Roy H. Petrie

Respiratory movements in fetal rhesus monkeys

Abstract Fetal tracheal pressure was recorded continuously for prolonged periods in awake, restrained rhesus monkeys. Other parameters recorded included fetal blood pressure, heart rate, eye movements, and EEG. Fetal arterial blood samples were obtained intermittently for determination of pH and respiratory gas tensions. The observations spanned the interval from approximately 115 days gestation until term. Changes in tracheal pressure representing a variety of respiratory movements were observed. Isolated and repetitive gasping movements exceeded 30 mm. Hg negative pressure. Rhythmic and rapid irregular breathing movements of lesser intensities were also recorded. These breathing movements occupied approximately two thirds of the time in the healthy fetuses. Somatic and eye movements were more frequent and the heart rate and blood pressure more irregular during the periods of respiratory activity than during the intervening quiet times. Fetal breathing movements disappeared during fetal stress and failed to develop in fetuses which did not exhibit normal pH and respiratory gas tensions following operation.

Hyperventilation during labor.

Abstract The effect of maternal hyperventilation during labor was studied in 20 patients. Fetal scalp blood samples were analyzed for pH, pO 2 , pCO 2 , and base excess and compared with maternal free-flowing venous blood samples taken at the same time. Samples were obtained for baseline values and repeated during and following a period of active hyperventilation. Both maternal and fetal pH rose with hyperventilation. No fetal acidosis was observed even in the 5 cases of severe maternal hypocarbia. Maternal pCO 2 during labor was low even prior to intentional hyperventilation. Both maternal and fetal pCO 2 decreased, the maternal change being greater than the fetal. There was a slight but statistically significant decrease in the fetal pO 2 during hyperventilation. However, fetal oxygen levels remained within physiologic range throughout the study.

Cardiac systolic time intervals in fetal monkeys: Pre-ejection period

The systolic time intervals of the fetal cardiac cycle were studied by means of simultaneous recordings of electrocardiogram (ECG) and ultrasound Doppler cardiogram (DCG) in chronic preparations of fetal rhesus monkeys. Recordings were made under physiologic conditions as well as during various experimental stresses. The pre-ejection period (PEP) showed no significant relationship with heart rate in the unstressed fetuses, but the acceleration of heart rate induced by epinephrine was accompanied by shortening of PEP. The PEP increased with advancing fetal age. The PEP was inversely correlated with left ventricular end-diastolic pressure and arterial pulse pressure, but showed a positive correlation with both systolic and diastolic arterial blood pressure. The PEP also exhibited strong negative correlation with arterial blood pH. the prolongation was essentially the same whether acidosis was of respiratory or metabolic origin. The PEP increased slightly but significantly during nonacidemic hypoxemia; however, there was no correlation between Pao2 and PEP Epinephrine shortened the PEP significantly, whereas the effect of atropine was inconsistent. Alteration of the plasma glucose level by injection of insulin or glucose did not affect PEP. These findings demonstrate that the PEP may be a useful indicator of fetal cardiac performance, reflecting both myocardial contractility and the hemodynamic state of the cardiovascular system.

The effect of magnesium sulfate on fetal heart rate variability and uterine activity

The effect of magnesium sulfate on fetal heart rate (FHR) variability and uterine activity is evaluated in 19 preeclamptic patients at term in active labor. Magnesium sulfate was given by intramuscular injection in nine patients and by intravenous infusion in 10 patients after an intravenous loading dose over a period of 15 minutes. No significant change was noted in FHR variability. There was only a transient, mild decrease in the frequency of uterine contractions during the magnesium sulfate loading dose, and there was no significant change in the intensity of uterine contractions. The conclusion is that, when magnesium sulfate is used for treatment of mild preeclampsia in patients at term in established labor, there is no clinically significant effect on FHR variability or uterine activity.

Oxytocin to Induce Labor

Oxytocin is a highly successful and safe agent for inducing labor and has a fairly large therapeutic index. It has, however, minimal, but not trivial, antidiuretic and vascular activity when used in large doses. Therefore, to induce labor, low-dose oxytocin dosing regimens that produce efficacious uterine activity and avoid side effects are recommended. Oxytocin should be used in the lowest possible doses necessary to effect a clinical response. Diligence must be exercised when monitoring labor and fetal well-being. Hofbauer, the first to use oxytocin to induce labor, said in 1927 that oxytocin, with its power of producing regular, rhythmical and forcible uterine contractions, should be regarded as a most beneficent and valuable agent, which, however, should always be employed with care and a realisation of its limitations and dangers. His words remain valid today.

