Impact of central hypercapnic chemosensitivity on enhanced ventilation in patients after the Fontan operation

Central hypercapnic chemosensitivity (Chemo) influences the enhanced ventilatory and sympathetic responses in heart failure patients; however, its influence on these responses in Fontan patients is unknown.

To measure Chemo and compare the results with rest and exercise ventilatory characteristics in Fontan patients.

We measured Chemo (l/min/mmHg), hemodynamics, pulmonary function, cardiac autonomic nervous and neurohumoral activities and compared the results with the ventilatory response during exercise in 42 Fontan patients and 12 referents. Chemo did not differ significantly between the Fontan patients (1.5 +/- 0.9) and referents (1.3 +/- 0.4). However, a higher Chemo in addition to lower resting arterial oxygen saturation (SaO(2)) and higher dead space ventilation (Vd/Vt) independently determined a higher resting minute ventilation (VE) and, except for the Chemo, these factors also independently determined the higher resting ventilatory equivalent for carbon dioxide output (VE/VCO(2)) (p<0.05-0.001). At peak exercise, the higher Chemo as well as the higher peak Vd/Vt and aerobic exercise capacity independently determined the higher peak VE and VE/VCO(2) (p<0.01-0.001). Among cardiac autonomic and neurohumoral activities, only the higher plasma norepinephrine concentration was associated with higher Chemo in Fontan patients (r=0.40, p<0.01) and age was correlated positively with Chemo in the high Chemo (> or =2.1) Fontan patients (n=10).

In addition to lower SaO(2) and higher Vd/Vt, an increased Chemo associated with sympathetic activation has a significant impact on accelerated rest and exercise ventilation in some Fontan patients, especially in adult patients.