography as an intracavitary thrombus, and the correct diagnosis was recognized only at the time of surgical intervention.

Adolescent↗

PubMed1998

Contribution of synchronized atrial systole to left ventricular contraction in the newborn pig heart.

Synchronized atrial contraction may be much more important in the newborn, who has a faster heart rate and a less compliant ventricle, than in the adult. We therefore investigated the extent by which synchronized atrioventricular contraction contributes to cardiac output and cardiac work in a neonatal circulation, and whether this effect can be fully explained by the Starling mechanism. In neonatal piglets, left ventricular pressure and volume (conductance catheter) were measured during atrial and ventricular pacing. By manipulating preload during atrial pacing, end-systolic pressure and volume, stroke work, and dP/dtmax were compared at the same end-diastolic volume as indices of contractility. Finally, end-diastolic pressure-volume relationships were assessed to investigate the validity of using end-diastolic pressure as an indicator of preload. We found a significant contribution of synchronized atrial contraction; cardiac output increased 27% when pacing mode was switched form ventricular to atrial. The mechanism by which this was achieved is entirely the enhancement of ventricular filling and thus the Starling effect; contractility was unaffected by pacing mode. This large and important effect can be explained by slowed relaxation (compared with the adult ventricle), which impairs passive filling during the ventricular relaxation phase, and makes active filling during atrial contraction more important. In addition, we found that the use of end-diastolic pressure as an indicator of preload, instead of end-diastolic volume, leads to serious misinterpretations, due to not only the nonlinearity of this relationship, but also the possible shifts in this relationship with certain interventions.

Animals↗

PubMed1997

Hemodynamic effects of chronic prenatal ventricular pacing for the treatment of complete atrioventricular block.

BACKGROUND: Increasing the heart rate of the fetus with cardiac failure caused by complete AV block (CAVB) may allow delivery of a full-term, stable neonate with preserved ventricular function. Direct fetal pacing may be a feasible method to achieve this, but the effect of pacing on the structure and function of the rapidly developing fetal heart is unknown. METHODS AND RESULTS: CAVB was created in fetal lambs at 80% gestation by cryoablating the AV node. Epicardial ventricular pacing at 130 bpm was achieved by use of a pacemaker placed under the pectoral muscles. The fetus was returned to the uterus and allowed to continue to term. Ventricular function was assessed 1 week after birth in 7 lambs with CAVB and 10 control lambs. By use of the conductance catheter technique, the end-systolic pressure-volume relationship was determined at different heart rates, pacing conditions, and inotropic states. The contractility was not different between the two groups at their baseline heart rates and rhythms or when they were paced synchronously compared with asynchronously. Also, both groups responded significantly and similarly to inotropic manipulation, indicating preserved contractile reserve. Finally, in both groups, increased heart rates were associated with increased contractility, indicating an intact force-frequency relationship. CONCLUSIONS: We conclude that chronic epicardial ventricular pacing is well tolerated by the fetus, can be successfully applied as a treatment for CAVB, and does not adversely affect myocardial function in the rapidly developing, immature heart.

Animals↗

PubMed1997

The effect of sarcoplasmic reticulum blockade on the force/frequency relationship and systolic contraction patterns in the newborn pig heart.

We investigated the relationship between heart rate and contractility in seven anaesthetized young piglets by measuring contractility at different atrial pacing rates. To study the origin of this relationship we repeated the measurements after blocking the sarcoplasmic reticulum calcium release channel with ryanodine. We assessed contractility using indices derived from instantaneous left ventricular pressure and volume measured by micromanometric and conductance catheters during rapid inferior vena cava occlusion, thus generating the end-systolic pressure-volume relationship, which was characterized by its slope Ees, and the maximum rate of change of ventricular pressure (dP/dtmax)/end-diastolic volume relationship, also characterized by its slope. All animals showed an increase in contractility with increasing heart rate (intact force/frequency relationship) which was abolished after ryanodine. The most striking effect of ryanodine on baseline haemodynamics was the dramatic decrease of dP/dtmax to about 50% of its original value, while peak developed pressure and Ees did not change. We conclude that the young piglet, despite its immaturity, has a functional sarcoplasmic reticulum, illustrated by an intact force/frequency relationship. In addition, blockade of the sarcoplasmic reticulum in vivo has profoundly different effects during early and late systole, indicating that indices of contractility derived during different parts of the cardiac cycle represent different aspects of systole.

