Biphasic response of respiratory frequency to hypercapnea in preterm infants.

The time course of the transient ventilatory response to a sudden change in inspired gas from room air to 4% CO2 in air was examined in 11 healthy preterm neonates. Changes in minute ventilation (VI), tidal volume (VT), and respiratory frequency (f) were determined over 4 to 5 min of CO2 inhalation during both quiet (QS) and active sleep (AS) in each infant. In both states there was a brisk increase of mean VI in response to 4% CO2, while mean VT increased more slowly and mean f only increased transiently at 1 to 2 min. Exponential curve fitting to the change in VI and VT for each infant accounted for 64 +/- 20% of the variance in VI during QS as compared to 30 +/- 18% during AS (p less than 0.003). In only six infants did exponential curves fitted to the changes in VI and VT during QS reach 90% of their steady state values within 4 to 5 min of CO2 exposure. Their time to reach 90% of steady state was always shorter for VI than VT (p less than 0.01). Frequency showed a biphasic response with a transient rise at 1 to 2 min (p less than 0.05) and return to control levels at steady state. These data indicate that not all preterm infants reach a new level of steady state ventilation within 4 to 5 min of 4% CO2 inhalation. Furthermore, many infants exhibit a biphasic response of f over time which causes VI to reach steady state prior to VT.

Analysis of water soluble vitamins by high pressure liquid chromatography.

Resolution of the water-soluble vitamins--pyridoxin, riboflavin, niacinamide, vitamin B12, thiamin, ascorbic acid, niacin and folic acid--by high pressure liquid chromatography was examined on two bonded-phase columns, muBondapak C18 and muBondapak NH2. The effect on the retention times of individual vitamins and the separation of a multivitamin sample was determined using varying proportions of water/methanol as the eluting solvent and by addition of various salts, buffer solutions and PIC reagents to the water/methanol. Each vitamin was able to be eluted satisfactorily from muBondapak C18. It was found that seven vitamins could be resolved from a multivitamin mixture in a single analysis in several solvent systems with the total time for the analyses being always less than 40 min. With muBondapak NH2, all the vitamins except folic acid were eluted and six vitamins could be resolved from a mixture in a single analysis. The speed of analysis was greater with muBondapak NH2 with all compounds eluted in 15 min and the peaks were sharper. The order of elution was essentially the reverse of that obtained with muBondapak C18.