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Biomedical subjects

J A Magovern

Publications and source records attributed to J A Magovern.

At least 19 recordsLinked to original sources
PubMed1999

Intermittent stimulation enhances function of conditioned muscle.

Skeletal muscle is highly adaptable in that its metabolic and contractile characteristics are largely regulated by its pattern of use. It is known that muscle phenotype can be manipulated via chronic electrical stimulation to enhance fatigue resistance at the expense of contractile power. Type 2A fibers are fatigue resistant, powerful, and considered most desirable for cardiac assist purposes. We have found that 12-wk of intermittent-burst stimulation produces a high percentage of 2A fibers and increases fatigue resistance and power in rabbit latissimus dorsi muscle. Fixed-load endurance tests were used to quantify fatigue resistance among normal and trained muscle groups. Control muscles were found to fatigue completely within 10-20 min. Muscles stimulated continuously for 6 wk retained 35% (71.5 +/- 19.5 g. cm) of their initial stroke work at 40 min. Muscles stimulated 12 h/day for 12 wk had the highest initial stroke work (449.7 +/- 92.4 g. cm) and the highest remaining stroke work (234.7 +/- 50.1 g. cm) at 40 min. Results suggest that employing regular resting periods during conditioning preserves strength in fatigue-resistant muscle.

Animals↗
PubMed1998

Morbidity, cost, and six-month outcome of minimally invasive direct coronary artery bypass grafting.

BACKGROUND: Minimally invasive direct coronary artery bypass grafting (MIDCABG) promises to reduce the morbidity of coronary bypass, but this has not been proved. METHODS: This retrospective study compares the morbidity, mortality, cost, and 6-month outcome of patients less than 80 years old undergoing elective left internal mammary artery to left anterior descending artery bypass grafting via MIDCABG (n = 60) or sternotomy (n = 55) between January 1995 and December 1996. There were no differences between the groups in mean age, sex distribution, or preoperative risk level. The left internal mammary artery was mobilized from the fifth costal cartilage to the subclavian artery in all patients. The anastomoses were done with a beating heart in the MIDCABG group and with cardioplegic arrest in the sternotomy group. RESULTS: There were no operative deaths in either group. The MIDCABG patients had a lower transfusion incidence (10/60 [17%] versus 22/55 [40%]; p< or =0.02) and a shorter postoperative intubation time (2.1+/-4.2 versus 12.6+/-9 hours; p< or =0.0001). One patient in each group was reexplored for bleeding. Three sternotomy patients (3/55, 5%) required ventilatory support for greater than 48 hours, but no MIDCABG patient was ventilated for more than 24 hours. Median postoperative length of stay was 4 days for MIDCABG and 7 days for sternotomy. Estimated hospital costs were $11,200+/-3100 for MIDCABG and $15,600+/-4200 for CABG (p < 0.001). The reduced morbidity and cost of MIDCABG was found mostly in high-risk patients. At 6-month follow-up, 5 MIDCABG patients (5/60, 8%) had evidence of recurrent ischemia involving the left anterior descending artery, primarily the result of anastomotic stricture. CONCLUSIONS: This analysis shows that MIDCABG reduces the initial morbidity and cost of coronary bypass, but some patients require subsequent reintervention. Long-term follow-up is needed before MIDCABG can be judged better than traditional bypass, but the initial results are promising, especially in high-risk patients.

Case-Control Studies↗
PubMed1998

Early chest tube removal after video-assisted thoracoscopic wedge resection of the lung.

