Noninvasive Measurement of Pulsatile Blood Volume Changes Its Usefulness in Peripheral Vascular Disease Joseph M. Van De Water, MD,
l
Memphis, Tennessee
Bruce E. Mount, BS, Duarte, California Kenneth E. Chandler, MD, Memphis, Tennessee Joseph J. McCaughan,
Jr, MD, Memphis, Tennessee
Robert E. Shade, PhD, Memphis, Tennessee
At the present time most patients with occlusive arterial disease are brought to operation based on their history, physical findings, and vascular anatomy as demonstrated by angiography. However, it is the amount of blood flow delivered to the tissues in question which determines whether or not the patient has symptoms and seeks medical attention. Vascular surgeons have long recognized the need for an objective means to quantitate this tissue perfusion. Such a measurement would provide physiologic data to detect the presence of occlusive disease and hence to substantiate the patient’s symptoms. It could also be used to determine the rate of disease progression and to document the degree of improvement after operation. Present available technics for assessing arterial perfusion of the extremities are usually invasive, time consuming, or complicated to perform. The problem has been to develop a noninvasive technic that is simple to perform, provides quick and reproducible results, and can be repeated as often as desired. A plethysmographic instrument utilizing bioelectric impedance was developed, which measures pulsatile blood volume changes, The instrument is compact in size and simple to operate and has a digital dispIay of a parameter we call “Pulsatile Flow,” (PF,) which is derived from the pulsatile volume measurement. PF, is obtained by continuously differentiating the measured pulse volume waveform with respect to time and inserting a zero baseline at the negative peaks of the waveform. This waveform is averaged during a fixed time period to produce a number, PF,,
From the Departments of Surgery and Physiology, University of Tennessee, and Veterans AdministrationHospital. Memphis, Tennessee, and Department of Electronics Instrumentation,City of Hope National Medical Center, Duarte. California. This study was supported by VA Research Project #8960-01. * Present address and reprint requests: Veterans AdministrationHospital, Davis Park, Providence, Rhode Island 02920.
590
in cc/min [l-3]. (Figure 1.) Using this instrument, we have measured PF, in a segment of the calf 15 cm long, 5 cm above the medial malleolus, in 100 normal, healthy, eighteen to forty year old patients and obtained a mean value of 103 f 24 cc/min. Subsequent measurements in a large series of patients have revealed that any value less than 50 cc/min (that is, 2 standard deviations below this mean) is highly suggestive of significant occlusive disease. We have been using this technic routinely to evaluate patients with potential vascular problems in the lower extremities and more recently in the upper extremities. The following cases are presented as an example of the usefulness of the technic. Case Reports
Case I. A seventy-eight year old white male (#4470) presented with a six month history of left thigh claudication at one block and rest pain at night relieved by dependency. The left femoral pulse was absent, the right was diminished, and all distal pulses were absent. PF, was 35 cc/min in the left leg and 41 cc/min in the right leg. An angiogram showed a markedly diseased distal aorta with complete obstruction of the left common iliac artery and a high grade stenosis of the right superficial femoral artery at Hunter’s canal. The patient underwent an aortofemoral Y graft. Postoperatively, PF, was 110 cc/min in the left leg and 70 cc/min in the right leg. Case II. A sixty year old white male (#2028) was admitted complaining of aching pain in both feet and ankles, but worse on the left, particularly when walking. Femoral pulses were diminished; popliteal and pedal pulses were absent. The left great toe was cyanotic and cool and had a subungal infection. Translumbar aortogram [4] revealed a complete left superficial femoral block at Hunter’s canal. With use of saphenous vein, left femoral popliteal bypass was performed. Postoperatively, PF, was 52 cc/min in the left leg as compared with a preoperative value of 18 cc/ min.
