Evaluation of the accuracy of a new ultrasonic fetal heart rate monitor NIELS
H.
LAUERSEN,
M.D.
HOWARD
M.
HOCHBERG,
M.D.
MICHAEL
E.
D.
B.S.E.E.
GEORGE,
New York, New York, and Cranbury,
New Jersey
An indirect Doppler fetal monitoring system has been developed and ualidated by computer comparison of simultaneous fetal heart rate (FHR) with Doppler and scalp ECG of high-risk patients during labor. The dz;fference in measurement of FHR averaged 0.3 b.p.m., and 93 per cent of the Doppler FHR measures were within 10 b.p.m. of the ECG FHR. If interinstrument dsfference is discounted, 96 per cent were within IO b.p.m. All types of decelerations and variability were well a@roximated. Doppler FHR from the instrument described may be relied upon as valid clinical information and may be obtained from over 90 per cent of labor patients with 93 per cent accuracy.
THE RECENT increased interest in fetal heart rate monitoring (FM) for ascertaining intrapartum fetal well being and improving fetal outcome has produced a need for simplified and improved FM techniques. The majority of the published studies described a direct fetal electrocardiogram (ECG) monitoring system. Although the direct or internal FM scalp electrode technique may be highly accurate and may entail little patient restriction, it has limitations. Direct monitoring can be applied only after a cervical dilatation of at least 2 to 3 cm. and after rupture of the fetal membranes. The application is somewhat difficult and it requires some skill to correctly attach the electrode, which, furthermore, usually must be applied by a physician. Recently there has been some concern about an increased incidence of postpartum endometritis among patients who have been monitored internally, compared to nonmonitored patients.‘, * There have been instances of perforation of the fetal fontanelle, bleeding, and infection associated with the use of fetal scalp
electrodes3, 4, 6 It is common experience that up to 2.0 electrodes per case may often be required because of electrode misplacement or dislodgement.’ Electrodes tend to loosen, especially after vaginal examinations and excessive patient motion. Patient agitation may cause interference and produce a poor record. Unusual QRS wave forms may cause erratic counting if care is not taken, and improper placement of the electrode may produce incorrect counting. The maternal ECG has been obtained and the maternal heart rate recorded instead of the fetal heart rate (FHR) in and fetal heart patients with fetal death. ‘-lo Maternal rate have been added together, producing a spurious tachycardia. ‘i Totally spurious results have also been recorded.” Therefore, there seems to be a need for a reliable noninvasive external or indirect fetal monitoring technique that could be applied in premature labor, or when a patient is admitted in early labor, before rupture of the membranes. It can be applied by the nursing staff, as soon as a patient is admitted to the delivery suite, without the presence of a physician. Although indirect FM’s are commercially available, they are regarded as screening tools,‘3 perhaps because they may produce a poor yield of usable data, or some erroneous data,” and they may be difficult to operate. Emphasis was therefore directed toward the development of a more practical indirect fetal monitoring system by utilizing an improved and more sensitive Doppler ultrasonic technique. This report describes
From the Department of Obstetrics and Gynecology, The New York Hospital-Cornell Medical Center, and Roche Medical Electronics, Inc. Received
for publication
Revised
February
Acce$ied &p&t O&&&s
February
September
12, 1975.
9, 1975. 24, 1976.
requests: Niels H. Lauersen, M.D., Department and Gynecology, The New York 11 Medical Center, 530 E. 70th St., New 10021.
of
1125
1126
Lauersen,
Hochberg,
and George
Fig. 1. Oscilloscope photograph of Dopper and ECG from the fetal heart. Three components are clearly seen. One immediately precedes the QRS and is synchronous with the fetal P(W), most likeh representing atria1 contraction. Another immediately follows the QRS (III), most likely representing the closure of the A-V valves. A third (03) appears before atria1 contraction, most likely representing A-V valve opening. 04 and III remain constantly related to each other. 03 is ah&et constantlv related to DZ and thus appears more centered as the rate slows. As the rate slows it mav confuse Doppler counting circuits which do not account for this component. the development and validation of an external Doppler FHR monitor designed to provide results approaching the accuracy of the FHR by ECG. After this system was developed a study was designed to test the accuracy and reliability of the FHR data on high-risk patients admitted in labor at the New York Hospital-Cornell Medical Center. These patients were monitored in the clinical environment as part of their usual care. Previous publications report only visual observation of simultaneous Doppler FHR and scalp ECG FHR, without rigorous analysis of the accuracy.r3, ” This report describes the computer comparison of the FHR produced by Doppler with that produced by simultaneously obtained fetal scalp EGG.
