ARTICLES |
Oh, S.Y.; Guy, R.H.
Title Effects of iontophoresis on the electrical properties
of
human skin in vivo
Journal International Journal of Pharmaceutics
124
1
SEP 19
Year 1995
Page 137-142
Address RH Guy
Univ Calif San Francisco
Sch Pharm
Dept Pharm
San Francisco, CA 94143
USA
Serial# 0378-5173
Keys iontophoresis; skin impedance; skin resistance;
transdermal
drug delivery; percutaneous
absorption
EXCISED HUMAN-SKIN; TRANSDERMAL
DELIVERY
Abs. Preliminary measurements have been made of the
effect of
iontophoresis on the electrical
properties;of human skin in
vivo. Skin impedance was
measured as a function of
frequency and as a function
of applied direct (i.e.,
iontophoretic) current.
The resistance of the skin was then
determined from the accumulated
impedance data in the
normal way. After the electrode
chambers were attached to
the forearm,and the pretreatment
resistance had stabilized,
direct current was applied
and the % change from baseline
resistance was determined.
At the end of current passage,
the recovery of resistance
was monitored for up to 4 h.
Current application involved
three current densities
applied for three different
times (combined in such a way
that three consistent amounts
of total charge were
delivered): 10 mu A/cm(2)
for 10, 20 and 50 min; 50 mu
A/cm(2) for 2, 4 and 10
min; and 100 mu A/cm(2) for 1, 2
and 5 min. Current application
caused skin resistance to
drop rapidly (at all currents,
most of the change occurs
within 10 seconds of beginning
the current flow). At all
current levels, the decrease
in skin resistance leveled off
at a value which was dependent
upon current density, but
somewhat independent of
time of current application: 10 mu
A/cm(2)-approx. 45% of pretreatment
value; 50 mu A/cm(2)-
approx. 20% of pretreatment
value; and 100 mu A/cm(2)-
approx. 10% of pretreatment
value. The time required for
recovery of skin resistance
increased with (a) increasing
lime of current application
(at constant current density),
and (b) increasing current
density. It is concluded that
measurements of skin impedance
(and derived values of skin
resistance) in vivo, in
man, can therefore provide direct
electrical evaluation of
the effects of iontophoresis on
the tissue. Such measurements,
we believe, are of vital
importance with respect
to the long-term application of
iontophoresis as a method
of drug delivery.
Oh, S.Y.; Guy, R.H.
Title Effects of iontophoresis on the electrical properties
of
human skin in vivo
Journal International Journal of Pharmaceutics
124
1
SEP 19
Year 1995
Page 137-142
Address RH Guy
Univ Calif San Francisco
Sch Pharm
Dept Pharm
San Francisco, CA 94143
USA
Serial# 0378-5173
Keys iontophoresis; skin impedance; skin resistance;
transdermal
drug delivery; percutaneous
absorption
EXCISED HUMAN-SKIN; TRANSDERMAL
DELIVERY
Abs. Preliminary measurements have been made of the
effect of
iontophoresis on the electrical
properties;of human skin in
vivo. Skin impedance was
measured as a function of
frequency and as a function
of applied direct (i.e.,
iontophoretic) current.
The resistance of the skin was then
determined from the accumulated
impedance data in the
normal way. After the electrode
chambers were attached to
the forearm,and the pretreatment
resistance had stabilized,
direct current was applied
and the % change from baseline
resistance was determined.
At the end of current passage,
the recovery of resistance
was monitored for up to 4 h.
Current application involved
three current densities
applied for three different
times (combined in such a way
that three consistent amounts
of total charge were
delivered): 10 mu A/cm(2)
for 10, 20 and 50 min; 50 mu
A/cm(2) for 2, 4 and 10
min; and 100 mu A/cm(2) for 1, 2
and 5 min. Current application
caused skin resistance to
drop rapidly (at all currents,
most of the change occurs
within 10 seconds of beginning
the current flow). At all
current levels, the decrease
in skin resistance leveled off
at a value which was dependent
upon current density, but
somewhat independent of
time of current application: 10 mu
A/cm(2)-approx. 45% of pretreatment
value; 50 mu A/cm(2)-
approx. 20% of pretreatment
value; and 100 mu A/cm(2)-
approx. 10% of pretreatment
value. The time required for
recovery of skin resistance
increased with (a) increasing
lime of current application
(at constant current density),
and (b) increasing current
density. It is concluded that
measurements of skin impedance
(and derived values of skin
resistance) in vivo, in
man, can therefore provide direct
electrical evaluation of
the effects of iontophoresis on
the tissue. Such measurements,
we believe, are of vital
importance with respect
to the long-term application of
iontophoresis as a method
of drug delivery.
