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Cat sartorius muscle: An isolated perfused skeletal muscle preparation for microvascular research
MICROVASCULAR
RESEARCH
5,401-409 (1973)
Cat Sartorius Muscle: An Isolated Perfused Skeletal Muscle Preparation for Microvascular Research1 K. S. BURTON Department of Physiology, College of Medicine, University of Arizona, Tucson, Arizona 85724 Received June 15,1972 The cat sartorius muscle is an example of a skeletal muscle which can be isolated and transilluminated for studies of the microcirculation. This preparation can be used for constant-flow or constant-pressure experiments, and for studies of reactive hyperemia, exercise hyperemia, and autoregulation in skeletal muscle. Detailed procedures are described for the isolation of the muscle. Some of the advantages and limitations in the use of this preparation are also discussed.
For the direct study of the microcirculation, it is often desirable to use a preparation which can be completely isolated with its blood supply intact, and is thin enough to be transilluminated. There are few skeletal muscle preparations currently in use which fulfill both of these criteria. One preparation which satisfies both requirements is the sartorius muscle of the cat (Burton and Johnson, 1971).The sartorius muscle is superficially located on the hindlimb and is easily accessible.For cats under 2.5 kg, it has regions less than 250 pm thick. The blood supply from the femoral artery and vein is easily isolated. For studies of red cell flow in capillaries, we have found the sartorius muscle to 'be an excellent preparation. MATERIALS
AND METHODS
Two slightly different procedures are described for the isolation and mounting of the muscle. The first procedure is more time consuming, but allows one to becomefamiliar with the vascular communication betweenthe sartorius muscle, and deeperleg muscles. The second procedure requires a good knowledge of the vascular anatomy in the more distal portions of the muscle. It has the advantagesof allowing a more rapid isolation of the muscle, and providing easiermounting of the muscle. We feel one should master the first procedure to gain familiarity with the vascular anatomy of the muscle. It may then be desirable to use the second procedure. The sartorius muscle is a superficial muscle of the hindlimb, which is found on the medial surface of the thigh (Crouch, 1969).Its origin is the cranial half of the crest of the ilium, and its insertion is on the proximal end of the tibia, and on the patella. The medial edge of the muscle is immediately adjacent to the femoral artery and vein. The part of the muscle which is removed for study is indicated in Fig. 1. This section is from 1 This study was supported by a grant-in-aid from the American Heart Association, and NIH grant AM 12065. 401 Copyright 0 1973 by Academic Press, Inc. All
rights
of reproduction
in any form
reserved.
402
BURTON
the body wall to the knee. The dimensions of this portion of the muscle are about 9 cm long x 4 cm wide. The mass of the isolated muscle averages 5 g. The blood supply of the muscle is primarily from the lateral circumflex femoral vessels, and secondarily from one or two small branches of the femoral artery and vein. These latter supply vessels arise close to the junction of the femoral and saphenous vessels. In addition, there are small arteries and veins supplying the more distal and lateral areas of the muscle. These come from the descending genicular artery and vein, and are ligated and cut in the isolation of the muscle. The blood supply of the muscle is illustrated in Fig. 1. Also shown in this figure are several branches from the femoral artery and vein which are ligated and cut in the isolation of the sartorius.
FIG. 1. Schematic drawing of the sartorius muscle preparation. The proximal end of the muscle is at the upper right. Vessels which supply the muscle are indicated. Also indicated are branches from the femoral artery and vein which are ligated and cut in the isolation procedure.
The cat is anesthetized with 75 mg/kg of alpha-chlorolose iv, and placed on its back with its hind legs spread to expose the medial region of the thigh. The initial step is to make an incision just medial to the femoral and saphenous vessels, extending from the body wall to about 2 cm below the knee. A similar incision is made along the lateral margin of the leg. These incisions are shown in Fig. 2(A). The skin covering the muscle is left in place as long as possible to provide protection for the preparation. Throughout the surgery, exposed areas of the muscle are kept moist with warmed bathing solution (37°C). The bathing solution used is the commercially available McGaws Physiological Irrigating Solution, adjusted with Trizma buffer to pH 7.4. Working through the medial incision, the fascia covering the leg muscles is separated by blunt dissection. This reveals the muscular branches from the femoral vessels, which are immediately ligated and cut. By lifting the fascia which covers the more distal portions of the saphenous artery and vein, it is possible to identify the edge of the sartorius muscle, and to begin to separate the sartorius from the deeper muscles (Fig. 2B). As the muscle is separated along the medial edge, the descending femoral artery and vein and the descending genicular vessels are exposed. These are all ligated and cut. In ligating these vessels, caution is exercised to avoid constricting the small feeding vessels which arise in this region
CAT SARTORIUS MUSCLE
403
from the fem.oralartery and vein. The separation of the sartorius from the deepmuscles is continued proximally until the medial edge of the muscle is freed along the length of the incision. Continuing by blunt dissection, the fascia attaching the sartorius to the deeperthigh muscles is separatedlaterally for 2 or 3 cm.
