Biomedical subjects
P J Bex
Publications and source records attributed to P J Bex.
Sharpening of drifting, blurred images.
The perceived blur of moving images is less than expected given the sluggish temporal response of the visual system. This suggests that a motion deblurring mechanism may exist to preserve the positional acuity and sharpness of moving images. Furthermore, when sequences of blurred stills are presented, observers report that the moving image is in sharp focus raising the possibility that there is a mechanism which may sharpen the appearance of moving, blurred images. We have measured the effects of velocity and contrast on the perceived blur of drifting, blurred images (sine gratings and blurred edges). Subjects matched the perceived blur of drifting, blurred images to that of static, blurred images in a dimly lit room. It was found that perceived blur was inversely related to drift speed and contrast. The results confirm that moving, blurred images may appear sharper than when they are static. This finding is not consistent with some models of motion deblurring since these account only for the preservation of sharp contours that are present in the image and not for the sharp appearance of images that are in fact blurred.
Periventricular/intraventricular hemorrhage following early and delayed umbilical cord clamping. A randomized controlled trial.
OBJECTIVE: To test the hypothesis that early compared with delayed clamping of the umbilical cords of low-birthweight babies may increase the incidence of periventricular/intraventricular hemorrhage (PVH/IVH). DESIGN: Randomized controlled trial. SETTING: The labor wards of 3 teaching hospitals of the University of the Witwatersrand, Johannesburg. PATIENTS: Women expected to give birth to babies weighing less than 2000 g. INTERVENTIONS: Allocation by randomly ordered, sealed cards to a policy either of clamping the umbilical cord immediately after delivery, or, if possible, delaying cord clamping for 1 to 2 min. MAIN OUTCOME MEASURES: Ultrasound diagnosis of PVH/IVH about 24 h after birth by an observer blind to the allocation of each patient. RESULTS: PVH/IVH was diagnosed in 8/40 (20%) of neonates following delayed umbilical cord clamping and 11/46 (24%) following early cord clamping (odds ratio 0.80; 95% confidence interval, 0.29 to 2.20). CONCLUSIONS: This study does not confirm that early clamping of the umbilical cord may contribute to the initiation of PVH/IVH in low-birthweight neonates, but further studies are required before the hypothesis can be rejected with confidence.
Hasty clamping of the umbilical cord may initiate neonatal intraventricular hemorrhage.
Intraventricular hemorrhage may result from surges in systemic vascular pressure, particularly when cerebral blood flow autoregulation is impaired by asphyxia, and the germinal matrix vasculature is immature. We postulate that early interruption of umbilical arterial blood flow may cause a rise in blood pressure sufficient to contribute to the development of intraventricular hemorrhage in susceptible neonates.
Perineal management during childbirth and subsequent dyspareunia.
Sexual function following childbirth was studied by means of a retrospective postal questionnaire. Dyspareunia measured on an analogue scale relative to pre-pregnancy values (mean values) was significantly greater three months after a mediolateral episiotomy (35%) than after vaginal delivery with intact perineum (9%) or Caesarean Section (16%) and similar to the value following second degree perineal laceration (29%). At 12 months the latter had returned to pre-pregnancy values, while that following episiotomy remained significantly elevated (17%).