Mean PDI Research Articles

PREDICTORS OF DEVELOPMENTAL OUTCOME AT 12 MONTHS OF <1250 GRAM INBORN NEONATES

Prediction of poor developmental outcome (MDI or PDI <68, 2SD below the mean) in very low birthweight (VLBW) infants (≤1250 gms.) at time of hospital discharge would facilitate early intervention and parental counseling. All VLBW infants born at Medical Center Hospital were followed for 2 years in a program providing periodic developmental evaluation. Of 17,694 infants born in 1979-1981,166 (0.9%) weighed ≤1250 gms. and 76 (46%) survived. Of these, 56 (74%) have been successfully followed for at least one year. Mean birthweight and gestational age were 1024 gms. (range 709-1250) and 29 weeks (range 25-37). Mean MDI on the Bayley exam was 96 (range <50-140) and mean PDI was 88 (range <50-122). Nine infants (16%) had a MDI or PDI score <2SD below the mean. The following parameters were examined as single strong predictors of poor outcome: Apgar scores 0-3, presence of intraventricular hemorrhage, duration of time on ventilator or oxygen, parental age, parental education, family income, mode of delivery, and presence of apnea. Poor outcome was positively correlated with apnea (p=.03). Apnea requiring ventilation was an especially strong predictor of poor outcome (p=.002). Although other factors in combination may predict poor outcome, we suggest that VLBW infants with apnea, especially apnea requiring ventilation, be identified as particularly at risk for poor developmental outcome.

Force reserve of the diaphragm in patients with chronic obstructive pulmonary disease.

The fatigue threshold of the human diaphragm in normal subjects corresponds to a transdiaphragmatic pressure (Pdi)-inspiratory time integral (TTdi) of about 15% of Pdimax. The TTdi of resting ventilation was measured in 20 patients with chronic obstructive pulmonary disease (COPD) and ranged between 1 and 12% of Pdimax (mean 5%). TTdi was significantly related to total airway resistance (Raw) (r = 0.57; P less than 0.05). Five of these patients were asked to voluntarily modify their TI/TT (ratio of inspiratory time to total cycle duration; from 0.33 to 0.49) so as to increase their TTdi from a control value of 8% to an imposed value of 17% of Pdimax. The imposed pattern induced a progressive decline in the high-frequency (150-350 Hz)/low-frequency (20-40 Hz) power ratio (H/L) of the diaphragm electromyogram (fatigue pattern), quantitatively similar to that seen in normal subjects breathing with similar TTdi levels. The decay in H/L was followed by a progressive fall in mean Pdi meanly due to decrease in gastric pressure swings. It is concluded that 1) the force reserve of the diaphragm in COPD patients is decreased because of a decrease in Pdimax; 2) the remaining force reserve of the diaphragm can be exhausted by even minor modifications in the breathing pattern; and 3) at a TI/TT of 0.40 our COPD patients can increase their mean Pdi 3-fold before reaching a fatiguing pattern of breathing compared with 8-fold in normal subjects.

Variation in Population Levels of Phytophthora cinnamomi in Eucalyptus Forest Soils of Eastern Victoria

The behaviour of Phytophthora cinnamomi Rands was examined over a 2 year period on newly cleared and replanted eucalypt sites in the coastal forests of eastern Gippsland, rated as of low, moderate and high die-back hazard in relation to the drainage and disease characteristics of the original forest cover and surrounding trees. The fungus behaved like a saprophytic survivor. Maximum population levels, assessed as a 'population density index' (PDI), occurred within the soil influenced directly by the root mass. The PDI in adjacent bare soil was very low. The PDI depended, inter alia, on fungal pathogenesis, soil temperature and soil moisture. Mean maximum PDI values recorded respectively for the high, moderate and low hazard sites were in the ratio of about 8/4/1. This ratio was directly related to the depth of the clay pan beneath the surface. There was a marked seasonal variation in PDI, most pronounced on the high hazard site and least on the low hazard site. The minimum and maximum values were recorded in June (winter) and December-March (summer) respectively. Moderately heavy rainfall had little effect on the PDI in well-drained soils, even during midsummer when soil temperatures were optimum for fungal populations to increase. Fire affected PDI values only temporarily. PDI values in the surface soil were greater than at a depth of 75 cm, and the distribution of the fungus through the soil profile was influenced by soil texture. Before canopy closure occurred, PDI values were greater under eucalypt species tolerant to root rot than under sensitive species. Canopy closure reduced the seasonal fluctuation in soil temperature and, on sites where tree growth was vigorous, the reduction in PDI was striking. Addition of fertilizers to the soil had no direct effect on the PDI, the reduction observed being an indirect effect produced possibly by accelerated growth, increased transpiration and rapid canopy closure. These results suggest that root rot-sensitive eucalypt species growing on coastal sites with impeded drainage will prove vulnerable to die-back, and that any form of logging activity that reduces the amount of green cover on infected sites will aggravate root rot if the fungus is present. Consequently it will not be possible to manage these stands by conventional methods. On steeper, well-drained sites the disease should not prove to be a serious hazard except in exceptionally wet summer and autumn periods.