RELIEF OF THE AIR HUNGER OF BREATHHOLDING - A ROLE FOR PULMONARY STRETCH RECEPTORS

Fowler (Fowler, W.S., 1954, J. Appl. Physiol. 6:539-545) showed that r ebreathing, despite worsening P-CO2 and O-2 saturation, relieved the d istress of breathholding; he suggested a role for vagal input in the r elief. We studied effects on respiratory sensation of breathholding an d rebreathing in normals, patients with bilateral lung transplants (LT ), who have a decrease in number of pulmonary stretch receptors (PSR), and heart transplant recipients (HT). Subjects held their breath unti l distress became intolerable, rebreathed various combinations of CO2 and O-2, then performed another maximal breathhold. Respiratory distre ss was rated continuously (visual analog scale) by each subject. Both LT and HT had earlier onset of and more rapidly developing distress du ring breathholding, resulting in shorter breathhold times, than normal s. Relief with rebreathing was neither as rapid nor as great in LT as in HT and normals. Our findings suggest that mechanisms that produce r espiratory distress in HT and LT are similar, but differ from normals. However, reduction in distress on rebreathing is more rapid and great er in HT and normals than in LT. This is compatible with the loss duri ng rebreathing of the inhibitory effect of PSR input on neural mechani sms that lead to respiratory distress.