Author - Olmi R
Author - Bini M
Author - Ignesti A
Author - Feroldi P
Author - Spiazzi L
Author - Bodini G
Title - Hyperaemia evaluation in clinical diathermy
by four-
electrode impedance measurements.
- English
- Article
- Olmi
R, Natl Res Council, Iroe, Via Panciatichi 64,
Florence, ITALY
- The
four-electrode electrical impedance measurement
technique is proposed for the evaluation of the hyperaemia
variation in tissues treated by diathermic therapy. An
impedance meter suitable for such measurements is
described, and an electrical model of the heated tissues,
concerning the impedance variation during diathermy and
its relation with hyperaemia, is presented.
The occurrence of the substantial contribution of blood to
the overall transverse impedance is demonstrated by
comparing the experimental results with those arising from
a 2D electrical/thermal model of the treated tissues. A
two-admittance model is proposed to explain the electrical
behaviour of the tissues treated by diathermy. The model
allows us to separate the impedance variation due to the
temperature dependence of tissue conductivity from that
due to the change of tissue blood content.
The results of preliminary measurements of tissue
impedance on healthy volunteers treated by electromagnetic
diathermy are presented and discussed, showing the
feasibility of impedance detection of hyperaemia
variations inside tissues.
Journal - Phys Med Biol 1997 JAN;42(1):251-261
Olthof, C.G.; Jansen, P.G.M.; Devries, J.P.P.; Kouw, P.M.;
Eijsman, L.; Delange, J.J.;
Devries, P.M.J.M.
Title Interstitial fluid volume during cardiac surgery
measured by
means of a non-invasive
conductivity technique
Journal Acta Anaesthesiologica Scandinavica
39
4
MAY
Year 1995
Page 508-512
Address CG Olthof
Free Univ Amsterdam Hosp
Dept Anaesthesiol
POB 7057
1007 MB Amsterdam, Netherlands
Serial# 0001-5172
Keys colloid osmotic pressure; conductivity technique;
coronary
pulmonary bypass; interstitial
fluid volume
CARDIOPULMONARY BYPASS;
WATER; IMPEDANCE; INVITRO
Abs. Fluid accumulation in the interstitium is frequently
found
after cardiac surgery. In
extreme this can lead to
pulmonary and myocardial
oedema. The origin of this
accumulation is not exactly
known and may be twofold. It is
probably a combination of
the noninfectious whole body
inflammatory response and
a change in Starling forces due
to a decrease in colloid
osmotic pressure (COP) which is
caused by the primed extracorporeal
circuit. To study the
changes in interstitial
fluid volume (ISFV) a non-invasive
conductivity technique was
used. The relationship between
temperature and conductivity
was first investigated in
vitro. A linear relationship
was found between conductivity
and different saline solutions
and temperature. From the in
vitro experiments it can
be concluded that temperature
corrected conductivity does
not depend on haematocrit.
After the in vitro experiments
eleven patients undergoing
cardiac surgery were studied.
During the first minutes of
cardiopulmonary bypass (CPB)
a steep significant decrease
in COP to 61.4+/-6.9% (from
19.6+/-1.1 to 12.0+/-1.2 mmHg),
and a rise in ISFV to 105.5+/-2.8%
(from 12.3+/-1.4 mS to
14.0+/-1.3 mS) was noticed.
After this decrease COP
increased significantly,
till the end of the operation, but
did not reach the pre-operative
level. An increase in ISFV
was noticed till the rewarming
point. After this point no
significant change in ISFV
was noticed. Furthermore, a
significant correlation
was found between the fluid balance
and the ISFV increase at
the start, at the end of CPB, and
at the end of the operation.
From the in vivo experiments
it can be concluded that
the non-invasive conductivity
technique in a valuable
acquisition for the investigation
of ISFV changes during cardiac
surgery. It shows that the
changes in ISFV are mainly
disturbed during the first part
of CPB probably due to a
marked decrease in COP.
Author - ORourke MF
Author - Gallagher DE
Title - Pulse wave analysis.
