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1. After a 4 min period of maximal exercise in 10 normal subjects (14 studies), there was a consistent decrease in total blood volume and a consistent increase in erythrocyte indices, which were maximal immediately after exercise. Peripheral platelet and leucocyte counts increased, but did not reach maximal values until 5-10 min after the end of exercise. 2. The distributions of 99mTc-labelled erythrocytes (five studies), 111In-labelled platelets (five studies) and 111In-labelled granulocytes (four studies) were monitored with a gamma-camera immediately after injection and before and after maximal exercise performed 60 min after injection. 3. Labelled erythrocytes equilibrated rapidly between the spleen and circulating blood after injection, whereas labelled platelets and granulocytes equilibrated more slowly. After exercise, each cell type was released from the spleen with a time course that was the reciprocal of the time course of the corresponding cell count in peripheral blood. Thus, whereas the radioactivity of 99mTc-labelled erythrocytes in the spleen, which fell to 0.46 (SD 0.09) of the pre-exercise value, increased towards its baseline value as soon as exercise was completed, the radioactivities of 111In-labelled platelets and 111In-labelled granulocytes decreased, to respective minimum values of 0.61 (0.09) and 0.63 (0.09) of the pre-exercise levels, 5-10 min after the end of exercise. The exercise-induced changes in lung radioactivity for each cell type, and their time courses, broadly reflected those in the corresponding cell counts in peripheral blood. Liver radioactivity tended to decrease for each cell type.(ABSTRACT TRUNCATED AT 250 WORDS)

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The benefits of inhaled therapy in ventilated neonates are recognized, but the reliability of drug delivery in nebulizer-ventilator circuits is uncertain. We quantified the effect of changing variables. Twenty-three freshly killed rabbits (1.15-1.9 kg) were ventilated via a tracheostomy by a pressure-limited, time-cycled ventilator (Neovent). A radioaerosol of 99Tcm pertechnetate from an Ultravent nebulizer (Mallinkrodt) was fed into the proximal ventilator tubing. Two 3-minute nebulizations at "standard settings" were followed by 2 at altered pressure, frequency, gas flow, I:E ratio, or position of the nebulizer in the circuit. Each nebulization was followed by a 3-minute gamma camera image and total deposited radioactivity was measured in excised lungs and trachea. Images demonstrated good peripheral aerosol deposition. At standard settings, lung deposition averaged 2.8% of the aerosol released. This was decreased markedly by reducing tidal volume (ventilator pressures) and residence time of aerosol (I:E ratio). Reduced gas flow decreased deposition slightly, presumably by increased particle size and marginally reduced tidal volume. Deposition did not change with increased frequency; increased minute ventilation was offset by decreased residence time of the aerosol. We conclude that the Ultravent nebulizer can be used to nebulize drugs in a standard neonatal circuit, although the dose delivered is small. Tidal volume and aerosol residence time are important determinants of aerosol delivery.