Comparison of cardiac output determinants in response to progressive upright and supine exercise in cystic fibrosis patients

This study was designed to characterize the cardiac output (Q$ sb{ rm c}$) response to progressive submaximal upright (U) exercise in CF patients. Secondly, the Q$ sb{ rm c}$ adjustments were compared to those of similar supine (S) exercise, in an attempt to assess myocardial accommodation to the enhanced ventricular preload in the S posture. Q$ sb{ rm c}$ generally increased with exercise intensity in both U and S positions, although gr.IV plateaued at 50% VO$ sb2$max (S). Maximal stroke volume index (SI) was achieved at 50% VO$ sb2$max (U) in all groups, except gr.IV and at 30% VO$ sb2$max (S) in all groups. The change from U to S posture resulted in a significant (p $ le$.05) increase in SI at rest and for every submaximal exercise in gr.I, but not in CF patients, independent of disease severity eg(Rest:gr.I:27 $ pm$ 7(U) vs 39 $ pm$ 8(S); gr.II:24 $ pm$ 5vs28 $ pm$ 10; gr.III:18 $ pm$ 4 vs 22 $ pm$ 5; gr.IV:17 $ pm$ 4 vs 20 $ pm$ 6 ml/bt/m$ sp2$). These observations suggest a limitation in ventricular volume accommodation in CF patients which becomes apparent under the S exercise conditions