The Americsn Journal of Surgery
Blood Volume Changes
Case III. A seventy-two year old black male (#8349) was admitted with pain in the right leg and purulent necrosis of the right great toe. He did not have hypertension and diabetes. Femoral pulses were normal, popliteal pulses were diminished, and pedal pulses were absent. PF, was 10 cc/min in the right leg and 12 cc/min in the left leg. Angiography revealed extensive small vessel disease with no localized areas of high grade stenosis or occlusion. Right lumbar sympathectomy was performed. The resulting PF, was noted to be 14 cc/min in the right leg and 11 cc/min in the left leg-essentially unchanged. However, as a result of the redistribution of flow in favor of the skin, the trophic changes have improved. Case IV. A fifty-six year old male (# 7629) with a one month history of pain in the right thigh and leg accompanied by numbness in the foot after ambulation was admitted to the hospital. Pulses on the right were diminished (femoral, three fourths of normal limits, popliteal, half of normal limits; and dorsal pedal and posterior tibia1 were absent) but on the left were within normal limits. As part of the patient’s workup for what was believed to be peripheral vascular disease, PF, measurements were made in both legs. Surprisingly, the results were 96 cc/min on the right and 88 cc/min on the left; the planned angiogram was cancelled. Repeat neurologic examination revealed decreased right great toe extension and impaired sensation; the patient was transferred to the Neurosurgical Service. A myelogram showed complete block at the fourth lumbar vertebra. Laminectomy with excision of the herniated disc was subsequently performed, giving him complete relief of symptoms.
Case V. A fifty-nine year old white male ( # 8557) had acute ileofemoral venous thrombosis after repair of an incisional hernia. The left lower extremity was swollen and cyanotic; ankle pulses were questionably present. Compromised arterial blood flow was feared. However, when measured, the PF, was noted to be excellent at 140 cc/min. Therefore, thrombectomy was not indicated. Heparin therapy was continued and the leg eventually healed. Case VI. A fifty-five year old white male (# 1766) presented with numbness and weakness of the left arm with episodes of dizziness of several months’ duration. The left radial pulse was markedly diminished, but carotid pulses were within normal limits and free of any bruits. PF, in the left arm was 30 cc/min as compared with 80 cc/min in the right arm. A transfemoral percutaneous angiogram of the aortic arch revealed stenosis at the takeoff of the left subclavian artery and a “steal” from the left vertebral artery. A left common carotid artery Dacron@ bypass graft to the left subclavian artery was constructed; his symptoms were relieved.
Case VII. A sixty year old white male (#6329) was admitted with complaints of transient left monocular blindness and left hand numbness. Bilaterally, radial and ulnar pulses were judged to be three fourths and half of normal limits, respectively. It was, therefore, not surprising to find a PF, measurement of 131 cc/min in the left arm
Volume 132.November1976
Figure 1. PF, measurement of the calf of a patient with claudfcation and rest pain. Note the placement of electrodes at 2, 4, f0, and 12 inches, respectively above the medial malleolus.
and 146 cc/min in the right arm. These excellent and essentially similar values were corroborated by angiography, which revealed no significant lesions. Thus, it was apparent that his symptoms were due neither to a “steal” nor to any other type of vascular insufficiency; he was transferred off the Vascular Service. Case VIII. A thirty-three year old white male (# 4670) had right brachial artery thrombosis after cardiac catheterization. The distal brachial, radial, and ulnar pulses were not palpable. Even minimal activity caused pain in the forearm. An angiogram revealed occlusion of the brachial artery just proximal to the elbow. A reversed basilic vein graft was placed in an end-to-side fashion, giving him relief of his arm claudication. The improvement in symptoms was documented with a return of normal pulses and an increase in PF, to 108 cc/min as compared with a preoperative value of 34 cc/min. Comments
Plethysmography has been utilized for many years in the evaluation of extremities believed to be compromised by arterial insufficiency [5-81. Since volume changes are related to flow, various plethysmographic devices including the oscillometer and, of course, the physician’s finger tips have found widespread acceptance. Since we can observe and measure volume changes, it is thus possible to determine the rate of volume change in a given limb segment. This is the first derivative of volume with respect to time and is obtained electronically in the instrument. A
591
Van De Water et al
increased or decreased surrounding tissue resistance caused by variations in tissue volume, such as edema, fatty tissue, and varicose veins. While doing our clinical studies, we have performed various experiments in the laboratory. In one of these, we have pumped blood through a dog’s aorta tunneled through a 10 pound piece of sausage to simulate a leg. With this pseudoleg, we have obtained good correlations between PF, and actual flow as measured by an electromagnetic flowmeter with efflux pumped into a beaker. (Figure 2.) These experiments indicate that even though the PF, calculation is not a true total flow measurement, it may have a linear correlation with arterial flow [12]. Summary
Flgure 2. Graph of the relationship between the values oi PF, obtained from the bioelectrc Impedance plethysmograph (ordinate) and the actual How as measured in a beaker (abscissa).
