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PubMed1982

The mechanism of late deceleration of the heart rate and its relationship to oxygenation in normoxemic and chronically hypoxemic fetal lambs.

The responses of fetal heart rate and blood pressure to a transient reduction in uterine blood flow were studied in normoxemic and chronically hypoxemic lambs. In normoxemic fetuses, a reduction in uterine blood flow, if prolonged sufficiently, produced reflex bradycardia mediated through chemoreceptors and was associated with a decrease in carotid arterial PO2 to below 20 torr. The bradycardia was associated with a marked decrease in left ventricular output as measured by electromagnetic flowmeter; both were abolished by atropine. In chronically hypoxemic fetuses, a reduction in uterine blood flow produced a delayed deceleration of the heart rate which consisted of three components: reflex bradycardia due to chemoreceptor stimulation; baroreceptor-mediated reflex bradycardia which involved the slow and late recovery of the heart rate; and nonreflex bradycardia which was probably secondary to hypoxic myocardial depression. Quantitative analysis revealed a relationship between the components of delayed deceleration and the status of fetal oxygenation prior to the reduction in uterine blood flow. The lower the carotid arterial PO2, the shorter was the delay in the onset of bradycardia, the greater the decrease in heart rate, and the more prolonged the duration of bradycardia. The conclusion is that the response of fetal heart rate to a transient reduction in uterine blood flow is related to the duration of the reduction and to the status of fetal oxygenation prior to the decrease in uterine blood flow.

Animals↗
PubMed1985

Antepartum nonstress fetal heart rate monitoring: systematic analysis of baseline patterns and decelerations as an adjunct to reactivity in the prediction of fetal risks.

A total of 1552 antepartum nonstress tests performed during the week before delivery are analyzed with respect to both reactivity and the presence of pathologic baseline patterns (tachycardia, bradycardia, diminished beat-to-beat variability) or decelerations. Correlation with mode of delivery and condition of the newborn infant shows that, irrespective of nonstress test reactivity, the presence of baseline anomalies and/or decelerations is associated with significantly increased perinatal morbidity and mortality. Nonstress test analysis, if systematic, that is, not restricted to reactivity alone, makes it possible to better detect fetuses at high perinatal risk, in which case closer surveillance would be indicated.

Apgar Score↗
PubMed1998

Cyclic AMP decreases the availability of 5-phosphoribosyl-1-pyrophosphate and decelerates de novo purine synthesis in rat hepatocytes.

Cyclic adenosine monophosphate (cAMP) was found to decrease the availability of 5-phosphoribosyl-1-pyrophosphate (PRPP) and to decelerate the rate of de novo purine synthesis in suspensions of adult rat hepatocytes. Glucagon did not affect these parameters. The glucagon antagonist des-His1[Glu9]glucagon amide (DHGA), and the protein kinase C activator 1,2-dioctanoyl-sn-glycerol (DOG) were also found to lower PRPP availability. Incubation of the hepatocytes with dbcAMP or with DHGA, did not alter the activity of PRPP synthetase in the hepatocyte lysates, indicating that the above effects are not mediated through the activity of this enzyme. The possibility that the decrease in PRPP availability reflects increased consumption associated with accelerated pyrimidine synthesis is discussed. The decelerated rate of de novo purine synthesis is probably secondary to the decreased PRPP availability.

Animals↗
PubMed1999

Effects of chronic anterior cruciate ligament deficiency on muscle activation patterns during an abrupt deceleration task.

