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Biomedical subjects

P A Koen

Publications and source records attributed to P A Koen.

8 recordsLinked to original sources
PubMed1993

Homogeneous model immunoassay of thyroxine by phase-modulation fluorescence spectroscopy.

We describe a homogeneous competitive model immunoassay for determination of thyroxine by multifrequency phase-modulation fluorescence. Using a nonradiative energy transfer transduction mechanism, B-phycoerythrin conjugated to thyroxine is the energy donor and a carboxymethylindocyanine dye conjugated to anti-thyroxine antibody is the energy acceptor. Energy transfer from B-phycoerythrin to the acceptor results in a decreased lifetime and/or phase angle. The fluorescence lifetime change reflects the extent of energy transfer. In the competitive immunoassay format, the donor-thyroxine conjugate and an analytical sample of thyroxine compete for acceptor-antibody binding sites, resulting in a phase angle change which is dependent on the amount of thyroxine in the sample. Dose-response curves of phase angle versus thyroxine concentration are comparable to steady-state intensity curves. Since phase-modulation lifetime measurements are largely independent of total signal intensity, sources of optical interference are minimized. The potential for whole blood measurements exists since the energy transfer lifetime method can be extended to longer wavelengths.

Antibodies↗
PubMed1988

Fluorocarbon ventilation: maximal expiratory flows and CO2 elimination.

Elimination of CO2 during liquid ventilation is dependent on flow, diffusion, and the liquid's capacitance for CO2. Maximum expiratory flow (Vmax) and diffusion dead space were measured in vivo in 12 young cats during liquid fluorocarbon (FC-80) ventilation to determine the effect of breathing frequency on maximum CO2 elimination. All animals were maintained (PaO2 = 255 +/- 19 SEM mm Hg, PaCO2 = 35 +/- 1 SEM mm Hg, pH = 7.31 +/- 0.01 SEM) within physiologic range during 1-4 h of liquid ventilation. The Vmax in air (26 +/- 1 SEM liter/min) and in liquid (1.2 +/- 0.2 SEM liter/min) was determined by volume displacement plethysmography. Diffusion dead space (VDdiff) during liquid ventilation as a ratio of alveolar volume (VA) was well correlated (r = 0.84, p less than 0.005) with the average time (tav) the liquid was in the lung [VDdiff/VA = 0.89 e (-0.053 tav)]. Alveolar ventilation, CO2 elimination (VCO2), and PaCO2 were not affected by breathing frequency (f) when tidal volume was adjusted appropriately during steady state liquid ventilation. Predicted maximum CO2 elimination (VCO2max) determined from Vmax and VDdiff was 24 ml/min at a f of 3-3.5 breaths/min. The maximum was found to be strongly dependent on f with much less dependency on fixed dead space (anatomic plus equipment) and wave shape characteristics. Elimination of CO2 decreased at low values of f due to inadequate ventilation and at high values of f due to inadequate diffusion time. From a comparison of experimentally determined steady state VCO2 to theoretically predicted VCO2max, the results demonstrate a f-related functional reserve capacity for CO2 elimination during liquid ventilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Diaphragmatic pressures: transvenous vs. direct phrenic nerve stimulation.

Diaphragmatic force, determined by stimulating the phrenic nerve while simultaneously measuring the pressures in a closed respiratory system, was assessed in five anesthetized dogs over a 5-h period to evaluate the inherent variability of this technique. Transdiaphragmatic pressure (Pdi) was measured at functional residual capacity during stimulation (120 Hz, 0.2-ms duration) of one phrenic nerve by either direct phrenic nerve stimulation (DPNS) or transvenous phrenic nerve stimulation (TPNS). An analysis of variance showed no significant (P greater than 0.50) change during the 5-h period. There was a significant correlation (r = 0.94, P less than 0.001) between Pdi obtained by TPNS and that obtained by DPNS. It is concluded that either DPNS or TPNS can be used to evaluate diaphragmatic strength over a 5-h period and that TPNS can be used in lieu of DPNS.

Animals↗
PubMed1978

Positive end expiratory pressure: effects on lung mechanics of premature lambs.

Pulmonary mechanics were determined at 0, 3, 6, and 10 cm H2O positive and expiratory pressure (PEEP) in premature lambs at a mean gestational age of 134 days. Functional residual capacity increased (p less than 0.005) by 7% (1.6 ml/kg) per cm H2O PEEP. Dynamic lung compliance and specific compliance significantly decreased by 10% (0.11 ml/cm H2O/kg) and 9% (0.0051 l/cm H2O) per cm H2O PEEP, respectively, for PEEP above 3 cm H2O level. Inspiratory lung resistance increased significantly (p less than 0.05) only between 0 and 6 cm H2O PEEP while expiratory lung resistance increased (p less than 0.05) between 0 cm H2O PEEP and all higher levels. The data suggest that PEEP in excess of 3 cm H2O produces undesirable effects on lung mechanics in premature lambs. These results may be important in predicting contraindications and potential complications of positive pressure breathing in the newborn.

Animals↗
PubMed1978

Pulmonary lavage in preterm lambs.

Pulmonary function was studied before and after bilateral lung lavage with oxygenated FC-80 fluorocarbon liquid in seven perterm lambs, 134 days of gestation. Measurements of transpulmoary pressure, airflow, tidal volume, and functional residual capacity (FRC) enabled calculation of lung resistance and compliance, specific compliance, and work of breathing. Immediately postlavage, arterial oxygen tension (PaO2) decreased significantly (P less than 0.05) by 41% from control values. In addition, at 1 hr postlavage, lung compliance significantly decreased (P less than 0.01) by 43% from control levels. Lung resistance, FRC work of breathing arterial carbon dioxide tension, and pH postlavage were not significantly different from prelavage values. The mean volume of FC-80 remaining in the lungs at 1 hr postlavage was 32% of the instilled volume. These data indicate that lung lavage with a low surface tension liquid has a relatively small effect on lung mechanics of the premature lung.

Animals↗
PubMed1977

Instrumentation for measuring functional residual capacity in small animals.

A system for measuring functional residual capacity (FRC) by the dilution method was evaluated to determine its suitability for use in neonates and small animals. The system makes use of rapid, automatically triggered valves for precise closure at end expiration. Results of a theoretical error analysis and experimental in vitro tests are presented and indicate that the measuring error in FRC is related to the FRC-to-initial rebreathing bag volume ratio. With a 200-ml bag volume one standard deviation of the calculated error was 16% for a 50-ml, 9.1% for a 100-ml, and 5.8% for a 200-ml FRC.

Animals↗