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APPLICATION OF NOCTURNAL ELECTROBIOIMPEDANCE VOLUMETRIC ASSESSMENT: A FEASIBILITY STUDY IN MEN WITHOUT ERECTILE DYSFUNCTION
Vol. 161, 1137-1140, April 1999 Prcnfed in U.S.A.
APPLICATION OF NOCTURNAL ELECTROBIOIMPEDANCE VOLUMETRIC ASSESSMENT: A FEASIBILITY STUDY IN MEN WITHOUT ERECTILE DYSFUNCTION L. DEAN KNOLL*
AND
JEROME H. ABRAMS
From the Center for Urological Treatment and Research, Nashville, Tennessee, and Department of Surgery, Veterans AffairsMedical Center, Minneapolis, Minnesota
ABSTRACT
Purpose: Electrobioimpedance volumetric assessment is based on the principle of delivering a constant, nondetectable alternating current to a tissue segment. A potential difference measured between the electrodes is converted to impedance. Since impedance changes with variations in blood flow, penile volumetric change is measured noninvasively. We applied this procedure to the development of a new device to evaluate erectile activity nocturnally, and we report o u r findings in men with no history of erectile dysfunction. Materials and Methods: Our study group comprised 10 men with a mean age of 44 years who had no history of erectile dysfunction. The NEVAt device consists of a small recording device attached to the upper thigh, and 3 small adhesive electrode pads placed over the hip and on the penile base and glans, respectively. Each subject used the NEVA device for 2 nights. Results: Overall 20 nights of electrobioimpedance volumetric assessment were recorded. Tumescence monitoring revealed 3 to 6 erections per night per subject (mean 3.45)lasting 10 to 50 minutes (mean 17). As determined from the impedance measurements, mean volume change was 14.4ml. with a 213% mean volume change over baseline. Conclusions: The new NEVA device is small, comfortable to wear and easy to use. It determines the number and duration of erectile events and percentage increase of blood volume changes during these events in normal men in a noninvasive manner. Future directions of study include a comparison to men with erectile dysfunction and analysis of the dynamic information of the NEVA data. KEY WORDS:penis, erection, erectile dysfunction, blood volume
Penile erection is a complex neurovascular phenomenon involving coordination of hemodynamic events and interaction of psychological, hormonal, neurological and structural factors. External measurements of penile circumference have been used in the past to determine penile volume in the flaccid and erect states.'-4 These circumferential measurements represent all penile tissues, including penile skin, subcutaneous tissues, tunica albuginea and corpus spongios u m with the urethral lumen. As a result of including noncorporeal cavernous tissues in the measurement of penile circumference, circumference and consequently penile volume have been overestimated. To determine penile blood volume others have explored the use of labeled blood pool, tracer washout, tracer wash in combined blood pool tracer and tracer washout examinations, and xenon Information derived from these studies represents the basic cornerstone of the understanding of erectile physiology, and these studies are the major source of quantitative information on penile blood volume and flow. High resolution ultrasonography and pulsed Doppler analysis provide accurate and reproducible measurements of penile blood volume before and after erection."." Penile volume has been determined using the formula, volume in cm.j = area in cm.' x length in cm., where area is the measured cross-sectional area of the corpora and length is the physical measurement of penile length. Recently penile volume has
been derived as a function of tissue mechanical characteristics, cavernous expandability and intracavernous pressure,12.13 Electrical bioimpedance has been used in physiological applications for 3 decades. Nyboer first used changes in thoracic electrical bioimpedance to calculate cardiac output.I4 Many others have modified the original concept to permit the measurement of cardiac output in a simple, noninvasive, relatively inexpensive, reproducible manner.'"-'' In electrical bioimpedance assessment a nondetectable constant alternating current is applied to a tissue segment and a potential difference is measured between the electrodes. Tissue impedance changes with variations in blood flow. The application of this technology has led to the development of the NEVA device for nocturnal electrobioimpedance volumetric assessment of the penis. The device measures penile length, cross-sectional area and volume. It also determines the number and duration of erectile events, and penile blood volume change associated with these events. We report the characteristics of t h e device, theory of operation and data in a population of patients with no history of erectile dysfunction. MATERIALS AND METHODS
