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Biomedical subjects

D C Harrison

Publications and source records attributed to D C Harrison.

At least 217 records · Page 12Linked to original sources

Effect of varying differentiator frequency response on recorded peak dP/dt.

The effects of varying the differentiator cutoff frequency on the recorded peak first derivative of left ventricular pressure were assessed. High fidelity, solid state pressure transducers and recording equipment were used. In the canine heart with a basic periodicity of 1-3 Hz, the differentiator frequency response required to record an accurate peak dP/dt is influenced by the value of peak dP/dt. In the range of peak dP/dt between 1 500 and 9 000 mm Hg/s (200 and 1 200 kPa/s), a differentiator cutoff frequency of at least 90 Hz was required to record accurately peak dP/dt.

Animals↗

Investigation of the safe withdrawal period for propranolol in patients scheduled for open heart surgery.

The time necessary for dissipation of radioactive labelled propranolol and its metabolites and the cardiac effects of this agent in the hearts of patients undergoing open-heart surgery were studied. Isoprenaline produced chronotropic and inotropic responses in atrial muscle in tissue bath studies which were normal 8 to 12 hours after withdrawing propranolol. After the administration of either 25 or 75 muCi of 14C-labelled propranolol, the myocardial tissue concentration declined to insignificant levels between 24 and 28 hours. We conclude that withdrawal of propranolol therapy 24 to 48 hours before cardiac surgery should be acceptable.

Cardiac Surgical Procedures↗

Effect of propranolol on left ventricular function, segmental wall motion, and diastolic pressure-volume relation in man.

Precise quantitation of the effects of the non-selective beta adrenergic blocking drug propranolol (3.15 mg/kg body weight) on left ventricular function, segmental wall motion, and diastolic pressure-volume relation in man has been performed. High fidelity left ventricular pressure measurements and simultaneous single-plane angiocardiograms were recorded on a video disc and volumes calculated by a light-pen computer system. Systolic segmental wall motion was computer analysed using the long axis-quadrasection method. Patients were transvenously atrially paced to maintain a constant heart rate. The haemodynamic effects of propranolol may vary depending upon the extent of pre-existing myocardial disease. In some patients ventricular function, as measured by ejection fraction, may be reduced. This reduction in ejection fraction appears to result from overall reduction in segmental wall motion, but also from accentuation of segmental wall abnormalities. These results are consistent with the thesis that beta adrenergic blocking drugs may inhibit compensatory sympathetic mechanisms. The diastolic effects of propranolol may include quite substantial increases in ventricular volumes in those patients with impaired cardiac function. With respect to the intact human ventricle, propranolol may increase diastolic volume for a given level of ventricular pressure. Thus, in a static sense, the ventricle in these patients could be viewed as being more compliant after propranolol administration. However, the fact that the length-tension relation, as measured by the slope of the logarithmic pressure versus volume plot is unaltered by propranolol, suggests that the muscle comprising the ventricle itself exhibits no alteration in its passive elastic properties.

Angiocardiography↗

Acute circulatory effects of dopamine in patients with pulmonary hypertension.

Twenty-one patients, 11 with normal pulomonary artery pressures and 10 with pulmonary hypertension, had haemodynamic measurements performed before and during dopamine infusion while undergoing cardiac catheterization, in order to evaluate the circulatory effects of dopamine in pulmonary hypertension. In both groups on average, heart rate, pulmonary artery mean pressure, aortic mean pressure, and cardiac index increased significantly, while systemic vascular resistance fell significantly during dopamine administration. In neither group did the average pulmonary vascular resistance or right ventricular end-diastolic pressure change significantly. We conclude that dopamine is a safe and potentially useful drug for the treatment of reduced cardiac output, even in patients with pulmonary hypertension.

Blood Pressure↗

Sinus node function in the denervated human heart. Effect of digitalis.