Animals↗

PubMed1997

Left ventricular pressure and volume data acquisition and analysis using LabVIEW.

To automate analysis of left ventricular pressure-volume data, we used LabVIEW to create applications that digitize and display data recorded from conductance and manometric catheters. Applications separate data into cardiac cycles, calculate parallel conductance, and calculate indices of left ventricular function, including end-systolic elastance, preload-recruitable stroke work, stroke volume, ejection fraction, stroke work, maximum and minimum derivative of ventricular pressure, heart rate, indices of relaxation, peak filling rate, and ventricular chamber stiffness. Pressure-volume loops can be graphically displayed. These analyses are exported to a text-file. These applications have simplified and automated the process of evaluating ventricular function.

Analog-Digital Conversion↗

PubMed1997

Acute elevation of coronary venous pressure does not affect left ventricular contractility in the normal and stressed swine heart: implications for the Fontan operation.

OBJECTIVE: After the Fontan operation the right atrium and, thus, the coronary sinus are connected to the pulmonary arterial system, which causes the coronary venous pressure to increase. We investigated the acute effects of elevation of coronary venous pressure on baseline hemodynamics, coronary venous flow, and left ventricular contractility. METHODS: In acutely instrumented pigs, during complete right heart bypass and during constant cardiac output, pressure in the right atrium, right ventricle, and coronary sinus was altered by a height-adjustable reservoir. At various levels of coronary venous pressure (up to 4 kPa or up to 30 mm Hg), flow from the reservoir was measured and left ventricular hemodynamics and contractility were measured from catheter-derived left ventricular pressure and (conductance) volume data. Contractility of the left ventricle was assessed by the end-systolic pressure-volume relationship derived during an unloading intervention by adjusting the bypass pump speed. RESULTS: Left ventricular end-diastolic pressure increased slightly (about 5%) with each kilopascal increase in coronary venous pressure, most likely related to diastolic ventricular interaction. No other changes in hemodynamic parameters occurred. Neither coronary venous flow nor left ventricular contractility was influenced by changes in coronary venous pressure. Imposing myocardial stress with dobutamine, 10 microg/kg per minute, did not change these findings. CONCLUSION: Increasing coronary venous pressure to 4 kPa in the intact circulation with intact autoregulation does not affect coronary flow or left ventricular contractility. We found no experimental evidence for the usefulness of diversion of the coronary sinus to the left atrium during Fontan-type operations

Adrenergic beta-Agonists↗

PubMed1997

One-stage complete unifocalization in infants: when should the ventricular septal defect be closed?

BACKGROUND: The decision whether to close the ventricular septal defect at the time of unifocalization in patients with pulmonary atresia, ventricular septal defect, and major aortopulmonary collaterals may be difficult. The purpose of this study was to develop morphologic and physiologic methods to aid in deciding whether to close the ventricular septal defect in patients undergoing one-stage unifocalization. METHODS: Between July 1992 and April 1996, 27 infants with pulmonary atresia, ventricular septal defect, and aortopulmonary collaterals were treated at our institution. Midline complete unifocalization was performed in 25 patients-the ventricular septal defect was closed in 17 and left open in eight. Two patients with severe distal collateral stenoses underwent staged unifocalization. Pulmonary artery and collateral sizes were measured from preoperative angiograms and used to calculate the indexed cross-sectional area of the total neopulmonary artery bed. An intraoperative pulmonary flow study previously validated with experiments in neonatal lambs was performed in six patients: the unifocalized neopulmonary arteries were perfused with a known flow and pulmonary artery pressures were recorded. RESULTS: The neopulmonary artery index was greater in patients who underwent ventricular septal defect closure than in those who did not (p = 0.001), although the values did overlap. This index correlated with the postoperative right ventricular/left ventricular pressure ratio (p = 0.037). Mean pulmonary artery pressures obtained during the intraoperative flow study and after bypass were comparable. CONCLUSION: The total neopulmonary artery index correlates with postrepair right ventricular/left ventricular pressure ratio and is useful in deciding when to close the ventricular septal defect if it is larger than 200 mm2/m2. The pulmonary flow study is helpful in deciding whether to close the ventricular septal defect in all patients.

