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Biomedical subjects

L J Groome

Publications and source records attributed to L J Groome.

At least 37 records · Page 2Linked to original sources
PubMed1994

Heart rate changes following habituation testing of the motor response in normal human fetuses.

We examined the heart rate (HR) response immediately following habituation testing in 54 normal human fetuses between 34 and 40 weeks of gestation to determine if cardiac self-regulation was a function of the rate of motor habituation. All fetuses received eight trials of a 1-s vibroacoustic stimulus (VAS) with a 10-s interstimulus interval. A score of 0-10 was assigned for each trial based on subjective assessment of intensity and duration of the fetal motor response. Motor habituation was evaluated in terms of the rate of response decrement over trials. For each fetus the average post-VAS HR was calculated in 1-min blocks for the first 7 min following habituation testing. When subjects were divided into slow and fast motor habituators, we found that fetuses who were slow habituators displayed a significantly greater increase in HR above baseline at each of the first 7 min following habituation testing as compared to fetuses whose motor response habituated more rapidly, F(1,52) = 4.88, P = 0.03. However, there was no difference between slow and fast motor habituators in the rate at which the HR returned toward prestimulus levels. To further examine these results, we divided the 54 fetuses into four groups based on the medians of the slope of the post-VAS HR regression line and the variability in HR about this line. We found that fetuses whose HR decreased slowly after habituation testing displayed significantly greater variability in their cardiac response as compared to fetuses whose HR decreased more rapidly (chi 2 = 4.74, P = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1994

Spectral analysis of heart rate variability during quiet sleep in normal human fetuses between 36 and 40 weeks of gestation.

Respiratory sinus arrhythmia (RSA) is a clinical manifestation of the parasympathetic nervous system which can be identified in the high-frequency region of the heart rate variability (HRV) power spectrum. The purpose of this study was to determine the relative contribution of RSA to overall HRV for human fetuses in quiet sleep. The study population consisted of 13 normal human fetuses between 36 and 40 weeks of gestation for whom data were collected during spontaneous breathing and normally occurring apneic periods. Fetal breathing was monitored continuously using real-time sonography. The fetal electrocardiogram was captured transabdominally in 3-min blocks at a rate of 833 Hz and fetal R-waves were extracted from the raw signal using adaptive signal processing techniques. Fetal behavioral state was determined at the beginning and end of each 3-min data collection period. The fetal R-wave interbeat intervals (IBIs) were converted to equally-spaced, time-based data, and linear detrending of the time series was accomplished by subtracting the mean heart period from each weighted IBI. Total power (TP, 0.0-2.5 Hz) was divided into RSA (0.4-1.0 Hz), high-frequency (HF, 0.2-2.5 Hz), low-frequency (LF, 0.04-0.2 Hz), and very-low-frequency (VLF, 0.0-0.04 Hz) regions, and the power densities were summed to determine the absolute power for each frequency component. A total of 81 3-min blocks (mean per subject 6.3, range 2-14) were available for analysis. Eleven (85%) of 13 fetuses demonstrated a HF peak during fetal breathing, and RSA accounted for approximately 20% of the TP.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrocardiography↗
PubMed1994

Motor and cardiac response during habituation testing: demonstration of exaggerated cardiac reactivity in a subgroup of normal human fetuses.

In this study we wanted to determine: (1) whether or not a relationship existed between the rate of habituation of the fetal motor response and changes in the fetal heart rate (FHR), and (2) if this relationship could be used to identify a subgroup of fetuses who exhibited exaggerated cardiac reactivity during habituation testing. Thirty-nine normal human fetuses between 34 and 40 weeks of gestation were evaluated. Habituation testing consisted of a 1 second vibroacoustic stimulus with a 10 second interstimulus interval for eight trials. The motor response was observed using real-time sonography, and a score of 0 to 10 was assigned for each trial based on subjective assessment of the fetal response. Motor habituation was evaluated in terms of the rate of response decrement in movement over trials (Re). Subjects were initially divided into slow and fast motor habituators based on the median of Re, and it was found that fetuses whose motor response habituated slowly displayed a significantly greater increase in heart rate compared with fetuses who habituated more rapidly (F1,37 = 8.61; P = 0.0057). Cardiac reactivity was then defined as "the average increase in FHR above the mean prestimulus value during the last half of the testing period." When the data were divided into quadrants based on medians, we identified seven (18%) fetuses who habituated rapidly but who also displayed high cardiac reactivity. We conclude that there is a significant relationship between the magnitude of the increase in FHR above baseline and the rate of motor habituation in normal human fetuses.

