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Biomedical subjects

R C Chiu

Publications and source records attributed to R C Chiu.

At least 109 records · Page 6Linked to original sources
PubMed1986

Antibiotic prophylaxis in vascular surgery: pharmacokinetic study of four commonly used cephalosporins.

Plasma levels of antibiotics often do not correlate well with their tissue levels. To determine optimal antibiotic coverage for prophylactic effect in vascular surgery, we studied the tissue pharmacokinetics of four cephalosporins in dogs: cefazolin, cefoxitin, cefamandole, and moxalactam for 3 hours after a single (25 mg/kg) intravenous injection. The minimal inhibitory concentration (MIC) of these antibiotics for the three most common pathogens involved in graft infections (Staphylococcus aureus, S. albus, and Escherichia coli) and their tissue concentration (TC) in the plasma, muscle, subcutaneous tissue, and aortic wall were assayed. The data are presented as TC/MIC ratio. Cefoxitin and moxalactam failed to achieve an effective therapeutic TC/MIC ratio (greater than 10) for S. aureus and S. albus in all the tissues studied whereas cefoxitin and cefamandole were above therapeutic levels. All antibiotics achieved an effective therapeutic ratio against E. coli, but cefamandole performed better (p less than 0.05) than cefoxitin; the latter reached effective levels at 3 hours. Cefamandole attained the most effective bioactive aortic tissue levels when the three most common pathogens were considered together and should therefore be considered as an antibiotic agent of choice for prophylaxis in vascular surgery.

Animals↗
PubMed1986

Response of hypertrophic heart myocardial glycogen to GIK and hypovolemic shock.

Glucose-insulin-potassium (GIK) given during myocardial ischemia or anoxemia results in improved myocardial function and augments energy reserves of myocardial glycogen (MG). Because many patients with heart disease also have myocardial hypertrophy, our purpose was to examine whether similar elevations in MG can occur in hypertrophic hearts with GIK administration and to study the effect of hypovolemic shock on those MG levels. Mongrel dogs (n = 5) with myocardial hypertrophy underwent serial myocardial biopsies of the left (LV) and right (RV) ventricles, and blood samples were followed by GIK infusion (14.5 ml/kg/hr) for 2 hr. after which the dogs were subjected to 2 hr of hypovolemic shock (mean arterial pressure = 40 mmHg). It was found that after GIK infusion MG was consistently elevated in both RV (.43 +/- .02 to .60 +/- .04 g%) and LV (.63 +/- .07 to .71 +/- .01 g%) and FFA declined (.20 +/- .05 to .05-.01 mEq/liter). The MG responded to hypovolemia by further significant elevations (RV 1.16 +/- .33; LV .82 +/- .17), as did FFA (.38 +/- .21). These results indicate that hypertrophic hearts can indeed respond to GIK infusion by increasing MG in both the RV and LV, as do normal hearts. These hearts then submitted to hypovolemic shock showed a further elevation of MG. The elevated insulin levels post-GIK resulted in suppression of FFA. Thus GIK administration may have a sparing effect on energy stores of the heart during hypovolemic shock, which could have clinical implications in the treatment of patients with hypertrophic myocardia.

Animals↗
PubMed1986

Predictive power of penile/brachial index in diagnosing male sexual impotence.

To evaluate the diagnostic power of penile/brachial index (PBI) in patients studied for male sexual impotence, we prospectively interviewed 503 patients referred to our vascular laboratory for PBI measurements. Since the predictive values of diagnostic tests are affected by the prevalence of the disease in the population studied, we calculated the independent likelihood ratio for various PBI levels obtained. For the purpose of this analysis, "organic" impotence was defined as occurring in patients who had no nocturnal erections, whereas "clinical" impotence was defined as occurring in those patients who could not achieve penetration during intercourse. The patients were divided into four groups by the presence or absence of risk factors, including peripheral vascular disease (PVD) and diabetes mellitus. Patients taking medications that may affect potency (n = 175) were excluded from this analysis. The results show that the predictive power of PBI is less in diabetic patients with PVD and least in those without either PVD, diabetes, or drugs. In patients with PVD but no other risk factors, PBI is highly diagnostic with a sharp cut-off point at 0.6. Thus, the diagnostic power of PBI can be improved by considering the risk factors in the patients studied.