Adolescent↗

PubMed1997

Evaluation of Gianturco coils for closure of large (> or = 3.5 mm) patent ductus arteriosus.

OBJECTIVES: This report evaluates the use of Gianturco coils to close large patent ductus arteriosus (PDAs) (> or = 3.5 mm) and describes transvenous delivery of 0.052-in. (0.132-cm) Gianturco coils. BACKGROUND: Coil closure of PDAs has become increasingly popular. However, the technique has significant limitations when used to close large PDAs. This report evaluates patient characteristics, PDA anatomy, hemodynamic variables, delivery technique and coil geometry to determine predictors of success. METHODS: Between January 1995 and January 1997, 16 of 118 patients undergoing catheterization for PDA closure were found to have large PDAs. Their median age and weight were 14 months (range 3 months to 43 years) and 8.5 kg (range 3.5 to 73), respectively. The mean PDA diameter was 4.3 mm (range 3.5 to 5.9). Closure of PDAs was attempted using transcatheter delivery of 0.038-in. (0.096-cm) and 0.052-in. coils. Differences in clinical, anatomic, hemodynamic and technical variables between successes and failures were compared. RESULTS: Eleven (69%) of 16 patients had successful closure of their PDA. Failures occurred only in patients < 8 months of age with an indexed PDA diameter > 7 mm/m and a pulmonary/systemic flow ratio > or = 2.8:1. Use of 0.052-in. coils tended to reduce the incidence of embolization and the number of coils needed for closure. CONCLUSIONS: Patients > 8 months of age can have successful closure of large PDAs with currently available Gianturco coils. The 0.052-in. Gianturco coils can be used safely to close large PDAs in infants as small as 6 kg. Increased experience and improved coil design may improve closure rates of large PDAs in infants.

Cardiac Catheterization↗

PubMed1997

Perinatal left ventricular performance in fetal sheep: interaction between oxygen ventilation and contractility.

Left ventricular (LV) output nearly triples at birth, in association with increases in serum catecholamines. Similar increases in catecholamines in utero, however, do not increase output. We hypothesized that catecholamines increase contractility in utero, but that output cannot increase until LV loading conditions are changed by oxygen ventilation. To address this hypothesis, we studied nine fetal sheep acutely placed in a warm water bath (40 degrees C). Conductance and manometric catheters were placed in the LV to generate pressure-volume loops during caval occlusion in the nonventilated and oxygen-ventilated states, each under control, dobutamine, and propranolol conditions. Contractility was estimated by the end-systolic pressure-volume relationship, preload by end-diastolic volume, and afterload by arterial elastance. Oxygen ventilation increased LV output 1.4-fold, despite a decrease in contractility to about three-fourths of the nonventilated value. Heart rate remained constant, whereas preload increased and afterload decreased significantly. During oxygen ventilation, dobutamine increased output to 2.3 times the control, nonventilated value, associated with increases in contractility and heart rate and no change in preload and afterload. Although dobutamine increased contractility and heart rate similarly in the nonventilated and oxygen ventilated states, output increased significantly more during ventilation. Similarly, propranolol decreased contractility and heart rate equally in both states, but output decreased far more during ventilation. Thus, oxygen ventilation is associated with advantageous changes in LV load such that the positive inotropic and chronotropic effects of dobutamine are translated into greater increases in LV output.

