Acta physiol. scand. 1979. 105. 195-203 From the Department of Physiology, the Department of Gynaecology and Obstetrics, Sahlgrenska sjukhuset, and the Department of Pediatrics I, Ostra sjukhuset, University of Goteborg?,Sweden
ECG-changes in the fetal lamb during asphyxia in relation to beta-adrenoceptor stimulation and blockade BY
K.-H. HOKEGARD, K. KARLSSON, 1. KJELLMER and K. G. ROSBN Received 31 May 1978
Abstract HOKEGARD, K.-H., K. KARLSSON, I. KJELLMER and K. G. R O S ~ NECG-changes , in the fetal lamb during asphyxia in relation to beta-adrenoceptor stimulation and blockade. Acta physiol. scand. 1979. 105. 195-203. Progressive changes in the S-T interval of the fetal electrocardiogram (FECG) were studied in 14 lamb fetuses, acutely exteriorized and subjected to graded hypoxla. The aims of the study were to investigate whether beta-adrenoceptor stimulation and hypoxia exerted additive or potentiating effects on the FECC and several cardiovascular parameters and whether the hypoxic changes of the FECG could be blocked by beta-adrenoceptor blocking agents. The FECG changes were studied in order to correlate them with cardiovascular function, as measured by heart rate, mean arterial pressure, end diastolic pressure, maximum dP/dt and combined cardiac output, estimated by the thermodilution method, as well as with blood gases, acid base status, blood lactate and glucose. Injections of small doses (0.02 to 0.4pg kg-l min-’) of isoprenaline induced the same pattern of changes in the FECG as we have previously recorded during hypoxia. By increasing the isoprenaline dose an increase in the duration of the FECG changes and amplitude of the T-wave changes was obtained. Propranolol was found to completely abolish the FECG changes induced by isoprenaline, as well as by mild hypoxia. During severe hypoxia the FECG changes could not be abolished by propranolol. Our previous findings indicated that the hypoxic changes could be regarded a s a sign of myocardial glycolysis. Thus, the present finding that even small doses of isoprenaline given to the fetus, initiates the same pattern of FECG changes corroborate this hypothesis.
The fetal electrocardiogram (FECG) is used in clinical practice mainly as a means to obtain an indicator of fetal heart rate (FHR). While it is generally accepted that FHR is an indicator of fetal well-being during pregnancy and labour, the diagnostic value of the FECG is controversial. Although alterations in the pattern of the FECG have been detected during labour (Davidsen 1971, Pardi et al. 1974) by using the fetal scalp electrode, these alterations are believed to be preceded by changes in the FHR (Hon and Lee 1963, Lee and Hon 1965, Davidsen 1971). Several investigators have shown changes in the FECG during hypoxia using experimental models (Enhorning and Westin 1954, Stern et al. 1961, Gelli and Gyulai 1969, MuellerHeubach et al. 1971, Myers 1972, Morishmia et al. 1975). Although changes in the S-T interval were readily apparent, it was stated that the use of FECG for the detection of fetal asphyxia will be limited. 195
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ROSBN
Our own animal experiments revealed progressive and reproducible changes in the S-T interval of the FECG during graded hypoxia both in mature guinea-pig fetuses and lamb fetuses (RosCn and Kjellmer 1975). The metabolic background of these changes of the FECG was studied from different aspects. R o d n and Isaksson (1976) demonstrated a parallelity between the FECG changes and the depletion of myocardial glycogen during graded hypoxia in guinea-pig fetuses. The significance of this finding was supported by the relationship found between the increase in the amplitude of the T wave and the degree of metabolic acidosis as well as the accumulation of lactate in the exteriorized fetal lamb (Rosen et al. 1976). These findings together with the relationship found between the appearance of the FECG-changes and decrease in PaO, (Rosen, Hokeggrd and Kjellmer 1976) indicate that the progressive FECG changes reflect myocardial glycogenolysis. Alterations in the FECG pattern consistently preceded signs of failing cardiovascular function and occurred well in advance of any bradycardia (RosCn, HokegArd and Kjellmer 1976). Thus, there are a good many observations indicating that progressive changes in the S-T interval reflect myocardial glycogenolysis and early hypoxic stress. The augmentation of glycogenolysis in heart muscle by beta-receptor stimulation is well known (Mayer et al. 1967). Our own preliminary experiments indicated that the betareceptor stimulating agent, isoprenaline, initiated the same typical pattern of changes in the FECG as hypoxia. Therefore it was considered of interest to elucidate the influence of beta-adrenoceptor stimulation and blockade on the FECG. The aims of the present study were to investigate whether beta-adrenoceptor stimulation and hypoxia exerted additive or potentiating effects in the FECG and several cardiovascular parameters and whether the hypoxic changes of the FECG could be blocked by betaadrenoceptor blocking agents.
Material and methods The experiments were conducted on 9 ewes of mixed breed with 14 fetuses acutely exteriorized. The gestational age was dated in 2 ewes and was estimated from fetal weight and crown-rump length in 7 ewes, using standard curves (Joubert 1956). In a first series of 5 ewes with 8 fetuses, the experiments were conducted according to the methods described earlier ( R o s h , Hokeglrd and Kjellmer 1976). Their gestational age ranged from 109 to 132 days (term 147 days) and their weight from 1 060 to 3 370 g (2 244+228 g, mean value f S.E.). The left jugular vein of the fetus was cannulated and 0.1 to 1O.Opg (0.04 to 9.0 pg/kg) isoprenaline was given i.v. in single injections. Via the same catheter, the beta-blocking agent, propranolol, was given in doses varying from 0.05 to 2 mg (0.02 to 0.83 mg/kg). Fetal and maternal blood pressure, p H and blood gas tensions were measured, fetal heart rate and end diastolic pressure were registered, combined fetal cardiac output was estimated and the FECG recorded with a CR-lead. The ewes (and thereby the fetuses) were exposed to alternate periods of normoxia and hypoxia. The hypoxia was induced by ventilating the ewe with gas mixtures containing 9-15?, 0, in N, and in some experiments with an addition of 10-20% CO,. The hypoxic changes in the ECG pattern were quantified according to the scoring system previously described: The appearance of negative T wave changes, the amplitude exceeding that of the P waves. Maximally negative T wave changes. A gradual decrease in the amplitude of the negative T wave changes. An elevation of the S-T segment and the T wave, the amplitude of the T wave being higher than that of the P wave. Grade V: A maximal increase in the amplitude of the T wave. Grade VI: A decrease in the amplitude of the T wave during continuous hypoxia.