zero baseline is chosen; then the resulting flow-related curve is integrated to give a measurement in cc/min [I]. With plethysmography only volume changes can be measured; steady state flow is not detected. Rather than use a mechanical plethysmograph such as popularized in the form of a strain gauge by Strandness and Bell [ 71 or a pneumatic cuff used by Darling et al [9], we have chosen to use bioelectric impedance. This technic has been extensively studied, especially by Nyboer [6] and Allison [IO] in this country. By simply measuring the changes in electrical resistance with the arrival of each pulse wave and using a resistivity factor for blood, it is possible to convert this electrical wave into a mechanical volume wave. The use of an electrical interface instead of a mechanical volume interface has seemed to us to be simpler and more adaptable to the clinical setting. For reasons of both patient safety and accuracy, we use a high frequency (100 kHz) sinusoidal oscillator with a low current (1.0 mA). Under these conditions, resistance (R) is more properly referred to as impedance (Z), but continues to account for the major portion of Z (the phase angle averages 16’, so that capacitive reactance is small [II]). The instrument is calibrated internally with a standard resistance change equivalent to 1 cc of volume change in a standard segment 15 cm in length. The circuitry automatically corrects for resistance changes due to
592
A clinical trial was made of a new noninvasive technic for the measurement of arterial blood volume changes in a limb segment. The instrument employed is small, portable, provides a digital display in cc/min, is readily calibrated, gives reproducible values of the segmental pulsatile volume change and Pulsatile Flow, or PF,, and can then be used to screen patients with peripheral vascular disease and to assess postoperative results. References 1. Mount BE, Barela JR, Van De Water JM: Measurement of pulsatile volume changes in the extremities by impedance plethysmography. Proc ACEMB 25: 148, 1972. 2. Mount BE, Van De Water Jfvl: Estimation of peripheral arterial blood flow. Angiology 26: 165, 1975. 3. Van De Water JM, Mount BE: Impedance plethysmography in the lower extremity, p 91. Venous Surgery In Lower Extremity (Swan KG, ed). St. Louis, H. Green, 1975. 4. Gammill S, Craighead C: Translumbar aortography updated. Surg Gynecol Obstet 140: 59. 1975. 5. Karpman HL, Payne JH, Winsor T: A practical, systematic laboratory approach to the SW of the peripheral circulation. Ann Intern Med 53: 306, 1960. 6. Nyboer J: Electrical impedance plethysmography: a physical and physiologic approach to peripheral vascular study. Clrculation 2: 611, 1950. 7. Strandness DE Jr, Bell JW: Peripheral vascular dlsease: diagnosis and objective evaluation using a mercury strain gauge. Ann Surg 161: 3, 1965. 8. Whitney RJ: The measurement of volume changes in human limbs. J Physiol121: 1, 1953. 9. Darling RC, Raines JK, Brener BJ, Austen WG: Quantitative segmental pulse volume recorder: a clinical tool. Surgery 72: 873, 7972. 10. Allison RD: The effects of aging, vascular disease and hypertension on the peripheral pulse volume. J Am Geriatr Sot 16: 39, 1968. 11. Pacela AF: Bioelectric impedance measurements as a method of screening for peripheral vascular disease and deep VWIOUS thrombosis. Beckman lnstr Biophy Res Corp, CRR-26. 1971. 12. Mount BE, Grayson MA, Van De Water JM: An impedance plethysmograph for clinical arterial pulse volume measurement: standardization and verification of pulse volume recordings. JAAMI 10: 55. 1976.