Adult↗
PubMed1985

Reuse of permanent cardiac pacemakers.

Cardiac pacemakers are part of a growing group of expensive implantable electronic devices; hospitals in which 100 pacemakers are implanted per year must budget over $300 000 for these devices. This cost represents a considerable burden to health care resources. Since the "life-span" of modern pacemakers often exceeds that of the patients who receive them, the recovery and reuse of these devices seems logical. Pacemakers can be resterilized and tested with current hospital procedures. Reuse should be acceptable under Canadian law, but the manner in which the pacemakers are recovered and the patients selected should follow careful guidelines. Every patient should provide written informed consent before receiving a recovered pacemaker. Properly executed, reuse of pacemakers should provide a high level of health care while maintaining or reducing the cost of these devices.

Aged↗
PubMed1985

Perioperative Holter monitoring and computer analysis of dysrhythmias in cardiac surgery.

In order to increase the accuracy and efficiency of studying perioperative dysrhythmias, 52 patients undergoing cardiac surgery were fitted preoperatively with a Holter monitor adapted for intraoperative recording, and the preoperative, intraoperative and early postoperative cardiac electrical activities were classified with a digital computer. Forty patients underwent coronary artery bypass grafting (CABG), eight had valve replacements, and four had combined procedures. The results showed the following: (1) high incidence of various dysrhythmias occurring during anesthesia induction and thoracotomy prior to aortic cross-clamp; (2) high incidence of continued atrial activity during cardioplegia; (3) lack of correlation between peak serum CPK-MB levels and dysrhythmias; and (4) a higher overall incidence of dysrhythmias in valve patients. Adapting the Holter monitor technique for cardiac surgery can solve the problem of observer vigilance inherent to such a study using a human "monitor watcher," and facilitate the accurate analysis of the vast amount of data obtained. This is important in quantitating the electrophysiologic effects of various perioperative interventions, such as the anesthetic agents, beta-blockers, calcium antagonists, and cardioplegic solutions.

Arrhythmias, Cardiac↗
PubMed1985

Left ventricular assistance in dogs using a skeletal muscle powered device for diastolic augmentation.

A pulse train stimulator was developed for skeletal muscle stimulation synchronous to the myocardium. Left ventricle contraction was augmented by a stimulated rectus abdominis muscle pedicle grafted into the left ventricular wall. A miniaturized and programmable stimulator was built. The stimulation parameters for this device were optimized and the configuration of a skeletal muscle powered assist device for cardiac assistance was investigated in acute canine experiments. A hydraulic balloon preparation was used to characterize stimulation parameters and to compare rectus abdominis, latissimus dorsi and pectoralis major muscles as power sources. Assist devices evaluated included a left ventricle apico-aortic conduit with a central pumping chamber and an extra-aortic balloon pump. The pumping chambers were either wrapped by the rectus abdominis and latissimus dorsi pedicles, or placed deep into the pectoralis major. The optimal stimulation parameters were pulse trains of 200 msec duration containing pulses 240 mu wide at a frequency of 35 pulses/second. There was no fatigue over a ten hour period despite stimulation at a rate of 120 contractions/minute. Muscle dissection and selection were determinants of fatigability. However, counter-pulsation was possible regardless of the muscle selected. The most efficient device was an extra-aortic balloon pump. There was a consistent increase in subendocardial viability index (DPTI/TTI). The advantages in using a skeletal muscle power source for diastolic rather than systolic assistance were established.

Abdominal Muscles↗
PubMed1985

Effects of abdominal aneurysmectomy, aortoiliac bypass grafting and angioplasty on male sexual potency: a prospective study.

The preoperative frequency and postoperative status of male sexual potency was studied prospectively in 46 patients who underwent abdominal aortic aneurysmectomy, aortoiliac and aortofemoral bypass grafting, or percutaneous transluminal angioplasty of the iliac artery. The patients with aortic aneurysms were older; approximately half of them were potent. The frequency of impotence was highest in patients who underwent aortoiliac bypass, and correlated well with their low penile to brachial pressure index. Patients who had angioplasty had more localized lesions, a higher penile to brachial pressure index and the lowest rate of impotence. Postoperatively, 13% of the patients regained nocturnal erection and 10% became functionally potent (defined as the ability to achieve penetration). The improvements were similar in bypass and angioplasty patients. No patient experienced deterioration in sexual potency and all showed a markedly improved thigh to brachial pressure index postoperatively. Routine aortoiliofemoral artery angiograms were of limited value in predicting the status and outcome of sexual potency in this series of patients.

