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Biomedical subjects

R C Chiu

Publications and source records attributed to R C Chiu.

152 records · Page 9Linked to original sources
PubMedDate not supplied

Binocular blindness following dynamic cardiomyoplasty.

A 40-year-old man with viral cardiomyopathy underwent uncomplicated dynamic cardiomyoplasty. On the third postoperative day, he was rescued from an 8-hour period of severe cardiogenic shock. Eleven days postoperatively, he was withdrawn and uncooperative, preferring to be left alone. He then complained of total blindness, which persisted to his sudden death on postoperative day 26. Clinical examination revealed no neurological abnormality except for signs consistent with a diagnosis of ischemic optic neuropathy. The optic nerve in the scleral canal is especially vulnerable to hypoperfusion. Blindness has been reported following severe hemorrhage, bilateral neck dissection, and has an incidence of 1 per 1100 cases following cardiopulmonary bypass. Anemia and hypotension may be consistent risk factors predisposing patients to this catastrophic complication.

Adult↗
PubMedDate not supplied

Mechanisms of dynamic cardiomyoplasty: current concepts.

Dynamic cardiomyoplasty is an operation that is undergoing worldwide clinical evaluation. It had been developed to utilize the patient's own skeletal muscle to assist the failing heart. Although the clinical and quality of life benefits of cardiomyoplasty have been reported in most patients, the results of quantitative hemodynamic analyses have been less consistent. This has prompted the reevaluation of the mechanisms of dynamic cardiomyoplasty other than simple cardiac compression by the wrapped muscle. There is good evidence to suggest that the following, either together or in part, comprise some of the mechanisms of dynamic cardiomyoplasty: (1) direct systolic assist; (2) myocardial (wall stress) sparing effect; (3) remodeling/girdling effect; and (4) angiogenesis. Current concepts and potential additional mechanisms are discussed and integrated, based on a review of the literature and our own recent studies.

Cardiomyoplasty↗
PubMedDate not supplied

Hemodynamic response to in situ latissimus dorsi muscle stimulation: implications in dynamic cardiomyoplasty.

Dynamic cardiomyoplasty (DCM) involves the electrical stimulation of a pedicled latissimus dorsi muscle flap wrapped around the falling ventricle as a means of cardiac assist. To further elucidate a potential neurohumoral mechanism for improvement of cardiac output after myoplasty, we evaluated the hemodynamic effects of in situ stimulation of the latissimus dorsi muscle (in the absence of cardiomyoplasty). In seven mongrel dogs, a nerve cuff electrode (Medtronic 6901) was placed around the left thoracodorsal nerve (TDN). This was attached to a pulse generator (Medtronic, Itrel 7420), delivering a 4.0 volt, 0.19 second on, 0.81 second off, 33 Hz, 210 microsecond pulse width, cyclic bursts similar to that used in DCM. Stroke volume index (SVI) and other hemodynamic parameters as well as plasma norepinephrine (NE) levels were measured at five stages: baseline, stimulator on at 0, 2, and 5 minutes, and stimulator off at 30 minutes after. The animals were then subjected to 4 weeks of rapid pacing at 240 beats/min (Medtronic 8329) to induce heart failure, and as the rapid pacing was discontinued, measurements were repeated as above. After rapid pacing, cardiac function was significantly depressed, and NE was elevated (133 +/- 69 versus 500 +/- 353 pg/mL, p < 0.05). In the normal hearts, TDN stimulation increased SVI, heart rate, systemic pressure, and NE levels. In heart failure, however, no significant changes in cardiac function and NE levels were noted. In conclusion, our data indicate that in the normal hearts, afferent impulses from TDN stimulation alone may augment cardiac function by means of a neurohumoral effect that is not seen in severe heart failure. The implications of these findings in DCM are discussed.

Animals↗
PubMedDate not supplied

Blood flow to the latissimus dorsi muscle pouch during chronic counterpulsation stimulation.

