James V. Maloney

Effects of pulsatile assistance and nonpulsatile flow on subendocardial perfusion during cardiopulmonary bypass

We compared the effects of pulsatile and nonpulsatile perfusion in 12 dogs on extracorporeal circulation. In beating empty and fibrillating hearts at 37 degrees and 28 degrees C, coronary blood flow was measured by flowmeter and microspheres at diastolic pressures ranging between 50 and 130 mm Hg. At fixed systemic flow rates (range, 600 to 2,400 ml/min), pulsatile perfusion produced a transient (3 to 4 second) augmentation of diastolic pressure and then resulted in the following: (1) decreased peripheral vascular resistance (p less than 0.05); (2) unchanged peak diastolic pressure (compared with nonpulsatile perfusion); (3) decreased mean aortic pressure (6 to 37%) (p less than 0.05); (4) decreased coronary blood flow (10 to 45%) (p less than 0.05); and (5) decreased subendocardial blood flow (from 512 to 438 ml/100 gm/min) (p less than 0.05). Pulsatile perfusion in beating hearts (37 degrees or 28 degrees C) did not reduce subendocardial vascular resistance, but did improve subendocardial perfusion by 27% and 36% in fibrillating hearts at 37 degrees and 28 degrees C, respectively. We conclude that with the exception of ventricular fibrillation, pulsatile assistance offers no advantage over nonpulsatile perfusion and has the potential disadvantage of requiring higher pump flow rates to achieve any desired level of coronary and subendocardial flow.

Phasic Coronary Flow: Intraoperative Evaluation of Flow Distribution, Myocardial Function, and Reactive Hyperemic Response

Using visual inspection of phasic flow patterns and understanding their physical determinants, intraoperative decisions regarding flow distribution, function of revascularized myocardium, and collateral communications can be made. Mean flow measurements cannot provide this information. Systolic compressive forces across most of the normally contracting left ventricle limit systolic myocardial perfusion. Consequently, normal flow through the left anterior descending, left circumflex, and dominant right coronary artery (supplying the inferior left ventricle) is predominantly diastolic (greater than 60%) and remains so during reactive hyperemia. Representative examples from 100 consecutive revascularizations are presented showing that when more than 40% of flow is systolic in the right coronary artery, high mean flows (greater than 100 ml/min) may go predominantly to the right rather than the left ventricle; in the case of the left coronary artery, high mean flow may supply myocardium undergoing infarction or replaced by scar rather than normally contracting muscle. When more than 60% of flow is diastolic without reactive hyperemia, borderline mean flow (40 to 60 ml/min) may indicate lack of distal ischemia rather than fixed distal resistance.

Coronary revascularization in "high" versus "low-risk" patients: The role of myocardial protection.

Postoperative mortality, infarction, and need for inotropic support are reportedly increased following myocardial revascularization in “high-risk” patients. We believe these complications result from inadequate protection of the compromised myocrardium and should not occur with greater frequency in “high-risk” than “Low-risk” patients if the heart is optimally protected during the entire course of the operative procedure. Results following revascularization in 50 consecutive “low-risk” and 50 consecutive “high-risk” patient were analyzed. One or more of the following factors were present in the “high-risk” group; ventricular dysfunction-ejection fraction < 0.4, preinfarction angina, evolving infarction, recent infarction (less than 2 weeks), and refractory venticular tachyarrhythmia. The following principles were used in all patients to minimize ischemic injury: 1) avoidance of pre-bypass hypo- or hypertension, 2) limitation of ischemic arrest to less than 12 minutes, 3) avoidance of ventricular fibrillation, and 4) prolongation of total bypass as necessary to repay the myocardial oxygen debt. Postoperative inotropic support was required in 10% of “high” and 10% of “low-risk” patients; new postoperative infarction developed in 10% of “high” vs. 10% “low-risk” patients; death occurred in 2% of “high” vs. 4% “low-risk” patients. These results are comparable and indicate that optimum myocardial protection allows safe revascularization in the “high-risk” patient.

THE DIRECT EFFECTS OF PRESSURE BREATHING ON THE PULMONARY CIRCULATION

The effects of pressure breathing on the systemic and pulmonary circulations are of practical concern to the anesthesiologist because the technique of controlled respiration is so commonly employed. During World War I1 the contributions of physiologists interested in aviation medicine added greatly to our knowledge of the effects of positive airway pressure on the systemic circulation. The present discussion is concerned with a less well understood aspect of the problem : the direct effects of pressure breathing on the blood vessels within the lungs.

A rational process for the reform of the physician payment system.

ObjectiveAnalysis of the resource-based relative value scale (RBRVS) for physician payment indicates that in 1996, hourly reimbursement rates will be unrelated to the intensity of work and income will be unrelated to hours worked. A “consensus method” of payment is proposed as an alternative to the RBRVS. BackgroundAs with the method of the RBRVS study, a pilot survey asked a specialty-representative cohort of physicians to assign dimensionless numbers to the relative value of work in 15 specialties using the Hsiao et al. definition of work intensity as “time modified by, a) mental effort, b) clinical judgment, c) technical skill, and d) physical effort under stress.” The consensus method is similar to that of the Hsiao method, except there is no mathematical transformation of the raw data to establish specialty work values once the data are collected. A comparative analysis was then made of work hours, reimbursement rates, and annual income with 1) the customary prevailing and reasonable system (CPR, pre-1992),2) the RBRVS system (1996), and 3) the proposed consensus system. ResultsThe RBRVS intends that physicians be reimbursed on the basis of time and intensity of work. Neither the CPR nor the RBRVS systems accomplish this objective when the data and computational methods of the Physician Payment Review Commission are used with independently determined work intensity to compute hourly reimbursement rates in the specialties. The consensus method shows the desired direct linear correlation of income with both length of the physicians work week and intensity of effort. It rates the primary care specialties as a group more highly than the RBRVS. ConclusionThe proposed consensus method meets the original intent of the RBRVS to reimburse physicians on the basis of the resource input of time as modified by the criteria of Hsiao et al.

