The effect of nifedipine on skin flap survival in rats.

Maintaining the viability of an extended skin flap remains one of the continuing challenges in reconstructive surgery. As flaps lengthen, viability becomes more unpredictable and necrosis of distal segments can occur. The specific mechanisms involved in determining flap survival remain unclear, but vasoconstriction within the flap microcirculation appears to play a significant role in regulating flap viability. Vasodilators have been used, with limited success, in an attempt to improve survival of ischemic skin flaps in rats. One such agent, nifedipine, a calcium channel blocker, demonstrated conflicting results when used to improve rat skin flap survival, despite its potent vasodilating properties. A standard rat flap model was used to help clarify the potential of nifedipine to salvage ischemic skin flaps. Alterations in flap perfusion were assessed using a laser Doppler flowmeter and dermofluorometry in an attempt to characterize nifedipine's mechanism of action on flap preservation. Increased flap survival was demonstrated in treatment animals when compared to controls. Despite significant improvement in flap viability, perfusion measurements failed to confirm increased flow within the flap microcirculation. Although the mechanisms of action remain speculative, nifedipine may have important therapeutic potential in improving skin flap survival in a clinical setting.

In vivo stimulation of connective tissue accumulation by the tripeptide-copper complex glycyl-L-histidyl-L-lysine-Cu2+ in rat experimental wounds.

The tripeptide-copper complex glycyl-L-histidyl-L-lysine-Cu2+ (GHK-Cu) was first described as a growth factor for differentiated cells. Recent in vitro data showed that it possesses several properties of a potential activator of wound repair. We investigated the effects of GHK-Cu in vivo, using the wound chamber model described previously (Schilling, J.A., W. Joel, and M.T. Shurley, 1959. Surgery [St. Louis]. 46:702-710). Stainless steel wire mesh cylinders were implanted subcutaneously on the back of rats. The animals were divided into groups that received sequential injections into the wound chamber of either saline (control group) or various concentrations of GHK-Cu. At the end of the experiments, rats were killed, wound chambers were collected, and their content was analyzed for dry weight, total proteins, collagen, DNA, elastin, glycosaminoglycans, and specific mRNAs for collagens and TGF beta. In the GHK-Cu-injected wound chambers, a concentration-dependent increase of dry weight, DNA, total protein, collagen, and glycosaminoglycan contents was found. The stimulation of collagen synthesis was twice that of noncollagen proteins. Type I and type III collagen mRNAs were increased but not TGF beta mRNAs. An increase of the relative amount of dermatan sulfate was also found. A control tripeptide, L-glutamyl-L-histidyl-L-proline, had no significant effect. These results demonstrate that GHK-Cu is able to increase extracellular matrix accumulation in wounds in vivo.

Tissue expansion and cutaneous blood flow.

The effect of controlled skin expansion in blood flow was investigated using the dermofluorometer. Twenty-eight subcutaneous pockets in seven pigs were divided into three groups. Group 1: subcutaneous pockets with a gradually inflated 200-cc tissue expander over 12 days, then deflated and observed for 6 days. Group 2: subcutaneous pockets with a noninflated 200-cc tissue expander. Group 3: subcutaneous pockets elevated without placement of a tissue expander. Measurements taken 30 to 45 minutes after partial inflation of the tissue expander showed a decrease in blood flow while blood flow was increased 30 to 45 minutes after deflation of the tissue expander. The increase in blood flow, however, was not evident 6 days after the expander in group 1 was deflated.

Facial muscle reinnervation: a comparison of neuromuscular pedicle with direct nerve implant.

