An effective combination of anaesthetics for 6-h experimentation in the golden Syrian hamster

Lung volume reduction surgery does not improve diaphragmatic contractile properties or atrophy in hamsters with elastase-induced emphysema

It is claimed that lung volume reduction surgery (LVRS) improves inspiratory muscle function. As diaphragm structure and function are not directly appraisable in patients, we studied the effects of LVRS on the diaphragm in vitro contractile properties and morphology in hamsters with elastase-induced emphysema. Four months after intratracheal instillation of elastase (40 U/100 g), hamsters underwent either bilateral LVRS (LVRS, n = 11) or a sham operation (SHAM, n = 8). Four animals died during the perioperative period in LVRS (n = 7). Hamsters instilled with saline served as control (CTL, n = 8). Animals were studied at the age of 9 mo. LVRS was associated with a significant 25% decrease in functional residual capacity compared to SHAM (p < 0.05). Compared with CTL, LVRS and SHAM showed a significant 18% and 14% reduction in diaphragm mass, respectively (p = 0.02). LVRS had a significantly decreased twitch tension compared to CTL and SHAM (p < 0.01). Both LVRS and SHAM showed increased resistance to muscle fatigue compared with CTL. The histochemical analysis revealed a significant shift from type IIx/b toward type IIa fibers in LVRS and SHAM compared with CTL. In conclusion, emphysema is associated with functional adaptations but LVRS does not appear to beneficially alter the diaphragm contractile and morphological characteristics in hamsters with elastase-induced emphysema.

Changes in dorsal cochlear nucleus blood flow during noise exposure

Changes in dorsal cochlear nucleus (DCN) blood flow during noise exposure were assessed using both intravital microscopy (IVM) and laser Doppler flowmetry (LDF). Mature Syrian golden hamsters were anesthetized, tracheotomized and implanted with a carotid artery catheter for monitoring blood pressure and infusion of fluorescent dye. An occipital craniectomy was performed and the cerebellum partly aspirated for access to the DCN. Fluorescent dye was infused to enhance observations of the DCN surface using a customized IVM. Red blood cell velocity, vessel diameter and blood pressure were continuously monitored. Subjects were presented with 110 dB SPL broad-band noise for 15 min. A second group was presented with the same protocol for laser Doppler assessment of blood-flow changes. Control groups included animals not exposed to noise using both IVM and laser Doppler measures. Additional control measurements were obtained for noise-exposed and control groups with laser Doppler measures obtained from the obex, a brainstem structure with no known auditory function. Arterioles of the DCN showed a low-frequency oscillatory pattern of red blood cell velocity in control animals and in baseline conditions of the noise-exposure group. Presentation of noise abolished these velocity oscillations. Additionally, significant decreases in both red blood cell velocity and vessel diameter were measured during stimulation. These microvascular measures recovered slightly during the post-stimulus period. Laser Doppler measures of the overall blood flow in the nucleus were consistent with IVM findings. Measurements from DCN and obex in groups not exposed to noise, and animals exposed to noise and measured from the obex, showed stable oscillatory flow. These data show exposure to noise eliminates oscillatory patterns of blood flow and induces decreases in vascular perfusion. Furthermore, these changes appear specific to the auditory structure studied.

The effect of respiratory and lactic acidosis on diaphragm function

The relative effects of respiratory and metabolic acidosis on diaphragm function are not known. To determine these effects, we compared the effects of respiratory and lactic acidosis on the contractile properties of the diaphragm. We estimated diaphragmatic performance from the change in transdiaphragmatic pressure after supramaximal stimulation of the phrenic nerves in an open-chested, casted-abdomen dog. Similarly, we stimulated the gastrocnemius motor nerve and examined force production and relaxation rate to determine if there was a difference in the response of this skeletal muscle. There was a fall in diaphragm performance with respiratory acidosis (77.1 +/- 16.9 cm H2O versus 93.8 +/- 15.0 cm H2O baseline), but not with lactic acidosis (96.7 +/- 15.7 cm H2O versus 93.8 +/- 15.0 cm H2O baseline); and the gastrocnemius was unaffected by either acidosis. The changes with respiratory acidosis were similar to those seen with diaphragmatic fatigue and had similar relaxation rate changes, suggesting that intracellular pH may play a mechanistic role in respiratory muscle fatigue. In addition, the absence of a respiratory acidosis effect on a non-diaphragmatic skeletal muscle's function represents another physiologic difference between the diaphragm and other skeletal muscles.