Case Study on Skeletal Muscle Physiology
"Time to scrub in," says Dr. Hodges. The appendectomy you are about to observe is your second surgical case in surgical technician school. The patient, David Sims, is an 18- year-old male who was healthy until two days ago when he began having severe abdominal pain, fever, and vomiting resulting in a diagnosis of appendicitis. David is in excellent health and has never had surgery before, so you anticipate the procedure to go smoothly.
Your instructor asked the anesthesiologist, Dr. Hodges, if you can observe her today during the procedure. "All of the patient's vital signs and lab work are within normal limits so we are good to go," says Dr. Hodges as David is brought into the operating room. You help get David ready by applying the heart monitor, oxygen saturation monitor, and blood pressure cuff. After David has been sedated, Dr. Hodges places a special tube down his esophagus to measure his core body temperature and another in his trachea (an endotracheal tube) to help him breathe during the procedure. While Dr. Hodges places the endotracheal tube, she comments, "His jaw muscles are a bit tight so it is very important to check and record his vital signs every 10 minutes. That is your job today while I monitor his respiratory status."
The case has been in progress for about 20 minutes when you notice David's heart rate jump up to 120bpm, setting off the ECG alarm on the monitor. You are concerned and ask, "Can he feel what is happening? His heart rate just went up." Dr. Hodges looks at you and asks, "What is his core temperature?" You show her the chart and see that David's temperature has gradually begun to rise and is now 101.8° F (38.8° C). Dr. Hodges' face turns serious and she says, "His exhaled carbon dioxide levels have also begun to rise. We need to get the malignant hyperthermia cart right away!"
David is now two days post-operative and is recovering in the Surgical Intensive Care Unit. You recall all of the activity that occurred to save his life by treating his malignant hyperthermia. You researched this condition and discovered that it is an inherited disease. While under general anesthesia, the affected person will experience a rapid rise in body temperature and severe muscle contractions. Dr. Hodges drops by to see David and says to you, "I was impressed how you handled yourself during a very stressful situation. Good job."
Short Answer Questions:
1. David's body temperature rises above normal during the surgery (hyperthermia). How does skeletal muscle tissue contribute to body temperature?
2. During malignant hyperthermia, there is an increased amount of calcium released into the sarcoplasm of skeletal muscle cells.
a. What organelle stores calcium in muscles cells?
b. Describe the events that must occur in the muscle cell before calcium is released from this organelle.
3. Jaw muscle contraction (masseter spasm) is one of the key physical findings seen in David's case of malignant hyperthermia. Explain how calcium functions to cause contraction of a skeletal muscle cell.
4. Dr. Hodges notes that David's exhaled carbon dioxide levels are elevated. List all the metabolic pathways that function to synthesize ATP for skeletal muscle contraction. Which of these pathways produces carbon dioxide as a by-product?
5. Malignant hyperthermia causes a hypermetabolic state in skeletal muscle, which is triggered by high demands for ATP during uncontrolled muscle contractions.
a. b. c.
What is the role of ATP in cross bridge cycling? What is the role of ATP in generating a resting membrane potential? What is the role of ATP in maintaining calcium concentration gradients?
6. Dantrolene is the only drug available to treat malignant hyperthermia. It works by inhibiting calcium channels of the terminal cisterns of the sarcoplasmic reticulum. Explain how this inhibition helps to terminate skeletal muscle contraction. What effect would this have on David's body temperature?