A method for noninvasive beat-by-beat visualization of His bundle signals.

BACKGROUND: Invasive recording of His bundle signals (HBS) in electrophysiological study (EPS) is important in determining HV interval, the time taken to activate the ventricles from the His bundle. Noninvasive surface measurements of HBS are attempted by averaging typically 100-200 cardiac cycles of ECG time series in body surface potential mapping (BSPM) and in magnetocardiography (MCG) which records weak cardiac magnetic fields by highly sensitive detectors. However, noninvasive beat-by-beat extraction of HBS is challenged by ramp-like atrial signals and noise in PR segment of the cardiac cycle. METHODS: By making use of a signal-averaged trace showing prominent HBS as a guide trace, we developed a method combining interval-dependent wavelet thresholding (IDWT) and signal space projection (SSP) technique to eliminate artifacts from single beats. The method was applied on MCG recorded on 21 subjects with known HV intervals based on EPS and noninvasive signal-averaging, including five subjects with BSPM recorded subsequently. The method was also applied on stress-MCG of a subject featuring autonomic dynamics. RESULTS: HBS could be extracted from 19 out of 21 subjects by signal-averaging whose timing differed from EPS between -8 and 11 ms as tested by 2 observers. HBS in single beats were seen as aligned patterns in inter-beat contours and were appreciable in stress-MCG and conspicuous than BSPM. The performance of the method was evaluated on simulated and measured MCG to be adequate if the signal-to-noise ratio was at least 20 dB. CONCLUSIONS: These results suggest the use of this method for noninvasive assessments on HBS.

Antimicrobial activity of amniotic fluid against Chlamydia trachomatis, Mycoplasma hominis, and Ureaplasma urealyticum.

Amniotic fluids obtained by amniocentesis at 16 weeks to term were examined for the presence of Chlamydia trachomatis, Mycoplasma hominis, and Ureaplasma urealyticum. Of 140 fluids tested, none harbored chlamydiae, and only one harbored mycoplasma, M. hominis. A number of amniotic fluids were subsequently tested for their ability to inhibit the growth of these microorganisms. Amniotic fluids and chlamydial suspensions in a 2:1 ratio were incubated 30 to 90 minutes before their inoculation in McCoy cells. Procedures were followed for chlamydial isolation. Genital mycoplasmas were incubated with amniotic fluid samples for 24 or 48 hours at 35 degrees C. Growth in amniotic fluid specimens was compared with growth in pseudoamniotic fluid and broth controls. Fourteen amniotic fluid specimens collected from gestations of 16 to 40 weeks, were found to be inhibitory to the formation of inclusions of C. trachomatis in McCoy cells. Ten amniotic fluid specimens (16 to 39 weeks, gestation) demonstrated various degrees of inhibition against M. hominis, and three fluids were inhibitory to the growth of Ureaplasma. The inhibitor was heat and protease resistant and activity was proportional to concentration. The molecular weight of the inhibitor was probably greater than 10,000 daltons, and pH, although perhaps a contributing factor, was not the cause of the inhibition.

Positive correlation between mature amniotic fluid optical density readings and the absence of neonatal hyaline membrane disease.

Fetal pulmonary maturity is generally determined by analyzing amniotic fluid for surfactants. This task is accomplished by lipid extraction of the fluid and resolution, identification and quantitation of the isolated lipids with thin-layer chromatography. These methods are lengthy, cumbersome and often not available on demand. A quick, simple, reliable and economical test therefore would be highly desirable. We have been able to correlate an optical density (OD) reading of amniotic fluid at 650 nm greater than or equal to 0.15 with the absence of hyaline membrane disease (HMD). For 428 fluids in which an OD reading of greater than or equal to 0.15 was found and delivery occurred within 48 hours, HMD was present in only two infants. The accuracy of the test was 99.53% , with a false-positive rate of 0.47%. With the use of this simple and accurate test one can satisfy the requirement of an on-demand test to determine fetal pulmonary maturity.

