Maximum voluntary ventilation as a sensitive measure to monitor the ventilatory function in cervical spondylotic myelopathy
Study design:A prospective clinical cohort study.Objectives:To test if maximum voluntary ventilation (MVV), which is currently underutilized in diseases, serves for assessing subclinical ventilatory impairment in cervical spondylotic myelopathy (CSM).Setting:Kochi Medical School, Japan.Methods:We studied ventilatory function in 49 CSM patients and 20 age- and sex-matched control patients with either lumbar stenosis or lower limb osteoarthritis. All patients underwent ventilatory function studies consisting of flow volume curves, vital capacity (VC) and the MVV in 12 s before and after surgery. Tetraparesis was assessed by the functional scale of the Japanese Orthopaedic Association (JOA).Results:The CSM group had significantly smaller %forced VC , %peak expiratory flow rate (%PEFR) and %MVV than the control group preoperatively. In contrast to the control group, the CSM group showed a significant increase in %MVV from 74.9±18.7% preoperatively to 80.3±19.0% postoperatively (P<0.005), but not in any other ventilatory measures. This postoperative increase in %MVV significantly correlated with the JOA score (r=0.493; P<0.001). As a possible effect of diaphragmatic recovery, the %PEFR significantly increased postoperatively only in patients with the primary site of involvement at or rostral to C3–4.Conclusion:Of the various ventilatory measurements, MVV was most sensitive to changes in tetraparesis in CSM, presumably because MVV, unlike the other ventilatory measures, reflects the coordination in addition to the strength of respiratory muscles.