Properties and applications of the average interparticle distance.

The first and second moment operators are used to define the origin invariant shape and size of a molecule or functional group, as well as expressions for the distance between two electrons and the distance between an electron and a nucleus. The measure of molecular size correlates quite well with an existing theoretical measure of molecular volume calculated from isodensity contours. Also, the measure of size is effective in predicting steric effects of substituents which have been measured experimentally. The electron-electron and electron-nuclear distances are related to components of the Hartree-Fock energy. The average distance between two-electrons can model the Coulomb energy quite well, especially in the case of localized molecular orbitals. The average distance between an electron and a nucleus is closely related to the electron-nuclear attraction energy of a molecule.

Nonplanar aromatic compounds. 5. A atrategy for the synthesis of cis-10b,10c-dimethyl-10b,10c-dihydropyrenes. First crystal structure of a cis-10b,10c-dimethyl-10b,10c-dihydropyrene.

Through the use of a potentially removable tether, a heavily substituted 10b,10c-dimethyl-10b,10c-dihydropyrene (DMDHP), 20, was synthesized exclusively as the cis-isomer. It exists as the major component (20:1) in an equilibrium with its valence isomer syn-[2.2]metacyclophanediene 19. An X-ray crystal structure determination of 20, a cis-(2,7)-10b,10c-dihydropyrenophane, provided the first experimental measurements of the cis-DMDHP skeleton. The observed bond alternation in the [14]annulene was found to be larger than that of the corresponding trans-DMDHP framework. Prior MMPI calculations, on which previous discussion of the structure of the cis-DMDHP system had been based, are in very good agreement with the experimental results. Our own DFT calculations predict a more symmetric and more bond equalized structure than was observed in 20.

Endo-exo and facial stereoselectivity in the Diels-Alder reactions of 3-substituted cyclopropenes with butadiene.

A computational examination of the four modes of addition in the Diels-Alder reactions of 3-substituted cyclopropene derivatives (substituents: BH(2), CH(3), SiH(3), NH(2), PH(2), OH, SH, F, and Cl) with butadiene have been carried out at the B3LYP/6-31++G(d)//HF/6-31++G(d) level. The degree of stabilization of these derivatives at the ground state correlates with the electronegativity of the substituent. This attenuation of reactivity and differences in steric interactions are the only factors needed to explain both the high facial selectivity and the differences in the endo-exo selectivity seen in these reactions. Furthermore, evidence is presented that indicates that stabilization by an interaction involving the syn C-3 hydrogen of cyclopropene and butadiene is small or irrelevant in controlling the endo-exo selectivity of the Diels-Alder reaction.

Prognostic significance of the development of left bundle conduction defects following aortic valve replacement.

The association of intraventricular conduction defects and aortic valvular disease is widely recognized. This study was undertaken to evaluate the effects on survival of left bundle conduction defects (LBCDs) as a consequence of aortic valve replacement. A total of 133 patients were followed between 1 and 70 months after operation, with a mean follow-up of 32.1 months. The incidence of intraoperative LBCDs was 31.6% or 42 patients. There were 13 deaths in the group of 42 patients with LBCDs compared to eight deaths in the group of 91 patients without such abnormalities (p less than 0.01). Sudden death occurred in five of 42 patients with postoperative LBCDs and two of 91 patients with normal intraventricular conduction (p less than 0.025). The survival rate in these patients with significant aortic stenosis and normal intraventricular conduction was 89.9%, whereas if LBCD had occurred after operation, the survival rate was 65.7% (p less than 0.005). If the LBCD was accompanied by a left axis deviation, the survival rate was 21.7%. Sudden death may be due either to a tachyarrhythmia or perhaps to progression from LBCD to complete heart block or trifascicular block. It is important that this group of patients be monitored closely after operation. There may be an indication to insert prophylactic permanent pacemakers in this group.

Acute and early experimental tricuspid valvular stenosis in dogs.

