[1] We used airborne altimetry measurements to determine the volume changes of 23 glaciers in the western Chugach Mountains, Alaska, United States, between 1950/1957. Average net balance rates ranged between À3.1 to 0.16 m yr À1 for the tidewater and À1.5 to À0.02 m yr À1 for the nontidewater glaciers. We tested several methods for extrapolating these measurements to all the glaciers of the western Chugach Mountains using a process similar to cross validation. Predictions of individual glacier changes appear to be difficult, probably because of the effects of glacier dynamics, which on long (multidecadal) timescales, complicates the response of glaciers to climate. In contrast, estimates of regional contributions to rising sea level were similar for different methods, mainly because the large glaciers, whose changes dominated the regional total, were among those measured. For instance, the above sea level net balance rate of Columbia glacier (À3.1 ± 0.08 km 3 yr À1 water equivalent (weq) or an equivalent rise in sea level (SLE) of 0.0090 ± 0.0002 mm yr

Development of autonomic nervous control of basal heart rate was studied in unanesthetized fetal lambs (93 days to term) and newborn lambs (2–29 days), using atropine and/or propranolol blockade. Fetal lambs showed a progressive increase in parasympathetic restraint of heart rate; vagal influence in the newborn lamb was similar to the term fetus. Sympathetic stimulation of fetal heart rate declined toward term, possibly due to the strongly increasing parasympathetic influence. Sympathetic influence in the newborn was similar to the early-gestation fetus. Intrinsic heart rate was about 185 beats/min throughout the fetal and newborn life span studied. Thus changes in basal heart rate resulted from a different balance of the sympathetic and parasympathetic components of the autonomic nervous outflow.

The immediate transient baroreceptor sensitivity was measured in 9 conscious fetal and 7 conscious newborn lambs for periods of at least 35 days following bolus injections of phenylephrine (20–50 μg/kg). Mean sensitivities were unchanged throughout gestation from 105 days at 6.7 ± 0.4 msec/cm H₂O (n = 45) and were insignificantly different from those in the newborn period, 5.9 ± 0.4 msec/cm H₂O (n = 78). In contrast, baroreflex sensitivities were less in 2 fetuses and 2 newborn lambs when pressures were increased by chronically implanted thoracic aortic balloon cuffs; they were 3.03 ± 0.11 (n = 127) and 0.91 ± 0.11 msec/cm H₂O (n = 61), respectively. ‘Steady-state’ heart period-arterial pressure curves indicate that the baroreflex operates down to levels of 40 cm H₂O in the fetus which is lower than that achieved in the adult of other species, rabbit and man.

For some time it has been suggested that breathing movements are made "in utero" and recently measurements of tracheal pressure and lung liquid flow in chronic fetal preparations have led to the hypothesis that rapid changes in these parameters are the result of respiratory muscle activity. To test this hypothesis diaphragmatic electrical activity was measured in seven chronic unanesthetized fetal sheep preparations and correlated with lung liquid flow and tracheal pressure. Diaphragmatic activity led to a fall of tracheal pressure and movement of a small volume of lung liquid into the lung. After the activity ceased, tracheal pressure returned to normal and flow diminished to zero or was directed out of the lung. The breathing pattern was unassociated with the net movement of lung liquid out of the lung. A histogram of the interval between breaths revealed a changing pattern of activity throughout gestation. The pattern was significantly altered after premature delivery of one animal with a respiratory problem. These observations provide evidence that respiratory muscles are active "in utero" and that the pattern of activity changes throughout gestation.

During fetal life the lung develops as a liquid-filled structure with low blood flow compared with postnatal life. We studied the effects of liquid expansion of the fetal lung by measuring vascular conductance in perfused lungs in situ and arterial diameters in excised lungs of fetal lambs. Pulmonary vascular conductance invariably rose as the lung was deflated from its initial volume; maximal deflation to residual volume increased conductance 122%. With reexpansion, conductance fell progressively, culminating in cessation of flow at lung volumes of twice the initial volume. These changes persisted after vagotomy and thoracic sympathectomy and therefore were mechanical in character. Lung expansion from residual volume initially expanded 300- to 500-micron arteries but compressed arteries greater than 1,500 micron. Further expansion reduced the caliber of all arteries. Thus increasing lung liquid volume progressively constricts the pulmonary circulation in the fetus. Because the fetal pulmonary vascular resistance-lung volume relationship differs from that of the U-shaped form found in adult lungs, concepts based on the adult pulmonary circulation are not appropriate for liquid-filled fetal lungs.