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Biomedical subjects

H Rahn

Publications and source records attributed to H Rahn.

At least 37 records · Page 2Linked to original sources
PubMed1983

Altitude adaptation: organisms without lungs.

Organisms which depend upon diffusive transfer for their external gas can, by structural modification, adjust to the increase of the diffusion coefficient at altitude. In avian eggs, reduced water loss is achieved by a reduction of the pore area which matches the increase in diffusivity so that the functional conductance remains similar to that at sea level and presumably prevents dessication of the embryo. What modifications occur in the tracheal system of insects is not known. In plants there are observations of increased as well as decreased conductance at altitude which at least appear to rule out temperature and partial pressure of the ambient CO2 as chief determinants for altering the conductance (8). In organisms with convective transport systems, changes in the environment and metabolic demands are satisfied by appropriate changes in ventilation. In organisms with diffusive gas transport, the response is provided by structural changes. Such changes, however, do not result in equivalent transfer rates for all the gases, since the diffusion coefficients for CO2, O2 and water vapor differ by a ratio of 0.78 : 1.0 : 1.2, respectively.

Adaptation, Physiological↗
PubMed1983

Patterns of wet suit diving in Korean women breath-hold divers.

Work shifts, diving pattern, diving lung volumes, and counterweights were studied in professional Korean women breath-hold divers wearing wet suits. One of the major differences, compared with their diving pattern only a few years ago when wearing cotton suits, is the prolongation of the diving shifts from 70 to 180 min in the summer and 10 to 120 min in the winter. In sustained diving the average dive and surface times in a 5-m dive are 32 and 46 s, and in a 10-m dives, 43 and 85 s, respectively. During a 3-h shift the total bottom time for harvesting is 37 min in 5-m dives and 17 min in 10-m dives. Rates of descent and ascent are 0.55 and 0.84 m/s. The wet suit divers adjust their counterweights to obtain a 12% positive buoyancy at the surface of sea water in contrast to the 8% positive buoyancy of cotton suit divers. The average lung volumes before and after a dive are 79% and 64% of their vital capacities, values similar to those of previous cotton suit divers.

Adaptation, Physiological↗
PubMed1982

Embryonic oxygen consumption and growth of Laysan and black-footed albatross.

The constraints placed on diffusive gas exchange by the eggshell and the adaptive features of embryonic respiration and metabolism in large Laysan and black-footed albatross eggs (300 g) during prolonged incubation (65 days) were examined in naturally incubated eggs on Sand Island, Midway, in the Northwestern Hawaiian Islands. A low eggshell gas conductance and slow growth rate were associated with a relatively low oxygen consumption (MO2) throughout incubation. Just prior to internal pipping (IP) of the inner shell membrane and penetration of the air space, the MO2 (pre-IP MO2) was approximately 1,250 ml O2 (STPD).day-1 for both species, resulting in air cell O2 and CO2 tensions of 106 and 40 Torr, respectively. During the 4- to 5-day pipping-to-hatching interval, O2 uptake increases rapidly as pulmonary respiration is initiated. Hatchling O2 consumption averaged 3,700 ml O2 (STPD).day-1 or about three times the pre-IP MO2. Data support the hypothesis that embryonic metabolism among Procellariiformes is related to the extent to which the incubation period deviates from the expected value based on initial egg mass.

Animals↗
PubMed1982

Changes in eggshell conductance after transfer of hens from an altitude of 3,800 to 1,200 m.

Hens acclimated to an altitude of 3,800 m (PB 480 Torr) were transferred to 1,200 m (PB 657 Torr). Eggs were collected before departure and daily after the transfer so that changes in eggshell conductance could be studied. Over the next 2 mo eggshell conductance increased 30%, presumably to compensate for the 37% reduction (from 657 to 480 Torr) in gas diffusivity at the lower altitude. Measurements of shell thickness and number of pores in the shell allow one to calculate that most of the change in total pore area occurred by an increase in cross-sectional area of individual pores.

Adaptation, Physiological↗
PubMed1982

Role of diffusion in gas exchange of the avian egg.

The pore system of the avian eggshell provides a unique exchange surface for the transport of gases. The dimensions of the microscopic pores do not change with time, and gas transport through them is essentially limited to diffusion. According to Fick's law of diffusion, eggshell conductance of a given gas will vary directly with the diffusion coefficient of the gas. This principle is illustrated by monitoring changes in air space CO2 in metabolizing eggs subjected to changes in barometric pressure or to substitutions of He and SF6 for N2 in the ambient atmosphere.

Animals↗
PubMed1981

In vivo O2 and water vapor permeability of the hen's eggshell during early development.

The area of the chorioallantois was measured from the time it makes contact with the eggshell membranes on day 6 until it has completely enveloped the egg content on day 12. The oxygen uptake and air cell O2 tension were also determined during this period. These observations allow one to calculate that the O2 flux is confined to those areas of the shell which cover the chorioallantois and that the O2 permeability of the shell (including the outer membrane), KO2, is constant. The water vapor permeability of the shell, KH2O, was also measured. Since the ratio of KH2O/KO2 is essentially equal to the ratio of their diffusion coefficients, DH2O/DO2, it suggests a common diffusion path for O2 and water molecules.