Grade I: Grade 11: Grade 111: Grade IV:
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A second series of 4 ewes with 6 fetuses was used to establish a quantitative dose-response relationship between isoprenaline and FECG changes. Their gestational age ranged from 128 to 138 days (132k2, mean value & S.E.) and their weight from 2 330 to 2 950 g (2 530+ 100). Maternal and fetal blood pressure, blood gas tensions and pH, fetal heart rate and FECG were registered in the same way as in the first series. In order to get a quantitative measurement of the high and peaked T waves, a ratio between the amplitude of the QRS complex and the T wave (T/QRS ratio) was calculated (Fig. 1). Left ventricular pressure was monitored with a micro-tip sensitive catheter (Millar instruments), inserted via the left carotid artery. Maximum dP/dt was derived electronically from this signal and continuously recorded. The thermodilution method (Hedvall e#al. 1973) was also used for estimation of the combined fetal cardiac output (“CO”), but instead of injecting saline of room temperature into the left ventricle as in the first series, it was injected into the inferior vena cava through a catheter inserted via the femoral vein. The left jugular vein was cannulated and isoprenaline was administered continuously with an infusion pump in stepwise higher doses of 0.044, 0.076, 0.143, 0.22, 0.78 and 4.4 pg/min in order to estimate a dose-response curve. This was done both during normoxia and hypoxia before and after betaadrenoceptor block. The beta-blocking agent propranolol was given through the same catheter in the left jugular vein in doses varying from 0.02 to 0.5 rng (0.01 to 0.19 mg/kg).
Results Beta-adrenoceptor stimulation In the first series, isoprenaline was given i.v. in single doses ranging from 0.04 to 9.0 pg/kg to 8 fetuses. In each case isoprenaline induced the same alterations of the FECG pattern as hypoxia. A relationship was found between the dose of isoprenaline and the increase in T wave amplitude, as well as the duration of the ECG changes. Fig. 2 gives an example of recordings made after the injection of 1.0 ,ug (0.4 ,ug/kg) isoprenaline. The whole sequence of alterations of the S-T interval, accounted for in the ECG-scoring system is demonstrated. 3 seconds after I O p g lsoprenaline 100
ARTERIAL BLOOD PRESSURE. rnrn Hg 5 l: inn.
IV
1
I sec
LEFT VENTRICULAR PRESSURE, rnrn Hg I50
HEART beals/rnin RATE
]:
4
ELECTROCARDIOGRAM Precordial lead
Fig. 2. Fetal electrocardiogram changes after the injection of 1 .Opg (0.4 ,ug/kg) isoprenaline. Note the rapid progression in the S-T interval.
I98
K.-H. HOKEGLRD, K . KARLSSON, I . KJELLMER AND K. G .
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IO08T/QRS ratio
06040 2. 0I00
MAP
rnrn Hg
Six fetuses at normoxia f SEM
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fetuses with hypoxia
o---oFour I
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08 lsoprenaline pg/rnin
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N H'YPOXIA Fig. 3. Effect of isoprenaline infusion on the T/QRS ratio of the fetal electrocardiogram, fetal heart rate, mean arterial pressure, maximum dP/dt and combined cardiac output both during normoxia and hypoxia.
In order to further elucidate the influence of beta-adrenoceptor stimulation on the FECG and cardiovascular function and to estimate a dose-response curve, isoprenaline was continuously infused in step-wise higher doses in a second series. This group of 6 fetuses was quite homogeneous regarding gestational age and fetal weight. ECC-changes. Fig. 3 demonstrates the relationship between the increase in T wave amplitude and the dose of isoprenaline (6 fetuses). Hypoxia (4 fetuses) had an additive effect on the ECG changes which appeared earlier and with a higher T/QRS ratio (Grade V in the scoring system). At the highest dose of isoprenaline given during hypoxia the T/QRS ratio decreased again (Grade VI in the scoring system) in the only animal studied. Cardiovascular function. Fig. 3 also demonstrates the effect of isoprenaline on mean arterial pressure, fetal heart rate, maximum dP/dt and combined cardiac output. Both FHR, dP/dt and cardiac output increase gradually with increasing doses of isoprenaline. MAP shows no significant changes. The augmentation of cardiac performance caused by isoprenaline infusion was inhibited by the combination of hypoxia and acidosis. Fig. 3 demonstrates the combined effect of hypoxia and isoprenaline in 4 fetuses. After an initial increase associated with hypoxia both MAP, FHR, maximum dP/dt and "CO" decrease at increasing doses of isoprenaline. Bloodgases, p H , lactate andglycose. There was no change in PaO, during the isoprenaline infusions at normoxia. PaO, was 3.19 i 0 . 2 9 kPa before the infusions started and 3.09 k0.32
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FETAL LAMB, 123 days- 2120 g
ECG
scores
MAP m m Hg
"co" I/(min I, kg)
69 Ft@(kPo) PH 7 30, TIME, 5minutes
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HYPOXIA
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HYPOXIAtC02
Fig. 4. Changes in the fetal electrocardiogram, graded according to the scoring system, mean arterial pressure, fetal heart rate and combined cardiac output after isoprenaline and propranolol injections made both during normoxia, hypoxia and the combination of hypoxia and hypercarbia.
at the end of the infusions (mean value i S.E.). pH, however, decreased from 7.27 k0.04 to 7.17 20.06 and there was a lactate accumulation from 2.85 50.47 to 4.77 k 1.69 nimol/l. Blood glycose values did not change (1.47 k0.28 and 1.53 k0.30 mmol/l respectively). In the 4 fetuses subjected to both hypoxia and isoprenaline infusion the mean PaO, value was 3.53 (range 3.19-3.86) before hypoxia and decreased to 1.86 (range 1.06-2.66) during hypoxia and 1.83 (range 1.06-2.52) when isoprenaline infusion was added. The mean pH value was 7.15 (range 6.99-7.24) before hypoxia and decreased to 7.04 (range 6.89-7.18) during hypoxia and isoprenaline infusion. The mean lactate value was 5.94 (range 1.7111.32) before the hypoxic period and the concentration rose to 8.58 (range 1.71-13.16) mmol/l during hypoxia and isoprenaline infusion. Blood glycose values increased slightly from 1.96 (range 1.74-2.20) to 2.20 (range 2.07-2.36) mmol/l. In all these 4 fetuses the period of hypoxia combined with isoprenaline was preceded by periods of isoprenaline infusion without hypoxia. Beta-adrenoceptor blockade Propranolol was also given to the 8 fetuses of the first series in order to test whether betaadrenoceptor blockade interfered with the ECG changes induced by hypoxia. The degree of
200
K.-H. HOKEGKRD, K. KARLSSON, I. KJELLMER AND K. G. R O S ~ N
T/QRS ratio
MAP A rnrn Hg
04 “CO“
IArnin
2000
dP,d,.
