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Simple device for regulating the inflation of a balloon-tip catheter
SIMPLE DEVICE FOR REGULATING CATHETER
THE INFLATION
We describe a simple and inexpensive mechanical device which can be used with a standard syringe to control the injection of fluids. It was designed for use with, but not limited to, a balloon-tip catheter in order to allow a controlled and gradual inflation of the balloon-tip, and to maintain the desired level of inflation. The device was used in a series of experiments which required pressure to be applied to a mammalian spinal cord by the insertion of a balloon-tip catheter into the epidural space. Greater control over inflation of the balloon resulted in a more controlled application of compressive forces. The increased use of somatosensory evoked otential (SEP) to detect changes in the function o F the spinal cord during surgery, has led to a need to determine how the evoked response changes with applied cord trauma. Several methods have been devised to apply contusive or compressive forces to the cord, thereby causing a detectable deterioration of the SEP. These include the weight drop technique’, pressure application using a dual screw apparatus*, and inflation of a balloon-tip catheter in the dorsal epidural space3y4. Cracco and Evans3, and Uematsu and Rocca4, inserted known volumes of air into a balloon-tip catheter which was placed in the epidural space of an experimental animal, thereby producing acute transient pressures on the dorsal surface of the spinal cord. The latter experimenters measured this pressure by means of a transducer placed between the balloon-tip and the dura mater.
OF A BALLOON-TIP
In one of our series of experiments, compressive forces were applied to the spinal cord of rabbits using the balloon-tip catheter method. The injection of air into the catheter results in a rapid inflation of the balloon to a relatively large size. To produce a more gradual inflation of the balloon, we substituted a saline solution in place of air. We then needed to be able to regulate the volume of liquid injected. We designed a device consisting of two interlocking components made of Dehin (an acetal selected for ease of machining), an internal spring and an adjustable screw which fits into the bottom of the lower section, Figure 1. The barrel of a 3 cm3 disposable syringe fits into the upper section; the plunger, surrounded by the spring, fits into the lower section. The plunger is depressed or relaxed with the screw. A 360” turn of the screw displaces = 0.05 cm3 of fluid from the syringe; the range extends from full depression to full relaxation of the plunger. F@re 2 is a cross-sectional view. The apparatus was used in a series of experiments in which somatosensory evoked potentials were obtained before and after cord compression.
b
Figure 1 attached
cb
Controlled
I
f
r
1
inflation device with balloon-tip
2
Cross-sectional
view of the device
0 1986 Buttetworth & Co (Publishers) Ltd 0141-5425/86/040368-02 $03.00 388
J. Biomed.
2LIv
‘I
10
(. 1 cm.) Figure
catheter
Eng. 1986, Vol. 8, October
ms
Figure 3 Spinal evoked potentials recorded over a rabbit thoracic spine; 2000 records were ensembled averaged to visualize each response. a. Post-insertionlpre-inflation; b. immediately after mild trauma; c. 30 min after mild trauma; d. immediately after more severe trauma; e. 30 min after more severe trauma
The syringe was filled with 0.9% saline solution by adjusting the screw to allow the plunger to relax. The catheter was then fitted to the end of the syringe and the plunger depressed until slight inflation of the balloon was detected. The plunger was relaxed until the balloon was just deflated. This was repeated several times to remove any air bubbles from the balloon. The tip of the catheter was then placed in the epidural space of the spine. The balloon could then be inflated gradually by slowly injecting the desired amount of saline; the inflation could be held at any required level. Bipolar recordings of the potentials were obtained using needle electrodes anchored in the interspinous ligaments caudal to the vertebral processes. Responses were amplified 500 000 times, bandlimited to 10 Hz - 1 kHz and at least 2000 responses free of EMG or ECG artefact were ensemble averaged. A typical result is shown in Figure 3, from which it is apparent that cord compression produces changes in the evoked potential.
