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The aim of this study was to use ultrasound imaging to re-investigate the anatomy of the lactating breast. The breasts of 21 fully lactating women (1-6 months post partum) were scanned using an ACUSON XP10 (5-10 MHz linear array probe). The number of main ducts was measured, ductal morphology was determined, and the distribution of glandular and adipose tissue was recorded. Milk ducts appeared as hypoechoic tubular structures with echogenic walls that often contained echoes. Ducts were easily compressed and did not display typical sinuses. All ducts branched within the areolar radius, the first branch occurring 8.0 +/- 5.5 mm from the nipple. Duct diameter was 1.9 +/- 0.6 mm, 2.0 +/- 90.7 mm and the number of main ducts was 9.6 +/- 2.9, 9.2 +/- 2.9, for left and right breast, respectively. Milk ducts are superficial, easily compressible and echoes within the duct represent fat globules in breastmilk. The low number and size of the ducts, the rapid branching under the areola and the absence of sinuses suggest that ducts transport breastmilk, rather than store it. The distribution of adipose and glandular tissue showed wide variation between women but not between breasts within women. The proportion of glandular and fat tissue and the number and size of ducts were not related to milk production. This study highlights inconsistencies in anatomical literature that impact on breast physiology, breastfeeding management and ultrasound assessment.

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Breast volume and morphology of eight subjects were measured before conception and at intervals throughout pregnancy until 1 month of lactation. Breast volume before conception ranged from 293 to 964 ml. At the end of pregnancy the volume of breast tissue had increased by 145+/-19 ml (mean+/-S.E.M., n = 13 breasts, range 12-227 ml) with a further increase to 211+/-16 ml (n = 12 breasts, range 129-320 ml) by 1 month of lactation. Urinary excretion of lactose increased at 22 weeks of pregnancy, signalling the capacity of the breast to synthesize lactose at this time. During pregnancy, both the change in breast volume and the change in cross-sectional area of the areola were related to the concentration of human placental lactogen in the plasma. The growth of the nipple and the rate of excretion of lactose were related to the concentration of prolactin in the plasma. During the first 3 days after birth, the rate of excretion of lactose was related to the rate of excretion of progesterone. There was no relationship between the growth of the breast during pregnancy and the amount of milk produced at 1 month of lactation.

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Quantitative measurements were made of relative breast volume and milk production from 1 month of lactation until 3 months after weaning, and the storage capacity of the breasts was calculated. The increase in breast tissue volume from before conception until 1 month of lactation was maintained for the first 6 months of lactation (means+/-S.E.M.) (190.3+/-13.1 ml, number of breasts, nb = 46). During this period of exclusive breast-feeding, 24 h milk production from each breast remained relatively constant (453.6+/-201 g, nb = 48), and storage capacity was 209.9+/-11.0 ml (nb = 46). After 6 months, breast volume, milk production and storage capacity all decreased. There was a relationship between 24 h milk production and the storage capacity of the breasts, and these both appeared to be responding to infant demand for milk. At 15 months of lactation, the 24 h milk production of each breast was substantial (208.0+/-56.7 g, nb = 6), even though the breasts had returned to preconception size. This was associated with an apparent increased efficiency of the breast (milk production per unit breast tissue) after 6 months, which may have been due to redistribution of tissues within the breast. The possible causes of the decrease in breast volume are discussed.

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Colostrum and milk were collected from ten sows at frequent intervals from before farrowing until 9 d after farrowing. Ionized calcium, pH, and total concentrations of citrate, calcium, phosphate and magnesium were measured in whole milk. The diffusible fraction of the mammary secretion was separated by ultrafiltration and was used for the measurement of diffusible citrate, calcium, phosphate and magnesium. The pH before farrowing was 5.7, and increased to 6.5 on day 4 as total calcium and phosphate also increased. Before farrowing, total and diffusible citrate were 7.8 and 7.3 mM respectively, while diffusible phosphate was 11.9 mM, and these concentrations all decreased during the study period. Total magnesium ranged between 3.3 and 4.1 mM, while diffusible magnesium ranged between 2.0 and 3.1 mM. While these concentrations and patterns of change of diffusible calcium and citrate are quite different from those of women's milk during the first week after birth, theoretical physicochemical relationships between diffusible calcium and citrate, and ionized calcium and HPO4(2-) were corroborated by these results. We conclude that diffusible citrate plays an important role in the determination of the concentration of diffusible calcium. However, while citrate may be the major determinant of the total concentration of calcium in women's milk, this is not the case in sows' milk.

