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The Piezoelectric Pulse Sensor Device: A Prospective Evaluation
The Piezoelectric Pulse Sensor Device: A Prospective Evaluation Homayoun A. HashemL MD, Mira L. Katz, MLA, RVT,, Anthony P. Carter, BA, Robb P. Kerr, BA, RVT, and Anthony J. Comerota, MD, RVT,, Philadelphia, Pennsylvania
The goal of this prospective study of the piezoelectric pulse sensor device was to determine its technical applications and its ability to detect lower extremity occlusive arterial disease. Ten extremities (five volunteers) were evaluated to assess the ability to place the sensor in the correct anatomic position on a foot without a palpable pulse during cuff occlusion so that pulsatile flow would be detected following cuff deflation; its sensitivity as an end-point detector for pulsatile perfusion; and whether there is a linear qualitative pulse wave response with increasing perfusion pressures. Forty extremities (20 patients) with suspected occlusive arterial disease were studied to evaluate its capability of detecting perfusion as compared with the presence of a palpable pulse, an audible Doppler signal, and a foot volume waveform. The placement of the sensor on 10 normal limbs with temporary arterial occlusion resulted in a recordable waveform following cuff deflation in 100% of the dorsalis pedis arteries and in 10% of the posterior tibial arteries. The piezoelectric pulse sensor was as sensitive for detecting pulsatile perfusion as an audible Doppler signal and demonstrated a linear change in the waveform's amplitude and shape with incremental changes in perfusion pressure. In the 40 extremities with ankle/brachial indices ranging from 0.00 to 1.35, there was uniform agreement between pulse volume and Pulse Check waveforms. The piezoelectric pulse sensor is a sensitive method for monitoring lower extremity arterial perfusion when supplied by the dorsalis pedis artery; however, it is inadequate for the posterior tibial artery. This may be useful in monitoring revascularization procedures in the immediate postoperative period or monitoring the hemodynamic effectiveness of thrombolytic therapy. (Ann Vasc Surg 1994;8:367-371 .)
Multiple noninvasive modalities have been used in the diagnosis of lower extremity occlusive arterial disease. Current techniques available are the clinical examination, Doppler waveform analysis, ankle/brachial systolic pressure index (ABI) measurements, pulse volume recordings, and duplex imaging. Although each technique's advantages and limitations have been well documented, they have not been commonly used for the continuous monitoring of arterial perfusion. The abil-
From the Vascular Laboratory, Department of Surgery, Temple University Hospital Philadelphia, Pa. Reprint requests: Anthony J. Comerota, MD, RVT, Chief of Vascular Surgery, Temple University Hospital Broad and Ontario Streets, Philadelphia, PA 19140.
ity to monitor lower extremity arterial perfusion is important in patients receiving thrombolytic therapy and may be useful in the immediate postoperative period following lower extremity bypass procedures. Recently a piezoelectric pulse sensor device has been suggested as a method for continuous monitoring of patients with infrainguinal vascular reconstructions or thromboembolectomy in the immediate postoperative period. 1-3 However, the accuracy of this device has not been evaluated nor has it been compared to established diagnostic tests. The purposes of this study were ( 1 ) to evaluate whether the waveforms generated by Pulse Check correlated with those of pulse volume tracings, (2) to evaluate the sensitivity of the Pulse Check 367
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Hashemi et al.
compared with Doppler ultrasound in identifying pulsatile perfusion in the foot, (3) to evaluate whether the sensor can be placed accurately on the skin over the dorsalis pedis and posterior tibial arteries in the absence of a palpable pulse or Doppler signal, and (4) to evaluate if there is a linear qualitative pulse wave response with increasing perfusion pressures.
MATERIAL AND METHODS Ten normal, asymptomatic lower extremities (five volunteers) were prospectively examined to evaluate the accuracy of the Pulse Check system (Impra Inc., Tempe, Ariz.). All volunteers had bilaterally palpable dorsalis pedis and posterior tibial pulses and the ankle/brachial index for each artery was > 1.0. Twenty patients (40 extremities) with suspected lower extremity occlusive arterial disease were studied with the Pulse Check system to compare its waveform with a volume pulse waveform. Routine segmental pressures and pulse volume tracings were performed, and the Pulse Check waveforms were obtained by applying the sensor to t h e dorsum of the foot over the dorsalis pedis artery with the guidance of the Doppler signal. The piezoelectric pulse monitoring device consists of a pulse detection sensor and a display unit. The sensor is placed on the skin over the artery and adhesive strips secure its position (Fig. 1). A piezoelectric transducer within the sensor detects the radial movement of a pulsating artery.
