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Biomedical subjects

R D Gilbert

Publications and source records attributed to R D Gilbert.

At least 73 records · Page 4Linked to original sources
PubMed1984

Urinary and hemodynamic responses to blood volume changes in fetal sheep.

Because of the potential importance of the fetal kidney in regulating blood volume and amniotic fluid volume, and their composition, we studied renal and cardiovascular responses to changes in blood volume in 12 chronically-catheterized fetal sheep at 110-135 days gestation. During the hour following volume expansion with 50 ml of maternal whole blood, blood pressure rose by 14%, cardiac output by 11%, renal blood flow by 68% and urine output by 36%. Packed red cell volume rose from 31.3 to 34.0%, suggesting a net fluid loss from the circulation through the kidneys, as well as through peripheral and placental capillaries. During the hour following volume depletion by haemorrhage of 70-120 ml, blood pressure fell by 17%, cardiac output by 29%, renal flow by 46%, glomerular filtration rate by 19%, and urine output by 76%, compared to the preceding phase of the study. The urine-to-plasma osmolality ratio approached unity and urine sodium and U/Pcreatinine increased sharply. Following haemorrhage, fluid rapidly entered the circulation as evidenced by falling packed red cell volume and plasma protein concentration. The data support the hypothesis that the fetal kidney, although immature in some respects, effectively responds to maintain blood volume in the fetal sheep.

Animals↗
PubMed1983

Fracture of a polyurethane cardiac catheter in the aortic arch: a complication related to polymer aging.

An undated Cordis Ducor polyurethane coronary catheter fractured and separated in the aortic arch during a cardiac catheterization, and was removed with an intravascular retriever. The recovered specimen appeared brittle, prompting an investigation of the effects of aging on the tensile strength of 91 polyurethane catheters manufactured by Cordis and the United States Catheter and Instrument Company (USCI). Cordis catheters have stable tensile strength for five years from manufacture, but then deteriorate substantially by seven years, particularly at the bond between the catheter tip and the stainless steel-reinforced catheter body. The deterioration is associated with the microscopic appearance of deep cracks in the catheter lumen wall. USCI catheters showed a modest but significant loss of tensile strength by three years after manufacture at the catheter bond. It would seem prudent to place a three-year expiration date on USCI polyurethane catheters, similar to those already on Cordis catheters.

Adult↗
PubMed1983

Depression of respiratory function by pneumatic antishock trousers in traumatic quadriplegia.

A case of mild hypoventilation associated with an incompletely inflated pneumatic antishock suit in traumatic quadriplegia is presented. Pulmonary function studies were performed on the same patient 23 days later. Base line studies were performed and then repeated with the antishock suit inflated to 40 and then 100 mm Hg. Measurements were made of tidal volume (Vt), inspiratory reserve volume (IRV), expiratory reserve volume (ERV), forced vital capacity (FVC), forced vital capacity in one second (FEV1), and maximum voluntary ventilation (MVV). With increasing suit pressures, all parameters decreased with the exception of the ERV, which was initially zero. Traumatic quadriplegia must be added to the list of disorders in which caution must be used when considering the use of the abdominal compartment of the pneumatic antishock suit.

Accidents, Traffic↗
PubMed1983

Exercise responses in pregnant sheep: oxygen consumption, uterine blood flow, and blood volume.

In an attempt to explore the acute maternal responses to exercise we measured oxygen consumption, uterine blood flow, and blood volume in 13 chronically catheterized pregnant sheep at rest and while exercising on a treadmill. With maximal exercise O2 consumption increased 5.6 times, from a resting value of 5.8 +/- 0.3 (SE) to 32.1 +/- 2.8 ml X min -1 X kg -1, cardiac output increased 2.7 times, from 149 +/- 8 to 404 +/- 32 ml X min -1 X kg -1, and arteriovenous oxygen content difference increased 2.1 times, from 3.9 +/- 0.2 to 8.0 +/- 0.4 ml X dl -1. Total uterine blood flow decreased from a mean resting value of 292 +/- 6 to 222 +/- 19 ml X min -1 X kg fetus -1 near exhaustion during prolonged (40 min) exercise at 70% maximal oxygen consumption. Maternal blood volume decreased 14% (P less than 0.01) from 67.5 +/- 3.7 to 57.8 +/- 3.6 ml X kg -1 during this exercise period, with a 20% decrease in plasma volume without a change in red cell volume. We conclude that uterine blood flow decreases during maternal exercise. However, hemoconcentration helps to maintain a relatively constant oxygen delivery to the uterus.

Animals↗
PubMed1983

Exercise responses in pregnant sheep: blood gases, temperatures, and fetal cardiovascular system.