,ooo
mmHg/s
+
t
I
Fig. 5. Effect of propranolol on 4 fetuses subjected to hypoxia and acidosis. PaO, was 2,21+0.24 kPa before the injection and 1.97k0.39 after the injection. pH was 6.9850.13 before the injection and 6.91 0.09 after the injection (mean values S.E.).
I
2
3
4
5 minutes
Propranolol 0.20-0.25 mg
beta-blockade was tested by repeated injections of isoprenaline. The ECG changes induced by isoprenaline completely disappeared about 10 s after the propranolol injections. Fig. 4 demonstrates the pattern of events recorded in a lamb fetus (gestational age: 123 days). The first part of the figure illustrates the effect of isoprenaline (0.47pg/kg) on the combined cardiac output, heart rate and mean arterial pressure as well as the FECG. Alterations in the FECG pattern, elevation of the S-T segment with high and peaked T waves, were associated with a tachycardia and an increase in cardiac output from 0.61 to 0.78 l/(min x kg). A moderate hypoxia, induced by ventilating the ewe with 15%0,, elicited the same pattern of events in the FECG. These changes were immediately blocked by propranolol (0.05 mg/kg). This dose of propranolol was found to almost completely block the effect of a large dose of isoprenaline (4.7 pg/kg). In the last part of the figure the effect of beta-blockade associated with a severe hypoxia are demonstrated. No FECG changes were recorded until there were signs of failing cardiovascular function. These FECG changes could apparently not be blocked even by large doses of propranolol. Propranolol blocked the FECG changes elicited by moderate hypoxia in the two fetuses studied but did not alter the FECG changes associated with a severe hypoxia and a failing circulation (6 cases). The fetus was extremely susceptible to the combination of hypoxia and propranolol. In the second series propranolol blocked the cardiovascular effects of isoprenaline in the same way. These fetuses were also extremely susceptible to the combination of propranolol and hypoxia. In 4 fetuses the combination of acidosis, hypoxia and propranolol resulted in a rapid deterioration of fetal circulation and fetal death 3 to 6 min after the injection of 0.2 to 0.25 mg propranolol i.v. Fig. 5 illustrates the rapid decay of MAP, FHR, maximum dP/dt and “CO’. There is also a decrease in the amplitude of the maximally high and peaked T waves during hypoxia after propranolol injection, i.e. grade VI in the ECG scoring system.
ECG-CHANGES IN FETAL LAMB
20 1
Discussion The results demonstrate that small doses of isoprenaline given during normoxia can elicit the whole sequence of events in the FECG, previously recorded during hypoxia. This is in accordance with the view that glycogenolysis induced by beta-adrenoceptor stimulation via isoprenaline will produce the changes of the FECG. Most tissues respond to oxygen lack by increasing their rate of glycolysis, in parallel with the metabolic events elicited by betareceptor stimulation (Mayer et al. 1967). In asphyxiated animals adrenaline and noradrenaline may be released from the adrenal medulla leading to an increased rate of glycogen breakdown due to phosphorylase activation. This mechanism has been shown to operate in fetal lambs (Comline and Silver 1965). Jones and Robinson (1975) measured increased plasma catecholamine concentrations during hypoxia (fetal PaO, 18 mmHg) in the chronically catheterized fetal Iamb. They could demonstrate an increase in plasma adrenaline corresponding to that produced by the infusion of 0.4 pg kg-l min-l adrenaline. Thus, it appears that the dose of isoprenaline (0.02 to 0.4 pg kg-l min-') which we found to elicit alterations in the FECG pattern, is similar to the amounts of catecholamines secreted during hypoxia. Furthermore, an increase in the dose of isoprenaline resulted in an increase in the duration and amplitude of the T-wave changes in parallel with the pattern of changes recorded with increasing degree of fetal hypoxic stress. Alterations in the FECG with an increase in P wave and decrease in T wave amplitude together with a shortened P-R interval, have been recorded during catecholamine infusion into fetal rhesus monkey by Adamsons et al. (1971) using significantly higher dosage. Stern et al. also obtained higher T-waves after the administration of adrenaline (100 pg i.m.) to newborn babies (1960) and to human fetuses (1961). Isoprenaline gave a positive chronotropic and inotropic effect, the later nicely demonstrated by an increase in myocardial contractility as measured by an increase in max.dP/dt. There was a decrease in pH and an accumulation of blood lactate during isoprenaline infusions but no change in PaO,. These findings are compatible with an augmented glycogenolysis. Infusion of isoprenaline had an additive effect to hypoxia and acidosis with earlier and more pronounced FECG changes and seemed to give a more rapid deterioration of the fetal circulation. The positive chronotropic and inotropic effects of isoprenaline, as well as the negative chronotropic effect of propranolol, have previously been studied in lamb fetuses (Joelsson et al. 1972, van Petten and Willes 1970). In our study, even small doses of propranolol (0.01 to 0.19 mg/kg) completely abolished the FECG changes, produced either by isoprenaline or mild hypoxia. A different pattern was seen during more severe hypoxia with signs of failing cardiovascular function. In this situation beta-blockade had no influence on the ECG changes, consistent with the fact that asphyxia per se is a stimulator of phosphorylase activity in the myocardium (Mayer et af. 1967). The fetus was extremely susceptible to the combination of propranolol and hypoxia. This is likely to be the result of propranolol blocking the most important compensatory mechanisms on the circulatory (Downing et a/. 1969) as well as the metabolic side.
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K. KARLSSON, I. KJELLMER AND K. G .