After approval of the Western Institutional Review Board and obtaining informed consent 10 men 31 to 49 years old (mean age 44) with no history of erectile dysfunction were enrolled in our study. Each individual used the NEVA device for 2 consecutive nights. The NEVA system consists of a disposable electrode set, portable battery powered recorder weighing 5 ounces, host interface unit and computer program
Accepted for publication October 16, 1998. All authors have financial interest and/or other relationship with Urometrics, Inc. * Requests for reprints: 2400 Patterson St., Suite 101, Nashville, Tennessee 37203. turometrics, Inc., St. Paul, Minnesota. 1137
1138
APPLICATION OF NOCTURNAL ELECTROBIOIMPEDANCE VOLUMETRIC ASSESSMENT
from which the host computer downloads data (fig. 1). The disposable electrode set includes 1unit that terminates just proximal to the glans penis and 1 unit with 2 electrodes a known fixed distance apart placed at the base of the penis (fig. 2). The electrodes and recorder, which uses a 9 V. battery, monitor nocturnal tumescence for up to 3 nights. A Wien oscillator circuit in a 2 operational amplifier configuration with a gain controller generates a n alternating current signal from the direct current battery. The host interface and computer prepare the recorder for use and download data from the recorder for display or analysis on the physician computer. Hard copies of patient and electronically stored data are available. The NEVA system determines changes in volume by measuring the impedance within the penis. A 5 kHz. 150 pA. alternating current is sent from the electrode closest to the glans to the ground electrode on the hip (fig. 1). The remaining electrodes at the base of the penis measure impedance. The current is sufficiently low to eliminate any sensation of current passage. The electrode set placed at the base of the penis consists of electrodes separated by a fixed distance. As the cross-sectional area of the penis changes with increased FIG.2. Electrode placement ( I to 4 ) on penis. AC, alternating penile blwd volume, impedance measured by the base elec- current. trode decreases. With increased penile length the distance between the electrodes at the base and near the glans also increases, and there is a corresponding increase in impedance. For study purposes we assumed that the penis comprises a tissue (t)and a blood (b) Compartment, and each compartment has homogeneous admittance CY). Furthermore, we assumed that the compartments are parallel. Figure 3 shows an equivalent electrical circuit. A constant alternating current flowing Y through the total region yields admittance, which is the inverse of impedance, calculated as the complex ratio of the source Penile decomposition into current and voltage measured between the electrodes. Since the Equivalentcircuit blood and tissue filled regions admittance of parallel linear passive elements is the sum of the admittances of the individual elements, in this case blood FIG.3. Equivalent electrical circuit of penis. A,, cross-sectional and tissue, the admittance between 2 electrodes that bound a area of blood filled region. p resistivity of blood filled region. A,, cross-sectional area of tissue Ailed region. p , resistivity of blood filled segment of the penis is determined using the formula, Y = Yb+ region. L, length. Yb, admittance of blood filled region. Yt,admittance Y,. The individual admittances Yb and Y, of a homogeneous of tissue filled region. Y, admittance. region are found using the formulas, Y, = A,,/(p,L) and Y, = A+j(ptL), respectively, where A represents cross-sectional area, L represents length and p represents resistivity. Substituting the latter equations intn the former equation yields the expression for the admittance of the relevant segment, Y = AJp,, +
b
AJPJrn.
