BAM 8 (1), 1998

Table of Contents

Editorial               5        K Gealow, JC Chachques and P Grandjean: New Approaches in Dynamic Cardiomyoplasty  

Articles                7        Tissue velocity imaging for monotoring of skeletal muscle function in circulatory assist systems
                                       NR Grubb    [Full text pdf 253 Kb]  

                           11        Demand dynamic cardiomyoplasty. Improved clinical benefits by non-invasive monitoring of
                                       LD flap and long-term tuning of its dynamic contractile characteristics by activity-rest regime
                                       U Carraro, G Docali, M Barbiero, C Brunazzi, K Gealow, D Casarotto, and C Muneretto    [Full text pdf 356 Kb]  

                           17        Blood flow pattern in the thoracodorsal artery after dynamic cardiomyoplasty
                                       P Gerometta, S Di Matteo, M Agrifoglio, M Naliato, A Parolari, V Arena, N Valerio, and P Biglioli    [Full text pdf 187 Kb]  

                           21        A monitoring catheter for a dynamic cardiomyoplasty
                                       NW Guldner, P Klapproth, T Fischer, R Noel, and HH Sievers    [Full text pdf 284 Kb]  

                           27        Partial cardiac assistance begun immediately after Latissimus Dorsi muscle mobilization and  cardiomyoplasty
                                       VS Chekanov, VV Nikolaychik, MA Rieder, GV Tchekanov, LM Smith, and H Schmidt    [Full text pdf 337 Kb]  

                           35        Improved function in muscles trained via interval stimulation
                                       C Duan, DR Trumble, IY Christlieb, JA Magovern, and GJ Magovern Sr.    [Full text pdf 231 Kb]  

                           41        Latissimus dorsi stimulation in dynamic cardiomyoplasty: How should we proceed?
                                       K Gealow    [Full text pdf 173 Kb]  

                           51        Strategies for preserving muscle function for improved systolic assist in dynamic cardiomyoplasty
                                       WP Santamore, A Ali, R Stremel, B Chiang, M Kashem, NA-E Tobin, OS Carroll, PJ Barker, L Unger, AD Slater,
                                       L Gray, and G Tobin    [Full text pdf 213 Kb]  

Review               59        Aortomyoplasty
                                        G Bolotin, FH Van Der Veen, R Lorusso, JJ Schreuder, JB David, G Uretzky    [Full text pdf 223 Kb]  

Articles              67        Simultaneous measurement of tissue pO2 and perfusion during muscular contraction of the Latissimus Dorsi
                                       DJ Barren, PJ Etherington, JR Pepper, and CP Winlove    [Full text pdf 338 Kb]  

Myology News  75        International Workshop on Dynamic Cardiomyoplasty (IWDC98) Abstracts   [Full text pdf 418 Kb]

Tutorials in Cardiomyoplasty: Stimulation Protocols and Monitoring of the Latissimus Dorsi Flap

In this tutorial, recent progress in dynamic cardiomyoplasty (DCMP) research and new clinical approaches are presented. The clinical success of DCMP has so far been achieved despite the lack of a reliable tool for non-invasively monitoring the latissimus dorsi muscle (LD) contractile properties (e.g. peak contraction, contraction and relaxation velocities, etc.) after it is wrapped around the heart. Without such monitoring, careful selection of stimulation parameters for optimizing LD contractile properties and the synchrony between LD contraction and cardiac events is unrealizable. With such new tools available, new stimulation strategies for improving muscle performance can be tested for increasing short-term DCMP benefit and ensuring positive long-term outcomes. New monitoring techniques that can be immediately put to clinical practice are presented in this issue along with new stimulation strategies for enhancing LD function.

Grubb clearly describes how color Doppler tissue velocity imaging can be a useful and important tool in DCMP patient follow-up for evaluating both LD function and its effect on cardiac mechanics. Carraro and colleagues present a simple but potentially indispensable technique, implementing standard cardiology equipment, that provides a way to non-invasively monitor changes in LD contractile properties over time and to precisely synchronize muscle and cardiac function. Gerometta has used echo Doppler measurements of thoracodorsal blood flow to the LD in DCMP patients and has examined how this assessment might lend information about LD function and vitality. Guldner describes a device being developed for clinical use which monitors pressure between the heart and muscle wrap giving information about LD function and the coupling of LD contraction to cardiac events.