ROSBN
The question now to be asked is whether the predominant change in the FECG, the high and peaked T wave, is induced by the augmentation of myocardial glycogenolysis or is a direct effect of the high catecholamine output o n the function of the myocardial cell membrane. There are a number of findings in support of the former hypothesis namely: A: Even during the infusion of very high doses of isoprenaline during normoxia no maximal T wave changes were recorded. B: Hypoxia had a marked additive effect o n the occurrence of the high T waves indicating a mechanism other than beta-adrenoceptor stimulation, for example a direct stimulation of phosphorylase activity in the myocardium. C: Although propranolol rapidly abolished the effect of isoprenaline, as well as the ECG changes induced by mild hypoxia, no such response was seen o n the ECG during marked hypoxia further indicating another mechanism than beta-stimulation behind the ECG changes. D: During isoprenaline infusion there was a n increase in lactate concentration which is partly of cardiac origin (Dawes et a/. 1959). The conclusion to be made is that mild hypoxia initiates the ECG changes via a n actiyation of beta-adrenoceptors while severe hypoxia induces the ECG changes through a direct effect. Thus, progressive changes in the S-T segment of the F E C G during hypoxia seem t o reflect myocardial glycolysis induced by an imbalance between energy-yielding and energy consuming processes. This study was supported by grants from Goteborgs Lakaresallskap, the Faculty of Medicine, Goteborg, the Swedish Medical Research Council (2 591) and Prenatalforskningsfonden.
References and R. E. MYERS,Production of fetal asphyxia in the rhesus ADAMSONS, K., E. MUELLER-HEUBACH monkey by administration of catecholamines to the mother. Amer. J. Ohstet. Cynm. 1971. 109. 248-262. COMLINE, R. S., I. A. SILVER and M. SILVER, Factors responsible for the stimulation of the adrenal medulla during asphyxia in the fetal lamb. J. Physiol. (Lond.) 1965. 178. 211-238. DAWES,G. S., J. C. MOTTand H. J. SHELLEY, The importance of cardiac glycogen for the maintenance of life in foetal lambs and newborn animals during anoxia. J. Physiol. (Lond.) 1959. 146. 516-538. DAVIDSEN, P. C. B., The significance of the foetal electrocardiogram during labour with detailed report of one case. Acta obstet. gynec. sccmd. 1971. 50. 45-49. DOWNING, S. E., T. H. G A R D N Eand R J. M. ROCAMORA, Adrenergic support of cardiac function during hypoxia in the newborn lamb. Amer. J. Physiol. 1969. 217. 728-735. E N H ~ R N I NG.G ,and B. WESTIN,Experimental studies of the human fetus in prolonged asphyxia. Acta physiol. scancl. 1954. 31. 359-375. GELLI,M. G. and F. GYULAI, Effect of glucose infusion in the mother before delivery on the ECG of rabbit foetuses under anoxia. Acta obsret. gynec. scand. 1969. 48. 56-63. HEDVALL, G., 1. K J E L L M and ~ R T. OLSON, An experimental evaluation of the thermodilution method for determination of cardiac output and of intracardiac right-to-left shunts. Scanrl. J . clin. Lab. Znuest. 1973. 31. 61-68. HON, E. H. and S. T. LEE, The fetal electrocardiogram. I. The electrocardiogram of the dying fetus. Amer. J . Obstrr. Gynec. 1963. 87. 804-813. JOELSSON, I., M. D. BARTON, S. DANIEL, L. S . JAMES and K. ADAMSONS, The response of the unanesthetized sheep fetus to sympathicomimetic amines and adrenergic blocking agents. Amer. J. Obstet. Cynec. 1972. 114. 43-50. JONES,C. T. and R. 0. ROBINSON, Plasma catecholamines in foetal and adult sheep. J. Physiol. (Lond.) 1975. 248. 15-33. JOUBERT, D. M., A study of prenatal growth and development in the sheep. J. Agr. Sci. 1965.47. 382-393.
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LEE,S. T. and E. H. HON,The fetal electrocardiogram. IV. Unusual variations in the QRS complex during labor. Amer. J. Obstet. Gynec. 1965. 92. 1140-1148. MAYER,S. E., 8. J. WILLIAMS and J. M. SMITH,Adrenergic mechanisms in cardiac glycogen metabolism. Ann. N.Y. Acad. Sri. 1967. 139. 686-702. MORISHIMA, H. O . , S. S. DANIEL, R. T. RICHARDS and L. S. JAMES,The effect of increased maternal PaO, upon the fetus during labor. Amer. J . Obstet. Gynec. 1975. 123. 257-264. MUELLER-HEUBACH, E. and K. ADAMSONS, Surveillance of the fetus during the intrapartum period. MI. Sinai J . Med. 1971. 38. 4 2 7 4 3 9 . MYERS,R. E., Two patterns of perinatal brain damage and their conditions of occurrence. Amer. J . Ohstet. Gynec. 1972. 112. 246-276. PARDI,G., E. TUCCI, A. UDERZO and D. ZANINI,Fetal electrocardiogram changes in relation to fetal heart rate patterns during labor. Amer. J. Obstet. Gynec. 1974. 118. 243-250. VAN PETTEN, G. R. and R. F. WILLES, Beta-adrenoceptive responses in the unanaesthetized ovine foetus. Brit. J . Pharmacol. 1970. 38. 572-582. ROSBN,K. G . and I. KJELLMER, Changes in the fetal heart rate and ECG during hypoxia. Actaphysiol. scand. 1975. 93. 59-66. ROSEN, K. G. and 0. ISAKSSON, Alterations in fetal heart rate and ECG correlated to glycogen, creatinephosphate and ATP levels during graded hypoxia. Biol. Neonate. 1976. 30. 17-24. ROSEN,K. G., K.-H. HOKEGARD and 1. KJELLMER, A study of the relationship between the electrocardiogram and hemodynamics in the fetal lamb during asphyxia. Acta physiol. scand. 1976. 98. 275-284. ROSEN,K. G., A. HRBEK,K. KARLSSON, I. KJELLMER, T. OLSSONand M. RIHA,Changes in the ECG and somato-sensory evoked EEG responses (SER)during intrauterine asphyxia in the sheep. Biol. Neonate. 1976. 30. 95-101. STERN,L. and J. LIND,Neonatal T wave patterns. Acta paediat. scand. 1960. 49. 329-337. STERN,L., J. LINDand B. KAPLAN,Direct human foetal electrocardiography (with studies of the effect of adrenaline, atropine, clamping of the umbilical cord and placental separation on the foetal ECG). Biol. Neonat. (Basel) 1961. 3. 49-62.
