Influence of respiratory loading on left-ventricular function in cervical spinal cord injury

Cervical spinal cord injury (C-SCI) negatively impacts cardiac and respiratory function. As the heart and lungs are linked via the pulmonary circuit these systems are interdependent. Here, we utilized inspiratory and expiratory loading to assess whether augmenting the respiratory pump improves left-ventricular (LV) tilling and output in individuals with motor-complete C-SCI. We hypothesized IN end-diastolic volume (LVEDV) would increase and decrease with inspiratory and expiratory loading, respectively. Participants (C-SCI: 7M/1F, 35 +/- 7 years; able-bodied: 7M/1F, 32 +/- 6 years) were assessed under live conditions during 45 degrees head-up tilt; unloaded, inspiratory loading with -10 and -20 cmH(2)O oesophageal pressure (P-oes) on inspiration, and expiratory loading with +10 and +20 cmH(2)O P-oes on expiration. An oesophageal balloon catheter monitored P-oes and LV structure and function were assessed by echocardiography. In C-SCI only, (1) +20 cmH(2)O reduced LVEDV vs. unloaded (81 +/- 15 vs. 88 +/- 11 ml, P = 0.006); (2) heart rate was higher during +20 cmH(2)O compared to unloaded (P = 0.001) and +10 cmH(2)O (P = 0.002); (3) cardiac output was higher during +20 cmH(2)O than unloaded (P = 0.002); and (4) end-expiratory lung volume was higher during +20 cmH(2)O vs. unloaded (63 +/- 10 vs. 55 +/- 13% total lung capacity, P = 0.003) but was unaffected by inspiratory loading. In both groups, -10 and -20 cmH(2)O had no significant effect on LVEDV. These findings suggest greater expiratory positive pressure acutely impairs I,V filling in C-SCI, potentially via impaired venous return, mediastinal constraint and/or direct ventricular interaction subsequent to dynamic hyperinflation. Inspiratory loading did not significantly improve LV function in C-SCI and neither inspiratory nor expiratory loading affected cardiac function or lung volumes in able-bodied participants.