Acute and early (two months) experimental tricuspid valve stenosis was produced in 20 dogs. Clinical and hemodynamic alterations that resulted from severe anatomic tricuspid valve narrowing were surprisingly mild. In the acute stenosis studies, the normal tricuspid valve area of 8.2 +/- 0.3 sq cm was narrowed to less than 1.0 +/- 0.1 sq cm with a resulting right auricle-right ventricle diastolic gradient of 3.7 +/- 0.7 mm Hg. In early studies, a decrease in tricuspid valve area from 7.3 sq cm to 1.6 +/- 0.3 sq cm produced a diastolic gradient of 1.8 +/- o.2 mm Hg. After 60 days, overt signs of right-sided failure (pleural effusions and ascites) were absent, and histological evidence of passive congestion (liver and spleen) was unpredictable. The systemic and portal venous vascular beds appear to act as excellent buffers against increases in right-sided cardiac pressures. We conclude that isolated narrowing of the tricuspid valve must be very severe to cause notable clinical and hemodynamic changes.

A new instrument for surgical creation of an atrial septal defect.

An instrument for surgical creation of an atrial septal defect (ASD) was designed and tested in puppies weighing an average of 4.7 kg. Oxygen saturations were obtained in both atria, the superior vena cava, and the inferior vena cava before and after septectomy. The instrument has a cutting cylinder introduced into the right atrium (RA) through the right atrial appendage with a second part (base-plate) inserted into the left atrium (LA) just posterior to the interatrial groove. In 21 animals (Group 1), a single hole was created in dogs killed 48 hours later. In 9 animals (Group 2), an attempt was made to create two adjoining holes. In 14 animals (Group 3), a single hole was created and the dogs were allowed to triple their body weight before they were killed. Group 1 dogs demonstrated a 10% increase in average venae cavae--RA oxygen saturation immediately after septectomy and a 9.4 +/- 0.37 mm diameter of the ASD at death; in Group 2, there was a 14% average step-up and a 12.7 +/- 0.6 mm diameter of the ASD; and in Group 3, the diameter of the ASD was 11.5 +/- 0.4 mm, representing a 50% increase in average area with dog growth compared with that of Group 1. After this experience in the production of ASDs in 44 experimental animals, we find that this instrument seems to be reliable, simple, and safe.

Left ventricular function following aortic valve replacement: assessment by radionuclide ventriculography.

Left ventricular function following aortic valve replacement has been evaluated in 15 consecutive patients. Cold potassium cardioplegia was utilized for myocardial preservation. Left ventricular function was assessed by radionuclide ventriculography performed preoperatively and 3 months postoperatively. The predominant lesion was aortic insufficiency in 10 patients and aortic stenosis in five patients. All patients demonstrated improved ejection fractions at 3 months. The mean increases of ejection fraction in the aortic insufficiency group were 20% from the anterior (Ant.) position and 12.5% from the left anterior oblique (LAO) position; in the aortic stenosis group they were 15.2% (Ant.) and 14.8% (LAO). It is our contention that cold potassium cardioplegia is an effective means of myocardial preservation and that it showed no measurable deleterious effect on left heart function in this group of patients.

Wounds traversing two or more cardiac chambers. Case presentation of two survivors and review of the literature.

A review of the literature on patients who have survived wounds traversing two or more cardiac chambers is presented and two further cases are documented. The inital management of the patient should be directed toward control of hemorrhage or treatment of cardica tamponade or both. Cardiopulmonary bypass is helpful in repair of many intracardiac defects but is not absolutely essential for survival. Surface myocardial wounds should be sutured during the initial procedure to allow for immediate survival. A subsequent procedure may be indicated to correct intracardiac defects. Repair of injuries to the mitral and aortic valves should be directed at an attempt to reconstruct the damaged valve. If this is impossible, a prosthetic valve should be inserted. Injuries to the tricuspid and pulmonic valves probably warrant a conservative approach. Septal defects can be treated easily with Dacron patches or primary suture closure. Postoperative complications include all of those commonly seen with thoracic procedures, but infection is less prominent than one would anticipate, even when prostheses have been implanted. With early, aggressive management it is anticipated that more survivors of these serious wounds will be recorded.