- English
- Article
- ORourke MF, Univ
New S Wales, St Vincents Hosp, Med
Professor
Unit, Sydney, NSW 2010, AUSTRALIA
- Pulse wave analysis
in historical times Interpretation of
the arterial
pulse has been an important part of the
medical
examination from ancient times. Graphic methods
for clinical
pulse wave recording were introduced by Marey
in Paris
and by Mahomed in London last century. Mahomed
showed
how such recordings could be used to detect
asymptomatic
hypertension, and used them to chart the
natural
history of essential hypertension and to
distinguish
between this condition and chronic nephritis.
Interest
in arterial pulse analysis, as applied by
Mahomed,
lapsed with the introduction of the cuff
sphygmomanometer
100 years ago.
Modern
pulse wave analysis Analysis of the arterial pulse
is now
regaining favour as limitations of the cuff
sphygmomanometer
are better recognized (including the
ability
only to measure extremes of the pulse in the
brachial
artery). In addition, high-fidelity tonometers
have been
introduced for very accurate, non-invasive
measurement
of arterial pulse contour, and there is now a
better
understanding of arterial hemodynamics, and
appreciation
of disease and aging effects in humans. It is
now possible
to record the pulse wave accurately in the
radial
or carotid artery, to synthesize the ascending
aortic
pulse waveform, to identify systolic and diastolic
periods
and to generate indices of ventricular-vascular
interaction
previously only possible with invasive
arterial
catheterization. Pressure pulse wave analysis now
permits
more accurate diagnosis and more logical therapy
than was
ever possible in the past.
Journal - J Hypertension 1996 DEC;14:S147-S157
Osei, K.; Schuster, D.P.
Title Metabolic characteristics of African descendants:
A
comparative study of African-Americans
and Ghanaian
immigrants using minimal
model analysis
Journal Diabetologia
38
9
SEP
Year 1995
Page 1103-1109
Address K Osei
Diabet & Endocrine Clin
485 Mccampbell Hall
1581 Dodd Dr
Columbus, OH 43210 USA
Serial# 0012-186X
Keys glucose regulation; insulin; C-peptide; African
descendants
IMPAIRED GLUCOSE-TOLERANCE;
TYPE-2 DIABETES-MELLITUS; INSULIN
SENSITIVITY; BIOELECTRICAL
IMPEDANCE; PLASMA-INSULIN; SERUM-
INSULIN; PREVALENCE; POPULATION;
RESISTANCE; ADULTS
Abs. We have previously demonstrated that glucose-tolerant
American blacks manifest
significantly higher insulin
concentrations and a lower
insulin sensitivity than native
African blacks who reside
in their respective countries. It
is, however, unknown whether
the serum glucose, beta-cell
function and insulin sensitivity
are different in native
Africans and African-Americans
who reside in the same
environments. We have studied
68 healthy American blacks
and age- and weight-matched
30 African blacks recently
immigrated from Ghana residing
in Franklin County, Ohio,
USA. Each subject underwent
a standard oral glucose
tolerance test to determine
glucose tolerance status.
Insulin sensitivity index
(Si) and glucose effectiveness
(Sg) were measured by the
insulin-modified, frequently-
sampled intravenous glucose
tolerance test. The body
composition variables were
measured by the bioelectrical
impedance analyser and body
fat distribution pattern by the
waist-hip ratio. The clinical
characteristics were
identical in the African-American
and the African blacks;
the mean fasting serum glucose,
insulin and C-peptide
levels were not different.
Following the oral and
intravenous glucose administration,
the mean peak and
incremental areas of serum
glucose, insulin and C-peptide
were not different in the
two groups. The mean Si (3.1 +/-
0.7 vs 2.4 +/- 0.3 x 10(-4)
. (min/mu U . l(-1))(-1) and Sg
(2.5 +/- 0.3 vs 2.7 +/-
0.2 x 10(-2) . min(-1)) were not
significantly different
in the American and African blacks,
respectively. In summary,
the metabolic parameters measured
in the American blacks and
recent African immigrants were
identical. We speculate
that, in contrast to the indigenous
Africans who reside in their
native countries, migration to
the western world results
in rapid ''adaptation'' in
glucoregulation, beta-cell
function and insulin sensitivity,
similar to those of American
blacks.
Osei, K.; Schuster, D.P.
