Development of mock circulation models for the assessment of counterpulsation systems.

STUDY OBJECTIVE: This study entailed the development of mock circulation models to assess and compare the haemodynamic efficacy of extra-aortic counterpulsation (using trained skeletal muscle wrapped around the proximal descending aorta) and conventional intra-aortic balloon counterpulsation. DESIGN AND EXPERIMENTAL MATERIALS: Hydraulic Windkessel type lumped parameter models were used either in conjunction with native skeletal muscle or as a dynamic simulation of counterpulsation. The haemodynamic performance of the wrapped latissimus dorsi muscle of the normal sheep was assessed using an artificial load to simulate the pressurised proximal descending aorta. Mock circulation models of counterpulsation comprised Windkessel compliance chambers, laminar flow resistors, a blood analogue, a prosthetic blood pump, and a purpose made hydraulic counterpulsator. MEASUREMENTS AND MAIN RESULTS: An electrically stimulated muscle wrap, 5 cm in length, previously trained for 2 weeks at 3 V and 35 Hz, was assessed for haemodynamic performance in a mock circulation: volume of fluid displaced = 14.1(SD 1.8) ml; pressure increase from 100 mm Hg = 14.9(2.1) mm Hg; external work per contraction cycle = 180(70)mJ; external mean power = 800(100) mW. In a simulation of intra-aortic balloon counterpulsation, haemodynamic benefit (ie, an increase in proximal flow rate and endocardial viability ratio and a reduction in left ventricular stroke power) was assessed with respect to defined parameters. CONCLUSIONS: This paper demonstrates the potential of the mock circulation models both for the investigation of muscle wrap performance and for the comparison of extra-aortic muscle with intra-aortic balloon counterpulsation.

Variable adaptation of molecular mechanisms in relation to the use of autologous striated muscle to augment myocardial function.

Significant recent advances in molecular biology and protein biochemistry have allowed the examination of muscle function at gene and protein level. This article reviews the variable adaptation of molecular mechanisms in striated muscle. The adaptation and transformation of fast skeletal muscle in response to chronic electrical stimulation may have considerable importance in relation to the use of autologous skeletal muscle to augment myocardial function.

Aortic counterpulsation for up to 28 days with autologous latissimus dorsi in sheep.

This article reports the development and assessment of an entirely autologous extraaortic counterpulsation system using skeletal muscle (latissimus dorsi). The technique has been performed and assessed in 16 sheep to quantify the effectiveness of counterpulsation over periods up to 28 days and to optimize the stimulation regimens for muscle contraction and fiber-type transformation. Hemodynamic changes have been quantified by calculation of the endocardial viability ratio. This has shown an increase of between 12% and 89% for 28 days. The wide variety of increase observed has been related to the development of an optimum flap configuration. The technique of surface impedance monitoring of flap blood flow has allowed the start of electrical stimulation after 48 hours with the introduction of hemodynamic benefit (1:4 mode) during the process of fiber-type transformation (in situ training). Extraaortic counterpulsation with autologous latissimus dorsi has been shown to be effective and safe for as long as 28 days. It has not been associated with any thromboembolic or infective complications, which we attribute to the exclusion of any foreign material in the design.

Hidden foreign body as a cause of recurrent hemoptysis in a teenage girl.

Hemoptysis in a teenage girl caused by a foreign body located in the posterior segment of the left lower lobe is described. The patient was seen four years after the initial inhalation. The importance of taking a meticulous history and the use of computed tomography in the localization of the lesion are emphasized, and the use of the fiberoptic bronchoscope in peripheral lesions and in the investigation of hemoptysis is discussed.

Aortic root replacement and extraanatomic bypass for interrupted aortic arch in an adult.

We describe an unusual case of interrupted aortic arch, aneurysmal ascending aorta, and aortic regurgitation in a 24-year-old man. He presented with general malaise, weakness of his legs, and hypertension. A single-stage operation was performed in which the aortic root was replaced with concomitant extraanatomic bypass of the interrupted segment of the aortic arch. He made a full recovery and has returned to work.