The cyclic contraction of a skeletal muscle ventricle (SMV) stimulated in counterpulsation results in phasic perfusion of the muscle. Perfusion will occur primarily during cardiac systole when the muscle is relaxed. However, the resting preload of the SMV will be systolic arterial pressure, which will impede blood flow to the relaxed muscle. To determine the effect of chronic counterpulsation stimulation on the blood flow to an SMV and identify stimulation regimens that prevent the risk of chronic ischemia, SMVs were created in four mongrel dogs by implementing an implantable mock circulation device. The SMV was stimulated in counterpulsation for 4 weeks after a 2-week vascular delay period and 2 weeks of low-frequency muscle conditioning. During biweekly studies, the muscle was stimulated in four modes against preloads varying from 20 to 120 mm Hg. Resting blood flow decreased significantly at preloads greater than 60 mm Hg. Normalized blood flow increased between 10% and 30% during stimulation; greater increases corresponded to more demanding stimulation modes. The elevated blood flow during stimulation, however, decreased with increasing preload. Stroke work increased with increasing preload until preload exceeded 100 mm Hg. The decreased blood flow and increased stroke work occurring at higher preloads indicate that the supply/demand ratio becomes compromised with increasing preload. A hyperemic response occurred during the resting beats after a stimulated beat, increasing the volume blood flow by as much as 80%. This response occurred regardless of preload or stimulation rate. If the SMV relaxed before the onset of systole, a hyperemic response occurred within the stimulated beat.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Pulmonary artery counterpulsation with a skeletal muscle power source.

We evaluated the feasibility of using skeletal muscle (SM) to provide pulmonary artery (PA) counterpulsation in an acute pulmonary hypertension (PHT) model. PA counterpulsation was achieved in six dogs with a dual chambered pump powered by the latissimus dorsi muscle. A rate-responsive stimulator was used to make the muscle contract in counterpulsation. Graded PHT was induced by infusing 150 microns glass beads into the PA, while RV and PA pressures were monitored. With PA pressures ranging from 19/10 to 115/62 mmHg, effective counterpulsation was observed. The degree of counterpulsation was influenced by the extent of PHT induced, with the amount of RV tension-time index (TTI) unloading correlated with the level of PA systole (r = 0.92). Therefore, results were divided into two groups (Group 1: PA systole less than or equal to 40 mmHg, and Group 2: PA systole greater than 40 mmHg). In Group 1, RV TTI decreased from 11.29 +/- 0.76 to 9.99 +/- 0.72 mmHg.sec, PA diastole increased from 20 +/- 2.3 to 31 +/- 3.0 mmHg, and PA mean increased from 24 +/- 2.2 to 2.9 +/- 2.2 mmHg (all p less than 0.05). In Group 2, RV TT1 decreased from 15.12 +/- 1.83 to 10.99 +/- 0.90 mmHg.sec, PA diastole increased from 41 +/- 3.5 to 64 +/- 6.2 mmHg, and PA mean increased from 49 +/- 4.8 to 55 +/- 5.7 mmHg (all p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Power generation from four skeletal muscle configurations. Design implications for a muscle powered cardiac assist device.

The development of long term cardiac assist devices is currently limited by the lack of an appropriate totally implantable power source. Transformed fatigue resistant skeletal muscle has been proposed as such a power source. The goal of this study was to determine the optimal latissimus dorsi muscle (LDM) configuration capable of obtaining maximum power output. Four separate in situ configurations were prepared: a latex compliance chamber placed between the LDM and chest wall (Sub-Dorsi), a chamber wrapped in a skeletal muscle ventricle (Circular), linear measurements from the thoracolumbar origin (Linear Origin), and linear measurements from the humeral insertion (Linear Insertion). A device was designed to measure the power output from each configuration in watts per kilogram of muscle. Eight LDMs were acutely studied at varying levels of pre-load. Performance characteristics were measured in each configuration. Peak power outputs were as follows: Sub-Dorsi: 8.3 +/- 1.6 W/kg at 50 cc or 11.6 N pre-load; Circular: 16.4 +/- 6.2 W/kg at 50 cc or 16.9 N; Linear Origin: 47.1 +/- 4.4 W/kg at 23.4 N; and Linear Insertion generated 59.9 +/- 12.1 W/kg at 26 N. Analysis of variance comparison revealed a significance of p < 0.0001. A linear oriented LDM is capable of generating maximal power output. Confirmation of these findings in transformed, conformed, fatigue resistant muscle will provide important performance information essential for the optimal design of implantable muscle powered ventricular assist systems.

Animals↗