Respiratory adaptations in persons with spinal cord injury

• Gabi Mueller, MSc (Researcher)
• Maria Hopman, PhD (Project leader)
• Claudio Perret, PhD
• Lucas van der Woude, PhD

On June 16, 2008, Gabi Mueller defended her dissertation entitled: Respiration in Spinal Cord Injury: time-courses and training.

Summary

A spinal cord injury (SCI) causes lesion dependent impairments of respiratory muscles and thus may affect the respiratory system substantially. Respiratory complications increase with a higher lesion level and accordingly morbidity and mortality of individuals with SCI is substantially increased compared to the able bodied population (1, 4). In order to decrease respiratory complications, detailed knowledge of time-courses and lesion specific baseline characteristics of the respiratory function in subjects with SCI is needed. Thus, this thesis focused on baseline lung function and respiratory muscle pressure as well as on their time-courses during the first two years after injury, rib cage mobility, and respiratory muscle en-durance training of different subgroups with SCI.

In Chapter 1 a general overview of lesion specific impairments in SCI and its’ epidemiology is shown. Then, the current knowledge of respiratory mechanics and different methods of respiratory muscle training in able bodied individuals and subjects with SCI are discussed and summarized. At the end of the chapter, the purposes of the studies presented in this thesis and the methods applied are presented.

The aim of the study presented in Chapter 2 was to assess the influences of lesion and personal characteristics on respiratory function in subjects with SCI, one year after discharge from inpatient rehabilitation. We found that higher lesion levels are associated with lower lung function and especially lower respiratory muscle pressure generating capacity. Subjects with motor complete tetraplegia showed the highest impairments and expiratory muscle pressure was the most affected parameter in all subjects with SCI. Further, we present regression equations to estimate lesion specific lung function and respiratory muscle pressure for individuals with SCI, around two years post injury.

In Chapter 3 we present trajectories of lung function and respiratory muscle pressure during and one year after inpatient rehabilitation for four different lesion level groups of subjects with motor complete SCI. We found that respiratory function improved during inpatient rehabilitation, but only forced vital capacity, forced expiratory volume in 1 s and maximal inspiratory muscle strength further improved during the first year after discharge from inpatient rehabilitation. The fact that maximal expiratory muscle pressure already decreased during the first year after inpatient rehabilitation shows that interventions to improve expiratory muscle function should be an important issue in respiratory care of subjects with SCI.

The aim of the study presented in Chapter 4 was to adapt respiratory muscle endurance training using normocapnic hyperpnoea to the specific respiratory conditions of subjects with para- and tetraplegia, since this method was not used in subjects with SCI before. Thus, the aim was to find the level of ventilation that subjects with para-and tetraplegia can sustain for 10 to 20 minutes. These intensities may then be used as guidelines to implement respiratory muscle endurance training in subjects with SCI. In contrast to able bodied indi-viduals who sustain about 70% of their individual maximal voluntary ventilation (MVV) dur-ing 10 to 20 minutes, subjects with tetraplegia sustain only around 40% of their individual MVV during the target time and subjects with paraplegia are able to perform respiratory muscle endurance training at about 60% of their individual MVV for 10 to 20 minutes.

In Chapter 5 we assessed the effects of respiratory muscle endurance training, using normocapnic hyperpnoea exercise, on exercise performance in wheelchair racing athletes with SCI. Effects of respiratory muscle endurance training on upper extremity exercise performance have not yet been investigated. They may differ from effects reported on leg endurance exercise performance in able bodied individuals, due to the concurrent use of upper extremity muscles for locomotion and respiration. We found significant increases in respiratory muscle endurance after six weeks of respiratory muscle endurance training performed five times a week during 30 min each. Due to high inter-individual differences and small group sizes, increases in expiratory muscle pressure and exercise performance (10 km time-trial) were only significant within the training group, but not between the training and the control group. Nevertheless, this study provides interesting preliminary results that show the potential effects of normopcapnic hyperpnoea training on respiratory muscle endurance, upper body exercise performance and expiratory muscle pressure in subjects with SCI.

High blood lactate levels are produced during anaerobic exercise intensities and blood lactate is used as energy source during low intensity exercise by type I muscle fibres. Normocapnic hyperpnoea exercise is performed by respiratory muscles which mainly contain type I fibres. Normocapnic hyperpnoea at low intensities may be advantageous as a recovery strategy in order to preserve energy sources of the limb muscles. The aim of the study presented in Chapter 6 was to investigate the impact of low intensity normocapnic hyperpnoea on blood lactate disappearance after exhaustive arm exercise in comparison to passive and active recovery using the previously loaded muscle groups. The results showed that low intensity normocapnic hyperpnoea does not seem to enhance blood lactate disappearance after exhaustive arm exercise compared to passive or active recovery using the previously loaded muscle group. The magnitude of the involved muscle mass appears critical to effective active recovery.