Figure 4 shows the fixed length (b) and penile length to be measured (L,), Electrodes 3 and 4 bound segment at the base of the penis, and electrodes 2 and 4 bound segment L,. Using the formula for the admittance of the relevant segment the admittance of segments Y, and Y, is calculated using the formulas, Y, = Adp, + AJpJYL, and Y = (Ad& + AJpJlI L,, respectively. As an approximation, for blwd and tissue regions of uniform resistivity and cross-sectional area these latter 2 equations yield YJY, = L&, and L, = L, X YJY,,
FIG.4. Relevant length segments for determining penile length (L 1 LF, fixed length. Y,, fixed length admittance. Y,,penile length aJiittance.
FIG. 1. NEVA system components with electrodes attached to penis and hip.
respectively. Penile length is determined by the fixed length between the base electrodes times the ratio of the admittances of fixed and penile length (Y, and Y,, respectively). The volume (V) of the blood and tissue regions of the penis are calculated using the formulas, vt,= A, x L, and vt = 4 X L,, respectively. Solving for the areas and substituting into
APPLICATION OF NOCTURNAL ELECTROBIOIMPEDANCE VOLUMETRIC ASSESSMENT
the formula for the admittance of segment Yp yield the equation, V, = pb X (LP2 X Y, - [V,/pJ). We prevlously calibrated the value of V, (unpublished data). RESULTS
Electrobioimpedance measurements were obtained on 2 consecutive nights for 4.8to 9.1 hours. Using the aforementioned method of analysis impedance measurements were converted to penile length, cross-sectional area and volume per second. Graphs of penile length, cross-sectional area and volume versus time were construct4 for each study subject (fig. 5). The data were analyzed for the number and duration of erectile events, volume change and relative volume change normalized to the baseline penile volume of each subject at the beginning of the study. These men had a mean of 3.45 erectile events a night that lasted a mean of 17 minutes. Volume changes were expressed as the change in penile volume and the percent change over baseline volume at study onset. Mean volume change was 14.4ml. (mean 213%over baseline). The table summarizes the results in all 10 study subjects. DISCUSSION
Electrobioimpedance may be used for nocturnal assessment of penile length, cross-sectional area and volume. To our knowledge this report represents the first study of penile blood volume changes measured nocturnally in normal men using NEVA technology. An erectile event of at least a mean of 200% volume increase from a nonerect state was noted during nocturnal erectile activity in these subjects. Our results represent 20 nights of volumetric measurements to establish mean baseline values in normal men, and so this technology may be used to study individuals with pathophysiological conditions resulting in erectile dysfunction. In our study changes in impedance were mapped to changes in penile length, cross-sectional area and volume by modeling the penis as an electrical circuit. In our model the penis has compartments representing blood and tissue volume. The compartments are assumed to have Werent resistivities, although each is homogeneous with respect to resistivity. Assuming that the compartments are equivalent to a parallel circuit allowed us to determine penile length, volume and cross-sectional area. The NEVA system provides information in addition to the measurement of penile length, cross-sectional area and volume. It also provides data on the number and duration of
1139
Results No. erectile events Duration h i m . ) Vol. change (ml.) 9E Vol. increase over baseline
No. Pta.
Mean
20 20 20 19
3.45
?
Z 17.0 ? 14.4 Z 213 ?