Using these monitoring techniques, the safety and efficacy of new stimulation strategies can be tested. One short-coming of DCMP has been the lack of early post-operative benefit to the patient. New developments in DCMP should aim at providing more immediate, measurable benefit to the patient and maintaining this benefit long-term through careful monitoring and tuning of LD stimulation. The collection of papers presented in this tutorial teach a number of approaches toward achieving these goals. The idea of preserving LD mass, power capacity and preventing fiber injury is a common thread through all of the papers.

A cautious stimulation regime for delivering early hemodynamic benefit is proposed by Chekanov et al. based on their series of experiments over the past several years. To maintain hemodynamic benefits long-term, Guldner describes how careful LD monitoring can be used to design stimulation protocols aimed at preserving muscle function. Duan and colleagues present striking new research validating the benefits of intermittent stimulation for augmenting LD power and mass. The clinical implementation of intermittent stimulation for achieving more desirable LD contractile properties in long-term patients is described by Carraro and friends. Gealow has made an effort to review new and proposed concepts for improving training and chronic stimulation regimes based on clinical goals.

Finally, the surgical approach of using a vascular delay prior to DCMP may augment the improvements achievable by new stimulation protocols alone by preventing irreversible ischemic muscle injury associated with surgical mobilization. This modification to DCMP is now being evaluated clinically in at least three centers. The experimental development of this approach and its marked effect on early hemodynamic outcome in animals is reviewed in the article by Santamore and his colleagues.

In related articles, Barron et al. present some basic research aimed at revealing the details of perfusion and metabolism in a chronically stimulated LD. Fontaliran describes another new case of morphologically preserved LD in a long-term DCMP patient. A review of aortomyoplasty by Bolotin and colleagues reminds us that advances made in DCMP will be important in other applications of muscle-powered cardiac assist.

The information collected for this special issue represents many years of solid research providing experimental justification of new concepts that the physician can begin to use and test clinically. Most concepts described here can be safely implemented today for clinical validation and, accompanied by careful patient study, could reveal new ways of delivering cardiomyoplasty to further improve treatment for heart failure.

Kendra Gealow
University of Minnesota/Medtronic
7000 Central Avenue N.E.
Minneapolis, MN 55432 USA
tel 001 612 5744875
fax 001 612 5746420
e-mail kendra.gealow@medtronic.com

Juan C. Chachques
Hopital Broussais
Lab. Greffes Cardiaques 4me etage
96, Rue Didot
F-75014 Paris
tel +33 1 43959359
fax +33 1 45425049
e-mail jchachques@francemultimedia.fr

Dr. P.A. Grandjean
Bakken Research Center B.V.
Endepoldsdomein 5,
PO Box 1220,
6201 MP Maastricht, 6229 GW The Netherlands
tel 0031 433 566626; fax 0031 433 566509
e-mail pierre- andre.grandjean@medtronic.com

Tissue Velocity Imaging for Monitoring of Muscle Function in Circulatory Assist Systems

Neil R. Grubb
Cardiovascular Research Unit, University of Edinburgh, Department of Cardiology, Royal Infirmary of Edinburgh, Edinburgh, UK

In a series of studies we tested potential applications of tissue velocity imaging (TVI) for pre-surgical and post-surgical assessment in skeletal muscle circulatory assist systems. TVI is an ultrasound modality which is capable of measuring velocities within solid tissues such as skeletal muscle. An initial evaluation in healthy volunteers demonstrated that TVI can characterise the rapid phases of in-situ skeletal muscle contraction with high temporal and spatial resolution. In the clinical setting of cardiomyoplasty TVI provides information about electromechanical relationships in the stimulated myograft, and the effect of changes in stimulator settings on ventricular wall motion. These measurements may help optimize myograft stimulation in clinical practice. Finally, preliminary results show that TVI is capable of imaging skeletal muscle ventricle wall motion, and this application is the subject of more detailed evaluation. TVI is a useful non-invasive modality for the monitoring of skeletal muscle function
in cardiac assist systems.

Key words: cardiomyoplasty, skeletal muscle, skeletal muscle ventricles, Doppler ultrasound.
Basic Appl. Myol. 8 (1): 7-10, 1998

Neil R Grubb, Lecturer in Cardiology, Cardiovascular Research Unit, University of Edinburgh, Department of Cardiology, Royal Infirmary of Edinburgh, 1 Lauriston Place, Edinburgh EH3 9YW, UK, tel. 44 131 536 2749, fax 44 131 536 2744.

