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PubMed1994

Fetal heart rate decelerations and umbilical cord blood gas values.

Although fetal heart rate (FHR) monitoring is widely used for fetal surveillance, there is still disagreement about the value of cardiotocography and the interpretation of FHR patterns. We addressed this in a prospective study in which umbilical cord blood gas and pH values at the time of cesarean section were related to different FHR patterns classified prior to surgery. The patient population consisted of 56 pregnant women with singleton fetuses of gestational age between 37 and 43 weeks. Indication for cesarean section was late FHR decelerations in 16 cases and variable decelerations in 17. Twenty-three patients operated on electively, and without any FHR abnormalities, served as a reference group. Late FHR decelerations were associated with the lowest pH and PO2 levels in arterial as well as in venous blood. In the group with variable decelerations, the umbilical vein PO2 was similar to that of the reference group, whereas the PO2 value in the artery was significantly lower. Hence, in this clinical study a clear relationship was found between the different FHR patterns and changes in the acid-base balance.

Carbon Dioxide↗
PubMed2004

Intrapartum fetal pulse oximetry and fetal heart rate decelerations.

OBJECTIVES: To determine the behavior of fetal oxygenation (FSpO(2)) in different patterns of fetal heart rate decelerations (FHR). METHODS: A total of 787 decelerations were studied. RESULTS: FSpO(2) decreased significantly during decelerations, especially when the alteration was prolonged. CONCLUSIONS: Modifications in FHR occur simultaneously with alterations in FSpO(2), although the latter do not persist in time. Different degrees of FSpO(2) seen prior to deceleration are an expression of fetal respiratory status.

Adolescent↗
PubMed2005

Predicting prolonged fetal heart rate deceleration following intrathecal fentanyl/bupivacaine.

BACKGROUND: Intrathecal opioids for labor analgesia are occasionally associated with fetal heart rate abnormalities. We wanted to identify risk factors for this occurrence. METHODS: The fetal tracings of 151 consecutive patients were reviewed for the period including 30 min before and 60 min after combined spinal-epidural analgesia using intrathecal bupivacaine with fentanyl. Their progress of labor at injection was also recorded. RESULTS: Lack of fetal head engagement (odds ratio 5.5, 95% CI 2.1-14.2) and the presence of variable fetal heart rate decelerations (odds ratio 3.6, 95% CI 1.6-8.4) were associated with prolonged fetal heart rate deceleration after combined spinal-epidural analgesia. CONCLUSION: This case-control study suggests that if the fetal head is not engaged or if the fetus is experiencing variable decelerations, there is an increased risk of prolonged fetal heart rate deceleration following intrathecal fentanyl/bupivacaine. This finding must now be confirmed in a cohort study.

Adult↗
PubMed1991

Umbilical artery blood flow velocity waveforms during variable deceleration of the fetal heart rate.

Blood flow velocities of the umbilical arteries were measured by Doppler ultrasonography during variable decelerations of the fetal heart rate. The flow velocity waveforms, being normal between uterine contractions, showed either an unchanged flow velocity waveform with an exclusive fetal heart rate effect on end-diastolic velocities or a rapid change to absent and reverse diastolic flow during the decelerations, indicating an abrupt increase in placental resistance with a halt in placental perfusion. Computer-aided reconstruction of the fetal heart rate curve revealed the exact temporal relationship between the reduction of umbilical artery perfusion and deceleration of fetal heart rate. We showed that variable decelerations of fetal heart rate can be observed during only slightly changed umbilical perfusion or can be caused by a halt in placental perfusion, which does not necessarily mean an absence of any movement of the fetal blood column, but is a result of a systolic forward and diastolic reverse flow to the same extent.

Blood Flow Velocity↗
PubMed1984

The significance of fetal heart rate decelerations during nonstress testing.

Over a 9-month time span, eight gravid women at high risk had fetal heart rate decelerations on nonstress tests (NSTs). This form of antepartum evaluation, the standard at our institution, was performed 918 times on 476 women during this period. Decelerations were required to be between 1 and 10 minutes in duration and less than 90 bpm, or greater than 40 bpm below baseline, for inclusion. Of the eight women (1.7% of the total tested), four had reactive and four nonreactive NSTs. All eight had contraction stress tests (CSTs) that were negative by definition. Of four women allowed to labor, two (50%) required cesarean section for fetal distress. Two instances of fetal death (25%) occurred during observation periods of 36 and 48 hours. Two infants were growth retarded, and two had abnormal cord positions. NSTs showing decelerations of this type, regardless of reactivity or of follow-up CST, are abnormal and should be viewed with alarm. In term pregnancy, such fetuses should be delivered. In preterm pregnancy with nonreactive NSTs, decelerations may also be valid grounds for delivery. Some discrimination is possible in preterm pregnancies when the NST is reactive.