Annals of Vascular Surgery
The transducer is constructed of a piezoelectric polyvinylidine fluoride foil 28 ~m thick stretched between raised protrusions on a plastic frame (Fig. 2). Each transducer is 27.9 m m long and 13.5 m m wide with an active area of 377 m m 2, and the flame is mounted on a compressible foam block. When the transducer is placed firmly againt the skin, underlying tissue displacement causes the foil to stretch and relax, generating a charge proportional to the change in foil length: The electric charge is captured in silk-screened silver electrode patterns on both surfaces of the foil, and the resultant current produces a voltage signal across a resistor) The display unit converts the transducer's signal into a visual waveform that varies with the elastic displacement of the artery and provides paper hard copy. Since patients have different vessel elasticities and systemic blood pressures, there is no absolute numeric value of the signal strength. In addition, the signal amplitude can be altered by changing the gain setting (range 1 to 10). The pulse volume tracings (Medasonics, Fremont, Calif.) were obtained at the ankle level in volunteers and at the foot in patients. Pulse volume waveforms are produced by indirectly measuring limb volume changes resulting from pulsatile blood flow. The changes in volume cause a proportional pressure change in the air of t h e cuff, and a pressure transducer converts the pressure changes into an analog recording. Ten normal legs were used to evaluate three different applications of the Pulse Check system.
Fig. 1. The Pulse Check sensor applied to the dorsum of the foot to monitor the dorsalis pedis artery.
Vol. 8, No. 4 1994
To assess the reliability of sensor placement in the absence of a palpable pulse or audible Doppler signal, a blood pressure cuff was placed at the ankle and inflated to suprasystolic pressure. The sensor was blindly placed on the skin over the anatomic location of the dorsalis pedis and posterior tibial arteries in the volunteers. The ankle pressure cuff was deflated and pulse wave recordings obtained. To evaluate the ability to detect pulsatile perfusion, ankle pressures were obtained bilaterally using the Pulse Check's waveform and an audible Doppler signal simultaneously. To correlate the waveform from the Pulse Check and the pulse volume tracing at the ankle, both waveforms were compared at different perfusion pressures by incrementally inflating a calf pressure cuff to pressures creating ABIs of 0.75, 0.50, 0.25, and 0. In addition, the Pulse Check was used in 20 patients with occlusive arterial disease to evaluate the reliability of its pulse wave in relation to the presence of a palpable pulse, an audible Doppler signal, and a foot volume waveform.
RESULTS The blind placement of the Pulse Check's sensor on the 10 normal legs with temporary vascular occlusion resulted in a recordable waveform from 100% of the dorsalis pedis arteries but only 10% of the posterior tibial arteries when blood flow was restored. In determining the Pulse Check's ability to detect pulsatile perfusion w h e n measuring ankle pressures, the waveform returned
Piezoelectric pulse sensor device
369
within 2 m m Hg pressure of the audible Doppler signal in all 10 extremities. Although the Pulse Check's waveform is different from the pulse volume tracing, both types of waveforms had a similar decrease in amplitude with incremental occlusion using a proximal pressure cuff (Fig. 3). The Pulse Check results in the 20 patients are listed in Table I. There was a good correlation between the pulse volume tracing and the Pulse Check waveform. In one extremity without a dorsalis pedis pulse or Doppler signal, a waveform could not be obtained with either technique.