FIG. 2. (A). Illustration of the incisions made to begin exposure of the sartorius muscle. The proximal end is to the right. The arrow at (a) indicates the media1 incision, and (b) indicates the lateral incision. (B). View through the medial incision with the fascia cleared away. The femoral vessels distal to the femoral-saphenousjunction are visible at (a). The arrow at (b) indicates the saphenous vein. The proximal end of the muscle is to the left. (C). The extent to which the sartorius is separated from the deeper thigh muscles. The orientation is the same as in (B).
Figure 2 (C) shows the sartorius lifted by its fascial covering, and reveals the degree of separation from the deepermuscles.In this separation procedure, small vesselswhich connect the sartorius with deep musclesare occasionally encountered. Theseare doubly ligated and cut. An attempt was made to use an electrostatic cautery to coagulate these very small branches. However, it was noted that after extensive use of the cautery, the blood flow through the isolated muscle was very low, and this procedure was abandoned.
404
BURTON
With the medial half of the muscle separated from the deeper muscles, the lateral edge can now be freed. Through the lateral incision, the fascia covering the edge of the muscle is separated. When the edge of the muscle is located, it is freed by blunt dissection along the length of the patellar ligament, starting about 1 cm proximal to the knee. We find it most convenient to cut this ligament close to the muscle, and in this manner free the muscle to within about 5 mm distal to the knee. Ligatures are then attached to the
FIG. 3. (A). Lateral view of the sartorius muscle. The arrow at (b) indicates the lateral edge of the muscle. Note the ligatures attached to the edge. The muscle has been cut across the distal end at (a). (B). Lateral view showing the muscle cut free at both distal (left) and proximal (right) ends. The arrow indicates the main branch of the lateral circumflex femoral vessels which are to be ligated and cut.
edge of the muscle to aid in lifting the muscle. The fascia still connecting the sartorius to the deeper muscles may then be easily separated. With the sartorius completely separated from the deep thigh muscles across the width of the muscle, the next procedure is to cut it free at both the distal and proximal ends. Figure 3 illustrates how this is done. The skin flap, which has been left in place, is cut distally, and pulled forward to expose the muscle. To free the muscle, small masses of fibers are doubly tied distal to the knee, and the muscle cut between the ties. Note that
CAT SARTORIUS MUSCLE
405
the saphencms vessels are left intact to maintain the muscle in its normal position as an aid to later procedures. Ligatures are not trimmed since they will be needed later in mounting t’he muscle. The branch of the femoral nerve which innervates the muscle is now isolated and a sufficient length for stimulation is obtained. The proximal end of the muscle is then ligated in a similar manner to the distal end, and cut. However, the most medial group of fibers are ligated but not cut. This is done to avoid tearing the muscle frorn the femoral artery. When the muscle is ligated, care is used to avoid constricting the arterial and venous branches of the lateral circumflex femoral vessels. In addition, one must be careful to avoid tearing the muscle between the ligatures. In Fig. 3(B), the muscle has been lifted to expose the lateral circumflex vessels (arrow). When these have been carefully exposed, they are ligated and cut. With the muscle lifted in this position, the other branches of the femoral nerve are exposed. These may be left intact, although ligating and cutting the nerve does simplify the surgery. With the muscle now completely freed, a section of the femoral artery and vein, proximal to the lateral circumflex femoral branch, are cleared for cannulation. Since the lateral circumflex vessels arise quite close to the body wall, this procedure is usually tedious, and frequently involves ligating branches of the femoral vessels which are inside the body wall. Some of these branches are indicated in Fig. 1. For example, the deep caudal epigastric, the external pudendal, and the deep femoral artery and vein are usually ligated and cut. The extent. to which the femoral vessels are cleared for cannulation is a matter of personal preference. However, when they are cannulated, the cannula must not