The American Journal 8f Surgery
l
Memphis, Tennessee
Bruce E. Mount, BS, Duarte, California Kenneth E. Chandler, MD, Memphis, Tennessee Joseph J. McCaughan,
Jr, MD, Memphis, Tennessee
Robert E. Shade, PhD, Memphis, Tennessee
At the present time most patients with occlusive arterial disease are brought to operation based on their history, physical findings, and vascular anatomy as demonstrated by angiography. However, it is the amount of blood flow delivered to the tissues in question which determines whether or not the patient has symptoms and seeks medical attention. Vascular surgeons have long recognized the need for an objective means to quantitate this tissue perfusion. Such a measurement would provide physiologic data to detect the presence of occlusive disease and hence to substantiate the patient’s symptoms. It could also be used to determine the rate of disease progression and to document the degree of improvement after operation. Present available technics for assessing arterial perfusion of the extremities are usually invasive, time consuming, or complicated to perform. The problem has been to develop a noninvasive technic that is simple to perform, provides quick and reproducible results, and can be repeated as often as desired. A plethysmographic instrument utilizing bioelectric impedance was developed, which measures pulsatile blood volume changes, The instrument is compact in size and simple to operate and has a digital dispIay of a parameter we call “Pulsatile Flow,” (PF,) which is derived from the pulsatile volume measurement. PF, is obtained by continuously differentiating the measured pulse volume waveform with respect to time and inserting a zero baseline at the negative peaks of the waveform. This waveform is averaged during a fixed time period to produce a number, PF,,
From the Departments of Surgery and Physiology, University of Tennessee, and Veterans AdministrationHospital. Memphis, Tennessee, and Department of Electronics Instrumentation,City of Hope National Medical Center, Duarte. California. This study was supported by VA Research Project #8960-01. * Present address and reprint requests: Veterans AdministrationHospital, Davis Park, Providence, Rhode Island 02920.
590
in cc/min [l-3]. (Figure 1.) Using this instrument, we have measured PF, in a segment of the calf 15 cm long, 5 cm above the medial malleolus, in 100 normal, healthy, eighteen to forty year old patients and obtained a mean value of 103 f 24 cc/min. Subsequent measurements in a large series of patients have revealed that any value less than 50 cc/min (that is, 2 standard deviations below this mean) is highly suggestive of significant occlusive disease. We have been using this technic routinely to evaluate patients with potential vascular problems in the lower extremities and more recently in the upper extremities. The following cases are presented as an example of the usefulness of the technic. Case Reports
Case I. A seventy-eight year old white male (#4470) presented with a six month history of left thigh claudication at one block and rest pain at night relieved by dependency. The left femoral pulse was absent, the right was diminished, and all distal pulses were absent. PF, was 35 cc/min in the left leg and 41 cc/min in the right leg. An angiogram showed a markedly diseased distal aorta with complete obstruction of the left common iliac artery and a high grade stenosis of the right superficial femoral artery at Hunter’s canal. The patient underwent an aortofemoral Y graft. Postoperatively, PF, was 110 cc/min in the left leg and 70 cc/min in the right leg. Case II. A sixty year old white male (#2028) was admitted complaining of aching pain in both feet and ankles, but worse on the left, particularly when walking. Femoral pulses were diminished; popliteal and pedal pulses were absent. The left great toe was cyanotic and cool and had a subungal infection. Translumbar aortogram [4] revealed a complete left superficial femoral block at Hunter’s canal. With use of saphenous vein, left femoral popliteal bypass was performed. Postoperatively, PF, was 52 cc/min in the left leg as compared with a preoperative value of 18 cc/ min.