Acoustic Stimulation↗
PubMed1994

Early heart rate response of normal human term fetuses to vibroacoustic stimulation.

We examined cardiac reactivity in the first 45 seconds following a single 1 second vibroacoustic stimulus (VAS) to determine if the prestimulus fetal heart rate (FHR) pattern was predictive of the immediate post-VAS heart rate response. Forty-nine normal human fetuses between 37 and 41 weeks of gestation were observed to enter quiet sleep and remain in that state for 3 to 5 minutes before testing. In general, VAS elicited an initial acceleratory response of approximately 20 beats/min above the mean prestimulus heart rate followed by a deceleratory response to an average of approximately 4 beats/min below baseline values. Fetuses with different average prestimulus heart rate patterns generally differed in their early cardiac response to VAS: when compared to a high baseline FHR, a low resting heart rate was associated with a greater increase in heart rate above baseline (r = -0.401; P = 0.03), a greater decrease below prestimulus values (r = -0.312; P = 0.03), and a greater difference between maximum and minimum heart rates (r = -0.465; P = 0.001). Higher baseline heart rates were associated with lower FHR variability in the prestimulus period (r = -0.422; P = 0.009). When we examined the time course of the early response, we found that fetuses that achieved a maximum heart rate quickly exhibited less of an increase above prestimulus values (r = 0.894; P = 0.005), displayed a greater decrease below baseline (r = 0.507; P = 0.0002), and reached the minimum heart rate faster (r = 0.575; P = 0.0001) than fetuses that required longer to achieve a maximum cardiac response.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1993

Randomized trial of prophylactic antibiotic therapy after preterm amnion rupture.

OBJECTIVE: Our purpose was to determine whether maternal administration of prophylactic ampicillin or erythromycin after preterm amnion rupture is associated with maternal or neonatal benefits. STUDY DESIGN: Women with singleton pregnancies between 24 and 33 weeks 6 days of gestation were eligible if they had no immediate indication for delivery. After giving informed consent, patients were randomized either to receive ampicillin (erythromycin if penicillin allergic) until delivery or to enter a control group. Women whose cervical cultures were positive for either group B streptococci or Neisseria gonorrhoeae received treatment. Tocolytics and corticosteroids were not used. RESULTS: From January 1990 to February 1992 117 patients (antibiotics 59, control 58) were recruited and analyzed. Prophylactic antibiotics were associated with a longer latent phase (mean 12 vs 7.0 days, p = 0.004) and fewer maternal infectious complications (29% vs 60%, p = 0.001). A higher incidence of neonatal necrotizing enterocolitis was observed in the treatment group (14% vs 3.5%, p = 0.05). Other neonatal complications, including death, were lower in the treatment group, but none attained statistical significance (p = 0.09 to 0.33). CONCLUSION: The use of prophylactic antibiotics in selected patients after preterm amnion rupture appears to have a demonstrable maternal benefit. Large, multicenter trials may demonstrate a significant neonatal benefit or confirm any adverse outcomes.

Adult↗
PubMed1993

Behavioural state change in normal human fetuses following a single vibroacoustic stimulus: effect of duration of quiet sleep prior to stimulation.

