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H Rahn

Publications and source records attributed to H Rahn.

At least 19 recordsLinked to original sources
PubMed1990

The acoustocardiogram: a noninvasive method for measuring heart rate of avian embryos in ovo.

A method is presented for measuring the heart rate of avian eggs noninvasively during the last half of incubation. The technique involves briefly placing an egg in tightly sealed vessel containing an inexpensive condenser microphone. The amplified output of the microphone, termed the acoustocardiogram (ACG), is nearly sinusoidal in shape and synchronous with the electrocardiogram. The ACG can also be obtained by mounting the microphone directly on the shell with Plasticine. The method offers advantages over previously described techniques in simplicity, low cost, and noninvasiveness.

Animals↗
PubMed1988

A blood-gas nomogram of the chick fetus: blood flow distribution between the chorioallantois and fetus.

This paper presents equations for quantifying the relationships between the O2 and CO2 concentrations and tensions in the blood of the 18-day chick fetus. A blood-gas nomogram showing these relationships is presented. Starting with the reported chorioallantoic artery and vein gas tensions and using the blood-gas equations, the range of embryonic arterial and venous gas tensions as well as the distribution of the cardiac output and the degree of mixing between the chorioallantoic and embryonic circulations are explored. It is concluded that at least 65% of the blood in the chorioallantoic artery consists of blood of embryonic mixed venous composition. A model of the blood flow distribution is proposed in which chorioallantoic and embryonic flows are equal, with 70% of the blood returning from the tissues of the embryo going to the chorioallantois and vice versa.

Allantois↗
PubMed1988

Diffusive resistance of avian eggshell pores.

Resistance to gas diffusion through the avian eggshell resides in the microscopic pores which penetrate the shell. We calculated the resistance to water vapor diffusion of individual pores in the shells of 23 species of avian eggs, based on measurements of pore dimensions taken from drawings of 321 pore casts published by Tyler (1962, 1964, 1965) and Tyler and Simkiss (1959). Diffusive resistances were calculated from Fick's first law, using a 100-segment model of each pore. In addition, we added 2 series resistances, calculated from Stefan's law, to account for boundary layer resistances at the inner and outer pore apertures. Convective resistances for the same 100-segment model were computed from Poiseuille's law. A special, symmetrically branching model is presented for the diffusive resistance of the branched pores of ostrich eggshells, based on the drawings of Tyler and Simkiss (1959). The total aperture resistance was less than 6.2% of total pore resistance, while the outside aperture effect was on average only 1.5%. The calculated average pore conductance for all species was 5.4 micrograms (day Torr)-1, about three times higher than the average value of 1.6 micrograms (day Torr)-1 obtained by dividing measured shell conductance by the number of pores (Ar and Rahn, 1985). A possible explanation for this discrepancy is advanced. However, it is to be noted that in spite of the discrepancy, both calculated and functional values of pore conductance appear to be independent of egg mass.

Animals↗
PubMed1988

Air cell gas tensions of the chick embryo at sea level and altitude: the contribution of Aggazzotti, 1914.

This historical note draws attention to the forgotten but remarkable study of A. Aggazzotti of Italy who in 1914 described for the first time the changes in O2 and CO2 tensions during the course of development of the chick embryo and repeated these observations at an altitude of 3000 m. When his gas tension data are recalculated and compared with those obtained by Wangensteen et al. at sea level and altitude, 60 years later, the agreement is good.

Air↗
PubMed1988

Regional differences in diffusive conductance/perfusion ratio in the shell of the hen's egg.

Are both gas exchange and gas tensions uniform in different regions of the developing hen's egg? To answer this question we measured the O2 uptake and CO2 production of the whole egg, and at the same time the O2 and CO2 tensions of the air cell. The gas exchange ratio (R) of the whole egg differed from R calculated from air cell PO2 and PCO2 values, in agreement with the findings of Visschedijk [Br. Poultry Sci. 9:173-184 (1968)], who measured gas exchange separately over both the air cell region and the remainder of the egg. We constructed a diffusive shell conductance/perfusion (G/Q) line on the O2-CO2 diagram from a blood nomogram for the chick embryo in late development [Olszowka et al., Fed. Proc. 46:512 (1987)], and used this to analyze our results. The G/Q ratio for the area of shell over the air cell differs from that for the remainder of the egg. Our analysis permits us to calculate, for each area, the regional shell conductance, blood flow, and O2 and CO2 tensions in the gas spaces between the shell and the chorioallantoic capillaries.

Animals↗
PubMed1987

Regional differences in shell conductance and pore density of avian eggs.

Minidesiccators were attached to the middle and to the blunt and pointed ends of avian eggs of six different species and from their mass change over time the regional shell gas conductance was determined. Later the pore density and shell thickness of these areas were measured. All species showed a decline in regional shell conductance and pore density from the blunt end to the pointed end. With the blunt end over the air cell as a reference point, the regional conductance of the middle and the pointed end declined to 88 and 63%, while pore density fell to 81 and 63%, respectively. The six species represent four orders of birds, and the results suggest that differences in regional conductance may be a relatively common characteristic of bird eggs, that differences in regional pore conductance are proportional to the pore density, and that therefore the conductance of individual pores in any one species is relatively constant.