DISCUSSION In this study we evaluated the technical application, limitations, and the ability of the Pulse Check system to detect lower extremity occlusive arterial disease. The results demonstrate that the sensor can be placed on the dorsum of the foot without the guidance of a palpable pulse or Doppler signal and that pulsatile blood flow from the dorsalis pedis artery can be monitored. The sensor, however, cannot be used to monitor the posterior tibial artery because the anatomy of this site prevents secure attachment to the skin. The Pulse Check waveform can be used to detect pulsatile perfusion in the dorsalis pedis artery. The amplitude and shape of the waveform, like a pulse volume tracing, is affected by varying degrees of proximal occlusion. The Pulse Check system demonstrated a waveform in patients w h e n a pulse volume tracing was also present. In this group of patients the ABIs
Fig. 2. The polyvinylidine fluoride foil on the Pulse Check sensor is stretched between the raised protrusions on the plastic frame.
370
Annals of Vascular Surgery
Hashemi et al.
Table I. Comparison of pulse volume recording and pulse check amplitude ABI No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Extremity
ABI
PVR amplitude (ram)
PC amplitude (ram)
Gain
Pulse
R L R L R L R L R L R L R L R L R L R L R L R L R L R L R L R L R L R L R L R L
1.01 1.13 1.08 1.17 0.77 0.67 0.48 1.06 1.07 1.22 0.70 0.57 0.67 0.78 0.49 0.46 0.58 0.54 0.63 0.63 0.69 0.55 0.81 0.79 1.16 0.50 0.56 0.54 0.82 0.89 0.68 0.59 0.94 0.49 1.35 1.19 0.40 0.00 0.68 0.58
6 4 11 18 2 3 3 8 9 9 17 14 7 4 2 1 1 2 5 5 5 4 13 5 9 1 1 3 9 1 5 3 32 19 25 18 3 0 7 4
12 8 9 32 1 5 9 22 26 20 15 5 5 2 1 1 3 3 8 5 25 18 12 5 13 4 4 4 13 8 15 5 22 8 27 20 2 0 13 7
6 6 4 4 4 4 6 4 4 6 6 6 8 6 6 6 7 7 1 4 5 6 8 8 4 7 6 6 6 6 6 7 4 4 5 6 6 6 6 6
Doppler Doppler Palpable Palpable Doppler Doppler Doppler Palpable Palpable Palpable Palpable Doppler Doppler Doppler Doppler Doppler Doppler Doppler Palpable Palpable Palpable Palpable Doppler Doppler Palpable Doppler Doppler Doppler Palpable Doppler Palpable Doppler Palpable Palpable Palpable Palpable Doppler Absent Doppler Doppler
ABI = dorsalis pedis ankle brachial index; PVR = pulse volume recording; PC = Pulse Check.
Vol. 8, No. 4 1994
Piezoelectric pulse sensor device
371
~ECH~K
%, ABI 1.00
ABI 0.25 11i
Fig. 3. Pulse volume a n d Pulse Check w a v e f o r m recorded f r o m a n o r m a l extremity. Differences in w a v e f o r m s are d e m o n s t r a t e d in a p a t i e n t w i t h a n ABI of 1.00 a n d 0.25.
ranged from 0.40 to 1.35. This demonstrates that the system correlates well with the pulse volume tracing in patient's with various degrees of occlusive arterial disease,
CONCLUSION The Pulse Check device can be used to monitor lower extremity arterial perfusion supplied by the dorsalis pedis artery. The sensor can be accurately placed on the dorsum of the foot in patients with vascular occlusion to monitor restoration of perfusion in the dorsalis pedis artery. With the constant gain setting on the instrument, changes in arterial perfusion can be qualitatively measured by changes in the waveform's amplitude and shape. The advantages of using the Pulse Check system is its simplicity and its ability to be used
as a continuous monitoring device. This system may be useful in operating rooms, recovery rooms, intensive care units, and radiology suites. The Pulse Check system may prove to be especially useful in monitoring revascularization procedures in the immediate postoperative period or w h e n monitoring the hemodynamic effectiveness of thrombolytic therapy, assuming reperfusion occurs through the anterior tibial artery, REFERENCES 1. Cavaye DM, Yabbara MR, Kopchok GE, et al. Continuous piezoelectric pulse-sensor monitoring of peripheral vascular reconstructions. Vasc Surg 1992;26:718-722. 2. Fogarty TJ, Hermann GD. New techniques for clot extraction and managing acute thromboembolic limb ischemia. Vasc Surg 1991;3:197-203. 3. Gupta SK, Dietzek AM, Veith FJ, et al. Use of a piezoelectric film sensor for monitoring vascular grants. Am J Surg 1990; 160:182-186.
