Frequency dependence of capnography in anesthetized rabbits.

Aspirative capnography may be of help to diagnose early childhood asthma, but clinical usefulness in young children is limited by the relatively high respiratory rate. This study aimed to characterize the [Formula: see text] time course during airway constriction in 8 anesthetized rabbits, artificially ventilated at 30, 60 and 80breaths/min. Methacholine was inhaled to double the respiratory resistance measured at 8Hz by the forced oscillation technique. The capnogram shape changed in response to both methacholine and ventilatory frequency. Slope of phase II, the peak of first-order time derivative and trough of the second-order time derivative of the [Formula: see text] signal, were significantly attenuated after methacholine compared with baseline at all breathing rates (p<0.02). Moreover, significant correlations between respiratory reactance and resistance were observed with the phase III slope and the angle described by phase II and phase III (p<0.01). It is concluded that capnography may be useful to identify acute airway changes related to bronchoconstriction, even at high breathing frequencies.

Functional consequences of isolated nerve stretch: experimental long-term static loading.

The maximum longitudinal tension that can be applied to the stumps of a divided peripheral nerve during surgical repair is not precisely defined. Uncertainty about the threshold of unacceptable nerve tension may be due to the lack of studies on isolated and reproducible stretch, i.e., on quantified elongation without concomitant compression, crush, or transection. The authors devised a simple method for producing isolated, long-term static loading of the nerve in vivo without concomitant compression, crush, or transection. Tension was applied to intact and crushed sciatic nerves in the rat, stretching them by 15 or 30 percent of their initial length, and the corresponding functional consequences were evaluated. Results showed that no measurable functional deficit resulted from stretching a segment of intact nerve to a length 30 percent greater than its initial length. In contrast, a significant delay in functional recovery resulted from stretching a crushed nerve by the same amount. A practical conclusion may be that the site of application of stretch forces during surgical repair, i.e., the location of coapting stitches, could play an important role in clinical practice.

The effects of dopamine infusion on regional blood flow in newborn lambs.

The purpose of this project was to investigate the effects of high rates of dopamine infusion on cardiac output and regional blood flow in the lamb. We studied eight unanesthetized newborn lambs (mean age 7 +/- 2 days) during a 15-min baseline period and while infusing dopamine at 5-, 20-, 80-, and 160 micrograms/kg/min. We measured cardiac output and mean aortic, pulmonary arterial and left atrial pressures, and organ blood flow using radionuclide-labeled microspheres at each rate of dopamine infusion. Cardiac output increased significantly with increasing rates of infusion up to 80 micrograms/kg/min but decreased at 160 micrograms/kg/min. Aortic, pulmonary arterial, and left atrial pressures increased at rates of infusion above 5 micrograms/kg/min. Blood flow to all organs was unchanged at the 5 micrograms/kg/min rate of infusion of dopamine while blood flow to the brain and heart increased at the 80 micrograms/kg/min rate of infusion and blood flow to the gut and kidney decreased. We conclude that dopamine is an effective inotropic agent in the newborn lamb but that an inotropic:afterload mismatch exists at high infusion rates. Despite an increase in cardiac output at low rates of infusion, dopamine did not selectively vasodilate the vascular bed of any organs tested. Furthermore, at high rates of infusion dopamine actually impaired blood flow to the gut and kidney.