Capillary-tube scanner for mechanized microbiology. A photoelectric scanner measures growth in agar-filled capillaries and gives a new approach to microbiology.

Growing microcolonies of bacteria can be detected by their light-scattering property. We have described a system in which growing bacteria in glass capillaries filled with nutrient agar are counted as the capillaries move through a narrow beam of light. Increased counts after incubation indicate the presence of viable organisms in the original sample; the equipment can detect colonies when they grow to a diameter of 8 microm. Aerobic, anaerobic, and facultative organisms can grow in the capillary environment. The sensitivities of several organisms to antibiotics were determined by adding antibiotics to the agar before the capillaries were filled.

Fluorescence decay times: proteins, coenzymes, and other compounds in water.

The fluorescence decay time (tau) was 2 to 5 nanoseconds for proteins and 4 to 5 nanoseconds for flavin, pyridine nucleotide, and vitamin B(6)coenzymes; tau varied widely in 48 compounds measured in water. Altholugh reported values of tau for a few of the soluttions studied were in excellenlt agreement. previously "calculated" lifetimes, in severall instances, are apparently erroneous. Nonexponential decay was detectable with our "nanosecond-flash" apparatus, a modification of the first commercially aavilable unit for determination of tau.

Fiber-optic sensors for biomedical applications.

In this article the development of fiber-optic sensors for biomedical applications is reviewed. Light-carrying fibers are potentially useful in oximetry, dye dilution measurements, laser-Doppler velocimetry, and fluorometry; as physical sensors of temperature, pressure, and radiation; and as chemical sensors of pH, partial pressure of blood gases, and glucose. Emphasis is placed on the principles and ideas used in the various devices rather than on detailed descriptions or critical discussions.

Acute respiratory failure. Survival following ten days' support with a membrane lung.

An 11-year-old boy with acute lymphoblastic leukemia in remission developed a bilateral pneumonia which rapidly progressed to acute respiratory failure. During 9 days of intensive therapy the patient's respiratory status progressively deteriorated. When it became impossible to maintain the arterial oxygen tension (PAO2) above 40 mm.Hg by conventional means, extracorporeal blood-gas exchange with a membrane lung was begun. After 5 days of bypass the patient's respiratory function began to improve, and he was weaned from the membrane lung on the tenth day. Seven days later he was discharged from the hospital and is currently in excellemt health 23 months after bypass. This perfusion, the longest successful effort to provide respiratory assist with a membrane lung, attests to the efficacy of this therapeutic modality.

Correlation of esophageal conductance measurements with aortic and left ventricular diameters and stroke volume.

Esophageal conductance measurements were correlated with hemodynamic events in 9 dogs chronically instrumented for measurement of left ventricular (LV) and aortic pressures, LV short axis and descending aortic diameters, and aortic blood flow. A four-electrode conductance catheter was positioned in the esophagus. Both an internal and an internal/external configuration were examined during anesthesia with hemodilution, pulmonary lavage and dobutamine infusion. LV stroke volume was altered by caval occlusion at each intervention. Stroke conductance was highly correlated to aortic or LV diameters and stroke volume over a range of diameters depending on the electrode configuration. Esophageal conductance measurements are directly influenced by local hemodynamic events adjacent to the site of measurement.

Picomole quantitation of ammonia by flow-through fluorometry.

A new fiber optic fluorometer has been used to measure picomole amounts of ammonia. The method is based on the enzymatic conversion of alpha-ketoglutaric acid and ammonium ion to glutamate with associated oxidation of NADH. The decrease in NADH fluorescence is used to quantify sample ammonia content. The method is rapid and reproducible and is capable of resolving differences as small as 0.3 pmol between samples containing 0-7 pmol.

A colorimeter for measurement of picomole quantities of urea.

We described a new colorimeter for the measurement of picomole quantities of urea in nanoliter volume fluid samples. The diacetyl monoxime reaction was used to produce a colored product from urea. The method is capable of resolving differences of 10 pmoles between samples containing 0 to 225 pmoles.

A fiber optic PCO2 sensor.

The theory, construction and performance of a catheter tip optical PCO2 probe is described. The sensor, called the Opticap, is made with plastic fiber optics. One fiber carries light to the sensitive tip which is a silicone rubber tube 0.6 mm dia. X 1.0 mm long filled with a phenol red-KHCO3 solution. Ambient PCO2 controls the pH of the solution which influences the optical transmittance of the phenol red. A second fiber carries the transmitted signal to a receiver; the resulting electrical signal is linearly related to the PCO2 over the range of 2.7 to 10.7 kPa. The probe was tested as a tissue PCO2 sensor on the cerebral cortex of the cat and as an arterial PCO2 sensor. Drift over one day's use was 0.6 KPa or less and individual probes have been used as long as 12 weeks.

Inhibition of calcium absorption in the cortical thick ascending limb of Henle's loop by furosemide.

The effect of luminal furosemide on calcium transport across the cortical thick ascending limb of Henle's loop was studied. Cortical thick ascending limbs were dissected from rabbit kidneys and perfused in vitro. Calcium concentrations in perfused and collected tubule fluids were measured by continuous-flow microcolorimetry. Tubules were perfused at slow flow rates and parathyroid hormone was added to the bathing solution to maximize the difference between perfusate and collectate calcium concentrations. Furosemide simultaneously and reversibly inhibited the lumen-positive transepithelial voltage and calcium absorption. In the presence of furosemide perfusate-minus-collectate calcium concentration difference was smallest under conditions that minimized the residual transepithelial voltage. It was concluded furosemide inhibits calcium absorption in the cortical thick ascending limb of Henle's loop by reducing the lumen-positive transepithelial voltage that drives passive calcium ion transport.