The goal of this prospective study of the piezoelectric pulse sensor device was to determine its technical applications and its ability to detect lower extremity occlusive arterial disease. Ten extremities (five volunteers) were evaluated to assess the ability to place the sensor in the correct anatomic position on a foot without a palpable pulse during cuff occlusion so that pulsatile flow would be detected following cuff deflation; its sensitivity as an end-point detector for pulsatile perfusion; and whether there is a linear qualitative pulse wave response with increasing perfusion pressures. Forty extremities (20 patients) with suspected occlusive arterial disease were studied to evaluate its capability of detecting perfusion as compared with the presence of a palpable pulse, an audible Doppler signal, and a foot volume waveform. The placement of the sensor on 10 normal limbs with temporary arterial occlusion resulted in a recordable waveform following cuff deflation in 100% of the dorsalis pedis arteries and in 10% of the posterior tibial arteries. The piezoelectric pulse sensor was as sensitive for detecting pulsatile perfusion as an audible Doppler signal and demonstrated a linear change in the waveform's amplitude and shape with incremental changes in perfusion pressure. In the 40 extremities with ankle/brachial indices ranging from 0.00 to 1.35, there was uniform agreement between pulse volume and Pulse Check waveforms. The piezoelectric pulse sensor is a sensitive method for monitoring lower extremity arterial perfusion when supplied by the dorsalis pedis artery; however, it is inadequate for the posterior tibial artery. This may be useful in monitoring revascularization procedures in the immediate postoperative period or monitoring the hemodynamic effectiveness of thrombolytic therapy. (Ann Vasc Surg 1994;8:367-371 .)
Multiple noninvasive modalities have been used in the diagnosis of lower extremity occlusive arterial disease. Current techniques available are the clinical examination, Doppler waveform analysis, ankle/brachial systolic pressure index (ABI) measurements, pulse volume recordings, and duplex imaging. Although each technique's advantages and limitations have been well documented, they have not been commonly used for the continuous monitoring of arterial perfusion. The abil-
From the Vascular Laboratory, Department of Surgery, Temple University Hospital Philadelphia, Pa. Reprint requests: Anthony J. Comerota, MD, RVT, Chief of Vascular Surgery, Temple University Hospital Broad and Ontario Streets, Philadelphia, PA 19140.
ity to monitor lower extremity arterial perfusion is important in patients receiving thrombolytic therapy and may be useful in the immediate postoperative period following lower extremity bypass procedures. Recently a piezoelectric pulse sensor device has been suggested as a method for continuous monitoring of patients with infrainguinal vascular reconstructions or thromboembolectomy in the immediate postoperative period. 1-3 However, the accuracy of this device has not been evaluated nor has it been compared to established diagnostic tests. The purposes of this study were ( 1 ) to evaluate whether the waveforms generated by Pulse Check correlated with those of pulse volume tracings, (2) to evaluate the sensitivity of the Pulse Check 367
368
Hashemi et al.
compared with Doppler ultrasound in identifying pulsatile perfusion in the foot, (3) to evaluate whether the sensor can be placed accurately on the skin over the dorsalis pedis and posterior tibial arteries in the absence of a palpable pulse or Doppler signal, and (4) to evaluate if there is a linear qualitative pulse wave response with increasing perfusion pressures.
MATERIAL AND METHODS Ten normal, asymptomatic lower extremities (five volunteers) were prospectively examined to evaluate the accuracy of the Pulse Check system (Impra Inc., Tempe, Ariz.). All volunteers had bilaterally palpable dorsalis pedis and posterior tibial pulses and the ankle/brachial index for each artery was > 1.0. Twenty patients (40 extremities) with suspected lower extremity occlusive arterial disease were studied with the Pulse Check system to compare its waveform with a volume pulse waveform. Routine segmental pressures and pulse volume tracings were performed, and the Pulse Check waveforms were obtained by applying the sensor to t h e dorsum of the foot over the dorsalis pedis artery with the guidance of the Doppler signal. The piezoelectric pulse monitoring device consists of a pulse detection sensor and a display unit. The sensor is placed on the skin over the artery and adhesive strips secure its position (Fig. 1). A piezoelectric transducer within the sensor detects the radial movement of a pulsating artery.