We examined 96 normal human fetuses between 37 and 41 weeks of gestation to determine the relationship between the duration of the active state following a single vibroacoustic stimulus (VAS) and the time spent in prestimulus state 1F, i.e. quiet sleep (QS). All fetuses were observed to enter state 1F prior to testing. After remaining in this state for 3 min, each fetus was randomized into one of three groups: no stimulation (Group I, N = 32); a single 1-s VAS delivered after 3-5 min of QS (Group II, N = 33); and a single 1-s VAS delivered after 18-20 min of QS (Group III, N = 31). Fetuses in Groups I, II, and III were otherwise behaviourally indistinguishable. Heart rate and eye and body movements were monitored until the fetus either returned to state 1F and remained in that state for 3 min or did not return to state 1F within 60 min. Of the 64 fetuses who were stimulated, 62 responded, indicating that there was no effect of prestimulus state duration on the sensitivity to VAS. Fetuses stimulated after 18-20 min of QS behaved similarly to fetuses who entered an active period spontaneously.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1993

Developmental trends in fetal habituation to vibroacoustic stimulation.

Habituation is a measure of the ability to inhibit responding and is a more mature form of behavior than is persistent responding. We examined the developmental trend in habituation of the fetal startle response to repeated vibroacoustic stimulation in 90 normal human fetuses between 28 and 40 weeks of gestation. Fetal movement was graded according to the nature of the behavioral response: general startle (3), fast limb movement (2), slow rolling movement (1), and no movement (0). A significant developmental difference (p < 0.0004) in the rate of habituation was found, with response decrement occurring faster in fetuses of more than 32 weeks of gestation. Furthermore, by dividing the patients into three gestational age groups, it was determined that the greatest change in the rate of habituation occurred between 28 and 32 weeks and 32 and 36 weeks. We conclude that the rate of fetal habituation may be determined by the degree of maturation of the neural circuitry governing this form of nonassociative learning.

Acoustic Stimulation↗
PubMed1992

The relationship between heart rate and eye movement in the human fetus at 38-40 weeks of gestation.

The purpose of this study was to compare two different methods for assessing fetal heart rate (FHR)--fetal eye movement (FEM) synchronization: (1) periods of high (HV) and low (LV) variability in the FHR and the presence (EM) and absence (NEM) of FEM were determined by visual inspection and the degree of association between FHR and FEM was assessed in terms of the fraction of study time for which no periods of LV-NEM and HV-EM could be identified; and (2) the maximum cross-correlation coefficient (rmax) and the lag at rmax (Lmax) were determined by direct computer analysis of FHR and FEM data for each fetus. Twenty normal human fetuses between 38 and 40 weeks of gestation were examined for a total of 2051 min (mean 103 min, range 72-150 min). In general, the state HV-EM was observed approximately twice as often as was the state LV-NEM; neither of these two states could be identified during 12.4% of the study time. The coefficient rmax was calculated assuming a sliding 3-min moving window, using either the average FHR (mean 0.53, range 0.31-0.85) or the variability in the FHR (mean 0.52, range 0.18-0.77). No relationship was found between rmax and Lmax calculated using the mean FHR and the fraction of time for which no state could be identified (P = 0.995). When the cross-correlation analysis was performed using FHR variability, a statistically significant relationship was found between the periods of no coincidence (of states LV-NEM and HV-EM) and rmax and Lmax (r2 = 0.32; P = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Eye Movements↗
PubMed1992

Neonatal periventricular-intraventricular hemorrhage after maternal beta-sympathomimetic tocolysis. The March of Dimes Multicenter Study Group.

