One unit (500 ml) of 10% Intralipid (an intravenous soy bean oil-egg yolk lecithin preparation) was infused into 20 normal subjects over 4 hr. Serum triglyceride concentration and plasma optic density (at 700 nm) increased to maximal levels of 339 +/- 102 mg/100 ml and 1.14 +/- 0.41, respectively, at the completion of the infusion, and returned to basal levels in most subjects within 4 hr. Pulmonary membrane diffusion was decreased in six subjects at rest and with exercise at 25 and 50% maximum oxygen uptake. Only one subject showed a minor change in PO2 and none showed clinical signs of ischemia. The changes in pulmonary diffusion reverted to basal levels when serum lipids were cleared. Heparin (60 IU/kg) prevented the marked increase in serum lipids and, as a consequence, the changes in pulmonary function. Changes in pulmonary function from Intralipid-induced lipemia are similar to those known to result from diet-induced lipemia. The findings suggest that in the presence of normal vasculature and pulmonary function, Intralipid-induced lipemia should cause no clinical consequences. However, patients with preexisting pulmonary or vascular disease may be at greater risk after Intralipid-induced lipemia.
The diffusing capacity of the homogeneous lung for carbon monoxide differs when measured by the steady state and single breath methods. Jones and Meade [1961] showed that measured single breath DLCOSB is too large by about 20% if time delays caused by breathing pattern effects are ignored. Here it is shown that measured DCLOSS using the Bohr method is too small by as much as 25% because of similar breathing pattern effects. Steady state and single breath experiments on normal subjects produce close agreement between adjusted values, suggesting that the homogeneous lung at rest is characterized by the same 'actual' DLCO parameter in both methods.The adjustment to DLCOSS depends on two important features ofthe periodic breathing pattern: (1) an 'effective' breath-holding time and (2) the diffusing capacity per unit volume averaged over a cycle. These correspond to T and k of the single breath method.The theoretical conclusions are based on steady state analysis of a homogeneous lung model. The dead space has fixed volume and plug flow. A lumped diffusion parameter DLCO characterizes the alveolar compartment. Alveolar CO concentration and volume are time dependent. Breathing patterns which were modelled were the square-wave (the periodic equivalent of the single breath method), the ramp and the ramp with a pause at the end of expiration. The latter closely approximates spontaneous breathing patterns which were measured.
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