Biochemical and structural adaptation of autologous skeletal muscle used for counterpulsation.

We have studied in a normal animal model (sheep), the biochemical and morphological adaptation of electrically stimulated skeletal muscle used for extra aortic counterpulsation. Immunocytochemical analysis of latissimus dorsi, using monoclonal antibodies to slow and fast myosin heavy chains, indicated an increase in the population of mixed fibres after stimulation for one week. By one month, up to 70% of fibres expressed both slow and fast myosin heavy chains in addition to the 15% of fibres expressing only slow myosin heavy chains. After 4 months, the population of mixed fibres was further transformed towards purely slow fibres to give values of 40 and 67% of fibres expressing only slow myosin heavy chain at 4 and 6 months, respectively. Increased staining, both in intensity and area, for NADH tetrazolium reductase activity (an enzyme of the oxidative metabolic pathway) was detected by 28 days. An increase in mitochondrial number was observed also by 28 days, further indicating a shift towards an oxidative metabolism. The molecular adaptation of latissimus dorsi was achieved by stimulation every fourth cardiac cycle at 35 Hz, 3 V, initiated 48 hours after the operation; this being a marked reduction in the delay from operation prior to stimulation. Evaluation of other regimes indicated that more frequent modes, or an increase in voltage or frequency, caused damage to the muscle during the early phase of molecular adaptation. A thorough understanding of the time sequence of the different adaptive processes is required to determine the ideal regime of stimulation initiated promptly after mobilisation of the muscle; aimed at harvesting the maximum amount of energy from the autologous muscle.

Surgical treatment of hydrothorax complicating continuous ambulatory peritoneal dialysis.

Acute hydrothorax is a well recognized complication of continuous ambulatory peritoneal dialysis (CAPD) and is usually regarded as a contra-indication to the further use of this form of dialysis. We report the first case of treatment by surgical closure of a communication between the peritoneal and the right pleural cavity enabling CAPD to continue successfully. The development of an acute hydrothorax on CAPD is therefore not a reason to abandon this form of dialysis and can be treated by a simple thoracic surgical procedure.

Dysrhythmias following coronary artery surgery. A comparison between cold cardioplegic and intermittent ischaemic arrest (32 degrees C) with the effect of right coronary endarterectomy.

Dysrhythmias, particularly of supraventricular origin, are an important cause of morbidity following coronary artery bypass grafting (CABG). This study compared the incidence of dysrhythmias in patients undergoing CABG using either cold crystalloid cardioplegia or intermittent ischaemic arrest (32 C). We conclude that the incidence correlated well with right coronary endarterectomy irrespective of the technique of myocardial preservation employed and to the exclusion of other variables.

The incidence of significant pericardial effusion and tamponade following major aortic root surgery.

OBJECTIVE: To examine the hypothesis that the incidence of significant pericardial effusion following aortic root surgery is higher than anticipated after cardiac surgery. DESIGN: A retrospective data analysis. SETTING: A tertiary referral centre for cardiothoracic surgery. SUBJECTS: All patients undergoing aortic root surgery either with or without aortic valve replacement between January 1991 and July 1993. RESULTS: Three patients developed late cardiac tamponade (7-10 days post-operatively) and a further three developed clinically significant pericardial effusions as a result of post-pericardiotomy syndrome. The 31.6% (95% confidence limit: 12.5-56%) incidence of significant pericardial effusions following aortic root surgery is therefore significantly higher than anticipated after cardiac surgery (0.8-6). CONCLUSION: These data support the hypothesis that the incidence of significant pericardial effusion following aortic root surgery is higher than anticipated after cardiac surgery. We recommend that echocardiography is routinely performed during the post-operative period in these patients to exclude significant pericardial effusions.

Development of an opiate-based anaesthetic technique for use in dogs with cardiomyopathy.