Evaluation of sinus node function was performed in 5 patients with an intact cardiac autonomic nervous system (group I), and in 8 patients with a transplantated, denervated heart (group 2). After baseline data were recorded, the electrophysiological studies were repeated in all group I patients and in 6 of the 8 group 2 patients, 45 to 60 minutes after the administration of digoxin 1.25 mg intravenously. Baseline cycle length, sinus node recovery time, and sinoatrial conduction time were significantly shorter in the transplanted heart than in those with intact autonomic innervation, but correction of the sinus node recovery time and sinoatrial conduction time for heart rate abolished these differences. Digoxin produced a small increase in cycle length, sinus node recovery time, and sinoatrial conduction time which did not reach statistical significance in this small study group of patients with innervated hearts. In the denervated, transplanted patients, no change in cycle length occurred after digoxin in any patient. The sinus node recovery time was unaffected by glycoside administration in 3 of 6 patients, while the sinoatrial conduction time was unchanged in 4 of 6. In one group 2 patient, digoxin produced first degree sinoatrial node exit block, and in a second patient, 2:1 sinoatrial nodal exit block developed. The mechanisms responsible for these effects in the denervated heart are not clear.

Adult↗

Perioperative myocardial infarction during cardiac surgery. Diagnosis, ECG and enzyme testing.

The detection of perioperative myocardial infarction is complicated by the variety of electrocardiographic changes normally seen concomitantly with cardiac surgery. Unequivocal electrocardiographic diagnoses based on new Q wave development and evolution of ST and T segments are virtually always confirmed by inappropriately high postoperative enzyme test results. For those patients exhibiting nondiagnostic but suggestive electrocardiographic changes, enzyme testing provides a valuable adjunct in determining whether infarction has indeed taken place. Enzyme testing, similarly, in and of itself, cannot provide the dichotomous situation between those patients experiencing infarction and those who are not. SGOT and LDH appear the most reliable indicators of infarction. CPK is quite volatile with sporadic occurrences of high enzyme elevations without obvious clinical or electrocardiographic explanation. The Ck isoenzymes provide a highly specific test for myocardial damage. However, their sensitivity is sufficiently great that a relatively minor cardiac manipulation may result in uninterpretable results.

Angina Pectoris↗

Effect of digoxin on atioventricular conduction. Studies in patients with and without cardiac autonomic innervation.

The effect of digoxin on atrioventricular (a-v) conduction was compared in five patients with an intact cardiac autonomic nervous system (Group I) and seven patients who had undergone cardiac transplantation (Group II), in whom we have previously shown the transplanted heart to be completely denervated. Small decreases in the atrial effective refractory period (ERP) (from 262 plus or minus 12 to 254 plus or minus 11 msec) and atrial functional refractory period (FRP) (from 304 plus or minus 12 msec) were observed in Group I patients after digoxin, but these changes were not significant. However, significant increases in the A-V nodal ERP (from 315 plus or minus 18 msec to 351 plus or minus 17 msec, P less than 0.05), and A-V nodal FRP (from 426 plus or minus 42 to 460 plus or minus 46 msec, P less than 0.01) were produced by digoxin and were unrelated to changes in cycle length. In Group II patients with denervated hearts, changes in atrial ERP (from 246 plus or minus 4 to 243 plus or minus 6 during spontaneous sinus rhythm; from 204 plus or minus 10 to 216 plus or minus 8 msec during atrial pacing) and atrial FRP (from 311 plus or minus 12 to 316 plus or minus 11 msec during spontaneous sinus rhythm; from 254 plus or minus 12 to 260 plus or minus 10 msec during atrial pacing) were not significant. However, in contrast to the Group I patients, the digoxin-induced changes in A-V nodal ERP (from 280 plus or minus 22 to 297 plus or minus 18 msec during atrial pacing) and FRP (from 368 plus or minus 18 to 377 plus or minus 18 msec during spontaneous sinus rhythm; from 334 plus or minus 13 to 346 plus or minus 16 msec during atrial pacing) were also statistically insignificant. Our results demonstrate that the electrophysiologic effects of digoxin on atrioventricular conduction in man are most marked in the atrioventricular node and are dependent on cardiac innervation

Adult↗

Dose response effectiveness of propranolol for the treatment of angina pectoris.

