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Biomedical subjects

D S Richards

Publications and source records attributed to D S Richards.

At least 19 recordsLinked to original sources
PubMed1992

The perinatal management of severe laryngeal stenosis.

BACKGROUND: Conditions that completely occlude the fetal larynx are rare. We describe the perinatal course of an infant with severe congenital subglottic stenosis, for whom the prenatal recognition of airway occlusion led to enhanced neonatal management. CASE: Serial ultrasound examinations from 23-37 weeks' gestation led to the diagnosis of upper airway obstruction in the fetus of a 29-year-old woman. Significant findings included fetal ascites, echogenic enlarged lungs, and a dilated fluid-filled trachea. The infant was delivered in a level III hospital with a neonatologist and anesthesiologist in attendance. The cord was not clamped until a tracheostomy was secured. CONCLUSION: Upper-airway obstruction can be diagnosed prenatally by the presence of secondary manifestations. Infant survival may depend on foreknowledge of the pathology and prompt, directed efforts at bypassing the airway obstruction.

Adult↗
PubMed1992

Sound levels in the human uterus.

OBJECTIVE: We sought to determine the degree to which noises and voices are attenuated or enhanced as they pass into the uterus. METHODS: In eight parturients, a hydrophone in the uterus was used to measure sound pressure levels for externally generated one-third-octave band noises, male and female voices, and the subject's voice. RESULTS: Low-frequency sounds (0.125 kHz) generated outside the mother were enhanced by an average of 3.7 dB. There was a gradual increase in attenuation for increasing frequencies, with a maximum attenuation of 10.0 dB at 4.0 kHz. Sound attenuation was slightly less if the insonation was from in front of the woman rather than behind. Intrauterine sound levels of the mother's voice were enhanced by an average of 5.2 dB, whereas external male and female voices were attenuated by 2.1 and 3.2 dB, respectively. The effect of frequency on attenuation, the differences between front and back insonation, and the differences between speakers in attenuation were all statistically significant. CONCLUSIONS: The intrauterine environment is rich with externally generated sounds. This may imply fetal risk from maternal noise exposure and may aid in understanding fetal imprinting from prenatal exposure to voices.

Acoustics↗
PubMed1991

Effects of vibration frequency and tissue thickness on intrauterine sound levels in sheep.

Pure-tone sinusoidal mechanical vibratory stimuli ranging in frequency from 4 to 4000 Hz were applied to the ventral abdominal wall of pregnant ewes, and intrauterine sound pressure levels were recorded with a hydrophone 5, 10, 15, and 20 cm from the surface. There were significant decreases in sound pressure levels with increasing frequencies (p less than 0.0001) and increasing depth (p = 0.01). There was no significant interaction between these two variables. An electronic artificial larynx was also activated on the abdominal wall, resulting in quite high sound pressure levels (mean, 119 dB) measured 5 cm from the surface, with a significant decrease in sound pressure levels as the thickness of the intervening maternal tissues increased (p = 0.005). These results suggest that the frequency of vibratory stimulus used and the thickness of the maternal abdominal wall could influence fetal response to the vibroacoustic stimulation test by affecting intrauterine sound pressure levels.

Acoustic Stimulation↗
PubMed1991

A platform for biological sequence comparison on parallel computers.

We have written two programs for searching biological sequence databases that run on Intel hypercube computers. PSCANLIB compares a single sequence against a sequence library, and PCOMPLIB compares all the entries in one sequence library against a second library. The programs provide a general framework for similarity searching; they include functions for reading in query sequences, search parameters and library entries, and reporting the results of a search. We have isolated the code for the specific function that calculates the similarity score between the query and library sequence; alternative searching algorithms can be implemented by editing two files. We have implemented the rapid FASTA sequence comparison algorithm and the more rigorous Smith-Waterman algorithm within this framework. The PSCANLIB program on a 16 node iPSC/2 80386-based hypercube can compare a 229 amino acid protein sequence with a 3.4 million residue sequence library in approximately 16 s with the FASTA algorithm. Using the Smith-Waterman algorithm, the same search takes 35 min. The PCOMPLIB program can compare a 0.8 million amino acid protein sequence library with itself in 5.3 min with FASTA on a third-generation 32 node Intel iPSC/860 hypercube.

Algorithms↗
PubMed1990

The case for routine umbilical blood acid-base studies at delivery.

One of the major goals of obstetricians is to prevent fetal asphyxia. Unfortunately, the commonly used clinical indicators (fetal heart rate monitoring, meconium staining of the amniotic fluid, and Apgar scores) do not have acceptable accuracy in establishing the presence of fetal asphyxia. These subjective assessments often overdiagnose fetal asphyxia and on occasion may fail to detect its presence. The only scientific, objective means of diagnosing fetal asphyxia at delivery is through umbilical blood acid-base studies. This test is convenient, noninvasive, and accurate. The routine use of umbilical blood acid-base studies is a major asset to the obstetric team in determining (1) the presence of asphyxia and its consequences, (2) the efficacy of interventions to prevent fetal asphyxia, and (3) the mechanisms responsible for fetal acidosis.

