The breathing patterns of identical twins.

The resting breathing patterns of healthy adult identical twins were compared to see if there was any possible genetic component in the determination of this pattern. From breath-by-breath analysis of airflow, measured with a pneumotachometer (9 pairs of twins), the pattern of breathing was quantified in terms of individual respiratory variables; inspiratory time (TI), expiratory time (TE), total breath duration (TTOT), VT/TI, TI/TTOT, and by taking TI, TE and VT all together (TRIAD). Also, the airflow shape was quantified by harmonic analysis (ASTER). A second study was performed under more strictly defined conditions of rest and where the respiratory variables were estimated with respiratory inductance plethysmography to eliminate the possible effect of a facemask (5 pairs of twins). In each study, for each variable, the differences within twin-pairs were compared to the differences within random-pairs from the same subject population. In both studies, there were highly significant similarities within twin-pairs in the pattern of breathing, being best demonstrated when the entire 'shape' of the pneumotachogram (ASTER) or the spirogram (TRIAD) was considered.