Two methods of reinnervation, the neuromuscular pedicle (NMP) and the nerve implant (NI), were compared in a model using the rabbit's denervated mentalis muscle. Results from evoked electromyographic (EMG) and muscle tension studies (twitch and tetanic contraction) provided the basis of comparison. In addition, the timing of denervation was studied (ie, at the time of implantation of the NMP or NI, or 2 weeks following implantation). The NMP achieved more rapid reinnervation and produced stronger contractions than the NI. Demonstrable reinnervation with an NMP was accelerated when the implantation occurred prior to the denervation. This was not the case with the NI. There was poor correlation between the evoked EMG potential and the strength of both twitch and tetanic contraction. It was concluded on the basis of this study that muscle tension provided a more accurate means of assessing reinnervated muscle function. Of the two methods, the NMP would seem, therefore, to be the technique of choice when it is available. The NI is certainly effective and should be used when a satisfactory NMP is not available.

Reinnervation of the trapezius muscle.

The eleventh cranial nerve shoulder syndrome, which results from denervation of the trapezius muscle, contributes significantly to the postoperative morbidity of radical neck dissections. Multiple techniques exist for the reinnervation of muscles that have injured motor nerves. Reinnervation of denervated trapezius muscles was examined in the New Zealand white rabbit by use of three techniques of reinnervation: (1) neuromuscular pedicle transfer of the accessory nerve from the trapezius muscle, (2) direct accessory nerve implantation, and (3) neuromuscular pedicle transfer of the accessory nerve from the sternocleidomastoid muscle. The reinnervated trapezius muscles were examined grossly by direct nerve stimulation, electrophysiologically by evoked electromyography, and histologically by enzymatic muscle staining and silver-reducing nerve staining. The gross, electrophysiologic, and histologic results confirmed successful reinnervation of the trapezius muscle within 6 weeks of operation. No significant difference was observed between the various techniques of reinnervation.

Laryngeal chemoreflex: anatomic and physiologic study by use of the superior laryngeal nerve in the piglet.

The laryngeal chemoreflex (LCR) was investigated in 21 piglets (ages 6 to 80 days old) with the use of physiologic and histologic techniques. The central projection of the superior laryngeal nerve (SLN) was determined in 14 animals by use of horseradish peroxidase-wheat germ agglutinin. Ipsilateral labeling of the solitary tract nucleus was seen. The caudal extent of the labeling varied with age. Sensory labeling of the nucleus ambiguus was present bilaterally in three younger animals and unilaterally in older piglets. Bilateral labeling of the nucleus dorsomedialis was seen in all ages. Apneic and cardiovascular response to water stimulation of laryngeal mucosa and the laryngeal adductor reflex (LAR) were examined in 16 piglets. Blunting of the apneic and cardiovascular response was seen after sacrifice of a single SLN. Hypoxia did not significantly affect the LAR or apnea duration in animals with only one intact SLN. A contralateral LAR was found in younger animals. Relevance to the LCR is also discussed.

Reinnervation of skeletal muscle: a comparison of nerve implantation with neuromuscular pedicle transfer in an animal model.

In recent years there has been increased interest in the possibility of reinnervating paralyzed muscles, particularly the muscles of the face and of the larynx. There has been dispute over the relative effectiveness of different approaches. This study was undertaken to compare direct nerve implantation with the transfer of a neuromuscular pedicle using denervated strap muscles in a rabbit model. Reinnervation was carried out both immediately after denervation and after a delay period. Evidence of return of function was obtained by a method of long-term electromyographic monitoring and was confirmed electrically by evoked electromyography and muscle tension measurement and histologically by brain stem uptake of horseradish peroxidase. Both methods of nerve transfer produced consistently functional neuromuscular units, with physiological activity and muscle strength comparable with those in normally innervated controls. Return of function was apparent within 6 weeks of both nerve implantation and neuromuscular transfer; with this model, neither method showed a clear advantage over the other.

The effect of alpha-adrenergic stimulation and blockade on perfusion of myocutaneous flaps.