This research was supported by the Natural Sciences and Engineering Research Council of Canada. E. Morin R.N. Scott M. Olive PO Box 4400,
Bio-engineering Institute, University of New Brunswick Fredericton, NB, E3B 5A3 Canada
Bohlman, H.H. et al. Spinal cord monitoring of experimental incomplete cervical spinal cord injury, spine 198 1, 6, 428-436 Kojima, Y. et al. Evoked spinal potentials as a monitor of spinal cord viability, spine 1979, 4, 47 l-477 Cracco, R.Q. and Evans, B. Spinal evoked potential in the cat: effects of asphyxia, strychnine, cord section and compression, Electroenceph. Gin. Neurophysiol. 197 8, 44, 187-201 Uematsu, S. and Rocca, U. Effea of acute compression, hypoxia, hypothermia and hypovolemia on the evoked potentials of the spinal cord, Electromyogr. Clin. Neurophysiol. 1981, 21, 229-252
BlODYNAMICS:ClRCULATlON Y.C. Fung
Springer- Verlag, Berlin, FRG, 1984,404 pp $36.00 ISBN 3-540-90867-6 This book is part of a series, the first volume of which has previously appeared as ‘Biomechanics’. The present book is concerned with the mechanics of the circulation, and area in which Professor Fung has made notable and important contributions. The first chapter discusses the physical principles underlying any consideration of the circulation. The chapter, and its associated appendix, are both brief and will be inadequate for most readers. The author recognises that it will need to be extensively supplemented, and suggests reference to ‘Biomechanics’. The second chapter, dealing with the heart, opens the detailed discussion of the circulation. It starts simply with an account of the Windkessel model, and the stress distribution in the left ventricle. modelled as a thick walled hemispherical shell. These are followed by detailed, but largely qualitative, discussions of the geometry and materials of the heart, and aspects of electrical and mechanical events during the cardiac cycle. The treatment once again becomes more mathematical in the discussion of the fluid mechanics in the heart and stresses in the heart wall. The theoretical
development is never very extended, and it is unclear how well actual events are described by the models being discussed. The third chapter on blood flow in arteries is the longest in the book. It covers the subject in considerable depth, dealing with the effects of pulsatile flow and the geometrical non-uniformity and viscoelasticity of vessel walls, in addition to the simpler and more basic ideas of fluid flow in straight tubes. The chapter does tend to be a catalogue of work done rather than a critical appraisal, and this impression is further strengthened by the bibliography associated with the chapter which runs to more than 200 entries. The chapter on the veins is mainly concerned with the problem of elastic stability and flow in collapsible tubes, but also contains a brief account of pulmonary circulation. The chapter on the microcirculation describes the anatomy and the pressure distribution in the microcirculation. The mathematics in this chapter is largely concerned with flow at very low Reynolds numbers. There is also an extended discussion on model experiments on the interaction of leucocytes and the vascular endothelium.
J. Biomed.
Eng. 1986, Vol. 8, October
369
THE INFLATION
We describe a simple and inexpensive mechanical device which can be used with a standard syringe to control the injection of fluids. It was designed for use with, but not limited to, a balloon-tip catheter in order to allow a controlled and gradual inflation of the balloon-tip, and to maintain the desired level of inflation. The device was used in a series of experiments which required pressure to be applied to a mammalian spinal cord by the insertion of a balloon-tip catheter into the epidural space. Greater control over inflation of the balloon resulted in a more controlled application of compressive forces. The increased use of somatosensory evoked otential (SEP) to detect changes in the function o F the spinal cord during surgery, has led to a need to determine how the evoked response changes with applied cord trauma. Several methods have been devised to apply contusive or compressive forces to the cord, thereby causing a detectable deterioration of the SEP. These include the weight drop technique’, pressure application using a dual screw apparatus*, and inflation of a balloon-tip catheter in the dorsal epidural space3y4. Cracco and Evans3, and Uematsu and Rocca4, inserted known volumes of air into a balloon-tip catheter which was placed in the epidural space of an experimental animal, thereby producing acute transient pressures on the dorsal surface of the spinal cord. The latter experimenters measured this pressure by means of a transducer placed between the balloon-tip and the dura mater.
OF A BALLOON-TIP
In one of our series of experiments, compressive forces were applied to the spinal cord of rabbits using the balloon-tip catheter method. The injection of air into the catheter results in a rapid inflation of the balloon to a relatively large size. To produce a more gradual inflation of the balloon, we substituted a saline solution in place of air. We then needed to be able to regulate the volume of liquid injected. We designed a device consisting of two interlocking components made of Dehin (an acetal selected for ease of machining), an internal spring and an adjustable screw which fits into the bottom of the lower section, Figure 1. The barrel of a 3 cm3 disposable syringe fits into the upper section; the plunger, surrounded by the spring, fits into the lower section. The plunger is depressed or relaxed with the screw. A 360” turn of the screw displaces = 0.05 cm3 of fluid from the syringe; the range extends from full depression to full relaxation of the plunger. F@re 2 is a cross-sectional view. The apparatus was used in a series of experiments in which somatosensory evoked potentials were obtained before and after cord compression.