The Americsn Journal of Surgery
Blood Volume Changes
Case III. A seventy-two year old black male (#8349) was admitted with pain in the right leg and purulent necrosis of the right great toe. He did not have hypertension and diabetes. Femoral pulses were normal, popliteal pulses were diminished, and pedal pulses were absent. PF, was 10 cc/min in the right leg and 12 cc/min in the left leg. Angiography revealed extensive small vessel disease with no localized areas of high grade stenosis or occlusion. Right lumbar sympathectomy was performed. The resulting PF, was noted to be 14 cc/min in the right leg and 11 cc/min in the left leg-essentially unchanged. However, as a result of the redistribution of flow in favor of the skin, the trophic changes have improved. Case IV. A fifty-six year old male (# 7629) with a one month history of pain in the right thigh and leg accompanied by numbness in the foot after ambulation was admitted to the hospital. Pulses on the right were diminished (femoral, three fourths of normal limits, popliteal, half of normal limits; and dorsal pedal and posterior tibia1 were absent) but on the left were within normal limits. As part of the patient’s workup for what was believed to be peripheral vascular disease, PF, measurements were made in both legs. Surprisingly, the results were 96 cc/min on the right and 88 cc/min on the left; the planned angiogram was cancelled. Repeat neurologic examination revealed decreased right great toe extension and impaired sensation; the patient was transferred to the Neurosurgical Service. A myelogram showed complete block at the fourth lumbar vertebra. Laminectomy with excision of the herniated disc was subsequently performed, giving him complete relief of symptoms.
Case V. A fifty-nine year old white male ( # 8557) had acute ileofemoral venous thrombosis after repair of an incisional hernia. The left lower extremity was swollen and cyanotic; ankle pulses were questionably present. Compromised arterial blood flow was feared. However, when measured, the PF, was noted to be excellent at 140 cc/min. Therefore, thrombectomy was not indicated. Heparin therapy was continued and the leg eventually healed. Case VI. A fifty-five year old white male (# 1766) presented with numbness and weakness of the left arm with episodes of dizziness of several months’ duration. The left radial pulse was markedly diminished, but carotid pulses were within normal limits and free of any bruits. PF, in the left arm was 30 cc/min as compared with 80 cc/min in the right arm. A transfemoral percutaneous angiogram of the aortic arch revealed stenosis at the takeoff of the left subclavian artery and a “steal” from the left vertebral artery. A left common carotid artery Dacron@ bypass graft to the left subclavian artery was constructed; his symptoms were relieved.
Case VII. A sixty year old white male (#6329) was admitted with complaints of transient left monocular blindness and left hand numbness. Bilaterally, radial and ulnar pulses were judged to be three fourths and half of normal limits, respectively. It was, therefore, not surprising to find a PF, measurement of 131 cc/min in the left arm
Volume 132.November1976
Figure 1. PF, measurement of the calf of a patient with claudfcation and rest pain. Note the placement of electrodes at 2, 4, f0, and 12 inches, respectively above the medial malleolus.
and 146 cc/min in the right arm. These excellent and essentially similar values were corroborated by angiography, which revealed no significant lesions. Thus, it was apparent that his symptoms were due neither to a “steal” nor to any other type of vascular insufficiency; he was transferred off the Vascular Service. Case VIII. A thirty-three year old white male (# 4670) had right brachial artery thrombosis after cardiac catheterization. The distal brachial, radial, and ulnar pulses were not palpable. Even minimal activity caused pain in the forearm. An angiogram revealed occlusion of the brachial artery just proximal to the elbow. A reversed basilic vein graft was placed in an end-to-side fashion, giving him relief of his arm claudication. The improvement in symptoms was documented with a return of normal pulses and an increase in PF, to 108 cc/min as compared with a preoperative value of 34 cc/min. Comments
Plethysmography has been utilized for many years in the evaluation of extremities believed to be compromised by arterial insufficiency [5-81. Since volume changes are related to flow, various plethysmographic devices including the oscillometer and, of course, the physician’s finger tips have found widespread acceptance. Since we can observe and measure volume changes, it is thus possible to determine the rate of volume change in a given limb segment. This is the first derivative of volume with respect to time and is obtained electronically in the instrument. A
591
Van De Water et al
increased or decreased surrounding tissue resistance caused by variations in tissue volume, such as edema, fatty tissue, and varicose veins. While doing our clinical studies, we have performed various experiments in the laboratory. In one of these, we have pumped blood through a dog’s aorta tunneled through a 10 pound piece of sausage to simulate a leg. With this pseudoleg, we have obtained good correlations between PF, and actual flow as measured by an electromagnetic flowmeter with efflux pumped into a beaker. (Figure 2.) These experiments indicate that even though the PF, calculation is not a true total flow measurement, it may have a linear correlation with arterial flow [12]. Summary
Flgure 2. Graph of the relationship between the values oi PF, obtained from the bioelectrc Impedance plethysmograph (ordinate) and the actual How as measured in a beaker (abscissa).