Infection and phagocytosis as possible mechanisms of rupture in premature rupture of the membranes.

The concept that premature rupture of the membranes is due to an infectious process is well accepted. However, no definitive data implicating a particular microorganism or a mechanism of action have been advanced. By the use of our recently developed experimental in vitro amnion-chorion reaction vessel model we have studied the effect of the peroxidase-hydrogen peroxide-halide antimicrobial system on these membranes. We have noted that amnion, chorion, decidua, and placental macrophages all possess peroxidase activity. Tissues collected from deliveries following labor (vaginal) are significantly higher in activity than those collected from deliveries with no labor (cesarean section). A mobilization of enzyme from macrophages to amnion appears to occur in the laboring patient. Increased protein hydrolysis is noted in membranes collected from patients without labor subjected to the peroxidase-hydrogen peroxide-halide cytotoxic system when compared with membranes from laboring patients. Bursting pressures of membranes collected from patients without labor are shown to be decreased when the membranes were incubated in the presence of lysolecithin or in the presence of amniotic fluid and phospholipase A2.

Phagocytosis and onset of human labor.

An in vitro experimental model has been developed which allows the study of amnion lysosomal enzyme release under controlled conditions. Briefly, a layer of human amnion membrane mounted on a specially designed reaction vessel serves as the reaction surface. We have noted that the addition of particulate material to these membranes incubating in pseudoamniotic fluid results in an increased release of the lysosomal marker enzyme N-acetylglucosaminidase when compared to the release in the absence of particles. This release is completely inhibited by iodoacetate and slightly by azide. A similar increased release is also noted with the use of term amniotic fluid as incubation medium when compared to centrifuged (30,000 g/20 min) amniotic fluid. Lecithin and lysolecithin were effective in releasing increasing amounts of enzyme. This increased release was noted only from membranes of placentas collected from subjects who had undergone cesarean section prior to labor. Membranes collected from vaginal deliveries after labor showed a baseline increased release but no further stimulation upon the addition of any of the substances. These results suggest that the release of lysosomal enzymes from amnion membranes is brought about by substance(s) present in amniotic fluid. Very probably, these are surfactants. The interaction of these substances with amnion cells would eventually result in an exponential burst of prostaglandin synthesis, which would result in labor.

Surfactants, L/S ratio, amniotic fluid optical density and fetal pulmonary maturity.

Optical density readings of amniotic fluids of 0.15 or greater at 650 nm have been noted to correlate with fetal pulmonary maturity. The amniotic fluid absorbance has been shown to be due not only to lecithin and sphingomyelin but also to other surfactants, including phosphatidyl glycerol and inositol. The addition of lecithin and sphingomyelin to previously centrifuged amniotic fluid (i.e., optical) density less than 0.001: L/S ratio, nondetectable) results in an increase in absorbance. At any simulated L/S ratio, the addition of phosphatidyl glycerol and/or phosphatidyl inositol results in a further increase in optical density. It is suggested that optical density readings represent more closely the surfactant composition of amniotic fluid than L/S ratios; therefore, it appears that optical density measurements are a better predictor of fetal pulmonary development than are L/S ratios.

A microtechnique for studying chemiluminescence response of phagocytes using whole blood and its application to the evaluation of phagocytes in pregnancy.