BACKGROUND: Traditional management of chest tubes after a wedge resection of peripheral pulmonary tissue often lasts several days. We evaluated the safety and efficacy of early chest tube removal in the recovery room after uncomplicated video-assisted thoracoscopic surgical wedge resections of the lung. METHODS: From December 1995 to July 1997, 59 patients underwent video-assisted thoracoscopic surgical wedge resection for indeterminate pulmonary nodules (n = 33) or interstitial lung disease (n = 26). We prospectively evaluated early chest tube removal in the last 33 patients; 18 patients with nodules and 15 with interstitial lung disease. Patients who were in the early removal group had chest tubes removed within 90 minutes of the surgical procedure. Criteria for early removal were established and met before chest tube removal. There was no difference between groups with respect to age, sex, comorbidities, or pathologic evaluation of resection specimens. RESULTS: Ninety-four percent (31 of 33) of patients considered for early chest tube removal met criteria for immediate tube removal. Air leak and excessive drainage prohibited early removal in 2 patients. Patients who were managed traditionally averaged 3.3 days with chest tubes--1.8 days on suction, 1.3 days on water seal. Patients who had early removal of their chest tubes had a shorter postoperative stay (2.0+/-1.0 versus 3.9+/-2.1 days, p = 0.001) and fewer chest roentgenograms (2.8+/-2.1 versus 5.1+/-2.0, p = 0.001). There were no differences in complications including small pneumothoraces (5 in the early removal group, 7 in the traditional management group), which were managed with observation alone. Total narcotic requirements were greater in the traditional management group (54+/-44.8 versus 24.6+/-22.9 morphine milligram equivalents, p = 0.005). CONCLUSIONS: Early chest tube removal after video-assisted thoracoscopic surgical wedge resection of peripheral pulmonary tissue appears to be a safe and cost-effective practice if strict criteria for removal are met.

Adult↗
PubMed1998

Transient ischemia does not limit subsequent ischemic regional dysfunction in humans: a transesophageal echocardiographic study during minimally invasive coronary artery bypass surgery.

OBJECTIVES: This study sought to assess the effects of sequential coronary artery occlusion during minimally invasive coronary artery bypass graft surgery (CABG) on hemodynamic variables and left ventricular systolic function by means of transesophageal echocardiography (TEE). BACKGROUND: Clinical and experimental studies suggest a protective effect of ischemic preconditioning in patients with acute coronary syndromes. However, the effect of repetitive myocardial ischemia on myocardial mechanical function in humans is not completely understood. METHODS: Seventeen patients with left anterior descending coronary artery (LAD) stenosis > or =70% and normal rest left ventricular systolic function referred for minimally invasive CABG underwent intraoperative TEE for assessment of regional left ventricular wall motion and measurement of hemodynamic variables at baseline (baseline 1), during a 5-min coronary occlusion (occlusion 1), after a 5-min reperfusion period (baseline 2) and a during a second coronary occlusion during bypass anastomosis (occlusion 2). RESULTS: Left ventricular wall motion score (LVWMS) increased significantly from baseline (16.0) to occlusion 1 (21.4+/-3.1 [mean +/- SD], p < 0.05) and occlusion 2 (21.8+/-3.1, p < 0.05). No difference in LVWMS was noted between occlusions 1 and 2. Pulmonary artery systolic pressure increased significantly from baseline (25+/-6 mm Hg) to occlusion 1 (32+/-7 mm Hg, p < 0.05) and occlusion 2 (33+/-6 mm Hg, p < 0.05). Pulmonary artery diastolic pressure also increased significantly from baseline (12+/-4 mm Hg) to occlusion 1 (16+/-4 mm Hg, p < 0.05) and occlusion 2 (16+/-4 mm Hg, p < 0.05). No significant differences in pulmonary artery pressures were noted between occlusions 1 and 2. CONCLUSIONS: Ischemic dysfunction was precipitated by the 5-min LAD occlusion, as shown by the increase in LVWMS and pulmonary artery pressure. However, a 5-min coronary occlusion and the resulting ischemia do not alter regional left ventricular systolic function during subsequent ischemia in humans.

Aged↗
PubMed1998

Minimally invasive direct coronary artery bypass: anesthetic, monitoring, and pain control considerations.