Animals↗
PubMed1987

Pores and gas exchange of avian eggs: a review.

Pores of the avian eggshell provide the only communicating channels for the exchange of molecules between the developing embryo and the external environment. These trumpet-shaped ducts are microscopic. Their number and effective pore radius increase with egg mass from ca. 300 and 3 microns in 1 gm eggs to about 30,000 and 13 microns, respectively, in 500 gm eggs (Ar and Rahn, Respir. Physiol. 61:1-20, 1985). The total volume of all the gases that diffuse through these pores is large. For example, up to the time when internal pipping takes place, when pulmonary ventilation is initiated, about 20 liters (O2 + CO2 + water vapor) have passed through 10,000 pores of an 80 gm egg. The rules governing this exchange of gases are best described by Fick's first law rather than by Stefan's law, which describes the transfer of gases across stomata of plants. Data are presented for those species for which the water vapor conductance, the oxygen flux at the preinternal pipping stage, the rate of incubation water loss, and the number of pores in the egg have been established. These conductances and flux rates are directly proportional to the number of pores. These relationships suggest that, in spite of differences in egg mass and incubation time, in most birds the average conductance of individual pores is similar, namely, 1.5 microgram (d X torr)-1 and that the average O2 and water vapor flux per pore are 60 and 54 microliters X d-1, respectively. These values are similar to the estimates previously presented (Ar and Rahn, '85).

Animals↗
PubMed1987

Temperature and metabolism of chick embryos and hatchlings after prolonged cooling.

Is a new quasiequilibrium state of metabolism and egg temperature reached after chick embryos and hatchlings are exposed to prolonged cooling? During the last half of the incubation period the chicken egg maintains a temperature above that of the ambient air temperature of 38 degrees C. This difference increases from about 0.2 degree C at 11 days to 2 degrees C just before hatching and to 3 degrees C by 7 days posthatching. When eggs or hatchlings are then exposed to room air at 28 degrees C, a new quasiequilibrium state is reached in 5 hr (defined as a change in egg temperature of less than 0.1 degree C X hr-1). The new difference between egg and ambient temperature varies from about 0.1 degree C at 11 days to 1.2 degrees C just before hatching, but increases in the hatchling from 6 degrees C right after hatching to 10 degrees C 5 days later. During the quasiequilibrium state at 24 degrees C the metabolic rate is maintained at about 40% of the control value up to hatching time, but thereafter rapidly increases to 70-95% by day 1. In a few cases emergence from the shell was not necessary for increases in quasiequilibrium temperature and metabolic rate.

Animals↗
PubMed1987

Diffusion-induced convective gas flow through the pores of the eggshell.

Although gas exchange across the avian eggshell has been treated as a simple diffusion process heretofore, the nonequimolar nature of diffusive fluxes engenders a convective flow and thus causes an overpressure (delta Ph) within the shell relative to the surrounding atmosphere. The convective flow must be taken into account in assessing the driving forces and corresponding flows of the gases involved. Using the nonmetabolizing hen's egg as a model, we describe the interactions of diffusion and convection as they affect water vapor and inert gas exchange through the pores. A typical infertile hen's egg containing water vapor at 50 torr and immersed in dry air (the situation in a desiccator at 38 degrees C) will lose about 900 cm3 d-1 of water vapor by a combination of diffusion and convection. Diffusion is the predominant process, accounting by calculation for 96% of total water loss as vapor. The remaining 4% of water vapor exits by convection, which also carriers with it 480 cm3 d-1 of air. We measured delta Ph caused by this total convective flow across the shell in air, He-O2, and He, and found values of about 1, 4, and 8 mm H2O, respectively. A theoretical treatment of gas flow through pores based on Fick's and Poiseuille's laws yields delta Ph values somewhat lower than those measured. Possible reasons for the discrepancy are discussed, together with implications of our findings for gas exchange and conductance measurements in metabolizing eggs.

Animals↗
PubMed1987

Influence of eggshell pore shape on gas diffusion.

We describe the influence of pore shape in the hen's eggshell on calculated resistance to diffusion. These calculations are based on measurements of 70 pore casts, pictures of which were published by Tyler (In: Recent Advances in Food Sciences, Butterworth, London, Vol. 1, 1962). Single-pore resistance was estimated from Fick's first law as the summed resistances of 100 cylindrical segments in series and the calculated boundary layer resistance at the pore apertures. In addition, we constructed an average pore profile from all measurements. The calculated average single pore water vapor conductance (3.2 micrograms X day-1 X torr-1) is about twice the measured literature value. The presence of organic material in the pore openings is discussed as one of several possible reasons for this discrepancy. Average diameter should not be used to calculate conductance of trumpet-shaped pores. The narrow part of the pores plays a dominant role in total pore conductance, and pore shape must be taken into account when estimating conductance from pore dimensions.

Animals↗
PubMed1987

Nest microclimate and incubation water loss of eggs of the African ostrich (Struthio camelus var. domesticus).