In an effort to examine the effects of maternal exercise on the fetus we measured maternal and fetal temperatures and blood gases and calculated uterine O2 consumption in response to three different treadmill exercise regimens in 12 chronically catheterized near-term sheep. We also measured fetal catecholamine concentrations, heart rate, blood pressure, cardiac output, blood flow distribution, blood volume, and placental diffusing capacity. Maternal and fetal temperatures increased a mean maximum of 1.5 +/- 0.5 (SE) and 1.3 +/- 0.1 degrees C, respectively. We corrected maternal and fetal blood gas values for the temperatures in vivo. Maternal arterial partial pressure of O2 (PO2), near exhaustion during prolonged (40 min) exercise at 70% maximal O2 consumption, increased 13% to a maximum of 116.7 +/- 4.0 Torr, whereas partial pressure of CO2 (PCO2) decreased by 28% to 27.6 +/- 2.2 Torr. Fetal arterial PO2 decreased 11% to a minimum of 23.2 +/- 1.6 Torr, O2 content by 26% to 4.3 +/- 0.6 ml X dl -1, PCO2 by 8% to 49.6 +/- 3.2 Torr, but pH did not change significantly. Recovery was virtually complete within 20 min. During exercise total uterine O2 consumption was maintained despite the reduction in uterine blood flow because of hemoconcentration and increased O2 extraction. The decrease of 3 Torr in fetal arterial PO2 and 1.5 ml X dl -1 in O2 content did not result in major cardiovascular changes or catecholamine release. These findings suggest that maternal exercise does not represent a major stressful or hypoxic event to the fetus.

Animals↗
PubMed1983

Fetal growth and placental diffusing capacity in guinea pigs following long-term maternal exercise.

To determine the critical level of maternal exercise which produces effects on fetal weight and placental diffusing capacity, we measured the relationship between increasing levels of exercise and its effect on the fetus. Hartley guinea pigs with dated pregnancies were exercised on a treadmill (9.7 m/min at a 6.5% gradient) at one of five exercise levels (0, 15, 30, 45, and 60 min/day). We measured placental diffusing capacity for carbon monoxide (DPCO) fetal body and organ weights, placental weight, and maternal body and heart weights near term (63-64 days). Fetal body weight, kidney weight, and placental weight decreased as a function of increasing exercise level, decreasing 13, 13, and 21% respectively at 60 min/day exercise. DPCO1 decreased from a control value of 2.92 +/- 0.23 to 2.33 +/- 0.10 ml. min-1 torr-1 kg fetal wt in the 15 min/day exercise group, 2.17 +/- 0.08 in the 30 min/day group 2.16 +/- 0.11 in the 45 min/day group, and 2.65 +/- 0.31 in the 60 min/day exercise group. The decrease in placental weight along with the decrease in DPCO per kg of fetal weight suggests that with progressive maternal exercise the fetus is compromised by a smaller than normal placenta with less diffusing capacity.

Animals↗
PubMed1983

Placental exchange area in guinea pigs following long-term maternal exercise: a stereological analysis.

We have used stereological techniques to measure the peripheral labyrinth exchange area of the guinea pig placenta in groups of animals which were exercised 0, 15, 30, 45, or 60 min daily throughout pregnancy. The surface area of the maternal lacunae in the peripheral labyrinth decreased linearly as a function of exercise duration, and the maternal volumes of each exercised group were consistently lower, but not linearly. Placental diffusing capacity for carbon monoxide decreased as a function of exercise duration (r = - 0.88, P less than 0.05). Placental CO diffusing capacity was directly proportional to both maternal surface area of a given volume of peripheral labyrinth (mm2/mm3) (r = 0.43, P less than 0.01), and to the total surface area of the placenta (mm2 . g/mm3) (r = 0.53, P less than 0.001). In addition, diffusing capacity correlated to the total fetal surface area (mm2 . g/mm3), (r = 0.53, P less than 0.001). Average fetal and placental weights did not change significantly in the different exercise groups. Individual fetal weights were proportional to placental diffusing capacity and to both the total maternal and fetal placental exchange area. These results demonstrate for the first time that diffusing capacity of the guinea pig placenta is a function of the surface area of the placenta.

Animals↗
PubMed1982

Effects of afterload and baroreceptors on cardiac function in fetal sheep.