Stiffening of the thoracic cage decreases rib cage mobility and respiratory function, especially in subjects with chronic tetraplegia (2, 3). Thus, improvements in rib cage mobility should be a further aim of respiratory care in subjects with SCI. To determine which intervention should be used to achieve this goal, an easy to perform and highly reproducible measurement method of rib cage mobility should be available. In Chapter 7 we present a new method to assess rib cage mobility in humans, using computed tomography. We showed that this method is highly reproducible in able bodied individuals and subjects with tetraplegia and thus useful for clinical practice.

In Chapter 8 we assessed differences in rib cage mobility and diaphragmatic movements between able bodied individuals and subjects with chronic, motor complete tetraplegia, us-ing the method described in chapter 7. Knowledge of such differences is important in order to quantify changes achieved in subjects with tetraplegia due to respiratory interventions, aiming at improvements in rib cage mobility. We found that rib cage mobility of individuals with chronic tetraplegia is reduced but not absent, whereas movement of the diaphragm is intact. Further, we present data of absolute differences in rib cage mobility and diaphragm movement between able bodied individuals and gender, age and height matched persons with chronic tetraplegia, including 95% confidence intervals.

In Chapter 9 the current knowledge from former studies and data from this thesis on time-courses of respiratory function after injury and lesion specific impairments in respiratory function in SCI were discussed in a comprehensive way. Further, the potential of respiratory muscle endurance training to improve respiratory function in SCI was reviewed and dis-cussed from previous studies and available data from this thesis. In addition, the issue of rib cage mobility and it’s consequences on respiratory function were summarized and ideas to increase rib cage mobility were presented. Finally, we discussed some consequences and ideas for future research in order to improve respiratory function, decrease respiratory com-plications and health care costs and thus increase quality of life and life expectancy of sub-jects with spinal cord injury.

Gabi Mueller has built a reference value calculator. This calculator is based on regression equations and will calculate predicted lung volumes and respiratory muscle strength values for people with a motor complete SCI (AIS A or B) between C4 and T12, aged 18-80 years, time post injury > 6 months, and with no acute respiratory illness/disorders.

Download the reference calculator here!

References

1. Brown R, DiMarco AF, Hoit JD, and Garshick E. Respiratory dysfunction and management in spinal cord injury. Respir Care 51: 853-868;discussion 869-870, 2006.
2. Estenne M, and De Troyer A. The effects of tetraplegia on chest wall statics. Am Rev Respir Dis 134: 121-124, 1986.
3. Estenne M, Heilporn A, Delhez L, Yernault JC, and De Troyer A. Chest wall stiffness in patients with chronic respiratory muscle weakness. Am Rev Respir Dis 128: 1002-1007, 1983.
4. Zeilig G, Dolev M, Weingarden H, Blumen N, Shemesh Y, and Ohry A. Long-term morbidity and mortality after spinal cord injury: 50 years of follow-up. Spinal Cord 38: 563-566, 2000.

Publications from this thesis

• Prediction models and development of an easy to use open-access tool for measuring lung function of individuals with motor complete spinal cord injury. Mueller G, de Groot S, van der Woude L, Perret C, Michel F, Hopman M.T.E. J Rehabil Med. 2012; 44(8): 642-7.
• Time-courses of lung function and respiratory muscle pressure generating capacity after spinal cord injury: A prospective cohort study. Mueller G, de Groot S, van der Woude L, Hopman MT. J Rehabil Med. 2008 Apr;40(4):269-76.
• Optimal intensity for respiratory muscle endurance training in patients with spinal cord injury. Mueller G, Perret C, Spengler CM. J Rehabil Med 2006; 38(6):381-386.
• Effects of respiratory muscle endurance training on wheelchair racing performance in spinal cord injured athletes: a pilot study. Mueller G, Perret C, Hopman M.T.E. Clin J Sport Med. 2008; 18:85-88.
• Impact of low intensity isocapnic hyperpnoea on blood lactate disappearance after exhaustive arm exercise. Perret C, Mueller G. Br J Sports Med 2007; 41:588-591.
• Reproducibility of computed tomography to assess rib cage mobility in humans. Mueller G, Perret C, Hofer P.J, Michel F, Berger M, Hopman M.T.E. Submitted.
• Rib cage mobility of individuals with chronic tetraplegia is reduced but not absent, whereas mobility of the diaphragm is intact. Mueller G, Perret C, Michel F, Berger M, Hopman M.T.E. Submitted.