Seventeen patients received placebo medication during a 12-week run-in period, followed by four double-blind study periods of six weeks each, during which time placebo, 80 mg, 160 mg and 320 mg propranolol dosages were administered. Examination of the frequency of angina episodes and nonprophylactic nitroglycerin consumption revealed significant beneficial clinical responses for both the 160 and 320 mg dosages. Exercise testing also demonstrated increased exercise tolerance (320 mg dose) with a shift of the exercise end point from pain to fatigue in seven of 17 patients. The interrelationships between propranolol daily dosage, clinical response assessed by percent reduction in anginal episodes, beta-adrenergic blockade measured by percent reduction in exercise heart rate and serum levels were examined. In general, serum levels of 30 ng/ml, when drawn 90 to 180 minutes following the last oral dose, were required to achieve a 25% or greater reduction in angina frequency. Serum levels above 30 ng/ml were similarly correlated with a 20% or greater reduction in exercise heart rate at equivalent levels of exercise. Detailed examination of different patterns of clinical response with respect to beta-blockade, serum levels and oral doses are presented.

Administration, Oral↗

Arrhythmias in patients with mitral valve prolapse.

Resting ECGs, exercise treadmill tests and 24-hour ambulatory ECGs were recorded and analyzed in 24 unselected patients with mitral valve prolapse. Arrhythmias were frequent. There were three distinct groups of patients, defined on the basis of total number of premature ventricular contractions (PVCs) during the 24 hours; there were no PVCs in 25%, and frequent PVCs in 50%. Complex ventricular arrhythmias, including ventricular tachycardia in five patients, were found almost exclusively in the group with frequent PVCs. Fifteen of the 24 patients demonstrated atrial premature contractions (APCs) during the 24 hours. Complex atrial arrhythmias were found among patients with infrequent, as well as those with frequent, APCs. Supraventricular tachycardia was detected in seven of these patients. The incidence of ACPs decreased during sleep in 67% of the patients and showed no change during sleep in 33%. A poor correlation was found between symptoms recorded in patient diaries and changes noted on 24-hour ECG recordings. The peak PVCs/15 min and peak ACPs/15 min during a 24-hour period of monitoring was found to be an excellent guide to the total number of PVCs and APCs occurring during that period. This permits an accurate prediction of the total number of PVCs in 24 hours after performing an exact PVC count on only 15 minutes of ECG data. Finally, the 24-hour ambulatory ECG was sensitive than the treadmill test and both were superior to the 12-lead ECG for detecting arrhythmias in these patients.

Adult↗

The status of cardiac transplantation, 1975.

Since December 1967, 263 human cardiac transplant operations have been performed throughout the world. Eighty-two of these were performed at Stanford University Medical Center, In 1974, 27 such operations were performed, 15 at Stanford Survival rates for the entire Standford series are 48% at one year and 25% at three years; survival rates at one and three years for patients surviving the first three critical months after transplantation are 77% and 42%, respectively. Recipients under the age of 55 years, with New York Heart Association Class IV cardiac disability, are selected for transplant procedures according to criteria dictated by experience over the past seven years. A routine immunsuppressive regimen for organ transplantation, incorporating prednisone, azathioprine, and antithymocyte globulin is employed early postoperatively, and prednisone and azathioprine are used for indefinite maintenance therapy. Acute cardiac graft rejection in nearly all recipients is diagnosed by clinical signs, electrocardiographic changes, and percutaneous transvenous endomyocardial biopsy. Ninety-five percent of acute rejection episodes are reversible with appropriate immunosuppressive treatment, but infectious complications are common and have accounted for 56% of all postoperative deaths. The Stanford experience in cardiac transplantation has demonstrated the potential therapeutic value of this procedure. Maximum survival now extends beyond five years. Satisfactory graft function has been documented in long-term surviving patients, the majority of whom have enjoyed a high degree of social and physical rehabilitation.

