Steady-State Ventilatory Responses to Expiratory Resistive Loading in Quadriplegics

Abstract

Patients with quadriplegia have a limited capacity to recruit expiratory muscles and are deprived of respiratory-related feedback from the rib cage and abdominal wall. We wished to evaluate the compensatory strategies available to such patients during expiratory resistive loading (ERL) and to compare their responses with those of normal healthy individuals. In addition, to determine whether the quadriplegic subjects have a blunted sensory appreciation of added ERL, we also compared sensory detection thresholds (delta R50). Steady-state ventilatory responses to ERL (delta R = 12 cm H2O/L/s) were compared in seven quadriplegic patients (level of injury, C6, C7) and six age-matched normal subjects. Highly significant intergroup differences were evident in the extent of prolongation of expiratory time (TE) and total cycle duration (Ttot) during ERL; values of delta TE and delta Ttot in quadriplegics were, on average, 46% of those of normals (p < 0.001). Minute ventilation (VE) was defended to an equal or better extent in quadriplegics. ERL-induced changes in tidal volume, inspiratory duration, mean inspiratory and expiratory flows, and end-expiratory lung volume (EELV) were not significantly different. Average delta R50 in quadriplegics and normals were (mean +/- SD), 1.73 +/- 0.039 cm H2O/L/s and 1.62 +/- 0.4 cm H2O/L/s, respectively (p = ns). Quadriplegics, therefore, despite substantial sensory and motor deficits, defend ventilation and EELV as effectively as normal individuals and show no attenuation in the ability to detect an added expiratory resistance.

Respiratory Sensation and Ventilatory Mechanics during Induced Bronchoconstriction in Spontaneously Breathing Low Cervical Quadriplegia

“…Methacholine challenge tests were performed according to standardized protocols as previously described (1,2). Although prior experience indicates that individuals with quadriplegia can compensate as well as neurologically intact individuals to resistive loading (14), the following extra safety precautions were taken: a physician was in attendance at all times; the test was terminated if dyspnea became "severe" (5 on the Borg Scale) or FEV 1 decreased to 0.5 L; the nebulizer was driven by compressed oxygen to avoid oxygen desaturation; blood pressure was measured after each dose of methacholine to detect an autonomic reaction; and nebulized salbutamol and ipratropium bromide were immediately available.…”

“…However, conflicting results have been reported regarding the role of chest wall receptors in the perception of external resistive and elastic loads and volume change. Although sensory detection thresholds during expiratory resistive loading in quadriplegia are preserved, the quality of respiratory sensations differs from that of normal subjects (14). Detection thresholds for inspiratory resistive loading are impaired (increased) (9) and magnitude scaling of elastic and resistive loading is blunted (12) in quadriplegia, suggesting that chest wall receptors modulate the detection and intensity of respiratory sensations.…”

Anaesthesia for chronic spinal cord lesions

“…Tetraplegics achieve coughing by contraction of the clavicular portion of pectoralis major and this manoeuvre may be effective enough to cause dynamic airway compression [35]. Compensatory mechanisms are developed such that tetraplegics defend ventilation as well as normal subjects in the face of an expiratory resistance [36]. However, retention of secretions and atelectasis are common and ventilation/perfusion mismatch may occur.…”