Biomedical subjects
R C Chiu
Publications and source records attributed to R C Chiu.
Myocardial cations and trace metals in cardioplegia: a clinical study.
Cations and trace metals play important roles in the pathophysiology of myocardium, and understanding their changes during cardioplegia may be important in further refining the technique of myocardial protection. Serial myocardial, blood and urine samples were taken from 12 patients undergoing cardiac operation under cold cardioplegia. The concentrations of calcium, magnesium, zinc and copper were measured with an atomic absorption spectrometer. Myocardial magnesium levels were found to be significantly (P less than 0.05) depleted when the "cardioplegic" solution contained 0.69 mmol/l of magnesium, but this could be prevented by increasing the magnesium concentration of the infusate to 2.2 mmol/l. With calcium-free infusate, the myocardial calcium concentration decreased, but zinc and copper values did not change significantly. There were decreased serum concentrations of these cations and trace metals during tbe hemodilution cardiopulmonary bypass but their 24-hour excretions in urine were within normal range. Although the clinical importance of such changes remains to be elucidated, the information may be valuable in designing future cardioplegic solutions with optimal compositions.
In vivo mapping of pulmonary lymphatic pathways: a new technique.
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The effect of topically applied zinc on the healing of open wounds.
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Second primary bronchogenic carcinoma: life-table analysis of surgical treatment.
Twelve patients had curative resection of primary bronchogenic carcinoma. Eleven to 84 months later, a second primary bronchogenic carcinoma was discovered and was operated on. Six patients underwent wedge resection, while the others had a lobectomy or pneumonectomy. There was no operative mortality. Two patients survived longer than 5 years. In addition to these patients, 26 patients who also had successive surgical resections for primary lung cancers were collected from the literature. Two operative deaths were related to respiratory insufficiency. Life-table analysis of this accumulated series of 38 patients revealed the survival rate 1 year after the resection of a second tumor to be 70%, and 2 and 3 years later, 55% and 27%, respectively. Thus, in patients in whom a second primary carcinoma of the lung develops, successive resections tailored to preserve respiratory reserve are compatible with low operative mortality and, in some instances, long-term survival.
The importance of monitoring intramyocardial temperature during hypothermic myocardial protection.
In 50 patients undergoing cardiac operation, hypothermic cardioplegic solution was infused into the root of the aorta immediately after aortic cross-clamping. Cardiac standstill was achieved within 1 to 3 minutes. However, monitoring of intramyocardial temperature with a needle thermistor revealed that such core cooling is unpredictable (the intramyocardial temperature achieved ranged from 7 degrees to 33 degrees C), unstable (this temperature can rise at more than 0.5 degrees C per minute), and uneven (a difference of up to 17 degrees C was observed between the intramyocardial temperature of the anterior and posterior left ventricular sites). The area supplied by the stenotic coronary artery was least protected. Monitoring of intramyocardial temperature enables one to know when supplementary cooling is indicated. We conclude that widespread differences in this temperature during cardiac operation make monitoring advisable for optimal myocardial protection.
Pulmonary reperfusion syndrome.
"Reperfusion syndrome" of the lung may play a role in the pulmonary edema and hemorrhage that occur following pulmonary embolectomy, cardiopulmonary bypass, and shock. Bioenergetic, metabolic, and ultrastructural studies of canine lungs indicate that ventilated lung tissue could tolerate 5 hours of pulmonary arterial occlusion with minimal damage. However, a 24-hour interruption of pulmonary arterial blood flow produced a significant decrease in the ratio of adenosine triphosphate to adenosine disphosphate, and glycogen, and an increase in tissue lactate. Reperfusion of these lungs resulted in even more pronounced biochemical and ultrastructural deterioration, as well as gross pulmonary edema and hemorrhage. The lesion appears to be similar to the reperfusion damage that occurs in other organs, such as the kidney, and the skeletal and cardiac muscles.
On understanding coronary bypass surgery.
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Intraoperative blood-flow responses in coronary artery bypass grafts.
