Biomedical subjects

B N Fowler

Publications and source records attributed to B N Fowler.

10 recordsLinked to original sources

PubMed1985

Myocardial oxygen consumption with isoproterenol versus calcium chloride in hypocalcemic ventricular failure in dogs.

In 30 dogs on right heart bypass we compared the effects of isoproterenol with those of calcium chloride on myocardial oxygen consumption and on left ventricular function in the setting of ventricular depression produced by ionized hypocalcemia. In 22 dogs (Groups A and B) either isoproterenol or calcium chloride was infused, left ventricular function curves were generated, and end-diastolic pressure vs segment length plots were obtained. In 8 dogs (Group C), with initial hypocalcemia, both isoproterenol and calcium chloride were infused separately in random order to produce an equal decrease in left ventricular end-diastolic pressure at constant mean aortic pressure, heart rate, and cardiac output. Myocardial oxygen consumption and indices of left ventricular function were obtained. In Groups A and B, both drugs, when administered to the ventricle depressed by hypocalcemia, displaced left ventricular function curves upward and to the left. Left ventricular stroke work at constant left ventricular end-diastolic pressure increased (from 13.0 +/- 1.3 to 31.2 +/- 2.3 g X m for isoproterenol; from 13.9 +/- 2.5 to 32.5 +/- 2.5 g X m for calcium chloride). In Group C, there were no significant differences between left ventricular end-diastolic pressure, end-diastolic internal diameter, myocardial oxygen consumption, or peak left ventricular dP/dt in the hypocalcemic periods preceding isoproterenol and calcium chloride infusion. When the two drugs caused matched decreases in left ventricular end-diastolic pressure (-7.4 +/- 0.5 cm H2O for isoproterenol; -7.3 +/- 0.8 cm H2O for calcium chloride) there were similar decreases in end-diastolic internal diameter. However, isoproterenol was associated with a significantly greater (P less than 0.001) myocardial oxygen consumption (13.7 +/- 0.4 ml X 100 g-1 X min-1) than calcium chloride infusion (11.9 +/- 0.4 ml X 100 g-1 X min-1), as well as a greater peak left ventricular dP/dt (P less than 0.005).

Animals↗

PubMed1984

Interruption of the aortic arch: experience in 17 infants.

Between April, 1965, and August, 1982, 17 children ranging in age from 2 days to 4 years were identified as having interruption of the aortic arch and operated on at our institution. There were eight type A interruptions, eight type B interruptions, and one type C interruption. Associated intracardiac anomalies were present in all but 3 patients. These 3 children, who all had type A interruption, underwent repair by mobilization of the aorta and end-to-end reconstruction. The other 14 children had initial palliative operations. The 2 patients in Group 1 had type A interruption with associated ventricular septal defect (VSD), and underwent subclavian artery-aorta anastomosis. In Group 2, the palliative procedure consisted of placement of a Dacron tube graft in 1 patient with type A interruption and associated VSD, and placement of a polytetrafluoroethylene (PTFE) graft, division of the patent ductus arteriosus, and banding of the pulmonary arteries in 11 patients--2 with type A, 8 with type B, and 1 with type C interruption. Ten children (71%) survived initial palliation, 1 of the 2 in Group 1 and 9 of the 12 in Group 2. In Group 2, 5 children had interruption of the aortic arch (4, type B; 1, type C) with associated VSD; among the 4 who survived palliation, 3 subsequently have had successful closure of the VSD and 1 is awaiting closure. Among the patients who had palliative procedures, there are 6 long-term survivors (43%). In the total series, there are 9 long-term survivors (53%).(ABSTRACT TRUNCATED AT 250 WORDS)

Aorta, Thoracic↗

PubMed1982

Hypothermic ischemic arrest versus hypothermic potassium cardioplegia in human beings.

To determine if the addition of potassium enhances the myocardial protective effect of intracoronary perfusion hypothermia during aortic cross-clamping, 50 patients undergoing aortocoronary bypass grafting were studied in a randomized, prospective, double-blind fashion. Twenty-six patients received a cold crystalloid solution infused with a handheld syringe into the root of the cross-clamped aorta every 20 minutes, and 24 patients received the same solution but with 25 mEq/L of potassium chloride added, infused in a similar manner. Both groups were analyzed by mortality, rate of perioperative myocardial infarction (electrocardiographic changes, MB-CPK enzyme release, and preoperative and postoperative gated cardiac blood pool scans), intraoperative hemodynamic changes, intraoperative lactate determinations, postoperative arrhythmias, and requirement for pressor or intraaortic balloon pump support. One patient in the potassium cardioplegia group died (massive pulmonary embolism), and none in the hypothermic perfusion group died. Possible perioperative myocardial infarction was diagnosed by more than one marker in 4 of 26 patients in the hypothermic perfusion group and 5 of 24 patients in the potassium group (p = 0.61). There were no differences between the two groups in terms of hemodynamic changes, lactate production, postoperative arrhythmias, or the need for postoperative hemodynamic support. This study in human beings could not demonstrate a specific protective effect of potassium, beyond that afforded by myocardial perfusion hypothermia and wash-out. The data suggest that myocardial hypothermia, achieved through cold intracoronary arterial perfusion, may be the most important beneficial component of so-called cardioplegia for attaining effective intraoperative myocardial preservation in human beings.