Title Metabolic characteristics of African descendants:
A
comparative study of African-Americans
and Ghanaian
immigrants using minimal
model analysis
Journal Diabetologia
38
9
SEP
Year 1995
Page 1103-1109
Address K Osei
Diabet & Endocrine Clin
485 Mccampbell Hall
1581 Dodd Dr
Columbus, OH 43210 USA
Serial# 0012-186X
Keys glucose regulation; insulin; C-peptide; African
descendants
IMPAIRED GLUCOSE-TOLERANCE;
TYPE-2 DIABETES-MELLITUS; INSULIN
SENSITIVITY; BIOELECTRICAL
IMPEDANCE; PLASMA-INSULIN; SERUM-
INSULIN; PREVALENCE; POPULATION;
RESISTANCE; ADULTS
Abs. We have previously demonstrated that glucose-tolerant
American blacks manifest
significantly higher insulin
concentrations and a lower
insulin sensitivity than native
African blacks who reside
in their respective countries. It
is, however, unknown whether
the serum glucose, beta-cell
function and insulin sensitivity
are different in native
Africans and African-Americans
who reside in the same
environments. We have studied
68 healthy American blacks
and age- and weight-matched
30 African blacks recently
immigrated from Ghana residing
in Franklin County, Ohio,
USA. Each subject underwent
a standard oral glucose
tolerance test to determine
glucose tolerance status.
Insulin sensitivity index
(Si) and glucose effectiveness
(Sg) were measured by the
insulin-modified, frequently-
sampled intravenous glucose
tolerance test. The body
composition variables were
measured by the bioelectrical
impedance analyser and body
fat distribution pattern by the
waist-hip ratio. The clinical
characteristics were
identical in the African-American
and the African blacks;
the mean fasting serum glucose,
insulin and C-peptide
levels were not different.
Following the oral and
intravenous glucose administration,
the mean peak and
incremental areas of serum
glucose, insulin and C-peptide
were not different in the
two groups. The mean Si (3.1 +/-
0.7 vs 2.4 +/- 0.3 x 10(-4)
. (min/mu U . l(-1))(-1) and Sg
(2.5 +/- 0.3 vs 2.7 +/-
0.2 x 10(-2) . min(-1)) were not
significantly different
in the American and African blacks,
respectively. In summary,
the metabolic parameters measured
in the American blacks and
recent African immigrants were
identical. We speculate
that, in contrast to the indigenous
Africans who reside in their
native countries, migration to
the western world results
in rapid ''adaptation'' in
glucoregulation, beta-cell
function and insulin sensitivity,
similar to those of American
blacks.
Osypka, M.; Gersing, E.
Title Tissue impedance spectra and the appropriate frequencies
for
EIT
Journal Physiological Measurement
16
Suppl. 3A
AUG
Year 1995
Page A49-A55
Address M Osypka
Univ Gottingen
Zentrum Physiol & Pathophysiol
Humboldtallee 23
D-37073 Gottingen, Germany
Serial# 0967-3334
Abs. The complex impedance of each kind of tissue
depends on the
frequency in a characteristic
manner. Using appropriate
measuring frequencies, EIT
can provide a differentiating
insight into the interior
of a body. Therefore, a knowledge
of the tissue impedance
spectra of various organs is
essential for choosing the
appropriate frequencies.
The impedance data of various
tissues in different states
(normal, altered by ischaemia
or cancerous) show that the
characterizing differences
occur at frequencies below 500
kHz and down to a few kilohertz.
Moreover, the spectra show
that the imaginary component of
impedance essentially contributes
to the characterization
of the kind and state of
a tissue, even though the
dissipative and reactive
components are connected by the
Kramers-Kronig relations.
The course of a dispersion and
the position in the frequency
range, determined by the
distribution of the time
constants in the tissue, are
clearly presented by the
imaginary component.
Tomographic imaging combined
with spectroscopy for tissue
characterization requires
a frequency range of at least 10-
800 kHz. The upper frequency
limit depends on the fluid
content of the tissue under
investigation.
Osypka, M.; Gersing, E.
Title Tissue impedance spectra and the appropriate frequencies
for
EIT
Journal Physiological Measurement
16
Suppl. 3A
AUG
Year 1995
Page A49-A55
Address M Osypka
Univ Gottingen
Zentrum Physiol & Pathophysiol
Humboldtallee 23
D-37073 Gottingen, Germany
Serial# 0967-3334
Abs. The complex impedance of each kind of tissue
depends on the
frequency in a characteristic
manner. Using appropriate
measuring frequencies, EIT
can provide a differentiating
insight into the interior
of a body. Therefore, a knowledge
of the tissue impedance
spectra of various organs is
essential for choosing the
appropriate frequencies.