Animals↗

PubMed1996

Aortoventriculoplasty with the pulmonary autograft: the "Ross-Konno" procedure.

BACKGROUND: For patients with complex left ventricular outflow tract obstruction, including hypoplastic aortic anulus with or without severe diffuse subaortic stenosis, various aortoventriculoplasty procedures (e.g., Konno procedure and its modifications; extended aortic allograft root replacement) are important management options. In younger patients, however, reoperation for valve replacement is inevitably required, and anticoagulation issues pose additional problems. The pulmonary autograft provides a promising option for aortic valve replacement as part of the aortoventriculoplasty procedure in children. Long-term follow up shows that the pulmonary autograft functions well as the systemic arterial (neoaortic) valve and that valve growth occurs. METHODS: Between July 1993 and May 1995, 11 patients 4 days to 17 years old (median 12 months) underwent aortoventriculoplasty with pulmonary autograft (Ross-Konno procedure). The diagnoses were aortic stenosis with or without subaortic stenosis (n = 8), Shone complex (n = 2), and interrupted aortic arch with subaortic stenosis (n = 1). On average, 1.9 previous interventions had been performed per patient, including a previous Konno procedure in one patient. The aortic root was replaced with a pulmonary autograft valve. The left ventricular outflow tract was enlarged with a Dacron polyester fabric patch in two patients, with an allograft aortic patch in two patients and a right ventricular infundibular free wall muscular extension harvested in continuity with the autograft in seven patients. RESULTS: Intraoperative transesophageal echocardiographic assessment revealed mild aortic insufficiency in one patient. One patient had a residual left ventricular outflow tract gradient of 15 mm Hg. Significant complications were cardiac tamponade from bleeding (n = 1) and complete heart block necessitating a permanent pacemaker (n = 1). Follow-up ranged from 2 weeks to 16 months. To date, there have been no late deaths or reoperations. Follow-up echocardiography revealed mild autograft insufficiency in one patient and a 16 mm Hg residual left ventricular outflow tract gradient in one patient. CONCLUSIONS: Initial experience suggests that aortoventriculoplasty with the pulmonary autograft is an excellent alternative for young patients with complex left ventricular outflow tract obstruction. Because the pulmonary autograft has been shown to grow after implantation, reoperation on the left ventricular outflow tract is likely to be avoided.

Adolescent↗

PubMed1996

Fetal chemoreception: a developing story.

The central and peripheral chemoreceptors are critical to the efficient uptake and delivery of oxygen and the removal of carbon dioxide after birth. However, the importance and activity of fetal chemoreception has been questioned, since oxygen uptake and carbon dioxide removal are not regulated in the lungs in the fetus. Early studies suggested that chemotransduction-the conversion of a chemical stimulus to cardiovascular and ventilatory responses via the integration of chemoreceptor stimulation, neural afferent activity and neurohormonal effector mechanisms-was immature in its individual components or their interaction. However, it now appears that the chemoreceptor cascade is structurally and functionally intact in the late-term fetus, and responds actively to normal and other chemical stimuli. The differences between fetal and postnatal chemotransduction appear to be primarily dependent on the central inhibition of the ventilatory response, the inhibitory area being localized to the lateral pons. It appears to be mediated in part by a placental factor which is removed at birth, allowing for the expression of the ventilatory response. The suppression of this response is also responsible for the difference in the heart rate response: the postnatal tachycardia is caused by the lung inflation reflex; when abolished, bradycardia is seen, just as in the fetus. Despite the suppression of the ventilatory component of chemoreception, the fetal carotid chemoreceptor is more important than the aortic, even though it has been considered to be more important to ventilatory than to cardiovascular stability. This review discusses current knowledge of the various components of the mature chemoreceptor cascade, and presents the fetal story within that framework.

Animals↗

PubMed1995

Interaction between afterload and contractility in the newborn heart: evidence of homeometric autoregulation in the intact circulation.

