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Biomedical subjects

D E Fixler

Publications and source records attributed to D E Fixler.

At least 37 records · Page 2Linked to original sources
PubMed1981

Regional blood flows in newborn lambs during endotracheal continuous airway pressure and continuous negative pressure breathing.

Cardiovascular changes resulting from continuous distending alveolar pressure during endotracheal intubation (CPAP) and continuous negative pressure (CNP) were studied in two groups of healthy newborn lambs at 6 and 11 mm Hg and -6 and -11 mm Hg, respectively. Heart rate, left ventricular pressure, and arterial blood gases were unchanged in each group. Cardiac output decreased 16 and 15% at 6 and 11 mm Hg CPAP (P less than 0.05), respectively, whereas a fall of 9% occurred at both -6 and -11 mm Hg CNP (P greater than 0.05). Central venous pressure (mm Hg) rose from a control value of 7.0 +/- 1.4 (mean +/- S.E.) to 11 +/- 3.1 and 12 +/- 2.7 at 6 and 11 mm Hg CPAP (P less than 0.025), respectively, and decreased from a control of 7.7 +/- 0.7 to 5.8 +/- 0.5 at -6 mm Hg CNP and 4.8 +/- 1.3 at -11 mm Hg CNP (P less than 0.05). Jugular venous pressure also rose progressively with increasing CPAP (P less than 0.05), but was unchanged during CNP. Regional blood flow to the liver fell at both 6 and 11 mm Hg CPAP, whereas renal and gastrointestinal blood flows showed a tendency to decrease at 11 mm Hg CPAP. The removal of CPAP resulted in a prompt return of venous pressure, cardiac output, and regional blood flows to control values. Reductions in blood flows to the gastrointestinal tract at -6 mm Hg CNP and spleen at -11 mm Hg CNP were observed; blood flows returned toward control values when CNP was removed.

Animals↗
PubMed1981

Left ventricular hypertrophy in adolescents with elevated blood pressure: assessment by chest roentgenography, electrocardiography, and echocardiography.

The purpose of this study was to assess the prevalence of left ventricular hypertrophy in adolescents with persistently elevated blood pressures. Chest roentgenograms, electrocardiograms, and echocardiograms were performed on 50 adolescents with elevated blood pressure and 50 matched normotensive control subjects. No subject in either group demonstrated cardiomegaly on x-ray. Interpretation of the electrocardiograms indicated that similar numbers of both hypertensive (7/50) and control subjects (8/50) had ECG evidence of left ventricular hypertrophy. The echocardiograms showed that the mean left ventricular wall thickness (LVWT) in the hypertensive adolescents was 7.8 mm +/- 0.1 (SE), compared with 6.5 +/- 0.1 in the control subjects (P less than .001). When the measurements were indexed to body surface area, the difference remained highly significant. Indexed left ventricular mass (LVM)/body surface area (BSA) was also significantly greater (P less than .001) in the hypertensive (84.2 gm/sq m +/- 2.1) than in the control subjects (72.0 +/- 2.1). Using data from the normotensive control subjects, we defined the 95th percentile for both LVWT/BSA and LVM/BSA. Among hypertensive adolescents, 9/50 had LVWT/BSA and 8/50 had LVM/BSA above this level. For control subjects, only 1/50 had elevated LVWT/BSA values and 2/50 elevated LVM/BSA values. This study demonstrates that hypertensive adolescents have an increased prevalence of left ventricular hypertrophy and that echocardiography is the most useful noninvasive method to detect these changes.

Adolescent↗
PubMed1979

Distribution of cardiac output during induced isometric exercise in dogs.

Studies were designed to characterize the distribution of cardiac output during induced isometric exercise in anesthetized dogs. The response to isometric exercise involved significant increases in heart rate (+12 +/- 3%(SE)), mean arterial pressure (+13 +/- 2%), cardiac output (+26 +/- 8%), and respiratory minute volume (+75 +/- 26%); total peripheral resistance did not change significantly. Significant changes in blood flow were observed during isometric exercise in kidneys (-18 +/- 6%) and contracting limb muscles (+453 +/- 154%). Flow to liver (hepatic artery), spleen, brain, and myocardium remained near control values. Section of spinal dorsal roots L6-L7 abolished the responses to isometric exercise except for the increase in flow to exercising limb muscles. Alpha-adrenergic receptor blockade abolished the decrease in renal blood flow during isometric exercise; however, the increase in flow to exercising limb muscles was not affected by either alpha- or beta-adrenergic blockade.

