Various Concentrations Of O2 Research Articles

HYPOXIA IN PRETERM INFANTS: EVIDENCE FOR CENTRAL RESPIRATORY DEPRESSION

Hypoxia depresses ventilation in preterm infants. Because PACO2 does not rise, the decrease in ventilation has been attributed to a decrease in metabolism rather than to the central depressant effect of hypoxia. To determine whether central depression is present, we measured the ventilatory sensitivity to CO2 at varying inspired O2 concentrations in preterm infants. Eight babies (B.W.I to 2 kg;G.A.<36 weeks) were studied 10 times during the first 10 days of life. After breathing 21% O2 for 3 minutes, they were given 15,21,40 or 100% O2 for 4 minutes and then 2% CO2 plus the various concentrations of O2 for 4 minutes each. We determined respiratory minute volume and frequency, PACO2, PAO2 and heart rate. Ventilation was measured with a nosepiece and screen flowmeter, using a constant flow-through to eliminate dead space and valves. We plotted minute ventilation against PACO2 to assess the respiratory sensitivity at varying inspired O2 concentrations. The mean slopes of the CO2 response curves were 0.011, 0.022, 0.039 and 0.168 L/min/kg/mm Hg PACO2 with 15,21,40 and 100% inspired O2 respectively (p<0.05). Therefore, the more hypoxic the infant, the flatter was the response to CO2. These findings suggest: a)the respiratory center is depressed during hypoxia in preterm infants despite a decrease in PACO2; b) the response to inhaled CO2 is the opposite to that seen in male adults, where the higher the inspired O2 concentration, the flatter the response.

蔬菜類種子の発芽に及ぼす酸素及び炭酸ガス濃度の影響

Seed germination of 19 kinds of vegetables under various concentrations of O2 and CO2 was studied by means of the continuously aerating system, which proved to be satisfactory in keeping constant compositions of gas mixtures throughout the experiments.The most kinds of seeds examined required 10% or more O2 concentration for the practically normal germination, and the minimum O2 concentration that permitted any germination was 5% or below and little influenced by the temperature, although there was considerable variation among the kinds of crops.Cucumber and Welsh onion, which were germinable under the lowest O2 concentration, germinated over 20% under 1% O2 as much as in the atmosphere and over 50% under 2% O2. Cerely and radish, on the contrary, showed no or poor germination even under 5% O2 and were the highest O2 requisitors. The others, including four groups, Chinese cabbage and turnip, garland chrysanthemum and leaf mustard, pepper and tomato, carrot, cabbage, squash and edible burdock in this order, situated between the two above mentioned, regarding to their germinability under lower O2 concentrations.The inhibitory effect of CO2 in the 15% O2 series was not so conspicuous as was expected, and was recognized clearly only under the highest concentration (40% CO2). When O2 concentraion was lowered to 5%, germination was decreased and retarded markedly, and browning of roots and root tips was frequently induced under higher CO2 concentrations in this series.There seemed to be some differences among the seeds in their germinability under higher CO2 concentrations. Under 40% CO2 in both 15% and 5% O2 series, Welsh onion and Chinese ca bbage germinated over 70% as much as under 0% CO2, while carrot, radish and squash germinated poorly even under 20 CO2 in 15 O2 series.In the seeds of cruciferous plants and others, a kind of dormancy could be induced when O2 concentration was lowered but not absent, or more easily when CO2 was added with reduced O2. This artificially induced dormancy could be clearly broken by the low temperature treatment as well as the natural dormancy could be.