A spinal cord injury (SCI) causes a lesion-dependent loss of respiratory muscle innervation and function. This study aimed to evaluate the time course and key determinants of between-person variation in respiratory function after SCI.

Multi-center, prospective cohort (10 SCI units). Adult inpatients with acute, complete or incomplete cervical or thoracic SCI were eligible. Descriptive analysis were used for demographics. Mixed effects multilevel regression models with random intercepts (for center and person) were generated to segregate between-person from within-person variation. Modelled outcome parameters were: maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP), peak cough flow (PCF), forced vital capacity (FVC), forced expiratory volume in 1s (FEV1) and peak expiratory flow (PEF). Independent variables were sex, age, body height, time post injury/diagnosis, lesion etiology, lesion level and completeness as well as time-updated occurrence of pneumonia.

490 individuals, mean (SD) age of 51 (17) years, mean height 177 (9) cm. were enrolled between October 2016 & July 2021. 77% were male, 73% had a traumatic lesion and 54% had tetraplegia. MIP and MEP were 9 and 15cm H20 lower when preceded by any pneumonia event. Pneumonia was associated with a reduction in forced expiratory parameters thereafter, such as PCF (-45 l/min; 95% CI: -78 to -12 l/min) and PEF (-48 l/min; 95% CI: -77 to -20 l/min). Respiratory function measures showed a non-linear, decelerating increase with time post injury that leveled-off at maximum values towards the end of the first year. Respiratory muscle strength and lung function were consistently lower in the 60+ age group.