Demand Dynamic Cardiomyoplasty: Improved Clinical Benefits by Non-Invasive Monitoring of LD Flap and Long-Term Tuning of Its Dynamic Contractile Characteristics by Activity-RestRegime

Ugo Carraro, Giorgio Docali (1), Mario Barbiero (1), Cristiana Brunazzi (1), Kendra Gealow(2), Dino Casarotto (3) and Claudio Muneretto (4)
C.N.R. Unit for Muscle Biology and Physiopathology and Department of Biomedical Sciences, University of Padova, Italy, (1) Division of Cardiology, Legnago General Hospital (Verona), Italy, (2) Medtronic, Inc., Minneapolis, USA, (3) Cardiovascular Surgery, University of Padova, Italy and (4) Cardiovascular Surgery, University of Brescia, Italy

To many authors, cardiomyoplasty is a clinical reality, founded on the basis of its girdling effect which limits and/or reverses the progressive dilatation of a failing heart. Load-independent measurements of cardiac function demonstrate a real improvement of the heart energetics when analyses are compared before and after cardiomyoplasty. Standard indices of systolic function are not consistently improved. One of the factors limiting the systolic assistance of cardiomyoplasty is muscle performance after full conditioning of LD. Clinically, it is accepted that LD benefits the patient's quality of life only if its activation is optimally delayed after the sensed QRS complex in order to avoid mitral regurgitation. Since maximum instantaneous power of a fully conditioned LD is smaller than the peak power of the left ventricle, the grafted muscle could assist the heart during mid and late systolic phases. Such a short time window requires a fast, powerful contraction which is not delivered by a fully transformed LD. Monitoring LD function is essential for evaluating and implementing new concepts aimed at improving LD function for greater systolic benefit. We have developed a simple non-invasive method to analyse the dynamic characteristics of the LD flap during conditioning and chronic stimulation using a standard polygraph. To perform this monitoring we have implemented
the basic concept of tetanic fusion frequency analysis. By monitoring changes in fusion frequency over time, we hoped that it would be possible to adjust daily stimulation parameters in order to maintain a faster, more powerful muscle. In fact, this has now been achieved by implementing an activity-rest regime. After months of continuous daily stimulation it is possible
to reverse the fast-to-slow transformation by a demand stimulation protocol which allows the LD flap to rest during periods of low-activity, both day and night. With this lighter stimulation
regime, now used in patients at more than one-year of follow-up, substantial improvement in quality of life has occurred with a reduction in heart failure symptoms from N.Y.H.A. Class III to I. If these preliminary data can be substantiated by long-term results in these patients and
in future patients in an Italian Trial of Demand Dynamic Cardiomyoplasty (DDC), we are confident that DDC could offer long-standing benefits to manage pharmacologically-intractable heart failure.

Key words: Demand Dynamic Cardiomyoplasty, improved clinical benefits, non-invasive monitoring, human LD flap, dynamic contractile characteristics, activity-rest regime.
Basic Appl. Myol. 8 (1): 11-15, 1998

Prof. Ugo Carraro, Department of Biomedical Sciences, Viale G. Colombo 3, I-35121 Padova Italy, tel. +39 49 8276030, fax +39 49 8276040, Email bam@civ.bio.unip.it.

Blood Flow Pattern in the Thoracodorsal Artery after Dynamic Cardiomyoplasty

P Gerometta, S Di Matteo (1), M Agrifoglio (2), M Naliato (1), A Parolari (1), V Arena (2), N Valerio and P Biglioli (2)
Cliniche Gavazzeni, via Gavazzeni, 21, 24125 Bergamo, (1) Centro Cardiologico I. Monzino Foundation, via C. Parea, 4, 20138 Milano and (2) Department of Cardiovascular Surgery, University of Milan, Italy

To understand if a non invasive determination of blood flow to the Latissimus Dorsi Muscle (LDA) could be used as an indirect index of muscle viability, we postoperatively measured the thoracodorsal artery (TDA) blood flow variations during latissimus dorsi stimulation in 4 patients who had a cardiomyoplasty. The TDA was in all cases identified by a characteristic biphasic blood flow pattern. We measured diameter (mm), mean velocity (cm/sec), systolic/diastolic ratio (S/D) and calculated blood flow (ml/min) during 5 minutes of
latissimus dorsi stimulation at 2:1 and 1:1 synchronisation ratio while changing the voltage applied to the muscle so to obtain various strength of contraction. Mean blood flow was 33.75 ml/min in basal condition and increased to 42.83 ml/min during a synchronisation rate of 1:2 at a voltage of 150% of clinical setting. There was a further increase up to 50.99 ml/min for a synchronisation rate of 1:1 while, at the same time, a marked reduction of S/D ratio (from 4.29 to 1.97) was detected.
In conclusion blood flow in the TDA appears to be directly related to metabolic needs of the stimulated muscle and this non invasive technique can be useful to follow-up patients and control long term muscle viability.