SD
1.47 11.5 10 2
129 ____
erectile events, and change in volume over baseline per patient. The lightweight NEVA recorder may store up to 3 nights of data, which may then be downloaded to physician computers. In addition, the NEVA device may be worn safely by men with pacemakers. An issue that we addressed was the necessity of 2 nights of monitoring. The apparatus may interfere with normal sleep (the so-called first night effect). Because of its small size and nonconstricting electrodes attached to the penis, the NEVA system achieved excellent acceptance by the men in our study. All study participants stated that the device is easy to use and comfortable enough not to interfere with sleep. An analysis of all sessions showed that all nighttime recordings were comparable, which argues against the first night effect. Future studies of impotent patients or those with borderline impotence are required to confirm this finding. Future use of these data should allow definition of normal values for a wide range of ages in men with no history of erectile dysfunction. Although anatomical variations in penile length, cross-sectional area and volume are to be expected, one may reasonably expect to define normal ranges for the number and duration of erectile events, and fractional change in volume over baseline of these events. With the increase in number and types of noninvasive and invasive therapy available to treat erectile dysfunction, understanding the characteristics of patients without erectile dysfunction will be valuable to identify and quantify deviations from normal erectile behavior. CONCLUSIONS
We describe the use of nocturnal electrobioimpedance to assess penile erectile activity. The NEVA device is small, comfortable to wear and easy to use. It determines the number and duration of erectile events, and the percentage increase of blood volume changes during these events in a noninvasive manner. Our data represent normal erectile function. Future directions of study include comparisons of men with erectile dysfunction, an analysis of the dynamic data provided by the NEVA system, and comparison of electrobioimpedance data to duplex Doppler vascular scanning and conventional nocturnal penile tumescence testing. REFERENCES
FIG. 5. NEVA recorder output includes penile cross-sectional area, length and volume on y-axis plotted as function of time on x-axls.
1. Godec, C. J. and Cass, A. S.: Quantification of erection. J. Urol., 1 2 6 345, 1981. 2. Virag, R., Boulilly, P. and Virag, H.: Dimensions. volume and rigidity of the penis. Fundamental elements in the study of erection and its dysfunctions. Ann. Urol. (Paris),20: 244,1986. 3. Bancroft, J. and Bell, C.: Simultaneous recording of penile diameter and penile arterial pulse during laboratory-based erotic stimulation in normal subjects. J. Psychosom. Res., 29: 303, 1985. 4. Pueschel, S. M., Orson, J. M., Boylin, J. M. and Pezzullo, J . C.: Adolescent development in males with Downs syndrome. Amer. J. Dis. Child., 139: 236, 1985. 5. Shirai, M. and Nakamura, M.: Differential diagnosis of organic and functional impotence by the use of 131-I-human serum albumin. Tohoku J. Exp. Med., 101: 317, 1970. 6. Kim, S. C., Kim, K. B. and Oh, C. H.: Diagnostic value of the radioisotope erection penogram for vasculogenic impotence. J. Urol., 144: 888, 1990. 7. Shirai, M.: Determination of intrapenile blood volume using 99mTc-labeled autologous red blood cells. Tohoku J. Exp. Med.. 120: 377,1976.
1140
APPLICATION OF NOCTURNAL ELECTROBIOIMPEDANCE VOLUMETRIC ASSESSMENT
8 . Zuckier, L. S., Korupolu, G. R., Gladshtenyn, M., Sattenberg, R.,
Goldstein, R., Ricciardi, R., Goodwin, R., Melman, A. and Blaufox., M. D.: A non-imaging scintillation probe to measure penile hemodynamics. J. Nucl. Med., 36.2345, 1995. 9. Schwartz, A. N. and Graham, M. M.: Combined technetium radioisotope penile plethysmography and xenon washout: a technique for evaluating corpora cavernosal inflow and outflow during early tumescence. J. Nucl. Med., 32: 404, 1991. 10. Nelson, R. P. and Lue, T. F.: Determination of erectile penile volume by ultrasonography. J. Urol., 141: 1123, 1989. 11. Chen, K K., Chou, I., Chang, L. S. and Chen, M. T.: Sonographic measurement of penile erectile volume. J. Clin. Ultrasound, 2 0 247, 1992. 12. Udelson, D., Nehra, A,, Hatzichristou, D. G., Azadzoi, K., Moreland, R. B., Krane, J., Saenz de Tejada, I. S. and Goldstein, I.: Engineering analysis of penile hernodynamic and structural-dynamic relationships: part I-clinical implications of penile tissue mechanical properties. Int. J. Impotence Res., 1 0 15, 1998. 13. Udelson, D., Nehra, A,, Hatzichristou, D. G., Azadzoi, K., Moreland, R. B., Krane, R. J., Saenz de Tejada, I. S. and
