Respiratory Function after Spinal Cord Injury changes over time, consequences and effect of training

Karin Postma, MSc (Researcher)
Hans Bussmann, PhD (Project leader)
Janneke Haisma, MD, PhD
Michael Bergen, MD, PhD
Maria Hopman, MD, PhD
Henk Stam, MD, PhD

On January 20, 2015 Karin Postma defended her dissertation entitled: Respiratory Function after Spinal Cord Injury changes over time, consequences and effect of training

Summary

Survival rates and medical care following spinal cord injury (SCI) have improved largely over the last decades and have resulted in a decline of mortality during the first 2 years after injury. The mortality rates in the period thereafter have not changed substantially. Respiratory diseases, particularly lower tract respiratory infections, remain a common cause of early death and hospitalization in persons with chronic SCI. Therefore, in this thesis we focused on respiratory function after SCI. We studied changes in respiratory function, the prevalence of impaired respiratory function and consequences in the early years after inpatient rehabilitation. In addition, we studied the effects of a specific respiratory training program added to the usual inpatient rehabilitation treatment. For the first part of this thesis we used data of a Dutch multicenter prospective cohort study (the Umbrella and SPIQUE project). For the second part we conducted a multicenter randomized controlled trial (RCT) on the effects of resistive inspiratory muscle training (RIMT).

The introductory Chapter 1 describes background information concerning SCI, respiratory function, the effects of SCI on respiratory function, consequences of impaired respiratory function, and current respiratory management. In this chapter, a schematic representation of the assumed relationships between spinal cord injury, respiratory function and the consequences for general functioning are shown. A short description of the Umbrella and SPIQUE project is provided. The chapter concludes with the aims and outline of this thesis.

The aim of the study, described in Chapter 2, was to find a method to identify persons at risk for respiratory infection after inpatient rehabilitation. We studied whether parameters of pulmonary function measured at discharge could predict respiratory infections in the first year after discharge of inpatient rehabilitation. Both forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and peak expiratory flow (PEF) were significantly lower in persons who had had respiratory infection than in those who did not. With exception of FVC in liters, all parameters were moderately accurate predictors of respiratory infection in the first year after discharge of inpatient rehabilitation.

Chapter 3 concerns the study focused on changes in pulmonary function during the first 5 years after inpatient rehabilitation. We found that FVC increased 5.1% over that period. Although persons with complete tetraplegia had a significantly lower absolute pulmonary function than those with incomplete tetraplegia or persons with paraplegia, the changes over time were not different. However, changes in pulmonary function differed largely between persons. During the first year after inpatient rehabilitation, FVC declined in 14.9% of the persons (beyond the normal age-related decline). During the four years thereafter, FVC declined in 28.3% of the persons. We found several potentially modifiable determinants of declined FVC in the first year: low inspiratory muscle strength, high body mass index, declined peak power output, and declined peak oxygen uptake. Similar, but non-significant, patterns were observed for the period between one and five years after discharge.

Chapter 4 addresses the prevalence of impaired respiratory function, the incidence of respiratory infections and associations between respiratory function and health-related quality of life (HRQOL), 5 years after inpatient rehabilitation. Pulmonary function was impaired (FVC below 80% predicted) in 30.9% of the persons, 35.9% had impaired perceived cough strength, 18.4% experienced dyspnea at rest, and 29.0% experienced dyspnea during physical activities. Nine percent had had a respiratory infection in the year prior to the measurements. Furthermore, this study showed that FVC, impaired perceived cough strength and dyspnea were associated with social functioning. Dyspnea was also associated with other domains of quality of life (general health, mental health and vitality). More seriously impaired respiratory function was associated with lower quality of life.

In Chapter 5 we describe the results of our RCT concerning the effects of RIMT. The immediate and long-term effects of RIMT on respiratory function, respiratory complications, and HRQOL in persons with recent SCI who had impaired pulmonary function were assessed. Forty persons were included and randomized to the intervention or the control group. All persons received usual rehabilitation care. Additionally, persons in the intervention group trained 5 times a week for 8 weeks with a RIMT-threshold trainer. This training had a positive effect on the maximum inspiratory pressure (MIP), a measure of inspiratory muscle strength, immediately after the training period. At follow-up this effect was no longer significant. With exception of an immediate effect on mental health, we found no effects on other parameters of respiratory function, respiratory complications, or HRQOL. The results concerning respiratory complications should be interpreted with caution as the sample size for this outcome may have been too small.

In Chapter 6 we describe our study on longitudinal relationships between respiratory muscle strength and cough capacity. For this study we used data of the RCT described in chapter 5. We found that both MIP and maximum expiratory pressure (MEP) were significantly positively associated with peak cough flow (PCF). A 10 cm H2O higher MIP was associated with a 0.32 l/sec higher PCF. A 10 cm H2O higher MEP was associated with a 0.15 l/sec higher PCF. The association between MIP/MEP and PCF was mainly based on within-subject variance, indicating that improvement of respiratory muscle strength may lead to improvement in cough capacity in persons with SCI.

Finally, in Chapter 7 we describe the main findings of this thesis. Then we discuss the risks of complications, respiratory management and the consequences of impaired or declining respiratory function. We discuss the need for better follow-up care to prevent respiratory complications. Furthermore, we discuss the effects of RIMT, which persons benefit most, and the importance of sufficient inspiratory muscle strength. Finally, we address clinical implications and make recommendations for future research.

Read more about this project and the other SCI projects in Rotterdam in the newsletter of January 2012.

Publications

Predicting respiratory infection one year after inpatient rehabilitation with pulmonary function measured at discharge in persons with spinal cord injury. Postma K, Bussmann JB, Haisma JA, van der Woude LH, Bergen MP, Stam HJ. J Rehabil Med. Sep;41(9):729-33, 2009.
Changes in pulmonary function during the early years after inpatient rehabilitation in persons with spinal cord injury: a prospective cohort study. Postma K, Haisma JA, de Groot S, Hopman MT, Bergen MP, Stam HJ, Bussmann JB. Arch Phys Med Rehabil. 2013 Aug;94(8):1540-6.
Resistive inspiratory muscle training in persons with spinal cord injury during inpatient rehabilitation: a randomized controlled trial. Postma K, Haisma JA, Hopman MT, Bergen MP, Stam HJ, Bussmann JB. Phys Ther. 2014 Dec;94(12):1709-19.
Impaired respiratory function and associations with health-related quality of life in persons with spinal cord injury. Postma K, Post MWM, Haisma JA, Stam HJ, Bergen MP, Bussmann JBJ. Submitted.
Longitudinal relationship between respiratory muscle strength and cough capacity in persons with spinal cord injury. Postma K, Vlemmix LYM, Haisma JA, de Groot S, Sluis TAR, Stam HJ, Bussmann JBJ. Submitted.