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The effect of the temporal spacing and degree of milk removal by either expression or breastfeed on short-term (hour to hour) rates of milk synthesis was investigated. For four expressing mothers (three of whom had given birth prematurely), the relationship between milk produced at an expression and the time since the last expression showed that proportionally less milk is produced after intervals of 6-18 h than after intervals of less than 6 h (P < 0.0002). For five breastfeeding and four expressing mothers (three of whom had given birth prematurely), rates of milk synthesis (ranging from 0 to 56 ml/h) were linear between breastfeeds and expressions (intervals ranging from < 1 h to 6 h). Changes in rate of milk synthesis were not directly associated with the frequency of breastfeeds but rather with the degree of emptying of the breast (P < 0.05). These results indicate the importance of degree, rather than frequency, of breast emptying in the short-term control of human milk synthesis.

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The concentrations of lactose, glucose, glucose 6-phosphate (G6P), glucose 1-phosphate (G1P), UDPglucose (UDPglc), UDPgalactose (UDPgal), and inorganic phosphate (P(i)) (metabolites in the lactose synthesis pathway) were measured in mammary secretion from nondiabetic (ND) and insulin-dependent diabetic (IDD) mothers during the first 10 days postpartum to determine their relationship with the amount of lactose synthesized and their association with the delay in lactose synthesis in IDD mothers. For all mothers the concentrations of all metabolites were low initially, and in ND mothers the first increases occurred as follows: lactose--day 2; glucose, G6P and P(i)--day 3; G1P and UDPglc--day 4; and UDPgal--day 6. The first increases for IDD mothers occurred 1-4 days later than for ND mothers. The concentrations of glucose, G6P, G1P, UDPglc, and P(i) were related to the amount of lactose synthesized. Since the rate of lactose synthesis and concentrations of other metabolites were less than half-maximal while the concentration of glucose was low, and since there was a delay in the increase in mammary gland concentrations of glucose in IDD mothers, it is concluded that glucose availability has the potential to play a role in the regulation of the rate of lactose synthesis at lactogenesis II.

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The onset of copious milk secretion (lactogenesis II) in women occurs between 1 and 3 d after birth, and during this period the composition of breast milk changes. During the first 5 d of lactation we measured the concentrations of total, diffusible and ionized Ca (Catot, Cad, Ca2+), diffusible phosphate (Pid), diffusible citrate (Citd) and lactose in the breast milk. On day 1 after birth the concentrations (mean +/- SEM) were Catot, 5.71 +/- 0.30 mM; Cad, 2.66 +/- 0.19 mM; Ca2+, 2.90 +/- 0.18 mM; Pid, 0.26 +/- 0.16 mM; Citd, 0.25 +/- 0.03 mM and lactose, 76 +/- 11 mM. Between day 1 and day 4 the concentration of Catot increased 1.7-fold to 9.56 +/- 0.39 mM, Cad increased 1.8-fold to 4.75 +/- 0.26 mM, Ca2+ decreased by 20% to 2.33 +/- 0.13 mM, Pid increased 6.6-fold to 1.69 +/- 0.11 mM, Citd increased 20-fold to 5.06 +/- 0.21 mM, and lactose increased 2.3-fold to 173 +/- 4 mM. A high correlation has been found between [Cad] and [Citd] in the milk of both ruminant and non-ruminant species, which show a wide range in concentrations of [Cad] and [Citd], and the data fit a simple physicochemical model of ion equilibria in the aqueous phase of milk. The results of the present study confirm the relationship between [Cad] and [Citd] in human milk, even during lactogenesis II when the composition of the milk is changing very rapidly.