Human fetal oxygenation (tcPo2), heart rate variability and uterine activity following maternal administration of meperidine.

Fetal tcPo2 levels were measured in 10 patients following maternal administration of 50 mg of meperidine by intravenous route. About 3 minutes following injection of meperidine, tcPo2 values started to decline to reach the lowest value of 37 +/- 25% by 7 mins of injection. tcPo2 values recovered by about 15 mins following injection. These changes in fetal tcPo2 levels preceded transient minimal increase in FHR variability. The increase in FHR variability was followed immediately by a decrease in the indices of the FHR variability. The uterine activity began to decline below the predicted positive slope values shortly following injection of meperidine. This decline was maximum 15 mins post-injection, subsequently establishing a trajectory toward the positive values expected for unmedicated labor. Two patients receiving 25 mg intravenous meperidine demonstrated no decline in tcPo2 levels; however, in the patient receiving 75 mg of intravenous meperidine, the changes noted were similar to those observed following 50 mg of meperidine.

Response of ovine uterine blood flow to angiotensin II: Effect on the fetus

The effect of intravenous infusion of angiotensin II (2 to 200 ng/kg/min) on uterine blood flow and cardiovascular performance was studied in the normotensive, unanesthetized pregnant ewe. With low rates of infusion (2 to 4 ng/kg/min), only a transient increase in uterine blood flow, lasting 1 to 3 minutes, was observed. Higher rates (110 to 200 ng/kg/min) of infusion caused a decrease in uterine blood flow; this decrease was significantly correlated to the dose. Angiotensin II also caused a significant decrease in the maternal heart rate and an increase in mean maternal arterial blood pressure as the rate of infusion was increased. A high rate of infusion resulted in decreased fetal heart rate and PaO2, probably due to a marked reduction in uteroplacental blood flow.

Noninvasive fetal ECG mode fetal heart rate monitoring by adaptive digital filtering.

Beat-to-beat variability (BTBV) of the fetal heart rate (FHR) is considered an indication of the neural integrity and is an important prognostic indicator of fetal well-being. We report the initial evaluation of a recently developed abdominal fetal ECG (AFECG) mode of FHR monitoring using Adaptive Digital Filtering (ADF) to accurately obtain BTBV noninvasively. Five women in labor at term were monitored with the direct fetal scalp electrode (FSE) and simultaneously with the AFECG using ADF. A computer analysis of 3298 seconds (55 minutes) of data provided a one-to-one comparison of the R-R intervals. One analysis of the direct FSE data with a second simultaneous analysis from the same electrode, to serve as control, was compared with the noninvasive AFECG data. The study group has a standard deviation of only 1.50 bpm compared to 0.79 bpm for the control group. The AFECG method agrees with the direct FSE method within 1 bpm for 92.6% of the reported R-R intervals and within 2 bpm for 98.9% of the reported intervals. This new noninvasive AFECG technique with ADF provides a continuous record of instantaneous FHR and BTBV that may be relied upon to provide an accurate continuous clinical record. The reliability of the technique has yet to be determined over a wide range of subjects.

Clinical use of the Kleihauer-Betke test

Results of all Kleihauer-Betke (KB) tests performed in 1988, at a center with 4,201 deliveries, were reviewed. Two hundred and twenty-seven tests were performed on maternal specimens from 205 patients. Eighteen (8.8%) of the 205 patients had positive test results. Medical records were available for 147 (71.7%) of the patients, including 17 of the 18 patients with a positive result. Indications for testing were: vaginal bleeding (33%), maternal trauma (31%), unexplained fetal death (5%), Rh incompatibility (3%), fetal distress (3%), and miscellaneous (24%). Most of the tests were performed antepartum. In only one case, and without clear benefit, did the KB test prompt a clinical intervention. At least two of the 18 patients with positive test results had probable false positive results due to maternal hemoglobin F. Such false positive KB test results may be misleading. Further evaluation of the role of the KB test in obstetrical management is needed.

Cardiac systolic time intervals in fetal monkeys: Ventricular ejection time ☆

The VET of the fetal cardiac cycle, measured as the interval between the semilunar valve opening and closing signals of the ultrasound Doppler cardiogram, was studied in chronically catheterized fetal rhesus monkeys. VET varied inversely with FHR between approximately 150 and 250 bpm. Below 150 bpm, however, there was no further prolongation of VET. VET was not related to gestational age. VET, corrected for heart rate, was shortened in the presence of combined hypoxemia and acidosis, but not when either hypoxemia or acidemia was present alone. Corrected VET was shortened by epinephrine, but was not consistently altered by atropine. VET was not affected by changes in the concentration of glucose in fetal blood.