OBJECTIVE: This study examined the influence of chronic anterior cruciate ligament deficiency on muscle activation patterns displayed during abrupt deceleration, relative to timing of tibiofemoral shear forces (Fs) generated during the task. DESIGN: Experimental data were collected for both limbs of 11 chronic functional anterior cruciate ligament deficient subjects and 11 matched controls. METHODS: Electromyographic, high speed film and ground reaction force data were sampled as subjects landed in single-limb stance on a force platform after receiving a chest level pass and decelerating abruptly. Temporal characteristics of each muscle burst relative to initial foot-ground contact were derived and Fs were calculated from net joint reaction forces and the patellar tendon force occasioned by the net moments and inertial forces predicted about the knee. RESULTS: Compared to controls, anterior cruciate ligament deficient subjects displayed a delay in hamstring activation so that peak hamstring activity was more synchronous with initial contact and with the high Fs which occurred after initial contact. CONCLUSIONS: It was concluded the delayed hamstring activation was an adaptation developed to enable peak muscle activity to better coincide with the high anterior Fs, thereby stabilizing the injured limb against a giving-way episode via increased joint compression and posterior tibial drawer.

Adult↗
PubMed2001

The deceleration [correction of declaration] time of pulmonary venous diastolic flow is more accurate than the pulmonary artery occlusion pressure in predicting left atrial pressure.

OBJECTIVES: This study compared a prediction of mean left atrial pressure (P(LA)) ascertained by Doppler echocardiography of pulmonary venous flow (PVF), with predicted P(LA) using the pulmonary artery occlusion pressure (P(PAO)). BACKGROUND: In select patient groups, PVF variables correlate with P(PAO)) an indirect measure of P(LA). METHODS: In 93 patients undergoing cardiac surgery, we recorded with transesophageal echocardiography mitral valve early (E) and late (A) wave velocities, deceleration time (DT) of E (DT(E)), and pulmonary vein systolic (S) and diastolic (D) wave velocities, DT of D (DT(D)) and systolic fraction. The P(PAO) was measured using a pulmonary artery catheter zeroed to midaxillary level. A further catheter was held at midatrial level to zero a transducer and was then inserted into the left atrium. A prediction rule for P(LA) from DT(D) was developed in 50 patients and applied prospectively to estimate P(LA) in 43 patients. RESULTS: A close correlation (r = -0.92) was found between P(LA) and DT(D). Systolic fraction (r = -0.63), DT(E) (r = -0.61), D wave (r = 0.57), E wave (r = 0.52), and E/A ratio (r = 0.13) correlated less closely with P(LA). The mean difference between predicted and measured P(LA) was 0.58 mm Hg for DT(D) method and 1.72 mm Hg for P(PAO), with limits of agreement (mean +/- 2 SE) of -2.94 to 4.10 mm Hg and -2.48 to 5.92 mm Hg, respectively. A DT(D)) of <175 ms had 100% sensitivity and 94% specificity for a P(LA) of >17 mm Hg. CONCLUSIONS: Deceleration time of pulmonary vein diastolic wave is more accurate than P(PAO) in estimating left atrial pressure in cardiac surgical patients.

Aged↗
PubMed2005

Predictive value of late decelerations for fetal acidemia in unselective low-risk pregnancies.

We evaluated the clinical significance of late decelerations (LD) of intrapartum fetal heart rate (FHR) monitoring to detect low pH (< 7.1) in low-risk pregnancies. We selected two secondary and two tertiary-level institutions where 10,030 women delivered. Among them, 5522 were low-risk pregnancies. The last 2 hours of FHR patterns before delivery were interpreted according to the guidelines of the National Institute of Child Health and Human Development. The correlation between the incidence of LD (occasional, < 50%; recurrent, > or = 50%) and severity (reduced baseline FHR accelerations and variability) of LD, and low pH (< 7.1) were evaluated. Statistical analyses included a contingency table with chi2 and the Fisher test, and one-way analysis of variance with the Bonferroni/Dunn test. In the 5522 low-risk pregnancies, 301 showed occasional LD and 99 showed recurrent LD. Blood gases and pH values deteriorated as the incidence of LD increased and as baseline accelerations or variability was decreased. Positive predictive value for low pH (< 7.1) was exponentially elevated from 0% at no deceleration, 1% in occasional LD, and > 50% in recurrent LD with no baseline FHR accelerations and reduced variability. In low-risk pregnancies, information on LD combined with acceleration and baseline variability enables us to predict the potential incidence of fetal acidemia.

Acids↗
PubMed1998

Characterization and prognostic significance of variable decelerations in the second stage of labor.

