Rise In Head Research Articles

Head-to-cervix force: an important physiological variable in labour. 1. The temporal relation between head-to-cervix force and intrauterine pressure during labour.

To investigate the relation between the rise in intrauterine pressure and rise in fetal head to cervix force in normal, slow and induced labour. Prospective observational study. The labour ward of a London teaching hospital. Forty patients were recruited from the antenatal clinic and labour ward of a West London Hospital. Five had normal onset and progression of labour, 14 had slow progression of labour and 21 had induced onset of labour. Intrauterine pressure and head-to-cervix force was measured simultaneously using an intrauterine pressure catheter and a specially designed four sensor head-to-cervix force probe. For each contraction of each labour, scattergrams of force by pressure were plotted. Three patterns were observed. When the rise in pressure preceded the rise in force, a positive 'loop' was generated. When the rise in pressure and force occurred simultaneously a linear pattern was generated (a neutral 'loop'). When the rise in pressure lags the rise in force, a negative 'loop' was generated. In normally progressive labour the distribution of loops was 29.1%, 22.6% and 48.3%, respectively, in slow labour the distribution was 26.1%, 14.1% and 59.8% and in induced labour the distribution was 33.8%, 14.4% and 51.8%. These distributions were not statistically different. However, a higher proportion of negative loops was observed in labours augmented with oxytocin compared to those receiving no oxytocin (MW-U = 87, P = 0.036). No differences were observed comparing parity, use of PGE2, epidural analgesia, or mode of delivery. Contraction frequency (number/10 minutes) was inversely correlated to the percentage of negative loops (rs = -0.34, P = 0.033) and positively correlated with percentage of positive loops (rs = 0.36, P = 0.027). This is the first report of the temporal relation between intrauterine pressure and head-to-cervix force in labour. The most common pattern is that the rise in pressure lags the rise in force, suggesting that a seal has to be created between the fetal head and cervix before a rise in pressure can occur. When oxytocin is given in labour, a higher proportion of loops are negative indicating that there is poor application of the fetal head and cervix in a greater proportion of contractions.

Annual fluctuations of groundwater levels as a result of loading by surface moisture

Long-term hydrographs for deep confined aquifers in southern Saskatchewan, Canada, show annual fluctuations characterized by a gradual rise in head from October to May/June and a rapid drop from May/June to October. These fluctuations are distinctly different from the seasonal fluctuations observed in surficial and shallow semi-confined aquifers, which reflect the response of these aquifers to recharge derived from snow melt and early spring rains. On the basis of field data and theoretical considerations, it is demonstrated that seasonal fluctuations of the water table are not transmitted down to the deep aquifers, provided the confining layers are thick and have sufficiently low hydraulic diffusivity. The annual fluctuations in the deep aquifers thus do not reflect seasonal recharge to these aquifers. Plots of moisture accumulation (i.e. precipitation minus calculated areal evapotranspiration) are strikingly similar to the observed hydrographs for the deep aquifers, in timing and magnitude of the annual fluctuations. It is postulated that the annual head fluctuations in the deep confined aquifers reflect changes of the mechanical load on the formations, caused by seasonal changes of the soil moisture, snow, and storage at the water table. The deep confined aquifers thus act as large-scale, inexact, weighing lysimeters.

Uplift Pressure in Crack Below Dam

A specific analytical solution for flow through a horizontal crack of finite length drained by a series of vertical drains is presented. The solution is used to derive diagrams of uplift pressure on the base of a dam and to demonstrate the influence of drains on the distribution and magnitude of uplift forces. Our solution shows that there should be an almost linear drop in hydraulic head from the entrance to the crack at the heel of the dam to the line of drains, followed by a slight rise in head to the end of the crack. This is consistent with a previously suggested solution for porous media. The results show that drain holes are effective in substantially reducing uplift pressures in a crack and have the greatest influence when located between approximately one half and one fifth of the length of the crack from its upstream end.