occlude the lateral circumflex femoral vessels. These muscle preparations are used for transillumination studies, and it is desirable to have as thin a preparation as possible. Thus, as much fascia as possible is removed from the surfaces of the muscle. The procedure used to remove the fascia is to raise a small portion at a time with hemostats, and trim it away with a scalpel. There are numerous small vessels running between the muscle and the fascia. When the vessels bleed they are ligated as close to the muscle surface as possible. During the removal of the fascia, the muscle is kept completely moist with warm bathing solution. The sartorius, now read:y for cannulation, is shown in Fig. 4(A). It is quite transparent, with vessels less than 100 pm in diameter clearly visible. After the femoral artery and vein are cannulated, the saphenous vessels are ligated, and the preparation cut free. During the cannulation, inflow of blood to the muscle is usually occluded for less than 3 min. The muscle is mounted in a 7 x 12-cm aluminium frame using the ligatures attached to the edges of the muscle. The length of the preparation is adjusted to be similar to that of the intact muscle. Figure 4(B) shows the sartorius muscle mounted in the frame and on a microscope stage. The muscle is covered with Saran Wrap to prevent drying. The surgical procedure as outlined will provide a preparation which can be used successfully for transillumination studies. The technique is straightforward, and requires only a simple frame for mounting the isolated muscle. It also allows one to become thoroughly familiar with the vascular connections to the muscle. When complete familiarity has been achieved, certain modifications can be made in the procedure which decrease the time required for surgery, and also allow the muscle to retain a configuration more similar to that found in situ. The main modification is in the use of special clamps which hold the muscle at the proximal and distal ends. Each of the clamps consists ‘of two 4-mm diam brass rods which are covered with silastic tubing. The rods
406
BURTON
can be bolted together making a strong clamp. In addition to the use of the clamps, a slightly different surgical procedure is used. The clamp is shown in Fig. 5. The same initial incisions are used, but the skin flap is immediately cut free and pulled forward. The fascia medial to the saphenousvessels,and along the distal lateral
FIG. 4. (A). Lateral view of the sartorius muscle prepared for cannulation. The fascia has been removed from the surfaces of the muscle. The blood supply to the muscle is clearly visible. (B). Sartorius muscle, mounted and ready for transillumination. Ligatures have been used for mounting the muscle in its frame.
edgeof the muscle, is separatedas describedpreviously. The sartorius is then freed from the deepermuscles at the distal end so that the lower bar of one clamp can be inserted under the muscle. This must be done carefully to avoid rupturing the small branches of the descendinggenicular artery and vein. The top of the clamp is then bolted in place, compressing the muscle underneath the clamp. The muscle is cut free as illustrated in Fig. 5(A). Note that the muscle distal to the clamp is ligated to prevent bleeding. The muscle is now lifted, using the clamp, and the fascia binding the sartorius to the deeper
Fro. 5. (A). View of sartorius muscle with the distal clamp in place. The distal end of the muscle is at the top of the figure, (a) indicates the lateral edge, and (b) indicates the medial edge. (B). The sartorius muscle supported by the distal clamp. The femoral vessels have been cut distally from the femoral-saphenous junction. The lateral circumflex femoral vessels are clearly visible at the lower proximal end of the muscle. (C). The fascia has been removed from the surfaces of the muscle, and the femoral vessels are prepared for cannulation.
408
BURTON
thigh muscles is separated. This approach allows clearer exposure of the junction of the saphenous and femoral arteries and veins, and the lateral circumflex femoral vessels (Fig. 5(B)). These are ligated as before. The femoral artery and vein are then cleared
FIG. 6. (A). The sartorius muscle, cannulated and mounted. Note the adjustable side bars which allow the muscle to be stretched to the desired length. The proximal clamp (left) is notched so the cannuli will not be occluded. (B). Muscle mounted on a microscope stage ready for viewing.
