1. Lung Functions Upright and Supine in Children with Early Onset Scoliosis
G. Redding. V. Bompadre, R. DiBlasi, W. Krengel III, K. White
Seattle Children’s Hospital, Seattle, WA
USA

2. Background
Lung functions are measured in children with EOS when they are awake and upright. Lung and chest wall imaging (CT and MRI) are conducted with children supine.
Spine surgery is performed in children with EOS who are not upright.
It is unclear if position influences lung function in children with EOS, as has been reported in children with neuromuscular weakness disorders.

3. Hypotheses
Forced vital capacity is lower when children with EOS are supine compared to upright.
Respiratory muscle strength is reduced in children with EOS when supine compared to upright.
Respiratory muscle fatigability, measured using the time-tension index, is greater in children with EOS compared to published norms.
Respiratory muscle fatigability is greater when children with EOS are supine compared to upright.

4. Methods
Lung and respiratory muscle function were tested in 10 children with EOS as outpatients when well in the supine and upright position in random order on the same day.
Forced vital capacity (FVC) was measured first, Maximum inspiratory muscle pressure (MIP) second, and mouth occlusion pressure at 100 milliseconds (P0.1) was measured third. Respiratory rate and inspiratory time/time per breath were also measured in both positions.

5. Data Analysis
Comparisons of the following indices were made using a Wilcoxon (non-parametric) ranked test for significance:
FVC, MIP, Time-tension index (TTI)
Time tension index is calculated from the following equation:
TTI = Ti/Ttot x (p0.1 x 5 x Ti/MIP)

6. Patient Population 10 subjects (7 female, 3 male) 11+/-3 years old
Dx: congenital scoliosis = 5
syndromic scoliosis = 3
idiopathic scoliosis = 2
Previous spine surgery (growing constructs) =10
Spine fusion = 2
Cobb angle at testing = 62+/-18 degrees

7. Results by Position Index Upright Supine
FVC (% pred)* 58+/-19% 55+/-22%
MIP (mmHg)* 64+/ /-19
% predicted* 69+/-19% 54+/-15%
TTI / /-0.8
(normal TTI value = /-.007)
*p<0.5

8. TTmus In Children with Neuromuscular Weakness× × × × × × × × × ×
 = Normals
∆ = Neuromuscular Weakness
X = EOS without weakness
Mulreany L T, et al. J Appl Physiol 95:

9. Summary of Results
Lung function is slightly worse when supine than upright in children with EOS. This is driven by reduced inspiratory muscle strength (MIP).
Respiratory muscle fatigability is greater in children with EOS regardless of position.
Respiratory muscle fatigability is greater when supine than upright.
These differences are significant with regard to trend but small in magnitude.

10. Conclusions
Respiratory muscle function is slightly worse in the supine position in children with EOS compared to upright posture, when lung functions are clinically measured.
Estimates of lung function upright over-estimate how children with EOS breathe when prone or supine (sleeping, during certain imaging studies, and intra-operatively).