Breathing Pattern and Ventilatory Control in Chronic Tetraplegia

Abstract

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 (V_T) 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 (T_I), V_T, and the ratio of V_T to inspiratory time (V_T/T_I) were calculated breath by breath. A sigh was defined as any breath greater than two or more times an individual’s mean V_T. Minute ventilation, V_T/T_I, 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). V_T/T_I 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, V_T/T_I, 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.