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Doppler ultrasound in the evaluation of experimental microvascular grafts
Brifish Journal of Plasric Surgery (1984) 37, 596-601 0 1984 The Trustees of British Association of Plastic Surgeons
Doppler ultrasound in the evaluation of experimental microvascular grafts C. J. O’BRIEN, J. P. HARRIS and J. MAY Microsurgery Research Laboratory, Department of Surgery, University of Sydney, Australia
Summary-A study was made to evaluate the accuracy of Doppler ultrasound in assessing patency in experimental microvascular grafts in rats. In 20 animals, pre-operative assessment produced a phasic wave form and audio signal consistent with arterial flow when the Doppler probe was placed over the groin crease. Ten animals then had a sham operation exposing the femoral vessels through a groin crease incision. The remaining 10 had a 10 mm segment of femoral artery excised to simulate an occluded graft. These animals were re-assessed 18 to 20 days later and the wave form and audio signal of arterial flow were detectable in the sham operated animals with the probe placed below the groin incision. No signal was elicited at this site in the animals whose femoral arteries had been excised. When these principles were applied to 20 rats with microvenous grafts and 20 with 1 mm PTFE grafts in the femoral artery we predicted graft patency with 100% accuracy. This non-invasive technique is inexpensive and highly accurate.
Doppler ultrasound has proved a versatile and relatively inexpensive method of investigating a wide range of arterial and venous diseases in man (Yao and Bergan, 1974). In assessing long-term patency of experimental microvascular grafts the use of Doppler ultrasound may diminish the need for the more hazardous manoeuvres of exploration and arteriography. However, one limitation of the use of percutaneous ultrasound is the uncertainty of exactly which vessel is being studied. An occluded vessel may be interpreted as being patent because the observer is misled by flow through collaterals or other arteries in the region (Strandness et al., 1966). The aim of this study was to determine the accuracy of percutaneous ultrasound in assessing patency of femoral artery grafts in the rat. Materials and methods The study was conducted in the Microsurgery Research Laboratory in the Department of Surgery at the University of Sydney. Sixty Manchester hooded rats, weighing between 250 and 300 gm were used. All the rats were anaesthetised with intra-peritoneal pentobarbitone 6 mg per 100 gm body weight. This provided excellent operating conditions for up to 2 hours.
The Parks 802 non-directional Doppler with an 8 mm diameter probe emitting a 9.1 MHz ultrasonic signal was used. The skin of the right hind limb, groin and lower abdomen was shaved and the probe gently placed at an angle of 45” to the skin to obtain an optimal signal response (Fig. 1). “Aquasonic” Acoustic gel was used to facilitate ultrasonic transmission between the skin and probe. A Telectronics Biochart recorder, Type BRl, was used to obtain wave form recordings and stereo headphones were used for audio assessment. An established operative approach to the femoral vessels was used on each animal (Acland, 1980). This involved an oblique incision in the right groin crease and dissection of the lower abdominal fat pad, allowing it to be retracted laterally with the epigastric vessels, thus exposing the femoral artery and vein. Anastomoses for microvenous and prosthetic grafts were performed using interrupted 10/O nylon sutures on a BV-75 needle. Wounds were closed with a continuous 4/O silk skin suture. The study was carried out in two parts. Part A
Two groups of 10 rats (Al and A2) were used. Under anaesthesia all 20 had a pre-operative Doppler assessment. The probe was placed over 596
DOPPLER
ULTRASOUND
IN MICROVASCULAR
597
GRAFTS
Fig. 1
Fig. 2
Figure 1-The Doppler probe is placed at an angle of 45” over the right groin crease of the anaesthetised probe is held distal to the oblique groin crease incision to detect flow through the femoral artery.
