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. 2021 Jun 11;16(6):e0252916.
doi: 10.1371/journal.pone.0252916. eCollection 2021.

Pulmonary function with expiratory resistive loading in healthy volunteers

Jyotika Erram  1 , Monica Bari  1 , Antoinette Domingo  1 , Daniel T Cannon  1
Affiliations

Pulmonary function with expiratory resistive loading in healthy volunteers

Jyotika Erram et al. PLoS One. .

Abstract

Expiratory flow limitation is a key characteristic in obstructive pulmonary diseases. To study abnormal lung mechanics isolated from heterogeneities of obstructive disease, we measured pulmonary function in healthy adults with expiratory loading. Thirty-seven volunteers (25±5 yr) completed spirometry and body plethysmography under control and threshold expiratory loading of 7, 11 cmH2O, and a subset at 20 cmH2O (n = 11). We analyzed the shape of the flow-volume relationship with rectangular area ratio (RAR; Ma et al., Respir Med 2010). Airway resistance was increased (p<0.0001) with 7 and 11 cmH2O loading vs control (9.20±1.02 and 11.76±1.68 vs. 2.53± 0.80 cmH2O/L/s). RAR was reduced (p = 0.0319) in loading vs control (0.45±0.07 and 0.47±0.09L vs. 0.48±0.08). FEV1 was reduced (p<0.0001) in loading vs control (3.24±0.81 and 3.23±0.80 vs. 4.04±1.05 L). FVC was reduced (p<0.0001) in loading vs control (4.11±1.01 and 4.14±1.03 vs. 5.03±1.34 L). Peak expiratory flow (PEF) was reduced (p<0.0001) in loading vs control (6.03±1.67 and 6.02±1.84 vs. 8.50±2.81 L/s). FEV1/FVC (p<0.0068) was not clinically significant and FRC (p = 0.4) was not different in loading vs control. Supra-physiologic loading at 20 cmH2O did not result in further limitation. Expiratory loading reduced FEV1, FVC, PEF, but there were no clinically meaningful differences in FEV1/FVC, FRC, or RAR. Imposed expiratory loading likely leads to high airway pressures that resist dynamic airway compression. Thus, a concave expiratory flow-volume relationship was consistently absent-a key limitation for model comparison with pulmonary function in COPD. Threshold loading may be a useful strategy to increase work of breathing or induce dynamic hyperinflation.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Spirometry variables with and without expiratory loading.
Panel A: Forced vital capacity (FVC) was lower with 7 and 11 cmH2O of loading vs control (F[1.495, 55.31] = 77.71, p<0.05). Panel B: Forced expired volume in 1 s (FEV1) was lower with 7 and 11 cmH2O of loading vs control (F[1.632, 60.38] = 67.54, p<0.05). Panel C: FEV1/FVC was lower with 7 and 11 cmH2O of loading vs control (F[1.870, 69.17] = 5.553, p<0.05). Panel D: Peak expiratory flow (PEF) was lower with 7 and 11 cmH2O of loading vs control (F[1.513, 55.99] = 72.69, p<0.05). *Post hoc test showing different from control (p<0.05).
Fig 2
Fig 2. Spirometry data for volunteers with additional imposed expiratory loading of 20 cmH2O (n = 11).
Panel A: FVC was reduced with expiratory resistance (F[1.4, 14.4] = 23.6, p<0.05). Panel B: FEV1 was reduced with expiratory resistance (F[2.0, 20.4] = 17.6, p<0.05). Panel C: FEV1/FVC was reduced with expiratory resistance (F[2.3, 22.6] = 3.9, p<0.05). Panel D: PEF was reduced with expiratory resistance (F[1.3, 13.2] = 22.0, p<0.05). *Different from control (p<0.05).
Fig 3
Fig 3. Rectangular area ratio group data and a representative participant.
Panel A Rectangular Area Ratio (RAR) measured with and without imposed expiratory loading (F[1.855, 77.90] = 3.711, p<0.05). Panel B A representative participant without any loading in which the RAR = 0.54. Panel C The same participant in which the loading of 7 cmH2O resulted in RAR = 0.49. Panel D The same participant in which the flow-volume relationship was at 11 cmH2O loading resulted in RAR = 0.45. *Different from control (p<0.05).
Fig 4
Fig 4. Airway resistance (Raw).
Panel A Airway resistance (Raw) measured with and without imposed expiratory loading (F[1.531, 27.55] = 446.0, p<0.05). Panel B ΔRaw represents Raw with the control values subtracted (t[18] = 10.18, p<0.05). *Different from control (p<0.05).
Fig 5
Fig 5. FRC measured with and without imposed expiratory loading.
Fig 6
Fig 6. Rectangular Area Ratio (RAR) vs individual primary pulmonary function variables measured with and without imposed expiratory loading.
Panels C, D, F show a correlation but one that is of no clinical importance. Pearson, p value, and where appropriate the coefficient of determination is included on the figures.
Fig 7
Fig 7. Rectangular Area Ratio (RAR) vs airway resistance variables with and without imposed expiratory resistance.
Panels A and B show no correlation between the variables.
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