Development of the Doppler ultrasonic FHR monitor Distinct Doppler ultrasound (DUS) signals are obtainable from virtually all fetuses after the second trimester, and are easily obtainable from almost all patients in labor, rendering them particularly suitable for monitoring FHR.‘“-I7 Several commercial monitors utilize the DUS principle but they may show the
distressing inability to record tachycardias of over 160 to 180 b.p.m., and a peculiar tendency to count at double the FHR at lower rates (especially rates of 90 b.p.m.).” When the signal becomes weak, as during contraction, a false deceleration or indication of artifact (e.g., pen-lift) may occur. The records may be marked by prolonged periods of unphysiologic “jitter” and unphysiologic baseline variability. In general they are regarded and promoted as screening instruments used to decide when to resort to internal methods.‘” The physiologic properties of the Doppler signal were explored to help understand these problems. The over-all philosophy was to design a Doppler system which would be easy to use, would provide a fetal heart motion Doppler signal of adequate strength and clarity for automatic counting, and which would largely exclude Doppler from other moving structures. ‘l‘he system should also allow for relative lateral motion of transducer and fetal heart. A system was designed which would enhance ultrasonic rellections from certain distances from the transducer and reduce those from others, in essence accepting the ultrasonic reflections from a plane parallel to the abdomen. ‘This
Volume Number
125 8
Accuracy of ultrasonic FHR monitor
1127
Fig. 2. Comparability of beat-to-beat vs. three-beat average for FHR display. The variability patterns on the FHR display are composed of the sum of the “beat-to-beat” changes of up to 15 to 20 heart beats. Ultrasonic records tend to show increasing apparent, but artifactual, beat-to-beat change (“jitter”) with decreasing signal amplitude, this “jitter” tending to totally obscure the long-term variability patterns. Three-beat averaging destroys the “jitter” and retains the variability. This illustration shows there is essentiallv no visible difference between a FHR processed by beat-to-beat or three-beat average, even with thk ECG.
would allow the operator to “range in” on the best sounding fetal heart Doppler to optimize signal clarity. This “depth ranging” capability is accomplished by superimposing a digital code on the transmitted 2 megaHertz continuous ultrasonic wave and awaiting return of the code. As the ultrasonic propagation time through tissue is known, the expected time from various distances is known. By the use of correlation techniques, the system accepts only ultrasonic reflections at the distances selected by the operator. The correlation technique also enhances the selected reflection threefold and reduces reflections from other distances by 30-fold. By selecting the depth which produces the loudest, clearest, fetal heart Doppler, all returns from this area are so enhanced and other Doppler sources are largely excluded. The correlation also allows use of lower power because of the electronic signal enhancement. Continuous wave ultrasound allows lower power ( were cyclic. This might produce spurious beat-to-beat changes if the system were to shift from one component to another as they cyclically changed. These data clearly indicated possible solutions. The ultrasonic spectrographs and filter data were used to choosy a Doppler domain where the signal-to-noise is optimized and fetal motion, abdominal motion Doppler, and maternal arterial Doppler are minimized. The system adapts to the changes in number of components to avoid counting the A-V valve opening as another beat during bradycardia, and further adapts to follow tachycardias. The system adapts rapidly to
changes in signal amplitude. It contains a short-term memory to help determine where a potentially weak signal might be and focus the systems attention at this point. This circuit also helps the system lock onto one Doppler component and not shift until another becomes clearly predominant, helping lo prevent spurious beat-to-beat “jitter.” The lolv-signal false-deceleration problem was also approached by finding the lveakest DUS signal reliably countable and barring data display if the signal dropped below this level for at least 5 seconds. For this system, this level is eight to 40 times smaller than typical DUS in labor and has a signal-to-background amplitude of about 1.5 LO I. Further study of DUS beat-to-bear FHR display showed apparent but artifactual beat-to-beat changes (“jitter”) as the Doppler weakened because the signal became less distinct and thus it was more difficult t.o trigger on the exact same point with each beat. A running three-beat average of the heart rate (in beats per minute) allowed retention of underlying variabilit! patterns and prevented their destruction by the “jitter” of weakening signal. In no way does this change the variability patterns, as they are usually composed of over 10 heart beats (Fig. 2). The causes of false artifact indication were studied by playing tape-recorded DUS data into a fetal monitor. designed to circumvent the above problems.