the right thigh of the rat just below the concavity of the groin and a phasic audio signal and wave form, consistent with pulsatile arterial blood flow, were obtained. The 10 rats of Group Al then had a sham operation with exposure only of the femoral vessels followed by skin closure to allow norma scarring. The 10 rats of Group A2 had a 10 mm segment of femoral artery excised to simulate an occluded graft. After 18 to 20 days all the rats were anaesthetised and re-examined. The Doppler probe was placed on the thigh immediately distally to the
rat. Figure 2-The
Doppler
oblique groin incision (Fig. 2). If the audio signal of pulsatile flow was present the wave form was recorded. If there was no audible signal the probe was moved proximally until pulsatile flow was detected and then a wave recording was made. If flow was detected only above the groin incision a radio opaque skin suture was used to mark this site. All the animals were then subjected to laparotomy and, via a silastic catheter of 1.25 mm external diameter placed in the abdominal aorta,
Al N“l PREOPERATIVE 8th JULY 1983
TRACING
Al No1 POSTOPERATIVE 26th JULY 1983
TRACING
Al NO3 PREOPERATIVE 8th JULY 1983
TRACING
Al N”3 POSTOPERATIVE 26th JULY 1983
TRACING
Fig. 3 Figure 3-Pre-operative (left) and post-operative (right) Doppler recordings showing the plastic wave form of arterial flow in two rats with patent femoral arteries (Group Al). The height of the trace has no correlation with flow: however, the shape of the wave form with a steep upstroke in systole is consistent with normal arterial flow in the rat.
598
BRITISH JOURNAL
OF PLASTIC SURGERY
:a is
arteriography was performed by the injection of 1 ml of 2% lignocaine followed by 3 to 4 ml of 65% meglumine diatrizoate (Angiografin). The Doppler and arteriographic findings in Groups Al and A2 were then compared to detect objective differences between sham operated animals, known to have a patent femoral artery (Group Al) and those not to have a patent femoral artery (Group A2). Part B In the second part of the experiment two groups of 20 rats (Bl and B2) were used. In Group Bl, a 10 mm segment of autogenous ipsilateral femoral vein was anastomosed to a defect in the right femoral artery as an interpositional graft. In Group B2 an 8 mm segment of 1 mm internal diameter Polytetrafluroethylene (Gore-Tex) was anastomosed to the same site. The animals were anaesthetised at a mean of 40 days later and, with
the data obtained from Part A of the study, patency of the grafts was determined by placing a Doppler probe over the thigh distal to the groin incision. The Doppler findings were confirmed by exploration of the thigh and arteriotomy distal to the graft in 10 rats from each group and by laparotomy and arteriography in the remaining 10 from each group. Results
Pre-operative Doppler assessment of the 20 animals in Group Al and A2 produced a strong phasic audio signal over the medial aspect of the hind limb below the groin crease. This was associated with a regular phasic wave form and was evidence of pulsatile flow. The heart rate of the rats was 300 to 400 beats per minute requiring a chart speed of 50 mm per second to produce the best wave form.
DOPPLER
ULTRASOUND
IN MICROVASCULAR
GRAFTS
A2 No1 PREOPERATIVE TRACING 14th JULY 1983
599
A2Nol POSTOPERATIVE TRACING 3rdAUGUST 1984
:
A2 No5 PREOPERATIVE TRACING 14th JULY 1983
. .
-:
:-
~:
L-
:
1
;
!
-.::-L_:
A2N“SPOSTOPERATIVE TRACING 3rdAUGUST 1984 Fig. 5
Figure 5-Pre-operative (left) and post-operative (right) Doppler recordings of rats having femoral arteries excised (Group AZ). The phasic wave form of arterial flow present pre-operatively is absent at re-assessment at 18 to 20 days.
While the triphasic pattern described as being normal for arterial flow (Strandness et al., 1966) was not present the phasic pattern of pulsatile flow was evident (Fig. 3). When these rats were re-assessed at 18 to 20 days the sham operated rats of Group Al had the normal audio signal and wave form recordable distal to the groin crease incision. Examples of preand post-operative recordings are shown in Fig. 3. Arteriography confirmed the presence of a patent femoral artery in these animals (Fig. 4). In Group A2, with the right femoral artery excised, no audio signal was detected below the groin crease at 18 to 20 days. As the probe was moved more proximally the signal of pulsatile flow became evident above the groin incision allowing a phasic wave form to be recorded. In Fig. 5 examples of pre- and post-operation recordings of Group A2 are shown. Arteriography showed that, with no flow through the femoral artery, the probe was detecting arterial flow in the iliac artery. The radio opaque suture (arrowed on the X-ray in Fig. 6) marks the site of the audible signal but does not directly overlie the artery because, with the probe held at 45” to the skin, the Doppler will detect flow a little more proximally. In Group Bl, 17 of 20 autogenous vein grafts (85%) were judged to be patent at a mean of 40 days and in Group B2, 16 of 20 Gore-Tex grafts (80%) were judged to be patent using the Doppler
ultrasound. Sample wave forms are shown (Fig. 7). Exploration and arteriography confirmed these findings in every case. Patent grafts were readily detected and the audio signal and phasic wave forms were elicited even more easily than with the patent femoral arteries of Group Al.