OBJECTIVE: Our objective was to determine if the rate of periventricular-intraventricular hemorrhage is increased in the offspring of women who received a beta-sympathomimetic agent as part of the management of preterm labor. STUDY DESIGN: This retrospective study consists of 2827 women who were delivered of a singleton, live infant free of congenital neurologic anomalies between 25 and 36 completed weeks of gestation during a multicenter preterm birth prevention trial. The data were analyzed, adjusting for type of tocolytic agent, race, infant sex, gestational age, birth weight, health care center, route of delivery, indication for delivery, intrapartum fetal distress, respiratory distress syndrome, and neonatal sepsis. RESULTS: The overall incidence of periventricular-intraventricular hemorrhage in this population was 5.6%. In a univariate analysis in which no adjustment was made for potentially confounding variables, beta-sympathomimetic tocolysis was found to be associated with nearly a fourfold increase in the incidence of periventricular-intraventricular hemorrhage when compared with the use of either magnesium sulfate or no tocolytic agent. The results of a multivariate regression analysis revealed that beta-sympathomimetic agents were associated with a statistically significant increase in the overall incidence of periventricular-intraventricular hemorrhage (odds ratio 2.47, 95% confidence interval 1.34 to 4.56, p = 0.004) and a similar, but not significant, increase in the incidence of grades 3 and 4 periventricular-intraventricular hemorrhage (odds ratio 2.50, 95% confidence interval 0.96 to 6.48, p = 0.06). CONCLUSION: beta-Sympathomimetic tocolytic therapy may be associated with a more than twofold increase in the incidence of neonatal periventricular-intraventricular hemorrhage.

Birth Weight↗
PubMed1991

Oligohydramnios: antepartum fetal urine production and intrapartum fetal distress.

Animal and human studies suggest that fetal oliguria is a normal physiologic response to hypoxemia. To assess the clinical significance of this observation, we studied (before their admission) 51 fetuses of women whose pregnancies were complicated by oligohydramnios at greater than or equal to 38 weeks' gestation. We found that the mean hourly fetal urine production decreased significantly in relation to the severity of subsequent intrapartum fetal compromise. The mean antepartum rate was 95 ml/hr in the 21 fetuses with a normal intrapartum heart rate pattern; this fell to 59 ml/hr in the 18 fetuses who had an abnormal intrapartum heart rate pattern but who responded to intrauterine resuscitation. The rate was 33 ml/hr in the 12 fetuses who were delivered by cesarean section as a result of fetal distress. These findings suggest that oligohydramnios associated with fetal oliguria may be used to identify those fetuses who have less intrinsic or uteroplacental reserve than do those of women with oligohydramnios who have a higher rate of fetal urine production.

Adult↗
PubMed1991

A theoretical analysis of the effect of placental metabolism on fetal oxygenation under conditions of limited oxygen availability.

The purpose of this theoretical paper is to examine the effects of placental metabolism on fetal oxygenation under conditions of limited oxygen availability. Features of the mathematical model used here include: (1) ordinary non-linear differential equations defining the oxygen partial pressure profiles in the maternal and fetal streams for a concurrent flow pattern; (2) the presence of maternal and fetal blood flow shunts; (3) consumption of oxygen by a metabolically active placenta; and (4) modification of the fetal input to the placenta by changing the rate of fetal oxygen consumption in response to changes in the rate of oxygen delivered to the fetus via the umbilical vein. Model parameters were chosen to be well within the range of values cited in the literature. Based on these calculations, we conclude that: (1) under normal conditions, approximately one-half of the fetal uterine-umbilical venous oxygen partial pressure difference can be attributed to placental oxygen consumption; (2) utilization of fetal oxygen to help maintain the metabolic activities of the placenta does not significantly impair fetal oxygenation under normal conditions; (3) consumption of oxygen by the placenta will have a significant detrimental effect on the rate of oxygen delivered to the fetus if oxygen availability is compromised; and (4) for the same rate of maternal oxygen delivered to the placenta, maternal hypoxemia has a significantly greater adverse effect on fetal oxygenation than does maternal anemia.

Computer Simulation↗
PubMed1987

Concentration dependence of protein permeability across the canine visceral pleura.