Animals↗
PubMed1979

Cardiovascular response to isometric exercise in normal adolescents.

The purpose of this study was to document the cardiovascular response to submaximal isometric handgrip (IHG) exercise in 32 normal adolescents. Left ventricular (LV) dimensions and systolic time intervals were recorded using echocardiography; blood pressure was measured by sphygmomanometry both at rest and during IHG exercise at 25% maximum contraction. This level of isometric exercise produced significant (p less than 0.001) increases in mean heart rate, systolic, diastolic and mean blood pressures. Despite this response LV diastolic and systolic dimensions remained unchanged during exercise; hence, stroke volume remained constant. Cardiac index increased by 22% (p less than 0.001) due to the increase in heart rate. Systemic vascular resistance did not change significantly. LV ejection indices, including shortening fraction, mean Vcf and systolic time intervals also remained unchanged, except for an increase in LV ejection time index (p less than 0.025). These data indicate that the cardiovascular response to submaximal isometric exercise in normal adolescents is similar to that reported in adults. This study demonstrates that sustained isometric stress testing in adolescents is safe and provides normal hemodynamic values.

Adolescent↗
PubMed1979

Hypertension screening in schools: results of the Dallas study.

The purpose of this study was to determine the prevalence of persistent blood pressure elevations in an eighth-grade population composed of three ethnic groups, and to determine the feasibility of using school health facilities for hypertension screening. Blood pressure was recorded in 10,641 subjects (90% of the total eighth-grade population) in the Dallas Independent School District. Blacks made up 46% of the population; non-Latin whites, 40.1%; and Latin-Americans, 13.9%. On the first blood pressure screening, 8.9% had systolic or diastolic pressures or both at or above the 95th percentile. Of those whose blood pressures were elevated on the first examination, 98.3% were reexamined. After the third examination, 1.2% continued to have systolic hypertension, and 0.37% diastolic hypertension. No student had diastolic pressure above 90 mm Hg on all three examinations. The prevalence of persistent hypertension was similar for the three ethnic groups. Analysis of variation in blood pressure measurements revealed that the school nurses introduced a relatively small increase in variability. These data indicate that although school screening initially identifies large numbers of students as having inconstant pressure elevations, subsequent follow-up examinations show that less than 2% have persistent hypertension.

Adolescent↗
PubMed1979

Response of hypertensive adolescents to dynamic and isometric exercise stress.

Isometric handgrip and dynamic exercise stress tests were performed on 109 hypertensive and 74 normotensive subjects 14 to 17 years old. The hypertensive subjects had resting systolic or diastolic pressures persistently above the 95th percentile on four consecutive examinations. Blood pressures and ECGs were recorded during isometric handgrip (25% maximum effort for four minutes) and bicycle ergometry until the subject was exhausted. The hypertensive subjects increased systolic pressure by an average 16 mm Hg with isometric exercise and 53 mm Hg with dynamic exercise. Control subjects had similar pressure changes, averaging 18 and 54 mm Hg, respectively. During isometric handgrip stress, diastolic pressures increased 12 mm Hg in hypertensive subjects and 18 mm Hg in control subjects. Only two hypertensive adolescents developed systolic pressures exceeding 200 mm Hg during dynamic exercise stress, and none developed systolic pressures above 200 mm Hg during isometric exercise stress. None of the normotensive or hypertensive subjects developed cardiac arrhythmias and the prevalence of ST segment depression during maximal stress was less than 2% in both groups. Therefore, in adolescents with mild to moderate hypertension the risk of developing significant ECG or hemodynamic abnormalities during mild isometric or heavy dynamic exercise is small. We believe the decision to restrict physical activity of an adolescent with elevated pressures should be based on the development of abnormal ST segment depression, cardiac arrhythmias, or excessive blood pressures at the time of exercise stress testing.

Adolescent↗
PubMed1978

Morphologic analysis of the pulmonary vascular bed in infants exposed in utero to prostaglandin synthetase inhibitors.

Since the effects of prostaglandin synthetase inhibitors on the developing human fetal pulmonary vasculature are unknown, we studied the lungs of two infants, one whose mother took salicylates and the other whose mother took indomethacin during pregnancy. Lungs were fixed by perfusion and fifth generation (resistance) vessels identified. The infant with chronic exposure to aspirin had premature constriction of the ductus arteriosus, tricuspid insufficiency, increased pulmonary arterial medial width/external diameter ratio due to increased smooth muscle, and a decreased number of pulmonary vessels/cm2 lung tissue. The infant with short-term exposure to indomethacin had hypoxemia, increased pulmonary arterial m/d ratio due to increased smooth muscle, and a normal number of pulmonary vessels/cm2 lung tissue. These abnormalities may be due to the effects of prostaglandin synthetase inhibitor drugs on the ductus arteriosus and/or the pulmonary vessels of the human fetus.

