Montan et al, Vibro-acoustic Stimulation and fetal heart rate
j. Perinat. Med. 20 (1992) 331-336
331
Vibro-acoustic Stimulation does not alter the duration of high and jow fetaj hearf rafe variability episodes Sven Montan, Sabaratnam Arulkumaran, Margareta Nyman, Shan S Ratnam
Department of Obstetrics and Gynaecology, National University Hospital, National University Singapore, Singapore
l
Curriculum vitae
Introduction
Electronic recording of FHR patterns following vibro-acoustic Stimulation has been used for many years to evaluate fetal well-being [6, 12]. Accelerations provoked by vibro-acoustic Stimulation are generally accepted äs a normal response in healthy fetuses. In normal fetuses, the FHR patterns change with increasing maturity and periods of high and low FHR variability become more obvious towards term [17]. These patterns show diurnal variations [14, 15] gradually resembling the patterns of sleep and activity cycles observed in newbora infants [8]. The back ground sound level in the uterus in labour is known to be 60-80 dB [2] and the sound level in utero with vibro-acoustic Stimulation is about 110-120 dB [10]. Disturbance to the fetus caused by vibro-acoustic Stimulation may be unphysiological and potentially harmful. Possibility of catecholamine release [3], hearing defects [1] and undue alteration in the fetal movement and FHR pattern are under investigation [13]. Although some aspects of alteration of FHR pattern following vibro-acoustic Stimulation has been studied [4], little is known about the duration of disturbance reflected by alteration in the length of high and low FHR variability episodes. This study evaluates the influence of vibroacoustic Stimulation on high and low FHR variability episodes in high risk pregnancies when the fetus was stimulated during the period of low FHR variability. 1992 by Walter de Gruyter & Co. Berlin · New York
SVEN MONTAN was born in 1948. He studied medicine at the University of Lund, Sweden and obtained his medical degree in 1974. Specialist in obstetrics and gynaecology since 1979 and Ph. D. at the University ofLund in 1987. He is currently a Senior Teaching Fellow at the Department of Obstetrics and Gynaecology, National University Hospital, National University of Singapore.
2
Materials and methods
Twenty-one women with singleton pregnancies, in the third trimester, admitted to the antenatal ward of the National University Hospital were studied after informed consent. In each patient, studies were performed at the same time of the day one hour after a meal in the same low noise room, to minimize the effects of diurnal variations. The FHR was recorded using a Corometrics 145 antepartum fetal monitor (Corometrics, Wallingford USA). The mother was semi-recumbent. After at least 5 minutes of low baseline variability of the FHR recording, a vibro-acoustic stimulator (Corometrics, model 146) was held 2 cm above the maternal abdomen (sham Stimulation) or in contact with the maternal abdominal wall (contact Stimulation) over the fetal head
Brought to you by | Michigan State University Authenticated Download Date | 6/10/15 4:54 AM
332
Montan et al, Vibro-acoustic Stimulation and fetal heart rate