Arrhythmias, Cardiac↗

PubMed1982

Regional myocardial radiotracer kinetics in dogs using miniature radiation detectors.

An implantable device for continuous measurement of regional myocardial radioisotope activity was designed and validated. The probe consists of a 2-mm3 cadmium telluride crystal surrounded by lead foil housed in a 4.5-mm outer diameter steel cylinder. Activity in serial dilutions of thallium-201 measured by this miniature gamma detector correlated well with activity measured in the well counter (r = 0.99). In vivo probe measurements of regional myocardial thallium-201 activity in a canine model were compared with activity in punch biopsies, again with excellent correlation (r = 0.90). The crystal was mounted on a modified arterial clamp, which was inserted into the left ventricle through, the apex and situated on the endocardial surface of the anterior or posterior wall. It was thus possible to measure regional isotope activity without excessive background from the blood pool and opposite heart wall. The probe was found best suited for monitoring activities of isotopes with energies between 60 and 250 keV. With a pair of these devices, dynamic studies of the myocardial kinetics of radioisotopes such as thallium-201 in normal and ischemic myocardium are now possible.

Animals↗

PubMed1981

Relation between ionized calcium concentration and ventricular pump performance in the dog under hemodynamically controlled conditions.

The effect of plasma ionized calcium concentration on left ventricular function was studied in the canine heart on right heart bypass. Stroke volume, mean arterial pressure and heart rate were controlled. Plasma ionized calcium was lowered to 0.58 +/- 0.01 mM by citrate infusion and raised to 1.70 +/- 0.01 mM by calcium chloride infusion in random order in each dog. Left ventricular function at each of these ionized calcium levels was compared with that in an immediately preceding normocalcemic period. At a constant stroke work (16.9 +/- 0.2 g-m), sustained hypercalcemia was associated with a small decrease in left ventricular end-diastolic pressure (1.7 +/- 0.7 cm H2O, p less than 0.05) despite a marked increase in peak left ventricular dP/dt (first derivative of ventricular pressure) averaging 34 percent (p less than 0.001). Coronary blood flow, tension-time index and myocardial oxygen consumption were not significantly altered. Stroke work determined at a left ventricular end-diastolic pressure of 14 cm H2O, by interpolation in left ventricular function curves, was 11 +/- 4.4 percent above that at control normocalcemia (p less than 0.05). At a constant stroke work (16.9 +/- 0.2 g-m), sustained hypocalcemia was associated with a marked depression of left ventricular function as demonstrated by a substantial increase (from 4.9 +/- 0.3 to 12.7 +/- 1.1 cm H2O, p less than 0.0001) in left ventricular end-diastolic pressure (p less than 0.0001), decreased mean systolic ejection rate (p less than 0.01) and decreased peak left ventricular dP/dt (p less than 0.0001). Coronary blood flow increased (p less than 0.05) whereas myocardial oxygen consumption did not change significantly. A marked displacement of left ventricular function curves to the right (compared with curves obtained during normocalcemia) was observed, and stroke work determined at a left ventricular end-diastolic pressure of 14 cm H2O was 52 +/- 5.4 percent below control level (p less than 0.001). It appears that hypercalcemia, when initiated from a normal control level, provides only a small enhancement of ventricular pump performance (as indexed by the stroke work-left ventricular end-diastolic pressure relation) despite a marked increase in peak left ventricular dP/dt, whereas marked improvement of left ventricular performance may be expected when calcium infusion is initiated from an ionized calcium level that is below normal.

Animals↗

PubMed1981

Right ventricular distension and left ventricular compliance.