Discussion
In 1961 Franklin et al. described a method for recording blood flow in canine arteries using the principle of Doppler shift. High frequency sound emitted from a vibrating Piezo electric crystal was beamed diagonally across a moving column of blood. The back-scattered sound was changed in frequency by an amount proportional to the velocity of blood flow, received by a second crystal and then converted to an audible and recordable form. Although its initial application in microvascular surgery provided little benefit (McGregor and Morgan, 1973), by 1975 there were reports of the usefulness of Doppler ultrasound in locating donor and recipient vessels to facilitate transfer of free delto-pectoral (Aoyagi et al., 1975) and groin flaps (Karkowski and Buncke, 1965). Recent reports described intra-operative evaluation of microvascular anastomoses with the probe in direct
600
BRITISH JOURNAL
OF PLASTIC SURGERY
Fig. 6
Figure 6-Arteriogram of rat with a 10 mm segment of femol ral artery excised. The radio opaqpe skin sutures (arrowed) mar ,ks to
contact with the vessels under scrutiny (van Beek et al., 1975; Rossi et al., 1981). Using the intra-opera-
tive testing of anastomoses to predict survival of experimental free flaps, Jones and Greenhalgh (1983) reported an accuracy rate of 100% if separate venous and arterial evaluations were made. Percutaneous long-term follow-up of microvascular grafts using Doppler ultrasound has not, to our knowledge, been reported. We have attempted to develop a technique for reliably predicting the patency of grafts in the femoral region in the rat. The rat hind limb survives ligation and excision of the femoral artery by the development of collaterals. However, flow through individual collaterals is insufficient to be detected by the Doppler and therefore does not mislead the observer into thinking the femoral artery is patent when the probe is held just below the groin crease.
The non-directional Doppler used for this study was perfectly adequate for testing pulsatile flow in the rat femoral region. The audio signal itself has a distinctive phasic sound indicating arterial flow. The recorded wave form gives no more information than this and only provides an objective representation of the audible signal: however, the wave form depends on the probe position and steadiness for its shape. Conclusions In Part A of the study we concluded that with the Doppler probe placed below the groin crease incision the patent femoral artery produces a strong distinctive audio signal and a reproducible phasic waveform. No such responses are elicited at this site for up to 18 to 20 days if there is no flow through the femoral artery. When these criteria were applied to the 20 autogenous vein grafts and 20 Gore-Tex grafts in Part B we achieved 100%
DOPPLER
ULTRASOUND
IN MICROVASCULAR
GRAFTS
,
L_
:
_
‘I
NUMBER
6 Patent
38 Days.
NUMBER
NUMBER
NUMBER DOPPLER
Figure 7-Doppler differentiated: _
1 Occluded
RECORDINGS
NUMBER
33 Days.
OF P.T.F.E.
GRAETS.
DOPPLER
3 Patent
35 Days.
15 Patent
40 Days.
16 Occluded
40 Days.
RECORDINGS
OF
AL'TOGENOIJSVEIN
GRAFTS.
Fig. 7 recordings of PTFE (left) and autogenous vein grafts (right). Patent and occluded grafts were readily
accuracy in predicting the state of the grafts at a mean of 40 days post-operatively. The more invasive techniques of exploration followed by arteriotomy and laparotomy and arteriography confirmed our predictions. We believe that Doppler ultrasound provides a means of accurate and non-invasive assessment of patency in experimental microvascular grafts in the rat. Acknowledgements The authors gratefully acknowledge the assistance of Mrs Veronica Clarke and Miss Moya Cooney with the preparation of the manuscript. We are thankful also to W. L. Gore & Associates for supplying the prosthetic graft material. This work has been supported by a grant from the National Health and Medical Research Council (Australia), the J. B. Pye Fellowship from Royal Prince Alfred Hospital, Sydney and the John Brook-Moore FeIIowship from the University of Sydney.