Aged↗
PubMed1985

Wedge resection as an alternative procedure for peripheral bronchogenic carcinoma in poor-risk patients.

Although lobectomy is the procedure of preference for patients with peripheral, clinical Stage I bronchogenic carcinomas, wedge resection of the tumor may be a satisfactory alternative in poor-risk patients. Between 1965 and 1982, 197 patients with peripheral bronchogenic carcinomas were operated upon. Clinical staging was established by radiography, bronchoscopy, and mediastinoscopy. Ninety-seven patients underwent lobectomies and 100 had wedge resections. The decision to perform the wedge resection was made preoperatively in the majority of cases based on the assessment of operative risks. Compared to lobectomy patients, those who had wedge resections were older (70.3 +/- 0.5 versus 64.9 +/- 0.5 years, p less than 0.001) and had a lower 1 second forced expiratory volume (1.56 +/- 0.03 versus 1.94 +/- 0.03 ml, p less than 0.001), a lower arterial oxygen tension (70.5 +/- 1.1 versus 75.6 +/- 1.2 mm Hg, p less than 0.01), and a higher arterial carbon dioxide tension (41.7 +/- 0.6 versus 38.7 +/- 0.3 mm Hg, p less than 0.001). Despite their compromised preoperative respiratory functional status, the wedge resection group had a 30 day operative mortality (3% versus 2.1%) and morbidity comparable to those of the lobectomy group. Actuarial life-table analysis indicates the cumulative survival rate at 2 years after operation to be virtually identical between wedge and lobectomy groups (72% versus 74%), and even at 6 years the differences in survival rates (69% versus 75%) were not statistically significant. We conclude, therefore, that by performing wedge resections in selected poor-risk patients, one may reduce the operative mortality and morbidity to an acceptable range without seriously compromising their long-term survival.

Aged↗
PubMed1985

Transforming skeletal muscle for myocardial assist: a feasibility study.

Canine experiments were undertaken to determine the feasibility of transforming skeletal muscle for myocardial assistance. Initially, a rectus-muscle pedicle flap was used to power a ventricular assist conduit. A specially designed "pulse-train" stimulator produced skeletal muscle contractions capable of augmenting myocardial function. Statistically significant increases in either systolic or diastolic pressures were achieved by appropriate synchronization and signal delays of the stimulator. Then, the left rectus muscle was conditioned by stimulating it at low frequencies (2 to 10 Hz) for 6 to 12 weeks. The degree of transformation from type II (fast) to type I (slow) fibres was examined and the resultant tolerance to fatigue studied. Preliminary data show that a greater proportion of type I fibres is associated with increased resistance to fatigue. Such transformed skeletal muscle should therefore be more suited to power the cardiac assist devices.

Animals↗
PubMed1984

The effects of pulmonary atelectasis and reexpansion on lung cellular immune defenses.

Pulmonary atelectasis predisposes the lung to infection. This condition may be partly due to impaired cellular immune response of the collapsed lung segment. We postulated that atelectasis may affect alveolar macrophage (AM) antibacterial function. To test this hypothesis, atelectasis was induced in the right upper lobes of piglet lungs. Alveolar macrophages harvested by bronchoalveolar lavage of collapsed segments for up to 24 hours showed progressive depression of their phagocytic activity against Pseudomonas aeruginosa in vitro. However, their intracellular bactericidal activity did not change. Reexpansion of the atelectatic lobes with mechanical ventilation and 100% oxygen supplementation for four hours after six hours of atelectasis resulted in reversal of the impaired AM phagocytic activity. These observations presented insight into the mechanisms of susceptibility to lung infection in pulmonary atelectasis and the potential for its reversal.

Animals↗
PubMed1984

Myocardial protection: heparin-induced free fatty acid elevation during cardiopulmonary bypass and its prevention.

