Article

OBJECTIVE: To study the effect of posture on the hypercapnic ventilatory
responses (HCVR). DESIGN: Nonrandomized controlled study. SETTING: Rehabilitation
hospital and a pulmonary institute. PARTICIPANTS: Patients with neurologically
stable C(5-8) tetraplegia (n=12) and healthy control subjects (n=7).
INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Supine and seated forced
vital capacity (FVC) and HCVR, and supine and erect blood pressure. RESULTS: FVC
in the sitting position was reduced in patients with tetraplegia (52+/-13%
predicted); supine FVC was 21% higher (P=.0005). In the sitting position, HCVR
was lower in patients than in controls (0.8+/-0.4 vs 2.46+/-0.3 L/min/mmHg,
P<.001). Supine HCVR was not significantly different between the groups. When
HCVR was normalized to FVC, there was still a significant difference between
patients and controls in the sitting position. Patients with tetraplegia were
orthostatic (mean supine blood pressure 91+/-13 mmHg vs mean erect blood pressure
61+/-13 mmHg, respectively, P<.0001). The magnitude of the orthostatism
correlated with that of the postural change in HCVR (r=.93, P<.0001).
CONCLUSIONS: Respiratory muscle weakness may contribute to the attenuated HCVR in
tetraplegia. However, the observation that supine HCVR is still low even when
normalized to FVC suggests a central posture-dependent effect on the HCVR, which
may be linked to the postural effect on arterial blood pressure.

Langue : ANGLAIS