and activated for 5 seconds. Contact or sham Stimulation was at random (type of Stimulation reversed the next day) and the FHR record was continued in order to obtain a complete high and low FHR variability episode. Low FHR variability episodes were defined äs periods of at least five minutes duration of a stable FHR baseline, with decreased baseline variability with an amplitude less than 10 bpm, and occasional or no accelerations (pattern 1F described by NIJHUIS [9]). High FHR variability episodes were identified when the baseline FHR variability was greater than 10 bpm in amplitude with accelerations (pattern 2F, NIJHUIS [9]). Episodes included in the study were complete in that they were preceded and followed by a change from one type of variability to another. The duration of high and low baseline FHR variability episodes were determined to the nearest minute from the FHR trace. An acceleration was defined äs an abrupt increase in FHR of more than 15 bpm returning back to the baseline rate after reaching a peak. Tachycardia was defined äs an increase in baseline FHR by more than 15 bpm maintained for longer than three minutes. The amplitude and duration of the initial tachycardia, and the nature and duration of the FHR variability episodes immediately following contact vibro-acoustic stimulatin during low baseline FHR variability were compared with the effects recorded after sham Stimulation using the Student paired t-test and the Wilcoxon matched pair signed-rank test. Significance was accepted when p < 0.05. 3 Results
At least five minutes of low FHR variability followed by a complete high and low FHR variability episode after sham or contact vibroacoustic Stimulation could not be obtained in 8 patients (sham = 6 patients, contact = 2 patients), despite a mean recording time of 145 minutes (ränge 115 — 173 minutes). One patient responded to sham or contact vibro-acoustic Stimulation with decelerations and was excluded. Thus, there were 12 patients in the study. They were between 32 to 39 weeks of gestation, 9 were in cephalic presentation, two were presenting by the breech, and one was in transverse lie. The antenatal risk factors were hypertension in preg-
nancy (9), maternal heart disease (2) and placenta praevia (1). All women reported normal fetal movements and 5 of 9 hypertensives were on methyldopa 250 mg t. d. s. for hypertension in pregnancy. The patient data, mode of delivery and neonatal outcome in these 12 patients are given in table I. Table I. Patient data, mode of delivery and neonatal outcome in 12 patients with sham and contact vibroacoustic Stimulation — mean (SD) Materaal age at delivery in years Number of nulliparae Completed gestation in weeks at testing Completed gestation in weeks at delivery Number of caesarean section Number of male/female Apgar score < 7 at one minute/ at 5 minutes Birth weight in g Length of neonate in cm Head circumference in cm Placental weight in g
27.8 (5.7) 5 36.1 (2.2) 38.1 (1.9) 6 6/6 4/1 2813 (606) 48.1 (2.6) 32.8 (1.2) 553 (124)
All 12 fetuses stimulated with contact vibroacoustic Stimulation during low FHR variability responded with a transient baseline tachycardia which continued in 10 fetuses with high FHR variability after returning to the baseline rate; two fetuses went back to low FHR variability after 2 and 8 minutes, respectively. The mean amplitude of the response was 32.5 bpm (SD 9.4, ränge 10—45 bpm). The amplitude of tachycardia rarely exceeded the size of the largest acceleration noted during the preceding or subsequent high FHR variability period. The mean duration of the tachycardia, and the mean duration of high FHR variability immediately following tachycardia are presented in table II. The baseline FHR following the episode of tachycardia was not signiflcantly different from the baseline FHR before the Stimulation despite the increased variability and the number of accelerations (table III). Following SHAM Stimulation low FHR variability continued in 9 patients for more than one minute after the sounding, and in the remaining 3, accelerations were seen, but no case of transient tachycardia. The mean duration of high and low FHR variability episodes following sham or contact vibro-acoustic Stimulation were not signiflcantly different and are presented in table IV.