The constraint of the right ventricle (RV) on the end-diastolic pressure-volume (PV) relationship of the nonischemic and ischemic left ventricle (LV) was studied. The model used was the isovolumic beating LV, with separately perfused ejecting RV with controlled RV distension. The effect of augmented RV distension on the nonischemic LV PV relationship was examined. A change from mild [right ventricular end-diastolic pressure (RVEDP) = 1.5 mm Hg] to severe (RVEDP = 16 mmHg) RV distension resulted in a significant leftward shift of the LV PV relationship. Ischemia was produced for 90 min by reducing flow in the cannulated left main coronary artery and the effect of two levels of stable RV distension on the PV relationship of the ischemic LV was examined. Mild RV distension and moderate (RVEDP = 6 mmHg) RV distension were used. In both groups, there was a progressive leftward shift in the LV PV relationship that was significant by 60 min of ischemia. No change was seen in nonischemic controls. Ventricular relaxation, as described by the time constant of isovolumic relaxation, T, was impaired throughout ischemia but was not sufficiently prolonged to explain the above changes. Thus, the time course of change in the LV PV relationship during ischemia differs from that previously reported after pacing-induced ischemia in humans. Neither the external constraint of the RV nor incomplete relaxation explains this difference.

Animals↗

PubMed1980

Aortic valve replacement: a 9-year experience.

Experience with aortic valve replacement over a 9-year period is reviewed. Hospital mortality was 5.0%, with an additional late mortality of 15.0% during a mean follow-up period of 4.3 years. There was a 7.5% mortality among the 93 patients who were operated on using direct coronary perfusion. There were no early deaths among the 48 patients operated on using cold cardioplegic arrest. Paravalvular leaks developed in 20 patients, and 9 had reoperation. There were no early deaths following elective reoperations for prosthetic valve dysfunction, but urgent reoperation was associated with a 40% mortality. Eighty percent of all patients are still alive at a maximum follow-up of 9 years. Eighty-six percent of the survivors who were in New York Heart Association Functional Class III or IV before operation are now in Class I or II. Hypothermic cardioplegic arrest was found to be preferable to coronary perfusion as a method of myocardial protection during aortic valve replacement. Patients with paravalvular leaks who have a history of left ventricular failure prior to aortic valve replacement should be considered candidates for early elective reoperation, owing to the significantly greater mortality associated with urgent reoperation.

Adolescent↗

PubMed1980

Late graft patency and symptom relief after aorta-coronary bypass.

One hundred six consecutive patients underwent elective or emergency coronary artery bypass grafting (CABG) between January, 1974, and November, 1975. There were 90 men of an average age of 54 years and 16 women an average of 64 years. Unstable angina (preinfarction angina, angina decubitus, and crescendo angina) was present in 54 patients of this group and eight were in congestive heart failure. Sixty-two of the 106 had previously had myocardial infarctions and four had evolving infarctions. There were four operative deaths (3.8%) and one early hospital death (less than 30 days' hospitalization). Perioperative infarction occurred in five of the survivors. Of the 197 grafts placed in the 101 survivors, 94% were patent by angiography at 1 to 2 weeks (175 of 187 vein grafts and 10 of 10 left internal mammary grafts). At 1 to 2 years after CABG, 62% of the survivors consented to repeat angiography at which time 94% of the grafts were patent (101 of 108 vein grafts and seven of seven left internal mammary grafts). Clinical follow-up of 81 of the 101 survivors at 1 year found 99% of them to be asymptomatic or improved. Repeat clinical follow-up of all survivors (99 of 101) at 3 to 4 years found 93.9% asymptomatic or improved. Overall survival, including operative deaths, was 92.4% at 4 years.

Adult↗

PubMed1980

Regional myocardial protection: use of a new method to compare cold potassium cardioplegia with hypothermic coronary perfusion.

A new canine model was developed to compare two cardiplegic agents using each heart as its own control. Paired piezoelectric crystals were implanted into the left anterior descending and circumflex regions. The percentage of shortening (systolic shortening/end-diastolic segment length X 100) was assessed in each region on right-heart bypass over a range of cardiac outputs. Durng 100 minutes of ischemic arrest the left anterior descending and circumflex regions were perfused separately every 20 minutes with either cold buffered saline or cold KCl cardioplegia solutions. After recovery, the percentage of shortening after ischemic arrest was determined. The percentage of shortening in the region protected by KCl was unchanged (12.5 +/- 5.0 to 13.0 +/- 4.6%) after arrest, but was markedly decreased in the buffered saline region (11.3 +/- 5.9 to 3.2 +/- 4.9%) (p < 0.001, n = 6). This model should facilitate the comparison of two cardioplegic solutions.

Animals↗

PubMedDate not supplied

Left main coronary artery embolism: a case report.

A 27-year-old man had recurrent myocardial infarction found to be due to coronary embolism to the left main coronary artery with downstream embolization. The presumed etiology of thromboembolism was idiopathic cardiomyopathy. A unique method of treatment with Fogarty catheter retrieval was used.

Adult↗