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A Ar

Publications and source records attributed to A Ar.

At least 19 recordsLinked to original sources
PubMed2003

Mathematical analysis of atelectasis formation in middle ears with sealed ventilation tubes.

AIM: A mathematical model was developed to identify time periods of atelectasis induction in middle ear (ME) ventilated via ventilating tubes (VT). Atelectatic ears are characterized by a total gas pressure lower than 760 mmHg. METHODS: Ventilating tubes were deliberately sealed and ME gas content changed in the presence of a preset blood gas pressure. Once sealed, CO2 rapidly diffuses out of the blood via lining tissues into the ME cleft. This results in initially a total ME pressure rise followed by a decrease in subatmospheric pressures. Time periods for atelectasis reformation was determined once ME pressure crossed the 760 mmHg value and continued to decline as the atelectasis reached higher grades. RESULTS: Time periods calculated by the model varied from 18 to 125 min in ME cavities ranging in volume from 0.5 to 3.5 mL, respectively. These results were calculated for conditions of venous blood in the lining mucosa blood and are consistent with prior clinical tests that measured an induced return to previous atelectasis state following the closure of the VT in 33 tested ears within 25-120 min (43 min on average). CONCLUSIONS: The model demonstrates that under the above conditions, diffusive gas transfer in relation to blood gas content is the leading mechanism to alterations in ME pressure and volume. It may be used as a tool to determine ME physiological cavity volume of ears with VT.

Carbon Dioxide↗
PubMed2001

Gas exchange and energy metabolism of the ostrich (Struthio camelus) embryo.

We measured oxygen consumption (V(O(2))) and carbon dioxide emission (V(CO(2))) rates, air-cell gas partial pressures of oxygen (P(A)O(2)) and CO(2) (P(A)CO(2)), eggshell water vapour conductance and energy content of the ostrich (Struthio camelus) egg, 'true hatchling' and residual yolk, and calculated RQ and total oxygen consumption (V(O(2)tot)) for ostrich eggs incubated at 36.5 degrees C and 25% relative humidity. The V(O(2)) pattern showed a drop of approximately 5% before internal pipping. V(O(2)) just prior to internal pipping agrees with allometric calculations. Despite the higher incubation temperature compared to other studies, and the resultant shorter incubation duration (42 days), V(O(2)tot) (91.7 l kg(-1)) was similar to a previously reported value. RQ values during the second half of incubation (approx. 0.68) were lower than expected for lipid catabolism. Prior to internal pipping, P(A)O(2) and P(A)CO(2) were 98 and 48.3 torr (13.1 and 6.4 kPa), respectively. The growth pattern of the ostrich embryo is different from the typical precocial pattern, showing a time delay in the rapid growth phase. As a result, the lowered overall energy expenditure for tissue maintenance, as compared to other species, is reflected in the low yolk utilization and high residual yolk fraction of the whole hatchling dry mass. These could also result from the relatively short incubation period of the ostrich egg, thereby evading desiccation by excess water loss.

Animals↗
PubMed2001

Allometric relationships between embryonic heart rate and fresh egg mass in birds.