Elevated serum free fatty acids (FFA) adversely affect the hypoxic or ischemic myocardium by impairing cardiac function, decreasing contractility, and increasing arrhythmogenicity . Heparin, an anticoagulant used routinely in cardiac surgery, elevates circulating FFA. The purpose of this study was to determine the magnitude of FFA elevation in cardiac surgery patients and to establish, in dogs, a dose-response of FFA to heparin and to test whether glucose-insulin-potassium (GIK) solution could prevent heparin-induced rise in FFA. In 52 patients undergoing cardiopulmonary bypass (CPB), serial blood samples were obtained for FFA determination before and after heparin (300 IU/kg) administration. Then in seven normal dogs, heparin at a dose of 80 or 300 IU/kg was given. In another group of five dogs either GIK solution or NaCl were infused, while intravenous heparin (300 IU/Kg) injection was given. Each dog acted as its own control. It was found that there was a twofold increase in circulating serum FFA after heparin administration during cardiac surgery in patients, reaching the toxicity level of greater than 0.80 meq/liter. One-third of these patients had elevations of FFA level above the arrhythmogenic threshold of greater than 1.20 meq/liter. In the canine experiments low-dose heparin (80 IU/Kg) resulted in milder elevations of FFA for a shorter duration. Dogs given saline and high-dose heparin (300 IU/Kg) had responses similar to those seen in human patients undergoing cardiac surgery, while GIK abolished the elevation of serum FFA in response to high-dose heparin, eventually reducing FFA to below preheparin levels.

Adult↗
PubMed1984

The pulmonary effects of opiate blockade in septic shock.

Sepsis remains the most common associated factor in acute respiratory failure (ARF). Endogenous opiates are known to have both respiratory and cardiovascular depressant effects. Because there is a high level of circulating endogenous opiates in sepsis, the possible role of opioids in the ARF syndrome seen in sepsis was studied. Sixteen piglets were infused with an LD100 dose (7.5 X 10(10) organisms/kg) of live Escherichia coli (Type 09-41). The pigs were hemodynamically monitored. Serial blood samples were taken for arterial blood gases and lactate. Serial lung biopsies were taken for determining wet/dry lung weight ratios and for histology. Group I (n = 8): septic shock controls without naloxone; group II (n = 8): naloxone treated, given as 2 mg/kg/hr intravenous boluses, starting within 1 min of E. coli infusion. All animals died of septic shock. Survivors at 150 min in group II had a higher blood pressure than group I (67.7 +/- 5.33 SEM vs 39.0 +/- 9.39) and cardiac output was also greater (1.07 +/- 0.23 vs 0.25 +/- 0.25). By 210 min, group I had no survivors (0/8) while 3/8 in group II survived. Pulmonary vascular resistance in group II at 90 and 120 min (870.8 +/- 274.1 and 942.5 +/- 12.9, respectively) was lower than in group I (2868.3 +/- 843.6 and 4156 +/- 1067). The PO2 was markedly better in group II and at 90 min; controls had a PO2 70.7 +/- 13.0, while group II had a PO2 111.4 +/- 8.4 (P less than 0.05). PCO2 levels showed a progressive rise in group I from 39.25 +/- 1.4 to 49.4 +/- 8.57.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1984

Complement (C3, C4) consumption in cardiopulmonary bypass, cardioplegia, and protamine administration.

Anaphylatoxins produced by complement activation have been postulated to be responsible for postperfusion syndrome and protamine hypotension in patients undergoing cardiac surgical procedures. The consumption of serum complement components C3 and C4, which reflects the classic and alternate pathway activations of the complement system, was studied in 22 patients undergoing cardiac operations. Prior to the onset of cardiopulmonary bypass, the complement levels were within normal range. Rapid reduction in both C3 and C4 within minutes of cardiopulmonary bypass indicated rapid complement activation. Such a reduction in complement levels could not be accounted for by either hemodilution or transfusion of complement-poor blood. Aortic cross-clamping and cold potassium cardioplegia followed by myocardial reperfusion did not lead to further consumption of C3 and C4. Slow intravenous infusion of protamine sulfate after cardiopulmonary bypass did not change C3 and C4 levels significantly in our patients, although protamine and heparin-protamine complex have been shown to activate complement components in vitro. In another group of 9 similar cardiac surgical patients, C3 and C4 were found to return to normal levels within 24 hours after operation. This study thus confirms the rapid activation of the complement system by cardiopulmonary bypass but fails to demonstrate further activation of the complement system by cardioplegia or protamine administration.

Adult↗