The fetal cardiac function curve, the relationship between cardiac output and right atrial pressure, was studied in 17 chronically catheterized fetal sheep. Combined biventricular cardiac output was measured by thermodilution while right atrial pressure was either lowered by haemorrhage, or raised by infusion of 5% (w/v) glucose. Cardiac output rose as right atrial pressure increased from 2 to 6 mmHg, but at higher right atrial pressures (up to 15 mmHg) cardiac output reached a plateau and remained constant at approximately 500 ml/min per kg. The normal right atrial pressure of 4.6 +/- 0.6 mmHg (SEM) placed these fetuses near the plateau of their cardiac function curves. When aortic pressure was increased from 11 to 16 mmHg by a methoxamine infusion, the cardiac function curve was depressed, maximum cardiac output on the plateau averaging only about 340 ml/min per kg. Ganglionic blockade with hexamethonium did not alter the position of the cardiac function curve, suggesting baroreceptors did not affect cardiac function. The cardiac function curve was shifted upward significantly during an isoproterenol infusion, which kept descending aortic pressure in the normal range by dilating the peripheral vasculature. If cardiac function was represented by the relationship between stroke work and right atrial pressure, no physiologically significant differences could be detected among the four conditions. Therefore, fetal cardiac function is normally near maximum, very sensitive to afterload and uninfluenced by baroreceptors. Cardiac output, however, with volume loading during beta-receptor stimulation, can be increased provided arterial pressure does not increase.

Animals↗
PubMed1981

Effects of hypoxia on the closing pressure of the canine systemic arterial circulation.

We studied the relationships among closing pressure (Pc) and indices of systemic arterial resistance (Ra) and compliance (Ca) during hypoxic hypoxia (HH) and carbon monoxide hypoxia (COH) in anesthetized dogs with cardiac bypass and constant ventilation. Closing pressure was measured as the lowest level to which arterial pressure (Pa) fell after inflow to the arterial bed was reduced suddenly to zero. Since the fall of Pa to Pc could be well-described as a single exponential function of time and since Pc was always greater than outflow (venous) pressure. Ra and CA were determined by applying a "vascular waterfall" model to the arterial bed. During HH, Pc increased while Ra and Ca decreased. During COH, Pc and Ra decreased, but Ca did not change. The Pc results indicate that during HH, but not COH, a large portion of the systemic arterial bed experienced a marked increase in vasomotor tone, a qualitative difference that would have been missed if Pc had not been measured. The relationship among Pc, Ra, and Ca during hypoxia suggest these indices may have been determined largely by different portions of the arterial bed in which tone changed independently.

Animals↗
PubMed1981

Compliance of the fetal sheep liver.

To estimate the importance of the liver as a fetal blood reservoir, we measured the compliance of the liver in eight near-term fetal sheep in utero. Balloon-tipped catheters were positioned above and below the entry of the hepatic veins into the inferior vena cava. Then the hepatic artery and portal vein were ligated and a flow probe placed around the common umbilical vein, the only remaining blood supply to the fetal liver. The balloons were inflated to block hepatic outflow momentarily while flow into the liver and pressure at the outflow of the liver were recorded continuously. Compliance was obtained from the pressure--volume curves and averaged 3.74 +/- 0.49 (SEM) ml/mmHg per 100 g of liver or 1.02 +/- 0.09 ml/mmHg per kg body weight. We were able to simulate these responses with a simple mathematical model of the hepatic circulation with constant compliance and pre- and post-sinusoidal resistances to blood flow. In a second group of none fetal sheep in utero whole body vascular compliance was estimated by measuring the venous pressure rise following the infusion of 60 ml of warm 5% (w/v) glucose in water during a 20 s interval. Whole body compliance averaged 3.66 +/- 0.37 ml/mmHg per kg body weight. Thus, the liver is responsible for about 28% of the whole body compliance on the fetal sheep and may function, therefore, as a significant blood reservoir.

Animals↗
PubMed1980

Control of fetal cardiac output during changes in blood volume.

Changes in cardiac output (Qco), heart rate, right atrial pressure, (Pra), and mean systemic pressure (Pms) in response to blood volume changes were measured in chronically prepared fetal sheep. With a 10% decrease in blood volume, fetal cardiac output, measured with the microsphere technique, decreased significantly from 592 +/- 28 to 471 +/- 32 ml . min-1 . kg-1. Heart rate changed little from control animals (163 +/- 5) to those with decreased volume (161 +/- 10 beats/min). Right atrial pressure decreased significantly from 5.4 +/- 0.4 to 4.2 +/- 0.6 mmHg. Mean systemic pressure decreased from 13.8 +/- 0.3 to 10.5 +/- 0.6 mmHg. With a 10% increase in fetal blood volume, cardiac output rose insignificantly to 632 +/- 38 ml . min-1 . kg-1. However, right atrial pressure increased significantly to 8.9 +/- 0.6 mmHg and mean systemic pressure increased significantly to 16.5 +/- 0.8 mmHg with the increased volume. Heart rate again changed little (153 +/- 9 beats/min). The fact that cardiac output rose only a small amount, whereas right atrial pressure rose sharply with an increased blood volume, suggests that the fetal heart is operating near the upper limit of its Starling function curve. As a result, there is very limited cardiac reserve for increases in fetal cardiac output.