The characteristics of variable decelerations (VD) in the second stage of labor and the relationship between the number, frequency, or severity and neonatal outcome have not been studied. We have analyzed the characteristics of VD in the second stage of labor and their prognostic significance in the prediction of Apgar scores. In this descriptive study, fetal heart tracings containing VD from 250 singleton, vaginal deliveries between June 1994 and July 1996 were reviewed blinded to outcome information. Excluded were: (1) deliveries at <36 weeks, (2) uninterpretable tracing, (3) absence of VD in second stage of labor, and (4) absence of exam establishing beginning of second stage of labor. VD characteristics evaluated: shape (U, V, W); anterior and posterior "shoulders"; slow return to baseline (< or = 30-degree curve); cumulative depth of VD per 10 min, second stage oxytocin dose. Outcome information collected: method of delivery, birth weight and Apgar scores. Statistical analysis included regression and analysis of variance (ANOVA). The mean maternal age was 32+/-5 years and gestational age 39+/-1.3 week. In the second stage of labor, the mean oxytocin dose was 3+/-5 mu/min, length of the second stage 65+/-57 min, total number of VD averaged 21+/-17 and uterine contractions 26+/-22 per patient. The percentage of VD <100 bpm was 50+/-27%, VD <70 bpm 13+/-20%, anterior shoulders 76+/-30%, posterior shoulders 75+/-30% and slow return to baseline 12+/-17%. The number of VD significantly increased with the length of the second stage of labor (r=0.85, p <0.001). The total number and percentage of VD <70 bpm were inversely correlated with 5-min Apgar score (p=0.038, 0.015 respectively). The sum of the depth of VD/length of second stage as well as the percentage of VD with anterior and/or posterior shoulders and slow return to baseline were not significantly related to Apgar scores (p=0.08, 0.72, 0.73, 0.99, respectively). Patients with a higher percentage of decelerations with slow return to baseline had a higher rate of operative vaginal deliveries (20 vs. 11 %, p=0.002); but no significant differences in Apgar scores compared with those with spontaneous delivery (p=0.9). Second stage VD <70 bpm were significantly associated with lower 5-min Apgar scores. Although the presence of VD with a slow return to baseline was significantly associated with operative delivery, there was no difference in 5-min Apgar scores.

Adult↗
PubMed2001

Activation of the alpha(2A)-adrenoceptor mediates deceleration of the deaggregation component of the response to ADP or 5-HT in human platelets in vitro.

Platelet aggregation requires the concomitant activation of at least one G(i)- and one G(q)-coupled receptor. Epinephrine (EPI) amplifies the response elicited by a number of agonists for platelet aggregation. This study tested the hypothesis that platelet alpha(2A)-adrenoceptor activation causes deceleration of the deaggregation component of the platelet aggregation response when activated concomitantly with the G(q)-coupled adenosine diphosphate (ADP) P2Y(1) or 5-hydroxytryptamine(2A) receptor. The time course of the aggregation response of human platelet-rich plasma following activation of combinations of two or three receptors was assessed by turbidometry using lepirudin anticoagulation. Simultaneous activation of specific two- and three-receptor combinations was achieved using selective antagonists for the P2Y(12) and P2Y(1) receptor subtypes. Steady-state and kinetic parameters, obtained using a four-compartment kinetic model, were used to assess the effects on the net aggregation response. Graded alpha(2A)-adrenoceptor activation was associated with a concentration-dependent decrease of the rate constant of deaggregation. Activation of both ADP receptor subtypes and the alpha(2A)-adrenoceptor produced a concentration-dependent, mutual amplification of the aggregation response. In addition, when three receptors were simultaneously activated, mutual amplification of the aggregation response was observed at physiologically relevant concentrations of epinephrine or norepinephrine (NE) and ADP. We propose that similar to the P2Y(12) receptor, activation of the alpha(2A)-adrenoceptor decelerates the deaggregation component shifting the balance toward increased net aggregation. The effects of EPI and NE on the aggregation response may contribute to the mechanism of increased thrombotic risk present in certain pathophysiological and disease states.