OBJECTIVES: We undertook the present study to determine whether afterload and contractility interact in the hearts of newborn lambs. We specifically investigated whether stepwise increases in afterload increase contractility. BACKGROUND: Several studies in the isolated and intact adult dog heart have shown that afterload and contractility are not independent determinants of cardiac performance; rather, they interact. Afterload and contractility are unlikely to interact in the newborn heart because the factors that may mediate the interaction in the adult are missing in the newborn. METHODS: We measured contractility at different steady state levels of afterload in seven newborn lambs under complete anesthesia. Contractility was measured by three different indexes: end-systolic pressure-volume relations (slope and volume position); preload-corrected first derivative of left ventricular pressure (dP/dtmax); and preload-corrected stroke work. Left ventricular pressure and volume were measured with a micromanometer and conductance catheter, respectively. Preload and afterload were manipulated by inflating or deflating a balloon catheter in the inferior vena cava and descending thoracic aorta, respectively. Data are expressed as mean value +/- 1 SD. RESULTS: Stepwise increases in afterload increased contractility, independent of which of the three indexes was used. The slope of the end-systolic pressure-volume relation increased from a mean baseline value of 4.44 +/- 2.43 to 6.69 +/- 2.89 kPa/ml at the highest level of afterload. Concomitantly, volume at 14 kPa of the end-systolic pressure-volume relation decreased from 3.34 +/- 1.52 ml at baseline to 1.12 +/- 0.83 ml at the highest afterload. The other two indexes showed qualitatively similar changes. Beats selected from unloading interventions on the basis of the same end-diastolic volume for each level of afterload showed no difference in stroke volume. CONCLUSIONS: This study in newborn lambs demonstrates that stepwise increases in afterload increase contractility considerably and that this enables the heart to maintain stroke volume at different levels of afterload. This forms direct evidence for the existence of homeometric autoregulation in the intact newborn heart.

Analysis of Variance↗

PubMed1995

Effect of indomethacin on cerebral blood flow and oxygenation in the normal and ventilated fetal lamb.

Indomethacin lowers fetal and neonatal brain blood flow and may reduce the risk of periventricular-intraventricular hemorrhage. However, concerns have been raised that cerebral O2 metabolism may be compromised at lower cerebral perfusion pressures. In 17 near-term lamb fetuses, changes in brain blood flow and cerebral O2 metabolism (CMRO2) were measured at mean carotid arterial pressures (MCBP) ranging from 8 to 70 mm Hg. MCBP was adjusted by inflating balloon occluders around the aortic isthmus and brachiocephalic trunk. This was done before and during intrauterine pulmonary ventilation and oxygenation. Nine fetuses were pretreated with indomethacin (1 mg/kg i.v.); eight served as control. Changes in brain blood flow were assessed from carotid arterial blood flow (Qcar, mL/min) measured with flow transducers. In 15 animals, brain blood flow was also measured intermittently by radionuclide-labeled microspheres (Qbrain). Qcar correlated closely with Qbrain (r = 0.94, p < 0.0001); this relationship was not altered by indomethacin or by ventilation with oxygen. In the nonventilated fetuses, indomethacin decreased Qcar at pressures above the lower limit of cerebral autoregulation (43 mm Hg). However, at MCBP below 44 mm Hg, Qcar with indomethacin was not significantly different from controls. CMRo2 fell when MCBP was decreased below 30 mm Hg (range 8-29 mm Hg), but there was no significant difference between control and indomethacin-pretreated fetuses. In the ventilated fetuses, indomethacin reduced the slope of the pressure-flow relationship above the lower limit of cerebral autoregulation (43 mm Hg), suggesting improved cerebral autoregulation. When MCBP was decreased below 44 mm Hg (range 10-43 mm Hg), indomethacin did not lower Qcar or CMRO2 as compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

PubMed1995

Effect of drugs on chemoreceptor responsiveness in fetal sheep.

