Effects of Respiratory Training on Heart Rate Variability and Baroreflex Sensitivity in Individuals With Chronic Spinal Cord Injury

Abstract

ObjectiveTo evaluate the effects of pressure threshold respiratory training (RT) on heart rate variability and baroreflex sensitivity in persons with chronic spinal cord injury (SCI). DesignBefore-after intervention case-controlled clinical study. SettingSCI research center and outpatient rehabilitation unit. ParticipantsParticipants (N=44) consisted of persons with chronic SCI ranging from C2 to T11 who participated in RT (n=24), and untrained control subjects with chronic SCI ranging from C2 to T9 (n=20). InterventionsA total of 21±2 RT sessions performed 5 days a week during a 4-week period using a combination of pressure threshold inspiratory and expiratory devices. Main Outcome MeasuresForced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), and beat-to-beat arterial blood pressure and heart rate changes during the 5-second-long maximum expiratory pressure maneuver (5s MEP) and the sit-up orthostatic stress test, acquired before and after the RT program. ResultsIn contrast to the untrained controls, individuals in the RT group experienced significantly increased FVC and FEV1 (both P<.01) in association with improved quality of sleep, cough, and speech. Sympathetically (phase II) and parasympathetically (phase IV) mediated baroreflex sensitivity both significantly (P<.05) increased during the 5s MEP. During the orthostatic stress test, improved autonomic control over heart rate was associated with significantly increased sympathetic and parasympathetic modulation (low- and high-frequency change: P<.01 and P<.05, respectively). ConclusionsInspiratory-expiratory pressure threshold RT is a promising technique to positively affect both respiratory and cardiovascular dysregulation observed in persons with chronic SCI.