Key words: cardiomyoplasty, thoraco-dorsal artery, blood flow, heart failure, Doppler technique.
Basic Appl. Myol. 8 (1): 17-20, 1998

Gerometta Piersilvio, Cliniche Gavazzeni, via Gavazzeni, 21, 24125 Bergamo, Italy, fax +39 35 322376.

A Monitoring Catheter for Dynamic Cardiomyoplasty

Norbert W. Guldner, Peter Klapproth, Thomas Fischer, Ralf Noel and Hans-H. Sievers
Clinic of Cardiac Surgery, Medical University of Lubeck, Germany

Measurement of the pressure developed between a dynamic cardiomyoplasty (DCMP) wrap and the myocardium was evaluated as a possible method for monitoring skeletal muscle contractile force and the synchronization of the myostimulator-induced DCMP contraction in relation to the heart cycle. A newly designed implantable monitoring catheter was tested in goats (n = 3) for a six-month duration. A small fluid-filled balloon attached to a monitoring catheter was placed between the myocardium and the DCMP wrap. The catheter ended in a subcutaneous access port used for pressure monitoring. Sharp pressure signals produced by the contracting DCMP were obtained in all animals at the beginning of the study. An 86% reduction of the initial amplitude of the pressure curve occurred after six months of stimulation in two goats. In the third goat, no contraction could be verified, and the DCMP was considered failed. Pressure signals transferred from the contracting myocardium could be characterized into defined segments of contraction, ejection and filling. This information allows mechanical synchronization of the DCMP contraction with the desired period of the heart cycle. The DCMP monitoring catheter successfully tranferred signals relating to the functional state of the DMCP wrap and its mechanical coupling to the heart cycle. We expect that with the use of this catheter we
can better understand and optimize DMCP as a therapy for end-stage heart failure.

Key words:
Basic Appl. Myol. 8 (1): 21-25, 1998

Dr. Norbert W. Guldner, Klinik für Herzchirurgie, Medizinische Universität zu Lübeck, Germany, tel. 0049 451 2108, fax 0049 451 2051.

Partial Cardiac Assistance Begun Immediately after Latissimus Dorsi Muscle Mobilization and Cardiomyoplasty

Valeri S. Chekanov, Victor V. Nikolaychik, Michelle A. Rieder, Guennady V. Tchekanov, Luke M. Smith and Donald H. Schmidt
Milwaukee Heart Project, Milwaukee, WI, USA

Cardiomyoplasty, in which the latissimus dorsi muscle (LDM) assists the heart, is a relatively new surgical treatment for heart failure. Currently, the LDM is unstimulated for the first two weeks postoperatively, then stimulated for the next four weeks with one or two impulses every
other heart beat. We wanted to determine if the LDM could provide assistance earlier than six weeks postoperatively. In four control sheep electrical stimulation (ES) was not applied to the LDM; in four sheep, ES was begun two hours after LDM mobilization; in another four sheep, ES mimicking cardiac assist (work-rest regimen) was added to the protocol twice daily for 30 minutes. In animals with the protocol mimicking cardiac assist, contractile force (CF) changed minimally on days 6, 11, and 16 following two successive 30 minute fatigue tests (98 3%; 102 3%, and 104 2 % respectively). The typical ischemic state of the mobilized LDM was not aggravated with this protocol. The percent area occupied by capillaries increased to 5.04 0.33% (compared with 3.02 0.6% in control muscle). In the control series, CF decreased to 85 4%, 78 3%, and 77 3% on days 6, 11, and 16, respectively. We concluded that a cautious stimulation regimen using a work-rest protocol and a slow rate of contraction does allow for earlier partial cardiac assist.

Key words: Cardiomyoplasty, cardiac assist, latissimus dorsi muscle, electrical stimulation, contractile force.
Basic Appl. Myol. 8 (1): 27-34, 1998

Valeri S. Chekanov, M.D., Ph.D.945 N. 12th Street, W419 P.O. Box 342 Milwaukee, WI 53201-0342 USA, tel. 414 219 7899, fax 414-219-6266.

