Surgical anatomy of the petrous canal and posterior cranial fossa in relation to hearing preservation in surgery of acoustic neuroma

The suboccipital (retrosigmoid) and the middle fossa routes are recommended for preservation of hearing in surgery for acoustic neuroma. We carried out a comparative study of the critical distances and bony landmarks on 520 petrous bones. Unlike the transtemporal route, the suboccipital approach offers no landmarks for identification of the common crus, the vestibule or the facial nerve; the lateral portion of the internal auditory canal is not always seen. The fundus can be seen in only 50% of bones without opening the labyrinth.     

Functional residual capacity in normal neonates and children up to 5 years of age determined by a N2 washout method

Functional residual capacity (FRC) was determined in 50 infants by a simplified N2 washout method. Fourteen infants were preterm, four full-term newborns and the rest were 1 month to 5 yr of age. Weight ranged from 1.19 to 25.8 kg. The method gave well reproducible values with a mean coefficient of variation of 3.9%. The FRC values are equally well correlated to weight and length (r = 0.98). The correlation with weight is linear, intercepting the x axis (FRC = 0) at a weight of 480 g, the one with length is best described by a power curve. The course of the regression lines reflects the observation that FRC per kg weight or per cm length is lower in neonates than in larger infants. The FRC measurements are in the same range as values obtained by other investigators using the N2 washout or He-dilution techniques. The values are significantly smaller than thoracic gas volume measurements obtained by plethysmography. This difference may be due to air trapping or to possible methodological problems with the plethysmographic technique. The data demonstrate that FRC can be measured easily and accurately in preterm and older infants using a N2 washout technique.     

Long-term implantation of a system of electrical stimulation of paralyzed laryngeal muscles in dogs

Electrical stimulation of the posterior cricoarytenoid muscle, synchronized with inspiration, was achieved in dogs utilizing a radio frequency stimulus triggered by a chest wall expansion transducer. This system brings about abduction of the paralyzed vocal cord for the entire duration of inspiration, which allows a normal flow of air through the larynx. The implantable part of that system was tested successfully in chronic experiments (up to 11 months) in dogs with experimental paralysis of the recurrent laryngeal nerve. We feel that the system may be suitable for pacing the paralyzed human larynx.     

Binaural acoustic reflex activity following monaural noise exposure in decerebrate chinchillas

Acoustic reflex thresholds, latencies and magnitudes were recorded binaurally in decerebrate chinchillas suffering monaural, temporary noise trauma. Simultaneous recordings of cochlear microphonics from both cochleae during monaural reflex stimulation served as an index for acoustic reflex dynamics. Baseline values of threshold, latency and magnitude were recorded from ipsilateral and contralateral ears prior to a monaural 2-hour exposure to a 0.5-kHz octave-band noise at 100 dB SPL. Reflex dynamics were measured immediately after exposure and again following 1 h of recovery. Cochlear microphonic input-output functions for the exposed ear were completed prior to and after cessation of the noise and after 1 h of recovery. Acoustic reflex threshold and magnitude increased and latency decreased following exposure to noise for both the ipsilateral and contralateral recording conditions. Reflex activity in the nonexposed ear was unaffected. Reflex properties returned to pre-exposure values following recovery. These responses followed the same time course as changes in cochlear sensitivity. Alterations in reflex response following noise exposure is caused by changes at purely peripheral sites.     

Effect of distal endotracheal bias flow on PaCO2 during high frequency oscillatory ventilation

In order to evaluate the effect of distal endotracheal bias flow during HFOV on PaCO2 we studied adult rabbits with normal lungs and those who had meconium-induced lung dysfunction. Animals were studied while 1.0, 1.4 and 1.8 ml/kg tidal volumes (VT) were delivered by a high frequency oscillator. In animals with normal lungs and a 1.0 liter/min distal bias flow, the PaCO2 decreased significantly (p less than 0.01) with all VT used. In animals with meconium instillation the decrease in PaCO2 was also significant (p less than 0.05) at all combinations of VT and distal bias flow. The higher the distal bias flow the more pronounced was the lowering effect on PaCO2. We conclude that during HFOV it is possible to improve CO2 elimination using small additional bias flow delivered near the tip of the endotracheal tube in animals with normal abnormal lung function. This may allow adequate alveolar ventilation with even smaller VT, thus reducing the risk of barotrauma.     