Intraoperative graft flow responses in 15 patients who underwent coronary artery bypass grafting (CABG) were studied systematically. The mean blood flow for 13 left anterior descending (LAD) coronary artery grafts was 64 +/- 20 ml/min and for 12 right coronary artery (RCA) grafts was 53 +/- 13 ml/min. Of these, systolic flow was dominant in one LAD and three RCA grafts, suggesting the perfusion of the right ventricle or the noncontractile left ventricle segment, or both. Five LAD and two RCA grafts had a negligible reactive hyperemic response, and the underlying cause for this can be futher examined by observing their phasic flow patterns. Temporary occlusion of the coronary artery proximal to the site of anastomosis produced increased flow in 8 grafts, indicating the presence of competitive flow; decreased flow was observed in 15 grafts, indicating the presence of proximal retrograde flow which may play a role in the proximal occlusion of the bypassed artery later. Thus intraoperative flow studies supplement the preoperative angiographic findings in elucidating the pathophysiology involved and are useful in evaluating CABG operations.
Effects of hypothermic K-cardioplegia and ATP-Mg solution on myocardial ATP content and function.
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Retrograde coronary sinus perfusion for myocardial protection during cardiopulmonary bypass.
The pathophysiology of retrograde coronary sinus perfusion was studied in a vented, nonworking heart in vitro. The fraction of nutritional blood flow, estimated with the trapping index of radioactive microspheres (15 +/- 5 mu), is approximately one-fifth of total flow. The funoff is primarily through the thebesian system and venovenous channels, as is shown with Microfil injection studies. These results suggest that retrograde coronary sinus perfusion would be of marginal value in revascularizing a working heart but would be effective in protecting a hypothermic, nonworking myocardium. Canine experiments indicate that retrograde coronary sinus perfusion can provide efficient core cooling of the myocardium during cardiopulmonary bypass even in the presence of complete coronary artery occlusion. It is technically simple, delivers cardioplegic solutions to the myocardium without the risk of coronary ostial injury, and can be employed in the presence of severe aortic insufficiency and open aortic root. Retrograde coronary sinus perfusion therefore appears to be a valuable alternative mode of myocardial protection during cardiac operations.
Levels of plasma cyclic AMP and insulin in cardiac surgery.
Cyclic AMP is a common second messenger for a variety of hormones such as catecholamine, glucagon, and growth hormone, which are affected by cardiac surgery. Changes in plasma cyclic AMP level may thus reflect an altered hormonal milieu. The effects of open-heart surgery on plasma cyclic AMP and its relation with serum insulin were studied in 33 adult patients who underwent cardiac surgery with cardiopulmonary bypass. Plasma cyclic AMP levels were markedly elevated during cardiopulmonary bypass and returned toward normal within several days after the operation. The serum insulin concentration remained low, and no positive correlation was found with plasma cyclic AMP level. The responses were similar in patients who had aorta-coronary bypass grafts and those who had valve replacements.
Septic shock: alterations in the second messenger system.
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Femorofemoral bypass: a valuable procedure.
Twenty-seven femorofemoral bypasses were performed in 25 patients with severe arteriosclerosis obliterans affecting the iliofemoral arteries. The series comprised 16 men and 9 women, aged 51 to 80 years. Nineteen patients were poor-risk cases with severe cardiorespiratory disease. Twenty-one patients had undergone vascular procedures previously without success. The operation was carried out: (a) as the primary procedure for very poor-risk patients in an attempt to salvage a limb, (b) to deal with unilateral limb occlusion of an aortoiliac--femoral prosthesis, or (c) as management of infected prosthetic grafts. Fourteen Dacron grafts and 13 saphenous veins were used for the bypasses. There were no operative deaths. Twenty-two patients were clinically improved, two required amputation later and one patient was lost to follow-up. Four patients, including three with preexisting graft infection, had wound infections that cleared with drainage and antibiotics. No other major complications occurred in this group of poor-risk patients. Femorofemoral bypass is safe and provides the surgeon with a useful method of revascularizing the limbs of selected patients.
Endobronchial lymphoscintigraphy (EBLS). New diagnostic modality.