J. Perinat. Med. 20 (1992) Brought to you by | Michigan State University Authenticated Download Date | 6/10/15 4:54 AM
333
Montan et al, Vibro-acoustic Stimulation and fetal heart rate Table Π. FHR response to contact vibro-acoustic Stimulation in low FHR variability in 12 patients
Amplitude of tachycardia (bpm) Duration of tachycardia (min) Subsequent duration of high FHR variability (min)
Mean
(SD)
Min
Max
32.5 7.1 49.5
(9.4) (3-3) (33.6)
10 1 0
45 12 111
Table ΠΙ. Mean baseline FHR (bpm) following sham and contact vibro-acoustic Stimulation in low FHR variability CONTACT n = 12
SHAM n = 12
Baseline FHR before Baseline FHR at the time of tachycardia Baseline FHR 0-5 min Baseline FHR 6-10 min Baseline FHR 11-20 min
Mean
(SD)
Range
Mean
(SD)
Range
137 —
(12)
115 to 150 115 to 155 115 to 150 115to 150
(11) (12)
115 to 150 155 to 190
ns
(13) (11) (12)
136 168 158 142 139
(8) (9) (10)
145 to 170 127 to 155 125 to 160
j. Perinat. Med. 20 (1992) 331-336
331
Vibro-acoustic Stimulation does not alter the duration of high and jow fetaj hearf rafe variability episodes Sven Montan, Sabaratnam Arulkumaran, Margareta Nyman, Shan S Ratnam
Department of Obstetrics and Gynaecology, National University Hospital, National University Singapore, Singapore
l
Curriculum vitae
Introduction
Electronic recording of FHR patterns following vibro-acoustic Stimulation has been used for many years to evaluate fetal well-being [6, 12]. Accelerations provoked by vibro-acoustic Stimulation are generally accepted äs a normal response in healthy fetuses. In normal fetuses, the FHR patterns change with increasing maturity and periods of high and low FHR variability become more obvious towards term [17]. These patterns show diurnal variations [14, 15] gradually resembling the patterns of sleep and activity cycles observed in newbora infants [8]. The back ground sound level in the uterus in labour is known to be 60-80 dB [2] and the sound level in utero with vibro-acoustic Stimulation is about 110-120 dB [10]. Disturbance to the fetus caused by vibro-acoustic Stimulation may be unphysiological and potentially harmful. Possibility of catecholamine release [3], hearing defects [1] and undue alteration in the fetal movement and FHR pattern are under investigation [13]. Although some aspects of alteration of FHR pattern following vibro-acoustic Stimulation has been studied [4], little is known about the duration of disturbance reflected by alteration in the length of high and low FHR variability episodes. This study evaluates the influence of vibroacoustic Stimulation on high and low FHR variability episodes in high risk pregnancies when the fetus was stimulated during the period of low FHR variability. 1992 by Walter de Gruyter & Co. Berlin · New York
SVEN MONTAN was born in 1948. He studied medicine at the University of Lund, Sweden and obtained his medical degree in 1974. Specialist in obstetrics and gynaecology since 1979 and Ph. D. at the University ofLund in 1987. He is currently a Senior Teaching Fellow at the Department of Obstetrics and Gynaecology, National University Hospital, National University of Singapore.
2
Materials and methods
Twenty-one women with singleton pregnancies, in the third trimester, admitted to the antenatal ward of the National University Hospital were studied after informed consent. In each patient, studies were performed at the same time of the day one hour after a meal in the same low noise room, to minimize the effects of diurnal variations. The FHR was recorded using a Corometrics 145 antepartum fetal monitor (Corometrics, Wallingford USA). The mother was semi-recumbent. After at least 5 minutes of low baseline variability of the FHR recording, a vibro-acoustic stimulator (Corometrics, model 146) was held 2 cm above the maternal abdomen (sham Stimulation) or in contact with the maternal abdominal wall (contact Stimulation) over the fetal head
Brought to you by | Michigan State University Authenticated Download Date | 6/10/15 4:54 AM
332
Montan et al, Vibro-acoustic Stimulation and fetal heart rate
