The actual value of in human amniotic fluid

Hypoxia-inducible factors regulate filaggrin expression and epidermal barrier function

A functional epidermal skin barrier requires the formation of a cornified envelope from terminally differentiating keratinocytes. During this process, multiple genetic and environmental signals coordinately regulate protein expression and tissue differentiation. Here we describe a critical role for hypoxia-inducible factors (HIFs) in the regulation of filaggrin expression and skin barrier formation. Similar to other mammalian tissues, fetal epidermis in mice is normally O₂-deprived. Simultaneous deletion of Hif1a and Hif2a in murine epidermis revealed defects in keratinocyte terminal differentiation and epidermal barrier formation. Mice lacking Hif1a and Hif2a in the epidermis exhibited dry flaky skin, impaired permeability barrier, and enhanced sensitivity to cutaneous allergens. These defects were correlated with stratum granulosum attenuation and reduced filaggrin expression. Hypoxic treatment of primary keratinocytes induced filaggrin (Flg) gene expression in a HIF1α- and HIF2α-dependent manner, suggesting that one mechanism by which Hif1a and Hif2a loss causes epidermal barrier defects in mice lies in Flg dysregulation. Therefore, low O₂ tension is an essential component of the epidermal environment that contributes to skin development and function.

Noninvasive oxygen partial pressure measurement of human body fluids in vivo using magnetic resonance imaging

RATIONALE AND OBJECTIVES

The oxygen partial pressure (pO2) of human body fluids reflects the oxygenation status of surrounding tissues. All existing fluid pO2 measurements are invasive, requiring either microelectrode/optode placement or fluid removal. The purpose of this study is to develop a noninvasive magnetic resonance imaging method to measure the pO2 of human body fluids.

MATERIALS AND METHODS

We developed an imaging paradigm that exploits the paramagnetism of molecular oxygen to create quantitative images of fluid oxygenation. A single-shot fast spin echo pulse sequence was modified to minimize artifacts from motion, fluid flow, and partial volume. Longitudinal relaxation rate (R1 = 1/T1) was measured with a time-efficient nonequilibrium saturation recovery method and correlated with pO2 measured in phantoms.

RESULTS

pO2 images of human and fetal cerebrospinal fluid, bladder urine, and vitreous humor are presented and quantitative oxygenation levels are compared with prior literature estimates, where available. Significant pO2 increases are shown in cerebrospinal fluid and vitreous following 100% oxygen inhalation. Potential errors due to temperature, fluid flow, and partial volume are discussed.

CONCLUSIONS

Noninvasive measurements of human body fluid pO2 in vivo are presented, which yield reasonable values based on prior literature estimates. This rapid imaging-based measurement of fluid oxygenation may provide insight into normal physiology as well as changes due to disease or during treatment.

Amniotic gas values and acid-base status during acute maternal hyperoxemia and hypoxemia in the early fetal sheep

OBJECTIVE

This study was undertaken to determine amniotic fluid gas values and acid-base balance during maternal hyperoxemia and hypoxemia in early pregnancy.

STUDY DESIGN

Anesthetized sheep (n = 12) in early and mid pregnancy (0.3 to 0.5 gestation) were subjected to hyperoxemia followed by hypoxemia. Amniotic fluid PO (2), pH, PCO (2), bicarbonate concentration, and base excess were monitored continuously with a multiparameter Paratrend (Diametrics Medical Inc, St Paul, Minn) sensor and compared between 0.3 and 0.5 gestation.

RESULTS

During maternal normoxemia all parameters were constant. At all gestational ages maternal hyperoxemia caused no changes apart from a rapid increase in amniotic fluid PO (2) (P <.001). Maternal hypoxemia led to a reduced amniotic fluid PO (2) (P <.001), whereas the PCO (2) and the bicarbonate concentration increased (P <.001). Changes in amniotic fluid gas values and acid-base balance were more pronounced at 0.3 gestation than at 0.5 gestation. Amniotic fluid Po(2) responded earlier to maternal hyperoxemia than to hypoxemia (9. 5 vs 14.3 minutes; P <.001). During hypoxemia maternal PaCO (2) changed faster than did amniotic fluid PCO (2) (P <.001).

CONCLUSIONS

Acute maternal hypoxemia during early pregnancy was quickly reflected in amniotic fluid gas values and acid-base balance, whereas hyperoxygenation induced the quickest changes in amniotic fluid PO (2). The metabolic effects of maternal hyperoxemia and hypoxemia were also more pronounced during early pregnancy than at mid pregnancy.

In-vivo measurement of intrauterine gases and acid-base values early in human pregnancy

A new multiparameter sensor that combines electrochemical and fibre-optic technology was used for continuous in-vivo investigation of pH, carbon dioxide partial pressure (PCO(2)), oxygen partial pressure (PO(2)), bicarbonate concentration (HCO(3)(-)), base excess, and oxygen saturation (O(2)Sat) early in human pregnancy. The sensor was inserted into the amniotic cavity and the placental bed of 16 pregnancies at 10-15 weeks gestation, before termination under general anaesthesia. Amniotic fluid and retroplacental blood from the same site were also aspirated and analysed by means of cartridges and a portable blood gas analyser. Eleven series of measurements were obtained. The variation in measurements over the 5 min of monitoring was </=10% for all parameters. The sensor was damaged during insertion into the amniotic cavity in one case and in the placental bed in four cases. Measurements of PO(2) in both the amniotic cavity and the placental bed and of pH in the placental bed were higher using the cartridges than in vivo. The results indicated that in-vivo monitoring of fetoplacental gas and acid-base with a sensor is stable and accurate. Such technology will be helpful in improving our understanding of the fetoplacental metabolism in normal and complicated pregnancies.

Does amniotic fluid analysis reflect acid-base balance in fetal blood?

OBJECTIVE

The purpose of the study was to examine whether the acid-base balance in amniotic fluid reflects the acid-base state in fetal blood.

STUDY DESIGN

The pH, PCO2, PO2, bicarbonate, and base excess concentrations were measured in umbilical venous, umbilical arterial, and maternal venous blood and in amniotic fluid samples obtained at fetoscopy. This was performed before intraamniotic termination of 16 normal pregnancies (mean gestation 19.4 weeks), as well as in 14 red blood cell isoimmunized pregnancies (mean gestation 28.4 weeks) undergoing fetoscopy for the diagnosis and treatment of fetal anemia.

RESULTS

In normal pregnancies, amniotic fluid pH and bicarbonate were significantly lower than umbilical venous and umbilical arterial blood concentrations, and this was due to the high concentration of base deficit in amniotic fluid. Whereas amniotic fluid PCO2 did correlate significantly with fetal umbilical venous PCO2 values, there was no correlation between other acid-base characteristics.

CONCLUSION

Simultaneous sampling of human fetal umbilical blood and amniotic fluid under the acute conditions of this study did not show significant correlations in acid-base values.