Regulation of breathholding time and sensation after heart-lung transplantation

To assess whether pulmonary vagal afferents affect the duration of breathholding, the associated respiratory distress and their dependence on lung volume, we studied seven heart-lung transplant (HLT) patients with chronic pulmonary denervation and seven matched control subjects. Voluntary breathholds were performed at 20% and 80% vital capacity (VC) after rebreathing a 7% CO2-93% O2 gas mixture. Time to breakpoint, oxygen saturation, and end-tidal PCO2 were measured. All subjects were questioned on their sensations during breathholding; in addition, quantitative assessment of the sensations was obtained using a visual analog scale (VAS) in the seven control subjects and four HLT subjects. Breathholding time was comparable in both groups at each lung volume but was invariably shorter (p < 0.0005) at 20% VC (mean +/- SD; HLT versus control subjects: 68 +/- 29 versus 79 +/- 29 s) than at 80% VC (corresponding values: 92 +/- 35 versus 103 +/- 30 s). Similar results were obtained after anesthesia of intact tracheal and upper airway receptors in five HLT subjects. Six subjects from each group spontaneously reported air hunger and found it easier to perform breathholding at 80% than at 20% VC. The VAS ratings generally showed a maximum score at breakpoint, which implies that the distress increased more rapidly at low than at high lung volume. We conclude that in the absence of vagal afferent innervation from the lungs: (1) the air hunger form of dyspnea is maintained; (2) the duration of breathholding is not substantially modified; and (3) breathholding time and sensations still vary as a function of lung volume.