References Actand, R. D. (1980). Microsurgery Practice Manual. St Louis: C. V. Mosby Company. Aoysgi, F., Fujioo, J. and Ohshiro, T. (1975). Detection of small vessels for microsurgery by a Doppler flowmeter. Plastic and Reconstructive Surgery, 55,372. van Beek, A. L., Link, W. J., Bennett, J. E. and Clover, J. L. (1975). Ultrasound evaluation of microanastomoses. Archives of Surgery, 110, 945.
Franklin, D. L., Schlegel, W. and Rushmer, R. F. (1961). Blood flow measured by Doppler frequency shift of back-scattered ultrasound. Science, 134, 564. Jones, B. M. and Greenhalgh, R. M. (1983). The use of the ultrasound Doppler flowmeter in reconstructive microvascular surgery. British Journal of PlasticSurgery, 36,245. Karkowski, J. and Buncke, IL J. (1975). A simplified technique for free transfer of groin flaps by use of a Doppler probe. Plasticand Reconstructive Surgery, 55,682. McGregor, 1. A. and Morgan, G. (1973). Axial and randompattern flaps. British Journal of Plastic Surgery, 26,202. Rossi, L. F. A., Hoare, M. R. and Greenhalgh, R. M. (1981). Per-operative proof of patency of microvascular anastomoses. Annals of the Royal College of Surgeons of England, 63,289. Strandness, D. E., McCutcheon, E. P. and Rushmer, R. F. (1966). Application of a transcutaneous Doppler flowmeter in evaluation of occlusive arterial disease. Surgery, Gynecology and Obstetrics, 122, 1039. Yao, J. S. T. and Bergan, J. J. (1974). Application of ultrasound to arterial and venous diagnosis. Surgical Clinics of North America, 54,23.
The Authors C. J. O’Brien, MB, BS, Microsurgery Research Fellow, Department of Surgery, University of Sydney. J. P. Harris, FRACS, Senior Lecturer in Surgery, Department of Surgery, University of Sydney. J. May, MS, FRACS, Professor of Surgery, Department of Surgery, University of Sydney. Requests for reprints to: Professor J. May, MS, FRACS, Department of Surgery, University of Sydney, NSW 2006, Australia.
Doppler ultrasound in the evaluation of experimental microvascular grafts C. J. O’BRIEN, J. P. HARRIS and J. MAY Microsurgery Research Laboratory, Department of Surgery, University of Sydney, Australia
Summary-A study was made to evaluate the accuracy of Doppler ultrasound in assessing patency in experimental microvascular grafts in rats. In 20 animals, pre-operative assessment produced a phasic wave form and audio signal consistent with arterial flow when the Doppler probe was placed over the groin crease. Ten animals then had a sham operation exposing the femoral vessels through a groin crease incision. The remaining 10 had a 10 mm segment of femoral artery excised to simulate an occluded graft. These animals were re-assessed 18 to 20 days later and the wave form and audio signal of arterial flow were detectable in the sham operated animals with the probe placed below the groin incision. No signal was elicited at this site in the animals whose femoral arteries had been excised. When these principles were applied to 20 rats with microvenous grafts and 20 with 1 mm PTFE grafts in the femoral artery we predicted graft patency with 100% accuracy. This non-invasive technique is inexpensive and highly accurate.
Doppler ultrasound has proved a versatile and relatively inexpensive method of investigating a wide range of arterial and venous diseases in man (Yao and Bergan, 1974). In assessing long-term patency of experimental microvascular grafts the use of Doppler ultrasound may diminish the need for the more hazardous manoeuvres of exploration and arteriography. However, one limitation of the use of percutaneous ultrasound is the uncertainty of exactly which vessel is being studied. An occluded vessel may be interpreted as being patent because the observer is misled by flow through collaterals or other arteries in the region (Strandness et al., 1966). The aim of this study was to determine the accuracy of percutaneous ultrasound in assessing patency of femoral artery grafts in the rat. Materials and methods The study was conducted in the Microsurgery Research Laboratory in the Department of Surgery at the University of Sydney. Sixty Manchester hooded rats, weighing between 250 and 300 gm were used. All the rats were anaesthetised with intra-peritoneal pentobarbitone 6 mg per 100 gm body weight. This provided excellent operating conditions for up to 2 hours.