for cannulation as previously described, and the fascia removed from the surface of the muscle. Figure 5(C) shows the muscle prepared for cannulation. After cannulation of the femoral artery and vein, a second clamp is inserted at the proximal end of themuscle. Care is exercised to insure that this clamp does not occlude the lateral circumflex
CAT SARTORIUS MUSCLE
409
femoral vessels.This requires clearing the muscle proximally about 1 cm more than in the first procedure. If stimulation studies are planned, the branch of the femoral nerve innervating the sartorius is isolated prior to application of the secondclamp. When the nerve is separated,the clamp is positioned and tightened, and the muscle is cut free by ligating and.cutting the muscle fibers proximal to the clamp. Side support bars are then added, as shown in Fig. 6(A) to rigidly maintain the muscle at the desired length. These bars are adjustable to allow flexibility in the size of the muscle segment. The preparation is then covered with Saran Wrap, and placed on the microscope stage as in Fig. 6(B). DISCUSSION Severalcharacteristics of the sartorius muscle make it a good choice for studies of the microcirculation in skeletal muscle. First, it is thin enough to be transilluminated, and has proved to be especially good for observation of capillary blood flow. About half of the isolated muscle is sufficiently thin to allow microscopic observation. It is important to use cats smaller than about 2.5 kg to insure that the muscle will be sufficiently thin for transillumination. The second major characteristic is that the blood supply to the muscle can be isolated and cannulated. After the muscle is isolated, approximately 75 y0 of the muscle is perfused via the normal supply vessels.This preparation can be used for constant-perfusion or constant-pressureexperiments, and also for reactive hyperemia, exercise hyperemia, and autoregulation studies. A minor consideration is the low volume flow rate through the muscle. For a 6-g muscle, it is usually about 0.2-0.3 ml/min. Another advantage in the use of this muscle preparation is its accessibility. It is superficially located, and can be removed with relative ease. Further, the muscle appears to remain in reasonably good condition for several hours (6 hr or more). However, certain precautions must be taken if the muscle is to remain viable. It is especially susceptible to drying, and must be kept moist at all times. This is also true throughout the surgery. The isolated muscle also seemssusceptible to hemorrhage if the venous pressureis elevated above 20 mmHg. ACKNOWLEDGMENTS The author expresses his thanks and appreciation to Dr. P. C. Johnson for his advice and encouragement in the study of this preparation. He also thanks Mrs. Susan Neighbors for her technical assistance, and Mrs. Mary Lou Oslund for her photographic assistance. REFERENCES BURTON,K. S., AND JOHNSON,P. C. (1972). Reactive hyperemia in individual capillaries of skeletal muscle. Amer. J. Physiol. 223, 511-524. CROUCH,J. E. (1969). In “Text-Atlas of Cat Anatomy,” pp. 114-115, 244247. Lea & Febiger, Philadelphia.
RESEARCH
5,401-409 (1973)
Cat Sartorius Muscle: An Isolated Perfused Skeletal Muscle Preparation for Microvascular Research1 K. S. BURTON Department of Physiology, College of Medicine, University of Arizona, Tucson, Arizona 85724 Received June 15,1972 The cat sartorius muscle is an example of a skeletal muscle which can be isolated and transilluminated for studies of the microcirculation. This preparation can be used for constant-flow or constant-pressure experiments, and for studies of reactive hyperemia, exercise hyperemia, and autoregulation in skeletal muscle. Detailed procedures are described for the isolation of the muscle. Some of the advantages and limitations in the use of this preparation are also discussed.
For the direct study of the microcirculation, it is often desirable to use a preparation which can be completely isolated with its blood supply intact, and is thin enough to be transilluminated. There are few skeletal muscle preparations currently in use which fulfill both of these criteria. One preparation which satisfies both requirements is the sartorius muscle of the cat (Burton and Johnson, 1971).The sartorius muscle is superficially located on the hindlimb and is easily accessible.For cats under 2.5 kg, it has regions less than 250 pm thick. The blood supply from the femoral artery and vein is easily isolated. For studies of red cell flow in capillaries, we have found the sartorius muscle to 'be an excellent preparation. MATERIALS
AND METHODS
Two slightly different procedures are described for the isolation and mounting of the muscle. The first procedure is more time consuming, but allows one to becomefamiliar with the vascular communication betweenthe sartorius muscle, and deeperleg muscles. The second procedure requires a good knowledge of the vascular anatomy in the more distal portions of the muscle. It has the advantagesof allowing a more rapid isolation of the muscle, and providing easiermounting of the muscle. We feel one should master the first procedure to gain familiarity with the vascular anatomy of the muscle. It may then be desirable to use the second procedure. The sartorius muscle is a superficial muscle of the hindlimb, which is found on the medial surface of the thigh (Crouch, 1969).Its origin is the cranial half of the crest of the ilium, and its insertion is on the proximal end of the tibia, and on the patella. The medial edge of the muscle is immediately adjacent to the femoral artery and vein. The part of the muscle which is removed for study is indicated in Fig. 1. This section is from 1 This study was supported by a grant-in-aid from the American Heart Association, and NIH grant AM 12065. 401 Copyright 0 1973 by Academic Press, Inc. All
rights
of reproduction
in any form
reserved.