ECG-changes in the fetal lamb during asphyxia in relation to beta-adrenoceptor stimulation and blockade BY
K.-H. HOKEGARD, K. KARLSSON, 1. KJELLMER and K. G. ROSBN Received 31 May 1978
Abstract HOKEGARD, K.-H., K. KARLSSON, I. KJELLMER and K. G. R O S ~ NECG-changes , in the fetal lamb during asphyxia in relation to beta-adrenoceptor stimulation and blockade. Acta physiol. scand. 1979. 105. 195-203. Progressive changes in the S-T interval of the fetal electrocardiogram (FECG) were studied in 14 lamb fetuses, acutely exteriorized and subjected to graded hypoxla. The aims of the study were to investigate whether beta-adrenoceptor stimulation and hypoxia exerted additive or potentiating effects on the FECC and several cardiovascular parameters and whether the hypoxic changes of the FECG could be blocked by beta-adrenoceptor blocking agents. The FECG changes were studied in order to correlate them with cardiovascular function, as measured by heart rate, mean arterial pressure, end diastolic pressure, maximum dP/dt and combined cardiac output, estimated by the thermodilution method, as well as with blood gases, acid base status, blood lactate and glucose. Injections of small doses (0.02 to 0.4pg kg-l min-’) of isoprenaline induced the same pattern of changes in the FECG as we have previously recorded during hypoxia. By increasing the isoprenaline dose an increase in the duration of the FECG changes and amplitude of the T-wave changes was obtained. Propranolol was found to completely abolish the FECG changes induced by isoprenaline, as well as by mild hypoxia. During severe hypoxia the FECG changes could not be abolished by propranolol. Our previous findings indicated that the hypoxic changes could be regarded a s a sign of myocardial glycolysis. Thus, the present finding that even small doses of isoprenaline given to the fetus, initiates the same pattern of FECG changes corroborate this hypothesis.
The fetal electrocardiogram (FECG) is used in clinical practice mainly as a means to obtain an indicator of fetal heart rate (FHR). While it is generally accepted that FHR is an indicator of fetal well-being during pregnancy and labour, the diagnostic value of the FECG is controversial. Although alterations in the pattern of the FECG have been detected during labour (Davidsen 1971, Pardi et al. 1974) by using the fetal scalp electrode, these alterations are believed to be preceded by changes in the FHR (Hon and Lee 1963, Lee and Hon 1965, Davidsen 1971). Several investigators have shown changes in the FECG during hypoxia using experimental models (Enhorning and Westin 1954, Stern et al. 1961, Gelli and Gyulai 1969, MuellerHeubach et al. 1971, Myers 1972, Morishmia et al. 1975). Although changes in the S-T interval were readily apparent, it was stated that the use of FECG for the detection of fetal asphyxia will be limited. 195
196
K.-H. HOKEGARD, K. KARLSSON, I . KJELLMER AND K . G .
ROSBN
Our own animal experiments revealed progressive and reproducible changes in the S-T interval of the FECG during graded hypoxia both in mature guinea-pig fetuses and lamb fetuses (RosCn and Kjellmer 1975). The metabolic background of these changes of the FECG was studied from different aspects. R o d n and Isaksson (1976) demonstrated a parallelity between the FECG changes and the depletion of myocardial glycogen during graded hypoxia in guinea-pig fetuses. The significance of this finding was supported by the relationship found between the increase in the amplitude of the T wave and the degree of metabolic acidosis as well as the accumulation of lactate in the exteriorized fetal lamb (Rosen et al. 1976). These findings together with the relationship found between the appearance of the FECG-changes and decrease in PaO, (Rosen, Hokeggrd and Kjellmer 1976) indicate that the progressive FECG changes reflect myocardial glycogenolysis. Alterations in the FECG pattern consistently preceded signs of failing cardiovascular function and occurred well in advance of any bradycardia (RosCn, HokegArd and Kjellmer 1976). Thus, there are a good many observations indicating that progressive changes in the S-T interval reflect myocardial glycogenolysis and early hypoxic stress. The augmentation of glycogenolysis in heart muscle by beta-receptor stimulation is well known (Mayer et al. 1967). Our own preliminary experiments indicated that the betareceptor stimulating agent, isoprenaline, initiated the same typical pattern of changes in the FECG as hypoxia. Therefore it was considered of interest to elucidate the influence of beta-adrenoceptor stimulation and blockade on the FECG. The aims of the present study were to investigate whether beta-adrenoceptor stimulation and hypoxia exerted additive or potentiating effects in the FECG and several cardiovascular parameters and whether the hypoxic changes of the FECG could be blocked by betaadrenoceptor blocking agents.
Material and methods The experiments were conducted on 9 ewes of mixed breed with 14 fetuses acutely exteriorized. The gestational age was dated in 2 ewes and was estimated from fetal weight and crown-rump length in 7 ewes, using standard curves (Joubert 1956). In a first series of 5 ewes with 8 fetuses, the experiments were conducted according to the methods described earlier ( R o s h , Hokeglrd and Kjellmer 1976). Their gestational age ranged from 109 to 132 days (term 147 days) and their weight from 1 060 to 3 370 g (2 244+228 g, mean value f S.E.). The left jugular vein of the fetus was cannulated and 0.1 to 1O.Opg (0.04 to 9.0 pg/kg) isoprenaline was given i.v. in single injections. Via the same catheter, the beta-blocking agent, propranolol, was given in doses varying from 0.05 to 2 mg (0.02 to 0.83 mg/kg). Fetal and maternal blood pressure, p H and blood gas tensions were measured, fetal heart rate and end diastolic pressure were registered, combined fetal cardiac output was estimated and the FECG recorded with a CR-lead. The ewes (and thereby the fetuses) were exposed to alternate periods of normoxia and hypoxia. The hypoxia was induced by ventilating the ewe with gas mixtures containing 9-15?, 0, in N, and in some experiments with an addition of 10-20% CO,. The hypoxic changes in the ECG pattern were quantified according to the scoring system previously described: The appearance of negative T wave changes, the amplitude exceeding that of the P waves. Maximally negative T wave changes. A gradual decrease in the amplitude of the negative T wave changes. An elevation of the S-T segment and the T wave, the amplitude of the T wave being higher than that of the P wave. Grade V: A maximal increase in the amplitude of the T wave. Grade VI: A decrease in the amplitude of the T wave during continuous hypoxia.
