The effects of whirlpools baths in labor: a randomized, controlled trial.

BACKGROUND: Showers and tubs in labor were not generally used in our center. When three whirlpool baths (Jacuzzis) were ordered as part of our renovations, a randomized, controlled trial was initiated to explore their effects on narcotic and epidural requirements. METHODS: This study employed an intent-to-treat design, and the sample size was estimated to account for the fact that some women would be unable to use the tub. The experimental group of 393 women was offered the tub during labor and the control group of 392 women received conventional care. RESULTS: No births occurred in the tub. The tub group required fewer pharmacologic agents than controls (66% vs 59%, p = 0.06), experienced fewer deliveries by forceps and vacuum (p = 0.019), and were more likely to have an intact perineum than the standard-care group (p = 0.019). Labor was longer for the tub group (p = 0.003), who coincidentally were more primiparous and in earlier labor on admission. No differences were noted in the low rates of maternal and newborn signs of infection in women with ruptured membranes. A subset of mothers expressed satisfaction with the tub experience and labor support. The cesarean rate among both groups was lower (8.9%) than our overall rate (16.6%) during the study period. CONCLUSIONS: Whirlpool baths in labor have positive effects on analgesia requirements, instrumentation rates, condition of the perineum, and personal satisfaction. Further study is being planned.

Interrod forces in aqueous gels of tobacco mosaic virus.

The lateral separation of virus rod particles of tobacco mosaic virus has been studied as a function of externally applied osmotic pressure using an osmotic stress technique. The results have been used to test the assumption that lattice equilibrium in such gels results from a balance between repulsive (electrostatic) and attractive (van der Waals and osmotic) forces. Results have been obtained at different ionic strengths (0.001 to 1.0 M) and pH's (5.0 to 7.2) and compared with calculated curves for electrostatic nad van der Waals pressure. Under all conditions studied, interrod spacing decreased with increasing applied pressure, the spacings being smaller at higher ionic strengths. Only small differences were seen when the pH was changed. At ionic strengths near 0.1 M, agreement between theory and experiment is good, but the theory appears to underestimate electrostatic forces at high ionic strengths and to underestimate attractive forces at large interrod spacings (low ionic strengths). It is concluded that an electrostatic-van der Waals force balance can explain stability in tobacco mosaic virus gels near physiological conditions and can provide a good first approximation elsewhere.

Effects of monovalent ion binding and screening on measured electrostatic forces between charged phospholipid bilayers.

In an effort to determine the role that monovalent ions play in the modification of intermembrane forces, we have measured these forces between charged phospholipid bilayers in monovalent ionic solutions. The osmotic stress technique allowed the net electrostatic pressure between the bilayers to be measured while their separation was concurrently determined by x-ray diffraction. Taken together, these measurements yielded electrostatic pressure as a function of bilayer separation. We have related measured pressures to the bilayer surface charge density and surface potential through an exact solution of the full nonlinear Poisson-Boltzmann equation for this system. Quantitative differences in bilayer separation amongst monovalent alkali metal cations indicated differential binding of these to phosphatidylglycerol (PG), phosphatidylserine (PS), and phosphatidic acid (PA); binding affinity series were determined for Li+, Na+, K+, Cs+, and TMA+ ions to these lipids. The anions Cl-, Br-, I-, and CH3COO- were found to have no differential effect on the repulsive forces between PS bilayers. Debye lengths for the electric double layer estimated from the slopes of the experimental pressure curves were consistently longer than predicted on the basis of classic Gouy-Chapman theory. Estimates of the van der Waals Hamaker coefficient between bilayers of PS and PG in salt solution were found to be weaker than between phosphatidylcholine bilayers in pure water, a difference possibly due to electromagnetic retardation and ionic screening.