Side Resistances Research Articles

Effects of L‐arginine on utero‐placental circulation in growth‐retarded fetuses

To evaluate the effects of L-arginine (ARG) infusion, the nitric oxide as substrate, on the utero-placental circulation at third trimester. Three groups of nine pregnant women each were infused i.v. with 30 g ARG, for 30 minutes. One group served as control, and the two remnants were composed by patients with intrauterine growth retardation with (IUGR-B) or without (IUGR-A) increased resistances in the utero-placental circulation. Changes of blood flow velocity waveforms of both uterine arteries and umbilical artery were recorded for 60 minutes. Blood pressure, serum nitrites/nitrates and growth hormone levels were also measured. No hemodynamic changes in utero-umbilical circulation were observed during infusion in any of the three groups. Considering the uterine arteries separately as placental and non-placental sided we found a significant decrease of non-placental side resistances in IUGR-B women. Indeed, the pulsatility index was lowered by 14%, in respect of baseline value. Serum nitrites/nitrates as well as serum growth hormone levels were significantly increased by ARG, in every woman, irrespective of the presence of fetal growth retardation. Blood pressure remained unaffected during infusion in every woman. These findings suggest that L-arginine infusion affects utero-placental circulation in patients with IUGR associated with increased uterine resistances. Such an action is specific and appears possibly to be mediated by a release of nitric oxide.

Limiting tip and side resistance: fact or fallacy? : Kulhawy, F H Proc of the Conference on Analysis and Design of Pile Foundations, San Francisco, California, 1–5 Oct 1984P80–P98. Publ New York: ASCE, 1984

The tip and side resistances of deep foundations do not reach a limit at a critical depth; instead, they increase with depth. For the tip, the rate of increase decreases with depth. For the side, the rate is a function of increasing overburden and decreasing K//0 with depth.

New Design Correlations for Piles in Sand

A critical review of the literature clearly shows that existing theories which are used to determine the bearing capacity of piles driven in sand are not satisfactory. Careful examination of the results of experimental studies indicates that existing theories fail to consider all significant parameters. Field load test data are used to determine which of the pile geometry and soil property parameters are significant. Special attention is given to the problem of residual stresses. Bearing capacity factors are calculated from measured unit point and side resistances. The bearing capacity factors are correlated with relative depth (depth of penetration to diameter ratio) and friction angle or relative density of sand. New design correlations are developed for use in predicting the bearing capacity of axially loaded piles in sand.