Animals↗
PubMed1980

Fetal cardiac output measured by four-way thermodilution.

To measure fetal cardiac output by thermodilution, we injected 2.5 ml of iced 5% glucose rapidly into the superior vena cava and recorded areas of temperature-time curves in the brachiocephalic artery (AS) and descending aorta (BS). One minute later we repeated the injection into the inferior vena cava and recorded areas under two curves (AI and BI). Cardiac output was calculated as Qco = H (AS + BI - AI - BS) (ASBI - AIBS), where H is the change in caloric content of the blood. In a mechanical model we found thermal results correlated well with timed collections (r = 0.98) with a slope of 0.995. In 7 acutely prepared fetal lambs, electromagnetic flow probe measurements of total cardiac output (descending aorta + brachiocephalic artery) correlated well (0.90) with thermal measurements. The slope (1.16) was significantly greater than 1.0, reflecting the inclusion of coronary and pulmonary flows in thermal, but not in flow probe, measurements. In 11 acutely and chronically prepared fetal lambs, the correlation between microsphere and thermal measurements was 0.81 with a slope of 1.09, not significantly different from 1.0. Hence, thermodilution gives results comparable to other methods and is convenient, indefinitely repeatable, inexpensive, and nonradioactive.

Animals↗
PubMed1978

Maternal placental vascular compliance in rabbits.

We studied compliance on the maternal side of the placenta of 20 New Zealand white rabbits, using 51Cr and 125I labels to determine erythrocyte, plasma, and whole-blood volumes per gram of placental tissue under varying maternal pressure conditions. At normal maternal arterial (Pa) and venous (Pv) pressures of 71.8 and 5.5 mmHg, placental blood volume (mean +/- SE) was 0.447 +/- 0.051 ml/g placental tissue. When venous pressure was raised (Pa = 45.5, Pv = 12.2) by occluding the inferior vena cava, blood volume increased to 0.729 +/- 0.068 ml/g, a significant 63% rise. However, when arterial pressure was lowered by occluding the aorta in two steps, dropping to Pa = 33.8, Pv = 7.0, and Pa = 13.5, Pv = 5.4, volume did not decrease significantly. We estimated intervillous space pressure (Pivs) from arterial and venous pressures assuming a ratio of venous to total resistance of 0.02. Compliance calculated from the slope of Pivs vs. volume was 0.0471 ml/mmHg per g. Maternal placental hematocrit averaged 27%, appreciably less than the circulating hematocrit of 38%. Overall, the results suggest that placental volume would be maintained during hypotension and would increase when venous pressure is elevated.

Animals↗
PubMed1977

Umbilical vascular compliance in sheep.

To explore the mechanical properties of umbilical vessels and to test for possible interactions between maternal and fetal circulations, we recorded pressure-volume curves from isolated in situ placentas of 17 sheep. We estimated static umbilical compliance by extrapolating to infinitely slow rates of volume change. We found that compliance averaged .231 +/- .014 SE ml/mmHg per kg fetal wt under control conditions, a value that increased 26.5% when maternal arterial pressure was lowered 85 mmHg (clamping the aorta), but did not change when venous pressure was raised 37 mmHg (clamping IVC). After replacing blood with kerosene which does not penetrate small vessels because of interfacial tension, we found arteries accounted for 22% and veins for 41% of total compliance, leaving 37% attributable to small placental vessels and surrounding tissue. We conclude that umbilical vessels are about one-half as compliant as adult vessels on a body-weight basis, but only slightly less compliant than vessels elsewhere in the fetal body. When maternal vessels expand they interact with surrounding placental tissue, displacing fetal blood and altering the apparent compliance of umbilical vessels.

Animals↗
PubMed1977

Rate of pH changes in blood plasma in vitro and in vivo.

The rate of pH decrease in dog blood after addition of CO2 (dissolved in saline) was measured in vitro with a combination pH electrode and fast-response amplifier. The pH change was found to have an apparent half time of 6.0 +/- 0.5 s at 38 degrees C, similar to that predicted by previous mathematical simulations on the basis of uncatalyzed CO2 hydration kinetics and the buffering characteristics of plasma. Measurements were also made in vivo in dogs by withdrawing blood rapidly from a carotid artery through a temperature-controlled chamber containing a pH electrode. When the flow was stopped, we measured the pH change which occurs in blood (after it leaves the lungs) as the slow dehydration of bicarbonate continues. The measured half time was 7.3 +/- 0.6 s, again agreeing well with predictions. Essentially the same half time was found when the direction of approach to chemical equilibrium was reversed by adding CO2 to the inspired air. The rate of the reactions could be increased markedly by hemolyzing the blood to release carbonic anhydrase into the plasma.

Animals↗