OBJECTIVE: Minimally invasive direct coronary artery bypass (MIDCAB) provides many anesthetic challenges including monitoring, managing myocardial ischemia, and pain control. The objective was to evaluate the monitoring requirements and the potential benefits of preischemic conditioning and intrathecal morphine sulfate in MIDCAB patients. DESIGN AND SETTING: This review was retrospective and unrandomized and was conducted at Allegheny University Hospitals, Allegheny General, Pittsburgh, PA. PARTICIPANTS: Sixty-four patients with single coronary artery lesions (> 70% obstruction) underwent attempted MIDCAB during a 1-year period between November 1995 and November 1996. Seven patients required conversion to conventional coronary artery bypass grafting (CABG) with cardiopulmonary bypass (CPB) and two patients required extended thoracotomy incisions. This report describes the remaining 55 patients who underwent MIDCAB. INTERVENTIONS: Some of the MIDCAB patients received intrathecal morphine before anesthetic induction. Ischemic preconditioning was assessed in a subset of patients. RESULTS: MIDCAB was performed in 55 of 64 patients. Transesophageal echocardiography (TEE) was used in all patients and a pulmonary artery catheter was used in 43% of patients. Esmolol was used in 25% of patients to reduce motion of the left ventricle (LV) during the left internal mammary artery (LIMA)-LAD anastomosis, but was used less often as the surgeons adapted to the use of a retractor that stabilized the ventricular wall adjacent to the site of the LIMA-LAD anastomosis. LAD occlusion caused reversible, regional systolic dysfunction by TEE in the anterior and apical LV segments. During LAD occlusion, nitroglycerin was used in 61% of patients and phenylephrine in 24%. Ischemic preconditioning did not prevent increases in systemic or pulmonary artery pressures during LAD occlusion. Most (85%) patients were extubated in the operating room. Intrathecal morphine decreased postoperative analgesic requirements. The mean hospital length of stay (LOS) was 4.0 +/- 1.7 days (range, 1 to 10 days). CONCLUSIONS: MIDCAB may reduce hospital LOS for patients with single vessel coronary artery lesions when compared with median sternotomy with a LIMA-LAD graft performed on cardiopulmonary bypass. Pharmacologic heart rate control during the LIMA-LAD anastomosis is not critical with the use of a surgical retractor which diminishes ventricular motion. A single 5-minute test LAD occlusion did not protect against subsequent regional ischemic dysfunction in our subset of patients with normal baseline function.

Adrenergic beta-Antagonists↗
PubMed1997

Functional properties of conditioned skeletal muscle: implications for muscle-powered cardiac assist.

Latissimus dorsi (LD) muscles of six canines were studied to assess changes induced by electrical conditioning and to quantify the capacity of these muscles to perform hemodynamic work. Muscles were conditioned using burst stimuli delivered over an 8-wk period. Contralateral LD were used as control. Muscles were tested in situ to simulate anticipated linear-pull cardiac assist conditions. This training process reduced muscle mass and cross-sectional area by 16 and 17%, respectively. Muscle phenotype shifted to a predominantly "slow" form by coordinate reduction of myosin heavy chain (MHC) 2A expression and increased expression of the MHC beta/slow form. Force generation was reduced by 54%, and contractile duration increased 13%. Fatigue resistance was markedly enhanced, and chronic stroke work increased from 0.19 to 0.72 mJ/g. The highest steady-state power output (2.06 mW/g) was obtained from one muscle fully converted to a slow phenotype. These data suggest that single LD trained via conventional techniques can provide energy sufficient for partial cardiac assistance but cannot sustain work levels needed to achieve total circulatory support.

Animals↗
PubMed1997

A permanent prosthesis for converting in situ muscle contractions into hydraulic power for cardiac assist.

The key to utilizing muscle power for circulatory support lies with the development of a practical scheme by which contractile energy may be collected and efficiently delivered to the bloodstream. This work describes initial in vitro testing of a prototype muscle energy converter (MEC) designed to transform the power of in situ muscle contractions into hydraulic form. The MEC resembles a simple piston pump and is designed for implant beneath the humeral insertion of the latissimus dorsi muscle. Bench tests were conducted to measure component function and to characterize device performance under various hydraulic loads. Under simulated muscle-pull conditions, MEC energy transfer capacity was found to be 170 mJ/stroke while operating at peak efficiencies (i.e., > 98% of input power converted into hydraulic energy and preload work). Transfer efficiencies dropped from 96 to 38% as mean generated pressures increased from 23 to 36 N/cm2 due to metal bellows flexion. These results demonstrate that a significant amount of contractile energy can be efficiently transformed to hydraulic power via this mechanism.

Heart-Assist Devices↗
PubMed1996

A model that predicts morbidity and mortality after coronary artery bypass graft surgery.