\‘oIume Number
125 X
Table
Accuracy
I. Clinical
data
and
record
for
E-5 (Fig.
Total time V/S monitoring
Monitoring abnormalities
monitor&g
Computer-analvzed cases: E-l 1 1. Poor progress labor 2. Cephalopelvic disproportion 3. Meconium
FHR
monitor
1129
evaluation
Indications CU.\? ‘VO
of ultrasonic
of
Occasional small, decelerations
early
outcome
2 hr., 24 min.
Cesarean section, Apgar 9. 10
90% usable FHR
2 hr.
Cesarean section, nuchal cord, Apgar 3, 10
100% usable FHR
Doppler
1. Premature rupture of membranes 2. Pitocin induction 3. Meconium
Severe variable erations
E-7 (Fig. 5)
1. 2. 3. 4. 5.
None
3% hr.
Cesarean section, Apgar 6. 8
8!1% usable FHR
Doppler
E-13
1. Cephalopelvic disproportion 2. Meconium staining
Variable decelerations, long periods of bradycardia
3 hr.
Cesarean section, Apgar 9. 10
90% usable FHR
Doppler
E-15
1. Post maturity 2. Prostaglandin induction
None
11 hr., 40 min.
3,260 Cm. fetus, Apgar 9, 10
98% usable FHR
Doppler
4)
Pre-eclampsia Primigravida Age 32 Pitocin induction Failure to progress
decel-
Doppler FHR record ezkzluation
E2
Doppler
E-37
1. Postmaturity 2. Induction 3. Failure to progress
Rare shallow decelerations
10 hr.
Cesarean section, meconium, cord around neck, Apgar 7 at 5 min.
968 usable FHR
Doppler
E-38 (Fig. 6)
1. Premature rupture of membranes 2. Induction 3. Relative CPD 4. Failure to progress
Rare variable decelerations
10% hr.
Cesarean section, Apgar 9, 10
95%’ usable FHR
Doppler
E-41
1. Gravida 4 2. Previous cesarean Sections X2 3. Previous colostomy 4. Poor prenatal care .i. Anemia-hematocrit 29% 6. Oxytocin induction
Rare variable decelerations
45 min.
Low outlet forceps, light meconiumstained fluid, Apgar 9, 10
Only 30 min. of record available for review; 85% usable Doppler FHR
M. c.
Rh Negative
Rare
75 min.
Apgar
9 1% usable FHR
Doppler
S.J.
1. Pre-eclampsia 2. Meconium 3. Cephalopelvic disproportion 4. Failure to progress
Rare variables
1% hr.
Cesarean section, 3.380 Gm. female, Apgar 7, 9
96%’ usable FHR
Doppler
M. N.
Postmaturity
Accelerations 190 b.p.m.
8 hr., 20 min
Apgar
90% usable FHR
Doppler
The
resultant
which the
phases
computed beat-to-beat
dominant
the
*PDP 11145, sachusetts.
were
entered
into
FHR
for
interval
change
component
Digital
decelerations
each
between varied
Equipment
from
intervals. time
Corp.,
to
the
a computer,* as well
as
counting
artifactual,
to time
and
was responsible lift) and “jitter” These to be quite
might
component,
pre-
Mas-
9, 10
circuits
predominant
The
Maynard,
9. 10
sudden
studies small,
suddenly producing
“beat-to-beat” for for also
shift
to a newly
an apparent, change.
