To determine if external ventricular constraint significantly limits fetal left ventricular (LV) stroke volume and can thus account for the plateau of the fetal ventricular function curve, we studied nine fetal lambs (142 to 144 days' gestation) after partial delivery by cesarean section (halothane anesthetic). LV stroke volume (electromagnetic flow probe), LV end-diastolic pressure, and external ventricular constraint (intrapericardial pressure [liquid-filled balloon]) were measured over a range of end-diastolic pressures under two conditions: with a closed chest and closed pericardium and with an open chest and open pericardium. Stroke volume recorded during open chest and open pericardium exceeded those recorded during closed chest and closed pericardium at any given end-diastolic pressure (p < 0.01). Decreases in external ventricular constraint significantly increased LV transmural pressure (preload) and substantially increased fetal LV stroke volume. Thus the plateau of the fetal ventricular function curve was largely a result of external ventricular constraint limiting LV preload, not necessarily a result of myocyte immaturity.

Although it is recognized that a thorough understanding of the biology of incubation is important in the conservation of marine turtles, the difficulties entailed in obtaining measurements of the clutch environment have led to a paucity of data in this area. This paper describes the measurement of gas exchange and temperature from an array of points in the egg chambers of five loggerhead turtles on the beach at Mon Repos, Queensland, Australia. Water table level was also measured in the hatchery in which these turtle eggs were incubating. The result demonstrated a decrease in oxygen and an increase in carbon dioxide partial pressure in these clutches over the latter half of incubation. Small partial pressure differences between measurement points at the periphery of the egg chamber and the egg shaft in relation to the center of the clutches were found for oxygen and carbon dioxide. Temperatures on average in the egg chambers of the control site and the experimental clutches followed the general pattern of the surface temperature and during the summer of 198687 clutch temperatures rose from approximately 26-33 C. Over the latter half of incubation there was an increase in the temperature at the center of the two experimental egg chambers in comparison with the control site. Daily variations in temperature were most evident on the surface with the variations becoming less as one moved towards the lower periphery of the clutch. Further, the water table level fell by 40 cm and followed the general tidal level in the 3-4 d observation periods. A daily periodic rhythm was also evident in the water table level. These data supplement our knowledge regarding the environment of development and demonstrate similar features to those reported in earlier studies.

The lungs of the New Caldeonian gecko Rhacodactylus leachianus were examined by means of gross dissection and light and electron microscopy. This tropical species, which is the largest living gecko, possesses two simple, single-chambered lungs. Right and left lungs are of similar size and shape. The lung volume (27.2 ml.100 g-1) is similar to that of the tokay (Gekko gecko) but differs in that the gas exchange tissue is approximately homogeneously distributed, and the parenchymal units (ediculae) are very large, approximately 2 mm in diameter. The parenchymal depth varies according to the location in the lung, being deepest near the middle of the lung and shallowest caudally. Scanning and transmission electron microscopy reveal an unusual distribution of ciliated cells in patches on the edicular walls as well as on the trabeculae. Secretory cells are very numerous, particularly in the bronchial epithelium, where they greatly outnumber the ciliated cells. The secretory cells form a morphological continuum characterized by small secretory droplets apically and large vacuoles basally. This continuum includes cells resembling type II pneumocytes but which are devoid of lamellar bodies. Type I pneumocytes similar to those of other reptiles cover the respiratory capillaries, where they form a thin, air-blood barrier together with the capillary endothelial cells and the fused basement laminae. The innervation, musculature, and vascular distribution in R. leachianus are also characterized. Apparent simplification of the lungs in this taxon may be related to features of its sluggish habits, whereas peculiarities of cell and tissue composition may reflect demands of its mesic habitat.

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In the sheep, fetal lung development proceeds to a later stage of maturity than in smaller laboratory animals. Of the four stages in pulmonary development recognizable in this species - embryologic, pseudoglandular, canalicular, and aveolar - the latter three are described in the present study using histologic, morphometric, and ultrastructural techniques. During the pseudoglandular stage, the major airways developed centrifugally. Cartilaginous, glandular, muscular, vascular, and neural elements were present in major airway walls from an early age. During the canalicular stage, volume expansion of the lung was accomplished by rapid growth of large terminal spaces. In the final stage, alveoli were formed following subdivision of the large terminal spaces by alveolar crests. The alveolar lining epithelium differentiated during the latter two stages producing a large increase in alveolar surface area, particularly during the alveolar stage; a large increase in pulmonary capillary surface area also accompanied alveolar development. Thus, just prior to birth, the fetal sheep lung has a well-developed air-way system and alveolar network, in preparation for postnatal gas exchange.

15 fetal lambs were instrumented on approximately day 100 (term 147 days) with small catheters in their jugular veins, carotid arteries and tracheas and fine electrodes in their diaphragms and on the lateral surfaces of their thoraces. Measurements were made intermittently of carotid arterial pressure, jugular venous pressure, amniotic fluid pressure, ECG and electrical activity in the diaphragm for 2-hour periods up to day 120. From day 120, two hourly recordings were made daily and samples of lung liquid taken until day 130. On this day, studies of lung mechanics were made on selected fetuses. From day 120, 8 animals were treated with the compound NA872 and 7 animals were given a control infusion of normal saline. In comparison to control animals the lecithin-sphingomyelin (L:S) ratio increased in the test fetuses from days 125--130; respiratory activity (diaphragmatic EMG) was suppressed in the test animals suggesting a more mature respiratory system; but resting lung volume on the test animals was smaller. Heart rate decreased as rapidly in the test animals while changes in systemic vascular pressures were similar. These results indicate that while the lungs are more 'mature' in that L:S ratio is increased, resting lung volumes are smaller, and respiratory activity is decreased. They raise the interesting questions of the influence of fetal respiratory activity on lung and thoracic cage development and the possible direct action of the drug NA872 on the respiratory pattern generator and the lung.

The pressure-diameter relations of pulmonary blood vessels 800–3600 μ in diameter were measured in an isolated dog lung preparation from radiographs taken with a fine focus (300 × 280 μ) X-ray tube. Intravascular pressures were varied from 10 to 45 cm H2O in relation to alveolar pressure at the bottom of the lung. In general, arteries were more distensible than veins and the relative change in diameter of the smaller vessels was greater than that of the larger vessels over the same pressure range. From 10–30 cm H2O the smallest arteries (800–1200 μ) increased their diameter by 65% and the largest arteries (3200–3600 μ) by 20%. Under the same conditions, small veins (800–1200 μ) increased by 25% and large veins (2400–2800 μ) changed by only 10%. All vessels increased their stiffness as intravascular pressure was raised. Between 17 and 22 cm H2O the mean Young's modulus for arteries was 632 ± 54 gm wt/cm2 and veins 1476 ± 158 gm wt/cm2.