The Parks 802 non-directional Doppler with an 8 mm diameter probe emitting a 9.1 MHz ultrasonic signal was used. The skin of the right hind limb, groin and lower abdomen was shaved and the probe gently placed at an angle of 45” to the skin to obtain an optimal signal response (Fig. 1). “Aquasonic” Acoustic gel was used to facilitate ultrasonic transmission between the skin and probe. A Telectronics Biochart recorder, Type BRl, was used to obtain wave form recordings and stereo headphones were used for audio assessment. An established operative approach to the femoral vessels was used on each animal (Acland, 1980). This involved an oblique incision in the right groin crease and dissection of the lower abdominal fat pad, allowing it to be retracted laterally with the epigastric vessels, thus exposing the femoral artery and vein. Anastomoses for microvenous and prosthetic grafts were performed using interrupted 10/O nylon sutures on a BV-75 needle. Wounds were closed with a continuous 4/O silk skin suture. The study was carried out in two parts. Part A
Two groups of 10 rats (Al and A2) were used. Under anaesthesia all 20 had a pre-operative Doppler assessment. The probe was placed over 596
DOPPLER
ULTRASOUND
IN MICROVASCULAR
597
GRAFTS
Fig. 1
Fig. 2
Figure 1-The Doppler probe is placed at an angle of 45” over the right groin crease of the anaesthetised probe is held distal to the oblique groin crease incision to detect flow through the femoral artery.
the right thigh of the rat just below the concavity of the groin and a phasic audio signal and wave form, consistent with pulsatile arterial blood flow, were obtained. The 10 rats of Group Al then had a sham operation with exposure only of the femoral vessels followed by skin closure to allow norma scarring. The 10 rats of Group A2 had a 10 mm segment of femoral artery excised to simulate an occluded graft. After 18 to 20 days all the rats were anaesthetised and re-examined. The Doppler probe was placed on the thigh immediately distally to the
rat. Figure 2-The
Doppler
oblique groin incision (Fig. 2). If the audio signal of pulsatile flow was present the wave form was recorded. If there was no audible signal the probe was moved proximally until pulsatile flow was detected and then a wave recording was made. If flow was detected only above the groin incision a radio opaque skin suture was used to mark this site. All the animals were then subjected to laparotomy and, via a silastic catheter of 1.25 mm external diameter placed in the abdominal aorta,
Al N“l PREOPERATIVE 8th JULY 1983
TRACING
Al No1 POSTOPERATIVE 26th JULY 1983
TRACING
Al NO3 PREOPERATIVE 8th JULY 1983
TRACING
Al N”3 POSTOPERATIVE 26th JULY 1983
TRACING
Fig. 3 Figure 3-Pre-operative (left) and post-operative (right) Doppler recordings showing the plastic wave form of arterial flow in two rats with patent femoral arteries (Group Al). The height of the trace has no correlation with flow: however, the shape of the wave form with a steep upstroke in systole is consistent with normal arterial flow in the rat.
598
BRITISH JOURNAL
OF PLASTIC SURGERY
:a is
arteriography was performed by the injection of 1 ml of 2% lignocaine followed by 3 to 4 ml of 65% meglumine diatrizoate (Angiografin). The Doppler and arteriographic findings in Groups Al and A2 were then compared to detect objective differences between sham operated animals, known to have a patent femoral artery (Group Al) and those not to have a patent femoral artery (Group A2). Part B In the second part of the experiment two groups of 20 rats (Bl and B2) were used. In Group Bl, a 10 mm segment of autogenous ipsilateral femoral vein was anastomosed to a defect in the right femoral artery as an interpositional graft. In Group B2 an 8 mm segment of 1 mm internal diameter Polytetrafluroethylene (Gore-Tex) was anastomosed to the same site. The animals were anaesthetised at a mean of 40 days later and, with
the data obtained from Part A of the study, patency of the grafts was determined by placing a Doppler probe over the thigh distal to the groin incision. The Doppler findings were confirmed by exploration of the thigh and arteriotomy distal to the graft in 10 rats from each group and by laparotomy and arteriography in the remaining 10 from each group. Results
Pre-operative Doppler assessment of the 20 animals in Group Al and A2 produced a strong phasic audio signal over the medial aspect of the hind limb below the groin crease. This was associated with a regular phasic wave form and was evidence of pulsatile flow. The heart rate of the rats was 300 to 400 beats per minute requiring a chart speed of 50 mm per second to produce the best wave form.