Annals of Vascular Surgery
The transducer is constructed of a piezoelectric polyvinylidine fluoride foil 28 ~m thick stretched between raised protrusions on a plastic frame (Fig. 2). Each transducer is 27.9 m m long and 13.5 m m wide with an active area of 377 m m 2, and the flame is mounted on a compressible foam block. When the transducer is placed firmly againt the skin, underlying tissue displacement causes the foil to stretch and relax, generating a charge proportional to the change in foil length: The electric charge is captured in silk-screened silver electrode patterns on both surfaces of the foil, and the resultant current produces a voltage signal across a resistor) The display unit converts the transducer's signal into a visual waveform that varies with the elastic displacement of the artery and provides paper hard copy. Since patients have different vessel elasticities and systemic blood pressures, there is no absolute numeric value of the signal strength. In addition, the signal amplitude can be altered by changing the gain setting (range 1 to 10). The pulse volume tracings (Medasonics, Fremont, Calif.) were obtained at the ankle level in volunteers and at the foot in patients. Pulse volume waveforms are produced by indirectly measuring limb volume changes resulting from pulsatile blood flow. The changes in volume cause a proportional pressure change in the air of t h e cuff, and a pressure transducer converts the pressure changes into an analog recording. Ten normal legs were used to evaluate three different applications of the Pulse Check system.
Fig. 1. The Pulse Check sensor applied to the dorsum of the foot to monitor the dorsalis pedis artery.
Vol. 8, No. 4 1994
To assess the reliability of sensor placement in the absence of a palpable pulse or audible Doppler signal, a blood pressure cuff was placed at the ankle and inflated to suprasystolic pressure. The sensor was blindly placed on the skin over the anatomic location of the dorsalis pedis and posterior tibial arteries in the volunteers. The ankle pressure cuff was deflated and pulse wave recordings obtained. To evaluate the ability to detect pulsatile perfusion, ankle pressures were obtained bilaterally using the Pulse Check's waveform and an audible Doppler signal simultaneously. To correlate the waveform from the Pulse Check and the pulse volume tracing at the ankle, both waveforms were compared at different perfusion pressures by incrementally inflating a calf pressure cuff to pressures creating ABIs of 0.75, 0.50, 0.25, and 0. In addition, the Pulse Check was used in 20 patients with occlusive arterial disease to evaluate the reliability of its pulse wave in relation to the presence of a palpable pulse, an audible Doppler signal, and a foot volume waveform.
RESULTS The blind placement of the Pulse Check's sensor on the 10 normal legs with temporary vascular occlusion resulted in a recordable waveform from 100% of the dorsalis pedis arteries but only 10% of the posterior tibial arteries when blood flow was restored. In determining the Pulse Check's ability to detect pulsatile perfusion w h e n measuring ankle pressures, the waveform returned
Piezoelectric pulse sensor device
369
within 2 m m Hg pressure of the audible Doppler signal in all 10 extremities. Although the Pulse Check's waveform is different from the pulse volume tracing, both types of waveforms had a similar decrease in amplitude with incremental occlusion using a proximal pressure cuff (Fig. 3). The Pulse Check results in the 20 patients are listed in Table I. There was a good correlation between the pulse volume tracing and the Pulse Check waveform. In one extremity without a dorsalis pedis pulse or Doppler signal, a waveform could not be obtained with either technique.
DISCUSSION In this study we evaluated the technical application, limitations, and the ability of the Pulse Check system to detect lower extremity occlusive arterial disease. The results demonstrate that the sensor can be placed on the dorsum of the foot without the guidance of a palpable pulse or Doppler signal and that pulsatile blood flow from the dorsalis pedis artery can be monitored. The sensor, however, cannot be used to monitor the posterior tibial artery because the anatomy of this site prevents secure attachment to the skin. The Pulse Check waveform can be used to detect pulsatile perfusion in the dorsalis pedis artery. The amplitude and shape of the waveform, like a pulse volume tracing, is affected by varying degrees of proximal occlusion. The Pulse Check system demonstrated a waveform in patients w h e n a pulse volume tracing was also present. In this group of patients the ABIs
Fig. 2. The polyvinylidine fluoride foil on the Pulse Check sensor is stretched between the raised protrusions on the plastic frame.