Female↗
PubMed1988

The slope of fetal heart rate deceleration is predictive of fetal condition during repeated umbilical cord compression in sheep.

The relationship between components of fetal heart rate deceleration and fetal arterial blood gas values or plasma catecholamine concentrations was investigated by repeated complete umbilical cord compression in chronically instrumented fetal lamb. Fetal arterial pH and bicarbonate levels decreased, while plasma norepinephrine and epinephrine concentrations increased more than tenfold. The slope of the descending limb of the fetal heart rate deceleration curve decreased and correlated strongly with fetal arterial pH, bicarbonate, and logarithmic plasma norepinephrine and epinephrine concentrations. Fetal arterial pH and bicarbonate levels were significantly lower in the group with lower fetal heart rate deceleration slope, and a greater plasma catecholamine concentration in this group suggested a redistribution of blood flow to vital organs. Therefore, during repeated umbilical cord compression, the fetal acid-base and hormonal state was predicted by the fetal heart rate deceleration slope. This relationship may be applicable to human fetuses in the diagnosis of fetal distress caused by umbilical cord compression during labor.

Acidosis↗
PubMed1996

Fetal cerebral, circulatory, and metabolic responses during heart rate decelerations with umbilical cord compression.

OBJECTIVE: The purpose of this study was to determine the cerebral, circulatory, and metabolic responses of the ovine fetus near term to umbilical cord compression with variable-type fetal heart rate decelerations. STUDY DESIGN: Nine fetal sheep, at 0.9 of gestation, were studied before, during, and after umbilical cord occlusion for 1-minute and again after repetitive 1-minute cord occlusions every 5 minutes for 1 hour, with resultant fetal heart rate decelerations of approximately 90 beats/min. Brachiocephalic arterial and sagittal venous blood was analyzed for oxygen content, blood gases and pH, glucose, and lactate. Cerebral and upper body blood flow was measured with the microsphere technique. RESULTS: Umbilical cord occlusion with moderate to severe variable-type fetal heart rate deceleration resulted in an immediate drop in arterial PO2 by approximately 7 torr, an increase in PCO2 by approximately 9 torr, and a small but significant increase in lactate levels. Cerebral oxidative metabolism was well maintained but required an increase in fractional oxygen extraction because the variable change in cerebral blood flow was insufficient to maintain oxygen delivery. A redistribution of upper body blood flow was evident, with that to the bran and heart variably maintained or increased whereas that to muscle tissue was markedly decreased. Repetitive umbilical cord occlusion over 1 hour resulted in a significant drop in fetal arterial pH, with the acidemia mixed as PCO2 increased approximately 6 torr, whereas lactate levels increased almost fourfold. CONCLUSION: Although cerebral oxidative metabolism appears to be well maintained during moderate to severe variable-type fetal heart rate decelerations with umbilical cord occlusion, the need to increase fractional oxygen extraction and the redistribution of blood flow from carcass tissues may contribute to an accumulation of lactic acid both within the brain and systemically when such an insult occurs repeatedly.

Animals↗
PubMed2000

Age-related differences in collision detection during deceleration.

Observers were presented with displays simulating a 3-D environment with obstacles in the path of motion. During the trial, observer motion decelerated at a constant rate and was followed by a blackout prior to the end of the display. On some trials the rate of deceleration resulted in stopping before the collision, whereas on other trials the rate of deceleration resulted in a collision with the obstacles. The observer's task was to detect which trials simulated an impending collision. Proportion of collision judgments was greater for older as compared with younger observers when a collision was not simulated. Older observers showed less sensitivity to detect collisions than younger observers did, particularly at high speeds. The age-dependent results are discussed in terms of analyses based on tau and constant deceleration. The results suggest that increased accident rates for older drivers may be due to an inability to detect collisions at high speeds.

Accidents, Traffic↗
PubMed1995

Correlation of fetal heart rate decelerations following acoustic stimulation with perinatal outcome.