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The feasibility of using sequential breast volume measurements as a method of studying short-term rates of milk synthesis in women has been established. We have developed a rapid Computerized Breast Measurement system for the determination of breast volume, based upon the Shape Measurement System. A circle encompassing all the breast tissue is drawn in black face paint on the subject's skin. Six patterns of sixty-four horizontal light stripes are projected onto the breast and chest wall surface. A CCD camera relays video images to a computer, which produces a model of the chest by active triangulation. The volume of the breast and the chest wall segment enclosed by the circle is then calculated. The precision of the method was dependent upon the subject repositioning carefully. The coefficient of variation of replicate measurements was 1.6%. The accuracy of the method was established by comparing the change in breast volume before and after a breast-feed with the amount of milk removed by the infant as determined by test weighing. There was a close relationship between the removal of milk by the infant (x) and the change in breast volume (y), (r = 0.93, n = 73, y = 1.10x - 3.25). The rates of milk synthesis between breast-feeds, for six women determined on one to eight occasions, varied from 11 to 58 ml/h. The results show that the amount of milk available in the breast is not necessarily an important determinant of the amount of milk removed by the infant at a breast-feed.

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Lactose synthesized in the mammary gland can pass into the bloodstream by either a paracellular or transcellular pathway. In nonpregnant, nonlactating women, the concentration of lactose in the blood plasma was 1.5 +/- 0.1 microM (mean +/- SEM) in 9 women and undetectable in another 11 women. During pregnancy, this concentration was 3.7 +/- 0.4 microM at 10-21 weeks of gestation, with an increase to 8.7 +/- 1.8 microM by 38-40 weeks of gestation. At the initiation of lactation, the concentration of lactose peaked 3-5 days after birth, with a mean peak concentration of 75 +/- 18 microM, and then decreased to 30 +/- 8 microM when lactation was well established at 6 weeks after birth. These findings suggest that the mammary glands are synthetically active by the beginning of the second trimester of pregnancy and reach maximum synthetic capacity soon after birth. Measurement of concentrations of lactose in the blood plasma during pregnancy and lactation may allow an assessment of the successful initiation of both lactogenesis I and II.

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Metabolites in the lactose synthesis pathway were measured in human milk during established lactation. The mean concentrations (range) were: lactose, 198 mM (175-233); glucose, 1.5 mM (0.1-2.4); glucose 6-phosphate, 11 microM (4-23); glucose 1-phosphate, 2.7 microM (1.6-6.8); UDP-glucose, 2.7 microM (0.6-6.0); UDP-galactose, 0.7 microM (less than 0.1-2.5); inorganic phosphate, 2.2 mM (0.8-2.9). During storage of milk within the breast for 2 h, glucose 6-phosphate concentration increased by 1.4 +/- 0.5 microM, while UDP-glucose decreased by 1.0 +/- 0.4 microM. None of the other metabolites showed significant changes in concentration during this period. Only glucose showed a circadian rhythm in concentration, with the highest concentrations between 1400 and 1800 h. The volumes of milk produced by the mothers ranged from 178 to 1,739 ml/24 h. Despite this variation, there were no significant relationships between the 24-h average concentrations of glucose, glucose 6-phosphate, glucose 1-phosphate, UDP-glucose, UDP-galactose, or inorganic phosphate and the amount of lactose produced over 24 h.