Adult↗
PubMed1977

Hemodynamic alterations during septal or right ventricular ischemia in dogs.

This study indicates that in dogs, ischemic injury to just the ventricular septum has little effect on left ventricular function. The data demonstrate that ischemic injury to either the right ventricular free wall or the ventricular septum alters right ventricular function and/or compliance, suggesting that both regions play a role in maintaining right ventricular performance. That septal contraction supports right ventricular function may explain why in earlier studies, right ventricular pressure development and output were little affected by severe injury to the free wall.

Animals↗
PubMed1977

Echocardiography of premature infants with pulmonary disease: a noninvasive method for detecting large ductal left-to-right shunts.

Echocardiography was used to evaluate premature infants with large patent ductus arteriosus (PDA) shunts and proved lung disease. A PDA producing large left-to-right shunting also causes left atrial enlargement. Since the left atrial diameter (LAD), measured by ultrasound, normally varies with body size, its value was compared to that of the aortic root diameter (AO) to adjust for body size variations. In those infants with pulmonary disease but no significant PDA, the range of LAD/AO ratios was similar to that of the control group. In patients with a proved large PDA the ratios were significantly higher. The ultrasound ratio returned to normal in all cases following surgical ligation of the PDA.

Aorta↗
PubMed1977

Influence of mannitol on maintaining coronary flows and salvaging myocardium during ventriculotomy and during prolonged coronary artery ligation.

We investigated whether prolonged infusion of hypertonic mannitol results in a sustained increase in coronary flow and reduces myocardial necrosis after ventriculotomy or two hours of circumflex coronary artery occlusion. Cardiac outputs, intracardiac pressures, and heart rates did not differ between mannitol and control animals. Those receiving mannitol after ventriculotomy had coronary flows to myocardium near the incision which did not differ from controls. During coronary occlusion, mannitol did increase flow to ischemic and peri-ischemic regions by one hour, but this increase was not sustained at two hours. On histologic examination, myocardial necrosis involving the right ventricular free wall in the ventriculotomy animals and the posterior papillary muscle and subadjacent free wall in the coronary occlusion animals, did not differ between the mannitol treated and control groups. The data obtained in the present study, combined with those from earlier evaluations of the influence of mannitol during ventriculotomy and myocardial ischemia, suggest that mannitol's ability to increase coronary flow to injured areas of myocardium is relatively short-lived.

Animals↗
PubMed1977

Coronary reserve and right ventricular function in awake newborn lambs with persistent right ventricular hypertension.

Right ventricular function curves as measured by right ventricular stroke work were normal in all control lambs, whereas three of five lambs with banded pulmonary arteries had relatively flat curves. Left ventricular function was similarly normal in the control group as compared to a near zero slope function curve in the banded group. Regional myocardial blood flow to the septum and right and left ventricles was similar in control and banded lambs. At rest right ventricular coronary vascular resistance was lower in the banded than in the control group and decreased in both groups during both isoproterenol and dextran stress states. In general, both groups had a similar ratio of right to left ventricular oxygen supply to demand ratio. These results show first that there is minimal, if any, biventricular functional reserve in lambs with persistent right ventricular hypertension, and second, that there is substantial coronary vascular reserve in both normal and banded groups.

Animals↗
PubMed1977

Continuous airway pressure breathing with the head-box in the newborn lamb: effects of regional blood flows.

Continuous airway pressure delivered by a head-box is an accepted means of treating clinical hyaline membrane disease. To investigate hemodynamic alterations resulting from its use, eight newborn lambs, 1 to 6 days of age, were studied at 6 and 11 mm Hg of positive pressure, while spontaneoulsy breathing room air. Organ blood flows and cardiac output were measured with 25 micron-diameter radioactive microspheres. Heart rate, left ventricular pressure, and arterial blood gases did not change during the study. Jugular venous pressures increased from 6.4 mm Hg to 18.6 and 24.2 mm Hg at 6 and 11 mm Hg, respectively (P less than .005). Cardiac output decreased approximately 20% at either intrachamber pressure setting. Renal blood flow fell 21% at 11 mm Hg. No significant changes in blood flow were found in the brain, gastrointestinal tract, spleen, heart, or liver when compared to control flows. Of particular interest was the finding of a 28% reduction in ocular blood flow at 6 mm Hg and 52% at 11 mm Hg. From these results, we conclude that substantial cardiovascular alterations may occur during the application of head-box continuous airway pressure breathing, including a significant reduction in ocular blood flow.