Grade I: Grade 11: Grade 111: Grade IV:
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A second series of 4 ewes with 6 fetuses was used to establish a quantitative dose-response relationship between isoprenaline and FECG changes. Their gestational age ranged from 128 to 138 days (132k2, mean value & S.E.) and their weight from 2 330 to 2 950 g (2 530+ 100). Maternal and fetal blood pressure, blood gas tensions and pH, fetal heart rate and FECG were registered in the same way as in the first series. In order to get a quantitative measurement of the high and peaked T waves, a ratio between the amplitude of the QRS complex and the T wave (T/QRS ratio) was calculated (Fig. 1). Left ventricular pressure was monitored with a micro-tip sensitive catheter (Millar instruments), inserted via the left carotid artery. Maximum dP/dt was derived electronically from this signal and continuously recorded. The thermodilution method (Hedvall e#al. 1973) was also used for estimation of the combined fetal cardiac output (“CO”), but instead of injecting saline of room temperature into the left ventricle as in the first series, it was injected into the inferior vena cava through a catheter inserted via the femoral vein. The left jugular vein was cannulated and isoprenaline was administered continuously with an infusion pump in stepwise higher doses of 0.044, 0.076, 0.143, 0.22, 0.78 and 4.4 pg/min in order to estimate a dose-response curve. This was done both during normoxia and hypoxia before and after betaadrenoceptor block. The beta-blocking agent propranolol was given through the same catheter in the left jugular vein in doses varying from 0.02 to 0.5 rng (0.01 to 0.19 mg/kg).
Results Beta-adrenoceptor stimulation In the first series, isoprenaline was given i.v. in single doses ranging from 0.04 to 9.0 pg/kg to 8 fetuses. In each case isoprenaline induced the same alterations of the FECG pattern as hypoxia. A relationship was found between the dose of isoprenaline and the increase in T wave amplitude, as well as the duration of the ECG changes. Fig. 2 gives an example of recordings made after the injection of 1.0 ,ug (0.4 ,ug/kg) isoprenaline. The whole sequence of alterations of the S-T interval, accounted for in the ECG-scoring system is demonstrated. 3 seconds after I O p g lsoprenaline 100
ARTERIAL BLOOD PRESSURE. rnrn Hg 5 l: inn.
IV
1
I sec
LEFT VENTRICULAR PRESSURE, rnrn Hg I50
HEART beals/rnin RATE
]:
4
ELECTROCARDIOGRAM Precordial lead
Fig. 2. Fetal electrocardiogram changes after the injection of 1 .Opg (0.4 ,ug/kg) isoprenaline. Note the rapid progression in the S-T interval.
I98
K.-H. HOKEGLRD, K . KARLSSON, I . KJELLMER AND K. G .
ROSPN
IO08T/QRS ratio
06040 2. 0I00
MAP
rnrn Hg
Six fetuses at normoxia f SEM
I
I Meanvalues
fetuses with hypoxia
o---oFour I
0'
08 lsoprenaline pg/rnin
0
N H'YPOXIA Fig. 3. Effect of isoprenaline infusion on the T/QRS ratio of the fetal electrocardiogram, fetal heart rate, mean arterial pressure, maximum dP/dt and combined cardiac output both during normoxia and hypoxia.
In order to further elucidate the influence of beta-adrenoceptor stimulation on the FECG and cardiovascular function and to estimate a dose-response curve, isoprenaline was continuously infused in step-wise higher doses in a second series. This group of 6 fetuses was quite homogeneous regarding gestational age and fetal weight. ECC-changes. Fig. 3 demonstrates the relationship between the increase in T wave amplitude and the dose of isoprenaline (6 fetuses). Hypoxia (4 fetuses) had an additive effect on the ECG changes which appeared earlier and with a higher T/QRS ratio (Grade V in the scoring system). At the highest dose of isoprenaline given during hypoxia the T/QRS ratio decreased again (Grade VI in the scoring system) in the only animal studied. Cardiovascular function. Fig. 3 also demonstrates the effect of isoprenaline on mean arterial pressure, fetal heart rate, maximum dP/dt and combined cardiac output. Both FHR, dP/dt and cardiac output increase gradually with increasing doses of isoprenaline. MAP shows no significant changes. The augmentation of cardiac performance caused by isoprenaline infusion was inhibited by the combination of hypoxia and acidosis. Fig. 3 demonstrates the combined effect of hypoxia and isoprenaline in 4 fetuses. After an initial increase associated with hypoxia both MAP, FHR, maximum dP/dt and "CO" decrease at increasing doses of isoprenaline. Bloodgases, p H , lactate andglycose. There was no change in PaO, during the isoprenaline infusions at normoxia. PaO, was 3.19 i 0 . 2 9 kPa before the infusions started and 3.09 k0.32
199
ECG-CHANGES IN FETAL LAMB
FETAL LAMB, 123 days- 2120 g
ECG
scores
MAP m m Hg
"co" I/(min I, kg)
69 Ft@(kPo) PH 7 30, TIME, 5minutes
77 7 29
I
15x0;.
HYPOXIA
93 7 12 129602
104
6 9f 6 %02
HYPOXIAtC02
Fig. 4. Changes in the fetal electrocardiogram, graded according to the scoring system, mean arterial pressure, fetal heart rate and combined cardiac output after isoprenaline and propranolol injections made both during normoxia, hypoxia and the combination of hypoxia and hypercarbia.
at the end of the infusions (mean value i S.E.). pH, however, decreased from 7.27 k0.04 to 7.17 20.06 and there was a lactate accumulation from 2.85 50.47 to 4.77 k 1.69 nimol/l. Blood glycose values did not change (1.47 k0.28 and 1.53 k0.30 mmol/l respectively). In the 4 fetuses subjected to both hypoxia and isoprenaline infusion the mean PaO, value was 3.53 (range 3.19-3.86) before hypoxia and decreased to 1.86 (range 1.06-2.66) during hypoxia and 1.83 (range 1.06-2.52) when isoprenaline infusion was added. The mean pH value was 7.15 (range 6.99-7.24) before hypoxia and decreased to 7.04 (range 6.89-7.18) during hypoxia and isoprenaline infusion. The mean lactate value was 5.94 (range 1.7111.32) before the hypoxic period and the concentration rose to 8.58 (range 1.71-13.16) mmol/l during hypoxia and isoprenaline infusion. Blood glycose values increased slightly from 1.96 (range 1.74-2.20) to 2.20 (range 2.07-2.36) mmol/l. In all these 4 fetuses the period of hypoxia combined with isoprenaline was preceded by periods of isoprenaline infusion without hypoxia. Beta-adrenoceptor blockade Propranolol was also given to the 8 fetuses of the first series in order to test whether betaadrenoceptor blockade interfered with the ECG changes induced by hypoxia. The degree of
200
K.-H. HOKEGKRD, K. KARLSSON, I. KJELLMER AND K. G. R O S ~ N
T/QRS ratio
MAP A rnrn Hg
04 “CO“
IArnin
2000
dP,d,.