and activated for 5 seconds. Contact or sham Stimulation was at random (type of Stimulation reversed the next day) and the FHR record was continued in order to obtain a complete high and low FHR variability episode. Low FHR variability episodes were defined äs periods of at least five minutes duration of a stable FHR baseline, with decreased baseline variability with an amplitude less than 10 bpm, and occasional or no accelerations (pattern 1F described by NIJHUIS [9]). High FHR variability episodes were identified when the baseline FHR variability was greater than 10 bpm in amplitude with accelerations (pattern 2F, NIJHUIS [9]). Episodes included in the study were complete in that they were preceded and followed by a change from one type of variability to another. The duration of high and low baseline FHR variability episodes were determined to the nearest minute from the FHR trace. An acceleration was defined äs an abrupt increase in FHR of more than 15 bpm returning back to the baseline rate after reaching a peak. Tachycardia was defined äs an increase in baseline FHR by more than 15 bpm maintained for longer than three minutes. The amplitude and duration of the initial tachycardia, and the nature and duration of the FHR variability episodes immediately following contact vibro-acoustic stimulatin during low baseline FHR variability were compared with the effects recorded after sham Stimulation using the Student paired t-test and the Wilcoxon matched pair signed-rank test. Significance was accepted when p < 0.05. 3 Results
At least five minutes of low FHR variability followed by a complete high and low FHR variability episode after sham or contact vibroacoustic Stimulation could not be obtained in 8 patients (sham = 6 patients, contact = 2 patients), despite a mean recording time of 145 minutes (ränge 115 — 173 minutes). One patient responded to sham or contact vibro-acoustic Stimulation with decelerations and was excluded. Thus, there were 12 patients in the study. They were between 32 to 39 weeks of gestation, 9 were in cephalic presentation, two were presenting by the breech, and one was in transverse lie. The antenatal risk factors were hypertension in preg-
nancy (9), maternal heart disease (2) and placenta praevia (1). All women reported normal fetal movements and 5 of 9 hypertensives were on methyldopa 250 mg t. d. s. for hypertension in pregnancy. The patient data, mode of delivery and neonatal outcome in these 12 patients are given in table I. Table I. Patient data, mode of delivery and neonatal outcome in 12 patients with sham and contact vibroacoustic Stimulation — mean (SD) Materaal age at delivery in years Number of nulliparae Completed gestation in weeks at testing Completed gestation in weeks at delivery Number of caesarean section Number of male/female Apgar score < 7 at one minute/ at 5 minutes Birth weight in g Length of neonate in cm Head circumference in cm Placental weight in g
27.8 (5.7) 5 36.1 (2.2) 38.1 (1.9) 6 6/6 4/1 2813 (606) 48.1 (2.6) 32.8 (1.2) 553 (124)
All 12 fetuses stimulated with contact vibroacoustic Stimulation during low FHR variability responded with a transient baseline tachycardia which continued in 10 fetuses with high FHR variability after returning to the baseline rate; two fetuses went back to low FHR variability after 2 and 8 minutes, respectively. The mean amplitude of the response was 32.5 bpm (SD 9.4, ränge 10—45 bpm). The amplitude of tachycardia rarely exceeded the size of the largest acceleration noted during the preceding or subsequent high FHR variability period. The mean duration of the tachycardia, and the mean duration of high FHR variability immediately following tachycardia are presented in table II. The baseline FHR following the episode of tachycardia was not signiflcantly different from the baseline FHR before the Stimulation despite the increased variability and the number of accelerations (table III). Following SHAM Stimulation low FHR variability continued in 9 patients for more than one minute after the sounding, and in the remaining 3, accelerations were seen, but no case of transient tachycardia. The mean duration of high and low FHR variability episodes following sham or contact vibro-acoustic Stimulation were not signiflcantly different and are presented in table IV.
J. Perinat. Med. 20 (1992) Brought to you by | Michigan State University Authenticated Download Date | 6/10/15 4:54 AM
333
Montan et al, Vibro-acoustic Stimulation and fetal heart rate Table Π. FHR response to contact vibro-acoustic Stimulation in low FHR variability in 12 patients
Amplitude of tachycardia (bpm) Duration of tachycardia (min) Subsequent duration of high FHR variability (min)
Mean
(SD)
Min
Max
32.5 7.1 49.5
(9.4) (3-3) (33.6)
10 1 0
45 12 111
Table ΠΙ. Mean baseline FHR (bpm) following sham and contact vibro-acoustic Stimulation in low FHR variability CONTACT n = 12
SHAM n = 12
Baseline FHR before Baseline FHR at the time of tachycardia Baseline FHR 0-5 min Baseline FHR 6-10 min Baseline FHR 11-20 min
Mean
(SD)
Range
Mean
(SD)
Range
137 —
(12)
115 to 150 115 to 155 115 to 150 115to 150
(11) (12)
115 to 150 155 to 190
ns
(13) (11) (12)
136 168 158 142 139
(8) (9) (10)
145 to 170 127 to 155 125 to 160