DOPPLER
ULTRASOUND
IN MICROVASCULAR
GRAFTS
A2 No1 PREOPERATIVE TRACING 14th JULY 1983
599
A2Nol POSTOPERATIVE TRACING 3rdAUGUST 1984
:
A2 No5 PREOPERATIVE TRACING 14th JULY 1983
. .
-:
:-
~:
L-
:
1
;
!
-.::-L_:
A2N“SPOSTOPERATIVE TRACING 3rdAUGUST 1984 Fig. 5
Figure 5-Pre-operative (left) and post-operative (right) Doppler recordings of rats having femoral arteries excised (Group AZ). The phasic wave form of arterial flow present pre-operatively is absent at re-assessment at 18 to 20 days.
While the triphasic pattern described as being normal for arterial flow (Strandness et al., 1966) was not present the phasic pattern of pulsatile flow was evident (Fig. 3). When these rats were re-assessed at 18 to 20 days the sham operated rats of Group Al had the normal audio signal and wave form recordable distal to the groin crease incision. Examples of preand post-operative recordings are shown in Fig. 3. Arteriography confirmed the presence of a patent femoral artery in these animals (Fig. 4). In Group A2, with the right femoral artery excised, no audio signal was detected below the groin crease at 18 to 20 days. As the probe was moved more proximally the signal of pulsatile flow became evident above the groin incision allowing a phasic wave form to be recorded. In Fig. 5 examples of pre- and post-operation recordings of Group A2 are shown. Arteriography showed that, with no flow through the femoral artery, the probe was detecting arterial flow in the iliac artery. The radio opaque suture (arrowed on the X-ray in Fig. 6) marks the site of the audible signal but does not directly overlie the artery because, with the probe held at 45” to the skin, the Doppler will detect flow a little more proximally. In Group Bl, 17 of 20 autogenous vein grafts (85%) were judged to be patent at a mean of 40 days and in Group B2, 16 of 20 Gore-Tex grafts (80%) were judged to be patent using the Doppler
ultrasound. Sample wave forms are shown (Fig. 7). Exploration and arteriography confirmed these findings in every case. Patent grafts were readily detected and the audio signal and phasic wave forms were elicited even more easily than with the patent femoral arteries of Group Al.
Discussion
In 1961 Franklin et al. described a method for recording blood flow in canine arteries using the principle of Doppler shift. High frequency sound emitted from a vibrating Piezo electric crystal was beamed diagonally across a moving column of blood. The back-scattered sound was changed in frequency by an amount proportional to the velocity of blood flow, received by a second crystal and then converted to an audible and recordable form. Although its initial application in microvascular surgery provided little benefit (McGregor and Morgan, 1973), by 1975 there were reports of the usefulness of Doppler ultrasound in locating donor and recipient vessels to facilitate transfer of free delto-pectoral (Aoyagi et al., 1975) and groin flaps (Karkowski and Buncke, 1965). Recent reports described intra-operative evaluation of microvascular anastomoses with the probe in direct
600
BRITISH JOURNAL
OF PLASTIC SURGERY
Fig. 6
Figure 6-Arteriogram of rat with a 10 mm segment of femol ral artery excised. The radio opaqpe skin sutures (arrowed) mar ,ks to
contact with the vessels under scrutiny (van Beek et al., 1975; Rossi et al., 1981). Using the intra-opera-
tive testing of anastomoses to predict survival of experimental free flaps, Jones and Greenhalgh (1983) reported an accuracy rate of 100% if separate venous and arterial evaluations were made. Percutaneous long-term follow-up of microvascular grafts using Doppler ultrasound has not, to our knowledge, been reported. We have attempted to develop a technique for reliably predicting the patency of grafts in the femoral region in the rat. The rat hind limb survives ligation and excision of the femoral artery by the development of collaterals. However, flow through individual collaterals is insufficient to be detected by the Doppler and therefore does not mislead the observer into thinking the femoral artery is patent when the probe is held just below the groin crease.