This was a retrospective study of acoustic stimulation response and perinatal outcome of 688 fetuses undergoing nonstress testing. Acoustic stimulation was performed within 7 days of delivery, and responses were classified based on the presence of an acceleration, deceleration, or both. Responses were correlated with perinatal outcome. Abnormal outcome was defined as: cesarean section for nonreassuring fetal heart rate patterns with an acidotic umbilical artery cord gas; delivery at less than 32 weeks for nonreassuring antenatal fetal testing; meconium aspiration syndrome or mechanical ventilation at 36 weeks or greater; neonatal seizures; 5-minute Apgar score less than 7; and stillbirth. Fetuses who demonstrated deceleration responses were significantly more likely to have abnormal perinatal outcomes when compared with those with acceleration responses (p < 0.001). Although combination acceleration-deceleration responses were more often associated with abnormal perinatal outcome when compared with pure acceleration responses, differences were not significant. A deceleration response following acoustic stimulation is associated with increased risk for adverse perinatal outcome and may merit further evaluation.

Acoustic Stimulation↗
PubMed1991

Deceleration requirements and the control of pointing movements.

When a limb is moved from one position to a target object, the limb and the target frequently collide. Often, the goal of the movement is to strike the target with a particular magnitude of impact. For single-aiming movements, impact forces have been shown to increase systematically with both an increased movement amplitude and a decreased movement time, thus providing deceleration to the moving limb. Models of speed-accuracy trade-off, however, have neglected to account for the contribution of these impact forces in the control of accurate movements. The aim of this experiment was to examine the modifications in the control strategy as a function of the amount of impact force a subject is allowed to use in decelerating his or her limb. Results showed that the structure of the acceleration-time functions was dictated by the amount of impact force subjects were allowed to use in decelerating the limb. Movement endpoint variability decreased as more impact force was used. The experiment suggests that the impact with a target is an important contributor to the deceleration of the moving limb and a critical determinant of movement organization.

Journal Article↗
PubMed2001

The effect of variable heart rate decelerations on intraventricular hemorrhage and other perinatal outcomes in preterm infants.

OBJECTIVE: We investigated the hypothesis that repetitive variable heart rate decelerations in labor are associated with an increased incidence of neonatal complications in premature infants. METHODS: This was a retrospective case-control study. Singleton fetuses weighing between 750 and 2500 g at 25-35 weeks' gestation were considered for the study. Fetuses delivered by Cesarean section prior to labor were excluded. Heart rate traces were retrieved from an electronic archive and were assessed for the presence of variable decelerations. Cases had at least three variable decelerations in the hour prior to delivery and were matched 1:1 with controls for gestation, sex and birth weight. RESULTS: A review of 6500 deliveries yielded 41 matched pairs. The groups were compared for the following outcomes. Measures of acute morbidity were cord pH at delivery, 5-min Apgar score and resuscitation; measures of chronic morbidity were intraventricular hemorrhage, periventricular leukomalacia, necrotizing enterocolitis and death. There was no difference in measures of acute morbidity between the groups. The incidence of chronic morbid outcome measures in the cases was six (15%) vs. one (2.5%) in controls (p = 0.01). CONCLUSIONS: This study suggests that variable decelerations in preterm infants are associated with chronic morbidity, particularly intraventricular hemorrhage through a mechanism independent of fetal acidemia. Further study is required to determine whether these infants would benefit from early Cesarean section.

Acute Disease↗
PubMed1996

Ventilation with constant versus decelerating inspiratory flow in experimentally induced acute respiratory failure.

BACKGROUND: Recognition of the potential for ventilator-associated lung injury has renewed the debate on the importance of the inspiratory flow pattern. The aim of this study was to determine whether a ventilatory pattern with decelerating inspiratory flow, with the major part of the tidal volume delivered early, would increase functional residual capacity at unchanged (or even reduced) inspiratory airway pressures and improve gas exchange at different positive end-expiratory pressure levels. METHODS: Surfactant depletion was induced by repeated bronchoalveolar lavage in 13 anesthetized piglets. Decelerating and constant inspiratory flow ventilation was applied at positive end-expiratory pressure levels of 22, 17, 13, 9, and 4 cm H(2)O. Tidal volume, inspiration-to-expiration ratio, and ventilatory frequency were kept constant. Airway pressures, gas exchange, functional residual capacity (using a wash-in/washout method with sulfurhexafluoride), central hemodynamics, and extravascular lung water (using the thermo-dye-indicator dilution technique) were measured. RESULTS: Decelerating inspiratory flow yielded a lower arterial carbon dioxide tension compared to constant flow, that is, it improved alveolar ventilation. There were no differences between the flow patterns regarding end-inspiratory occlusion airway pressure, end-inspiratory lung volume, static compliance, or arterial oxygen tension. No differences were seen in hemodynamics and oxygen delivery. CONCLUSIONS: The decelerating inspiratory flow pattern increased carbon dioxide elimination, without any reduction of inspiratory airway pressure or apparent improvement in arterial oxygen tension. It remains to be established whether these differences are sufficiently pronounced to justify therapeutic consideration.