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OBJECTIVE: To determine if intraluminal production of CO2 leads to underestimation of gastric intramural pH (pHi) by tonometry. DESIGN: Nonrandomized controlled study. PATIENTS: Healthy volunteers. INTERVENTIONS: NG tonometers were placed in healthy volunteers. Some of the volunteers (n = 11) were pretreated with ranitidine to prevent secretion of protons into the gastric lumen. Others (n = 13) were untreated (i.e., gastric acid secretion was uninhibited). MEASUREMENTS AND MAIN RESULTS: Gastric pHi was calculated from the arterial (HCO3-) and the tonometrically determined intraluminal PCO2 using the Henderson-Hasselbalch equation. Intraluminal PCO2 was significantly higher in the control group (54 +/- 14 torr [7.2 +/- 1.9 kPa]) than in the ranitidine-treated group (42 +/- 4 torr [5.6 +/- 0.4 kPa], p = .02). Mean gastric luminal pH was 1.9 +/- 0.6 in the control group as compared with 6.7 +/- 0.7 in volunteers treated with ranitidine (p less than .01). Mean calculated gastric pHi was 7.30 +/- 0.11 in the untreated group and 7.39 +/- 0.03 in the ranitidine-treated group (p less than .03). CONCLUSIONS: These data suggest that intraluminal production of CO2 from the titration of gastric HCO3- by secreted H+ can result in the underestimation of gastric pHi by tonometry. This phenomenon can be eliminated by H2-receptor blockade.

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The changes in three different indices of 1,25-dihydroxyvitamin D (1,25(OH)2D) biological activity were studied longitudinally in 35 women during late pregnancy and lactation and in 26 control women. Measurements were made of maternal serum total 1,25(OH)2D and free 1,25(OH)2D concentration (by centrifugal ultrafiltration) and the free 1,25(OH)2D index (the molar ratio of total 1,25(OH)2D and vitamin D binding protein (DBP]. During late pregnancy total 1,25(OH)2D concentrations were significantly elevated when compared to controls, as were free 1,25(OH)2D and DBP concentrations and the free 1,25(OH)2D index. Serum total 1,25(OH)2D, free 1,25(OH)2D and DBP concentrations all fell dramatically during the first 2 weeks of lactation with total 1,25(OH)2D and free 1,25(OH)2D concentrations falling to levels below those of controls. During the course of lactation both total 1,25(OH)2D and free 1,25(OH)2D levels rose significantly although they were not different from controls at 18 weeks of lactation. In contrast, the free 1,25(OH)2D index fell during the first 2 weeks of lactation, but remained at this level, significantly lower than controls. Neither urinary calcium excretion nor dietary calcium intake correlated with total or free 1,25(OH)2D, DBP, or the free 1,25(OH)2D index. The disagreement in the results of free 1,25(OH)2D concentration and free 1,25(OH)2D index demonstrates that these two approaches to measuring biologically active 1,25(OH)2D are not equivalent. In attempting to account for the increased calcium requirements of human reproduction we conclude that in pregnancy any of the 1,25(OH)2D measurements may be appropriate. In lactation, however, either 1,25(OH)2D is not a major factor or 1,25(OH)2D biological activity is inadequately represented by any of the currently available methods.

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One of the concerns clinicians have relates to the interpretation of noninvasive pulse oximeters in newborns since at birth high levels of fetal hemoglobin (HbF) is present in the blood. Accurate in vivo studies of pulse oximeters in infants with predominantly HbF cannot be easily performed. Therefore, the objective of this in vitro study was to determine whether the presence of high levels of HbF in the blood can significantly affect the accuracy of noninvasive pulse oximeters. It is evident from our results that there is no perceptible difference in the 650-1000 nm wavelength region, which is commonly used in pulse oximetry, between the optical absorption spectra of hemolyzed whole adult and fetal blood. Our observations are in good agreement with in vivo studies published by other investigators showing considerable correlations between SpO2 measured by a pulse oximeter and SaO2 values analyzed in vitro by an IL 282 CO-Oximeter.

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An in vitro tissue model was developed for specific application to noninvasive transmittance pulse oximetry. The model was used to assess the effect of variations in carboxyhemoglobin concentration on noninvasive measurements of arterial hemoglobin oxygen saturation. The predictive nature of this model is important for a better understanding of the limitation of pulse oximetry and for the improved design of pulse oximeters.

