Norwitz, L6pez Bernal, and Starkey
Turnbull AC. Prostaglandins, chorioamnionitis and preterm labour. Br J Obstet Gynaecol 1987;94: 1156-8. 19. Romero R, Wu YK, Brody D, Oyarzun E, DuffGW, Durum SK. Human decidua: a source of interleukin-1. Obstet Gynecol 1989;73:31-4. 20. Santhanam U, Avila C, Romero R, et al. Cytokines in normal and abnormal parturition: elevated amniotic fluid
September 1992 Am J Obstet Gynecol
interleukin-6 levels in women with premature rupture of membranes associated with intrauterine infection. Cytokines 1991;3:155-63. 21. Norwitz ER, Starkey PM, L6pez Bernal A. Prostaglandin D. production by term human decidua: cellular origins defined using flow cytometry. Obstet Gynecol 1992;80 [In press].
Physiologic baroreceptor activity in the fetal lamb Akihiko Wakatsuki, MD, Yuji Murata, MD. Yuko Ninomiya, MD, Naoki Masaoka, MD, James G. Tyner, and Krishna K. Kutty Orange, California OBJECTIVE: We investigated the influences of gestational age and behavioral state on fetal baroreceptor activity. STUDY DESIGN: Two protocols were used to analyze jow-voltage fast activity and high-voltage slow activity in eight chronically instrumented ovine fetuses at. days 127 to 142. In protocol 1 correlation of fetal heart rate to mean arterial blood pressure was assessed under physiologic conditions, and the linear regression slope of fetal heart rate on mean arterial pressure was calculated. In protocol 2 an injection of 7.5 I1g of norepinephrine was given during consecutive behavioral cycles. The ratio of fetal heart rate decrease to mean arterial pressure increase was determined as representing baroreceptor activity. RESULTS: Under protocol 1 the slope was steeper in high-voltage slow activity (2.33 ± 1.03) than in low-voltage fast activity (0.89 ± 0.37) (n = 21, P < 0.001), indicating that fetal heart rate changes are sensitive to blood pressure changes during high-voltage slow activity. Under protocol 2 inverse relationships were found between the ratio of fetal heart rate decrease to mean arterial pressure increase and gestational age in low-voltage fast activity and high-voltage slow activity. CONCLUSION: Fetal baroreceptor activity increased during high-voltage slow activity and decreased with gestational age. (AM J OaSTET GVNECOL 1992;167:820-7.)
Key words: Baroreceptor reflex activity, fetal lamb, behavioral state, gestational age Heart rate decelerations have been frequently observed in human fetuses before 30 weeks' gestation,I.3 in animal fetuses born prematurely,. and in human neonates. 5 The mechanism of these decelerations may be reflex vagal nerve mediated! It has been reported that the increase in cholinesterase activity during gestation may help protect the mature fetus from severe bradycardia. 4 The physiologic implications of fetal From the Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of California, Irvine, College of Medicine, UCI Medical Center. Presented in part at the Thirty-eighth Annual Meeting of the Society for Gynecologic Investigation, San Antonio, Texas, March 20-23,
1991.
Received for publication June 25, 1991, revised April 27, 1992; accepted May 4, 1992. Reprint requests: Yuji Murata, MD, Division ofMaternal-Fetal M edicine, Department of Obstetrics and Gynecology, University of California, Irvine College of Medicine, UCI Medical Center, PO Box 14091, Orange, CA 92613-1491.
6/1/39052
820
heart rate (FHR) decelerations at early gestational ages and during the quiet behavioral state are not understood well enough to apply in clinical practice in perinatal medicine. The purpose of this study was to quantitatively evaluate baroreceptor reflex activities at differing gestational ages and behavioral states in chronically instrumented fetal lambs.
Material and methods Surgical preparation. The fetal lambs of eight timemated Columbia-Rambouillet cross-bred sheep were chronically instrumented between 127 and 142 days' gestation (term 145 days). All animals were maintained in a facility approved by the American Association for the Accreditation of Laboratory Animal Care and in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals. Before implementation research
Baroreceptor activity in fetal lamb
Volume 167 Number 3
Norepinephrine 7.5Jl1
-=
120
I
1 min
821
I
~
E
!