A safe, simple method of visualizing deep intrathoracic lymph nodes and determining regional tracheobronchial lymphatic drainage with colloidal radionuclides has been developed. The tracer is injected submucosally via a bronchoscope and lymph node scanning is performed at least 2 hours later. The technique was developed and tested in seven canine experiments. Endobronchial lymphoscintigraphy (EBLS) has been performed in 43 patients undergoing routine bronchoscopic examination. 99mTc phytate, 198Au colloid, and 99mTc antimony sulfide have been used; the last appears to have been the most satisfactory. The primary lymphatic drainage from selected sites of the tracheobronchial tree could be determined. Up to five lymph nodes have been visualized, with an average of 2.1 lymph nodes seen in those patients with lymph node visualization. Four patterns of lymphatic drainage were seen; ipsilateral ascending, contralateral ascending, descending, and no spread of injected colloid. In some cases cervical and celiac lymph nodes were seen. In combination with conventional diagnostic methods, EBLS in many cases clarified the extent and nature of underlying disease.
A new implantable burst generator for skeletal muscle powered aortic counterpulsation.
Skeletal muscle (SM) can be used for long-term circulatory assist. To generate contractions of appropriate duration and strength, SM requires bursts of electrical pulse trains. Presently, the implantable pulse train stimulator for SM assist is unable, at different heart rates, to adjust pulse burst duration or delay time, adversely affecting timing of counterpulsation. A prototype implantable microprocessor based stimulator (Medtronic Prometheus) has been developed to address this issue. The purpose of this study was to test this generator in an acute dog model. A dual chambered counterpulsation device was connected to the aorta in six dogs, using the latissimus dorsi to power the pump. The generator was connected by sensing/stimulating leads to the heart/left thoracodorsal nerve, programmed to give bursts of 2 V, 30 Hz, and pulse widths of 180 microsecs. Burst delay and duration was set as a fixed percent of the R-R interval of the EKG. The baseline aortic pressures ranged from 75/33 to 118/87 mmHg. During counterpulsation, diastolic pressure increased from 17 to 50 mmHg (30-111% increase). With changing heart rates, the pulse generator spontaneously readjusted its burst delay and duration, maintaining optimal diastolic counterpulsation without systolic interference. We conclude that this new pulse generator can stimulate SM for counterpulsation at varying heart rates, and is suitable for implantation in chronic studies.
LD-PACE II: a new cardiomyostimulator for cardiac bioassist.
The LD-PACE II was designed for use in cardiomyoplasty, aortomyoplasty, and skeletal muscle ventricles. All parameters specified as programmable can be changed in a noninvasive manner (using a programming interface wand connected to a computer using the Windows 95/98 environment). Two new functions may be very useful clinically, based on experimental research. 1. Work-rest regimen. The LD-PACE II is able to deliver alternating periods of muscle contractions and rest. Work and rest periods may be programmed independently between 1 and 120 minutes in increments of 1 minute. The work-rest regimen may be useful clinically if muscle contractions are needed for cardiac assist postoperatively. 2. Night/day regimen. This feature allows for a change in the ratio of muscle contractions according to a patient's activity level. During the day the cardiosynchronization ratio may be set from 1:1 to 1:4, and during the night it may be set for 1:8 to 1:16. This allows the muscle to have a long rest period, prevents overuse, and prolongs battery life. These two new features make this cardiomyostimulator very attractive for cardiomyoplasty in particular. The addition of the work-rest and night-day regimens allow the muscle to rest for periods during the day to prevent overuse, subsequent damage, and potential atrophy.
Cardiomyoplasty: comparison of latissimus dorsi muscles of three large mammals with that of human.
Cardiomyoplasty has the potential to become an alternative therapy for congestive heart failure patients and is presently in Phase III clinical trials. In experimental studies, it is necessary to use an animal with muscle characteristics that resemble those of humans. Therefore, the purpose of this study was to compare morphological and biochemical characteristics of the latissimus dorsi muscle (LDM) of three common large mammals with those of human. Of the three mammals studied, the goat had the most overall similarities to the human when comparing mitochondrial capacity, percent fiber types, fiber areas, myofibrillar (MF)-AT-Pase activity, and 72-kDa heat shock protein (HSP) content. The pig was dissimilar to the human in its fiber-type arrangement, glycolytic capacity, percent fiber type, MF-ATPase activity, and HSP-72 content. The dog differed from the human in that it had high-mitochondrial enzyme activity, a fiber-type profile consisting of all high-aerobic fibers, and fiber cross-sectional areas that were nearly half those of humans. These findings show that the LDM of the goat most resembles that of the human.