Goldstein, I.: Engineering analysis of penile hemodynamic and structural-dynamic relationships: part 11-clinical implications of penile buckling. lnt. J. Impotence Res., 10: 25, 1998. 14. Nyboer, J.: Electrical Impedance Plethysmography. Springfield, Illinois: Charles C. Thomas Co., 1959. 15. Kubicek, W. G., Karnegis, J. N., Patterson, R. P., Witsoe, D. A. and Mattson, R. H.: Development and evaluation of a n impedance cardiac output system. Aerospace Med., 31: 1208,1966. 16. Kubicek, W. G., From, A. H. L., Patterson, R. P., Witsoe, D. A,, Castaneda, A,, Lillehei, R. C. and Ersek, R.: Impedance cardiology as a noninvasive measure to monitor cardiac function. J. Assn. Adv. Med. Instrum., 4 79, 1970. 17. Keim, H.J., Wallace, J. M., Thurston, H., Case, D. B., Drayer, J. I. and Laragh, J. H.: Impedance cardiology for determination of stroke index. J. Appl. Physiol., 41: 797,1976. 18. Bernstein, D. P.: Continuous noninvasive real-time monitoring of stroke volume and cardiac output by thoracic electrical bioimpedance. Crit. Care Med., 14: 898,1986. 19. Bernstein, D. P.: A new stroke volume equation for thoracic electrical bioimpedance: theory and rationale. Crit. Care Med., 1 4 904,1986.
APPLICATION OF NOCTURNAL ELECTROBIOIMPEDANCE VOLUMETRIC ASSESSMENT: A FEASIBILITY STUDY IN MEN WITHOUT ERECTILE DYSFUNCTION L. DEAN KNOLL*
AND
JEROME H. ABRAMS
From the Center for Urological Treatment and Research, Nashville, Tennessee, and Department of Surgery, Veterans AffairsMedical Center, Minneapolis, Minnesota
ABSTRACT
Purpose: Electrobioimpedance volumetric assessment is based on the principle of delivering a constant, nondetectable alternating current to a tissue segment. A potential difference measured between the electrodes is converted to impedance. Since impedance changes with variations in blood flow, penile volumetric change is measured noninvasively. We applied this procedure to the development of a new device to evaluate erectile activity nocturnally, and we report o u r findings in men with no history of erectile dysfunction. Materials and Methods: Our study group comprised 10 men with a mean age of 44 years who had no history of erectile dysfunction. The NEVAt device consists of a small recording device attached to the upper thigh, and 3 small adhesive electrode pads placed over the hip and on the penile base and glans, respectively. Each subject used the NEVA device for 2 nights. Results: Overall 20 nights of electrobioimpedance volumetric assessment were recorded. Tumescence monitoring revealed 3 to 6 erections per night per subject (mean 3.45)lasting 10 to 50 minutes (mean 17). As determined from the impedance measurements, mean volume change was 14.4ml. with a 213% mean volume change over baseline. Conclusions: The new NEVA device is small, comfortable to wear and easy to use. It determines the number and duration of erectile events and percentage increase of blood volume changes during these events in normal men in a noninvasive manner. Future directions of study include a comparison to men with erectile dysfunction and analysis of the dynamic information of the NEVA data. KEY WORDS:penis, erection, erectile dysfunction, blood volume
Penile erection is a complex neurovascular phenomenon involving coordination of hemodynamic events and interaction of psychological, hormonal, neurological and structural factors. External measurements of penile circumference have been used in the past to determine penile volume in the flaccid and erect states.'-4 These circumferential measurements represent all penile tissues, including penile skin, subcutaneous tissues, tunica albuginea and corpus spongios u m with the urethral lumen. As a result of including noncorporeal cavernous tissues in the measurement of penile circumference, circumference and consequently penile volume have been overestimated. To determine penile blood volume others have explored the use of labeled blood pool, tracer washout, tracer wash in combined blood pool tracer and tracer washout examinations, and xenon Information derived from these studies represents the basic cornerstone of the understanding of erectile physiology, and these studies are the major source of quantitative information on penile blood volume and flow. High resolution ultrasonography and pulsed Doppler analysis provide accurate and reproducible measurements of penile blood volume before and after erection."." Penile volume has been determined using the formula, volume in cm.j = area in cm.' x length in cm., where area is the measured cross-sectional area of the corpora and length is the physical measurement of penile length. Recently penile volume has