60
= ~
~
o 220 140
60 Fig. 1. Arterial blood pressure (FBP) and FHR response after 7.5 flog norepinephrine bolus injection in the fetal lamb at 140 days of gestation.
protocols were approved by the Animal Research Committee, University of California, Irvine. After 24 hours of fasting, the ewe was given 12 to 14 mg xylazine (Rompun) anesthetic intramuscularly, with 1% lidocaine used locally as needed. With the ewe in the lateral position the uterus was exposed by a midline abdominal incision. The fetal head was delivered through a hysterectomy incision and covered with a surgical glove filled with warm saline solution. Catheters were inserted in the fetal carotid artery, jugular vein, and trachea. The electrodes for electrocardiography were sutured under the skin of the fetal thorax. Paired stainless steel screw electrodes were placed bilaterally in the parietal skull for electrocardiogram recording. The FHR was obtained from the electrocardiogram. An open-end catheter was placed in the amniotic cavity to measure intrauterine pressure. Additional catheters were placed in the maternal femoral artery and vein for blood pressure and drug administration. All catheters and electrodes were exteriorized to the flank of the ewe. Experimental procedure. The animals were kept in an air conditioned facility with food and water available as desired. Intravenous ampicillin (200 mg/kg per day) and gentamicin (6 mg/kg per day) were administered after surgery to mother and fetus, with ampicillin (1 gm/day) administered into the amniotic cavity for 3 to 4 days. Maternal and fetal arterial pH, blood gases, and hematocrits were checked daily. For the determination of pH and gases approximately 0.6 ml of arterial
blood was collected anaerobically and measured by Corning pH/blood gas analyzer, model 168 BGA (Ciba Corning Diagnostics, Medfield, Mass.) at 37° C. Fetal well-being was determined by the following criteria: pH> 7.30, POe> 16 mm Hg, Peo. < 50 mm Hg, hematocrit> 30%. Fetal arterial blood pressure, FHR, electrocorticogram, tracheal pressure, intrauterine pressure, and maternal blood pressure were continuously monitored after the surgery by polygraph (eightchannel rectilinear recorder, model R612, Sensor Medics, Anaheim, Calif.). Values of fetal blood pressure were corrected with intrauterine pressure as reference. Fetal behavioral states were analyzed from the electrocorticogram for low-voltage fast activity and high-voltage slow activity. Experiments were performed on or after the fifth postoperative day. All experiments were carried out between 9 AM and 5 PM with the ewe standing or lying quietly. In five fetal lambs FHR and mean arterial pressure were measured every 30 to 60 seconds during stable physiologic periods of 1.5 hours when both low-voltage fast activity and high-voltage slow activity states alternatively appeared. These states were determined retrospectively by electrocorticogram, and the measurements were taken at least 3 to 5 minutes after the start of a new state when these states were well established on electrocorticogram. A regression line for mean arterial pressure versus FHR was obtained. If the relationship was statistically significant, the regression line
822
Wakatsuki et al.
September 1992 Am J Obstet Gynecol
200
o LVFA
•
CD 0
180
E CI.
e
160
HVSA
o
0 0
= r-
0
c::.::
o
0
140
••
•
120~~--~--~~~~--~--~~~~--~
30
35
40
45
55
50
MAP (mmHg) Fig. 2. Relationship of FHR to mean arterial pressure (MAP) in high-voltage slow activity (HSVA) (closed circles) and low-voltage fast activity (LVFA) (open circles). Regression equations are as follows: LVFA: FHR = 245 - 2.01 (mean arterial pressure), r = 0.66, P < 0.00 I; high-voltage slow actiyity: FHR = 314 - 3.70 (mean arterial pressure), r = 0.88, P < 0.00 I.
Table I. Comparison of regression for FHR on mean arterial blood pressure of fetal lambs during low-voltage fast activity and high-voltage slow activity states Slope of regJ'essioll line
Sheep No.
