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A Ar

Publications and source records attributed to A Ar.

At least 37 records · Page 2Linked to original sources
PubMed1992

Non-invasive determination of heart rate in newly hatched chicks.

1. Using a flexible piezoelectric probe, we detected non-invasively the cardiogenic precordial movements of domestic fowl chicks and measured heart rate (HR) daily over the first week after hatching (day 0) for comparison with previously measured embryonic HR. 2. HR of the hatchlings was much more variable than embryonic HR. The mean HR at a given age also varied among the 5 chicks measured. 3. The overall mean HR was 280 +/- 20 (SD, n = 5) bpm on day 0. This value was similar to the prepipping HR and lower than that of externally pipped embryos. It increased to 342 +/- 39 bpm 3 days later.

Animals↗
PubMed1991

Oxygen uptake and chorioallantoic blood flow changes during acute hypoxia and hyperoxia in the 16 day chicken embryo.

Oxygen consumption rate (MO2) of hen eggs was measured on incubation day 16 (37.8 degrees C, 55% humidity) during acute exposure (90 min) to ambient hyperoxia (FI02 = 0.42) or hypoxia (FIO2 = 0.105). During the last part of these exposures, an H2 washout method was used to estimate relative changes in chorioallantoic membrane (CAM) blood flow, taking as an index the net change in the H2 washout rate constant between any experimental condition and the circulation arrested egg. Doubling normoxic FIO2 increased MO2 to an asymptotic value which was 4% above the normal (P less than 0.05; MO2 in normoxia = 890 mumols/h) even after correcting for the normoxic increase in MO2 with time during development (delta MO2/delta t = 21.5 mumols/h2; P less than 0.001). Halving FIO2 reduced MO2 calculated in the same way to 388 mumols/h. The estimate of the CAM blood flow, relative to normoxia, was 1.12 in hyperoxia (not significant, P = 0.05) and 0.68 in hypoxia (P less than 0.001). The limited changes in CAM blood flow and MO2 during hyperoxia indicate that they are both already close to their maximal values in normoxia. During acute hypoxia the 16 day embryo behaves as an oxygen-conformer; however, the small relative decrease in MO2 per unit of the flow index observed during hyperoxia suggests that the embryo can regulate its CAM blood flow to a small extent. The survival of the embryo and its recovery from hypoxia without a detectable O2 repayment suggest small if any anaerobic regulatory pathways and indicate a true metabolic depression.

Allantois↗
PubMed1987

Oxygen consumption of the chick embryo's respiratory organ, the chorioallantoic membrane.

A new technique based on stopping the chick embryo's blood circulation in the intact egg was used to measure in situ the chorioallantoic (CA) oxygen consumption, MCAO2, from incubation day 12 to 20. Total egg MO2, MTOTO2, and wet and dry masses of embryo and CA were also measured daily. Embryo MO2, MEMBO2, was calculated. Mean MCAO2 decreased from 71 mumol X h-1 (17% of MTOTO2, 24% of MEMBO2) at 12 days to 62 mumol X h-1 (5% of MTOTO2) at 20 days. Dry mass of CA did not change significantly. Water remained at a high level in CA (88-94%), but embryo water decreased from 93% to 82% between days 12 and 20. The fairly high level of MCAO2, more marked at young stages, calls for corrections in respiratory and circulatory embryonic variables derived from MTOTO2, such as CA blood flow, CA diffusive capacity for O2, and CA arterio-venous shunt. Mass specific values and intra-specific allometric relations in bird embryos should be recalculated on the basis of MEMBO2 instead of MTOTO2.

Allantois↗
PubMed1987

Improving turkey poult quality by correcting incubator humidity to match eggshell conductance.

One of the most important factors determining hatchability of avian eggs is their proper water budget during incubation. We show here that water budget changes of turkey eggs effect not only hatchability but also poult quality. In addition to an increase in hatchability of 3.3%, poult quality was increased by 7.3%. This was achieved by sorting eggs into low (less than 18.5), medium (18.5 to 22.0) and high (greater than 22.0) eggshell mass-specific water vapour, conductance categories and incubating them in matching incubation humidities of 21.8, 26.6 and 31.4 Torr, corresponding to relative humidities of 45, 55 and 65% at 37.5 degrees C, respectively. A total diffusive water loss of 11.5% (range 10 to 14%) of the initial egg mass in 25 d of incubation yielded maximal hatchability and poult quality.

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

Energy in avian eggs and hatchlings: utilization and transfer.

