Respiration and blood gases in the duck exposed to normocapnic and hypercapnic hypoxia

Cervical air sac oxygen profiles in diving emperor penguins: parabronchial ventilation and the respiratory oxygen store

Some marine birds and mammals can perform dives of extraordinary duration and depth. Such dive performance is dependent on many factors, including total body oxygen (O2) stores. For diving penguins, the respiratory system (air sacs and lungs) constitutes 30-50% of the total body O2 store. To better understand the role and mechanism of parabronchial ventilation and O2 utilization in penguins both on the surface and during the dive, we examined air sac partial pressures of O2 (PO2 ) in emperor penguins (Aptenodytes forsteri) equipped with backpack PO2  recorders. Cervical air sac PO2  values at rest were lower than in other birds, while the cervical air sac to posterior thoracic air sac PO2  difference was larger. Pre-dive cervical air sac PO2  values were often greater than those at rest, but had a wide range and were not significantly different from those at rest. The maximum respiratory O2 store and total body O2 stores calculated with representative anterior and posterior air sac PO2  data did not differ from prior estimates. The mean calculated anterior air sac O2 depletion rate for dives up to 11 min was approximately one-tenth that of the posterior air sacs. Low cervical air sac PO2  values at rest may be secondary to a low ratio of parabronchial ventilation to parabronchial blood O2 extraction. During dives, overlap of simultaneously recorded cervical and posterior thoracic air sac PO2  profiles supported the concept of maintenance of parabronchial ventilation during a dive by air movement through the lungs.

Serum calcium and parathormone during normal pregnancy in Malay women

OBJECTIVE

To ascertain the calcium status in normal pregnant Malay women.

METHODS

In a cross-sectional study, serum parathormone (PTH) and calcium concentrations, and 24-h urinary calcium excretion were estimated in age-matched normotensive pregnant women, over the 3 trimesters.

RESULTS

No statistically significant differences were evident in serum ionised calcium concentrations between the pregnant women in the 3 trimesters. Serum total calcium however, was significantly lower in women in the 3rd trimester of pregnancy (2.29+/-0.16, 2.26+/-0.13, and 2.16+/-0.12 mmol l(-1) in the 1st, 2nd, and 3rd trimesters, respectively; P < 0.001). Serum parathyroid hormone concentration was significantly higher in the 3rd trimester of pregnancy (3.37+/-3.31, 4.36+/-4.55, and 7.17+/-6.6 pg ml(-1) in the 1st, 2nd, and 3rd trimesters, respectively; P < 0.05). No significant differences were evident in serum sodium and potassium concentrations between the 3 groups. Urinary calcium excretion was significantly lower in women in the 3rd trimester of pregnancy (3.41+/-1.80, 3.56+/-3.31, and 2.46+/-1.71 mmol day(-1) in the 1st, 2nd, and in the 3rd trimesters, respectively; P < 0.05). No significant differences were evident in urine output, creatinine clearance, or in the excretion of sodium and potassium between the 3 groups.

CONCLUSIONS

It appears that a significant fall in serum total calcium occurs in the 2nd half of normal human pregnancy when there is also an increased fetal demand and perhaps also a relatively insufficient maternal intake and/or intestinal absorption. The lower urinary calcium excretion probably occurs secondary to this and may suggest a fall in total body calcium and an attempt by the body to conserve calcium. While under normal circumstances, this level of fall in total calcium may not be significant, the coincidence of occurrence of hypertensive disorders of pregnancy during this stage of pregnancy, and the evident link between low calcium intake and pregnancy-induced hypertension (PIH) and its possible amelioration with calcium supplementation, suggests a need to assess calcium status in pregnant women with a view to providing calcium supplementation during pregnancy.

