Lung mechanics in individuals with spinal cord injury: effects of injury level and posture

Individuals with spinal cord injury (SCI) exhibit reduced lung volumes and flow rates as a result of respiratory muscle weakness. These features have not, however, been investigated in relation to the combined effects of injury level and posture. Changes in forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), FEV1/FVC, forced expiratory flow at 50% vital capacity (FEF50) inspiratory capacity (IC), and expiratory reserve volume (ERV) were assessed by injury level in the seated and supine positions in 74 individuals with SCI. The main findings were 1) FVC, FEV1 and IC increased with descending SCI level down to T-10, below which they tended to level off; 2) supine values of FVC and FEV1 tended to be larger in the supine compared with the seated posture down to injury level T-1, caudad to which they were less than when seated; 3) IC increased proportionately more down to injury level L-1, below which it declined slightly and plateaued; 4) ERV was measurable even at high cervical injuries, was generally smaller in the supine position, reached peak values in both positions at T-10 injury level, and then rapidly declined at lower levels; 5) when subjects were separated according to current, former, and never smokers, only formerly smoking paraplegic individuals demonstrated spirometric values significantly less than paraplegic individuals who never smoked. Changes in spirometric measurements in SCI are dependent on injury level and posture. These findings support the concept that the increase in vital capacity in supine position is related to the effect of gravity on abdominal contents and increase in IC.