Intra-individual variation of particles in exhaled air and of the contents of Surfactant protein A and albumin

PLoS One. 2020 Jan 24;15(1):e0227980. doi: 10.1371/journal.pone.0227980. eCollection 2020.


Introduction: Particles in exhaled air (PEx) provide samples of respiratory tract lining fluid from small airways containing, for example, Surfactant protein A (SP-A) and albumin, potential biomarkers of small airway disease. We hypothesized that there are differences between morning, noon, and afternoon measurements and that the variability of repeated measurements is larger between days than within days.

Methods: PEx was obtained in sixteen healthy non-smoking adults on 11 occasions, within one day and between days. SP-A and albumin were quantified by ELISA. The coefficient of repeatability (CR), intraclass correlation coefficient (ICC), and coefficient of variation (CV) were used to assess the variation of repeated measurements.

Results: SP-A and albumin increased significantly from morning towards the noon and afternoon by 13% and 25% on average, respectively, whereas PEx number concentration and particle mean mass did not differ significantly between the morning, noon and afternoon. Between-day CRs were not larger than within-day CRs.

Conclusions: Time of the day influences the contents of SP-A and albumin in exhaled particles. The variation of repeated measurements was rather high but was not influenced by the time intervals between measurements.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Air / analysis
  • Albumins / isolation & purification*
  • Albumins / metabolism
  • Biomarkers / chemistry
  • Breath Tests
  • Exhalation / physiology
  • Female
  • Healthy Volunteers
  • Humans
  • Male
  • Middle Aged
  • Pulmonary Disease, Chronic Obstructive / diagnosis*
  • Pulmonary Disease, Chronic Obstructive / metabolism
  • Pulmonary Disease, Chronic Obstructive / pathology
  • Pulmonary Surfactant-Associated Protein A / isolation & purification*
  • Pulmonary Surfactant-Associated Protein A / metabolism
  • Respiratory System / chemistry*
  • Respiratory System / metabolism
  • Spirometry / methods


  • Albumins
  • Biomarkers
  • Pulmonary Surfactant-Associated Protein A

Supplementary concepts

  • Pulmonary Disease, Chronic Obstructive, Severe Early-Onset

Grant support

This research was supported by the Swedish Heart-Lung Foundation (ACO, grant number 20180209). The funder had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.