This
many “artifact indications” no apparent reason. showed
usually
the
less than
beat-to-beat 5 b.p.m.
but change (penchanges
Even
in the
130
Lauersen,
Hochberg,
and George
Fig. 4. Simultaneous beat-to-beat ECG and Doppler FHR variable decelerations. The upper record is derived Doppler. Rates from 90 to 180 b.p.m. are well represented. well followed by the Doppler-derived FHR.
records showing accurate representation from beat-to-beat ECC. the lower Severe decelerations and tat-hvcardia
Fig. 5. Simultaneous pre-eclamptic (top) shows
steepest b.p.m.
variable Periods
beat-to-beat ECG and Doppler FHR showing limited variability In both. patient in labor was treated with large doses of MgSO,. The beat-to-heat ECG loss of variability, well represented by the Doppler-derived FHR (bottom).
deceleration, of
severe
it rarelv
interference
pler from excessive fetal or patient the transducer, were characterized beat-to-beat of 25 b.p.m. unphysiologic
changes
of at least
exceeded with
motion, by many
25 b.p.m.
Serial
fetal
10 Dop-
of
The system 25 b.p.m.
or moving sequential
(because
changes
displayed.
or more were chosen as representing data, with the recognition that the! might represent arrhythmias. A circuit was added to check for discrepancies of over 25 b.p.m. in beat-to-beat FHR changes.
short
allows before
each
skip
interval).
physiologic information interference to prevent resulting
produced this
subsequent
range, because
This FHR
for up LO two sequential it indicates the data are
During If
of fr~ml XC’
a~ least time intervals
the
one
long
last
valid
are
out
the system bars displa\ it was most likelv derived
cha11ges
erratic and
one
FI-IR of ot
is the
rh
H.
LAUERSEN,
M.D.
HOWARD
M.
HOCHBERG,
M.D.
MICHAEL
E.
D.
B.S.E.E.
GEORGE,
New York, New York, and Cranbury,
New Jersey
An indirect Doppler fetal monitoring system has been developed and ualidated by computer comparison of simultaneous fetal heart rate (FHR) with Doppler and scalp ECG of high-risk patients during labor. The dz;fference in measurement of FHR averaged 0.3 b.p.m., and 93 per cent of the Doppler FHR measures were within 10 b.p.m. of the ECG FHR. If interinstrument dsfference is discounted, 96 per cent were within IO b.p.m. All types of decelerations and variability were well a@roximated. Doppler FHR from the instrument described may be relied upon as valid clinical information and may be obtained from over 90 per cent of labor patients with 93 per cent accuracy.
