Plasticity of Minute Ventilation, but Not Blood Pressure in Participants with Motor Incomplete Spinal Cord Injury

Research ObjectivesTo investigate the impact of mild intermittent hypoxia (MIH) on long term facilitation (LTF) of minute ventilation (VE) and blood pressure in those with a spinal cord injury (SCI).Design2-arm parallel design.SettingResearch Laboratory.ParticipantsThree Black Americans (age 43 ± 3.46, 1 Male, 2 Female) with a motor incomplete SCI (C4, T1, C7/T5) with signs and symptoms of autonomic dysfunction.Interventions8 days of MIH consisting of twelve two-minute bouts of hypoxia interspersed with two-minutes of normoxic recovery. Slight hypercapnia (+2 mmHg) was maintained throughout.Main Outcome MeasuresLong-term facilitation and progressive augmentation of VE (Liters/Min [L/min]) and LTF of blood pressure (BP). LTF is the difference between VE at baseline and recovery. Progressive augmentation (PA) was calculated as the difference in VE from the initial to final hypoxic exposures. Data presented as fractional changes ± standard error.ResultsLTF of VE was significant on day 1 (1.33 ± 0.12) and day 8 (1.19 ± 0.03, P ≤ 0.03). LTF was only found for tidal volume on day 8 (1.05 ± 0.003, P = 0.031) and no LTF was found for breathing frequency on either day (P ≥ 0.12). The magnitude of PA of VE was not different between day 1 and day 8 (+ 5.4 ± 3.4 vs (1.4 ± 0.73 L/min, P = 0.4, respectively). No significant LTF of systolic BP was found on day 1 (1.08 ± 0.08) or day 8 (1.16 ± 0.13, P ≥ 0.37). No significant LTF of diastolic BP was found on either day (P ≥ 0.32). No significant change in pulmonary function (FVC, FEV, MVV) was observed.ConclusionsMIH elicited LTF of VE after day 1 and 8. There was no augmented LTF or PA from day 1 to day 8. No LTF of systolic BP was found on either day. These data suggest that 8 days of MIH can elicit ventilatory plasticity with no sustained impact on resting BP.Author(s) DisclosuresNone.