The mean power function exponent for mouth pressure during elastic loading was similar in patients (1.02 ±0.67) and control subjects (0.74 ±0.71) (p = 0.36) (Fig 1). Because of the wide range of exponents exhibited by the patients, we considered whether two distinct subgroups existed in the ILD patients based on the exponent for added elastic loads. We compared anthropometric, lung function, exercise and dyspnea measures between 11 patients with an exponent >1 and nine patients with an exponent <1. Of the variables examined, only age differed significantly between the two subgroups. Patients with an exponent >1 were younger in age (53 ±14 years) compared with those with an exponent <1 (66 ±11 years) (p = 0.03).
The mean power function exponent for the heaviness of weights was nearly identical in both the patient (1.77 ± 0.55) and control groups (1.72 ± 0.53) (p = 0.85) (Fig 2). There was no significant correlation between exponents for the perception of elastic loading and for weight discrimination either in the patient group (rs=—0.18; p = 0.45) or in the control group (r8=-0.16; p = 0.65).
Correlations computed among values for magnitude scaling, lung function, exercise parameters and clinical dyspnea ratings for ILD patients are listed in Table 2. Clinical ratings of breathlessness were not significantly related to magnitude scaling of added elastic loads. However, significant correlations were observed between clinical dyspnea ratings and Dsb, peak Vo2 and ASaCVAVcv Specifically, scores from both the MRC scale and the BDI were reliably related to Dsb; scores on each of the three clinical instruments were significantly correlated with peak Vo2; and the BDI score was reliably related to ASa(VAVo2. Additional statistical analyses conducted in 13 patients with a comparable diagnosis (idiopathic pulmonary fibrosis and ILD due to connective tissue disease) showed results which were similar for the entire group of ILD patients.
Figure 1. Individual and mean (open circles with bars) exponents for mouth pressure for elastance breathing loads in normal subjects and in patients with ILD.
Figure 2. Individual and mean (open circles with bars) exponents for heaviness of lifting weights in normal subjects and in patients with ILD.
Table 2—Correlations among Values for Magnitude Scaling, Lung Function, Exercise Parameters and Clinical Dyspnea Ratings in Patients with ILD
|Variable||Clinical Dyspnea Ratings||Magnitude Scaling (Exponent for Mouth Pressure)|
|Exponent for mouth pressure||-0.02||-0.06||0.17|
|Peak Vo2 (n = 18)||— 0.75t||0.72t||0.841*||0.30|
|ASaOj/AVo* (n = 18)||0.32||-0.39||-0.49t||-0.29|