zero baseline is chosen; then the resulting flow-related curve is integrated to give a measurement in cc/min [I]. With plethysmography only volume changes can be measured; steady state flow is not detected. Rather than use a mechanical plethysmograph such as popularized in the form of a strain gauge by Strandness and Bell [ 71 or a pneumatic cuff used by Darling et al [9], we have chosen to use bioelectric impedance. This technic has been extensively studied, especially by Nyboer [6] and Allison [IO] in this country. By simply measuring the changes in electrical resistance with the arrival of each pulse wave and using a resistivity factor for blood, it is possible to convert this electrical wave into a mechanical volume wave. The use of an electrical interface instead of a mechanical volume interface has seemed to us to be simpler and more adaptable to the clinical setting. For reasons of both patient safety and accuracy, we use a high frequency (100 kHz) sinusoidal oscillator with a low current (1.0 mA). Under these conditions, resistance (R) is more properly referred to as impedance (Z), but continues to account for the major portion of Z (the phase angle averages 16’, so that capacitive reactance is small [II]). The instrument is calibrated internally with a standard resistance change equivalent to 1 cc of volume change in a standard segment 15 cm in length. The circuitry automatically corrects for resistance changes due to
592
A clinical trial was made of a new noninvasive technic for the measurement of arterial blood volume changes in a limb segment. The instrument employed is small, portable, provides a digital display in cc/min, is readily calibrated, gives reproducible values of the segmental pulsatile volume change and Pulsatile Flow, or PF,, and can then be used to screen patients with peripheral vascular disease and to assess postoperative results. References 1. Mount BE, Barela JR, Van De Water JM: Measurement of pulsatile volume changes in the extremities by impedance plethysmography. Proc ACEMB 25: 148, 1972. 2. Mount BE, Van De Water Jfvl: Estimation of peripheral arterial blood flow. Angiology 26: 165, 1975. 3. Van De Water JM, Mount BE: Impedance plethysmography in the lower extremity, p 91. Venous Surgery In Lower Extremity (Swan KG, ed). St. Louis, H. Green, 1975. 4. Gammill S, Craighead C: Translumbar aortography updated. Surg Gynecol Obstet 140: 59. 1975. 5. Karpman HL, Payne JH, Winsor T: A practical, systematic laboratory approach to the SW of the peripheral circulation. Ann Intern Med 53: 306, 1960. 6. Nyboer J: Electrical impedance plethysmography: a physical and physiologic approach to peripheral vascular study. Clrculation 2: 611, 1950. 7. Strandness DE Jr, Bell JW: Peripheral vascular dlsease: diagnosis and objective evaluation using a mercury strain gauge. Ann Surg 161: 3, 1965. 8. Whitney RJ: The measurement of volume changes in human limbs. J Physiol121: 1, 1953. 9. Darling RC, Raines JK, Brener BJ, Austen WG: Quantitative segmental pulse volume recorder: a clinical tool. Surgery 72: 873, 7972. 10. Allison RD: The effects of aging, vascular disease and hypertension on the peripheral pulse volume. J Am Geriatr Sot 16: 39, 1968. 11. Pacela AF: Bioelectric impedance measurements as a method of screening for peripheral vascular disease and deep VWIOUS thrombosis. Beckman lnstr Biophy Res Corp, CRR-26. 1971. 12. Mount BE, Grayson MA, Van De Water JM: An impedance plethysmograph for clinical arterial pulse volume measurement: standardization and verification of pulse volume recordings. JAAMI 10: 55. 1976.
The American Journal 8f Surgery