The microclimate of the nest and the rates of egg water loss were studied at weekly intervals throughout the 41-day incubation period in six ostrich nests. Overall mean values were a central egg temperature of 34.9 degrees C associated with saturation vapor pressure of 42 torr, a mean nest vapor pressure of 11 torr, and an ambient vapor pressure of 8.4 torr. The egg water loss increased from 4,000 to 4,800 mg X day-1 over the incubation period, and the total water loss was equal to 13.2% of the initial egg mass of 1,368 gm. The mean rate of water loss (4,403 mg X day-1) divided by the water vapor conductance of the shell (147 mg X day-1 X torr-1) equals 30 torr. When this value is added to the nest vapor pressure of 11 torr, it predicts an egg saturation vapor pressure of 41 torr, similar to that derived from the central egg temperature.

Animals↗
PubMed1986

Tolerance of chick embryos to low temperatures in reference to the heart rate.

Ten-day-old embryos were exposed to 28, 18 and 8 degrees C environments and their electrocardiograms (ECG) monitored. Embryos in 28 and 18 degrees C environments maintained a constant heart rate averaging 97 and 25 beats/min, respectively, followed by arrhythmias and cardiac arrest at 101 and 59 hr. Embryos in an 8 degrees C environment went into cardiac arrest after 2-4 hr, but recovered 20 hr later upon rewarming to 38 degrees C. Six to 20-day-old embryos exposed to 8 degrees C were examined for tolerance time after cardiac arrest. The younger the embryo the longer its tolerance to prolonged cardiac arrest.

Acclimatization↗
PubMed1985

Pores in avian eggshells: gas conductance, gas exchange and embryonic growth rate.

The number of pores (N) in eggshells of birds were counted in 161 species ranging in egg mass (W) from 0.9 to 500 g. In addition the water vapor conductance of the shell (G) mg X (d X Torr)-1, the water loss in the nest (M) mg X d-1, the incubation duration (I) d, and the shell thickness or pore length (L) micron are listed for each species when available. Allometric equations for all variables are given when regressed on egg mass. When log G is regressed on log N the slope is essentially 1.0 indicating that the G X N-1 for average pores in bird eggshells is 1.5 micrograms H2O X (d X Torr)-1 regardless of egg mass or incubation duration. According to Fick's law of diffusion such pores have a cross-sectional area to pore length ratio of 0.67 micron 2 X micron-1. Further analysis show that N, G, M, and the rate of oxygen consumption at the pre-internal pipping stage, are all directly proportional to the absolute mean growth rate of embryos (defined as 0.67 [W/I], g X d-1). Thus, single pores of typical eggshells not only have a similar conductance G X N-1, but also the metabolic rate and rate of water loss are matched to the pore conductance so that O2, CO2 fluxes per pore at the pre-internal pipping stage and water vapor flux per pore are similar among species, namely 68, 49 and 50 microliters X d-1, respectively. The partial pressure differences across the shell at the same stage are 42, 40 and 27 Torr, respectively. Ecological as well as taxonomical variation may alter some of the relationships predicted for the 'typical' egg in order to conserve a typical overall diffusive water loss.

Animals↗
PubMed1985

Transport by gas-phase diffusion: lessons learned from the hen's egg.

Diffusive gas transport obeys laws which differ from those of convective transport. Diffusive gas transport can be described as an elite transport system because it not only distinguishes between O2, CO2, and water vapor molecules, but it is also influenced by barometric pressure and the presence of particular inert gas species. In the presence of air binary diffusion coefficients are applicable, but in the presence of He or SF6 effective diffusion coefficients must be used. By contrast, convective transport is an egalitarian transport system which conveys O2, CO2, and water vapor without discrimination at any altitude or in the presence of any inert gas mixture. Experiments in progress offer the opportunity to delineate for the first time precise diffusion-perfusion ratios and their effects upon the gas-space O2 and CO2 tensions.

Animals↗
PubMed1984

Lung respiration, somatic activity and gas metabolism in embryonic chicks prevented from hatching by thiourea.

Treating chick embryos with high doses of thiourea (32.8 mumol) on day 17 of incubation resulted in prevention of hatching and of active breathing. Furthermore, thiourea also prevented the increase of O2 consumption and the marked increase of somatic activity associated with the final hatching act. These findings provide evidence for the importance of active breathing in the prenatal period to initiate pipping and hatching of the avian embryo.

Animals↗
PubMed1983

Replacement of diffusive by convective gas transport in the developing hen's egg.

Comparison of diffusive and convective transport equations for O2, CO2 or H2O in the gas-phase shows that for the same gas flux (ml . day-1) and the same pressure difference (Torr) one can substitute an effective air ventilation, VA (ml . day-1), for a given diffusive conductance, G, (ml . day-1. Torr-1). The theoretical relation is: VA = (RT) . G. Thus air ventilation of 865 ml . day-1 (BTPS) is required for each unit of G. This relation was tested in the developing chick embryo (days 15 to 19) by continuously ventilating the air space beneath the shell while the egg was maintained at 37.8 degrees C in air or submerged. During this exposure normal development, oxygen uptake, and gas tensions were maintained, verifying the theoretical prediction.

Animals↗