Human Chest Wall Function while Awake and during Halothane Anesthesia: I. Quiet Breathing

Background: Data concerning chest wall configuration and the activities of the major respiratory muscles that determine this configuration during anesthesia in humans are limited. The aim of this study was to determine the effects of halothane anesthesia on respiratory muscle activity and chest wall shape and motion during spontaneous breathing.

Methods: Six human subjects were studied while awake and during 1 MAC halothane anesthesia. Respiratory muscle activity was measured using fine-wire electromyography electrodes. Chest wall configuration was determined using images of the thorax obtained by three-dimensional fast computed tomography. Tidal changes in gas volume were measured by integrating respiratory gas flow, and the functional residual capacity was measured by a nitrogen dilution technique.

Results: While awake, ribcage expansion was responsible for 25 plus/minus 4% (mean plus/minus SE) of the total change in thoracic volume (Delta Vth) during inspiration. Phasic inspiratory activity was regularly present in the diaphragm and parasternal intercostal muscles. Halothane anesthesia (1 MAC) abolished activity in the parasternal intercostal muscles and increased phasic expiratory activity in the abdominal muscles and lateral ribcage muscles. However, halothane did not significantly change the ribcage contribution to Delta Vth (18 plus/minus 4%). Intrathoracic blood volume, measured by comparing changes in total thoracic volume and gas volume, increased significantly during inspiration both while awake and while anesthetized (by approximately 20% of Delta Vth, P < 0.05). Halothane anesthesia significantly reduced the functional residual capacity (by 258 plus/minus 78 ml), primarily via an inward motion of the end-expiratory position of the ribcage. Although the diaphragm consistently changed shape, with a cephalad displacement of posterior regions and a caudad displacement of anterior regions, the diaphragm did not consistently contribute to the reduction in the functional residual capacity. Halothane anesthesia consistently increased the curvature of the thoracic spine measured in the sagittal plane.     

A survey of parental views regarding their child's hearing loss: a pilot study.

OBJECTIVE: Assess parental perceptions of their child's sensorineural hearing loss care. METHODS: Families of pediatric patients diagnosed with a sensorineural hearing loss from 2000 to 2004 were sent a survey asking about their experiences with their child's hearing loss. RESULTS: One hundred eight of 389 families surveyed were studied. Thirteen percent did not know the results of the newborn screening. Twenty-two percent of the primary care physicians were not involved in the child's hearing evaluation. Forty percent of the patients underwent 4 or more audiologic tests before a diagnosis. The most common reason for delayed diagnosis was difficulty in obtaining an appointment with an audiologist. Sixty-two percent of families had difficulties obtaining hearing aids, and 58% noted difficulties obtaining cochlear implants. CONCLUSIONS: Families reported multiple obstacles to obtain timely diagnosis and treatment. Otolaryngologists may need to be more involved in the evaluation and treatment of these patients. EBM rating: C-4.     

Anesthetics Inhibit Acetylcholine-promoted Guanine Nucleotide Exchange of Heterotrimeric G Proteins of Airway Smooth Muscle

Background: Anesthetics inhibit airway smooth muscle contraction in part by a direct effect on the smooth muscle cell. This study tested the hypothesis that the anesthetics halothane and hexanol, which both relax airway smooth muscle in vitro, inhibit acetylcholine-promoted nucleotide exchange at the [alpha] subunit of the Gq/11 heterotrimeric G protein (G[alpha]q/11; i.e., they inhibit muscarinic receptor-G[alpha]q/11 coupling).

Methods: The effect of halothane (0.38 +/- 0.02 mm) and hexanol (10 mm) on basal and acetylcholine-stimulated G[alpha]q/11 guanosine nucleotide exchange was determined in membranes prepared from porcine tracheal smooth muscle. The nonhydrolyzable, radioactive form of guanosine-5'-triphosphate, [35S]GTP[gamma]S, was used as the reporter for G[alpha]q/11 subunit dissociation from the membrane to soluble fraction, which was immunoprecipitated with rabbit polyclonal anti-G[alpha]q/11 antiserum.

Results: Acetylcholine caused a significant time- and concentration-dependent increase in the magnitude of G[alpha]q/11 nucleotide exchange compared with basal values (i.e., without acetylcholine), reaching a maximal difference at 100 [mu]m (35.9 +/- 2.9 vs. 9.8 +/- 1.2 fmol/mg protein, respectively). Whereas neither anesthetic had an effect on basal G[alpha]q/11 nucleotide exchange, both halothane and hexanol significantly inhibited the increase in G[alpha]q/11 nucleotide exchange produced by 30 [mu]m acetylcholine (by 59% and 68%, respectively).