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Sensitive bioluminescent methods were developed to measure the metabolites glucose, glucose 6-phosphate (G6P), glucose 1-phosphate (G1P), UDP-glucose, and UDP-galactose in human milk and lactose and galactose in human plasma. The bioluminescent methods measured NADH produced by coupled enzymatic assays derived from equivalent spectrophotometric methods. We found that the long chain fatty acids in human milk (C10-C16) inhibited the bioluminescent reactions. This inhibition was overcome by adding defatted bovine serum albumin to the reaction mixture containing the bioluminescent enzymes. It also was necessary to modify methods of deproteinizing milk and blood plasma to accommodate small sample volumes. In the development of these assays emphasis was given to simplicity of reagent preparation, minimizing cost, and ease of use. The detection limit for the bioluminescent method for NADH was 0.28 nM for a 20-microliters sample. For the assays of the metabolites, recoveries ranged from 91 to 107%. For sample sizes of 2 to 5 microliters of protein free sample, the detection limits for milk were G1P, 0.09 microM; G6P, 0.05 microM; UDPhexose, 0.07 microM; UDP-Glc, 0.03 microM; glucose, 9 microM; and for plasma, lactose, 0.76 microM, galactose, 0.31 microM. The bioluminescent methods gave equivalent results to spectrophotometric methods for the measurement of blood lactose and milk glucose.

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The design and construction of a new optical reflectance sensor suitable for noninvasive monitoring of arterial hemoglobin oxygen saturation with a pulse oximeter is described. The reflectance sensor was interfaced to a Datascope ACCUSAT pulse oximeter that was specially adapted for this study to perform as a reflectance oximeter. We evaluated the reflectance sensor in a group of 10 healthy adult volunteers. SpO2 obtained from the forehead with the reflectance pulse oximeter and SpO2 obtained from a finger sensor that was connected to a standard ACCUSAT transmittance pulse oximeter were compared simultaneously to arterial blood samples analyzed by an IL 282 CO-Oximeter. The equation for the best fitted linear regression line between the reflectance SpO2 and HbO2 values obtained from the reference IL 282 CO-Oximeter in the range between 62 and 100% was: SpO2 (%) = 4.78 +/- 0.96 (IL); n = 110. The regression analysis revealed a high degree of correlation (r = 0.98) and a relatively small standard error of the estimate (SEE = 1.82%). The mean and standard deviations for the difference between the reflectance SpO2 and IL 282 measurements was 1.38 and 1.85%, respectively. This study demonstrates the ability to acquire accurate SpO2 from the forehead using a reflectance sensor and a pulse oximeter.

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Serum calcitriol and the free calcitriol index together with factors considered to regulate calcitriol production were measured in eleven patients with moderate chronic renal failure (MCRF) and eleven age- and sex-matched normal subjects. Although the serum dialysable calcium levels were similar in the two groups, there was depression of calcitriol levels and an elevation of PTH and nephrogenous cyclic AMP (NcAMP) levels in the MCRF patients. Furthermore, plasma phosphate levels were higher and the renal phosphate threshold was depressed in this patient group. When all subjects were grouped together calcitriol was positively correlated with GFR. When calcitriol levels were factored for GFR, to permit an assessment of calcitriol production per unit functioning renal mass, there was no significant difference between normal and MCRF subjects. To determine whether reserve for calcitriol production existed, six of the MCRF patients and six of the age- and sex-matched normal subjects received a low calcium diet for one week supplemented by cellulose phosphate to bind calcium within the gut. In both groups there was a significant rise in calcitriol, although the absolute levels were much lower in the MCRF patients than the normal subjects. These results suggest that calcitriol deficiency is a major feature of MCRF despite marked hyperparathyroidism. The rise in calcitriol levels in MCRF suggests persistent reserve secretory capacity in this condition. Therefore, the low serum calcitriol concentration may be due not only to structural renal damage, but also to suppression of calcitriol formation perhaps due to altered renal phosphate handling.

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