Biomedical subjects

M Davi

Publications and source records attributed to M Davi.

7 recordsLinked to original sources

PubMed1992

Amodal completion versus induced inhomogeneities in the organization of illusory figures.

An analysis is presented of a phenomenological model of illusory contours. The model is based on amodal completion as the primary factor giving rise to the illusory figure. In the experiment, conducted by the method of paired comparisons, the same parameter was manipulated in two series of equivalent configurations. The first series yielded examples of amodal completion, the second examples of illusory figures. Three groups of subjects evaluated the magnitude of completion, the brightness contrast of the illusory figure, and the contour clarity of the illusory figure. A control experiment was conducted, which demonstrated that in these configurations amodal completion and amodal continuation behave in the same way. Line displacement did not influence the brightness or the contour clarity of the illusory figures, though it influenced the magnitude of amodal completion. These results are in agreement with the energetic model developed by Sambin.

Adult↗

PubMed1992

The role of symmetry in determining perceived centers within shapes.

This study was designed to assess the effects of symmetry and plane of presentation on the determination of the perceptual center of flat figures. Experiment 1 demonstrates the existence of effects in improving center determination, both in the number of sides of the shape and in rotational and reflective symmetry (confounded in the experiment). Experiment 2 shows that the presentation plane has no effect on center determination. In Experiment 3, we divide the effects of the two symmetry types, showing that rotational symmetry alone is as effective as the presence of both symmetry types--that is, the presence of symmetry axes is not very useful in finding perceived centers.

Adult↗

PubMed1989

Decrease in plasma prostaglandin E2 is not essential for the establishment of continuous breathing at birth in sheep.

Depression of prostanoid concentrations by indomethacin induces continuous breathing in fetal sheep, but it is not known whether this is associated with changes in fetal behaviour. Furthermore, the relationship between changes in prostaglandin E2 (PGE2) concentration after delivery and the appearance of continuous breathing has not been examined. We hypothesized that the decrease in fetal PGE2 by infusion of indomethacin would induce continuous breathing and a change in behaviour such that the fetus should come to resemble a newborn lamb; and coinciding with the establishment of continuous breathing at birth, PGE2 concentrations would decrease to a critical level below that present in the fetus. We found that continuous breathing in fetal sheep induced by infusion of indomethacin was related to a decrease in PGE2 from 436 +/- 114 to 189 +/- 73 pg/ml (P less than 0.005) but that this was not associated with fetal wakefulness. In addition, measurements of carotid arterial PGE2 concentrations showed that the beginning of continuous breathing after birth occurred at a plasma concentration of PGE2 of 1245 +/- 260 pg/ml, a value about three times higher than the 422 +/- 53 pg/ml measured in the fetus during breathing activity. Together these findings suggest that PGE2 is not primarily involved in the establishment of continuous breathing at birth.

Animals↗

PubMed1988

Clinical trial of naloxone in birth asphyxia.

To determine whether endogenous opiates play a role in the pathogenesis of perinatal asphyxia, a blinded clinical trial of naloxone, a competitive opiate receptor blocker, was undertaken in infants with low 1-minute Apgar scores. Of 85 infants with 1-minute Apgar score 0 to 3, 44 received an injection of naloxone (approximately 0.4 mg/kg) and 41 received saline solution. In 108 infants with 1-minute Apgar score 4 to 6, 54 received naloxone and 54 saline solution. In neither group was there a significant effect of naloxone on respiratory frequency or heart rate up to 30 minutes after injection, nor at 24 hours of age. In both groups active muscle tone of upper and lower limbs was increased by naloxone, a response that may not be beneficial in the face of inadequate oxygen delivery to vital organs. We conclude that naloxone at this dose had no readily apparent benefit in the resuscitation of the asphyxiated newborn infant.

Adult↗

PubMed1988

Effect of increased arterial CO2 on fetal breathing and behavior in sheep.

We studied breathing and behavioral response to increased arterial CO2 (PaCO2) in 12 fetal sheep between 130 and 145 days of gestation. Of these 12 fetuses, 10 had an increase in PaCO2 through maternal rebreathing of CO2; in the other 2 fetuses CO2 was increased via an endotracheal tube and application of continuous distending airway pressure. We used our window technique to observe and videotape fetal behavior. The experiments consisted of recording breathing activity and behavior during resting conditions (1 low- and high-voltage ECoG cycle) and during administration of CO2. We measured electrocortical activity (ECoG), eye movements (EOG), electromyography of the diaphragm (EMGdi) and neck muscles, tracheal (Ptr), amniotic, and carotid arterial pressures. Administration of CO2 by the rebreathing technique produced an increase in the amplitude of breathing activity as reflected by an increase in Ptr from 5.0 +/- 0.6 to 12 +/- 1.9 mmHg (P less than 0.01) and an increase in SEMGdi from 32 +/- 4 to 77 +/- 8% max (P less than 0.001). Frequency increased due to a decrease in inspiratory (TI) and expiratory duration. Ptr/TI increased from 11.0 +/- 2.0 to 37.4 +/- 9.0 mmHg/s (P less than 0.05) and SEMGdi/TI increased from 67 +/- 7 to 221 +/- 28% max/s (P less than 0.001). Although the response was at times prolonged into the transitional high-voltage zone, it did not persist during established high-voltage ECoG.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1979

Effect of sleep state on chest distortion and on the ventilatory response to CO2 in neonates.

In 10 preterm and 10 term infants, the effect of sleep state on chest distortion and on the ventilatory response to CO2 was assessed. It was found that chest distortion and ventilatory response to CO2 were independent of sleep state. Chest distortion, however, was more frequent in preterm than in term infants. The authors suggest that the increased prevalence of chest distortion in preterm infants is related to their highly compliant chest wall rather than to differences in sleep state.

Carbon Dioxide↗

PubMed1975

Continuous determination of the oxygen dissociation curve for whole blood.

We report here the development of a new method that allows continuous determination of the oxygen dissociation curve for microsamples (600 mul) of whole blood under conditions of pH, pCO2, methemoglobin concentration, and 2,3-diphosphoglycerate content closely approaching those found in the circulatory system. The method consists of gradually oxygenating a blood sample by adding H2O2 in the presence of catalase (EC 1.11.1.6), to produce the reaction H2O2 leads to H2O + 1/2 O2. Because the total oxygen content of blood can be derived from the known rate of H202 addition and the pO2 is determined in the liquid phase by an oxygen electrode, the two functions (total O2 content) and (% oxygen saturation) vs. pO2 are simple to calculate. pCO2 and pH are controlled by adding base simultaneously with the gradual oxygenation of blood. The method described thus avoids the direct measurement of oxygen saturation of whole blood.

Autoanalysis↗