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Biomedical subjects

D G Talbert

Publications and source records attributed to D G Talbert.

At least 37 records · Page 2Linked to original sources
PubMed1990

Recurrent cyanotic episodes with severe arterial hypoxaemia and intrapulmonary shunting: a mechanism for sudden death.

The pathophysiology of recurrent cyanotic episodes has been investigated in 51 infants and children. Episodes began at a median age of 7 weeks (range 1 day to 22 months, 39 at less than 4 months). They were characterised by the rapidity of onset and progression of severe hypoxaemia with early loss of consciousness from cerebral hypoxia. The most common precipitating factor was a sudden naturally occurring stimulus from pain, fear, or anger. In uncontrolled trials, cyanotic episodes were reduced in frequency and severity by tetrabenazine (n = 15) and additional inspired oxygen (n = 10). Eight patients died suddenly and unexpectedly (four during cyanotic episodes). Twenty eight patients underwent physiological studies during cyanotic episodes. There was no evidence of seizure activity at the onset and although prolonged absence of inspiratory effort with continued expiratory efforts was common, breathing sometimes continued. Episodes were not caused by upper airway obstruction and sometimes occurred during positive airway pressure ventilation. The rapidity of fall in arterial oxygen pressure and continued breathing suggested a right to left shunt of sudden onset. The results of contrast echocardiography and lung imaging studies confirmed that this was occurring within the lungs. These cyanotic episodes included both intrapulmonary shunting and prolonged expiratory apnoea. They are best explained by interactions between central sympathetic activity, brainstem control of respiration and vasomotor activity, reflexes arising from around and within the respiratory tract, and the matching of ventilation to perfusion in the lungs. They are a cause of sudden unexpected death in infancy and early childhood.

Child↗
PubMed1990

Amniotic pressure in disorders of amniotic fluid volume.

Amniotic pressure was measured in 49 pregnancies with abnormal quantities of amniotic fluid. Among 17 with polyhydramnios, the pressure was always above the normal mean for gestation and exceeded the upper limit of normal in nine. In polyhydramnios, amniotic pressure correlated positively with the depth of the deepest pool (r = 0.65, P = .04) and negatively with fetal PO2 (r = -0.57, P = .03) and pH (r = -0.56, P = .04). Amniotic pressure was raised in all those with a deepest pool of greater than 15 cm, and was normal in all with a deepest pool less than 15 cm. Amniotic pressure fell significantly with drainage of amniotic fluid in those with raised pressure (mean 12.7 mmHg, 95% confidence interval 7.0-18.3; P = .002) but not in those with normal pressure (mean 0.3, 95% confidence interval -3.2 to +3.9; P = .82). Restoration of normal amniotic pressure in one pregnancy was accompanied by marked improvement in fetal acid-base status. Among 24 pregnancies with severe oligohydramnios, amniotic pressure was always below the normal mean, falling below the lower limit of normal in eight; whereas in another eight pregnancies with mild/moderate oligohydramnios, amniotic pressure was scattered evenly within the normal range. Amnioinfusion of 55-500 mL of normal saline in cases of severe oligohydramnios led to a significant rise in pressure (4.7 mmHg, 95% confidence interval 3.5-5.9; P less than .0001). We conclude that amniotic pressure is high in polyhydramnios and low in oligohydramnios. Pressure monitoring may be beneficial during amnioinfusion and therapeutic amniocentesis.

Acid-Base Equilibrium↗
PubMed1989

Intrauterine manometry: technique and application to fetal pathology.

A technique is described for measuring pressure within the amniotic cavity and within fetal vessels and/or body compartments. Two saline-filled catheters were connected at one end to needles inserted during indicated invasive procedures and at the other to silicon strain gauge transducers. In 36 pregnancies with normal liquor volume, stable intra-amniotic pressure (IAP, range 1-14 mmHg) increased with gestation (r = 0.48, p less than 0.01). In pregnancies complicated by severe oligohydramnios, IAP was less than or equal to 1 mm Hg and rose to normal levels with saline amnioinfusion. Raised IAP (range 17-26 mm Hg), found in pregnancies with gross polyhydramnios, fell with drainage of amniotic fluid. Subtraction manometry was used to determine supra-amniotic pressure within the intervillus space, umbilical vein, umbilical artery, abdominal and thoracic cavities, and the urinary tract in normal and/or pathological fetuses. Low intravesical and intrapelvicalyceal pressures (median 6.5, range 2-10 mm Hg) were noted in fetuses with obstructive uropathies. Intrauterine subtraction manometry appears to be a useful tool in the understanding of fetal pathophysiology and may be of clinical benefit in the therapeutic drainage and infusion of amniotic fluid and in the assessment of certain fetal disease states.