Water and protein movement across the pulmonary endothelial-visceral pleural membrane of spontaneously breathing anesthetized dogs was analyzed to determine if the protein concentration at the microvascular membrane (Cpro) influences microvascular permeability. The left lung was enclosed in a water-impermeable membrane, creating a visceral pleural space (VPS); fluid and solute fluxes were determined as the filtration or reabsorption of water and protein in the VPS. The plasma protein concentration was experimentally varied by plasmapheresis with saline replacement while the pleural fluid protein concentration was varied by introducing different concentrations of plasma mixed with saline into the VPS. Hydrostatic pressures were maintained within a physiologic range (pulmonary capillary pressure 12.1-16.1 mm Hg). The plasma protein concentration fell as low as 1.98 g/dl, and Cpro, calculated as the mean of the plasma and pleural fluid protein concentrations, ranged from 1.73 to 6.23 g/dl. The relationship between Cpro and the apparent homoporous diffusional permeability for protein (Phs), Phs(cm/sec X 10(-6] = 0.95 Cpro (g/dl) + 2.28, was highly significant (r = 0.87, P less than 0.01). In contrast, the hydraulic conductivity was not affected by a reduction in Cpro to this level (r = 0.21, P greater than 0.4). Although the solute concentration at the endothelial membrane should be considered when evaluating changes in protein permeability, under most experimental conditions the magnitude of this effect will be small.

Animals↗
PubMed1987

Spatial heterogeneity and microvascular fluid exchange: a simple macroscopic equation.

The effect of the spatial distribution of capillary membrane "pores" on the estimate for the hydraulic conductivity (Lp) and the reflection coefficient (sigma s) in the presence of an axial gradient in the hydrostatic pressure difference (delta P) is examined. The differential fluid balance is integrated along the length of the capillary and a simple analytic solution is obtained for a capillary membrane of arbitrary structure. The effective hydrostatic pressure difference, (delta P)eff, is not simply the average of the arterial [(delta P)a] and venous [(delta P)v] pressure differences but is instead found to be (delta P)eff identical to [(delta P)a + (delta P)v]/2 + kappa [(delta P)a - (delta P)v]/2, where kappa identical to 1 - 2 (Lp1/Lp). The two macroscopic coefficients, Lp and Lp1, are related to integrals of the pore density along the length of the capillary. Failure to account for spatial heterogeneity may lead to an incorrect interpretation of the experimental data, e.g., the estimate for sigma s could be greater than 1 or less than 0 depending on the pore distribution and pressure gradient along the capillary. The single capillary hydraulic conductivity measurements of Gore [1982), Amer. J. Physiol. 242, H268-H287) and data on the microvascular pressure distributions (Bohlen and Gore (1977), Microvasc. Res. 14, 251-264) are used to estimate the magnitude of these effects.

Capillaries↗
PubMed1986

Effect of hypoxia on permeability of pulmonary endothelium of canine visceral pleura.

To determine if hypoxia increases the permeability of the pulmonary capillaries of the visceral pleura, water and protein movement across visceral pleura of isolated blood-perfused lungs ventilated with 20% O2-5% CO2 or 0% O2-5% CO2 was analyzed in terms of a two-compartment model of fluid exchange. Lungs from mongrel dogs were enclosed in a water-impermeable membrane, thereby creating an artificial visceral pleural space (VPS); fluid flux was determined as the filtration or reabsorption of water and protein in the VPS. Hypoxic vasoconstriction was prevented by adding verapamil to the perfusate. Hydrostatic pressures were continuously monitored and samples of perfusate and pleural fluid were obtained for protein determinations. Pulmonary capillary pressure was varied between 5 and 20 Torr by changing venous pressure while the protein concentration gradient was varied from 0.5 to 6.6 g/dl by introducing different solutions of plasma mixed with saline into the VPS. The hydraulic conductivity (Lp) increased from 4.25 +/- 0.74 to 9.18 +/- 0.67 X 10(-7) ml X s-1 X mmHg-1 X cm-2 and the diffusional permeability (Pd) of protein increased from 1.29 +/- 0.28 to 4.06 +/- 0.44 X 10(-6) cm/s under hypoxic conditions (P less than 0.05). Inhibition of xanthine oxidase by the addition of allopurinol (10 mg/kg body wt) to the perfusate prevented the increase in Lp and Pd observed under hypoxic conditions. We conclude that free radicals generated via xanthine oxidase may be responsible for the increased permeability observed during severe hypoxia.

Animals↗
PubMed1985

A simple method for determining the homoporous solute-membrane permeability from plasma-to-lymph measurements.

