We studied the effects of alterations in lung fluid volume on growth and maturation of the fetal lung. In a chronic fetal sheep preparation, right fetal lung volume was decreased by drainage of lung fluid while the volume of the left lung was expanded by mainstem bronchus ligation leading to lung fluid retention. After an experimental period of 25 d (from 105 to 129 d of gestation, term = 145 d), the right (deflated) lung was significantly hypoplastic and contained less DNA than the controls; 175.15±55.18 vs. 346.77±61.97 mg, respectively; P < 0.001. In contrast, the left (expanded) lung was significantly hyperplastic and contained more DNA than the controls; 390.74±103.53 vs. 238.85±3332 mg, respectively; P = 0.001.Biochemical indices of lung maturation, including total phospholipids, phosphatidylcholine, and disaturated phosphatidylcholine content expressed per unit of tissue DNA, were no different when comparing the hypoplastic, hyperplastic, and control lungs. These findings demonstrate that fetal lung cell multiplication is influenced by local distension with lung fluid, while the biochemical maturation of fetal lung surfactant is under systemic

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.

This study has examined left (LV) and right ventricular (RV) myocardial morphometry in perfusion-fixed hearts of late-gestation sheep fetuses, neonatal lambs, and adult sheep. During development, myocyte size, intercapillary distance, and myocyte myofibrillar and mitochondrial volume densities increased, whereas capillary density, the myocyte-to-capillary ratio, and the myocyte matrix volume density decreased. RV myocytes were larger than LV myocytes in cross section in fetuses and 4-day-old lambs. LV and RV myocytes were of similar size in 7-day-old lambs. LV and RV myocytes were of larger in older lambs and adult sheep. Differences between LV and RV myocyte volume densities of myofibrils, mitochondria, and matrix were also observed in fetuses and young lambs. As well, variation in capillary size and density was apparent between ventricles in the fetal and neonatal periods. We conclude that, in the sheep heart, 1) LV and RV morphometric differences exist during fetal and postnatal development, 2) fetal LV and RV myocardial morphometry is consistent with an RV dominance in utero, 3) rapid growth of LV and RV myocytes occurs in the perinatal period, and 4) the relative size of LV and RV myocytes does not reflect a postnatal LV dominance until between 1 and 4 wk after birth.

No abstract

Summary Maturation of sleep/wake patterns is one of the most important physiological developments during the first year of life. In this study, we aimed to compare the use of actigraphy and parental sleep diaries (SD) for recording the development of sleep/wake patterns longitudinally in term infants in their own home environments over the first 12 months of life. Twenty healthy term infants (7F/13M) were studied for 3 days each month in their own homes over the first 12 months of life. Sleep/wake patterns were recorded using both SD and actigraphy (AW) (AW64, Mini Mitter Co. Inc., Sunriver, OR, USA). The development of sleep and wake was analysed over 24 h, during the day (08:00–20:00 hours) and during the night (20:00–08:00 hours). A total of 186 studies had complete data sets for both analysis methods. Overall, there was no difference between methods of measurement for determination of the total percentage of sleep or wake over 24 h, or for the total percentage of sleep or wake during the day. However, at night, AW scored less time asleep (73.3 ± 0.9%) and more time awake (26.7 ± 0.9%) compared with the SD (80.7 ± 1.04% and 19 ± 1.0%, respectively, P < 0.001). Mean percentage sleep during the day decreased from 51% at 1 month to 28% at 12 months with the 1‐month values being significantly higher than all other ages, while mean percentage sleep at night was only different between 1 month and 11 and 12 months. In conclusion actigraphy provides a useful tool for assessing the development infant sleep.