The impedance data of various
tissues in different states
(normal, altered by ischaemia
or cancerous) show that the
characterizing differences
occur at frequencies below 500
kHz and down to a few kilohertz.
Moreover, the spectra show
that the imaginary component of
impedance essentially contributes
to the characterization
of the kind and state of
a tissue, even though the
dissipative and reactive
components are connected by the
Kramers-Kronig relations.
The course of a dispersion and
the position in the frequency
range, determined by the
distribution of the time
constants in the tissue, are
clearly presented by the
imaginary component.
Tomographic imaging combined
with spectroscopy for tissue
characterization requires
a frequency range of at least 10-
800 kHz. The upper frequency
limit depends on the fluid
content of the tissue under
investigation.
Ouzounian, J.G.; Masaki, D.I.; Abboud, T.K.; Greenspoon, J.S.
TI Systemic vascular resistance index determined by thoracic
electrical bioimpedance predicts the risk for maternal
hypotension during regional anesthesia for cesarean delivery
SO American Journal of Obstetrics and Gynecology
VL 174
IS 3
DA MAR
YR 1996
PG 1019-1025
AF JG Ouzounian
Univ So Calif
Los Angeles Cty Med Ctr
Sch Med
Dept Obstet & Gynecol
Div Maternal & Fetal Med
Los Angeles, CA 90033 USA
SN 0002-9378
KW systemic vascular resistance index; maternal hypotension;
bioimpedance
CARDIAC STROKE VOLUME; IMPEDANCE CARDIOGRAPHY; EPIDURAL-
ANESTHESIA; THERMODILUTION; SECTION; OUTPUT; PREGNANCY;
FLOW
NO OBJECTIVE: Our purpose was to evaluate the predictive value
of the baseline systemic vascular resistance index for
the
development of maternal hypotension during regional
anesthesia for cesarean delivery.
STUDY DESIGN: Patients receiving a standardized spinal
or
epidural anesthetic for nonemergency cesarean delivery
were
studied prospectively. Hemodynamic data were obtained
noninvasively with an NCCOM-3 cardiac output monitor
(Borned Medical Manufacturing, Irvine, Calif.), which
uses
thoracic electrical bioimpedance to estimate stroke volume
and cardiac output. Measurements obtained were indexed
to
body surface area. The systemic vascular resistance index
was calculated from mean arterial pressure and thoracic
electrical bioimpedance-derived cardiac index. Hemodynamic
data obtained were analyzed to identify statistically
significant predictors of maternal hypotension.
RESULTS: Maternal hypotension occurred in 24 of 42 (57%)
patients studied. The incidence of hypotension did not
differ between the types of anesthesia: spinal 17 of 27
(62%) versus epidural 7 of 15 (47%, p = 0.48). The mean
interval to the onset of hypotension was 12.2 minutes
(SD
2.2 minutes, range 2 to 24 minutes). Mean (SD) baseline
maternal systolic blood pressure was higher in patients
who
had hypotension (145 torr [4]) than those who did not
(129
torr [4], p = 0.01). The mean (SD) baseline systemic
vascular resistance index was higher in patients who had
hypotension (633 [SD 36] dyne . cm . sec(-5)/m(2)) than
those who did not (454 [SD 29] dyne . cm . sec(-5)/m(2);
p
= 0.001). With receiver-operator characteristic curves,
a
baseline systemic vascular resistance index of 500 had
a
sensitivity of 83%, a specificity of 78%, a positive
predictive value of 83%, and a negative predictive value
of
78% for maternal hypotension (odds ratio 17.5, 95%
confidence interval 3.1 to 109.4). A baseline systolic
blood pressure of 140 torr had a sensitivity and
specificity of 42% and 72%, respectively (odds ratio 1.9,
95% confidence interval 0.4 to 8.8).
CONCLUSIONS: Baseline systemic vascular resistance index
obtained by noninvasive cardiac output monitoring with
thoracic electrical bioimpedance and systolic blood
pressure are useful to predict the risk for maternal
hypotension with regional anesthesia. Patients with
increased baseline systemic vascular resistance index
or
systolic blood pressure are at increased risk for
hypotension.