Acute Disease↗
PubMed1999

Simplified deceleration method for assessment of resistive forces in cycling.

PURPOSE: The purpose of this study was to develop and test a simplified deceleration technique for measurement of aerodynamic and rolling resistances in cycling. METHODS: Coast-down tests were performed in level hallways with an experienced cyclist as the rider. Average initial velocities were 2.5-12.8 m x s(-1)) The deceleration technique was simplified by the use on only three switches and a derivation that did not require an assumption that deceleration is constant. The effective frontal area (AC(D)) and coefficient of rolling resistance (CR) were then calculated through a derivation from the equation for resistive forces opposing motion. Method reproducibility was tested by comparison of results for four tests of 30 trials under identical conditions. Method sensitivity was tested by performing 30 trials with three different rider head positions and four different transported mass conditions. RESULTS: Analysis of variance revealed that there were no differences among the results in the reproducibility study for either AC(D) or C(R). Furthermore, the reproducibility tests revealed mean errors of only 0.66% and 0.70% for AC(D) and CR, respectively. ANOVA identified a significant increase (P < 0.001) in rolling resistance with external loading and a significant effect (P < 0.001) of head position on AC(D). Mean (+/-SD) values for AC(D) and C(R) from tests in a racing aeroposture with the head up, the head in line with the trunk, and the head in an intermediate position were 0.304 +/- 0.011, 0.268 +/- 0.010, and 0.262 +/- 0.013 m2, respectively. C(R) averaged 0.00368 in the three head positions. CONCLUSIONS: The findings indicate that this simplified deceleration technique is satisfactorily reproducible and sensitive for measurement of aerodynamic and rolling resistances in cycling.

Adult↗
PubMed2006

Approach for simultaneous measurement of two-dimensional angular distribution of charged particles. II. Deceleration and focusing of wide-angle beams using a curved mesh lens.

Recently, it was shown that using an ellipsoidal mesh in an einzel-type lens, spherical aberration can be corrected over a wide acceptance angle of up to 120 degrees. The present paper creates the possibility for beam analysis by achieving dramatic improvements in deceleration lens capabilities. This provides a scheme for simultaneous angular distribution measurement suitable for application to high-energy charged-particle beams up to around 10 keV. We consider the behavior of wide-angle charged-particle beams in electrostatic fields given by simple solutions of the Laplace equation, starting with a discussion on a spherically symmetric deceleration field. A beam focusing over a wide acceptance angle of 100 degrees is found in a special spherically symmetric field. However, in many cases of the spherically symmetric field, focusing of wide-angle beams is obstructed by the presence of spherical aberration. We show that the spherical aberration can be corrected by two kinds of deformation of the spherically symmetric field, a deformation of the field under a spherical boundary condition and an ellipsoidal deformation of the field. We study practical realization of such fields under the use of a few electrodes and a curved mesh (spherical or ellipsoidal mesh). Some variations of the arrangement of electrodes are considered, and simple designs of deceleration lenses with wide acceptance angles of up to 120 degrees are obtained. Here fine focusing of wide-angle beams can be achieved in a three-electrode deceleration lens with an ellipsoidal mesh.

Journal Article↗
PubMed2004

Slowing heavy, ground-state molecules using an alternating gradient decelerator.

We have decelerated a supersonic beam of 174YbF molecules using a switched sequence of electrostatic field gradients. These molecules are 7 times heavier than any previously decelerated. An alternating gradient structure allows us to decelerate and focus the molecules in their ground state. We show that the decelerator exhibits the axial and transverse stability required to bring the molecules to rest. Our work significantly extends the range of molecules amenable to this powerful method of cooling and trapping.