Previously, we have measured daily changes (developmental patterns) in embryonic heart rate (fh) in altricial and semi-altricial (ASA) birds (range of mean fresh egg mass approximately 1-20 g), semi-precocial seabirds (egg mass approximately 38-288 g) and precocial birds (egg mass approximately 6-1400 g). An allometric relationship between embryonic fh at 80 % of incubation duration (ID) and fresh egg mass (M) has been derived for six species of precocial bird (fh at 80 % ID=429M(-0.118)). In the present study, additional measurements of embryonic fh in three ASA species, the barn owl Tyto alba, the cattle egret Bubulcus ibis and the lanner falcon Falco biarmicus, were made to extend the egg mass range (20-41 g), and the allometric relationships of embryonic fh for these ASA birds and the precocial and semi-precocial (PSP) groups were investigated from published data. The developmental patterns of embryonic fh in three relatively large ASA species did not show a significant increase prior to the pipping period, unlike those in small ASA birds, but tended to be constant, with a subsequent increase during pipping. The allometric relationship derived for ASA birds was fh at 80 % ID=371M(-0.121) (r=-0.846, P<0.001, N=20) and that for PSP birds was fh at 80 % ID=433M(-0.121) (r=-0.963, P<0.001, N=13). The slopes were parallel, but fh of ASA embryos was low compared with that of PSP embryos with the same egg mass. In ASA birds, embyronic fh was maximal during the pipping (perinatal) period, and the maximum fh (fh(max)) was significantly related to fresh egg mass: fh(max)=440M(-0.127) (r=-0.840, P<0.001, N=20). The allometric relationships for fh at 80 % ID in PSP and fh(max) in ASA embryos were statistically identical. Accordingly, embryonic fh at 80 % ID in PSP birds and fh(max) during pipping in ASA birds can be expressed by a single allometric equation: fh=437M(-0.123) (r=-0.948, P<0.001, N=33).

Animals↗
PubMed2000

Embryonic heart rate measurements during artificial incubation of emu eggs.

1. Daily changes in embryonic heart rate (HR) of emu were determined non-invasively at 36 degrees C by acoustocardiography (ACG) during the last 30% of artificial incubation (predicted incubation time is 50 d). 2. The pattern of daily changes in mean HR of hatched embryos decreased from about 175 bpm to about 140 bpm towards the end of incubation. 3. The mean HR at 80% of incubation (ca. 170 bpm) was close to the value predicted from an allometric equation reported previously for precocial domesticated birds. 4. ACG could measure embryonic HR even during the external pipping period. 5. If the artificial external pipping procedure is timed correctly after internal pipping, it might aid the embryos in hatching. However, further investigation into this aspect is needed.

Animals↗
PubMed2000

Continuous measurements of instantaneous heart rate and its fluctuations before and after hatching in chickens.

There has been considerable interest in heart rate (fh) fluctuations in relation to cardiovascular control systems and foetal conditions during pregnancy in mammals. Prominent fluctuations in fh also occur in avian embryos, which are an important experimental model for studying developmental physiology. The present study determined the instantaneous fh of seven chick embryos continuously from the last stage of prenatal development (day 18), throughout the pipping (perinatal) period (days 19-21) until hatching and, subsequently, of newly hatched chicks (up to day 2). The distinctive patterns of instantaneous fh fluctuations took the form of specific changes within a broad mean fh baseline. Cyclic oscillations (ultradian rhythm) occurred until an early stage of the perinatal period, when the fh baseline started rising. Subsequently, the baseline dropped and respiratory arrhythmia began to appear concomitant with external pipping. During the final stage of external pipping, when the fh baseline rose again prior to hatching, three unique patterns of instantaneous fh fluctuations were evident: relatively long-lasting cyclic small accelerations, irregular intermittent large accelerations and short-term repeated large accelerations. Furthermore, repeated alternate occurrences of the latter two types of acceleration formed an additional oscillating pattern with a period of 10-15 min. During the early period after hatching, when the fh baseline reached its maximum, instantaneous fh changed relatively slowly accompanied by transient rapid decelerations, probably due to augmented vagal tone. Subsequently, the mean fh baseline dropped to its minimum, and a circadian rhythm and three types of previously reported fh fluctuations (types I-III) appeared. Developmental patterns of mean fh and the appearance of distinctive patterns of instantaneous fluctuations in fh and circadian rhythms were not influenced by an ultimate failure of hatching after a normal development. The demonstration of complex, repeatable patterns of fh fluctuation that change during development suggests that the avian embryo model should be useful in studying the phenomenon of fh fluctuation and its underlying causes.

Animals↗
PubMed1999

Analysis of heart rate in developing bird embryos: effects of developmental mode and mass.