,ooo
mmHg/s
+
t
I
Fig. 5. Effect of propranolol on 4 fetuses subjected to hypoxia and acidosis. PaO, was 2,21+0.24 kPa before the injection and 1.97k0.39 after the injection. pH was 6.9850.13 before the injection and 6.91 0.09 after the injection (mean values S.E.).
I
2
3
4
5 minutes
Propranolol 0.20-0.25 mg
beta-blockade was tested by repeated injections of isoprenaline. The ECG changes induced by isoprenaline completely disappeared about 10 s after the propranolol injections. Fig. 4 demonstrates the pattern of events recorded in a lamb fetus (gestational age: 123 days). The first part of the figure illustrates the effect of isoprenaline (0.47pg/kg) on the combined cardiac output, heart rate and mean arterial pressure as well as the FECG. Alterations in the FECG pattern, elevation of the S-T segment with high and peaked T waves, were associated with a tachycardia and an increase in cardiac output from 0.61 to 0.78 l/(min x kg). A moderate hypoxia, induced by ventilating the ewe with 15%0,, elicited the same pattern of events in the FECG. These changes were immediately blocked by propranolol (0.05 mg/kg). This dose of propranolol was found to almost completely block the effect of a large dose of isoprenaline (4.7 pg/kg). In the last part of the figure the effect of beta-blockade associated with a severe hypoxia are demonstrated. No FECG changes were recorded until there were signs of failing cardiovascular function. These FECG changes could apparently not be blocked even by large doses of propranolol. Propranolol blocked the FECG changes elicited by moderate hypoxia in the two fetuses studied but did not alter the FECG changes associated with a severe hypoxia and a failing circulation (6 cases). The fetus was extremely susceptible to the combination of hypoxia and propranolol. In the second series propranolol blocked the cardiovascular effects of isoprenaline in the same way. These fetuses were also extremely susceptible to the combination of propranolol and hypoxia. In 4 fetuses the combination of acidosis, hypoxia and propranolol resulted in a rapid deterioration of fetal circulation and fetal death 3 to 6 min after the injection of 0.2 to 0.25 mg propranolol i.v. Fig. 5 illustrates the rapid decay of MAP, FHR, maximum dP/dt and “CO’. There is also a decrease in the amplitude of the maximally high and peaked T waves during hypoxia after propranolol injection, i.e. grade VI in the ECG scoring system.
ECG-CHANGES IN FETAL LAMB
20 1
Discussion The results demonstrate that small doses of isoprenaline given during normoxia can elicit the whole sequence of events in the FECG, previously recorded during hypoxia. This is in accordance with the view that glycogenolysis induced by beta-adrenoceptor stimulation via isoprenaline will produce the changes of the FECG. Most tissues respond to oxygen lack by increasing their rate of glycolysis, in parallel with the metabolic events elicited by betareceptor stimulation (Mayer et al. 1967). In asphyxiated animals adrenaline and noradrenaline may be released from the adrenal medulla leading to an increased rate of glycogen breakdown due to phosphorylase activation. This mechanism has been shown to operate in fetal lambs (Comline and Silver 1965). Jones and Robinson (1975) measured increased plasma catecholamine concentrations during hypoxia (fetal PaO, 18 mmHg) in the chronically catheterized fetal Iamb. They could demonstrate an increase in plasma adrenaline corresponding to that produced by the infusion of 0.4 pg kg-l min-l adrenaline. Thus, it appears that the dose of isoprenaline (0.02 to 0.4 pg kg-l min-') which we found to elicit alterations in the FECG pattern, is similar to the amounts of catecholamines secreted during hypoxia. Furthermore, an increase in the dose of isoprenaline resulted in an increase in the duration and amplitude of the T-wave changes in parallel with the pattern of changes recorded with increasing degree of fetal hypoxic stress. Alterations in the FECG with an increase in P wave and decrease in T wave amplitude together with a shortened P-R interval, have been recorded during catecholamine infusion into fetal rhesus monkey by Adamsons et al. (1971) using significantly higher dosage. Stern et al. also obtained higher T-waves after the administration of adrenaline (100 pg i.m.) to newborn babies (1960) and to human fetuses (1961). Isoprenaline gave a positive chronotropic and inotropic effect, the later nicely demonstrated by an increase in myocardial contractility as measured by an increase in max.dP/dt. There was a decrease in pH and an accumulation of blood lactate during isoprenaline infusions but no change in PaO,. These findings are compatible with an augmented glycogenolysis. Infusion of isoprenaline had an additive effect to hypoxia and acidosis with earlier and more pronounced FECG changes and seemed to give a more rapid deterioration of the fetal circulation. The positive chronotropic and inotropic effects of isoprenaline, as well as the negative chronotropic effect of propranolol, have previously been studied in lamb fetuses (Joelsson et al. 1972, van Petten and Willes 1970). In our study, even small doses of propranolol (0.01 to 0.19 mg/kg) completely abolished the FECG changes, produced either by isoprenaline or mild hypoxia. A different pattern was seen during more severe hypoxia with signs of failing cardiovascular function. In this situation beta-blockade had no influence on the ECG changes, consistent with the fact that asphyxia per se is a stimulator of phosphorylase activity in the myocardium (Mayer et af. 1967). The fetus was extremely susceptible to the combination of propranolol and hypoxia. This is likely to be the result of propranolol blocking the most important compensatory mechanisms on the circulatory (Downing et a/. 1969) as well as the metabolic side.
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K. KARLSSON, I. KJELLMER AND K. G .
