Respiratory Training Improves Blood Pressure Regulation in Individuals With Chronic Spinal Cord Injury

Abstract

Objective: To investigate the effects of respiratory motor training (RMT) on pulmonary function and orthostatic stress-mediated cardiovascular and autonomic responses in individuals with chronic spinal cord injury (SCI).

Design: Before-after intervention case-controlled clinical study.

Setting: SCI research center and outpatient rehabilitation unit.

Participants: A sample of (N=21) individuals with chronic SCI ranging from C3 to T2 diagnosed with orthostatic hypotension (OH) (n=11) and healthy, noninjured controls (n=10).

Interventions: A total of 21±2 sessions of pressure threshold inspiratory-expiratory RMT performed 5d/wk during a 1-month period.

Main outcome measures: Standard pulmonary function test: forced vital capacity, forced expiratory volume in one second, maximal inspiratory pressure, maximal expiratory pressure, beat-to-beat arterial blood pressure, heart rate, and respiratory rate were acquired during the orthostatic sit-up stress test before and after the RMT program.

Results: Completion of RMT intervention abolished OH in 7 of 11 individuals. Forced vital capacity, low-frequency component of power spectral density of blood pressure and heart rate oscillations, baroreflex effectiveness, and cross-correlations between blood pressure, heart rate, and respiratory rate during the orthostatic challenge were significantly improved, approaching levels observed in noninjured individuals. These findings indicate increased sympathetic activation and baroreflex effectiveness in association with improved respiratory-cardiovascular interactions in response to the sudden decrease in blood pressure.

Conclusions: Respiratory training increases respiratory capacity and improves orthostatic stress-mediated respiratory, cardiovascular, and autonomic responses, suggesting that this intervention can be an efficacious therapy for managing OH after SCI.

Keywords: Autonomic nervous system; Blood pressure; Breathing exercises; Hypotension, orthostatic; Rehabilitation; Respiration; Spinal cord injuries.

Copyright © 2016 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1

Dynamics (mean ± SD/min) of systolic and diastolic blood pressure (SBP and DBP, black) and heart rate (HR, gray) during sit-up orthostatic stress test in individual with C4 AIS-A SCI (A38) before (A) and after (B) Respiratory Motor Training (RMT). Note that considerable drop in SBP (−20 mm Hg) and DBP (−11 mm Hg) characterizing orthostatic hypotension before RMT is not seen after RMT. Note also stability of the blood pressure and HR response achieved after RMT.

Figure 2

Dynamics (mean ± SD) of (A) systolic and (B) diastolic blood pressure (SBP and DBP) during orthostatic stress test in non-injured (NI) and SCI group before and after respiratory motor training (RMT). Note significant (p < .05) increase in both SBP and DBP in NI individuals (*) and significantly decreased SBP and DBP in SCI individuals in upright position compared to the values obtained in supine position before training (†) and SBP after RMT (•).Note also positive dynamics in both SBP and DBP in participants with SCI after RMT and no significant difference compared to supine baseline in DBP after training.

Figure 3

Change (mean ± SD) in (A) systolic and (B) diastolic blood pressure (SBP and DBP) during orthostatic stress test in seated position from supine baseline in SCI group before and after respiratory motor training (RMT). Note that RMT significantly (p < .05) mitigated the fall in both SBP and DBP observed before the RMT (•).

Figure 4

Baroreflex effectiveness index (BEI) (A) and baroreflex sensitivity (BS) (B) during orthostatic stress test in non-injured (NI) and SCI group before and after respiratory motor training (RMT) (mean ± SD/5 min). Note a significant (p < .05) supine-to-seated decrease in BEI in SCI individuals before training (†) and that this decrease was not significant during the late seated phase after RMT (•). Note also the positive trend toward NI control curve that is observed after RMT in both BEI and BS in seated position.

Figure 5

Low-frequency component of power spectral density (LF PSD) of heart rate (HR) (A); systolic (B) and diastolic blood pressure (SBP and DBP) oscillations (C) during orthostatic stress test in non-injured group (NI) and in SCI group before and after respiratory motor training (RMT) (mean ± SD/5 min). Note that compared to the supine baseline, in contrast to SCI individuals, all outcomes in NI individuals were significantly increased (p < .05) in seated position (*). Note also significantly decreased LF PSD of HR in SCI individuals in seated position before training (†) but no such significant difference in this outcome after training. In contrast to pre-training levels, LF PSD of SBP was significantly higher throughout seated period after RMT (•).

Figure 6

Distribution (A) and magnitude (B) of the low-frequency (0.04–0.15 Hz) negative cross correlation between heart rate (HR) and systolic blood pressure (SBP) during orthostatic stress test in non-injured group (NI) and in SCI group before and after respiratory motor training (RMT) (mean ± SD/5 min). In the panel A, the lag is given on the vertical axes where negative lag refer to changes in SBP leading HR and positive lags refer to SBP lagging HR. The magnitude of the correlation is indicated by the color density according the scale presented in vertical bars on right. The strong blue band around 2.5 s in NI represents responses characteristic of baroreflex function. Note that compared to supine baseline, in contrast to SCI individuals, the negative magnitude were significantly increased (p < .05) in seated position in NI individuals (*). Note also its significant decrease in SCI individuals in seated position before training (†) and no significant difference in this outcome after training (•) associated with positive change in distribution.

Figure 7

Distribution (A) and magnitude (B) of the high-frequency (0.15–0.4 Hz) negative cross correlation between heart rate (HR) and respiratory chest kinematics during orthostatic stress test in non-injured group (NI) and in SCI group before and after respiratory motor training (RMT) (mean ± SD/5 min). The lag is given on the vertical axes where negative lag refer to respiratory rate leading HR and positive lag refers to respiratory rate lagging the HR. The magnitude of the correlation is indicated by the color density according the scale presented in vertical bars on right. The red or blue bands around 0 sec represent positive (red) or negative (blue) correlation between HR and chest movements (positive correlation represents increase in HR during inspiration and decrease in HR during expiration). Note significantly (p < .05) improved the post-RMT correlation during orthostatic stress (seated position) compared to the pre-RMT levels (•).