Bird embryos may be regarded as developing in their thermo-neutral zone, at rest, and stay in the egg for a fixed period of time until hatching. It is therefore interesting to investigate if they follow the same 'rule' set for adult homeotherms, which states that, within a taxonomically or functionally defined category such as mammals or birds, the number of heart beats throughout the life span (sL) is more or less constant. This rule stems from the allometric relationships between heart rate (fH) and body mass (mB) and between sL and mB. As a step towards understanding the general allometric nature of avian embryonic physiology we analyzed the fH values of avian embryos in relation to their incubation span (sI). Data from 30 species were selected from the scientific literature for the analyses. Values obtained from invasive methods which were judged to grossly alter natural incubation conditions, or from undefined or unmatched temperature conditions were not used. These include most values obtained below the first 30% of the incubation. Also, data obtained after internal pipping were discarded since hatching activity influences them. Values for sI and egg mass (mE) as representatives of embryonic mass were also collected. Embryonic fH was normalized to 70.1-80% sI. At 20.1-30% sI it was only 85% of the value at 70.1-80% sI and increased to a plateau at about 50.1-60% sI. It was almost constant among species between 50.1 and 60% sI and pre-internal pipping (PIP) time and thus, the mean fH value between 50.1 and 60% sI and between 90.1 and 100% excluding pipped eggs (fH) was taken as a representative value for each given species. The fH (min-1) and the corresponding sI (days) values for the 30 species, scaled with mE (g) as follows: fH = 371.1.mE-0.112 and: sI = 12.29.mE+0.209. Both powers were significantly different from 0. The product of fH and sI (fH.sI), representing the total number of heartbeats throughout the incubation, scaled with mE for the entire data set as follows: fH.sI = 6.565 x 10(+6).mE+0.096, where the +0.096 power is significantly different from 0. Values for fH.sI from embryos of altricial birds tended to concentrate at the low mE end of the plot while those of the precocial ones tended towards the high end. Separate analyses showed that the mE power for the combined altricial and semi-altricial species (ASA), and the combined precocial and semi precocial species (PSP), of log fH.sI against log mE regressions, were both insignificantly different from 0. Thus, means of fH.sI for ASA and PSP were calculated. The mean ASA value of 7.27 x 10(+6) heartbeats for fH.sI, was significantly different from the mean PSP value of 10.93 x 10(+6). The difference of 3.66 x 10(-6) (33.5%) heartbeats can be attributed to either the more advanced stage of the PSP hatchlings at hatch, to the larger mE values of these hatchlings, to the difference in water fraction of the hatchlings or all. The result of a linear regression of fH.sI against the rate of sI completion (the inverse of incubation span, fI; day-1) was: fH.10(-6) = 0.205 + 3.940.sI-1. Thus, the faster is the average rate of development accomplished per day (shorter incubation) the higher is daily heart rate. Data tended to cluster such that large eggs, mostly of the PSP type with relatively low fH, complete 2-4% of their incubation per day, while small, ASA type eggs with relatively high fH, complete 6-8% of their incubation time per day. We conclude that, at this stage of knowledge, the data is insufficient to resolve whether the different modes of hatch stage alone can explain differences in the total number of heartbeats throughout embryonic life among all bird species, or egg mass and water content differences contribute variability. This should be investigated on a larger sample of species in more depth.

Animals↗
PubMed1999

Effects of drilling holes into the air cell of incubated goose eggs on distribution of oxygen partial pressures under the shell.

The purpose of this work was to measure changes in oxygen pressure in the air cell and under the eggshell (P(A)O2) of pre-pipping goose eggs before and after drilling holes into the air cell. Drilling a 0.6 mm (diameter of 0.9 mm) hole into the air cell caused an increase in air cell P(A)O2 of about 10 Torr. The rate of increase attenuated as hole area increased and reached about 21 Torr when the drilled area was 8.5 mm2. The P(A)O2 of intact eggs was not equally distributed under the shell. It was high in the air cell area (108 Torr) and decreased towards the pointed end (86 Torr). The increase in P(A)O2 after drilling a 4.9 mm2 hole was high in the air cell (18 Torr) and decreased with distance, becoming non-significant at the pointed end. The significant increase in P(A)O2 after drilling was limited to a distance of up to 38 mm along the shell from the edge of the air cell. This indicates that lateral diffusion in the shell membranes under the shell is limited. Drilling a hole of 3.5 to 4.9 mm2 was enough to increase air cell P(A)O2 in most of the eggs above the critical value of 100 Torr for hatching success. The increase in P(A)O2 was limited to about half the area of the shell and the average increase in P(A)O2 was 6.3 Torr (equivalent to a 0.9% increase in ambient O2). However, the blood perfusing chorioallantoic areas further away from the air cell edge may not be fully saturated with O2 and may not be sufficient to compensate fully for the low O2 availability caused by low eggshell conductance.