OBJECTIVES: This study was performed to develop a method for identifying patients at increased risk for morbidity or mortality after coronary artery bypass graft surgery. BACKGROUND: Postoperative morbidity is more common than mortality and is important because of its relation to cost. METHODS: Univariate and forward stepwise logistic regression analysis was used to retrospectively analyze a group of 1,567 consecutive patients who underwent bypass surgery between July 1991 and December 1992. We developed a model that predicted postoperative morbidity or mortality, or both, which was then prospectively validated in a group of 1,235 consecutive patients operated on between January 1993 and April 1994. A clinical risk score was derived from the model to simplify utilization of the data. RESULTS: The following factors, listed in decreasing order of significance, were found to be significant independent predictors: cardiogenic shock, emergency operation, catheterization-induced coronary artery closure, severe left ventricular dysfunction, increasing age, cardiomegaly, peripheral vascular disease, chronic renal insufficiency, diabetes mellitus, low body mass index, female gender, reoperation, anemia, cerebrovascular disease, chronic obstructive pulmonary disease, renal dysfunction, low albumin, elevated blood urea nitrogen, congestive heart failure and atrial arrhythmias. Observed morbidity and mortality for the validation group fell within the 95% confidence interval of that predicted by the model. Costs were closely related to the incidence of postoperative morbidity. CONCLUSIONS: Analysis of preoperative patient variables can predict patients at increased risk for morbidity or mortality, or both, after bypass surgery. Increased morbidity results in higher costs. Different strategies for high and low risk patients should be used in cost reduction efforts.

Aged↗
PubMed1996

A model for predicting transfusion after coronary artery bypass grafting.

BACKGROUND: Blood conservation has become an important issue in cardiac surgery. This study was undertaken to determine if the need of blood transfusion could be predicted from preoperative patient variables. METHODS: From January 1, 1992, to December 31, 1993, 2,033 patients having isolated coronary artery bypass grafting procedures were studied; 1,446 (71%) were male and 587 (29%), female. The mean age was 65.1 +/- 9.9 years (range, 31 to 88 years). Emergency operation, urgent operation, and reoperations were done in 78 (4%), 188 (9%), and 189 (9%) patients, respectively. In the entire group, 1,245 (61%) received transfusion during hospitalization, and 788 (39%) did not. Logistic regression analysis was used to construct a model that predicted the need of transfusion of packed red blood cells after coronary artery bypass grafting. A transfusion risk score was constructed by assigning points to independent predictive factors on the basis of the logistic regression coefficient and the odds ratio. Preoperative predictors of transfusion were emergency operation, urgent operation, cardiogenic shock, catheterization-induced coronary occlusion, low body mass index, left ventricular ejection fraction lower than 0.30, age greater than 74 years, female sex, low red cell mass, peripheral vascular disease, insulin-dependent diabetes, creatinine level greater than 1.8 mg/dL, albumin value lower than 4 g/dL, and redo operation. RESULTS: The mean transfusion risk score for patients receiving 0, 1 to 4, and greater than 4 units of packed red blood cells was 2.3 +/- 0.9, 5.2 +/- 3.0, and 9.6 +/- 3.5, respectively (p = 0.001). Patients with a score higher than 6 had a 95% transfusion incidence. The predictive model was validated on 422 patients having coronary artery bypass grafting from January 1 to May 31, 1994. The observed rates of the validation group fell within the 95% confidence intervals of the predicted rates. CONCLUSIONS: These data demonstrate that readily available patient variables can predict patients at risk for transfusion. Routine use of aprotinin and other adjustments of cardiopulmonary bypass should be considered to reduce transfusion in high-risk patients.

Adult↗
PubMed1996

Regional effects of aortomyoplasty in acute ischemia.

