Cardiac parasympathetic activity and ventricular diastolic interactions in individuals with spinal cord injury
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STUDY DESIGN: Cohort cross-sectional study. OBJECTIVE: To investigate the relationship between cardiac vagal activity and left ventricular filling at rest and during vagal stimulation, via the cold face test (CFT), in individuals with spinal cord injury (SCI). SETTING: University-based laboratory at Brock University, St. Catharines, ON, Canada. METHODS: A total of 12 able-bodied (age: 40 ± 8.5 years) and 13 SCI individuals (age: 41 ± 8.5 years; C4-T6; AIS: A-D) were recruited. Cardiac parasympathetic activity was assessed via heart rate variability (HRV) while LV filling was assessed by conventional echocardiography. All indices of HRV and diastolic function were obtained at rest and during cardiac vagal stimulation via the CFT. RESULTS: At baseline, the able-bodied group demonstrated strong positive correlations between HRV and early diastolic filling; however, such correlations were absent in the SCI group. The CFT resulted in elevated HRV with concomitant bradycardia in the able-bodied group, while the SCI group experienced no change in HRV or heart rate during the CFT. Able-bodied individuals showed a positive correlation between the change in HRV and the change in LV diastole during the CFT, which was attributed to increased cardiac vagal tone and not the change in heart rate, however, no relationships were observed in the SCI group. CONCLUSION: In able-bodied individuals, cardiac parasympathetic activity is associated with LV filling at rest and during elevated cardiac vagal tone. After SCI, there is a discord between vagal and LV diastolic activity, where changes in autonomic function do not influence LV filling, suggesting a disconnect between parasympathetic and cardiac function.
