Exertional dyspnea in older adults: the effects of mechanical unloading of the thorax.

Age-related changes in respiratory function that constrain ventilatory capacity could contribute to dyspnea on exertion (DOE) in older adults. However, whether mechanically unloading the thorax using an external cuirass device could reduce ventilatory constraints during exercise and decrease DOE in older adults is unknown. All participants (n = 39) performed two 6 min constant-load cycling tests: one without the cuirass (CTL) and one with -20cmH2O of continuous negative pressure (CNP-20). We measured ratings of perceived breathlessness (RPB), the exercise ventilatory response (V̇E/V̇CO2 slope), and end-expiratory (EELV) and end-inspiratory (EILV) lung volume. Following 6 min of cycling, n = 24 rated RPB ≤ 2 (-DOE: 71 ± 3 yr, 28 ± 5 kg/m2) and n = 15 rated RPB ≥ 3 (+ DOE, 70 ± 3 yr, 28 ± 8 kg/m2). During CTL, the + DOE group had a higher V̇E/V̇CO2 slope (-DOE: 30.1 ± 4.9; + DOE: 34.0 ± 4.7, p = 0.018), while PETCO2 was not different (-DOE: 42 ± 4; + DOE: 42 ± 3 mmHg, p = 0.816). CNP-20 decreased RPB in + DOE (Δ-1.5 ± 1.5, p = 0.002) but not -DOE (Δ0.4 ± 1.2, p = 0.116). CNP-20 increased EILV (-DOE: Δ3 ± 4%TLC, p = 0.006; + DOE: Δ4 ± 4%TLC, p = 0.001) and EELV (-DOE: Δ3 ± 3%TLC, p < 0.001; + DOE: Δ2 ± 3%TLC, p = 0.009) in both groups irrespective of DOE status. However, CNP-20 decreased the V̇E/V̇CO2 slope in + DOE (Δ -2.2 ± 3.2, p = 0.019) alone. An increased ventilatory response to exercise could explain why some older adults exhibit moderate to severe levels of exertional dyspnea. Although mechanically unloading the thorax shifted operational lung volumes, it could also attenuate the ventilatory response to exercise. Collectively, DOE in older adults may be driven by a complex interaction between altered respiratory mechanics and increased ventilatory response to exercise.