Acid-Base Equilibrium↗
PubMed1990

Ascites not due to congestive heart failure in a fetus with lupus-induced heart block.

Hydrops developing in fetuses with lupus-associated heart block has usually been assumed to result from congestive heart failure. We present a case in which fetal ascites associated with complete heart block resolved promptly after administration of betamethasone and prednisone to the mother, who had anti-SSA and who developed clinical lupus erythematosus. This resolution occurred with no demonstrable change in fetal cardiac function. We conclude that an immune mechanism, rather than congestive heart failure, was responsible for the fetal ascites.

Adult↗
PubMed1988

The effect of human amniotic fluid on the isolated perfused rat heart.

To test the hypothesis that amniotic fluid directly affects cardiac function, isolated rat hearts were perfused with varying concentrations of centrifuged and filtered human amniotic fluid. The most consistent change seen was a dose-dependent decrease in coronary flow rate. With 10% concentrations, a wide spectrum of changes was seen in both a positive and a negative direction for left ventricular pressure and change in pressure with respect to time, which were closely correlated with the degree of decrease in coronary flow rate. If amniotic fluid has a direct role in depressing cardiac function in amniotic fluid embolism, it may act by decreasing coronary flow rather than by directly suppressing myocardial activity.

Amniotic Fluid↗
PubMed1988

Elevated maternal serum alpha-fetoprotein with normal ultrasound: is amniocentesis always appropriate? A review of 26,069 screened patients.

We reviewed our experience with a policy of revising the estimated probability of an open neural tube defect for those cases in which maternal serum alpha-fetoprotein (MSAFP) was elevated and the ultrasound examination was normal. Assuming a sensitivity for the ultrasound diagnosis of neural tube defects of 90%, the risk estimate derived from the MSAFP was reduced by that amount when ultrasound was adequate and normal. When counseled regarding this revised risk estimate, 67% of our patients declined amniocentesis. The sensitivity for the ultrasound diagnosis of anencephaly in our series was 100%; for open spine defects, 80%; and for all open neural tube defects, 91%. The two patients in whom an open spine defect was not detected with ultrasound had elevated revised risk estimates. When appropriate criteria are met, the estimated sensitivity of ultrasound in diagnosing open neural tube defects may be used for counseling patients at risk for a fetus with an open neural tube defect.

Amniocentesis↗
PubMed1988

Elevated maternal serum alpha-fetoprotein with oligohydramnios: ultrasound evaluation and outcome.

Nineteen pregnancies evaluated for elevated maternal serum alpha-fetoprotein levels were found to have moderate to severe oligohydramnios. There were no survivors among six fetuses with ultrasound-diagnosed urinary tract anomalies. We followed 11 of the remaining 13 pregnancies with serial ultrasound examinations. When the second ultrasound examination demonstrated severely decreased amniotic fluid, the outcome was always poor (intrauterine death, perinatal death, or fetal deformations). Of the five cases in which the second ultrasound showed normal to moderately decreased fluid, there were four surviving infants. When no primary malformations are seen on the initial ultrasound examination, serial ultrasound evaluations of amniotic fluid volume help predict the pregnancy outcome.

Abortion, Induced↗
PubMed1988

Determinants of fetal heart rate response to vibroacoustic stimulation in labor.

To determine whether the fetal heart accelerates in response to a sound stimulus in labor, 40 women at various stages of labor were chosen at random to receive either a vibroacoustic stimulus or sham stimulus over the fetal head. Subsequent fetal heart rate (FHR) accelerations occurred to a significantly greater extent in study patients. One hundred thirty-two high- and low-risk patients were studied to determine correlations between the acceleration response and other maternal and fetal variables. There was a statistically significant negative correlation between the heart rate response to stimulation and three maternal variables: the degree of cervical dilation, the presence of ruptured membranes, and use of epidural anesthesia. The degree of fetal response did not correlate significantly with fetal distress at delivery or abnormal FHR tracings at the time of stimulation. Fewer than one-fifth of the fetuses manifested variable heart rate decelerations after the stimulation. In light of possible risks, the clinical use of the fetal acoustic stimulation test in labor should wait until its diagnostic value is better defined.

Acoustic Stimulation↗
PubMed1987

Prenatal sonographic diagnosis and management of a twin pregnancy with placenta previa and hemicardia.

The sonographic diagnosis of a twin pregnancy complicated by acardius anceps of one fetus, total placenta previa, uterine overdistension, and preterm labor is presented and management is discussed. Attempted selective fetocide is described, but was not successful. Clinical management of severe discordant sonographic dysmorphology is discussed, and diagnostic criteria for sonographic diagnosis of acardia are presented.

Abnormalities, Severe Teratoid↗