89-16 89.17
89-18
90-05 90-06
Gestational age (days)
136 141 130 134 136 140 142 129 133 135 137 139 131 137 129 131 132 133 134 136 141
Low-voltage fast activity
-1.53 - 1.08 - 1.32 - 1.37 -0.98 - 1.25 -1.15 -2.01 - 1.00 -0.68 -0.41 -0.81 -0.80 -0.39 -1.00 -0.73 -0.81 -0.87 -0.78 -0.41 -0.37
I
High-voltage slow activity
-2.43 -2.22 -1.95 -1.38 -2.69 -3.49 -1.27 -3.70 - 1.88 -1.34 -1.63 -2.18 -0.93 -1.65 -2.88 -1.48 -1.94 -1.13 -1.94 -4.30 -2.64
All are statistically significant at p < 0.01.
slope was considered to represent baroreceptor reflex activity. In six fetal lambs 7.5 fLg of norepinephrine was injected intravenously during consecutive behavioral states (two to 10 times). At least 10 minutes elapsed between successive norepinephrine injections. The ra-
tio of maximal FHR decrease to maximal mean arterial pressure increase (ilFHRI ilMAP) response to the norepinephrine injections (Fig. 1) was calculated to quantitatively represent fetal baroreAex activity." The standard dose of norepinephrine and the ilFHRI ilMAP ratio were aett'fminea from pilot ex-
Baroreceptor activity in fetal lamb 823
Volume 167 Number 3
periments conducted on three fetal lambs at 127, 129, and 138 days' gestation, respectively. In these norepinephrine was injected at five doses (2.5, 5.0, 7.5, 10.0, and 15.0 J.1g). The relation between AFHR and AMAP and norepinephrine dosage in low-voltage fast activity and high-voltage slow activity states was observed. Data analysis. The differences between low-voltage fast activity and high-voltage slow activity behavioral states were analyzed by paired t test and found significant. The regression line was analyzed by the leastsquares method, and regression slopes were compared by t test regression analysis. 7 Statistical significance was accepted at p < 0.05. All data were reported as mean ± SD.
100
LVFA State D
80
8'
e=~
:::: ...
• o
60
40
Turnbull AC. Prostaglandins, chorioamnionitis and preterm labour. Br J Obstet Gynaecol 1987;94: 1156-8. 19. Romero R, Wu YK, Brody D, Oyarzun E, DuffGW, Durum SK. Human decidua: a source of interleukin-1. Obstet Gynecol 1989;73:31-4. 20. Santhanam U, Avila C, Romero R, et al. Cytokines in normal and abnormal parturition: elevated amniotic fluid
September 1992 Am J Obstet Gynecol
interleukin-6 levels in women with premature rupture of membranes associated with intrauterine infection. Cytokines 1991;3:155-63. 21. Norwitz ER, Starkey PM, L6pez Bernal A. Prostaglandin D. production by term human decidua: cellular origins defined using flow cytometry. Obstet Gynecol 1992;80 [In press].
Physiologic baroreceptor activity in the fetal lamb Akihiko Wakatsuki, MD, Yuji Murata, MD. Yuko Ninomiya, MD, Naoki Masaoka, MD, James G. Tyner, and Krishna K. Kutty Orange, California OBJECTIVE: We investigated the influences of gestational age and behavioral state on fetal baroreceptor activity. STUDY DESIGN: Two protocols were used to analyze jow-voltage fast activity and high-voltage slow activity in eight chronically instrumented ovine fetuses at. days 127 to 142. In protocol 1 correlation of fetal heart rate to mean arterial blood pressure was assessed under physiologic conditions, and the linear regression slope of fetal heart rate on mean arterial pressure was calculated. In protocol 2 an injection of 7.5 I1g of norepinephrine was given during consecutive behavioral cycles. The ratio of fetal heart rate decrease to mean arterial pressure increase was determined as representing baroreceptor activity. RESULTS: Under protocol 1 the slope was steeper in high-voltage slow activity (2.33 ± 1.03) than in low-voltage fast activity (0.89 ± 0.37) (n = 21, P < 0.001), indicating that fetal heart rate changes are sensitive to blood pressure changes during high-voltage slow activity. Under protocol 2 inverse relationships were found between the ratio of fetal heart rate decrease to mean arterial pressure increase and gestational age in low-voltage fast activity and high-voltage slow activity. CONCLUSION: Fetal baroreceptor activity increased during high-voltage slow activity and decreased with gestational age. (AM J OaSTET GVNECOL 1992;167:820-7.)