402
BURTON
the body wall to the knee. The dimensions of this portion of the muscle are about 9 cm long x 4 cm wide. The mass of the isolated muscle averages 5 g. The blood supply of the muscle is primarily from the lateral circumflex femoral vessels, and secondarily from one or two small branches of the femoral artery and vein. These latter supply vessels arise close to the junction of the femoral and saphenous vessels. In addition, there are small arteries and veins supplying the more distal and lateral areas of the muscle. These come from the descending genicular artery and vein, and are ligated and cut in the isolation of the muscle. The blood supply of the muscle is illustrated in Fig. 1. Also shown in this figure are several branches from the femoral artery and vein which are ligated and cut in the isolation of the sartorius.
FIG. 1. Schematic drawing of the sartorius muscle preparation. The proximal end of the muscle is at the upper right. Vessels which supply the muscle are indicated. Also indicated are branches from the femoral artery and vein which are ligated and cut in the isolation procedure.
The cat is anesthetized with 75 mg/kg of alpha-chlorolose iv, and placed on its back with its hind legs spread to expose the medial region of the thigh. The initial step is to make an incision just medial to the femoral and saphenous vessels, extending from the body wall to about 2 cm below the knee. A similar incision is made along the lateral margin of the leg. These incisions are shown in Fig. 2(A). The skin covering the muscle is left in place as long as possible to provide protection for the preparation. Throughout the surgery, exposed areas of the muscle are kept moist with warmed bathing solution (37°C). The bathing solution used is the commercially available McGaws Physiological Irrigating Solution, adjusted with Trizma buffer to pH 7.4. Working through the medial incision, the fascia covering the leg muscles is separated by blunt dissection. This reveals the muscular branches from the femoral vessels, which are immediately ligated and cut. By lifting the fascia which covers the more distal portions of the saphenous artery and vein, it is possible to identify the edge of the sartorius muscle, and to begin to separate the sartorius from the deeper muscles (Fig. 2B). As the muscle is separated along the medial edge, the descending femoral artery and vein and the descending genicular vessels are exposed. These are all ligated and cut. In ligating these vessels, caution is exercised to avoid constricting the small feeding vessels which arise in this region
CAT SARTORIUS MUSCLE
403
from the fem.oralartery and vein. The separation of the sartorius from the deepmuscles is continued proximally until the medial edge of the muscle is freed along the length of the incision. Continuing by blunt dissection, the fascia attaching the sartorius to the deeperthigh muscles is separatedlaterally for 2 or 3 cm.
FIG. 2. (A). Illustration of the incisions made to begin exposure of the sartorius muscle. The proximal end is to the right. The arrow at (a) indicates the media1 incision, and (b) indicates the lateral incision. (B). View through the medial incision with the fascia cleared away. The femoral vessels distal to the femoral-saphenousjunction are visible at (a). The arrow at (b) indicates the saphenous vein. The proximal end of the muscle is to the left. (C). The extent to which the sartorius is separated from the deeper thigh muscles. The orientation is the same as in (B).
Figure 2 (C) shows the sartorius lifted by its fascial covering, and reveals the degree of separation from the deepermuscles.In this separation procedure, small vesselswhich connect the sartorius with deep musclesare occasionally encountered. Theseare doubly ligated and cut. An attempt was made to use an electrostatic cautery to coagulate these very small branches. However, it was noted that after extensive use of the cautery, the blood flow through the isolated muscle was very low, and this procedure was abandoned.
404
BURTON
With the medial half of the muscle separated from the deeper muscles, the lateral edge can now be freed. Through the lateral incision, the fascia covering the edge of the muscle is separated. When the edge of the muscle is located, it is freed by blunt dissection along the length of the patellar ligament, starting about 1 cm proximal to the knee. We find it most convenient to cut this ligament close to the muscle, and in this manner free the muscle to within about 5 mm distal to the knee. Ligatures are then attached to the
FIG. 3. (A). Lateral view of the sartorius muscle. The arrow at (b) indicates the lateral edge of the muscle. Note the ligatures attached to the edge. The muscle has been cut across the distal end at (a). (B). Lateral view showing the muscle cut free at both distal (left) and proximal (right) ends. The arrow indicates the main branch of the lateral circumflex femoral vessels which are to be ligated and cut.
