Influence of isocapnic hyperpnoea on maximal arm cranking performance

Isocapnic hyperpnoea has been shown to reliably produce fatigue of the diaphragm. The aim of the present study was to investigate whether incremental isocapnic hyperpnoea (IH_incr) impairs the arm exercise performance and alters the breathing pattern during subsequent maximal incremental arm cranking. Nine healthy volunteers performed an arm cranking test with prior IH_incr (AC_IH) and without prior IH_incr (AC_control). Minute ventilation (V_̇E), tidal volume (V_T), breathing frequency (f_b), O₂ uptake (O₂), CO₂ elimination (CO₂), respiratory exchange ratio (RER) and end-tidal partial pressure of CO₂ (P_ETCO₂) were measured at three different time intervals (t₁: the average of the 3.30th min to the 6.30th min, t₂: 1 min before the end, t₃: peak value) and expressed as mean (SD). V_T at t₁ and at t₃ was significantly (P<0.05) lower during AC_IH [AC_control: t₁: 1.3 (0.5) l, t_p: 1.9 (0.3) l; AC_IH: t₁: 1.1 (0.3) l, t_p: 1.6 (0.3) l]. f_b at t₁ and t₂ was significantly (P<0.05) higher during AC_IH [AC_control: t₁: 23 (4) breaths min^–1, t₂: 42 (14) breaths min^–1; AC_IH: t₁: 27 (5) breaths min^–1, t₂: 48 (14) breaths min^–1]. The maximal voluntary ventilation (MVV), measured before and immediately after the IH_incr, demonstrated a small but significant decrease from 157 (15) l min^–1 to 150 (14) l min^–1 (P<0.05) after the IH_incr. In conclusion, rapid shallow breathing occurred during maximal arm cranking exercise after IH_incr. The alteration was irrespective of the workload and had already occurred at the start of exercise.