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H Rahn

Publications and source records attributed to H Rahn.

At least 55 records · Page 3Linked to original sources
PubMed1977

Reduction of pore area of the avian eggshell as an adaptation to altitude.

Standard measurements of water vapor conductance in units of mg of H(2)O . day(-1) . torr(-1) (SI equivalent is mg of H(2)O . day(-1) . pascal(-1)) of fresh eggs of the red-winged blackbird (Agelaius phoeniceus) and the native chicken of India (Gallus gallus) collected at altitude are significantly less than those of eggs of the same species collected near sea level. This decrease is caused by a reduction of the total effective pore area of the eggshell at altitude. It appears to be proportional to the reduction in barometric pressure and the simultaneous increase in the diffusion coefficient of water vapor. Thus, reduction in pore area offsets increased diffusivity at altitude, and water vapor loss through the eggshell at any altitude remains the same as at sea level. The data suggest a structural adaptation of the shell to altered diffusivity of gases at altitude in order to prevent excessive water loss of eggs during natural incubation.

Journal Article↗
PubMed1977

Effects of high O2 and N2-O2 pressures on the physical performance of deer mice: preliminary studies.

Exposure of deer mouse colonies to oxygen tensions of 0.8, 1.0 and 1.5 ATA are accompanied by reductions in wheel-running activity. The magnitude of the reductions was correlated with the partial pressure of oxygen and duration of exposure. Efforts to minimize the toxic effects of high-pressure oxygen by simultaneous exposure to a high nitrogen tension were not effective. Earlier studies (8) showed that exposure to 13.8 atm nitrogen under normoxic conditions reduced running activity by 10%. When this same nitrogen tension was provided in each of the elevated oxygen environments, wheel-running activity deteriorated in a manner comparable to that observed in the absence of added nitrogen. Visual observations of social behavior and respiratory distress suggest that a nitrogen tension of 13.8 atm does not provide protection against oxygen toxicity.

Animals↗
PubMed1976

Effects of ambient pressures, He and Sf6 on O2 and CO2 transport in the avian egg.

The CO2 and O2 tnesions were determined in the air cells of 14-16 day old chicken eggs before and after transfer to a 21% O2 in He or SF6 atmosphere. In the former gas mixture the air-cell PCO2 (which reflects the arterialized blood PCO2) fell rapidly from 32 torr in air to 17 torr in He-O2 attaining a new steady state in 2-4 h. In the SF6-O2 mixture PCO2 rose from 36 torr in a similar period. A similar PCO2 increase was also observed when eggs were compressed to 2 atm of air while exposure to 0.5 atm with a 40% O2-N2 mixture decreased PCO2. Since gas transport across the eggshell is by gas phase diffusion, these findings can be explained by the changes in the diffusion coefficient of CO2 which increase in the presence of He and decrease in SF6. Furthermore, the diffusion coefficient is also inversely related to the absolute pressure. Quantitative prediction of the changes of PCO2 in the He and SF6 mixture cannot be made, since the binary diffusion coefficients are not necessarily applicable in a ternary gas mixture. However, effective diffusion coefficients in these multicomponent mixtures can be derived on the basis of the observed PCO2 changes.

Animals↗
PubMed1976

Narcotic potency of N2, A, and N2O evaluated by the physical performance of mouse colonies at simulated depths.

The physical performance of colonies of deer mice was studied in various inert gas environments at pressures up to 31 ATA. The mice were housed in habitats wherein their diurnal running activity and social interactions could be monitored. By transferring the portable habitats and mouse colonies to a high pressure chamber, the effects of elevated inert gas pressures were studied in socially and ecologically intact surroundings. Analysis of wheel-running performance showed that either 1.1 atm nitrous oxide, 7.2 atm argon, or 20.5 atm nitrogen reduced running activity to 50% of its control value. Behavioral observations revealed a deterioration of physical performance and social interaction with increasing inert gas pressures. A comparison was made between ED50 (the dose that will depress a particular response by 50%) values obtained by studying wheel-running activity and those published for single-reflex responses.

Animals↗