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Physiology II
Cardiovascular Case D

arteriovenous fistula 

the patient: a 27-year-old male 

chief complaint: throbbing headaches

history and clinical examination: This unemployed 27-year-old male appeared at the University Health Center complaining of throbbing headaches. His blood pressure was 184/52 mm Hg, his heart rate was 70 beats/min, and examination of his chest revealed an enlarged heart. On auscultation, a high-pitched systolic murmur and an accentuated second heart sound were noted. During the physical examination, the astute second-year UNE/COM student assigned to the patient noticed a ragged scar from a relatively recent injury on the inner aspect of the patient's left thigh. Palpation revealed a strong thrill in the area of the scar. The patient initially dismissed the scar as the result of an "accident", but in response to persistent questioning by the suspicious student he finally admitted that the scar had resulted from a gunshot wound. The bullet had not lodged in the tissue, and the patient had been able to treat the wound himself with basic first-aid measures. He had not sought further medical assistance because he did not wish to reveal the circumstances under which he had been shot. The patient was sent to Brighton Medical Center and admitted there to the surgical service.

STUDY QUESTIONS:

1. Is this patient's calculated mean systemic arterial pressure normal? What about resting cardiac output?  The mean pressure (about 105) is a little higher than normal.  The patients CO is increased.  This can be deduced from the widened pulse pressure.

2. What factors might have contributed to the wide pulse pressure observed in this patient?  The diastolic pressure was lower than normal because with the arteriovenous fistula there is less resistance than normal so the arterial blood could flow to the venous system more easily and quickly.  To compensate for the demands of the tissues, the heart pumped harder thus creating a greater systolic pressure.

3. How would you characterize this patient's left ventricular preload and afterload?  Support your answer with information from the case.  The preload was greater because of the larger muscle (greater tension) and increased blood flow.  The afterload was increased too because the heart had to contract to create a 184 mm Hg systolic pressure (This is Dr. Norton's definition of afterload...some texts will define afterload as the amount of pressure needed to open the aortic valves but this is not all the pressure the heart has to pump against.)

4. Why is this patient's heart rate normal?  So far he was able to compensate his CO by increasing his heart muscle mass thus increasing his contractility.

5. How is Starling's Law operating in this patient?  Greater stretch of the muscles = a greater contraction. 

 


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