Apnea of prematurity: I. Lung function and regulation of breathing

It has been suggested that apnea of prematurity may be caused by "immaturity" of central control of breathing. To test the validity of this hypothesis tidal volume (VT), alveolar ventilation (VA), alveolar Pco2 (Paco2), esophageal pressure change, and the slope of the CO2 response curve (delta Ve [minute ventilation]/delta Paco2) were determined in 18 infants with apnea (mean of 32 episodes of more than 20 seconds duration per day) and in 18 healthy newborns used as control subjects. The infants were matched for birth weight (1,068 g v 1,065 g), gestational age (30.2 weeks v 30.2 weeks), and postnatal age (8.6 days v 8.3 days). The results were as follows: Vt (4.4 +/- 1.0 mL/kg v 5.3 +/- 1.6 mL/kg), Va (96 +/- 21 mL/kg/min v 129 +/- 33 mL/kg/min), Paco2 (45.4 +/- 8.5 mm Hg v 35.6 +/- 4.7 mm Hg), esophageal pressure change (4.5 +/- 0.9 cm H2O v 6.0 +/- 1.8 cm H2O), delta Ve/delta Paco2 (20.2 +/- 10.6 mL/min/kg/mm Hg CO2 v 40.7 +/- 19.9 mL/min/kg/mm Hg CO2). There was a significant difference between infants with and without apnea for all measurements. The results indicate a decreased respiratory center output and a depressed ventilatory response to CO2 in infants with apnea. As there was no difference between the two groups in pulmonary mechanics or oxygenation, the findings support the hypothesis that a central disturbance in regulation of breathing is the cause of apnea in these infants.     

Respiratory rhythmically regulated electrical stimulation of paralyzed laryngeal muscles

Electrical stimulation of the posterior cricoarytenoid muscle, synchronized with inspiration, was achieved in dogs, utilizing a radio frequency stimulus triggered by a chest wall expansion transducer. This system brings about the abduction of the paralyzed vocal cord for the entire duration of inspiration, which allows a normal flow of air through the larynx. The stimulation system could be tested successfully in actual experiments in dogs with artificial paralysis of the recurrent laryngeal nerve. Its effectiveness could be proved through observation of the vocal cord movements (photographic documentation) and recording subglottic pressure variations. Transmission of stimulation energy is effected by electrical induction.     

Multilevel surgery in spastic diplegia: evaluation by physical examination and gait analysis in 25 children

Gait improvement surgery was performed on 25 ambulatory children with the diplegic type of cerebral palsy. Multiple soft tissue and bony procedures were performed (mean 8.2 procedures) according to criteria defined on the basis of physical examination and gait analysis. Relevant physical examination findings and kinematic and kinetic data in the sagittal plane were evaluated before surgery and at least 3 years after surgery. Physical examination showed a reduction in the ankle plantar-flexor power and in the range of hip flexion and ankle plantarflexion after surgery. Analysis of gait data showed significant improvements in the sagittal plane kinematics and the power generation at the hip and the ankle. At the knee joint there was maintenance of power of the flexor and extensor group of muscles on physical examination, with significant improvements in the kinematics after surgery. The authors conclude that well-selected surgery improves function of the spastic muscle. The importance of assessing clinical, kinematic, and kinetic data together for proper evaluation of gait is stressed.     

Microdialysis studies of D-amphetamine-evoked striatal dopamine overflow in young versus aged F344 rats: effects of concentration and order of administration

In order to measure the effects of different concentrations of D-amphetamine (D-AMPH) infusions on striatal dopamine (DA) overflow in young versus aged rats, and to determine the influence of preceding infusions on subsequent stimuli, two microdialysis studies were conducted. In the first study, D-AMPH (100, 200, and 2000 microM) was infused in ascending order of concentration, while in the second study the order of administration was reversed. The order of administration significantly affected DA overflow and extracellular levels of 3,4-dihydroxyphenylacetic acid (DOPAC). Generally, DA overflow was greater for a given concentration when it was administered first in a sequence than when it was administered later in a sequence. The two age groups did not differ on measures of DA overflow. The order of administration also significantly influenced the effect of D-AMPH on extracellular DOPAC, as the D-AMPH-related decreases in DOPAC were greater for a concentration when it was administered earlier versus later in the sequence. This effect was greater in the young rats than in the aged rats. D-AMPH also resulted in diminished levels of DOPAC in the aged rats compared to the young rats. These results suggest that between-groups studies may be more appropriate for determining the effects of different concentrations of D-AMPH on striatal DA overflow. They also demonstrate that while some measures of stimulus-evoked DA overflow may not differ between young and aged F344 rats, extracellular regulation of striatal DA (as measured by changes in DOPAC) may be altered. These alterations may contribute to age-related decreases in motor function.