edge of the muscle to aid in lifting the muscle. The fascia still connecting the sartorius to the deeper muscles may then be easily separated. With the sartorius completely separated from the deep thigh muscles across the width of the muscle, the next procedure is to cut it free at both the distal and proximal ends. Figure 3 illustrates how this is done. The skin flap, which has been left in place, is cut distally, and pulled forward to expose the muscle. To free the muscle, small masses of fibers are doubly tied distal to the knee, and the muscle cut between the ties. Note that
CAT SARTORIUS MUSCLE
405
the saphencms vessels are left intact to maintain the muscle in its normal position as an aid to later procedures. Ligatures are not trimmed since they will be needed later in mounting t’he muscle. The branch of the femoral nerve which innervates the muscle is now isolated and a sufficient length for stimulation is obtained. The proximal end of the muscle is then ligated in a similar manner to the distal end, and cut. However, the most medial group of fibers are ligated but not cut. This is done to avoid tearing the muscle frorn the femoral artery. When the muscle is ligated, care is used to avoid constricting the arterial and venous branches of the lateral circumflex femoral vessels. In addition, one must be careful to avoid tearing the muscle between the ligatures. In Fig. 3(B), the muscle has been lifted to expose the lateral circumflex vessels (arrow). When these have been carefully exposed, they are ligated and cut. With the muscle lifted in this position, the other branches of the femoral nerve are exposed. These may be left intact, although ligating and cutting the nerve does simplify the surgery. With the muscle now completely freed, a section of the femoral artery and vein, proximal to the lateral circumflex femoral branch, are cleared for cannulation. Since the lateral circumflex vessels arise quite close to the body wall, this procedure is usually tedious, and frequently involves ligating branches of the femoral vessels which are inside the body wall. Some of these branches are indicated in Fig. 1. For example, the deep caudal epigastric, the external pudendal, and the deep femoral artery and vein are usually ligated and cut. The extent. to which the femoral vessels are cleared for cannulation is a matter of personal preference. However, when they are cannulated, the cannula must not occlude the lateral circumflex femoral vessels. These muscle preparations are used for transillumination studies, and it is desirable to have as thin a preparation as possible. Thus, as much fascia as possible is removed from the surfaces of the muscle. The procedure used to remove the fascia is to raise a small portion at a time with hemostats, and trim it away with a scalpel. There are numerous small vessels running between the muscle and the fascia. When the vessels bleed they are ligated as close to the muscle surface as possible. During the removal of the fascia, the muscle is kept completely moist with warm bathing solution. The sartorius, now read:y for cannulation, is shown in Fig. 4(A). It is quite transparent, with vessels less than 100 pm in diameter clearly visible. After the femoral artery and vein are cannulated, the saphenous vessels are ligated, and the preparation cut free. During the cannulation, inflow of blood to the muscle is usually occluded for less than 3 min. The muscle is mounted in a 7 x 12-cm aluminium frame using the ligatures attached to the edges of the muscle. The length of the preparation is adjusted to be similar to that of the intact muscle. Figure 4(B) shows the sartorius muscle mounted in the frame and on a microscope stage. The muscle is covered with Saran Wrap to prevent drying. The surgical procedure as outlined will provide a preparation which can be used successfully for transillumination studies. The technique is straightforward, and requires only a simple frame for mounting the isolated muscle. It also allows one to become thoroughly familiar with the vascular connections to the muscle. When complete familiarity has been achieved, certain modifications can be made in the procedure which decrease the time required for surgery, and also allow the muscle to retain a configuration more similar to that found in situ. The main modification is in the use of special clamps which hold the muscle at the proximal and distal ends. Each of the clamps consists ‘of two 4-mm diam brass rods which are covered with silastic tubing. The rods
406
BURTON
can be bolted together making a strong clamp. In addition to the use of the clamps, a slightly different surgical procedure is used. The clamp is shown in Fig. 5. The same initial incisions are used, but the skin flap is immediately cut free and pulled forward. The fascia medial to the saphenousvessels,and along the distal lateral
FIG. 4. (A). Lateral view of the sartorius muscle prepared for cannulation. The fascia has been removed from the surfaces of the muscle. The blood supply to the muscle is clearly visible. (B). Sartorius muscle, mounted and ready for transillumination. Ligatures have been used for mounting the muscle in its frame.