Amniotic Fluid↗
PubMed1989

Pathophysiology of pressure changes during intrauterine transfusion.

Intraperitoneal and umbilical vein pressure readings were obtained during intrauterine transfusion in patients with Rh alloimmunization. In 15 nonacidotic fetuses, mean umbilical vein pressure before transfusion (4.5 mm Hg, SD = 2.3) increased by 4.6 mm Hg (delta umbilical vein pressure confidence intervals +2.8 to +6.4; p less than 0.0001) with transfusion. delta Umbilical vein pressure correlated positively with the increase in hematocrit level (r = 0.55; p less than 0.05) and negatively with gestational age (r = -0.58; p less than 0.05). Basal umbilical vein pressure was raised in the only acidotic fetus, whereas delta umbilical vein pressure was 0. Intraperitoneal pressure was recorded in 11 fetuses before and after transfusion, five of which were associated with fetal heart rate changes or preexisting ascites. Basal intraperitoneal pressure (2.5 mm Hg, confidence intervals 1.4 to 3.6) was significantly lower than basal umbilical vein pressure (confidence intervals, 3.2 to 5.8; p less than 0.02). In uncomplicated intraperitoneal transfusions, intraperitoneal pressure rose significantly (delta intraperitoneal pressure = +5.8; confidence intervals 2.9 to 8.8; p less than 0.005). In four transfusions associated with fetal bradycardia or tachycardia, delta intraperitoneal pressure (range, 16 to 26) was greater than in uncomplicated transfusions (range, 1 to 9). delta Intraperitoneal pressure was 0 in the fetus with ascites. These results implicate increases in umbilical vein pressure and intraperitoneal pressure in immediate complications of intrauterine transfusion, and support a role for intraperitoneal pressure monitoring during intraperitoneal transfusion.

Acid-Base Equilibrium↗
PubMed1989

Low amniotic pressure in oligohydramnios--is this the cause of pulmonary hypoplasia?

The mechanism by which oligohydramnios produces lung hypoplasia is not understood. The current theory that extrinsic compression of the fetal thorax causes hypoplasia, either by inhibiting breathing movements or by squeezing out lung liquid, is not supported by observational or experimental data, or by our finding of decreased amniotic pressure around the fetus in oligohydramnios. We hypothesize that lung hypoplasia results from excess loss of lung liquid because of a reduction in amniotic pressure, and hence an increase in the alveolar-amniotic pressure gradient. The magnitude of this increased pressure gradient is calculated to exceed the small standing tracheal pressure; thus low amniotic pressure overcomes the normal laryngeal retentive mechanisms and allows a larger quantity of lung liquid to escape. In the prevention of pulmonary hypoplasia, a role is suggested for the instillation of artificial amniotic fluid to restore normal amniotic pressure.

Amniotic Fluid↗
PubMed1987

Foetal heart rate and maternal emotional state.

Forty-five pregnant women rated themselves for hostility, depression and anxiety. Maternal and foetal heart rates were recorded while they listened to a tape through headphones. The foetuses of anxious mothers showed pronounced responses to certain taped stimuli but this effect was not found for mothers with high hostility or depression scores.

Anxiety↗
PubMed1986

The fetal phonogram: a measure of fetal activity.

In 12 pregnant mothers fetal sounds and infrasounds were recorded by means of a new compliance matched transducer and compared with a simultaneous ultrasound record of fetal activity. A defined pattern on the fetal phonograph correlated with 86% of the total fetal breathing detected with ultrasound, and a further distinctive pattern was associated with 90% of fetal movements. Examination of the fetal phonocardiogram when the fetus was breathing showed a significant increase in the short-term variability of both the systolic and diastolic times when compared with non-breathing episodes. The median amplitude variabilities for both the first and the second heart sounds were also significantly increased during fetal breathing. Measurement of fetal sounds and infrasounds with a compliance matched transducer offers a non-invasive method for assessment of fetal activity for long periods of time.