Adenosine↗
PubMed2001

Decelerational thoracic injury.

BACKGROUND: Among the five major decelerational thoracic injuries [myocardial contusion (MC), traumatic aortic disruption (TAD), sternal fracture (SF), flail chest (FC), and tracheobronchial disruption (TBD)], coexisting injuries are seemingly rare. METHODS: To test this hypothesis, we reviewed the records of all patients, with final diagnosis (FDX) codes of these injuries, treated at our Level I trauma center for the 10 years preceding 1997. RESULTS: Among 142 patients, all victims of motor vehicle crashes, there were 38 MC, 36 TAD, 33 FC, 28 SF, and 7 TBD. There were six coexisting injuries (3.5%). Three patients with coexisting injury died in the operating room. All three had TAD; one of these three had TBD plus MC; one had additionally FC and MC and the third had FC in addition to the TAD. One patient with SF and probable MC died in the emergency room. Two patients with FC and a coexisting injury survived. One had MC, the other SF. CONCLUSION: We conclude that these decelerational thoracic injuries, with the exception of sternal fracture, are sufficiently life threatening by themselves to cause fatality. When combined, the threat to life is potentiated. Death occurs at the scene or shortly after arrival in the ER. The diagnosis of one may help exclude the diagnosis of each of the other four. The role of sternal fracture in this paradigm remains an enigma.

Accidents, Traffic↗
PubMed2005

Acceleration- and deceleration-phase nonlinear Rayleigh-Taylor growth at spherical interfaces.

The Layzer model for the nonlinear evolution of bubbles in the Rayleigh-Taylor instability has recently been generalized to the case of spherically imploding interfaces [D. S. Clark and M. Tabak, Phys. Rev. E 71, 055302(R) (2005)]. The spherical case is more relevant to, e.g., inertial confinement fusion or various astrophysical phenomena when the convergence is strong or the perturbation wavelength is comparable to the interface curvature. Here, the model is further extended to the case of bubble growth during the deceleration (stagnation) phase of a spherical implosion and to the growth of spikes during both the acceleration and deceleration phases. Differences in the nonlinear growth rates for both bubbles and spikes are found when compared with planar results. The model predictions are verified by comparison with numerical hydrodynamics simulations.

Journal Article↗
PubMed2002

Alternate gradient focusing and deceleration of a molecular beam.

Neutral dipolar molecules can be decelerated and trapped using time-varying inhomogeneous electric fields. This has been demonstrated only for molecules in low-field seeking states, but can, in principle, be performed on molecules in high-field seeking states as well. Transverse stability is then much more difficult to obtain, however, since molecules in high-field seeking states always experience a force towards the electrodes. Here we demonstrate that an array of dipole lenses in alternate gradient configuration can be used to maintain transverse stability. A pulsed beam of metastable CO in high-field seeking states is accelerated from 275 to 289 m/s as well as decelerated from 275 to 260 m/s.

Journal Article↗
PubMed2002

Collective deceleration of relativistic electrons precisely in the core of an inertial-fusion target.

The energy deposition of a relativistic electron beam in a plasma can be managed through turning on or off fast beam-plasma instabilities in desirable regions. This management may enable new ways of realizing the fast-igniter scenario of inertial fusion. Collisional effects alone can decelerate electrons of at most a few MeV within the core of an inertial-fusion target. Beam-excited Langmuir turbulence, however, can decelerate even ultrarelativistic electrons in the core.

Journal Article↗
PubMed2004

Nonhydrogenic effects in the deceleration of Rydberg atoms in inhomogeneous electric fields.

Argon atoms in Stark states at n approximately 25 have been decelerated and accelerated in inhomogeneous electric fields. The acceleration and deceleration behavior can be understood only by considering the adiabatic Landau-Zener dynamics that take place at the avoided crossings between the Stark states and the limited fluorescence lifetimes of approximately 10 micros.

Journal Article↗
PubMed2005

Deceleration and electrostatic trapping of OH radicals.

