Attentional capabilities of reading-impaired children during dichotic presentation of phonetic and complex nonphonetic sounds.

Reading-impaired boys, who were deficient in nonverbal auditory processing skills, were tested on their ability to identify a single speech sound (CV) when presented in dichotic competition with a nontarget CV or complex nonspeech sound (bleat). Sixteen reading-impaired boys aged 9 to 14 and 16 age-matched controls were presented with 30 CV-CV pairs and 30 CV-Bleat pairs. No difference was found between the two groups in their ability to identify the target CV, regardless of whether the competing stimulus was phonetic or nonphonetic. It was concluded that reading-impaired children of the type studied here are characterized more by an attentional capacity limitation than by an inability to focus attention or by a specific inability to process phonetic information.

Event-related potentials during selective attention to speech sounds.

Event-related potentials (ERPs) were recorded from subjects while they selectively attended to sequences of stop-consonant syllables or sequences of tone pips of different frequencies. The ERP difference waveforms that distinguished attended from unattended speech sounds were highly similar in morphology and scalp distribution to the difference waveforms elicited by the tone pips. These results suggest that the attention mechanisms brought into play when selecting complex phonetic stimuli for further analysis are similar to those engaged when selecting between tones of different frequencies, in contrast with previous theoretical interpretations. Latency differences observed between the attention-related ERPs to simple and complex stimuli were attributed to differences in the duration of processing that makes these stimulus features available to attention mechanisms.

Conventional vs high-frequency jet ventilation in a piglet model of meconium aspiration: comparison of pulmonary and hemodynamic effects.

The pulmonary and cardiovascular effects of high-frequency jet (HFJV) and conventional (CV) ventilation were evaluated in a piglet model of meconium aspiration. A mixture of 20% human meconium and 0.9% saline solution was instilled deep into the trachea of 10 piglets, after which either HFJV or CV was administered for 4 hours. Arterial blood gases, cardiac output, mean pulmonary and systemic arterial pressures, pulmonary and systemic vascular resistances, and pulmonary mechanics were compared between groups. During the 4 hours of ventilation, PaO2 and PaCO2 were not statistically different between groups. The peak inspiratory pressure necessary to maintain PaCO2 in the preset range was approximately half as much in the HFJV group as in the CV group (P less than 0.002). Mean airway pressure was lower in the HFJV group only during the second hour (P less than 0.03). Cardiac output, mean aortic and pulmonary artery pressures, systemic and pulmonary vascular resistance, dynamic lung compliance, and pulmonary resistance were not statistically different between groups. Our results suggest that HFJV may be more effective than CV in the early stages of meconium aspiration syndrome because HFJV allows more efficient ventilation and adequate oxygenation at lower peak inspiratory pressures.

The effect of calcium antagonists on hypoxic pulmonary hypertension in the piglet.

Cardiovascular responses to the calcium antagonists verapamil and nifedipine were evaluated in a piglet model of hypoxic pulmonary hypertension. All animals were mechanically ventilated and paralyzed. Cardiac output (CO), pulmonary artery (Ppa) and aortic blood pressure (AoP), pulmonary wedge pressure, right atrial pressure (Pra), and arterial blood gases were measured prior to and after pulmonary hypertension was induced by hypoxia and after administration of calcium-blocking agents. Results were compared to a control group of piglets subjected to a similar period of hypoxia. Verapamil infusion (0.15 mg/kg) resulted in a rapid decrease in Ppa, AoP and pulmonary vascular resistance (p less than 0.05) which returned to baseline values by 15 min. Nifedipine (100 micrograms/kg) resulted in a decrease in Ppa at 1 min (p less than 0.05) which remained significantly lower than controls throughout the study period. AoP declined precipitously during the same time period (p less than 0.01). No significant change in Ppa was noted when nifedipine was administered at a dose of 10 micrograms/kg. For the most part, these drugs have a transient vasodilatory action on pulmonary as well as systemic circulation in this animal model; however, they might in higher doses be associated with significant systemic hypotension. For this reason, the use of these drugs in the treatment of hypoxic pulmonary hypertension in the neonate should be approached with caution.