The non-directional Doppler used for this study was perfectly adequate for testing pulsatile flow in the rat femoral region. The audio signal itself has a distinctive phasic sound indicating arterial flow. The recorded wave form gives no more information than this and only provides an objective representation of the audible signal: however, the wave form depends on the probe position and steadiness for its shape. Conclusions In Part A of the study we concluded that with the Doppler probe placed below the groin crease incision the patent femoral artery produces a strong distinctive audio signal and a reproducible phasic waveform. No such responses are elicited at this site for up to 18 to 20 days if there is no flow through the femoral artery. When these criteria were applied to the 20 autogenous vein grafts and 20 Gore-Tex grafts in Part B we achieved 100%
DOPPLER
ULTRASOUND
IN MICROVASCULAR
GRAFTS
,
L_
:
_
‘I
NUMBER
6 Patent
38 Days.
NUMBER
NUMBER
NUMBER DOPPLER
Figure 7-Doppler differentiated: _
1 Occluded
RECORDINGS
NUMBER
33 Days.
OF P.T.F.E.
GRAETS.
DOPPLER
3 Patent
35 Days.
15 Patent
40 Days.
16 Occluded
40 Days.
RECORDINGS
OF
AL'TOGENOIJSVEIN
GRAFTS.
Fig. 7 recordings of PTFE (left) and autogenous vein grafts (right). Patent and occluded grafts were readily
accuracy in predicting the state of the grafts at a mean of 40 days post-operatively. The more invasive techniques of exploration followed by arteriotomy and laparotomy and arteriography confirmed our predictions. We believe that Doppler ultrasound provides a means of accurate and non-invasive assessment of patency in experimental microvascular grafts in the rat. Acknowledgements The authors gratefully acknowledge the assistance of Mrs Veronica Clarke and Miss Moya Cooney with the preparation of the manuscript. We are thankful also to W. L. Gore & Associates for supplying the prosthetic graft material. This work has been supported by a grant from the National Health and Medical Research Council (Australia), the J. B. Pye Fellowship from Royal Prince Alfred Hospital, Sydney and the John Brook-Moore FeIIowship from the University of Sydney.
References Actand, R. D. (1980). Microsurgery Practice Manual. St Louis: C. V. Mosby Company. Aoysgi, F., Fujioo, J. and Ohshiro, T. (1975). Detection of small vessels for microsurgery by a Doppler flowmeter. Plastic and Reconstructive Surgery, 55,372. van Beek, A. L., Link, W. J., Bennett, J. E. and Clover, J. L. (1975). Ultrasound evaluation of microanastomoses. Archives of Surgery, 110, 945.
Franklin, D. L., Schlegel, W. and Rushmer, R. F. (1961). Blood flow measured by Doppler frequency shift of back-scattered ultrasound. Science, 134, 564. Jones, B. M. and Greenhalgh, R. M. (1983). The use of the ultrasound Doppler flowmeter in reconstructive microvascular surgery. British Journal of PlasticSurgery, 36,245. Karkowski, J. and Buncke, IL J. (1975). A simplified technique for free transfer of groin flaps by use of a Doppler probe. Plasticand Reconstructive Surgery, 55,682. McGregor, 1. A. and Morgan, G. (1973). Axial and randompattern flaps. British Journal of Plastic Surgery, 26,202. Rossi, L. F. A., Hoare, M. R. and Greenhalgh, R. M. (1981). Per-operative proof of patency of microvascular anastomoses. Annals of the Royal College of Surgeons of England, 63,289. Strandness, D. E., McCutcheon, E. P. and Rushmer, R. F. (1966). Application of a transcutaneous Doppler flowmeter in evaluation of occlusive arterial disease. Surgery, Gynecology and Obstetrics, 122, 1039. Yao, J. S. T. and Bergan, J. J. (1974). Application of ultrasound to arterial and venous diagnosis. Surgical Clinics of North America, 54,23.
The Authors C. J. O’Brien, MB, BS, Microsurgery Research Fellow, Department of Surgery, University of Sydney. J. P. Harris, FRACS, Senior Lecturer in Surgery, Department of Surgery, University of Sydney. J. May, MS, FRACS, Professor of Surgery, Department of Surgery, University of Sydney. Requests for reprints to: Professor J. May, MS, FRACS, Department of Surgery, University of Sydney, NSW 2006, Australia.