Low oxygen exposure does not cause pulmonary injury in the newborn rat.

BACKGROUND: Two recent studies have suggested that low levels of supplemental inspired oxygen may cause lung injury in preterm infants. AIMS: To assess lung injury of newborn rats exposed to 14 days of low-level variation of oxygen. STUDY DESIGN: Four groups were compared with 12 animals per group and 4 lung sections per animal. These were, a control group raised in room air and three groups raised in levels of inspired oxygen fluctuating around the following mean values: group Lo (mean FiO(2) 0.179), group N (mean FiO(2) 0.213), and group Hi (mean FiO(2) 0.247). The degree of oxygen variability was identical for each group. Lungs were inflated at 20 cm H(2)O, fixed and stained with H and E and Millers Elastin. SUBJECTS: Sprague Dawley albino newborn rats. OUTCOME MEASURES: Random alveolar areas were studied and analysed using imaging software to assess total amount of tissue and elastin, number of secondary septa, and mean linear intercept. RESULTS: There were no significant differences between the three experimental oxygen groups and the control group in terms of lung/body weight ratio and the measured markers of lung development. CONCLUSION: We conclude that low-level oxygen supplementation during early lung development does not affect alveolar development in the newborn rat.

A comparison of effects measured with isotonic and isometric recording: I. Concentration-effect curves for agonists.

Concentration-effect curves were obtained with carbachol tested on isolated preparations of guinea-pig ileum taken from adjacent sites in the same animal, one recorded isotonically, the other isometrically: similar experiments were made with histamine as agonist and with carbachol on rat uterus (in oestrus). The position and steepness of the curves was expressed as the values of [EC(50)] and the exponent, P: with carbachol or histamine on guinea-pig ileum the curves were significantly steeper with isotonic recording (P<0.02, sign test) and displaced towards lower concentrations (P<0.005) but there were significant correlations (P<0.05) between values obtained with tissues from the same animal. The curves for carbachol on the rat uterus were very steep: with isotonic recording the exponent (often eight or more) was consistently higher than with isometric (P<0.001): there was no significant displacement but there was a significant correlation (P<0.05) between values of [EC(50)] obtained with tissues from the same animal. Although the results obtained by the two methods are different, they are correlated. These effects are to be expected because with isotonic recording there can be no change in length until the tension exceeds the load and the tissue bulk sets an upper limit to shortening: the range within which an effect can be measured (the "operational window") is smaller. The observed effects on [EC(50)] and P have been reproduced with theoretical data.

A comparison of effects measured with isotonic and isometric recording: II. Concentration-effect curves for physiological antagonists.

If one drug, B, antagonizes another, A, by producing the opposite physiological effect, the antagonist concentration-effect curves should be affected by the recording system, which limits the range of agonist responses. With pieces of isolated guinea-pig ileum taken from adjacent parts of the same animal, one recorded isotonically, the other isometrically with the same load, the isotonic IC(50) values for (-)isoprenaline opposing carbachol or histamine were lower than the isometric values (P<0.01) but there was a significant correlation between them (P<0.01): the isotonic curves were steeper (P<0.01) and there were wider shifts in IC(50) before increasing the agonist reduced the maximum relaxation. In similar experiments with pieces of rat uterus in oestrus from the same animal, the concentration-effect curves for carbachol opposed by increasing concentrations of (-)isoprenaline or (-)adrenaline had slightly lower EC(50) values with isometric recording but there was a significant correlation (P<0.01) with isotonic values. The antagonist effect (ratio of the EC(50) relative to that for the control) was higher with isotonic recording (P<0.01 for (-)isoprenaline, P<0.025 for (-)adrenaline) and all (27) curves were steeper than the corresponding isometric curve (P<0.001). The influence of the method of recording on the results is expected from the narrower operational window and smaller upper limit to relaxation with isotonic recording. A way of obtaining measurements of IC(50) against a standard agonist effect is suggested in an Appendix.

Free-space wavelength-multiplexed optical scanner.

A wavelength-multiplexed optical scanning scheme is proposed for deflecting a free-space optical beam by selection of the wavelength of the light incident on a wavelength-dispersive optical element. With fast tunable lasers or optical filters, this scanner features microsecond domain scan setting speeds and large- diameter apertures of several centimeters or more for subdegree angular scans. Analysis performed indicates an optimum scan range for a given diffraction order and grating period. Limitations include beam-spreading effects based on the varying scanner aperture sizes and the instantaneous information bandwidth of the data-carrying laser beam.

Evaluation of the effect of haemodialysis on cardiac dysfunction in patients of chronic renal failure.

Thirty-eight patients with end stage renal disease who were on haemodialysis and had recurrent congestive cardiac failure were analysed. Echocardiographic findings were evaluated at start of haemodialysis and after 6 dialysis sessions. Seventeen cases (48%) had diastolic dysfunction, 11 (29%) systolic dysfunction 8 (18%) had normal echocardiogram and 2 (5%) had dilated left ventricle with normal ejection fraction. In the systolic dysfunction group the end diastolic diameter decreased after 6 dialysis sessions. In the diastolic dysfunction group the end diastolic diameter and ejection fraction decreased minimally. In the systolic dysfunction group 8 patients (42%) expired within 18 months with a mean survival of 5 months and in the diastolic dysfunction group 5 patients (28%) died within 18 months with a mean survival of 12 months.