Acute Disease↗

Analysis of left ventricular function in response to afterload changes in patients with mitral stenosis.

In order to assess left ventricular function in patients with rheumatic mitral stenosis, left ventricular function curves (plotting stroke work index vs left ventricular end-diastolic pressure) were constructed using angiotensin to augment, and nitroprusside to reduce, afterload. Hemodynamic responses to these alterations in afterload were measured. Resting ejection fractions and qualitative assessment of left ventricular angiographic contraction abnormalities were also determined. Changes in left ventricular end-diastolic pressure following afterload interventions could be linearly related to changes in mean aortic pressure, but mitral valve gradients were unaffected. Afterload reduction with nitroprusside did not augment cardiac output. Afterload elevation with angiotensin significantly depressed both cardiac output and calculated mitral valve areas. Patients with normal resting ejection fractions evidenced normal ventricular function curves and those with depressed ejection fractions showed flat or declining function curves. Contraction abnormalities, generally in the posterobasal area, correlated well with abnormal left ventricular function curves.

Adult↗

Inotropic effects of different calcium ion concentration on the embryonic chick ventricle. Comparison of single cultured cells and intact muscle strips.

The effects of changes in the calcium ion concentration in the medium bathin single beating cultured chick embryo ventricular cells were determined using an electro-optical monitoring technique for measuring the amplitude and velocity of cell wall motion. Although single cells showed significant decreases in the amplitude and velocity of cell wall motion during contraction when the calcium ion concentration was lowered from 1.8 mM to 0.9 mM, there were no significant changes in these parameters when the concentration was increased from 1.8 mM to 3.6 mM, and the magnitude of this response increased with increasing embryonic age. These results suggest that there is a reduced positive inotropic responsiveness in young chick embryo ventricular cells, which is particularly marked in the single cultured cell preparation because of the tendency of culturing techniques to select out immature cell populations.

Animals↗

Ostium primum defect in the adult: postoperative follow-up studies.

Twelve adult patients with ostium primum atrial septal defects (incomplete endocardial cushion defect) who underwent surgical repair of their lesions were evaluated in the late postoperative period. All had closure of the low-lying atrial septal defect, with suturing of the mitral valve cleft in 11 patients. Although the patients benefited symptomatically from the surgery, all had residual cardiac murmurs. Postoperative cardiac catheterization and left ventriculography in eight revealed successful closure of the atrial septla defect, but three demonstrated residual mitral insufficiency. In spite of the successful surgical repair in these patients, bacterial indocarditis prophylaxis should be continued in view of the residual murmurs and valvular abnormalities.

Adolescent↗

Comparison of 24 versus 12 hours of ambulatory ECG monitoring.

In order to assess the additional information obtained from 24 hours compared to 12 hours of ambulatory ECG (electrocardiogram) recording, we analyzed 72 ambulatory ECG monitoring tapes in which arrhythmias were present. In all cases the second 12 hours included the entire period of sleep. Only 38 of 233 (16 percent) episodes of arrhythmias, frequent premature ventricular contractions (PVC's), two or more PVC's in a row, multiform PVC's, ventricular bigeminy, trigeminy, premature atrial contractions (PAC's), and supraventricular tachyarrhythmias occurred for the first time in the second 12-hour period. New ventricular arrhythmias were detected during the second 12-hour period in 13 percent of the arrhythmic episodes. Although sleep resulted in a marked decrease in PVC frequency in 63 percent of 30 recordings, with frequent PVC's while awake, 8 percent had a significant increase during sleep. In contrast, short runs of supraventricular tachyarrhythmias occurred during the second 12 hours in 48 percent of cases, 66 percent of these while asleep. These data suggest that a 24-hour ambulatory ECG tape recording be utilized initially to characterize the occurrence and frquency of the patients' ambulatory arrhythmias during awake and sleep periods. Thereafter, additional ECG recordings for monitoring antiarrhythmic drug therapy can be accomplished with a 12-hour recording in more than 80 percent of patients

Adolescent↗