Table 2

Association of parameters derived from peak expiratory flow with outcome (time to loss of control in days after steroid withdrawal)

Separate models*Combined models*
ParameterHR (95% CI)†p ValueHR (95% CI)†p Value
14 days prewithdrawal n=83
Mean AM PEF (l/min)0.998 (0.995 to 1.001)0.2691.000 (0.996 to 1.003)0.913
CV AM PEF (%)1.11 (1.02 to 1.21)0.0211.10 (1.00 to 1.22)0.060
AM PEF autocorrelation0.48 (0.11 to 2.04)0.3190.65 (0.13 to 3.34)0.609
Sign of autocorrelation0.83 (0.48 to 1.41)0.4790.91 (0.51 to 1.64)0.764
14 days postwithdrawal n=53
Mean AM PEF (l/min)0.995 (0.990 to 0.999)0.0260.996 (0.992 to 1.001)0.155
CV AM PEF (%)1.31 (1.12 to 1.53)0.0011.22 (1.02 to 1.47)0.032
AM PEF autocorrelation5.29 (0.97 to 28.97)0.0552.55 (0.33 to 20.0)0.371
Sign of autocorrelation1.39 (0.59 to 3.29)0.4561.26 (0.51 to 3.07)0.619
Post–pre difference n=53
Mean AM PEF (l/min)0.945 (0.923 to 0.968)<0.0010.955 (0.932 to 0.979)<0.001
CV AM PEF (%)1.46 (1.20 to 1.78)<0.0011.32 (1.06 to 1.65)0.013
AM PEF autocorrelation3.29 (0.79 to 13.64)0.1010.91 (0.21 to 3.88)0.902

  • ↵* All Cox regression models were adjusted for age, sex, height and steroid dose. In the separate models, the parameters of interest (mean, coefficient of variation (CV), magnitude and sign of autocorrelation) were examined separately. In the combined models they were included in the same regression model. The sign of the autocorrelation was not used when looking at post–pre changes in the parameters of interest.

  • ↵† HR (95% CI) from Cox regression, describing relative risk of loss of control per unit change (1 l/min for PEF, 1% for CV and 1 for autocorrelation) in the relevant parameter. For example, a HR of 1.32 for the CV parameter indicates there is a 1.32 times increase in risk of loss of control for every 1% change in the CV.

  • AM PEF, morning peak expiratory flow.