Animals↗
PubMed1998

Quantitative analysis of gas losses and gains in the middle ear.

Quantitative analysis of the amount of gas entering and leaving the middle ear (ME) was performed in patients with central perforation or with ventilating tubes. Patients were divided into a 'balanced pressure group' (BP) where pressure remained close to atmospheric throughout the measuring period and an 'unbalanced pressure group' (UBP) where pressure decreased continuously throughout measurements. The rate of gas gain was 41.0 +/- 19.9 microl/h (mean +/- SD, n = 17) in the BP group, significantly higher than in the UBP group (21.4 +/- 9.6 microl/h, n = 8). The rate of gas loss was 34.8 +/- 17.7 and 36.1 +/- 15.9 microl/h in the BP and UBP groups, respectively. Deglutition frequency was 27 +/- 13.4 deglutition/h in the BP group, significantly higher than the deglutition frequency of the UBP group (16 +/- 8.9 deglutition/h). It seems that the amount of gas entering the ME per deglutition is rather stable and does not change significantly with ME pressure level. Negative ME pressure may result from decreased gas gain rate due to increased intervals between deglutitions and loss of interdependence between the rate of gas entering and leaving the ME.

Adolescent↗
PubMed1998

Rate of gas exchange in the middle ear of guinea pigs.

Gas exchange between blood in the middle ear (ME) mucosa and ambient ME gas may be limited by diffusion through tissue or blood perfusion. In order to study the limiting factors in ME gas exchange, a hole was drilled in the bulla of 14 anesthetized guinea pigs through which a mass spectrometer probe was inserted and sealed in place. The rate at which oxygen (O2), carbon dioxide (CO2), nitrogen, and argon concentrations changed toward their steady state values was recorded. From the exponential fitted curves, gas rate constants (Kg) were calculated. The ratio KCO2/KO2 was 4:1, which is lower than expected from a diffusion-limited process in an aqueous compartment. The different rate ratios of CO2 and O2 indicate a diffusion-limited process. However, the deviation of the KCO2/KO2 ratio from that expected in aqueous solutions may indicate the involvement of a lipid compartment in gas exchange or other physiological mechanisms such as local acidity.

Animals↗
PubMed1997

Antioxidant enzymatic activity in embryos and placenta of rats chronically exposed to hypoxia and hyperoxia.

Embryos exhibit lower enzymatic antioxidant activity (EAOA) than adults, in accordance with the low in utero oxygen concentration. We asked whether external oxygen stress can modulate embryonic EAOA and what the placenta role is a mediator between embryos and external milieu. Pregnant rats were exposed to hyperoxia (90% O2) or hypoxia (10% O2) during 8 days in the second or third trimester. Activities of catalase (CAT), superoxide dismutase and glutathione peroxidase (GPx) were measured in the term embryonic brain, lung and heart and liver; 2-week-old whole embryonic sac and placenta. In term "hyperoxic" embryos, only CAT increased by 30% in heart and lungs and liver. In the placenta, GPx increased by 31%. In term "hypoxic" embryos, only CAT activity decreased by 64%, 25% and 29% in brain, liver and placenta. In 2-week-old "hyperoxic" embryos CAT activity increased by 85% and GPx by 45% in the embryonic sac. In the placenta, GPx increased by 55%. The limited embryonic EAOA response is possibly due to maternal physiological buffering of oxygen supply. Placental EAOA is similar to other embryonic organs. It may protect the placenta proper, thus ensuring normal embryonic development.