BACKGROUND: Aortomyoplasty is a technique for achieving autogenous diastolic counterpulsation. This experiment was designed to determine if aortomyoplasty using conditioned latissimus dorsi muscle could improve regional myocardial function during coronary ischemia. METHODS: Six mongrel dogs underwent a staged operation in which the left latissimus dorsi was conditioned in situ for 4 weeks, then wrapped around the descending aorta and stimulated during diastole with each cardiac contraction. Regional ischemia was caused by occlusion of the left anterior descending coronary artery. Regional function was measured with somomicrometry in the region of ischemia and in a control area. An intraaortic balloon pump was inserted for comparison with aortomyoplasty performance. RESULTS: Coronary artery occlusion caused a significant decrease in the percentage of regional shortening (14.2 +/- 7.9 to -2.2 +/- 4.0; p = 0.001) and thickening (11.9 +/- 4.6 to -5.8 +/- 3.3; p < 0.001). Aortomyoplasty improved regional motion in both percentage shortening (-2.2 +/- 4.0 to 2.3 +/- 3.7; p = 0.008) and thickening (-5.8 +/- 3.3 to 2.8 +/- 1.9; p < 0.001). The intraaortic balloon pump also improved percentage shortening (-3.7 +/- 2.0 to 0.7 +/- 1.9; p = 0.01) and thickening (-5.0 +/- 2.8 to 2.4 +/- 3.8; p < 0.001), and was not significantly different than aortomyoplasty. CONCLUSIONS: These data show that aortomyoplasty has beneficial effects on ischemic left ventricular contractility, and may therefore be useful for treating inoperable coronary artery disease.

Acute Disease↗
PubMed1996

"Keyhole" coronary artery bypass surgery.

OBJECTIVE: The objective of this study was to identify the utility of "keyhole" thoracotomy approaches to single vessel coronary artery bypass surgery. SUMMARY BACKGROUND DATA: Although minimally invasive surgery is efficacious in a wide variety of surgical disciplines, it has been slow to emerge in cardiac surgery. Among 49 selected patients, the authors have used a left anterior keyhole thoracotomy (6 cm in length) combined with complete dissection of the eternal mammary artery (IMA) pedicle under thoracoscopic guidance or directly through the keyhole incision to accomplish IMA coronary artery bypass grafting (CABG) to the left anterior descending (LAD) coronary artery circulation or to the right coronary artery (RCA). METHODS: Keyhole CABG was accomplished in 46 of 49 patients in which this approach was attempted. All patients had significant (> 70%) obstruction of a dominant coronary artery that had failed or that was inappropriate for endovascular catheter treatment (percutaneous transluminal coronary angioplasty or stenting). Forty-four of the 49 patients had proximal LAD and 5 had proximal RCA stenoses. The mean age of the patients (35 men and 14 women) was 61 years, and their median New York Heart Association anginal class was III. The mean left ventricular ejection fraction was 42%. Femoral cardiopulmonary bypass support was used in 9 (19%) of 46 patients successfully managed with the keyhole procedure. Short-acting beta-blockade was used in the majority of patients (38 of 46) to reduce heart rate and the vigor of cardiac contraction. RESULTS: As 49 patients have survived operation, which averaged 248 minutes in duration. Median, postoperative endotracheal intubation time for keyhole patients was 6 hours with 25 of 46 patients being extubated before leaving the operating room. The median hospital stay was 4.3 days. Conversion to sternotomy was required in three patients to accomplish bypass because of inadequate internal mammary conduits or acute cardiovascular decompensation during an attempted off-bypass keyhole procedure Postoperative complications were limited to respiratory difficulty in three patients and the development of a deep wound infection in one patient. Nine (19%) of 46 patients received postoperative transfusion. There have been no intraoperative or postoperative infarctions, and angina has been controlled in all but one patient who subsequently had an IMA-RCA anastomotic stenosis managed successfully with percutaneous transluminal coronary angioplasty. CONCLUSIONS: These early results with keyhole CABG are encouraging. As experience broadens, keyhole CABG may become a reasonable alternative to repeated endovascular interventions or sternotomy approaches to recalcitrant single-vessel coronary arterial disease involving the proximal LAD or RCA.

Coronary Artery Bypass↗
PubMed1995

Alternatives to human heart replacement.

The continuing and increasing discrepancy between the number of available donor hearts and the number of patients who might benefit from cardiac transplantation has prompted efforts in the development of xenotransplantation, mechanical assist devices, and cardiomyoplasty techniques. We briefly review recent work in these three fields. The results of experimental xenotransplantation between closely related species are improving slowly with currently available drugs, and clinical trials in this field may be possible in the near future. Implantable ventricular assist devices are also at a stage of development where permanent implantation is likely to be followed by a reasonable and worthwhile period of patient survival. With regard to cardiomyoplasty, steady progress is being made in clarifying exact indications and patient selection, as well as confirming the potential benefits.