been derived as a function of tissue mechanical characteristics, cavernous expandability and intracavernous pressure,12.13 Electrical bioimpedance has been used in physiological applications for 3 decades. Nyboer first used changes in thoracic electrical bioimpedance to calculate cardiac output.I4 Many others have modified the original concept to permit the measurement of cardiac output in a simple, noninvasive, relatively inexpensive, reproducible manner.'"-'' In electrical bioimpedance assessment a nondetectable constant alternating current is applied to a tissue segment and a potential difference is measured between the electrodes. Tissue impedance changes with variations in blood flow. The application of this technology has led to the development of the NEVA device for nocturnal electrobioimpedance volumetric assessment of the penis. The device measures penile length, cross-sectional area and volume. It also determines the number and duration of erectile events, and penile blood volume change associated with these events. We report the characteristics of t h e device, theory of operation and data in a population of patients with no history of erectile dysfunction. MATERIALS AND METHODS
After approval of the Western Institutional Review Board and obtaining informed consent 10 men 31 to 49 years old (mean age 44) with no history of erectile dysfunction were enrolled in our study. Each individual used the NEVA device for 2 consecutive nights. The NEVA system consists of a disposable electrode set, portable battery powered recorder weighing 5 ounces, host interface unit and computer program
Accepted for publication October 16, 1998. All authors have financial interest and/or other relationship with Urometrics, Inc. * Requests for reprints: 2400 Patterson St., Suite 101, Nashville, Tennessee 37203. turometrics, Inc., St. Paul, Minnesota. 1137
1138
APPLICATION OF NOCTURNAL ELECTROBIOIMPEDANCE VOLUMETRIC ASSESSMENT
from which the host computer downloads data (fig. 1). The disposable electrode set includes 1unit that terminates just proximal to the glans penis and 1 unit with 2 electrodes a known fixed distance apart placed at the base of the penis (fig. 2). The electrodes and recorder, which uses a 9 V. battery, monitor nocturnal tumescence for up to 3 nights. A Wien oscillator circuit in a 2 operational amplifier configuration with a gain controller generates a n alternating current signal from the direct current battery. The host interface and computer prepare the recorder for use and download data from the recorder for display or analysis on the physician computer. Hard copies of patient and electronically stored data are available. The NEVA system determines changes in volume by measuring the impedance within the penis. A 5 kHz. 150 pA. alternating current is sent from the electrode closest to the glans to the ground electrode on the hip (fig. 1). The remaining electrodes at the base of the penis measure impedance. The current is sufficiently low to eliminate any sensation of current passage. The electrode set placed at the base of the penis consists of electrodes separated by a fixed distance. As the cross-sectional area of the penis changes with increased FIG.2. Electrode placement ( I to 4 ) on penis. AC, alternating penile blwd volume, impedance measured by the base elec- current. trode decreases. With increased penile length the distance between the electrodes at the base and near the glans also increases, and there is a corresponding increase in impedance. For study purposes we assumed that the penis comprises a tissue (t)and a blood (b) Compartment, and each compartment has homogeneous admittance CY). Furthermore, we assumed that the compartments are parallel. Figure 3 shows an equivalent electrical circuit. A constant alternating current flowing Y through the total region yields admittance, which is the inverse of impedance, calculated as the complex ratio of the source Penile decomposition into current and voltage measured between the electrodes. Since the Equivalentcircuit blood and tissue filled regions admittance of parallel linear passive elements is the sum of the admittances of the individual elements, in this case blood FIG.3. Equivalent electrical circuit of penis. A,, cross-sectional and tissue, the admittance between 2 electrodes that bound a area of blood filled region. p resistivity of blood filled region. A,, cross-sectional area of tissue Ailed region. p , resistivity of blood filled segment of the penis is determined using the formula, Y = Yb+ region. L, length. Yb, admittance of blood filled region. Yt,admittance Y,. The individual admittances Yb and Y, of a homogeneous of tissue filled region. Y, admittance. region are found using the formulas, Y, = A,,/(p,L) and Y, = A+j(ptL), respectively, where A represents cross-sectional area, L represents length and p represents resistivity. Substituting the latter equations intn the former equation yields the expression for the admittance of the relevant segment, Y = AJp,, +
b
AJPJrn.