Improved Function in Muscles Trained Via Interval Stimulation

Changping Duan, Dennis R. Trumble, Ignacio Y. Christlieb, James A. Magovern and George J. Magovern
Cardiothoracic Surgical Research, Allegheny University of the Health Sciences, Department of Surgery, Allegheny General Hospital, Pittsburgh, Pennsylvania, USA

Latissirnus dorsi (LD) muscles of eight rabbits were studied to test the hypothesis that periodic intervals of rest can improve the functional capacity of fatigue-resistant muscle. Animals were divided into two groups of four: one group stimulated continuously (24 hours/day) for six weeks while the other intermittently (12 hours/day) for 12 weeks. Contralateral LD were used as unstimulated control. Muscle strength and endurance were tested using a custom skeletal muscle ergometer and biopsies were collected for histochemical analysis. Isometric force measurements revealed a 105% increase in muscle strength due to interval stimulation while training via continuous stimulation reduced force generation by 47%. Isotonic stroke work in the 12-wk interval group was 115% higher than the 6-wk continuous group and 32% higher than control levels. After 40 minutes of uninterrupted work, the control group was completely fatigued while the 12-wk interval group continued to generate 222.0 g.cm of external work. Histologic data show increases in the number and size of fast oxidative fibers in the 12-wk interval group while 6-wk continuous training yielded smaller fibers dominated by the slow oxidative type. These findings suggest that intermittent rest periods may be important in maintaining contractile function in chronically stimulated skeletal muscle.

Key words: rest periods, stimulation, skeletal muscle, rabbits, contractile power.
Basic Appl. Myol. 8 (1): 35-39, 1998

Chanping Duan, Cardiothoracic Surgical Research, Allegheny University of the Health Sciences, Allegheny Campus (14th floor - South Tower), 320 East North Avenue, Pittsburgh, PA 15212, USA, phone 412 359 4132, fax 412 359 5071.

Latissimus Dorsi Stimulation in Dynamic Cardiomyoplasty: How Should We Proceed?

Kendra K. Gealow
Bakken Research Center, Medtronic, Inc., Maastricht, The Netherlands and Department of Surgery, University of Minnesota, Minneapolis, MN, USA

Improved understanding of the mechanisms of action in dynamic cardiomyoplasty (DCMP) and continued research in the stimulation of the latissimus dorsi muscle (LDM) contribute to the development of new stimulation strategies aimed at improving DCMP outcomes. Cautious initiation of LDM stimulation sooner after surgery than currently practiced may provide the patient earlier hemodynamic assistance. During training and chronic stimulation, adjustment of stimulation amplitude, number of pulses in a burst, the interval between pulses, the synchronization ratio and the synchronization delay will all have important effects on the acute and chronic contractile properties of the LDM, thus impacting its capacity to improve cardiac function. Allowing the LDM periods of rest each day can be extremely beneficial to the muscle and may ultimately improve clinical outcome. Non-invasive monitoring of LDM contraction is essential to implementing and testing new stimulation regimes. Recent development of such monitoring techniques allows safe clinical evaluation of experimentally validated concepts.
This review considers each LDM stimulation parameter in terms of improving LDM function and optimizing DCMP benefit during both training and chronic stimulation phases. Post-operative stimulation techniques currently possible with today's technology are discussed in light of recent research and clinical findings.

Key words: cardiomyoplasty, Latissimus dorsi, electrical stimulation.
Basic Appl. Myol. 8 (1): 41-50, 1998

Kendra Gealow, Medtronic, Inc., 7000 Central Ave. NE, M.S. P202, Minneapolis, MN 55432, USA.

