Search PubMed⌕ Search

Biomedical subjects

T R Harris

Publications and source records attributed to T R Harris.

At least 91 records · Page 5Linked to original sources
PubMed1979

Lung vascular permeability: inferences from measurements of plasma to lung lymph protein transport.

In chronically instrumented unanesthetized sheep, we measured steady-state hemodynamic and lung lymph responses to mechanically increased pressure and to intravenous infusions of histamine, Pseudomonas bacteria and E. coli endotoxin. Histamine, Pseudomonas bacteria and E. coli endotoxin caused exchanging vessel permeability to increase, as evidenced by high flows of protein rich lung lymph. This contrasts to the effects of increased pressure where lymph protein concentration falls as lymph flow increases. Microvascular sieving of proteins less than 100 Angstrom radius persisted in all increased permeability states, but with endotoxin, lymph clearance of larger proteins increased much more than with histamine or Pseudomonas. We compared several approaches to quantitative interpretations of lymph data and found that direct methods for calculating permeability-surface area products and reflection coefficients for proteins produced values which were difficult to interpret, probably because fundamental assumptions of the methods were violated in our experiments. A mathematical model based on multiple pore theory produced more plausible coefficients.

Animals↗
PubMed1978

An alternative phototherapy light combination.

Combinations of fluorescent lamps for phototherapy were evaluated in order to select one that maximizes blue light content (400 to 500 nanometers) for most effective photodegradation of bilirubin, maintains acceptable color balance for observing infant skin color, and requires minimal lamp replacement for low maintenance cost. The combination that best achieves these objectives consists of four special blue (Westinghouse F20T12-BB) and four broad spectrum (Verd-A-Ray F20T12-CC) lamps that produce blue radiation in excess of an array of eight conventional blue lamps, a spectrum closely approximating that of natural light, and at least 80% of the original blue radiation after 2,100 hours of use.

Biomedical Engineering↗
PubMed1978

Coronary capillary permeability and tissue volumes for sucrose and water in dogs: a comparison of bolus and constant infusion multiple-indicator methods.

This study was undertaken to determine the accuracy with which heart interstitial and water volumes could be determined from multiple-indicator dilution experiments on the coronary circulation in open-chest dog preparations. Sucrose permeability by extraction calculations was found to average 0.26 +/- 0.02 cm3 . (min . g tissue)-1. The extravascular sucrose volume averaged 0.15 cm3 . g-1 tissue by both multiple-indicator and post-mortem methods. Indicator-dilution tritiated water curves labelled 85% of the post-mortem water content.

Animals↗
PubMed1978

Effects of coronary flow reduction on capillary-myocardial exchange in dogs.

The effects of coronary flow reduction on tracer capillary permeability surface area (PS) and distribution volumes were studied in open-chest dog preparations. A mixture of 51Cr-labeled red blood cells, 125I-labeled albumin, [14C]sucrose, and tritiated water (3H2O) was introduced into a shunt connecting the carotid and left anterior descending coronary arteries. Sampling from the coronary sinus produced a multiple indicator curve from which [14C]sucrose PS and 3H2O volumes were computed. Curves were observed in control situations and after the cannula was partially clamped. In six dogs, cardiac lymph was collected and analyzed for total protein. Paired comparison of control and flow-restricted indicator curves showed that flow reduction decreased the absolute values of PS and tracer volumes. The ratio of sucrose volume to weight of perfused tissue increased with flow reduction. The ratio of sucrose PS to weight of perfused tissue increased with moderate flow reduction and decreased with severe flow reduction. The results suggest that flow reduction has two effects which competively affect exchange: 1) flow restriction reduces surface area by capillary derecruitment, and 2) the remaining functional capillaries appear to undergo an increase in permeability to small molecules.

Animals↗
PubMed1978

Pulmonary vascular effects of fat emulsion infusion in unanesthetized sheep. Prevention by indomethacin.

Pulmonary diffusing capacity and arterial blood Po(2) decrease in humans when 10% fat emulsion is infused. To study its effects on the pulmonary circulation and lung fluid balance, we infused 0.25 g/kg x h of a 10% fat emulsion (Intralipid, Cutter Laboratories, Inc., Berkeley, Calif.) into an awake sheep lung lymph preparation. The emulsion caused a sustained increase in pulmonary artery pressure to approximately twice base line with little change in left atrial pressure. Pa(O2) decreased an average 13 torr and lung lymph flow increased two- to threefold. Lymph/plasma total protein concentration fell as lymph flow increased; the magnitude of the lymph/plasma protein decrease was similar to that reported previously when lung vascular pressures were mechanically elevated. Heparin infusion (loading dose = 4,000 U, maintenance dose = 2,000 U/h) cleared the serum of triglycerides but did not alter the response to fat emulsion. Indomethacin infusion (loading dose = 5 mg/kg, maintenance dose = 3 mg/kg x h) blocked the rise in pulmonary artery pressure, the increase in lung lymph flow, and the fall in Pa(O2). Neither extravascular lung water nor [(14)C]urea lung vascular permeability surface area products were altered by fat emulsion infusion. We conclude that fat emulsion infusion in sheep increases lung microvascular filtration by increasing vascular pressures, but has no effect on vascular permeability. Since the effects are blocked by indomethacin, they may be prostaglandin mediated.