Figure 4 shows the fixed length (b) and penile length to be measured (L,), Electrodes 3 and 4 bound segment at the base of the penis, and electrodes 2 and 4 bound segment L,. Using the formula for the admittance of the relevant segment the admittance of segments Y, and Y, is calculated using the formulas, Y, = Adp, + AJpJYL, and Y = (Ad& + AJpJlI L,, respectively. As an approximation, for blwd and tissue regions of uniform resistivity and cross-sectional area these latter 2 equations yield YJY, = L&, and L, = L, X YJY,,
FIG.4. Relevant length segments for determining penile length (L 1 LF, fixed length. Y,, fixed length admittance. Y,,penile length aJiittance.
FIG. 1. NEVA system components with electrodes attached to penis and hip.
respectively. Penile length is determined by the fixed length between the base electrodes times the ratio of the admittances of fixed and penile length (Y, and Y,, respectively). The volume (V) of the blood and tissue regions of the penis are calculated using the formulas, vt,= A, x L, and vt = 4 X L,, respectively. Solving for the areas and substituting into
APPLICATION OF NOCTURNAL ELECTROBIOIMPEDANCE VOLUMETRIC ASSESSMENT
the formula for the admittance of segment Yp yield the equation, V, = pb X (LP2 X Y, - [V,/pJ). We prevlously calibrated the value of V, (unpublished data). RESULTS
Electrobioimpedance measurements were obtained on 2 consecutive nights for 4.8to 9.1 hours. Using the aforementioned method of analysis impedance measurements were converted to penile length, cross-sectional area and volume per second. Graphs of penile length, cross-sectional area and volume versus time were construct4 for each study subject (fig. 5). The data were analyzed for the number and duration of erectile events, volume change and relative volume change normalized to the baseline penile volume of each subject at the beginning of the study. These men had a mean of 3.45 erectile events a night that lasted a mean of 17 minutes. Volume changes were expressed as the change in penile volume and the percent change over baseline volume at study onset. Mean volume change was 14.4ml. (mean 213%over baseline). The table summarizes the results in all 10 study subjects. DISCUSSION
Electrobioimpedance may be used for nocturnal assessment of penile length, cross-sectional area and volume. To our knowledge this report represents the first study of penile blood volume changes measured nocturnally in normal men using NEVA technology. An erectile event of at least a mean of 200% volume increase from a nonerect state was noted during nocturnal erectile activity in these subjects. Our results represent 20 nights of volumetric measurements to establish mean baseline values in normal men, and so this technology may be used to study individuals with pathophysiological conditions resulting in erectile dysfunction. In our study changes in impedance were mapped to changes in penile length, cross-sectional area and volume by modeling the penis as an electrical circuit. In our model the penis has compartments representing blood and tissue volume. The compartments are assumed to have Werent resistivities, although each is homogeneous with respect to resistivity. Assuming that the compartments are equivalent to a parallel circuit allowed us to determine penile length, volume and cross-sectional area. The NEVA system provides information in addition to the measurement of penile length, cross-sectional area and volume. It also provides data on the number and duration of
1139
Results No. erectile events Duration h i m . ) Vol. change (ml.) 9E Vol. increase over baseline
No. Pta.