Allantois↗
PubMed1981

Changes in acid-base balance of chick embryos exposed to a He or SF6 atmosphere.

On day 16 of the chick embryo, a catheter was implanted in the allantoic vein carrying arterialized blood, and a syringe was attached to the blunt end of the shell connecting to the air cell. This technique allowed for repetitive sampling and analysis of air cell gas and arterialized blood when these eggs were exposed to a He-O2 or SF6-O2 atmosphere. Exposure to He-O2 reduced the arterial CO2 tension(PaCO2) from 36 to 17 Torr and increased pH by 0.17 units; exposure to SF6-O2 increased PaCO2 from 37 to 62 Torr and reduced the pH by 0.14 units. These responses were brought about by changes in the gas conductance of the shell, resulting in a diffusive hypocapnia and respiratory alkalosis in He-O2 and a diffusive hypercapnia and respiratory acidosis in SF6-O2. During a 4-h exposure to these foreign gases the observed pH changes were smaller than predicted because of marked shifts of HCO3- into the blood (SF6-O2) or out of the blood (He-O2).

Acid-Base Equilibrium↗
PubMed1980

The independent effects of atmospheric pressure and oxygen partial pressure on gas exchange of the chicken embryo.

CO2 production and air cell PCO2 were continuously measured during late development in the chicken egg while acutely exposed from one to three hours to various O2 concentrations ranging from 11 to 39%. A small but significant increase in metabolism, ca. 8%, was found when O2 concentration was above normal values, while a reduction to 70% was observed when O2 concentrations were below normal, and fell to 50% when maintained for three hours. These values were also compared with metabolic rates reported by Lokhorst and Romijn (1965, 1967)) who incubated eggs continuously at reduced O2 concentrations as well as under reduced barometric pressure, and showed that at the same ambient PO2 the metabolism was significantly higher in the eggs at reduced barometric pressure. We attribute this difference to the increased diffusion coefficient of O2 which is inversely related to the barometric pressure. It illustrates that the ambient partial pressure of O2 and ambient atmospheric pressure exert an independent effect upon gas exchange of the avian embryo.

Animals↗
PubMed1980

Carbon dioxide in the chick embryo towards end of development: effects of He and SF6 in breathing mixture.

Using an implanted CO2 electrode in the air cell of the chicken egg, its PCO2 could be followed continuously during the prenatal and paranatal period until hatching occurred. CO2 elimination rate was followed simultaneously. At various stages such eggs were subjects to 75 : 25% He/O2 and SF6/O2 atmosphere, resulting in a large decrease and increase, respectively, in air cell CO2 tension, indicating that during the prenatal stage all CO2 exchange was by gas phase diffusion transport across the pores of the shell. Measurements of the change in PCO2 as well as the CO2 output allowed one to calculate the effective diffusion coefficient for CO2 in the He and SF6 mixtures, which agreed well with the theoretical values calculated according to Wilke (1950). From the CO2 release or retention following exposure, respectively, to He or SF6 the CO2 capacitance values for blood and tissue could be calculated and agreed with values established in mammals. During the last period of development, the paranatal period, the change of PCO2 after replacement of N2 by He gradually declined, indicating that pulmonary ventilation was replacing diffusion through egg shell pores.

Animals↗
PubMed1980

Respiration of avian embryos - a comparative analysis.

All published values of the metabolic rates of avian embryos are brought together for analysis. A generalized pattern of O2 consumption during development of precocial eggs is determined and used to estimate the total amount of O2 consumed duirng development. The metabolic rates of avian eggs just prior to internal pipping (preIP MO2 is inversely proportional to the length of the incubation period. As in mammals, the mass specific metabolism of avian embryos is approximately equal to that of their parents, even though the parents are at least five times heavier. The total amount of O2 consumed per gram of fresh egg mass during development appears to be independent of egg mass and incubation period and averages 102 cm3 O2 . G-1. Calculated air cell O2 and CO2 tensions average 101 Torr and 40 Torr, respectively. Calculated air cell gas tensions are significantly correlated with egg mass but directly observed values are not, a discrepancy which remains to be resolved.

Animals↗
PubMed1980

Analysis of chorioallantoic gas exchange in the chick embryo.

To analyze the gas exchange mechanisms in the chorioallantois, PO2 and PCO2 were measured in air cell gas, in the allantoic artery and in the allantoic vein in chicken embryos on the 16th day of incubation. In addition, the O2 dissociation curve of blood, and O2 uptake and CO2 output of the embryo were determined. From O2 measurements performed in hypoxia (FIO2=0.14), normoxia and hyperoxia (FIO2=0.67), it was concluded that there was a sizable functional arterio-venous shunt amounting to 10-15% of the total chorioallantoic blood flow and that the diffusing capacity of the air cell-blood barrier for O2 was about 7 microliter . min-1. Torr-1. The CO2 measurements are in agreement with the model. In hypoxia, the air cell-blood transfer of O2 was markedly diffusion limited. The diffusion limitation effect was slight in normoxia, and not detectable in hyperoxia. At all oxygenation levels the effect of the shunt on blood arterialization was marked, particularly so in hyperoxia where the air cell-arterialized blood PO2 difference averaged 180 Torr.

Allantois↗