Ventilation and Breathing Pattern during Progressive Hypercapnia and Hypoxia after Human Heart-Lung Transplantation

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Abstract
The effects of human pulmonary denervation on the ventilatory responses to progressive hyperoxic hypercapnia and isocapnic hypoxia as well as the effect on resting breathing pattern were evaluated in nine female heart-lung transplant (H-LT) recipients. The results were compared to those obtained from 10 normal women of comparable age and stature. Testing was performed 2 to 37 months after H-LT (median, 7.5 months). Cardiac function was normal in all H-LT recipients. None of the patients had spirometric evidence of airway obstruction, while six had a restrictive pattern with forced vital capacities < 80% of predicted values. Resting minute ventilation (.ovrhdot.VE), tidal volume (VT), and ventilatory drive (VT/TI) in the H-LT recipients were not significantly different from those of the normal subjects. Inspiratory time (TI), however, was significantly shorter in the H-LT patients (1.64 .+-. 0.2 versus 2.09 .+-. 0.13 s, p = 0.035), and resting breathing frequency (F) tended to be greater in the H-LT recipients (16.27 .+-. 2.04 versus 12.82 .+-. 0.53 breaths/min, p = 0.052). The overall ventilatory response to hypercapnia was reduced after H-LT (0.91 .+-. 0.17 versus 1.5 .+-. 0.27 L/min/mm Hg Co2, p < 0.043), as was the F response (0.2 .+-. 0.09 versus 0.65 .+-. 0.13 breaths/min/mm Hg CO2, p < 0.01). The VT and VT/TI responses to hypercapnia did not differ between the H-LT recipients and normal subjects. There were no significant differences between the two groups with respect to the responses to progressive hypoxia. We conclude that pulmonary denervation in our H-LT patients is associated with a reduction in hypercapnic chemosensitivity as a result of altered ventilatory timing with a blunted F response.