A pulsed beam of ground state OH radicals is slowed down using a Stark decelerator and is subsequently loaded into an electrostatic trap. Characterization of the molecular beam production, deceleration, and trap loading process is performed via laser induced fluorescence detection inside the quadrupole trap. Depending on the details of the trap loading sequence, typically 10(5) OH (X2Pi(3/2),J=3/2) radicals are trapped at a density of around 10(7) cm(-3) and at temperatures in the 50-500 mK range. The 1/e trap lifetime is around 1.0 s.

Journal Article↗
PubMed2005

The root tip and accelerating region suppress elongation of the decelerating region without any effects on cell turgor in primary roots of maize under water stress.

To identify the region in which a root perceives a decrease in the ambient water potential and changes its elongation rate, we applied two agar blocks (1 x 1 x 1 mm(3)) with low water potential bilaterally to primary roots of maize (Zea mays) at various positions along the root. When agar blocks with a water potential of -1.60 MPa (-1.60-MPa blocks) or lower were attached to a root tip, the rate of elongation decreased. This decrease did not result from any changes in the water status of elongating cells and was not reversed when the -1.60-MPa blocks were replaced by -0.03-MPa blocks. The rate decreased slightly and was unaffected, respectively, when -1.60-MPa blocks were applied to the so-called decelerating region of the elongating zone and the mature region. However, the rate decreased markedly and did not recover for several hours at least when such blocks were attached to the accelerating region. In this case, the turgor pressure of the elongating cells decreased immediately after the application of the blocks and recovered thereafter. The decrease in elongation rate caused by -1.60-MPa blocks applied to the root tip was unaffected by additional -0.03-MPa blocks applied to the accelerating region and vice versa. We concluded that a significant reduction in root growth could be induced by water stress at the root tip, as well as in the accelerating region of the elongating zone, and that transmission of some signal from these regions to the decelerating region might contribute to the suppression of cell elongation in the elongation region.

Osmotic Pressure↗
PubMed1975

The aetiology, characteristics and diagnostic relevance of late deceleration patterns in routine obstetric practice.

A retrospective study is described in which all the late deceleration patterns seen in one obstetric unit over the course of 34 months have been reviewed with regard to their apparent aetiology, their characteristics and associated abnormal fetal heart rate patterns and the incidence of fetal distress. The results show that, regardless of the aetiology and the characteristics, the incidence of fetal distress (defined as a pH of less than 7-25 or an Apgar score of less than 7 at one minute) lies between 40 and 50 per cent. The implications of this degree of diagnostic inaccuracy are discussed and the importance of fetal blood sampling as the final arbiter in the diagnosis is emphasized. During the course of the study a significant relationship was demonstrated between the use of epidural analgesia and the incidence of late deceleration patterns. This finding is discussed.

Anesthesia, Epidural↗
PubMedDate not supplied

Using amnioinfusion for the relief of repetitive variable decelerations during labor.

Amnioinfusion is a method of replacing intrauterine amniotic fluid volume through intrauterine infusion of a saline solution using a pressure catheter. This method simply and effectively relieves variable decelerations not alleviated by the conventional measures of maternal position change and oxygen administration. The mechanisms underlying variable decelerations, the technique for amnioinfusion administration, and two case studies are reported. Nursing responsibilities regarding amnioinfusion include pattern recognition, assisting with or initiation of amnioinfusion, and maintenance and evaluation of this intervention.

Adult↗
PubMedDate not supplied

Amnioinfusion: a technique for the relief of variable deceleration.

Human and animal studies have demonstrated an association between decreased amniotic fluid and the occurrence of variable decelerations in the fetal heart rate. Amnioinfusion is a new investigational technique directed at decreasing the number and severity of variable decelerations by infusion of a normal saline solution into the uterine cavity. The technique may provide a mechanism for protecting the umbilical cord from compression and, thereby, ameliorating fetal distress. This article describes amnioinfusion and discusses related nursing implications for patients undergoing the procedure.

Amnion↗