Unravelling the relationship between functional capacity and physical activity in people with interstitial lung disease

Abstract

Functional capacity (FC) and functional performance are distinct domains of functional status. Low functional capacity (FC) is com-monly reported in people with interstitial lung disease (ILD). How-ever, the literature on functional performance - possible to be ob-jectively measured quantifying the physical activity (PA) levels - and on the relationship between FC and PA of this population is still scarce. Thus, this study aimed to: i) characterise the PA levels; ii) explore the relationship between FC and PA; and, iii) determine the distribution across the four quadrants of FC and PA of people with ILD. A retrospective cross-sectional study was conducted. PA levels were assessed with accelerometry (Actigraph® GT3X+), through steps/day and time spent in moderate-to-vigorous (MVPA) PA. Par-ticipants wore the Actigraph® for, at least, 4 consecutive days (7:00am-10:00pm). FC was assessed with the number of repetitions performed in the 1-minute-sit-to-stand (1-minSTS). PA levels were compared between three ILD diagnostic categories (i.e., fibrotic Hypersensitivity Pneumonitis [fHP], Idiopathic Pulmonary Fibrosis [IPF] and Connective Tissue Disease-related ILD [CTD-ILD]) and se-verity, using the ILD-GAP Index model (0-3, ≥ 4). U Mann-Whitney and Kruskal-Wallis tests were used to compare groups. Spearman’s Correlation was used to analyse the correlation between FC and PA. For the quadrants analysis, participants were divided into the fol-lowing: 1) low FC (1-minSTS < 70% predicted) and low PA (< 5,000 steps/day or < 150 min/week of MVPA) – “can’t do, don’t do”; 2) preserved FC (1-minSTS ≥ 70%), low PA (< 5,000 steps/day/< 150 min/week of MVPA) – “can do, don’t do”; 3) low FC (1-minSTS < 70% predicted), preserved PA (≥ 5,000 steps/day/ ≥ 150 min/week of MVPA) – “can’t do, do do”; 4) preserved FC (1-minSTS ≥ 70%), pre-served PA (≥ 5,000 steps/day/ ≥ 150 min/week of MVPA) – “can do, do do”. Forty-nine volunteers were included (68 [63-76] years; 23 [46.9%] male, FVC 84 [69-95]% predicted; DLCO 57 [40-73]% pre-dicted). PA levels ranged between 792-113,670 steps/day and 2-1,604 min. spent in MVPA. PA levels across ILD subtype were not different (p = 0.061-0.609) however, significant differences were found across disease severity (GAP0-3 = 41 GAP ≥ 4 = 8 steps/day p = 0.003, GAP0-3 = 41 GAP ≥ 4 = 8 MVPA p = 0.015). Significant, mod-erate and positive correlations were found between FC and PA for both, steps/day (rs = 0.53, p < 0.001) and MVPA (rs = 0.40, p = 0.005). Participants’ distribution on the FC and PA (steps/day) quad-rants was: 22 (45%) “can’t do, don’t do”; 7 (14%) “can do, don’t do”; 7 (14%) “can’t do, do do”; 13 (27%) “can do, do do”. Partici-pants’ distribution between FC and PA (MVPA) quadrants was: 20 (41%) “can’t do, don’t do”; 5 (10%) “can do, don’t do”; 9 (18%) “can’t do, do do”; 15 (31%) “can do, do do”. People with ILD tend to be physically inactive. PA levels decrease with ILD severity and there is a relationship between FC and PA in this population. Ap-plicability of the FC-PA quadrant may guide personalised interven-tions to optimise outcomes of these meaningful domains in ILD.