Auscultation↗
PubMed1986

Biophysical profile in the fetus from a phonographic sensor.

We have recently developed a phonographic transducer which is compliance-matched to the maternal abdomen. Using it, it is possible to monitor for long time periods, non-invasively and without discomfort, the sound and infra-sound produced by the fetus. Fetal heart sounds, fetal breathing, and fetal body movements can be recorded overnight in hospital or at home, and thereby provide a biophysical profile of fetal activity. Overnight recordings of fetal sounds and infra-sound together with maternal ECG and maternal breathing movements are currently being used to study mothers with normal and abnormal pregnancies.

Female↗
PubMed1986

The measurement of cardiac output by electrical impedance plethysmography in pregnancy. Are the assumptions valid?

The assumptions of the Kubicek technique for measurement of cardiac output by detection of changes in the chest wall electrical impedance have been re-examined. The fall in cardiac output in the latter half of pregnancy which Crawford's group calculated using the Kubicek technique can be almost entirely accounted for by a fall in the term dZ/dT of the Kubicek equation, as pregnancy progress. One key assumption of the Kubicek technique is a constant ejection flow rate equal to the initial flow as the pulmonary valve opens, which is multiplied by the estimated ejection time to obtain stroke volume. Initial flow rate is represented by the term dZ/dT in the Kubicek equation. Although this assumption has been shown to give a reasonable correlation with other techniques for measurement of cardiac output in the non-pregnant state, this may not be so for longitudinal studies in pregnancy because of the changes in lung mechanics and in the circulation which occur in this state. Crawford's data emphasizes the necessity for validating the Kubicek technique very critically during pregnancy.

Cardiac Output↗
PubMed1985

Prolonged expiratory apnoea: a disorder resulting in episodes of severe arterial hypoxaemia in infants and young children.

Ten infants with rapidly developing and severe episodes of hypoxaemia (15-120 s duration) were studied. In infants over 2 months old most episodes occurred when awake, after a sudden noxious stimulus. In younger infants frequent yet undetected episodes occurred during sleep and feeding. Arterial PO2 fell below 20 mm Hg within 20 s, and loss of consciousness, sometimes with convulsions, occurred after 30 s. Clinical observations, measurements of respiratory movements, air flow, oesophageal pressure, external oblique surface electromyogram, and, in two cases, chest fluoroscopy and microlaryngoscopy documented episodes of no inspiratory flow but continued expiratory activity at low lung volume with partial or complete glottic closure. In five infants, episodes continued despite tracheostomy or an indwelling nasotracheal tube. No intracardiac shunt could be demonstrated and the rapid fall in arterial PO2 was attributed to lack of ventilation at a maximum expiratory position in the presence of a rapid recirculation time. In five infants tested there was a low proportion of phosphatidylcholine in the tracheal aspirate. In one infant audible expiratory braking (grunting) was present for most of the awake time. This previously unrecognised mechanism for severe hypoxaemia may be one cause of neurodevelopmental damage and sudden death in infants and young children.

Abdominal Muscles↗
PubMed1985

A bimodal form of alveolar behaviour induced by a defect in lung surfactant--a possible mechanism for sudden infant death syndrome.

It is proposed that in the presence of a defective surfactant at a critical period in lung development, large areas of the lungs may collapse suddenly, greatly reducing oxygen stores, producing a right-to-left shunt, and deranging the breathing control system. Yet the situation may be reversed just as rapidly to an apparently normal one if the child responds appropriately. Such events may be repeated, unnoticed until either the condition improves or the child fails to respond in time. The latter situation may be one mechanism for a proportion of sudden and unexplained infant deaths.

Humans↗
PubMed1981

Electronic measurement of locomotion by means of pressure-sensitive floor mats.

This paper describes a method of adapting an observation room to record a child's position in the room and to give an index of the amount of locomotion. The adaptation consisted of under-carpet pressure mats, linked electronically to digital counters. This recording system showed a highly significant correlation with observational measurements of the same aspects of behaviour. It has potential as an aid in the diagnosis of abnormal behaviour states.

Child↗