This study was designed to examine the effects of the drugs ketamine, morphine, pentobarbital, and propranolol on fetal chemoreceptor responsiveness. Eleven fetal lambs (gestational age 125-133 d) were chronically instrumented with a catheter in a hindlimb artery and vein and a forelimb artery; a carotid arterial oximeter catheter was placed in six of these fetuses. An inflatable cuff occluder was placed around the maternal hypogastric artery. Acute fetal hypoxemia was induced repeatedly by reducing uterine blood flow. Fetal heart rate, arterial pressure, and carotid arterial oxygen saturation were monitored continuously before and after administering ketamine, morphine, pentobarbital, or propranolol to the fetus. The ratio delta heart rate/delta O2 saturation has been shown previously to be a reproducible index of chemoreflex response. The differences in baseline values and changes with drugs were compared by multiple regression analysis coded by effects. Chemoreflex response was markedly attenuated by ketamine and morphine but not by pentobarbital or propranolol. Because the cardiovascular response to hypoxemia is blunted by some drugs, caution should be exercised in interpreting heart rate responses to hypoxemia in the fetus when these drugs have been administered to the mother.

Acute Disease↗

PubMed1995

Effect of increased intra-abdominal pressure on hepatic extraction and clearance of fentanyl in neonatal lambs.

Fentanyl, an opioid metabolized by hepatic mixed function oxidases, is commonly administered as the primary anesthetic for neonates undergoing surgery. Pharmacokinetic studies have suggested that abdominal surgery in neonates decreases fentanyl clearance, contending that this results from increases in intra-abdominal pressure (IAP) decreasing hepatic blood flow. To examine the effects of IAP on hepatic blood flow and fentanyl clearance, we infused fentanyl to eight neonatal lambs, measured regional blood flows by using the radionuclide-labeled microsphere technique and determined hepatic fentanyl extraction and clearance and hepatic oxygen extraction and consumption at three levels of IAP: 0, 12 and 18 mm Hg. Increased IAP did not affect portal or hepatic blood flow or ductus venosus shunt. Fentanyl extraction was 16.5 +/- 3.0% (mean +/- S.E.) at 0 mm Hg of IAP. Increased IAP decreased hepatic extraction of fentanyl, thereby decreasing fentanyl clearance. Increased IAP did not affect hepatic oxygen extraction or consumption. In two additional animals in which serial measurements of hepatic blood flow were obtained, increased IAP (15 mm Hg) transiently decreased hepatic blood flow with recovery to control values at 2 hr. The authors conclude that fentanyl is poorly extracted by neonatal livers, in contrast to its large extraction ratio in adults. The decrease in fentanyl clearance with increased IAP is consistent with pharmacokinetic studies demonstrating decreased clearance in neonates undergoing abdominal surgery. However, the present study suggests that the mechanism of decreased clearance is decreased hepatic function (decreased fentanyl extraction) rather than decreased hepatic blood flow.

Abdomen↗

PubMed1994

Nonlinearity of the left ventricular end-systolic wall stress-velocity of fiber shortening relation in young pigs: a potential pitfall in its use as a single-beat index of contractility.