Temperature Profiles in Spheres Due to Electromagnetic Heating

This study predicts the steady state temperature rise in a homogeneous tissue sphere exposed to plane wave electromagnetic energy. The differential equation for heat transfer is solved, assuming heat transfer mechanisms of convection (due to blood flow), conduction, and evapotranspiration from the surface. The tissue heating is described by the specific absorption rate (SAR), which is a known function of the size and dielectric properties of the sphere and the frequency of the incident electro-magnetic energy. We consider the limiting cases of irradiation at very low frequencies, very high distance in the SAR is effectively averaged to produce a smoothly varying temperature increase. The results of this study are used to predict the maximum temperature rise in the human head, produced by an incident electromagnetic plane wave.

The role of groundwater in storm runoff

Groundwater plays a much more active, responsive and significant role in the generation, of storm and snow-melt runoff in streams than the recent literature on the subject suggests. Basin-wide trace experiments using environmental isotopes ( 18O, deuterium, tritium) and hydrometric studies carried out in hydrogeologically diverse watersheds, indicate that for all except the most intense rain storms and the most prolific melting days, groundwater dominates the runoff hydrographs in the study basins. The increased groundwater discharge during runoff events is apparently related to a rapid rise in hydraulic head along the perimeter of transient and perennial discharge areas. This groundwater ridging phenomenon probably arises from the almost instantaneous conversion of the near-surface tension-saturated capillary fringe into phreatic water. The ridging precedes, and is apparently independent of the response of the rest of the basin. In addition to its compatibility with several of the field observations commonly associated with contemporary concepts of runoff generation, the groundwater discharge theory explains some of the temporal variations in stream water chemistry which are not adequately accounted for by other theories.

Particle velocities in vertical pneumatic conveying systems

The calculation of pressure gradients in solid particle conveying systems requires a knowledge of particle velocities. In the following discussion it is shown that, in the case of large particles in vertical pipes, a general equation for particle velocities can be written in terms of the known particle and system properties and the empirical coefficients, Co, Co, and As, which relate the drag force and the solids force to the flow parameters. It is further shown that, for a given rate of solids flow, the excess pressure gradient due to the presence of the solids passes through a minimum as the airflow is changed and that at this minimum the particle velocity is independent of the solids factor A,. Moreover, if the multi-particle drag coefficient CD is approximately equal to the single particle drag coefficient Co,, then at the minimum, the relative velocity between the air and the solids is approximately 41% greater than the single particle terminal velocity in air. The flow of dilute suspensions of solid particles in air has been studied extensively and satisfactory explanations of the effect of a change in the airflow on the total pressure gradient and the stability of the suspension have been given (Zenz & Othmer 1960; Wen & Galli 1971; Kunii & Levenspiel 1969). In these texts the phenomenon of saltation in horizontal flow is described together with the sudden increase in the system pressure gradient which occurs when, at constant solids flow, the airflow falls below the saltation value. The equivalent choking velocity in vertical flow has also been described and the more gradual increase in pressure gradient as the airflow reduces beyond a pressure gradient minimum is recognised as being due to a fall in particle friction and to a rise in static head as the mixture density increases at lower air and particle velocities. A knowledge of particle velocities is necessary for predicting pressure drops accurately in such systems but no generally accepted analytical method exists which enables these velocities to be calculated. Some investigators have concluded that for vertical flow the relative velocity between the air and the solids is equal to the single particle terminal velocity. Others have refuted this assumption and produced data to show that the relative velocity is not a constant but increases with increasing air velocity. Basic analyses relating air/particle drag forces and frictional forces due to particle collisions have been published by Hinkle (1953) and by Wen & Galli (1971). In the Hinkle thesis the equation developed requires experimental data relating air and particle velocities before a solution for pressure drop can be found. The relationship which was found to correlate the measured particle and gas velocities is of an empirical nature and is of uncertain value outside the conditions in the test. Wen & Galli derive a general equation for horizontal flow which relates particle and gas velocities but its solution requires data on the solids frictions factor As together with an iterative or graphical solution for the solid particle velocity in terms of the air velocity. In the following analysis it is shown that in the case of vertical flow a general solution for particle velocities can be written in terms which include the solids factor As and the multiparticle drag coefficient CD. By considering only the excess pressure gradient due to the