Breathing Pattern and Ventilatory Control in Chronic Tetraplegia

Blunted ventilatory responses to carbon dioxide indicate that respiratory control is impaired when ventilation is stimulated in individuals with tetraplegia; however, respiratory control during resting breathing has not been extensively studied in this population. Our objective was to evaluate respiratory control and sigh frequency during resting breathing in persons with tetraplegia. A prospective, two-group comparative study was performed. Breathing pattern was assessed in ten outpatients with chronic tetraplegia and eight age- and gender-matched able-bodied controls. Subjects were noninvasively monitored for 1 h, while seated and at rest. Tidal volume (VT) was calculated from the sum of the anteroposterior displacements of the rib cage and abdomen and the axial displacement of the chest wall. Inspiratory time (TI), VT, and the ratio of VT to inspiratory time (VT/TI) were calculated breath by breath. A sigh was defined as any breath greater than two or more times an individual's mean VT. Minute ventilation, VT/TI, and sigh frequency were reduced in tetraplegia compared with controls (5.24 ± 1.15 vs. 7.16 ± 1.29 L/min, P < 0.005; 208 ± 45 vs. 284 ± 47 ml/s, P < 0.005; and 11 ± 7 vs. 42 ± 19 sighs/h, P < 0.0005, respectively). VT/TI was associated with sigh frequency in both groups (tetraplegia: R = 0.88; P = 0.001 and control: R = 0.70; P < 0.05). We concluded that reductions in minute ventilation, VT/TI, and sigh frequency suggest that respiratory drive is diminished during resting breathing in subjects with tetraplegia. These findings extend prior observations of disordered respiratory control during breathing stimulated by CO₂ in tetraplegia to resting breathing.