Previous investigators have demonstrated that polymorphonuclear neutrophils exhibit intense chemiluminescence (CL) during phagocytosis and the CL response can be used to study the cellular and humoral aspects of the phagocytic process. A microtechnique that used 10 microliters of whole blood as a source of phagocytes was developed and used to measure the phagocytic CL response during pregnancy. Increased sensitivity was achieved by the use of a high concentration of luminol (0.5 mM), prepared by sonication, as a CL amplifier. The high intensity of CL produced with luminol permitted the use of a scintillation counter in the IN coincidence mode, avoiding the necessity of dark-adapting the counting vials and reagents and working under subdued red light. The CL response was dose dependent on the number of phagocytes and/or particles (polystyrene spherules, opsonized zymosan, and E coli). The CL response was decreased by inhibitors that prevent particle uptake (iodoacetate and fluoride), inhibitors that prevent free-radical production (sodium benzoate and superoxide dismutase), and by inhibitors that inactivate myeloperoxidase (cyanide and azide). Results suggested that the phagocytic CL response in our assay system was dependent on O2 activation followed by the activated O2 species reacting with myeloperoxidase and chloride. The new technique was used to demonstrate a progressive increase with gestation in the phagocytic CL response in pregnancy and a rapid decrease to normal values at 1 week postpartum.

The effect of cervical/vaginal secretions on measurements of lecithin/sphingomyelin ratio and optical density at 650 nm.

Free-flowing amniotic fluid collected vaginally can be used in a reliable way for determination of fetal pulmonary maturity. Lavaging the vaginal/cervical area with sterile saline and examining the lavage fluid for lecithin/sphingomyelin (L/S) spots showed no detectable spots in the supernatants (one exception) and barely detectable L/S spots in the sediment. Vaginal-cervical saline-wash fluids did not affect fluid L/S ratios. Lavaging the vaginal-cervical area with abdominal amniotic fluid did not affect the L/S ratio of the original amniotic fluid.

Amniotic fluid optical density and neonatal respiratory outcome.

A simple, rapid, economical, and accurate test to assess fetal pulmonary maturity on a 24-hour basis, 7 days a week, is urgently needed. A 15-minute test has been developed that correlates well with fetal pulmonary maturity. Optical density (OD) readings at 650 nm of greater than or equal to 0.15 in pigment-free, centrifuged (2000 Xg, 10 minutes) amniotic fluids obtained from gestations of 33 to 42 weeks correlate with fetal pulmonary maturity (131 of 131, 100%). When OD readings are less than 0.15 in fluids from gestations of 24 to 40 weeks, and antepartum steroids are utilized, the incidence of respiratory distress syndrome (RDS) is 8.3% (14 of 169). The true false-negative rate in this group is therefore unknown.

24-hour urine creatinine excretion in pregnancy.

A total of 489 consecutive 24-hour urine collection from 162 patients were analyzed for creatinine excretion. The 24-hour creatinine excretion increased with the urine volume. Creatinine excretions in 24-hour urine collections were not statistically different between in- and out-patients. The results indicate that the mean urine creatinine per 24 hours is 1.08 g for 24-hour urine volumes between 500 and 1500 ml. For urine volumes greater than 1500 ml it is 1.22 g. For 24-hour urine volumes less than 500 ml, the mean creatinine is 0.63 g.

Enhanced killing of myeloperoxidase-coated bacteria in the myeloperoxidase-H2O2-Cl- system.

Bacteria preincubated with myeloperoxidase (MPO) are more readily killed upon the addition of H2O2 and Cl- than controls not subject to prior incubation. This effect was evidenced by decreased requirements of MPO and H2O2 (to approximately 33%) for equivalent bactericidal activity. MPO adsorbed onto the bacterial surface is not accessible to other competing substrates such as guaiacol and [1(-14)C] alanine. It appears that when MPO is adsorbed to the bacteria, it carries out a coupled reaction in which the activated chlorine directly attacks the bacterial cell surface.

Positive correlation of optical density at 650 nm. with lecithin/sphingomyelin ratios in amniotic fluid.

In this study, we have attempted to correlate optical density measurements of amniotic fluids with L/S ratios. We may conclude, with over a 98 per cent accuracy, that fluids having optical density readings of 0.15 and above, at 650 nm. will have an L/S ratio over 2.0. Fluids having optical density readings up to 0.05 will have L/S ratios of about 1.3. Finally, amniotic fluids having optical densities greater than 0.05 and less than 0.15 will have L/S ratios of approximately 1.5.