Time course of lipid‐laden pulmonary macrophages with acute and recurrent milk aspiration in rabbits

Abstract

High levels of lipid-laden macrophages (LLM) in bronchial washings have been associated with food aspiration. We studied the time course of appearance and clearance of LLM in rabbits undergoing either a single milk instillation, five weekly milk instillations or saline (control) instillations into the airways. Cells were obtained by bronchoalveolar lavage of intubated rabbits at uniform time intervals following the single or the last of five milk/saline instillations. LLM semi-quantitative indexes were derived using oil-red-O staining. Significantly elevated indexes were found in both milk groups 6 hr after milk instillation. In the single saline and milk instillation groups the indexes were not different beginning on the 4th day, and indexes from 8 of 9 rabbits had returned to baseline by the 6th day. However, indexes remained significantly elevated up to 17 days in the group receiving weekly milk instillations. Indexes from all rabbits in the repeat milk instillation group remained elevated for 12 days or longer. This group also developed increased numbers of binucleated macrophages. Quantitation of LLM in this model appears to be a sensitive indicator of recurrent lipid aspiration, these cells remaining in the airways for several days after the last aspiration event.

Lipid-laden macrophages in bronchoalveolar lavage fluid as a marker for pulmonary aspiration

“…The elevated LLM indices decrease to normal values within 2-4 days after a single milk aspiration, whereas recurrent aspiration leads to increased fat content of alveolar macrophages that lasts approximately 12 days. 8 Whether this time course of lipid metabolism by pulmonary macrophages is the same for endogenous lipids, which are likely to play a pertinent role in pulmonary diseases independent of aspiration, is unknown. However, we speculate that ingestion of endogenous lipids by macrophages occurs at the same rate as the ingestion of exogenous lipid; however, normalization of LLM indices may take longer in patients with pulmonary disease because of decreased clearance of mucus and macrophages.…”

“…The reference population of children without bronchopulmonary disease was described in detail elsewhere. 8 Briefly, all children were undergoing elective surgery for nonpulmonary illnesses under general anesthesia. 9 Children with respiratory symptoms such as recent or current upper or lower respiratory tract infection, a history of hyperreactive airway disease, or other atopic symptoms were excluded.…”

“…As gastric contents often contain lipid material that will be taken up by macrophages if introduced into the respiratory system, it has been postulated that the lipid content of alveolar macrophages may be a useful indicator for pulmonary aspiration. [1][2][3][4][5][6][7][8] With the availability of flexible bronchoscopes, bronchoalveolar lavage (BAL) is increasingly used in the investigation of pulmonary diseases in children.…”

Charcoal Is a Sensitive, Specific, and Stable Marker for the Diagnosis of Aspiration in Hamsters

“…One hundred macrophages were blindly counted after oil red O staining, each assigned a grade of 0 -4 according to the criteria of Colombo et al (7), the LLAM index being the sum, with a potential maximum of 400. The criteria for LLAM grading were 0, no red staining; 1, up to 25% of the cytoplasm opacified; 2, up to 50% opacified; 3, up to 75% opacified; and 4, totally opacified.…”

Advances in the diagnosis and management of chronic pulmonary aspiration in children

“…An LLMI may also vary depending on the amount of time since the last aspiration event. In an animal study using rabbits [56], the LLMI remained above 75 for 2 days in animals receiving a single tracheal instillation of milk and 5 days in animals having received weekly instillations.…”