Metabolic and ventilatory adjustments and tolerance of the bat Pteropus poliocephalus to acute hypoxic stress

We have investigated the maximum tolerance and the ventilatory responses of a bat, P. poliocephalus (PP), to normobaric hypoxic stress. PP can tolerate inspired PO2s (PiO2) down to 30 torr. This bat is one of the most hypoxia-tolerant non-hibernating species of mammals known, and has a tolerance which lies within the range of PiO2s reported for different birds. Unlike most mammals in its size range, PP maintains its normoxic oxygen consumption rate even in deep hypoxia. The maximum hypoxic ventilatory response (HVR), the air convection requirement (Vi/MO2), and the lung oxygen extraction (EL) ability of PP in deep hypoxia are all greater than those of other mammals. These and other data indicate that PP has a superior mammalian tolerance for hypocapnia. The magnitudes of both the V1/MO2 and the EL value of PP fall between those reported for Pekin ducks at corresponding PiO2s, and are inferior to the maximum capabilities of bar-headed geese. Thus, the tolerance and ventilatory adjustments of PP to deep hypoxia are intermediate between those of typical non-flying mammals and the most tolerant avian species, and suggest that at least some of this bat's respiratory adaptations for flight may serve as preadaptations for withstanding acute hypoxic stress.

Effects of hypobaria on parabronchial gas exchange in normoxic and hypoxic ducks

Cardio-respiratory parameters and air sac and blood gases were measured in the unrestrained, unanesthetized duck during exposure to normobaric (PB = 746 Torr) or hypobaric (PB = 253 Torr) normoxia (PIO2 = 143 Torr) and hypoxia (PIO2 = 41.5 Torr). Compared with normobaria at the same PIO2, hypobaria caused a statistically significant increase in ventilation during both normoxia and hypoxia, resulting in elevated PO2 and diminished PCO2 in the caudal thoracic and clavicular air sac, and in increased PaO2 and decreased PaCO2. Similarly, lactic acid production was elevated in hypobaria, and the resulting decrease in arterial pH may be responsible for the increase in ventilation. Despite these changes, there was no evidence for altered gas exchange efficiency during hypobaria. This suggests that no significant diffusion limitation is present in the air capillary gas phase in normobaria, that could have been diminished with hypobaria. It also suggests that the aerodynamic valving efficiency, present during inspiration at the level of the medioventral bronchi, is not affected by hypobaria. Although the mechanisms underlying the increased lactic acid production and ventilation are not understood, they may exert an advantageous effect on high altitude tolerance of the bird.

Morphometric analysis of osteosclerotic bone resulting from hexachlorobenzene exposure

Hexachlorobenzene (HCB) exposure has been shown to induce hyperparathyroidism and osteosclerosis in rats. Experiments were undertaken to investigate the effects of HCB-induced hyperparathyroidism and osteosclerosis on femur morphometry as well as femur breaking strength. Fischer 344 rats were dosed 5 d/wk for 15 wk with 0, 0.1, 1, 10, or 25 mg HCB/kg body weight. Hyperparathyroidism was produced in the two higher dose groups as reported previously (Andrews et al., 1989). Femur weight was significantly increased in the rats receiving 0.1, 1, and 25 mg HCB/kg body weight, whereas density was increased significantly at 1, 10, and 25 mg HCB/kg dose levels. Bone strength was also significantly increased at the three higher dose levels. Cross-sectional area of the midpoint of the femur was significantly increased at the 1 mg/kg HCB dose level. Cortical area and the proportion of the total area of the bone that the cortex occupied were significantly increased at the three higher dose levels. Medullary cavity area was significantly increased at the 0.1 mg/kg dose level but significantly decreased at the 2 higher dose levels of HCB. The right femur was significantly predominant to the left femur in weight, volume, and density through all dosing regimens. HCB exposure significantly altered bone morphometry and strength characteristics in the Fischer 344 rat.

Effects of normobaric and hypobaric hypoxia on ventilation and arterial blood gases in ducks

We measured ventilation (V1) and arterial blood gases in awake Pekin ducks exposed to normoxia at sea level, normobaric hypoxia achieved by lowering FIO2 at normal barometric pressure (NORMO), and hypobaric hypoxia achieved with a low pressure chamber and 21% O2 (HYPO). Average normoxic values were: V1 = 0.46 L . (kg.min)-1, PaO2 = 99.7 Torr, PaCO2 = 30.1 Torr. At PIO2 = 90 Torr, NORMO and HYPO measurements were not significantly different (P greater than 0.05). At PO2 = 46 Torr, NORMO V1 was less than HYPO V1 but blood gases were not significantly different: VI = 1.00 vs 1.45 L . (kg.min)-1; PaO2 = 31.3 vs 33.0 Torr; PaCO2 = 11.5 vs 10.6 Torr. Although both tidal volume (VT) and respiratory frequency (fR) were greater in HYPO, similar blood gases with NORMO and HYPO suggest similar parabronchial ventilation. The results suggest increased physiologic dead space, caused by reduced efficacy of aerodynamic valving, with reduced gas density in hypobaria.