edgeof the muscle, is separatedas describedpreviously. The sartorius is then freed from the deepermuscles at the distal end so that the lower bar of one clamp can be inserted under the muscle. This must be done carefully to avoid rupturing the small branches of the descendinggenicular artery and vein. The top of the clamp is then bolted in place, compressing the muscle underneath the clamp. The muscle is cut free as illustrated in Fig. 5(A). Note that the muscle distal to the clamp is ligated to prevent bleeding. The muscle is now lifted, using the clamp, and the fascia binding the sartorius to the deeper
Fro. 5. (A). View of sartorius muscle with the distal clamp in place. The distal end of the muscle is at the top of the figure, (a) indicates the lateral edge, and (b) indicates the medial edge. (B). The sartorius muscle supported by the distal clamp. The femoral vessels have been cut distally from the femoral-saphenous junction. The lateral circumflex femoral vessels are clearly visible at the lower proximal end of the muscle. (C). The fascia has been removed from the surfaces of the muscle, and the femoral vessels are prepared for cannulation.
408
BURTON
thigh muscles is separated. This approach allows clearer exposure of the junction of the saphenous and femoral arteries and veins, and the lateral circumflex femoral vessels (Fig. 5(B)). These are ligated as before. The femoral artery and vein are then cleared
FIG. 6. (A). The sartorius muscle, cannulated and mounted. Note the adjustable side bars which allow the muscle to be stretched to the desired length. The proximal clamp (left) is notched so the cannuli will not be occluded. (B). Muscle mounted on a microscope stage ready for viewing.
for cannulation as previously described, and the fascia removed from the surface of the muscle. Figure 5(C) shows the muscle prepared for cannulation. After cannulation of the femoral artery and vein, a second clamp is inserted at the proximal end of themuscle. Care is exercised to insure that this clamp does not occlude the lateral circumflex
CAT SARTORIUS MUSCLE
409
femoral vessels.This requires clearing the muscle proximally about 1 cm more than in the first procedure. If stimulation studies are planned, the branch of the femoral nerve innervating the sartorius is isolated prior to application of the secondclamp. When the nerve is separated,the clamp is positioned and tightened, and the muscle is cut free by ligating and.cutting the muscle fibers proximal to the clamp. Side support bars are then added, as shown in Fig. 6(A) to rigidly maintain the muscle at the desired length. These bars are adjustable to allow flexibility in the size of the muscle segment. The preparation is then covered with Saran Wrap, and placed on the microscope stage as in Fig. 6(B). DISCUSSION Severalcharacteristics of the sartorius muscle make it a good choice for studies of the microcirculation in skeletal muscle. First, it is thin enough to be transilluminated, and has proved to be especially good for observation of capillary blood flow. About half of the isolated muscle is sufficiently thin to allow microscopic observation. It is important to use cats smaller than about 2.5 kg to insure that the muscle will be sufficiently thin for transillumination. The second major characteristic is that the blood supply to the muscle can be isolated and cannulated. After the muscle is isolated, approximately 75 y0 of the muscle is perfused via the normal supply vessels.This preparation can be used for constant-perfusion or constant-pressureexperiments, and also for reactive hyperemia, exercise hyperemia, and autoregulation studies. A minor consideration is the low volume flow rate through the muscle. For a 6-g muscle, it is usually about 0.2-0.3 ml/min. Another advantage in the use of this muscle preparation is its accessibility. It is superficially located, and can be removed with relative ease. Further, the muscle appears to remain in reasonably good condition for several hours (6 hr or more). However, certain precautions must be taken if the muscle is to remain viable. It is especially susceptible to drying, and must be kept moist at all times. This is also true throughout the surgery. The isolated muscle also seemssusceptible to hemorrhage if the venous pressureis elevated above 20 mmHg. ACKNOWLEDGMENTS The author expresses his thanks and appreciation to Dr. P. C. Johnson for his advice and encouragement in the study of this preparation. He also thanks Mrs. Susan Neighbors for her technical assistance, and Mrs. Mary Lou Oslund for her photographic assistance. REFERENCES BURTON,K. S., AND JOHNSON,P. C. (1972). Reactive hyperemia in individual capillaries of skeletal muscle. Amer. J. Physiol. 223, 511-524. CROUCH,J. E. (1969). In “Text-Atlas of Cat Anatomy,” pp. 114-115, 244247. Lea & Febiger, Philadelphia.