Percent predicted equations depend on accurate height measures and this is challenging in nonambulatory subjects with contractures and scoliosis. 42 Limitations of FVC testing include subject cooperation and understanding of the testing and thus, FVC testing is performed with subjects who are 5В years of age or older. 40 For subjects unable to stand, arm span measurement estimate of height 41 or ulnar length can be obtained as a surrogate for height. Since 2013, the Global Lung Initiative (GLI) has established worldwide spirometric prediction equations utilizing height, age, gender, and ethnic group. Prior to 2013 a variety of prediction equations were available. 39 FVC results are compared to reference values derived from healthy subjects using spirometric prediction equations based on height, age, gender, and if available, ethnic group. Spirometers are maintained and data collected using testing protocols per American Thoracic Society and European Respiratory Society international standards.

FVC testing is captured using a spirometer and the best reproducible effort is recorded. It is an indirect measure of respiratory muscle strength, and is impacted by weakness of the external intercostal muscles and the diaphragm. 8,25ДЇVC is the maximal volume of air exhaled with maximally forced effort from a maximal inspiration and measured as a function of time. Key to reliable and reproducible pulmonary function testing is training of personnel to obtain the best possible efforts from the subject.

Schroth, in Spinal Muscular Atrophy, 2017 Vital CapacityДЇor type 2 and 3 SMA, absolute forced vital capacity (FVC) achieved the best reliability in a study of 20 subjects performing six pulmonary function measures (intraclass correlation coefficient of 0.98, a measure of reliability agreement between paired samples across two time points).

Spinal muscular atrophy type 3