A porcine myocutaneous flap model was utilized to assess the development of denervation adrenergic hypersensitivity and to determine the effects of the alpha-adrenergic blocking agent--phenoxybenzamine--on flap blood perfusion. During intravenous administration of norepinephrine, blood flow to the flaps and control skin was monitored simultaneously, using laser Doppler velocimetry and dermofluorometry. A relative decrease in myocutaneous flap blood flow, as compared to control skin in response to norepinephrine infusion, was observed at between 2 and 7 days following flap elevation. This is the same time period during which norepinephrine content of skin flaps is diminished, and suggests development of an increased sensitivity to adrenergic stimulation. Administration of phenoxybenzamine blunted norepinephrine-induced pressor responses and blocked development of adrenergic hypersensitivity in the porcine myocutaneous flap model. Phenoxybenzamine significantly increased flap blood perfusion (as measured by dermofluorometry).

Venous outflow obstruction in myocutaneous flaps: changes in microcirculation detected by the perfusion fluorometer and laser Doppler.

The effects of venous occlusion on the perfusion of porcine myocutaneous groin flaps were studied by means of the laser Doppler and the dermofluorometer. A consistent decrease in fluorometer readings following venous clamping with rebound to original or greater levels after unclamping was noted. A similar pattern was noted in laser Doppler studies. However, flow as measured by the Doppler remained significant (greater than 100 mV) even with venous outflow occlusion. It is hypothesized that the Doppler is more prone than the dermofluorometer to reflect non-nutritive flow in the flap during the early period following flap construction and, therefore, may be less accurate in the evaluation of actual flap microperfusion. The fluorometer was determined to be the more desirable instrument in monitoring the microcirculatory status of myocutaneous flaps during the immediate period after flap elevation and transposition.

Assessment of facial reinnervation by use of chronic electromyographic monitoring.

The study of muscle reinnervation has been difficult because of lack of an accurate, reproducible method to monitor return of function. Visual assessment relies on subjective interpretation. Histology provides anatomic, not functional, information. Electromyography and anatomic tracing have been most effective in evaluating physiologic return of muscle function. It has been difficult to assess the timing of functional return electromyographically because measurements are intermittent and electrode placement varies. A method was designed to allow long-term monitoring of electromyographic (EMG) activity in the facial musculature of the rabbit. Sixteen rabbits were monitored for at least 1 month or until return of normal EMG activity was identified. Various levels of injury (nerve crush, transection without repair, and transection with immediate end-to-end anastomosis) were evaluated. EMG evidence of reinnervation was seen in all animals with nerve crush injuries as well as those with anastomoses. Physiologic continuity of the nerves was then evaluated by retrograde transport of horseradish peroxidase. All muscles showing return of EMG activity had uptake of HRP into the appropriate brain stem motor neurons. The denervated muscles showed no HRP uptake. The information gained in this study shows potential for use of this technique in comparing functional return of muscle activity between different reinnervation methods.

Measurement of alternative blood flow in the porcine panniculus carnosus myocutaneous flap.

The dependence of a transposed myocutaneous flap on its own vascular pedicle for survival is time-related. The number of days required to establish effective sustaining perfusion from the periphery was assessed. Based on flap perfusion with associated vascular compression as monitored by the laser Doppler and dermofluorometer, adequate perfusion levels occurred at days 7 to 10 in the pig panniculus carnosus myocutaneous flap. It was established that all flaps will survive independent of the vascular pedicle when the laser Doppler readings are above 40 mV and the dermofluorometric readings are above 20%. The establishment of this baseline information now allows for the investigation of pharmacologic manipulation of the blood flow to diminish the duration of dependence on the transposed vascular pedicle.

Reinnervation of skeletal muscle with a neuromuscular pedicle.

In the past decade the otolaryngologist has become interested in the problem of muscle reinnervation as it relates to laryngeal and facial paralysis. Although reinnervation by neuromuscular pedicle transfer has shown promising results in the laboratory and clinic, some investigators have had difficulty in achieving reliable results with this procedure. To further assess the technique's validity, we investigated the neuromuscular pedicle. This study utilized a strap muscle neuromuscular pedicle transfer to a contralateral strap muscle in the rabbit. The results were analyzed by the use of a number of independent measures, including electrical stimulation of the nerve, muscle contractibility, electromyography, enzyme histochemistry, reduced-silver staining for normal fibers, and the retrograde transport of the enzyme marker horseradish peroxidase. The physiologic and anatomic results demonstrated that morphologic and functional reinnervation of the experimentally isolated muscle by the transferred neuromuscular pedicle occurred. The most convincing data were produced by gross electrical stimulation, twitch and tetanic contraction, and horseradish peroxidase labeling. Electromyographic activity and other histologic findings supported the above conclusions.

