Current concepts of vestibular nucleus function: transformation of vestibular signals in the vestibular nuclei

The vestibular nerve sends signals to the brain that code the movement and position of the head in space. These signals are used for a variety of functions, including the control of reflex and voluntary movements and the construction of a sense of self-motion. In order to carry out these functions, sensory vestibular signals need to be transformed in a variety of ways. Transformations are thought to occur at an early stage of sensory processing in the brain, and in many cases are apparent in the responses of neurons in the vestibular nuclei that receive direct inputs from the vestibular nerve. Several specific examples of sensory transformation in the vestibular nuclei are presented, and current hypotheses about the mechanisms that are used to produce the transformations are discussed.

A radiographic method for estimating lung volumes in sick infants

Estimation of lung volumes by conventional methods in sick infants is technically difficult and is the subject of controversy. In this study, we compared both thoracic gas volume (TGV), measured with an infant whole body plethysmograph, and functional residual capacity (FRC), determined by the nitrogen washout technique, to planimetric measurements of anteroposterior chest radiographs in 26 infants with bronchopulmonary dysplasia (BPD). The tidal volume (TV) of each patient was added to TGV and FRC because these were measured at the end of expiration whereas chest radiographs were taken at the end of spontaneous inspiration. The regression equations expressing the relationships between TGV and right+left lung field areas [A+B], and between FRC and lung areas are expressed as follows: [TGV+TV](mL) = 3.3 mL/cm2 x [A+B] cm2 + 24 mL and [FRC+TV](mL) = 3.5 mL/cm2 x [A+B] cm2 - 13.5 mL. Correlation coefficients of 0.9 and 0.7 for TGV and FRC, respectively, suggest a stronger correlation between TGV and lung areas than between FRC and lung areas. Lung areas measured by planimetry correlate closely with physiological measurement of lung volumes. We conclude that the planimetric method is an inexpensive and reliable technique for estimating lung volumes in young infants with BPD when chest radiographs are available.

In vivo response times for a heated skin surface CO2 electrode during rest and exercise

The continuous, noninvasive estimation of arterial carbon dioxide tension (PaCO2) by heated skin surface electrodes has recently become available for pediatric patients. Skin surface (PsCO2) electrodes can enhance the safety of procedures such as intubation, bronchoscopy, ventilator changes, sleep studies, or measurement of the ventilatory response to CO2 or hypoxia. However, clinical situations that include rapid changes in PaCO2 demand knowledge of the in vivo response time. We compared the response of a heated PsCO2 electrode to end tidal CO2 (PetCO2) during abrupt changes in inspired CO2 from room air to 7% CO2 and back to room air. We obtained 54 curves on nine healthy subjects. There was an initial lag time with less than a 10% change in PsCO2. Then PsCO2 approached PetCO2 exponentially. For subjects at rest changing from breathing room air to 7% CO2, the initial lag time was 40 +/- 2 seconds and the 50% response time of the exponential portion was 46 +/- 3 seconds. Thus, it took 86 seconds for the electrode to record a 60% response to an abrupt increase in inspired CO2. The initial lag and 50% response time were considerably shorter during exercise (30 +/- 2 and 33 +/- 2 seconds) and even shorter when switched from breathing 7% CO2 to room air (23 +/- 2 and 21 +/- 2 seconds). Exercise did not further reduce the response time when CO2 was initially elevated, suggesting the faster response time was due to vasodilation of the skin due to elevated CO2.(ABSTRACT TRUNCATED AT 250 WORDS)