An opiate-based anaesthetic technique has been developed for use in dogs with end-stage heart failure due to dilated cardiomyopathy. It has been used in dogs undergoing translocation of the left latissimus dorsi around the descending thoracic aorta to create an autologous counterpulsation system. Anaesthesia was induced with barbiturate (10 mg/kg thiopentone) and fentanyl (500 micrograms) and maintained by an infusion of fentanyl (0.5 micrograms/kg/minute) [corrected] in addition to halothane (0.1 to 0.5 per cent) and nitrous oxide (20 to 60 per cent). This technique provided safe anaesthesia for major intrathoracic surgery.

Early experience using a purpose-built pulse train stimulator for cardiac assistance with skeletal muscle.

We have developed and evaluated a prototype external pulse train stimulator for use with a new technique of circulatory assistance. This involves the use of skeletal muscle (latissimus dorsi) wrapped around the thoracic aorta as an entirely autologous extra-aortic counterpulsation system. The stimulator has been successful in initiating both muscle contraction at the desired part of the cardiac cycle (diastole) and the necessary fibre-type transformation required for long-term work (fatigue resistance). The background to the development of the stimulator and the early haemodynamic results are described in this paper. The evaluation of the prototype design and the areas for future development are discussed.

Skeletal muscle extra-aortic counterpulsation in dogs with dilated cardiomyopathy.

Skeletal muscle extra-aortic counterpulsation was performed in seven dogs with dilated cardiomyopathy. A left latissimus dorsi dynamic descending thoracic aortomyoplasty was used as the autologous counterpulsator. Pulse train stimulation in diastole was used to initiate contraction and fibre type transformation. Two of the dogs died within 48 hours of surgery. The device was successfully activated in the five remaining dogs, but in one individual it failed within 48 hours of activation. Serial echocardiographic examinations of dogs in which the device functioned successfully (n = 4) showed trends towards the decrease in the left ventricular systolic internal dimension, left ventricular diastolic internal dimension, E-point to septal separation and left atrial diameter in systole seven to 14 days following the procedure, although these changes failed to persist in the long-term. The results suggest that skeletal muscle for cardiac assistances such as extra-aortic muscle counterpulsation, might be a therapeutic option for dogs with cardiac failure due to dilated cardiomyopathy.

Oesteoarticular tuberculosis--an unusual presentation.

A patient presented with pain in the wrist and neck and X-rays showed destructive lesions of several carpal bones and cervical vertebrae. The carpal lesion was explored surgically and found to be tuberculous. Chemotherapy resulted in healing at both sites of disease.

Management of massive haemoptysis.

Massive haemoptysis is rare but associated with a high mortality. Even in a major regional cardiothoracic centre only one or two cases will be seen annually. As a consequence, no consensus about its investigation and management has emerged, with the result that much time may be lost on inappropriate investigation and treatment may be misdirected.

Splenic herniation. Case report.

A case of splenic herniation complicated by spurious hypertension is described. A misleading provisional diagnosis was made despite computerised tomography (CT Scan). Diaphragmatic herniation is discussed and the use of computerised tomography in the diagnosis of masses arising from the posterior aspect of the diaphragm is emphasized.

Persistent conduction disturbances following coronary artery bypass surgery: cold cardioplegic vs. intermittent ischaemic arrest (32 degrees C).

Two-hundred patients undergoing coronary artery bypass grafting were analysed to assess the incidence of new and persistent conduction disturbances in the postoperative period. Two groups, each of 100 patients, were studied. One group underwent surgery during cold crystalloid cardioplegic arrest with moderate whole-body hypothermia (28 degrees C). The second group was subjected to intermittent ischaemic arrest with mild whole-body hypothermia (32 degrees C). The incidence of postoperative conduction defects was significantly higher in the cardioplegic group.

Physiology and clinical applications of cardiopulmonary exercise testing.

Advances in the technology of gas exchange analysers have made cardiopulmonary exercise testing a relatively simple, cheap and reliable diagnostic tool. Its practice and uses include grading the severity of heart failure, evaluation of the cause of exertional dyspnoea and monitoring a patient's response to therapy. Areas of debate and future development are highlighted.