THE RECENT increased interest in fetal heart rate monitoring (FM) for ascertaining intrapartum fetal well being and improving fetal outcome has produced a need for simplified and improved FM techniques. The majority of the published studies described a direct fetal electrocardiogram (ECG) monitoring system. Although the direct or internal FM scalp electrode technique may be highly accurate and may entail little patient restriction, it has limitations. Direct monitoring can be applied only after a cervical dilatation of at least 2 to 3 cm. and after rupture of the fetal membranes. The application is somewhat difficult and it requires some skill to correctly attach the electrode, which, furthermore, usually must be applied by a physician. Recently there has been some concern about an increased incidence of postpartum endometritis among patients who have been monitored internally, compared to nonmonitored patients.‘, * There have been instances of perforation of the fetal fontanelle, bleeding, and infection associated with the use of fetal scalp
electrodes3, 4, 6 It is common experience that up to 2.0 electrodes per case may often be required because of electrode misplacement or dislodgement.’ Electrodes tend to loosen, especially after vaginal examinations and excessive patient motion. Patient agitation may cause interference and produce a poor record. Unusual QRS wave forms may cause erratic counting if care is not taken, and improper placement of the electrode may produce incorrect counting. The maternal ECG has been obtained and the maternal heart rate recorded instead of the fetal heart rate (FHR) in and fetal heart patients with fetal death. ‘-lo Maternal rate have been added together, producing a spurious tachycardia. ‘i Totally spurious results have also been recorded.” Therefore, there seems to be a need for a reliable noninvasive external or indirect fetal monitoring technique that could be applied in premature labor, or when a patient is admitted in early labor, before rupture of the membranes. It can be applied by the nursing staff, as soon as a patient is admitted to the delivery suite, without the presence of a physician. Although indirect FM’s are commercially available, they are regarded as screening tools,‘3 perhaps because they may produce a poor yield of usable data, or some erroneous data,” and they may be difficult to operate. Emphasis was therefore directed toward the development of a more practical indirect fetal monitoring system by utilizing an improved and more sensitive Doppler ultrasonic technique. This report describes
From the Department of Obstetrics and Gynecology, The New York Hospital-Cornell Medical Center, and Roche Medical Electronics, Inc. Received
for publication
Revised
February
Acce$ied &p&t O&&&s
February
September
12, 1975.
9, 1975. 24, 1976.
requests: Niels H. Lauersen, M.D., Department and Gynecology, The New York 11 Medical Center, 530 E. 70th St., New 10021.
of
1125
1126
Lauersen,
Hochberg,
and George
Fig. 1. Oscilloscope photograph of Dopper and ECG from the fetal heart. Three components are clearly seen. One immediately precedes the QRS and is synchronous with the fetal P(W), most likeh representing atria1 contraction. Another immediately follows the QRS (III), most likely representing the closure of the A-V valves. A third (03) appears before atria1 contraction, most likely representing A-V valve opening. 04 and III remain constantly related to each other. 03 is ah&et constantlv related to DZ and thus appears more centered as the rate slows. As the rate slows it mav confuse Doppler counting circuits which do not account for this component. the development and validation of an external Doppler FHR monitor designed to provide results approaching the accuracy of the FHR by ECG. After this system was developed a study was designed to test the accuracy and reliability of the FHR data on high-risk patients admitted in labor at the New York Hospital-Cornell Medical Center. These patients were monitored in the clinical environment as part of their usual care. Previous publications report only visual observation of simultaneous Doppler FHR and scalp ECG FHR, without rigorous analysis of the accuracy.r3, ” This report describes the computer comparison of the FHR produced by Doppler with that produced by simultaneously obtained fetal scalp EGG.
Development of the Doppler ultrasonic FHR monitor Distinct Doppler ultrasound (DUS) signals are obtainable from virtually all fetuses after the second trimester, and are easily obtainable from almost all patients in labor, rendering them particularly suitable for monitoring FHR.‘“-I7 Several commercial monitors utilize the DUS principle but they may show the
distressing inability to record tachycardias of over 160 to 180 b.p.m., and a peculiar tendency to count at double the FHR at lower rates (especially rates of 90 b.p.m.).” When the signal becomes weak, as during contraction, a false deceleration or indication of artifact (e.g., pen-lift) may occur. The records may be marked by prolonged periods of unphysiologic “jitter” and unphysiologic baseline variability. In general they are regarded and promoted as screening instruments used to decide when to resort to internal methods.‘” The physiologic properties of the Doppler signal were explored to help understand these problems. The over-all philosophy was to design a Doppler system which would be easy to use, would provide a fetal heart motion Doppler signal of adequate strength and clarity for automatic counting, and which would largely exclude Doppler from other moving structures. ‘l‘he system should also allow for relative lateral motion of transducer and fetal heart. A system was designed which would enhance ultrasonic rellections from certain distances from the transducer and reduce those from others, in essence accepting the ultrasonic reflections from a plane parallel to the abdomen. ‘This
Volume Number
125 8
Accuracy of ultrasonic FHR monitor
1127
Fig. 2. Comparability of beat-to-beat vs. three-beat average for FHR display. The variability patterns on the FHR display are composed of the sum of the “beat-to-beat” changes of up to 15 to 20 heart beats. Ultrasonic records tend to show increasing apparent, but artifactual, beat-to-beat change (“jitter”) with decreasing signal amplitude, this “jitter” tending to totally obscure the long-term variability patterns. Three-beat averaging destroys the “jitter” and retains the variability. This illustration shows there is essentiallv no visible difference between a FHR processed by beat-to-beat or three-beat average, even with thk ECG.