Animals↗
PubMed1997

Changes in enzymatic antioxidant activity in pregnant rats exposed to hyperoxia or hypoxia.

Pregnant rats were exposed to chronic hyperoxia or hypoxia to examine whether endogenous (pregnancy) and external (exposure to environmental) oxidative stresses have additive influences on inducing enzymatic antioxidant activity (EAOA). The activities of catalase, glutathione peroxidase (GPx) and superoxide dismutase (SOD) were measured in the brain, liver, lungs, heart, uterus and placenta in non-pregnant (N) and pregnant (P) rats after 1 week of exposure to normoxia, hyperoxia and hypoxia. An additional combined effect in EAOA was found only in the heart. In the lungs and liver, EAOA increased both in pregnancy and hyperoxia, but no additive combined effect was noticed. The brain and N uterus EAOA were not influenced by pregnancy or hyperoxia. In the placenta, only SOD and GPx activities increased. Hypoxia had a negligible effect on EAOA both in N and P rats. Generally, the EAOA response of P rats to environmental oxidative stress was higher than that of N rats. We conclude that the influence of pregnancy and external oxidative stress on EAOA are not simply additive.

Animals↗
PubMed1997

Dependence of middle ear gas composition on pulmonary ventilation.

The middle ear (ME) steady state gas composition resembles that of mixed venous blood. We changed arterial and venous blood gases by artificially ventilating anesthetized guinea pigs and measured simultaneous ME gas changes during spontaneous breathing, hyperventilation, and hypoventilation. During hyperventilation, PaCO2 and PvCO2 (a = arterial, v = venous) decreased from 46.0 and 53.0 mm Hg to 17.9 and 37.5 mm Hg, respectively, while PaO2 and PvO2 (85.6 and 38.2 mm Hg) did not change. This was accompanied by an ME PCO2 decrease from 70.4 to 58.8 mm Hg and a PO2 decrease from 36.8 to 25.4 mm Hg. During hypoventilation, PaCO2 and PvCO2 increased to 56.8 and 66.4 mm Hg, while PvO2 decreased to 21.8 mm Hg. The ME PCO2 increased simultaneously to 88.8 mm Hg and the ME PO2 decreased to 25.4 mm Hg. The ME PO2 decrease during hyperventilation may be explained by a 33% decrease in ME mucosa perfusion, calculated from the ME ventilation-perfusion ratio. This study shows that ME gas composition follows fluctuations of blood gas levels and thus may affect total ME pressure.

Animals↗
PubMed1996

O2 consumption in the in-vitro fetal side human placenta.

The relative dependence of placental O2 consumption (MO2) on O2 supply (SupO2) parameters, and the fraction of aerobic O2 utilization, was studied by in-vitro perfusion of the fetal side of term human placental lobes. Placental MO2 was a function of the combined effect of SupO2 parameters (PO2, perfusate flow rate, perfusate effective O2 solubility) and not of each separately. At SupO2 greater than 800 microliters/(min.lobe), MO2 saturated at 260 microliters/(min.lobe). No accumulation of O2 debt could be detected even after 2 h anoxia. Adding CN- or CO to perfusate did not abolish MO2, and a residual MO2 of 31-37% of control MO2 was measured. In its MO2, the placenta is a typical conformer tissue. This conformity enables conservation of O2 transfer to the embryo even when placental SupO2 is radically reduced. Only about 60-70% of placental MO2 is utilized in the aerobic respiratory pathway, while about 30-40% of the oxygen is used in other pathways.

Biological Availability↗
PubMed1996

Artificial increase of eggshell conductance improves hatchability of early laid goose eggs.