370
Annals of Vascular Surgery
Hashemi et al.
Table I. Comparison of pulse volume recording and pulse check amplitude ABI No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Extremity
ABI
PVR amplitude (ram)
PC amplitude (ram)
Gain
Pulse
R L R L R L R L R L R L R L R L R L R L R L R L R L R L R L R L R L R L R L R L
1.01 1.13 1.08 1.17 0.77 0.67 0.48 1.06 1.07 1.22 0.70 0.57 0.67 0.78 0.49 0.46 0.58 0.54 0.63 0.63 0.69 0.55 0.81 0.79 1.16 0.50 0.56 0.54 0.82 0.89 0.68 0.59 0.94 0.49 1.35 1.19 0.40 0.00 0.68 0.58
6 4 11 18 2 3 3 8 9 9 17 14 7 4 2 1 1 2 5 5 5 4 13 5 9 1 1 3 9 1 5 3 32 19 25 18 3 0 7 4
12 8 9 32 1 5 9 22 26 20 15 5 5 2 1 1 3 3 8 5 25 18 12 5 13 4 4 4 13 8 15 5 22 8 27 20 2 0 13 7
6 6 4 4 4 4 6 4 4 6 6 6 8 6 6 6 7 7 1 4 5 6 8 8 4 7 6 6 6 6 6 7 4 4 5 6 6 6 6 6
Doppler Doppler Palpable Palpable Doppler Doppler Doppler Palpable Palpable Palpable Palpable Doppler Doppler Doppler Doppler Doppler Doppler Doppler Palpable Palpable Palpable Palpable Doppler Doppler Palpable Doppler Doppler Doppler Palpable Doppler Palpable Doppler Palpable Palpable Palpable Palpable Doppler Absent Doppler Doppler
ABI = dorsalis pedis ankle brachial index; PVR = pulse volume recording; PC = Pulse Check.
Vol. 8, No. 4 1994
Piezoelectric pulse sensor device
371
~ECH~K
%, ABI 1.00
ABI 0.25 11i
Fig. 3. Pulse volume a n d Pulse Check w a v e f o r m recorded f r o m a n o r m a l extremity. Differences in w a v e f o r m s are d e m o n s t r a t e d in a p a t i e n t w i t h a n ABI of 1.00 a n d 0.25.
ranged from 0.40 to 1.35. This demonstrates that the system correlates well with the pulse volume tracing in patient's with various degrees of occlusive arterial disease,
CONCLUSION The Pulse Check device can be used to monitor lower extremity arterial perfusion supplied by the dorsalis pedis artery. The sensor can be accurately placed on the dorsum of the foot in patients with vascular occlusion to monitor restoration of perfusion in the dorsalis pedis artery. With the constant gain setting on the instrument, changes in arterial perfusion can be qualitatively measured by changes in the waveform's amplitude and shape. The advantages of using the Pulse Check system is its simplicity and its ability to be used
as a continuous monitoring device. This system may be useful in operating rooms, recovery rooms, intensive care units, and radiology suites. The Pulse Check system may prove to be especially useful in monitoring revascularization procedures in the immediate postoperative period or w h e n monitoring the hemodynamic effectiveness of thrombolytic therapy, assuming reperfusion occurs through the anterior tibial artery, REFERENCES 1. Cavaye DM, Yabbara MR, Kopchok GE, et al. Continuous piezoelectric pulse-sensor monitoring of peripheral vascular reconstructions. Vasc Surg 1992;26:718-722. 2. Fogarty TJ, Hermann GD. New techniques for clot extraction and managing acute thromboembolic limb ischemia. Vasc Surg 1991;3:197-203. 3. Gupta SK, Dietzek AM, Veith FJ, et al. Use of a piezoelectric film sensor for monitoring vascular grants. Am J Surg 1990; 160:182-186.