would allow the operator to “range in” on the best sounding fetal heart Doppler to optimize signal clarity. This “depth ranging” capability is accomplished by superimposing a digital code on the transmitted 2 megaHertz continuous ultrasonic wave and awaiting return of the code. As the ultrasonic propagation time through tissue is known, the expected time from various distances is known. By the use of correlation techniques, the system accepts only ultrasonic reflections at the distances selected by the operator. The correlation technique also enhances the selected reflection threefold and reduces reflections from other distances by 30-fold. By selecting the depth which produces the loudest, clearest, fetal heart Doppler, all returns from this area are so enhanced and other Doppler sources are largely excluded. The correlation also allows use of lower power because of the electronic signal enhancement. Continuous wave ultrasound allows lower power ( were cyclic. This might produce spurious beat-to-beat changes if the system were to shift from one component to another as they cyclically changed. These data clearly indicated possible solutions. The ultrasonic spectrographs and filter data were used to choosy a Doppler domain where the signal-to-noise is optimized and fetal motion, abdominal motion Doppler, and maternal arterial Doppler are minimized. The system adapts to the changes in number of components to avoid counting the A-V valve opening as another beat during bradycardia, and further adapts to follow tachycardias. The system adapts rapidly to
changes in signal amplitude. It contains a short-term memory to help determine where a potentially weak signal might be and focus the systems attention at this point. This circuit also helps the system lock onto one Doppler component and not shift until another becomes clearly predominant, helping lo prevent spurious beat-to-beat “jitter.” The lolv-signal false-deceleration problem was also approached by finding the lveakest DUS signal reliably countable and barring data display if the signal dropped below this level for at least 5 seconds. For this system, this level is eight to 40 times smaller than typical DUS in labor and has a signal-to-background amplitude of about 1.5 LO I. Further study of DUS beat-to-bear FHR display showed apparent but artifactual beat-to-beat changes (“jitter”) as the Doppler weakened because the signal became less distinct and thus it was more difficult t.o trigger on the exact same point with each beat. A running three-beat average of the heart rate (in beats per minute) allowed retention of underlying variabilit! patterns and prevented their destruction by the “jitter” of weakening signal. In no way does this change the variability patterns, as they are usually composed of over 10 heart beats (Fig. 2). The causes of false artifact indication were studied by playing tape-recorded DUS data into a fetal monitor. designed to circumvent the above problems.
\‘oIume Number
125 X
Table
Accuracy
I. Clinical
data
and
record
for
E-5 (Fig.
Total time V/S monitoring
Monitoring abnormalities
monitor&g
Computer-analvzed cases: E-l 1 1. Poor progress labor 2. Cephalopelvic disproportion 3. Meconium
FHR
monitor
1129
evaluation
Indications CU.\? ‘VO
of ultrasonic
of
Occasional small, decelerations
early
outcome
2 hr., 24 min.
Cesarean section, Apgar 9. 10
90% usable FHR
2 hr.
Cesarean section, nuchal cord, Apgar 3, 10
100% usable FHR
Doppler
1. Premature rupture of membranes 2. Pitocin induction 3. Meconium
Severe variable erations
E-7 (Fig. 5)
1. 2. 3. 4. 5.
None
3% hr.
Cesarean section, Apgar 6. 8
8!1% usable FHR
Doppler
E-13
1. Cephalopelvic disproportion 2. Meconium staining
Variable decelerations, long periods of bradycardia
3 hr.