Energy content of eggs, hatchlings, and egg components (albumen, yolk, true hatchling = hatchling without spare yolk, and spare yolk) and the energy spent for metabolism were analyzed in 50 species of birds divided into four maturity types. Mass-specific energy density on the basis of fresh egg content mass appears to be mass-independent within each maturity group but different among the groups. Mass-specific energy densities calculated on the basis of dry component mass are the same for albumen, yolk, and spare yolk in all maturity groups but are different for true hatchlings, precocial hatchlings being richer in energy than all others. The gross production efficiency (hatchling energy/egg energy) of 63.7% +/- 7.8 SD does not differ significantly among maturity types. Total production efficiency (true hatchling energy/egg energy minus spare yolk energy) averaged 57.0% +/- 7.0% (SD) in all types. The inefficiency attributed to fuel loss in metabolism is 34.7% +/- 11.0% (SD) of the total energy used; hence losses in extraembryonic tissues and meconium average 8.3% of the total energy used. The cost of transforming the chemical potential energy in the egg into living tissues (including maintenance costs) is about 0.5 J X J-1. The energy densities of the dry matter in the egg and the energy transformation efficiencies and costs seem to be independent of maturity type. The differences among maturity types reside in the different water concentrations in eggs and hatchlings, in the density of chemical potential energy in the dry matter of true hatchlings, and in the different amounts of energy transferred untransformed from the egg to the spare yolk.

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↗
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↗
PubMed1984

Increasing hatchability of turkey eggs by matching incubator humidity to shell conductance of individual eggs.

One of the most important factors determining hatchability of avian eggs is the proper water balance of the eggs during incubation. In turkey eggs, a total diffusive water loss (F) of 12 +/- 1% SD initial egg mass in 28 days, yielded maximal hatchability irrespective of the combination of eggshell water vapor conductance (G) and incubator humidity (PI), which brought about this water loss. A good correlation was found between G as obtained at the beginning of incubation and the final F in a given PI. The G in a random sample of 1256 fresh turkey eggs was normally distributed around the mean of 18.70 +/- 2.87 SD milligrams (100 g X day X torr)-1 (Coefficient of variation = 15.3%). The distribution of G in eggs with dead in the shell embryos had, in addition, two more peaks of G values [around 22.5 and 13.0 mg (100 g X day X torr)-1]. When eggs were sorted into low (less than 17), medium (17 to 20), and high (greater than 20) G categories, and incubated at low (19.4), medium (26.6), and high (33.9) torr PI, respectively, hatchability increased by a factor of 1.08. Poor hatchabilities were obtained in mismatching humidities and conductances. It seems that hatchability success may be experimentally improved if a correct rate of water loss is fitted to sorted eggs during incubation.

Animals↗
PubMed1981

Gas tension profile of the lung of the viper, Vipera xanthina palestinae.

Oxygen and carbon dioxide concentrations along the lung of five awake, resting Palestine vipers were continuously measured by mass spectrometry. Ventilatory volumes, body wall movements and heart rate were also measured. In the anterior part of the faveolar (respiratory) lung, oxygen and carbon dioxide concentrations returned to within 1% of inspired composition with each inspiration. Between breaths, changes of 0.5-2% in gas concentrations were seen in the faveolar region but practically no changes occurred in the caudal, non-respiratory lung (air sac) where mean oxygen and carbon dioxide concentrations of 16.4% and 2.5% respectively were recorded. The respiratory exchange ratio dropped from near 1.5 in the anterior faveolar region to zero in the transition zone to the air sac. Instantaneous R values declined with breath-holding time in each location along the length of the lung. Gas exchange appears greatest in the posterior faveolar region near the heart and there is evidence of cardiogenic gas mixing in this region. The posterior air sac may either passively respond to air movements in the anterior lung or it may participate in ventilation. During periods of extended breath-holding (10-15 min) pronounced body wall movements were seen but there was no air flow from the mouth and gas exchange continued in the lung with rapidly decreasing R.

Animals↗
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

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↗
PubMed1979

Solubility and partition coefficients for gases in rabbit brain and blood.

Solubility and partition coefficients for argon, methane, neon, nitrogen, and sulfur hexafluoride in normal saline, rabbit blood, and exsanguinated rabbit brain were determined in a two-step process that involved equilibration of the various aliquots, and subsequent analysis by gas chromatography. Brain-blood partition coefficient was specifically higher than one for argon, neon, and sulfur hexafluoride, and questionably significant (P less than 0.025) for nitrogen.

Animals↗