A model for staged compression of the vascular pedicle in a porcine myocutaneous flap.

There is a need for a laboratory model that would allow assessment of the effects of vascular pedicle compression in the myocutaneous flap. We describe a technique as used in the pig that responds to the needs of technical reproducibility and sequential compromise of vascular flow as measured by laser velocimetry and dermofluorometry.

Discriminative phonation in macaques: effects of anterior mesial cortex damage.

Lesion damage of the anterior midline hemisphere in M. mulatta results in impaired discriminative vocal activity. Destruction of the supplementary motor area (SMA) or pre-SMA greatly increases vocal response latency without similar changes in a non-vocal response. Discrimination and efficiency in performing the vocal and non-vocal responses are unaffected by this damage. The behavioral deficit reflects a specific loss in initiating vocal signals.

Otolaryngology/Head and neck surgery: laser Doppler velocimetry to predict skin flap survival.

The Scientific Board of the California Medical Association presents the following inventory of items of progress in otolaryngology/head and neck surgery. Each item, in the judgment of a panel of knowledgeable physicians, has recently become reasonably firmly established, both as to scientific fact and important clinical significance. The items are presented in simple epitome and an authoritative reference, both to the item itself and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, research workers or scholars to stay abreast of these items of progress in otolaryngology/head and neck surgery that have recently achieved a substantial degree of authoritative acceptance, whether in their own field of special interest or another.The items of progress listed below were selected by the Advisory Panel to the Section on Otolaryngology/Head and Neck Surgery of the California Medical Association and the summaries were prepared under its direction.

Prognostication of myocutaneous flap viability using laser Doppler velocimetry and fluorescein microfluorometry.

Formerly, flap perfusion was assessed clinically by gross evaluation of the amount of fluorescein in the developed flap prior to transfer. Recently the laser Doppler velocimeter and the perfusion microfluorometer have been developed as aids in perfusion assessment. We have used each instrument in a series of reconstructive procedures employing pectoralis or trapezius myocutaneous flaps and a series of pig groin myocutaneous flaps to assess the contribution of each to the prognostication of flap viability. While the laser Doppler does provide useful information, we have found that the microfluorometer is more selective in representing the hemodynamics of the developed flap.

Gillies' corner stitch revisited.

Gillies' corner stitch (GCS) has been generally accepted for closure of skin flap tips because it is commonly believed that this stitch provides the best chance for survival of a flap tip that may have a compromised blood supply. There are no experimental data, however, to support such an assumption. To test the hypothesis that other stitches might be equally efficacious, we evaluated flap tip survival after closure with two different suture techniques, the GCS and a vertical loop stitch ( VLS ). Factors used to evaluate flap tip viability were the measurement of RBC movement in the flap tip by laser Doppler technique and measurement of the length of flap tip necrosis. In our model, the GCS is not superior to the VLS in terms of flap tip survival.

Dynamic variations in blood flow as measured by laser Doppler velocimetry: a study in rat skin flaps.

Some of the measured variations of blood flow in skin flaps are reviewed. Ventral island skin flaps in rats are taken as an experimental model, and serial measurements using laser Doppler velocimetry have been made across the flaps for a period of up to 4 weeks postoperatively. The results demonstrate that areas of these flaps have periods of complete ischemia with no flow. These areas may survive. Conversely, apparently perfused areas later succumbed and became nonviable. The flow readings obtained are compared with fluorescence as a predictor of survival. The immediate and longer-term changes in flow across the length of these flaps are described. These findings are discussed with reference to the suggested methods of increasing the length of flap survival. The hypothesis of nonnutritive blood flow is also reassessed in the light of these findings.