Mean
20 20 20 19
3.45
?
Z 17.0 ? 14.4 Z 213 ?
SD
1.47 11.5 10 2
129 ____
erectile events, and change in volume over baseline per patient. The lightweight NEVA recorder may store up to 3 nights of data, which may then be downloaded to physician computers. In addition, the NEVA device may be worn safely by men with pacemakers. An issue that we addressed was the necessity of 2 nights of monitoring. The apparatus may interfere with normal sleep (the so-called first night effect). Because of its small size and nonconstricting electrodes attached to the penis, the NEVA system achieved excellent acceptance by the men in our study. All study participants stated that the device is easy to use and comfortable enough not to interfere with sleep. An analysis of all sessions showed that all nighttime recordings were comparable, which argues against the first night effect. Future studies of impotent patients or those with borderline impotence are required to confirm this finding. Future use of these data should allow definition of normal values for a wide range of ages in men with no history of erectile dysfunction. Although anatomical variations in penile length, cross-sectional area and volume are to be expected, one may reasonably expect to define normal ranges for the number and duration of erectile events, and fractional change in volume over baseline of these events. With the increase in number and types of noninvasive and invasive therapy available to treat erectile dysfunction, understanding the characteristics of patients without erectile dysfunction will be valuable to identify and quantify deviations from normal erectile behavior. CONCLUSIONS
We describe the use of nocturnal electrobioimpedance to assess penile erectile activity. The NEVA device is small, comfortable to wear and easy to use. It determines the number and duration of erectile events, and the percentage increase of blood volume changes during these events in a noninvasive manner. Our data represent normal erectile function. Future directions of study include comparisons of men with erectile dysfunction, an analysis of the dynamic data provided by the NEVA system, and comparison of electrobioimpedance data to duplex Doppler vascular scanning and conventional nocturnal penile tumescence testing. REFERENCES
FIG. 5. NEVA recorder output includes penile cross-sectional area, length and volume on y-axis plotted as function of time on x-axls.
1. Godec, C. J. and Cass, A. S.: Quantification of erection. J. Urol., 1 2 6 345, 1981. 2. Virag, R., Boulilly, P. and Virag, H.: Dimensions. volume and rigidity of the penis. Fundamental elements in the study of erection and its dysfunctions. Ann. Urol. (Paris),20: 244,1986. 3. Bancroft, J. and Bell, C.: Simultaneous recording of penile diameter and penile arterial pulse during laboratory-based erotic stimulation in normal subjects. J. Psychosom. Res., 29: 303, 1985. 4. Pueschel, S. M., Orson, J. M., Boylin, J. M. and Pezzullo, J . C.: Adolescent development in males with Downs syndrome. Amer. J. Dis. Child., 139: 236, 1985. 5. Shirai, M. and Nakamura, M.: Differential diagnosis of organic and functional impotence by the use of 131-I-human serum albumin. Tohoku J. Exp. Med., 101: 317, 1970. 6. Kim, S. C., Kim, K. B. and Oh, C. H.: Diagnostic value of the radioisotope erection penogram for vasculogenic impotence. J. Urol., 144: 888, 1990. 7. Shirai, M.: Determination of intrapenile blood volume using 99mTc-labeled autologous red blood cells. Tohoku J. Exp. Med.. 120: 377,1976.
1140
APPLICATION OF NOCTURNAL ELECTROBIOIMPEDANCE VOLUMETRIC ASSESSMENT
8 . Zuckier, L. S., Korupolu, G. R., Gladshtenyn, M., Sattenberg, R.,
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