ROSBN
The question now to be asked is whether the predominant change in the FECG, the high and peaked T wave, is induced by the augmentation of myocardial glycogenolysis or is a direct effect of the high catecholamine output o n the function of the myocardial cell membrane. There are a number of findings in support of the former hypothesis namely: A: Even during the infusion of very high doses of isoprenaline during normoxia no maximal T wave changes were recorded. B: Hypoxia had a marked additive effect o n the occurrence of the high T waves indicating a mechanism other than beta-adrenoceptor stimulation, for example a direct stimulation of phosphorylase activity in the myocardium. C: Although propranolol rapidly abolished the effect of isoprenaline, as well as the ECG changes induced by mild hypoxia, no such response was seen o n the ECG during marked hypoxia further indicating another mechanism than beta-stimulation behind the ECG changes. D: During isoprenaline infusion there was a n increase in lactate concentration which is partly of cardiac origin (Dawes et a/. 1959). The conclusion to be made is that mild hypoxia initiates the ECG changes via a n actiyation of beta-adrenoceptors while severe hypoxia induces the ECG changes through a direct effect. Thus, progressive changes in the S-T segment of the F E C G during hypoxia seem t o reflect myocardial glycolysis induced by an imbalance between energy-yielding and energy consuming processes. This study was supported by grants from Goteborgs Lakaresallskap, the Faculty of Medicine, Goteborg, the Swedish Medical Research Council (2 591) and Prenatalforskningsfonden.
References and R. E. MYERS,Production of fetal asphyxia in the rhesus ADAMSONS, K., E. MUELLER-HEUBACH monkey by administration of catecholamines to the mother. Amer. J. Ohstet. Cynm. 1971. 109. 248-262. COMLINE, R. S., I. A. SILVER and M. SILVER, Factors responsible for the stimulation of the adrenal medulla during asphyxia in the fetal lamb. J. Physiol. (Lond.) 1965. 178. 211-238. DAWES,G. S., J. C. MOTTand H. J. SHELLEY, The importance of cardiac glycogen for the maintenance of life in foetal lambs and newborn animals during anoxia. J. Physiol. (Lond.) 1959. 146. 516-538. DAVIDSEN, P. C. B., The significance of the foetal electrocardiogram during labour with detailed report of one case. Acta obstet. gynec. sccmd. 1971. 50. 45-49. DOWNING, S. E., T. H. G A R D N Eand R J. M. ROCAMORA, Adrenergic support of cardiac function during hypoxia in the newborn lamb. Amer. J. Physiol. 1969. 217. 728-735. E N H ~ R N I NG.G ,and B. WESTIN,Experimental studies of the human fetus in prolonged asphyxia. Acta physiol. scancl. 1954. 31. 359-375. GELLI,M. G. and F. GYULAI, Effect of glucose infusion in the mother before delivery on the ECG of rabbit foetuses under anoxia. Acta obsret. gynec. scand. 1969. 48. 56-63. HEDVALL, G., 1. K J E L L M and ~ R T. OLSON, An experimental evaluation of the thermodilution method for determination of cardiac output and of intracardiac right-to-left shunts. Scanrl. J . clin. Lab. Znuest. 1973. 31. 61-68. HON, E. H. and S. T. LEE, The fetal electrocardiogram. I. The electrocardiogram of the dying fetus. Amer. J . Obstrr. Gynec. 1963. 87. 804-813. JOELSSON, I., M. D. BARTON, S. DANIEL, L. S . JAMES and K. ADAMSONS, The response of the unanesthetized sheep fetus to sympathicomimetic amines and adrenergic blocking agents. Amer. J. Obstet. Cynec. 1972. 114. 43-50. JONES,C. T. and R. 0. ROBINSON, Plasma catecholamines in foetal and adult sheep. J. Physiol. (Lond.) 1975. 248. 15-33. JOUBERT, D. M., A study of prenatal growth and development in the sheep. J. Agr. Sci. 1965.47. 382-393.
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LEE,S. T. and E. H. HON,The fetal electrocardiogram. IV. Unusual variations in the QRS complex during labor. Amer. J. Obstet. Gynec. 1965. 92. 1140-1148. MAYER,S. E., 8. J. WILLIAMS and J. M. SMITH,Adrenergic mechanisms in cardiac glycogen metabolism. Ann. N.Y. Acad. Sri. 1967. 139. 686-702. MORISHIMA, H. O . , S. S. DANIEL, R. T. RICHARDS and L. S. JAMES,The effect of increased maternal PaO, upon the fetus during labor. Amer. J . Obstet. Gynec. 1975. 123. 257-264. MUELLER-HEUBACH, E. and K. ADAMSONS, Surveillance of the fetus during the intrapartum period. MI. Sinai J . Med. 1971. 38. 4 2 7 4 3 9 . MYERS,R. E., Two patterns of perinatal brain damage and their conditions of occurrence. Amer. J . Ohstet. Gynec. 1972. 112. 246-276. PARDI,G., E. TUCCI, A. UDERZO and D. ZANINI,Fetal electrocardiogram changes in relation to fetal heart rate patterns during labor. Amer. J. Obstet. Gynec. 1974. 118. 243-250. VAN PETTEN, G. R. and R. F. WILLES, Beta-adrenoceptive responses in the unanaesthetized ovine foetus. Brit. J . Pharmacol. 1970. 38. 572-582. ROSBN,K. G . and I. KJELLMER, Changes in the fetal heart rate and ECG during hypoxia. Actaphysiol. scand. 1975. 93. 59-66. ROSEN, K. G. and 0. ISAKSSON, Alterations in fetal heart rate and ECG correlated to glycogen, creatinephosphate and ATP levels during graded hypoxia. Biol. Neonate. 1976. 30. 17-24. ROSEN,K. G., K.-H. HOKEGARD and 1. KJELLMER, A study of the relationship between the electrocardiogram and hemodynamics in the fetal lamb during asphyxia. Acta physiol. scand. 1976. 98. 275-284. ROSEN,K. G., A. HRBEK,K. KARLSSON, I. KJELLMER, T. OLSSONand M. RIHA,Changes in the ECG and somato-sensory evoked EEG responses (SER)during intrauterine asphyxia in the sheep. Biol. Neonate. 1976. 30. 95-101. STERN,L. and J. LIND,Neonatal T wave patterns. Acta paediat. scand. 1960. 49. 329-337. STERN,L., J. LINDand B. KAPLAN,Direct human foetal electrocardiography (with studies of the effect of adrenaline, atropine, clamping of the umbilical cord and placental separation on the foetal ECG). Biol. Neonat. (Basel) 1961. 3. 49-62.