Animals↗
PubMed1976

Blood flow to respiratory, cardiac, and limb muscles in dogs during graded exercise.

The distribution of cardiac output was analyzed in six dogs, with the animals at rest and running on a level treadmill for 3 min at 3-4 mph (mild exercise) and 3 min at 6-8 mph (moderate exercise). Organ flows were measured using 25-mug-diam radioactive microspheres. Cardiac output averaged 2.5, 4.6, and 5.7 liters/min, for rest, mild exercise, and moderate exercise, respectively. The greatest change was in diaphragmatic flow which increased by 275% with mild exercise and 500% with moderate exercise. Flow to intercostal muscles increased by 160 and 186%, to the exercising gastrocnemius muscle by 153 and 224%, and to cardiac muscle by 57 and 109% during mild and moderate exercise, respectively. Renal and cerebral flows did not change significantly. Significant decreases in flow occurred in the small and large intestines during moderate exercise. It is concluded that the increase in cardiac output during submaximal exercise was redistributed in a manner which limited flow to the brain, intestines, and kidneys and increased flow flow to the diaphragm, heart, and limb muscles.

Animals↗
PubMed1976

Effect of hypertonic mannitol and isoproterenol on regional coronary flow following right ventriculotomy.

We studied the changes which occurred in regional coronary blood flow after right ventriculotomy and the subsequent effects of hypertonic mannitol or isoproterenol infusion. Regional coronary flows were measured with radioactive microspheres (9 micron) in open-chest anesthetized dogs. Either hypertonic mannitol (25%) was infused at 3.2 ml/min or 7.6 ml/min for 30 minutes, or normal saline at 7.6 ml/min for 30 minutes followed by isoproterenol at 0.05-0.10 mug/kg/min. In the mannitol treated animals right ventricular, left artrial and aortic pressures, heart rate, and cardiac output did not change significantly following vertical ventriculotomy, whereas in the saline-isoproterenol treated animals aortic pressures fell significantly. Coronary flow to the peri-incisional area fell from 41 to 24 ml/min-100 g (P less than 0.05) following ventriculotomy, increased by 34% (P less than 0.05) when osmolality rose after mannitol by 37 mOsm, but was unchanged with isoproterenol. The data indicate that a vertical ventriculotomy reduces flow to adjacent myocardium and that subsequent infusion of hypertonic mannitol at moderate rates significantly increases coronary flow to this region.

Animals↗
PubMed1976

The influence of combined intra-aortic balloon counterpulsation and hyperosomotic mannitol on regional myocardial blood flow in ischemic myocardium in the dog.

We investigated the combined effectiveness of intra-aortic balloon counterpulsation and hyperosmotic mannitol (25%) on regional myocardial blood flow during acute coronary insufficiency. Cardiac output and paced heart rate were held constant in chloralose-anesthetized dogs during right heart bypass. Acute coronary insufficiency was produced by ligation of the proximal left anterior descending coronary artery (LAD). Regional myocardial blood flow was measured using radioactive microspheres. Left ventricular end-diastolic pressure, mean aortic pressure, maximum left ventricular dp/dt, and hematocrit were unchanged by combined mannitol infusion and balloon pumping. Studies of combined treatment with balloon pumping and mannitol immediately after the second of two 13-minute consecutive reversible ligations of the LAD demonstrated that (1) collateral coronary blood flow increased 46% (P less than 0.02) in ischemic myocardium compared with mannitol infusion along during the first LAD ligation, and (2) collateral coronary blood flow increased 27% (P less than 0.05) in ischemic myocardium compared with balloon pumping along during the first LAD ligation. Studies in which combined treatment was delayed until 20 minutes after LAD ligation demonstrated that collateral coronary blood flow was elevated by 33% (P les than 0.05) in ischemic myocardium compared to control studies in which balloon pumping alone had no effect. The results suggest that the increase in collateral coronary blood flow was in part a result of an increased transmural pressure gradient produced by balloon diastolic augmentation and the ability of mannitol to reduce coronary vascular resistance in ischemic myocardium.

Animals↗