Cardiopulmonary function in exercising bar-headed geese during normoxia and hypoxia

To investigate possible physiologic mechanisms that allow the bar-headed goose to perform strenuous physical activity when flying at high altitude (e.g., above 9,000 m), we measured cardiopulmonary variables during running exercise (treadmill; 0.6 m.sec-1; 2 degrees incline) while the bird breathed either normoxic (21% O2) or hypoxic (7% O2) gases via a face mask. 1. During normoxic exercise, O2 uptake rate doubled and both ventilation and cardiac output increased. Blood gases and pH in arterial, mixed venous and blood from the leg, however, remained virtually unaltered. 2. Hypoxia at rest stimulated ventilation to rise but not cardiac output. The birds reached a steady state with virtually unaltered O2 uptake. 3. Exercise during hypoxia further stimulated ventilation, resulting in elevated arterial PO2 and O2 content compared to hypoxia at rest. However, O2 uptake increased only slightly, and cardiac output did not rise over the resting hypoxic value. The hyperventilation resulted in respiratory alkalosis and increased CO2 output, with R values being as high as 2.0. 4. It is concluded that neither ventilation nor pulmonary gas transfer were the limiting step in supplying O2 to the working muscles during hypoxic exercise in our experiments. It is more likely that muscle blood flow or diffusion from muscle capillaries to mitochondria, or both, determined the aerobic capacity under these conditions.

Efficiency of parabronchial gas exchange in deep hypoxia: measurements in the resting duck

Cardio-respiratory parameters and air sac and blood gases were measured in the unrestrained, unanesthetized duck during exposure to varied levels of inspired hypoxia. As ventilation increased with hypoxia, the gas partial pressures in the air sacs and in arterial blood approached the inspired values, the differences being less than 3 Torr for air sacs and less than 5 Torr for arterial blood. To analyze the relative significance of ventilation, diffusion and perfusion in limiting parabronchial gas exchange, the conductances for ventilation (Gvent), diffusion (Gdiff = O2 diffusing capacity) and perfusion (Gperf) were calculated at all hypoxic levels. With increasing hypoxia, down to PIO2 = 50 Torr, all three conductances increased. Whereas Gvent continued to increase beyond this level, Gdiff remained constant, at about 0.27 mmol.min-1.Torr-1, while Gperf decreased, from a value of 0.22 mmol.min-1.Torr-1 at PIO2 = 50 Torr to 0.12 mmol.min-1.Torr-1 at PIO2 = 30 Torr. This reduction in Gperf may result from a direct hypoxic effect on the heart. Whereas ventilation is the main limiting factor for parabronchial gas exchange at rest down to hypoxia levels of PIO2 = 50 Torr, perfusion becomes the main limiting factor at deeper hypoxia. It is suggested that the higher tolerance of hypoxia exhibited by birds compared to mammals is not due to the higher efficiency of parabronchial compared with alveolar gas exchange, but reflects the ability of birds to tolerate lower arterial PCO2 levels than mammals.

[Molecular aspects of high altitude respiration of birds. Hemoglobins of the striped goose (Anser indicus), the Andean goose, (Chloephaga melanoptera) and vulture (Gyps rueppellii)]

Respiration of birds at high altitude and the structural adaptation of avian hemoglobins are studied. Applying the method of the "minimal biological distance", hemoglobins of closely related species were sequenced and compared with each other. Physiological measurements and sequence data show that adaptation to hypoxic stress can be interpreted as exchange of one amino acid. The structural aspects of the genetical data are discussed on the basis of the atomic model of hemoglobin. High-altitude respiration is not a general characteristic of birds: the adaptation to high altitudes is the result of a specific mutation, thus distinguishing a species from its closest relatives in the lowland.