OBJECTIVES: We sought to evaluate in the young heart the primary assumptions on which the current use of the mean "velocity of fiber shortening corrected for heart rate" as a noninvasive index of contractility are based. BACKGROUND: End-systolic wall stress-velocity of fiber shortening relation has been applied as a single-beat, load-independent index of contractility in children. This use is based on poorly validated assumptions of linearity, parallel shifts with changing contractile state and inotropic sensitivity of the end-systolic wall stress-velocity of fiber shortening relation. METHODS: In eight anesthetized young piglets, 5F mciromanometric catheters were placed in the ascending aorta and balloon occlusion catheters in the descending aorta. End-systolic wall stress and velocity of fiber shortening were calculated from aortic pressure and M-mode echocardiography under six conditions: in three contractile states 1) baseline, 2) increased contractility during dobutamine infusion (10 micrograms/kg per min), and 3) decreased contractility after propranolol injection (1 mg/kg), each at two afterload states (normal and increased load by partial aortic occlusion). RESULTS: Dobutamine increased and propranolol decreased afterload-matched velocity of fiber shortening corrected for heart rate significantly to 140% and 77% of baseline, respectively. However, the slope of end-systolic wall stress-velocity of fiber shortening relation was much greater (251% of baseline) during dobutamine infusion, which also significantly decreased wall stress, and was much less (27% of baseline) after propranolol injection, which increased wall stress. CONCLUSIONS: The velocity of fiber shortening corrected for heart rate did change predictably with changes in contractility and as such can be used noninvasively in the temporal evaluation of individual patients undergoing therapeutic interventions or to define the natural history of a disease process. However, the relation on which it is based is not defined by parallel straight lines across contractile states, so that abnormal single point measurements may reflect only the nonlinearity of the relation rather than abnormalities in contractility. Thus, we recommend that the end-systolic wall stress-velocity of fiber shortening relation should not be used as a single-beat index of contractility.

Aging↗

PubMed1994

Relationship between brain blood flow and carotid arterial flow in the sheep fetus.

The present study investigates whether changes in total brain blood flow can be reliably estimated by changes in carotid arterial blood flow in fetal and perinatal lambs. We therefore compared carotid arterial blood flow, measured with implanted transit-time ultrasound transducers, with brain blood flow, measured by radioactive microspheres in fetal lambs during normal oxygenation and during pulmonary ventilation with oxygen, with PO2 ranging from levels normal for the healthy fetus to levels normally seen postnatally. Cerebral perfusion pressure was modified over a wide range to alter brain blood flow: it was decreased by balloon occlusion of the brachiocephalic trunk and increased by a balloon occluder around the aortic isthmus. Carotid arterial blood flow and brain blood flow were closely related (r = 0.97, p < 0.0001). The relationship was not altered at different levels of oxygenation. However, measurements during higher cerebral perfusion pressures, obtained during aortic isthmus occlusion, had a negative influence on the agreement between carotid arterial blood flow and brain blood flow. When excluding values obtained by aortic isthmus occlusion, changes of 20% or more in brain blood flow could be predicted with carotid arterial blood flow within a confidence limit of 95%. Blood flow measurements in the carotid artery may be useful to estimate changes in brain perfusion.

Animals↗

PubMed1993

Myocardial perfusion and performance after indomethacin administration in newborn lambs.

Indomethacin is a drug widely used to achieve pharmacologic closure of a patent ductus arteriosus in the premature infant. In several vascular beds (brain, kidney, intestine), indomethacin has been shown to cause vasoconstriction. Possible negative effects on myocardial blood flow and performance could be deleterious in premature infants with limited cardiac reserve. Before, during, and 30 and 60 min after administration of 1 mg.kg-1 of indomethacin in nine newborn lambs, we measured coronary blood flow velocity (Doppler flow probe around the left circumflex coronary artery), left ventricular (LV) pressure (by tip manometer) and volume (by conductance catheter technique), cardiac output, arterial pressure, arterial and venous saturations and calculated systemic and coronary vascular resistance, LV systolic function by the end-systolic pressure-volume relationship, and myocardial oxygen extraction. To investigate the effect of indomethacin on the flow regulation of the coronary vascular bed, we measured coronary flow and LV function under different levels of myocardial demand, achieved by stepwise occluding of the descending aorta. During indomethacin infusion, coronary and systemic vascular resistance increased significantly (by 43 and 76%, respectively), resulting in an increase in arterial pressure from 10.2 to 16.9 kPa, whereas neither coronary flow nor LV systolic function changed despite the increase in afterload. Thirty and 60 min after indomethacin, coronary and systemic vascular resistance had returned to baseline levels and LV systolic function remained unchanged. The relationship between coronary flow and cardiac demand was not different before or after indomethacin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