Animals↗
PubMed1978

Improved neonatal survival through maternal transport.

Data on outcome from 239 consecutive infants requiring neonatal intensive care following in utero maternal transport to a regional perinatal center were contrasted with those of 642 infants born in outlying hospitals and consecutively transported as newborns to regional intensive care centers during the same 30-month period (January 1974 through June 1976). Neonatal mortality was lower for maternal transport than for newborn transport infants in comparable groups of mortality risk (based on birthweight and gestational age), reaching levels of significant difference (P less than .05) for groups of premature infants weighing less than 1500 g and born prior to 34 weeks' gestation. A high-risk maternal transport system developed subsequent to a well established newborn transport and intensive care system broadens the scope of patients afforded neonatal intensive care and further reduces neonatal mortality and morbidity in the region it serves.

Arizona↗
PubMed1977

[14C]urea and [14C]sucrose as permeability indicators in histamine pulmonary edema.

To see whether, by avoiding red blood cell transport effects, [14C]-sucrose would be a more sensitive lung vascular permeability indicator than [14C]urea, we compared the effects of 4 microgram/kg-min intravenous histamine phosphate infusions on lung vascular permeability-surface area products (PS) for each indicator in the same unanesthetized sheep. Histamine caused hematocrit, PaCO2 and pHa to increase and pulmonary arterial pressure and Pa02 to decrease. [14C]Urea PS (integral extraction calculation) increased from a base line value of 14.7 +/- 1.5 SE ml/s to 17.7 +/- 1.3 (P less than 0.05) with histamine, but [14C]sucrose PS did not change (base line, 6.5 +/- 2.9; histamine, 5.8 +/- 1.2). We conclude that [14C]urea is probably a more useful permeability indicator in the lung circulation than [14C]sucrose, because urea is more sensitive to moderate increases in permeability.

Animals↗
PubMed1977

Lung function in infants and young children: functional residual capacity, tidal volume, and respiratory rats.

Functional residual capacity was measured by the closed-circuit, helium-equilibration method in 121 normal children 3 months to 6 years of age. Prediction equations for functional residual capacity for normal children of this age range are presented for the first time. This study demonstrates that some aspects of lung functiok can be studied relatively conveniently in young children.

Body Height↗
PubMed1977

Association of premature rupture of membranes with idiopathic respiratory distress syndrome.

A retrospective study involving all admissions to two neonatal intensive care centers over a 4-year period was carried out to assess the protective effect, or lack of it, of prolonged rupture of membranes (ROM) on the prevalence of idiopathic respiratory distress syndrome (IRDS) in premature infants. Significantly fewer cases of IRDS were found in patients in all gestational age groups when ROM was greater than 24 hours as compared with those with ROM of less than 12 hours' duration. However, prolonged ROM was not consistently associated with a difference in prevalence of respiratory failure accompanying IRDS, or in the prevalence of sepsis or neonatal mortality in this patient population. It is concluded that benefit to a premature infant in the form of reduced risk of developing IRDS is possible if the mother is allowed 24 hours after ROM before the delivery is initiated.

Female↗
PubMed1976

Chemorheological studies of the effect of heparin on the course of coagulation.

The influence of sodium heparin on viscoelastic change during coagulation was determined in vitro for whole blood samples from ten normal subjects at heparin concentrations ranging from 0 to 1.45 units/(ml whole blood). A four-parameter chemorheological model was used to describe the time course of coagulation as measured by the Weissenberg Rheogoniometer. One parameter compares closely with the whole blood activated partial thromboplastin time, while the other three may be related to the chemical kinetics of clotting. The chemorheological model and experimental techniques were then tested in a dog preparation. It was found that rheological measurements are more self-consistent than either thrombelastography or the activated partial thromboplastin time for the assay of in vivo heparin in two dogs.

Animals↗
PubMed1975

The quantitative effects of coronary-myocardial ischemia on the S-Q integrals of epicardial electrograms in the dog.

The purpose of this study was to measure the relationship between quantitative changes in an epicardial electrocardiographic complex and times of total occlusion and reactive hyperemia in the coronary vessel that supplied the myocardium beneath the electrode. Fifty-six experiments were performed on 9 open-chest dog preparations in which the left anterior descending coronary artery had been cannulated and connected by tubing to the left carotid artery. The shunt was totally occulded for 5, 10, 30, 60 and 90 sec intervals and the sugsequent reactive hyperemia was recorded with an extracorporeal electromagnetic flowmeter placed in the shunt. Potentials from an epicardial electrode placed over the probable area of perfusion of the artery were recorded and analyzed by a digital computer. The integral of each beat from the S to the Q point of the ECG complex was computed. The total electrophysiological change from baseline thus quantified was found to be linearly correlated with the volume of flow deprivation during occlusion (perfusion volume debt) and the volume of reactive hyperemic repayment. The study substantiates experimentally earlier exercise studies of patients with ischemic heart disease in which changes in the SQ integral were found to correlate linearly with exercise intensity. The results support the hypothesis that quantitative measures of the electrocardiographic complex may be used to document the severity of ischemia in mammalian ventricles.

Animals↗