Key words: Baroreceptor reflex activity, fetal lamb, behavioral state, gestational age Heart rate decelerations have been frequently observed in human fetuses before 30 weeks' gestation,I.3 in animal fetuses born prematurely,. and in human neonates. 5 The mechanism of these decelerations may be reflex vagal nerve mediated! It has been reported that the increase in cholinesterase activity during gestation may help protect the mature fetus from severe bradycardia. 4 The physiologic implications of fetal From the Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of California, Irvine, College of Medicine, UCI Medical Center. Presented in part at the Thirty-eighth Annual Meeting of the Society for Gynecologic Investigation, San Antonio, Texas, March 20-23,
1991.
Received for publication June 25, 1991, revised April 27, 1992; accepted May 4, 1992. Reprint requests: Yuji Murata, MD, Division ofMaternal-Fetal M edicine, Department of Obstetrics and Gynecology, University of California, Irvine College of Medicine, UCI Medical Center, PO Box 14091, Orange, CA 92613-1491.
6/1/39052
820
heart rate (FHR) decelerations at early gestational ages and during the quiet behavioral state are not understood well enough to apply in clinical practice in perinatal medicine. The purpose of this study was to quantitatively evaluate baroreceptor reflex activities at differing gestational ages and behavioral states in chronically instrumented fetal lambs.
Material and methods Surgical preparation. The fetal lambs of eight timemated Columbia-Rambouillet cross-bred sheep were chronically instrumented between 127 and 142 days' gestation (term 145 days). All animals were maintained in a facility approved by the American Association for the Accreditation of Laboratory Animal Care and in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals. Before implementation research
Baroreceptor activity in fetal lamb
Volume 167 Number 3
Norepinephrine 7.5Jl1
-=
120
I
1 min
821
I
~
E
!
60
= ~
~
o 220 140
60 Fig. 1. Arterial blood pressure (FBP) and FHR response after 7.5 flog norepinephrine bolus injection in the fetal lamb at 140 days of gestation.
protocols were approved by the Animal Research Committee, University of California, Irvine. After 24 hours of fasting, the ewe was given 12 to 14 mg xylazine (Rompun) anesthetic intramuscularly, with 1% lidocaine used locally as needed. With the ewe in the lateral position the uterus was exposed by a midline abdominal incision. The fetal head was delivered through a hysterectomy incision and covered with a surgical glove filled with warm saline solution. Catheters were inserted in the fetal carotid artery, jugular vein, and trachea. The electrodes for electrocardiography were sutured under the skin of the fetal thorax. Paired stainless steel screw electrodes were placed bilaterally in the parietal skull for electrocardiogram recording. The FHR was obtained from the electrocardiogram. An open-end catheter was placed in the amniotic cavity to measure intrauterine pressure. Additional catheters were placed in the maternal femoral artery and vein for blood pressure and drug administration. All catheters and electrodes were exteriorized to the flank of the ewe. Experimental procedure. The animals were kept in an air conditioned facility with food and water available as desired. Intravenous ampicillin (200 mg/kg per day) and gentamicin (6 mg/kg per day) were administered after surgery to mother and fetus, with ampicillin (1 gm/day) administered into the amniotic cavity for 3 to 4 days. Maternal and fetal arterial pH, blood gases, and hematocrits were checked daily. For the determination of pH and gases approximately 0.6 ml of arterial
blood was collected anaerobically and measured by Corning pH/blood gas analyzer, model 168 BGA (Ciba Corning Diagnostics, Medfield, Mass.) at 37° C. Fetal well-being was determined by the following criteria: pH> 7.30, POe> 16 mm Hg, Peo. < 50 mm Hg, hematocrit> 30%. Fetal arterial blood pressure, FHR, electrocorticogram, tracheal pressure, intrauterine pressure, and maternal blood pressure were continuously monitored after the surgery by polygraph (eightchannel rectilinear recorder, model R612, Sensor Medics, Anaheim, Calif.). Values of fetal blood pressure were corrected with intrauterine pressure as reference. Fetal behavioral states were analyzed from the electrocorticogram for low-voltage fast activity and high-voltage slow activity. Experiments were performed on or after the fifth postoperative day. All experiments were carried out between 9 AM and 5 PM with the ewe standing or lying quietly. In five fetal lambs FHR and mean arterial pressure were measured every 30 to 60 seconds during stable physiologic periods of 1.5 hours when both low-voltage fast activity and high-voltage slow activity states alternatively appeared. These states were determined retrospectively by electrocorticogram, and the measurements were taken at least 3 to 5 minutes after the start of a new state when these states were well established on electrocorticogram. A regression line for mean arterial pressure versus FHR was obtained. If the relationship was statistically significant, the regression line
822
Wakatsuki et al.