Animals↗
PubMed1994

Cardiothoracic surgery.

The necessity for making a major incision for a thoracic operation has been challenged. A continuing concern for patients with prosthetic cardiac valves and their physicians is the possibility of a defective prosthesis.

Cardiac Surgical Procedures↗
PubMed1994

Extracorporeal membrane oxygenation: preliminary results in patients with postcardiotomy cardiogenic shock.

Long-term survival at our institution for postcardiotomy cardiogenic shock patients supported with the BioPump is 36% (29/80 patients). A heparin-coated extracorporeal membrane oxygenator (ECMO), first introduced in 1991, may reduce organ injury associated with cardiopulmonary bypass. The device can be employed rapidly because it connects directly to the cardiopulmonary bypass cannula. In an effort to improve our results in the treatment of postcardiotomy cardiogenic shock, we used ECMO in 21 patients with this syndrome and accompanying complications. The patients were divided into three groups: group 1, ECMO after coronary artery bypass grafting; group 2, ECMO after mitral valve operation; and group 3, ECMO after open heart operation with prolonged cardiac arrest. Survival in group 1 was 80% with 12 of 14 patients discharged to home. All three deaths were caused by cardiac failure. Bleeding complications in this group were moderate. There was no evidence of disseminated intravascular coagulation, and levels of fibrin split products remained within the normal range. Postoperative complications included stroke (2), renal failure (1), mediastinitis (1), and prolonged respiratory failure (6). Mortality in group 2 was 100%. The major problem limiting recovery was left ventricular distention secondary to inadequate left ventricular decompression. Mortality in group 3 was 100%; all 4 died of brain death. Extracorporeal membrane oxygenation without left ventricular drainage clearly is not effective in patients undergoing mitral valve operations as it does not effectively decompress the left ventricle, but it was highly effective in treating postcardiotomy cardiogenic shock in our coronary artery bypass grafting patients. Extracorporeal membrane oxygenation also proved to be safe as the patient-related complications of stroke, renal failure, and mediastinitis were low. Our preliminary success with heparin-coated ECMO now needs to be confirmed by studies from other centers with larger groups of patients.

Adult↗
PubMed1994

Autogenous cardiac assist with chronic descending thoracic aortomyoplasty.

Alternative surgical treatments to orthotopic cardiac transplantation are needed for patients with heart failure. We hypothesized that descending thoracic aortomyoplasty with conditioned (fatigue-resistant) latissimus dorsi muscle could provide diastolic augmentation that would improve left ventricular function. Six mongrel dogs were studied. The left latissimus dorsi muscle was wrapped clockwise around the descending thoracic aorta. Left ventricular volume was measured with a conductance catheter. Aortic and left ventricular pressures were measured with a micromanometer. The following were measured after descending thoracic aortomyoplasty at baseline and with the descending thoracic aortomyoplasty stimulated 1:1 with the heart rate: stroke work, stroke volume, left ventricular peak pressure, maximum rate of increase of left ventricular pressure, diastolic relaxation time constant, peak rate of pressure decay, left ventricular end-diastolic pressure, endocardial viability ratio, mean diastolic aortic pressure, peak diastolic aortic pressure, and time-averaged aortic diastolic velocity. Before data collection, the latissimus dorsi was stimulated (5 pulses delivered at 33 Hz at a rate of 28 per minute for 4 weeks) with burst stimulation to induce fatigue resistance. Results (expressed as the mean +/- the standard error of the mean) showed significant improvement in the indices of ventricular contractility (maximum rate of increase of left ventricular pressure, 1,217 +/- 83 to 1,414 +/- 91 mm Hg/s) and diastolic relaxation mechanics (peak rate of pressure decay, 1,152 +/- 92 to 1,282 +/- 79 mm Hg/s; diastolic relaxation time constant, 43 +/- 2 to 38 +/- 2 ms). Significant differences were noted with stimulation at 1:1 in the endocardial viability ratio (0.90 +/- 0.05 to 1.14 +/- 0.04), an index of myocardial oxygen supply. Systemic diastolic pressures (peak diastolic aortic pressure, 95 +/- 6 to 107 +/- 5 mm Hg; mean diastolic aortic pressure, 92 +/- 6 to 102 +/- 6 mm Hg) and the time-averaged aortic diastolic velocity (1.5 +/- 0.6 to 3.3 +/- 1.0 m/s) increased significantly. We conclude that descending thoracic aortomyoplasty stimulation with conditioned latissimus dorsi muscle can improve indices of ventricular contractility, diastolic relaxation mechanics, diastolic pressures, and diastolic aortic velocity in the nonfailed canine heart. Further studies with the chronic failed heart model are required.