1. The purpose of this work was to test the possibility of increasing the hatchability of goose eggs with low mass specific eggshell gas conductance (Gsp), by drilling holes through the eggshell into the air cell, and thus solving both the low water loss rate and low oxygen availability problems. 2. A linear relationship was found between the area of a hole drilled and the apparent increase in eggshell gas conductance (G). Drilling more than one hole increased apparent G 3-6 times more than one hole only, of the same total area. 3. Hole-drilling did not increase egg contamination. The drilling of a 5 mm2 hole on day 17 of incubation increased hatchability both in laboratory tests and in commercial hatcheries (6.1% and 10.5% respectively). 4. Drilling holes on days 15 to 22 of incubation increased hatchability when the predicted mean water loss was lower than 14%. Drilling on day 25 did not have a significant effect, and drilling on day 11 of incubation was too early. 5. Drilling a hole into the aircell (during the second half of incubation) may increase hatchability of low conductance eggs, although oxygen pressure under the eggshell should then be checked in order to evaluate oxygen availability to the embryo.

Animals↗
PubMed1995

Heart and lung adaptations to pregnancy and lactation in a crocidurine shrew.

Heart and lung mass, rate of oxygen consumption (VO2), respiration rate (fR), tidal volume (VT), and heart rate (fH), were measured at rest and thermoneutrality in the shrew Crocidura russula monacha [(This shrew is claimed to be Crocidura suaveolens (Catzeflis, F., T. Maddalena, S. Hellwing and P. Vogel (1985). Unexpected findings on the taxonomic status of East Mediterranean Crocidura russula auct. (Mammalia, Insectivora). Zeitschrift fur Saugetierkunde 50: 185-201)] in nullipar (N), pregnant (P) and lactating (L) females. The heart mass of N females is large (0.86% of body mass) but fH is slow (70% of that expected by mammalian allometry), while lung mass is small (87% of expected) and fR is high (47% above expected). The 31% higher than expected expired ventilation (VE) matches the 25% higher than expected VO2. In P females the fH of 560 min-1 did not change but it increased in L females to 620 min-1. VE did not change in P females but decreased in L females from 11.3 ml center dot min-1 to 10.1 ml min-1. The normal VT decreased in P and L females from 47.3 mu l to 38.4 mu l and 37.8 mu l respectively. The lower than expected resting fH of N females may provide sufficient scope for increased heart work and oxygen supply during exercise. The large heart may be more efficient. Hyperventilation in N females is indicated by the calculated relatively high fractional concentration of oxygen in expired air (FECO2), and low fractional concentration of CO2 in expired air (FECO2) (17.7% and 3.2% respectively), the high oxygen partial pressure in alveolar gas (PAO2) and low alveolar CO2 (PACO2), 119 and 34 Torr respectively, which facilitate O2 transport through the lung air-blood barrier. The elevated VO2 in P and L females is achieved by increased respiratory efficiency from the normal 15%, to 24% and 29% respectively.

Adaptation, Physiological↗
PubMed1992

Nest ventilation explains gas composition in the nest-chamber of the European bee-eater.

The European bee-eater Merops apiaster builds a nest in soil banks comprising a horizontal corridor (159 cm) leading to a 3.4 L nest chamber. An adult and six eggs and/or nestlings occupy this nest for 60 d. Incubation and development are asynchronous. In order to evaluate the gas exchange pattern of the occupied nest, we measured the O2 diffusive conductance of the nest with the ambient environment (GNO2), its internal O2 and CO2 pressures (PNO2 and PNCO2), temperature (TN) and observed the sequences of development and the frequency of parental visits. We also measured the rate of O2 uptake (MO2) of the eggs, nestlings and adults. The GNO2 was 10.9 ml[STPD]/(h.Torr). The PNO2 dropped and the PNCO2 increased during incubation and growth to a maximal change of 24 and 23 Torr, respectively. Maximal MO2 of an egg and a nestling were 5.4 and 146 ml[STPD]/h, respectively. The MO2 of an adult at rest and at TN (27 degrees C) was 90.5 ml[STPD]/h. From clutch size, sequence of nest events, and the above values we have estimated a maximal nest chamber ventilation (VN) of 0.8 L/min necessary to prevent lowering PNO2 to 74 Torr below ambient PO2. This convection is achieved chiefly by the parental feeding visits (up to 40/h). Thus, movement along the corridor convects 1.2 L per visit.

Animals↗