September 1992 Am J Obstet Gynecol
200
o LVFA
•
CD 0
180
E CI.
e
160
HVSA
o
0 0
= r-
0
c::.::
o
0
140
••
•
120~~--~--~~~~--~--~~~~--~
30
35
40
45
55
50
MAP (mmHg) Fig. 2. Relationship of FHR to mean arterial pressure (MAP) in high-voltage slow activity (HSVA) (closed circles) and low-voltage fast activity (LVFA) (open circles). Regression equations are as follows: LVFA: FHR = 245 - 2.01 (mean arterial pressure), r = 0.66, P < 0.00 I; high-voltage slow actiyity: FHR = 314 - 3.70 (mean arterial pressure), r = 0.88, P < 0.00 I.
Table I. Comparison of regression for FHR on mean arterial blood pressure of fetal lambs during low-voltage fast activity and high-voltage slow activity states Slope of regJ'essioll line
Sheep No.
89-16 89.17
89-18
90-05 90-06
Gestational age (days)
136 141 130 134 136 140 142 129 133 135 137 139 131 137 129 131 132 133 134 136 141
Low-voltage fast activity
-1.53 - 1.08 - 1.32 - 1.37 -0.98 - 1.25 -1.15 -2.01 - 1.00 -0.68 -0.41 -0.81 -0.80 -0.39 -1.00 -0.73 -0.81 -0.87 -0.78 -0.41 -0.37
I
High-voltage slow activity
-2.43 -2.22 -1.95 -1.38 -2.69 -3.49 -1.27 -3.70 - 1.88 -1.34 -1.63 -2.18 -0.93 -1.65 -2.88 -1.48 -1.94 -1.13 -1.94 -4.30 -2.64
All are statistically significant at p < 0.01.
slope was considered to represent baroreceptor reflex activity. In six fetal lambs 7.5 fLg of norepinephrine was injected intravenously during consecutive behavioral states (two to 10 times). At least 10 minutes elapsed between successive norepinephrine injections. The ra-
tio of maximal FHR decrease to maximal mean arterial pressure increase (ilFHRI ilMAP) response to the norepinephrine injections (Fig. 1) was calculated to quantitatively represent fetal baroreAex activity." The standard dose of norepinephrine and the ilFHRI ilMAP ratio were aett'fminea from pilot ex-
Baroreceptor activity in fetal lamb 823
Volume 167 Number 3
periments conducted on three fetal lambs at 127, 129, and 138 days' gestation, respectively. In these norepinephrine was injected at five doses (2.5, 5.0, 7.5, 10.0, and 15.0 J.1g). The relation between AFHR and AMAP and norepinephrine dosage in low-voltage fast activity and high-voltage slow activity states was observed. Data analysis. The differences between low-voltage fast activity and high-voltage slow activity behavioral states were analyzed by paired t test and found significant. The regression line was analyzed by the leastsquares method, and regression slopes were compared by t test regression analysis. 7 Statistical significance was accepted at p < 0.05. All data were reported as mean ± SD.
100
LVFA State D
80
8'
e=~
:::: ...
• o
60
40
