A patient with Duchenne muscular dystrophy presents withfibrosis, where some of the contractile muscle fibers are replacedwith scar tissue, although the nervous system and neuromuscularjunction are not altered. In this patient the sarcomere length,muscle belly length, and fiber type distribution are equivalent toa control subject.
A. What would be the predicted change inmaximum isometric force and maximum unloaded shortening velocitycompared to a control subject. Describe using terms of musclearchitecture (sarcomere arrangement- parallel and series).
B. this patient the muscle is only able toproduce 200 N of maximum isometric force. The bicep tendon inserts5 cm from the elbow axis of rotation and the wrist is 50 cm fromthe axis of rotation of the elbow. When the elbow is bent at 90Ëš,what is the maximum force that the patient can withstand at thewrist? (assume negligible weight of the forearm).
C. In DMD, the diaphragm cannot produce therequired inspiration force. How is airflow altered duringinspiration? Describe in terms of pulmonary pressures andvolume.
D. A control subject is able to maintain asystemic arterial PO2 of 100 mmHg and a venousPO2 of 40 mmHg. A dystrophic patient is only able toreach an arterial PO2 of 60 mmHg and venousPO2 of 35 mmHg. How is O2 delivery altered?How would arterial PO2 be altered if this patient wasstrenuously exercising?
E. Treatments for DMD include gene therapies torestore dystrophin expression. However, this requires that thepatients maintain immunosuppression for their lifetime because thedystrophin produced is not recognized as self. What type ofadaptive immune cell produces an opsonizing agent? How are themuscle fibers affected by opsonization?
