Nevertheless, in the study conducted by O’Donnell et
al., the correlation between the magnitude of the
changes in the IC and Borg scores was strong, and they
concluded that this explained why dynamic hyperinflation
was causing dyspnea. However, correlations in
cross-sectional studies and longitudinal studies do not
necessarily match, and a statistical approach such as
correlation coefficients may not resolve this issue. Airflow
limitation causes dynamic hyperinflation, and
hence airflow limitation, dynamic hyperinflation and
dyspnea may be considered as the top of a pyramid, and
it may not be necessary to consider them in a linear,
causal relationship.