Journal Article↗
PubMed1995

Late fetal heart decelerations and changes in cerebral oxygenation during the first stage of labour.

OBJECTIVE: To test the hypothesis that late fetal heart rate decelerations are associated with a decrease in cerebral oxygenation. DESIGN: Changes in fetal cerebral concentrations of oxyhaemoglobin and deoxyhaemoglobin were measured by near infrared spectroscopy, before, during and after contractions with late fetal heart rate decelerations and compared with changes during contractions with no alteration of heart rate. SETTING: Teaching hospital obstetric unit. SUBJECTS: Ten women in labour at term. RESULTS: The changes in fetal cerebral oxyhaemoglobin and deoxyhaemoglobin concentrations that occurred during contractions were quantitatively similar, irrespective of the fetal heart rate changes. However, late fetal heart rate decelerations were associated with a significantly greater fall, after the uterine contraction, in the mean concentration of fetal cerebral oxyhaemoglobin of 0.52 mumol/100 g (SD 0.25) (P < 0.001) and a significantly greater rise in the mean concentration of deoxyhaemoglobin of 0.36 mumol/100 g (SD 0.35) (P < 0.01). CONCLUSION: Late fetal heart rate decelerations are associated with a significant decrease in cerebral oxygenation.

Adult↗
PubMed1998

Primary vagally mediated decelerations in heart rate during tonic rapid eye movement sleep in cats.

Rapid eye movement (REM) sleep results in profound state-dependent alterations in heart rate. The present study describes a novel phenomenon of a primary deceleration in heart rate that is not preceded or followed by increases in heart rate or arterial blood pressure and occurs primarily during tonic REM sleep. The goals were to characterize the primary decelerations and to provide insights on the underlying central and peripheral autonomic mechanisms. Cats were chronically implanted with electrodes to record electroencephalogram, pontogeniculooccipital wave activity in lateral geniculate nucleus, hippocampal theta rhythm, electromyogram, electrooculogram, respiration (diaphragm), and electrocardiogram. Arterial blood pressure was monitored from a carotid artery catheter. R-R interval fluctuations were continuously tracked using customized software. The muscarinic blocking agent glycopyrrolate (0.1 mg/kg i.v.) and the beta-adrenergic blocking agent atenolol (0.3 mg/kg i.v.) were administered in alternating sequence with a 90- to 120-min interval. Glycopyrrolate immediately eliminated the decelerations during REM sleep. Atenolol alone had no effect on their frequency. These findings suggest that a change in the centrally induced pattern of autonomic activity to the heart is responsible for the primary decelerations, namely, a bursting of cardiac vagal efferent fiber activity.

Adrenergic beta-Antagonists↗
PubMed2005

Deceleration time of systolic pulmonary venous flow: a new clinical marker of left atrial pressure and compliance.

The curvilinearity of the atrial pressure-volume curve implies that atrial compliance decreases progressively with increasing left atrial (LA) pressure (LAP). We predicted that reduced LA compliance leads to more rapid deceleration of systolic pulmonary venous (PV) flow. With this rationale, we investigated whether the deceleration time (t dec) of PV systolic flow velocity reflects mean LAP. In eight patients during coronary surgery, before extracorporeal circulation, PV flow by ultrasonic transit time and invasive LAP were recorded during stepwise volume loading. The t dec was calculated using two methods: by drawing a tangent through peak deceleration and by drawing a line from peak systolic flow through the nadir between the systolic and early diastolic flow waves. LA compliance was calculated as the systolic PV flow integral divided by LAP increment. Volume loading increased mean LAP from 11 +/- 3 to 20 +/- 5 mmHg (P < 0.001) (n = 40), reduced LA compliance from 1.16 +/- 0.42 to 0.72 +/- 0.40 ml/mmHg (P < 0.004) (n = 40), and reduced t dec from 320 +/- 50 to 170 +/- 40 ms (P < 0.0005) (n = 40). Mean LAP correlated well with t dec (r = 0.84, P < 0.0005) (n = 40) and LA compliance (r = 0.79, P < 0.0005) (n = 40). Elevated LAP caused a decrease in LA compliance and therefore more rapid deceleration of systolic PV flow. The t dec has potential to become a semiquantitative marker of LAP and an index of LA passive elastic properties.

Atrial Function, Left↗