Cerebrospinal fluid pressure during O2 encephalography and N2O inhalation.

Cerebrospinal fluid (CSF) pressure was studied in 8 patients and 5 dogs during pneumoencephalography (PEG) or ventriculography in which either O2 or N2O was used as the contrast gas prior to and during N2O inhalation. In 7 patients, the use of O2 as the contrast gas increased CSF pressure 8.7 torr (range 4 to 12 torr) following N2O inhalation. In 1 patient, when N2O was used as the contrast gas, CSF pressure did not change after N2O inhalation. These findings were confirmed in anesthetized animals ventilated at a constant PaCO2. The authors conclude that if N2O inhalation is required during PEG, maximum patient safety can be achieved if the contrast gas is also N2O.     

The maternal hypothalamic–pituitary–adrenal axis in the third trimester of human pregnancy

OBJECTIVE The third trimester of pregnancy is characterized by a mildly hyperactive hypothalamic–pituitary–adrenal (HPA) axis, possibly driven by elevated circulating levels of corticotrophin releasing hormone (CRH) of placental origin. In-vitro studies have demonstrated that glucocorticoids and oestrogen stimulate while progesterone inhibits the expression of CRH mRNA and/or protein, suggesting that several potential interactions between the placenta and the HPA axis may exist. DESIGN AND PATIENTS To investigate the detailed pattern of circulating immunoreactive (ir) CRH, ACTH, cortisol, oestradiol and progesterone during the third trimester of pregnancy, plasma samples were drawn serially every 30 minutes from 22 healthy pregnant women (age 32.0 ± 1.1 years, mean ± SE) between the 34th and 36th week of gestation. Ten women had plasma samples drawn between 0800 h and 2000 h (daytime group), and 12 between 2000 h and 0800 h (night-time group). The hormone concentrations obtained were analysed for pulsatility by the Detect program, for detection of circadian rhythmicity by comparison between the first and second 6-hour periods within each group by Student's t-test, and for time-dependent correlations by cross-correlation analysis. RESULTS All five hormones were secreted in a pulsatile fashion. There was no apparent circadian rhythm of CRH or oes tradiol secretion, whereas there was a clear circadian rhythm in plasma ACTH, cortisol and progesterone secretion, with the latter in reverse phase (P<0.05). No significant correlations were observed between CRH and ACTH, whereas, as expected, ACTH and cortisol concentrations were strongly correlated with each other over time (r=0.32 and 0.70 at lag time 30 minutes for the daytime and night-time groups, respectively), with ACTH leading cortisol. A weak positive correlation was observed between CRH and cortisol concentrations for the night-time group at lag time 0 minute, suggesting that the latter may have a positive effect on the former in vivo CONCLUSIONS These data suggest that placental CRH, although pulsatile, drives quantitatively the maternal HPA axis in the third trimester of pregnancy in a non-circadian, non-pulsatile fashion. The maternal HPA axis is probably driven in a circadian and pulsatile fashion by another major ACTH secretagogue, most likely AVP of parvocellular paraventricular nucleus origin.     

Three-dimensional human somatosensory evoked potentials

Median nerve somatosensory evoked potentials were recorded from 30 normal adults using conventional scalp derivations and an orthogonal bipolar surface electrode montage. This allowed the determination of the spatial orientation of the hypothetical centrally located equivalent dipole derived from the evoked response recorded in 3-dimensional voltage space. The 3-dimensional voltage trajectory describing changes in equivalent dipole orientation and magnitude revealed 4 major apices between 5 and 25 msec, 3 of which corresponded to the traditional P14, N20 and P25 peaks. A fourth apex at 17 msec was not as evident in the conventional recordings and signaled a transition from a vertical P14-N18 generator process to a horizontal N20 generator process. The normal within- and between-subject variability of trajectory apices, segments and planes are described, along with the theoretical and practical implications of this recording technique.     

Nitrous oxide administration in the presence of subcutaneous emphysema: An experimental model

Adverse effects may occur when patients with air in the pleural space or in the cerebral ventricles breathe nitrous oxide. We developed an animal model to learn whether similar adverse effects are associated with the inhalation of nitrous oxide when air is present in the subcutaneous space. We induced extensive subcutaneous emphysema in swine and measured oxygen and carbon dioxide tensions in systemic arterial and mixed venous blood; cardiac output; intravascular, airway, and pre-sternal subcutaneous pressures; total pulmonary-thoracic static compliance; and thoracic girth before and after a 45 minute period of breathing 75 per cent nitrous oxide in oxygen. Cardiac output decreased from 3.13 ± 0.511/min to 2.40 ± 0.621/min (p < 0.05); no other values changed significantly. No significant adverse cardiorespiratory effects resulted from the transfer of inhaled nitrous oxide to the subcutaneous space in this animal model.     

Colorimetric determination of penicillins and related compounds in intravenous solutions by nickel (II)-catalyzed hydroxamic acid formation

Solutions of ampicillin, carbenicillin, methicillin, oxacillin, penicillin G, and cephalothin in 5% dextrose were analyzed by nickel(II)-catalyzed hydroxylaminolysis. The reactions of these antibiotics were complete within 20 min at room temperature. Under the analytical conditions, molar absorptivities of the ferric-hydroxamate complexes ranged from 830 to 1005 liters/mole/cm. Coefficients of variation for the analysis of these antibiotics in 5% dextrose were typically less than 3% at concentrations of 1 mg/ml. Oxacillin was analyzed by the same method in normal saline and/or lactated Ringer solutions. The method also was applied to the analysis of chloramphenicol in aqueous solutions. Only ampicillin showed a significant decrease in concentration in 48 hr.     

Limited tissue distribution of the intestinal brush border myosin I protein

A myosinlike 105-110-kilodalton calmodulin-binding protein, brush border myosin I, found in the intestinal brush border has been linked to two seemingly disparate but possibly interacting functions of the brush border, namely, microvillar motility and vitamin D regulated calcium transport. If brush border myosin I were to function primarily as a myosinlike molecule powering cellular or microvillar motility, one might expect it to be found in a variety of tissues with microvilli such as the renal brush border and bile canaliculus. On the other hand, a more specialized function such as participation in vitamin D regulated calcium transport might dictate a more restricted tissue distribution for brush border myosin I. To determine the tissue distribution of brush border myosin I, we purified this protein to apparent homogeneity, generated antisera to it, and used the antisera to localize the protein within the intestinal epithelial cell by immunocytochemistry. We then screened a variety of other tissues (brain, lung, heart, liver, spleen, pancreas, kidney, and skeletal muscle) both for calmodulin-binding proteins as well as for brush border myosin I using Western blots and immunofluorescence. Our results indicate that the intestinal brush border myosin I is limited in its distribution to the intestinal brush border.