Strategies for Preserving Muscle Function for Improved Systolic Assist in Dynamic Cardiomyoplasty

William P. Santamore, Ahsan Ali, Richard Stremel, Ben Chiang, Kashem, Anne-Elise Tobin, Sean Carroll, John Barker, Lauren Unger, David Slater, Laman Gray, Jr, Gordon Tobin
Jewish Hospital Cardiothoracic Surgical Research Institute, Division of Thoracic and Cardiovascular Surgery, and Division of Plastic and Reconstructive Surgery, University of
Louisville School of Medicine, Louisville, Kentucky

Chronic heart failure continues to be a major cause of morbidity and mortality. Cardiomyoplasty (CMP) a surgical treatment for heart failure, has several potential advantages: skeletal muscle requires no external power source; each patient serves as his/her own donor; rejection is not a problem and immunosuppression is not necessary. This promising new technique appears to cause symptomatic improvement in patients with New York Heart Association class III heart failure. Objective improvement in systolic performance of the left ventricle appears small but remains to be further defined. Mechanisms of action may include a girdling effect that prevents progressive left ventricular dilatation. This effect may be independent of any role in augmenting
systolic performance.Although current efforts with cardiomyoplasty have not produced the
anticipated clear-cut benefits in cardiac function, consistent improvements in subjective function have resulted. Efforts in optimizing preconditioning protocols and skeletal muscle integrity should provide further improvements in cardiomyoplasty.

Key words: review, cardiomyoplasty, Latissimus dorsi muscle
Basic Appl. Myol. 8 (1): 51-58, 1998

William P. Santamore, PhD, Division of Thoracic and Cardiovascular Surgery, Department of Surgery, University of Louisville School of Medicine, Louisville, Kentucky 40292, phone 502 852 4345, fax 502 852 1795.

Aortomyoplasty

Gil Bolotin (1), Frederik H. Van Der Veen (2), Roberto Lorusso (3), Jan J. Schreuder (2), Joseph B. David (1), Gideon Uretzky (1)
(1) Departments of Cardiothoracic Surgery and Cardiology, Carmel Medical Center, Rappaport, Institute of Research in the medical sciences, Technion, Israel Institute of Technology, Haifa, Israel, (2) Department of Cardiology, Cardiovascular Research
Institute Maastricht, University of Maastricht, The Netherlands and (3) Department of Cardiac Surgery, Ospedale Civile, Brescia, Italy

Aortomyoplasty is a surgical procedure which should sustain the hemodynamic effects of intra-aortic balloon pump for the long run. This operation will probably be suitable for end-stage heart failure patients. The experimental results are encouraging but further experimental and clinical experience is required to evaluate the use of the procedure.

Key words: aortomyoplasty, skeletal muscle, congestive heart failure, cardiomyoplasty.
Basic Appl. Myol. 8 (1): 59-65, 1998

FH van der Veen, Department of Cardiology, Cardiovascular Research Institute Maastricht, University Hospital Maastricht, P. Debyelaan 25, 6227 HX Maastricht, tel. 31 43 387 7097, fax 31 43 387 5104, Email e.vanderveen@cardio.azm.nl.

Simultaneous Measurement of Tissue pO2 and Perfusion During Muscular Contraction of the Latissimus Dorsi

David J. Barron (1), Phillip J. Etherington (2), John R. Pepper (1) and Peter C. Winlove (2)
(1) Dept. of Cardiac Surgery, National heart and Lung Institute and (2) Physiological Flow Studies Group, Imperial College, London, United Kingdom

The latissimus dorsi muscle (LDM) receives its primary blood supply from a single nutrient artery located at its proximal insertion and it has not previously been established whether this effects the regional perfusion and nutrition of the muscle. A microelectrode technique was used to measure local oxygenation and perfusion simultaneously at multiple sites in the rabbit LDM at rest, during and after repeated muscular contraction induced by electrical stimulation with a fatigue-testing protocol. In the resting state there were no significant differences in perfusion or oxygenation in different regions of the LDM. However, the proximal perfusion was greater than distal perfusion during muscular contraction (increase from baseline 173 9% and 137 5%) and during the first 20 minutes of recovery. Tissue oxygenation was maintained at constant levels in the proximal region throughout contraction and recovery whereas there was a significant decrease in distal pO2 of 10.2 3.8mmHg during contraction and of 5.4 4.2mmHg during the first 20 minutes of recovery. The evidence suggests that distal areas of the LDM cannot maintain sufficient perfusion during contraction to prevent a fall in tissue pO2.This has important implications on the clinical applications of the LDM as a pedicled muscle flap for cardiac assistance.

Key words: microelectrodes, nitrous oxide clearance technique, electrical stimulation, microcirculation, skeletal muscle metabolism.
Basic Appl. Myol. 8 (1): 67-74, 1998

Mr. DJ Barron, FRCS, Dept. of Cardiac Surgery, National heart and Lung Institute, Dovehouse Street, London SW3 6LY, United Kingdom, tel. and fax 0171 351 8530.