The exact equation for ultrafiltration of a neutral solute across a homoporous membrane contains only two adjustable parameters, the reflection coefficient (sigma s) and the permeability coefficient (Ps)-surface area (S) product, Ps X S. Specifying sigma s and Ps X S therefore defines completely the dependence of the protein ratio (R) on the volume flow (Jv) for a homoporous membrane. The reflection coefficient is determined from the high Jv limit of R: lim Jv----infinity [R] = (1 - sigma s). The purpose of this paper is to present a simple procedure for estimating Ps X S from the slope of R as Jv approaches zero: lim Jv----0 [dR/dJv] = -sigma s/(Ps X S). Both relations are exact limits of the nonlinear neutral solute/homoporous membrane transport equation and thus provide a simple, yet rigorous, method for estimating sigma s and Ps X S.

Biophysical Phenomena↗
PubMed1984

Tension at the heme: a mathematical treatment of hemoglobin cooperativity.

The unique feature of this model is that both the fractional saturation and the free energy change are handled within the framework of the tension-displacement mechanism for hemoglobin co-operativity proposed by Perutz (1970, 1972), i.e. heme iron movement and associated changes in the protein globin internal tension, tau. Physically, tau is the force applied by the protein globin on the proximal histidine, preventing the iron stereochemistry from attaining the geometry preferred in the bound state. It is assumed that a change in position of the heme iron on ligand binding displaces the protein globin proportionately, thereby decreasing tau at neighboring sites; the resulting energy change is assumed to be delocalized throughout the flexible protein globin rather than localized at the heme group per se. The physical interpretation of the model parameters has important implications with regard to data analysis: first, structural data is used to fix the molecular displacements lt and lr; second, jt/jr provides a measure of the protein's intrinsic (i.e. tau = 0) affinity for the bound ligand, and third the set [Ei] is a property of the hemoglobin molecule only and can be determined, in principle, using structural data and optical absorption spectra. The calculated protein globin internal tension in the tense, unbound state (approximately 2 X 10(-5) dyne), determined from the fractional saturation data of Joels & Pugh (1958), is very similar (approximately 3.2 X 10(-5) dyne) to the value estimated by Hopfield (1973) from free energy considerations.

Carbon Monoxide↗
PubMed1984

Role of pulmonary lymphatics and interstitium in visceral pleural fluid exchange.

If the pulmonary lymphatics and/or interstitium of the lung participate in visceral pleural (VP) fluid exchange, then increasing the water content of the interstitial compartment by lymphatic ligation (L) should increase the filtration and/or decrease the absorption of fluid across the VP membrane. To test this hypothesis, the hydraulic conductivity (Lp) and diffusional permeability for protein (Pd) of the visceral pleura were determined in eight spontaneously breathing anesthetized chronic L dogs and seven sham-operated (S) controls. The left lung was enclosed in a water-impermeable membrane, creating a VP space; fluid flux was determined as the filtration or reabsorption of water and protein in the VP space. Intravascular and pleural pressures and the protein concentration of plasma and pleural fluid were monitored during two or more experimental periods in which different mixtures of plasma and saline were introduced in the VP space. At similar pulmonary capillary pressures, the extravascular lung water of the L animals [5.36 (+/- 0.32) g/g dry blood-free lung] was significantly (P less than 0.001) greater than that of the S dogs [3.79 (+/- 0.13)]. The Lp of the L dogs [6.8 (+/- 1.6) X 10(-7) ml X s-1 X cm-2 X Torr-1] was virtually identical (P greater than 0.8) to the 6.7 (+/- 1.4) ml X s-1 X cm-2 X Torr-1 of the S controls. Similarly, Pd in the L group [4.3 (+/- 0.5) X 10(-6) cm/s] was similar (P greater than 0.5) to that of the S animals [5.1 (+/- 1.1) X 10(-6) cm/s]. We conclude that neither the pulmonary lymphatics nor the interstitium of the lung contribute to VP fluid exchange.

Animals↗