Animals↗
PubMed1994

Dynamic descending thoracic aortomyoplasty: comparison with intraaortic balloon pump in a model of heart failure.

Descending thoracic aortomyoplasty (DTA) uses the latissimus dorsi muscle to compress the proximal descending thoracic aorta as an autogenous diastolic counterpulsator. We studied the hypothesis that DTA could confer hemodynamic benefits equivalent to those yielded by an intraaortic balloon pump (IABP) in dogs (n = 7) with heart failure. The left latissimus dorsi muscle was wrapped around the proximal thoracic aorta and subsequently electrically conditioned to induce fatigue resistance. Heart failure was produced by rapid ventricular pacing after muscle conditioning. Data were collected under three conditions: (1) after the induction of heart failure; (2) with the 20-mL IABP at 1:1; and (3) with the DTA stimulated at 1:1. Effective diastolic counterpulsation was achieved with both the IABP and the DTA. The mean diastolic aortic pressure increased from 66 +/- 5 mm Hg at baseline to 90 +/- 4 mm Hg with the IABP and to 75 +/- 4 mm Hg with the DTA. The left ventricular peak and end-diastolic pressures decreased with IABP (95 +/- 5 mm Hg versus 88 +/- 4 mm Hg and 16 +/- 4 mm Hg versus 12 +/- 4 mm Hg, respectively; p < 0.05) and with DTA (95 +/- 5 mm Hg versus 87 +/- 4 mm Hg and 16 +/- 4 mm Hg versus 12 +/- 4 mm Hg, respectively; p < 0.05). Counterpulsation with the IABP did not change the end-systolic pressure-volume relationship or the time constant for diastolic relaxation, whereas the DTA increased the end-systolic pressure-volume relationship (3.2 +/- 0.6 mm Hg/mL versus 4.0 +/- 0.7 mm Hg/mL; p < 0.05) and decreased the time constant for diastolic relaxation (49 +/- 5 msec versus 45 +/- 6 msec; p < 0.05). These data show that DTA using conditioned skeletal muscle can provide diastolic counterpulsation in animals with compromised cardiac function.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Ergometric studies of untrained skeletal muscle demonstrate feasibility of muscle-powered cardiac assistance.

The feasibility of biomechanical circulatory assistance hinges on the capacity of skeletal muscle to generate significant hemodynamic work. This study quantifies linear contractile energetics via a customized hydraulic ergometer. Six normal canine latissimus dorsi (LD) muscles (200 +/- 25 g) were evaluated. The muscles were not mobilized; thereby their collateral circulation was preserved. The humeral insertion of the LD muscle was transected and connected to the ergometer. Preload was adjusted to return the LD muscle to its in situ length, and one pulse train was delivered every second. The resulting contractions generated peak pressures of 134 +/- 17 mmHg with mean pressures during shortening of 102 +/- 12 mmHg. Flow rates averaged 5.45 +/- 0.26 l/min. Mechanical work output was calculated at 1.14 +/- 0.18 J/contraction, yielding an average power production of 4.57 +/- 0.72 W during shortening. Continuous LD output power, measured at 5.76 +/- 0.90 mW/g, compares favorably with the 3.48 mW/g typically generated by a 350-g human heart. We therefore conclude that skeletal muscle of sufficient mass can sustain work rates suitable for cardiac assistance despite the 50% power losses typically experienced after muscle training.

Animals↗