b
Figure 1 attached
cb
Controlled
I
f
r
1
inflation device with balloon-tip
2
Cross-sectional
view of the device
0 1986 Buttetworth & Co (Publishers) Ltd 0141-5425/86/040368-02 $03.00 388
J. Biomed.
2LIv
‘I
10
(. 1 cm.) Figure
catheter
Eng. 1986, Vol. 8, October
ms
Figure 3 Spinal evoked potentials recorded over a rabbit thoracic spine; 2000 records were ensembled averaged to visualize each response. a. Post-insertionlpre-inflation; b. immediately after mild trauma; c. 30 min after mild trauma; d. immediately after more severe trauma; e. 30 min after more severe trauma
The syringe was filled with 0.9% saline solution by adjusting the screw to allow the plunger to relax. The catheter was then fitted to the end of the syringe and the plunger depressed until slight inflation of the balloon was detected. The plunger was relaxed until the balloon was just deflated. This was repeated several times to remove any air bubbles from the balloon. The tip of the catheter was then placed in the epidural space of the spine. The balloon could then be inflated gradually by slowly injecting the desired amount of saline; the inflation could be held at any required level. Bipolar recordings of the potentials were obtained using needle electrodes anchored in the interspinous ligaments caudal to the vertebral processes. Responses were amplified 500 000 times, bandlimited to 10 Hz - 1 kHz and at least 2000 responses free of EMG or ECG artefact were ensemble averaged. A typical result is shown in Figure 3, from which it is apparent that cord compression produces changes in the evoked potential.
This research was supported by the Natural Sciences and Engineering Research Council of Canada. E. Morin R.N. Scott M. Olive PO Box 4400,
Bio-engineering Institute, University of New Brunswick Fredericton, NB, E3B 5A3 Canada
Bohlman, H.H. et al. Spinal cord monitoring of experimental incomplete cervical spinal cord injury, spine 198 1, 6, 428-436 Kojima, Y. et al. Evoked spinal potentials as a monitor of spinal cord viability, spine 1979, 4, 47 l-477 Cracco, R.Q. and Evans, B. Spinal evoked potential in the cat: effects of asphyxia, strychnine, cord section and compression, Electroenceph. Gin. Neurophysiol. 197 8, 44, 187-201 Uematsu, S. and Rocca, U. Effea of acute compression, hypoxia, hypothermia and hypovolemia on the evoked potentials of the spinal cord, Electromyogr. Clin. Neurophysiol. 1981, 21, 229-252
BlODYNAMICS:ClRCULATlON Y.C. Fung
Springer- Verlag, Berlin, FRG, 1984,404 pp $36.00 ISBN 3-540-90867-6 This book is part of a series, the first volume of which has previously appeared as ‘Biomechanics’. The present book is concerned with the mechanics of the circulation, and area in which Professor Fung has made notable and important contributions. The first chapter discusses the physical principles underlying any consideration of the circulation. The chapter, and its associated appendix, are both brief and will be inadequate for most readers. The author recognises that it will need to be extensively supplemented, and suggests reference to ‘Biomechanics’. The second chapter, dealing with the heart, opens the detailed discussion of the circulation. It starts simply with an account of the Windkessel model, and the stress distribution in the left ventricle. modelled as a thick walled hemispherical shell. These are followed by detailed, but largely qualitative, discussions of the geometry and materials of the heart, and aspects of electrical and mechanical events during the cardiac cycle. The treatment once again becomes more mathematical in the discussion of the fluid mechanics in the heart and stresses in the heart wall. The theoretical
development is never very extended, and it is unclear how well actual events are described by the models being discussed. The third chapter on blood flow in arteries is the longest in the book. It covers the subject in considerable depth, dealing with the effects of pulsatile flow and the geometrical non-uniformity and viscoelasticity of vessel walls, in addition to the simpler and more basic ideas of fluid flow in straight tubes. The chapter does tend to be a catalogue of work done rather than a critical appraisal, and this impression is further strengthened by the bibliography associated with the chapter which runs to more than 200 entries. The chapter on the veins is mainly concerned with the problem of elastic stability and flow in collapsible tubes, but also contains a brief account of pulmonary circulation. The chapter on the microcirculation describes the anatomy and the pressure distribution in the microcirculation. The mathematics in this chapter is largely concerned with flow at very low Reynolds numbers. There is also an extended discussion on model experiments on the interaction of leucocytes and the vascular endothelium.
J. Biomed.
Eng. 1986, Vol. 8, October
369