Cesarean section, Apgar 9. 10
90% usable FHR
Doppler
E-15
1. Post maturity 2. Prostaglandin induction
None
11 hr., 40 min.
3,260 Cm. fetus, Apgar 9, 10
98% usable FHR
Doppler
4)
Pre-eclampsia Primigravida Age 32 Pitocin induction Failure to progress
decel-
Doppler FHR record ezkzluation
E2
Doppler
E-37
1. Postmaturity 2. Induction 3. Failure to progress
Rare shallow decelerations
10 hr.
Cesarean section, meconium, cord around neck, Apgar 7 at 5 min.
968 usable FHR
Doppler
E-38 (Fig. 6)
1. Premature rupture of membranes 2. Induction 3. Relative CPD 4. Failure to progress
Rare variable decelerations
10% hr.
Cesarean section, Apgar 9, 10
95%’ usable FHR
Doppler
E-41
1. Gravida 4 2. Previous cesarean Sections X2 3. Previous colostomy 4. Poor prenatal care .i. Anemia-hematocrit 29% 6. Oxytocin induction
Rare variable decelerations
45 min.
Low outlet forceps, light meconiumstained fluid, Apgar 9, 10
Only 30 min. of record available for review; 85% usable Doppler FHR
M. c.
Rh Negative
Rare
75 min.
Apgar
9 1% usable FHR
Doppler
S.J.
1. Pre-eclampsia 2. Meconium 3. Cephalopelvic disproportion 4. Failure to progress
Rare variables
1% hr.
Cesarean section, 3.380 Gm. female, Apgar 7, 9
96%’ usable FHR
Doppler
M. N.
Postmaturity
Accelerations 190 b.p.m.
8 hr., 20 min
Apgar
90% usable FHR
Doppler
The
resultant
which the
phases
computed beat-to-beat
dominant
the
*PDP 11145, sachusetts.
were
entered
into
FHR
for
interval
change
component
Digital
decelerations
each
between varied
Equipment
from
intervals. time
Corp.,
to
the
a computer,* as well
as
counting
artifactual,
to time
and
was responsible lift) and “jitter” These to be quite
might
component,
pre-
Mas-
9, 10
circuits
predominant
The
Maynard,
9. 10
sudden
studies small,
suddenly producing
“beat-to-beat” for for also
shift
to a newly
an apparent, change.
This
many “artifact indications” no apparent reason. showed
usually
the
less than
beat-to-beat 5 b.p.m.
but change (penchanges
Even
in the
130
Lauersen,
Hochberg,
and George
Fig. 4. Simultaneous beat-to-beat ECG and Doppler FHR variable decelerations. The upper record is derived Doppler. Rates from 90 to 180 b.p.m. are well represented. well followed by the Doppler-derived FHR.
records showing accurate representation from beat-to-beat ECC. the lower Severe decelerations and tat-hvcardia
Fig. 5. Simultaneous pre-eclamptic (top) shows
steepest b.p.m.
variable Periods
beat-to-beat ECG and Doppler FHR showing limited variability In both. patient in labor was treated with large doses of MgSO,. The beat-to-heat ECG loss of variability, well represented by the Doppler-derived FHR (bottom).
deceleration, of
severe
it rarelv
interference
pler from excessive fetal or patient the transducer, were characterized beat-to-beat of 25 b.p.m. unphysiologic
changes
of at least
exceeded with
motion, by many
25 b.p.m.
Serial
fetal
10 Dop-
of
The system 25 b.p.m.
or moving sequential
(because
changes
displayed.
or more were chosen as representing data, with the recognition that the! might represent arrhythmias. A circuit was added to check for discrepancies of over 25 b.p.m. in beat-to-beat FHR changes.
short
allows before
each
skip
interval).
physiologic information interference to prevent resulting
produced this
subsequent
range, because
This FHR
for up LO two sequential it indicates the data are
During If
of fr~ml XC’
a~ least time intervals
the
one
long
last
valid
are
out
the system bars displa\ it was most likelv derived
cha11ges
erratic and
one
FI-IR of ot
is the
rh