Acute response to acid-base stress.

A method previously established in the experimental animal for predicting the acute response to either metabolic stress (bicarbonation administration) or respiraiory stress (manipulation of oxygenator gas during cardiopulmonary bypass) has been extended to man. The method is based on a single nomogram. The accuracy of the nomogram is demonstrated using data from 13 patients on cardiopulmonary bypass. Similar agreement obtains between the nomogram and data reported by others. The nomogram can be used to estimate the therapeutically required dose of bicarbonate.

Computers: the physical sciences and medicine

Although computer science is in its infancy, it has already contributed significantly to society in the fields of business and commerce, communication, exploration, and scientific discovery. In contrast, the contributions of computers to medicine have thus far been minimal for reasons which I shall discuss in a moment. It is this lack of application of computers to medicine which makes medicine one of the most fruitful areas for the computer-oriented scientist. I can promise you the rewards will be great for those of you who choose to apply your talent for the benefit of human health and welfare. There are two reasons for this: 1. The systematic methods of scientific thinking which naturally lead to success in the application of computers to a scientific discipline have already been developed, and they have proven phenomenally successful in such fields as high-energy physics and molecular biology. Discovery in the field of medicine waits like a ripe apple to be plucked by the computer-skilled scientist. 2. Society will generously support your efforts. The value judgment that society places on health and longevity ultimately is the same as that which the individual places on them. I have yet to see a man who is dying of cancer of the lung, whether he be laborer or corporation president, who would not trade all of his money, business, commerce, communication, and transportation for 18 more months of healthy existence. Therefore, the computer scientist who devotes his effort to promoting human health and welfare will be both generously supported and greatly appreciated by his fellow man.

Minderung des myokardialen Reperfusionsschadens mit hypocalcämischen, hyperkaliämischen, alkalischem Blut während der postischämischen Wiederaufsättigung mit Sauerstoff

In vorangegangenen Arbeiten konnten wir nachweisen, das ein zusatzlicher Myokardschaden nach ischamischem Herzstillstand durch die postischamische Reperfusion zwar signifikant verringert jedoch nicht vollstandig vermieden werden kann a) durch Herabsetzen des dem Zellaustausch zur Verfligung stehenden ionisierten Calciums (4) b) durch Erhohen des Kaliums zur Verringerung des Stoffwechsels bei weiterbestehendem Herzstillstand (5) oder c) durch Anheben des pH-Wertes auf 7.8 ZUID Ausgleich der postischamischen Acidose wahrend der Reperfusionsphase (6).

Water Distribution Abnormalities in Hypothyroid Dogs Due to Acid-Base Disturbances.

Previous work by Dörr et al. (1) in this laboratory has shown that a hypertonic NaHCO3 infusion increased extracellular water (ECW), measured as the rapidly equilibrating sucrose space, by 25% in hypothyroid dogs and only by 17% in euthyroid dogs. He suggested that this difference could be caused by an accumulation of mucopolysaccharides in the extracellular space of hypothyroids. Substantially increased amounts of the mucopolysaccharide, hyaluronic acid, have been found (2) in the extracellular space of humans and animals with myxedema (the chronic form of hypothyroidism). This material has been localized in the ground substance of connective tissues. It has been demonstrated (3) that its polyelectrolyte characteristics make hyaluronic acid a very influential substance in determining water and electrolyte distribution in the body. Engel (4), Engel et al. (5) and Joseph et al. (6) studied the ion and water binding characteristics of the ground substance of connective tissues, and showed that under hormonal influences the macromolecules comprising the tissue would depolymerize. Their work demonstrated that ion and water shifts between the various body fluids occurred as a result of this change in the physicochemical state of the ground substance. It is the hypothesis of this paper that the physicochemical state of the connective tissue ground substance is altered by changes in the hydrogen ion concentration of its environment (the interstitial fluid), and that these changes of state are particularly significant in the hypothyroid. Since a base infusion increased the extracellular and interstitial space in the hypothyroid as compared to the euthyroid, an acid infusion should yield comparable changes in the opposite direction. In the present study, a series of experiments was performed to measure the changes in water and electrolyte distribution in euthyroid and hypothyroid dogs as a result of an infusion of HCl.

The care and feeding of bioengineering: The pursuit of excellence at a fundamental level

It would be an appropriate keynote address at the quinquennial anniversary of the San Diego Symposium for Biomedical Engineering to review the accomplishments of our young science of bioengineering, to observe and analyze the status quo, and perhaps to point out the direction the field should take in the future. However, a keynoter should be provocative, this attribute being second in importance only to motherhood and brevity. In an effort to be provocative, I would like to limit my few words to a critical analysis of the current status of the interscience area be-