One hundred consecutive coarctation resections followed from one to thirteen years.

The technique of operative repair for coarctation of the aorta is now well standardized and the immediate surgical mortality has been lowered to less than 5% in most large series. Long term follow up, however, is only recently being reported. This paper describes the current status of 100 consecutive patients who underwent elective resection from 1--13 yr ago. There was only one operative death. In contrast with other reports, residual systemic hypertension is rare in the 97 survivors. These observations confirm that coarctation of the aorta can be repaired surgically with an acceptable operative mortality; the outlook of the survivors appears excellent.

An alternative approach to the closure of the Blalock-Taussig anastomosis at open-heart surgery.

Dissection for closure of a Blalock-Taussig shunt can occasionally be difficult or hazardous at the time of corrective operation. The technique traditionally used for closure of a Potts anastomosis, in which profound hypothermia and circulatory arrest are used, has been applied successfully in 11 operations for control of 12 Blalock-Taussig anastomoses. The technique is described.

Drip retrograde coronary sinus perfusion for myocardial protection during aortic cross-clamping.

Moderate hypothermia is one of the methods utilized for myocardial protection when the aortic root is cross-clamped but not opened. A combination of low-pressure, low-flow retrograde coronary sinus perfusion (RCSP) with oxygenated blood at moderate hypothermia (29 degrees C.) was demonstrated to yield significantly better protection to left ventricular function in dogs than does moderate hypothermia alone. Ventricular function was recorded before and after 1 hour of aortic cross-clamping at identical preloads and heart rates. Aortic pressure was returned to a level as close to base line as possible by constriction of the descending aorta. The average mean aortic pressure of the animals perfused retrograde at 29 degrees C. was returned to within 4 per cent of base line. By contrast, in the animals protected with moderate hypothermia alone, the pressure could be returned only to a level which was 37 per cent lower than base line. In animals protected with moderate hypothermia alone, cardiac output dropped 62 per cent, left ventricular stroke work (LVSW) 75 per cent, and peak dp/dt 44 per cent. In the animals protected with RCSP and moderate hypothermia, the cardiac output dropped 6 per cent, LVSW 9 per cent, and peak dp/dt 5 per cent. The differences in the changes noted between these two groups were significant for LVSW and dp/dt at a level of p less than 0.01 and for cardiac output and aortic pressure at a level of p less than 0.05. These results suggest that RCSP may be indicated when moderate hypothermia is otherwise chosen to be the sole source of myocardial protection.

Surgical management for acute coronary insufficiency with three year's follow-up.

In this report, acute coronary sufficiency is defined as unstable angina requiring narcotics for relief and an unstable electrocardiogram with or without transient mild enzyme elevations. Forty-five consecutive patients with this syndrome underwent coronary artery grafting with the saphenous vein within 48 hours of the onset of symptoms. They were followed for 3 years. There was an 8.8 per cent operative mortality rate. One long-term survivor sustained a fatal myocardial infarction 18 months postoperatively. One nonfatal myocardial infarction occurred 6 weeks postoperatively. Therefore, the 3 year cumulative mortality rate was 11 per cent and the 3 year myocardial infarction rate was 4 per cent. Thirty-eight patients are in Class I clinical status, 1 is in Class II, and 1 is in Class III.

Current status of the surgical treatment of truncus arteriosus.

Persistent truncus asteriosus is now correctable surgically in patients with favorable anatomy. Given pulmonary arteries of reasonable size arising from any source, successful correction is possible so long as irreversible pulmonary vascular disease has not occurred. Although the majority of children with this defect demonstrate increased pulmonary blood flow, systemic-pulmonary artery shunts can be used. Also, banding of the pulmonary artery, followed subsequently by successful total correction, has been described. Recent reports of a few successful total corrections in infancy, performed with the aid of deep hypothermia and circulatory arrest, may modify the current approach. Although the majority of the reported corrections have involved aortic homograft reconstruction of the pulmonary artery, we strongly favor a synthetic prosthesis containing a heterograft valve. Based upon our clinical experience and this review of the literature, a suggested management protocol is presented.