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dontwannasignup dontwannasignup
wrote...
13 years ago
Case Presentation
Allison Jacobson is a 19-year-old sophomore majoring in pre-medicine at the
University of Arizona. In the past few weeks leading up to final exams, Allison
has felt unusually tired despite receiving an adequate amount of sleep at night.
She also has had frequent headaches, and has experienced times when her heart
“felt like it was missing a beat.” Yesterday at lunch, Allison fainted while waiting
in line in the cafeteria. Initially, she attributed this episode to being unusually
tired and hungry, but later in the day she fainted again while waiting to mail a
package at the Post Office.
When Allison informed her mother about what had happened that day, her
mother immediately scheduled an appointment for Allison to see the family
physician. Though no abnormalities where found when he examined Allison, her
physician ordered a battery of diagnostic tests, including a head-up tilt (hut) test.

Questions
1. Define the following terms as they relate to cardiodynamics: stroke volume, end systolic volume, and
end diastolic volume. De?ne the following terms and state how each relates to systemic arterial
blood pressure: cardiac output and total peripheral resistance.
2. Explain the following: the Frank-Starling law of the heart, the control of cardiac activity by the
autonomic nervous system, and the baroreceptor re? ex in the maintenance of systemic blood
pressure.
3. Define the term dysautonomia, and brie? y describe the condition known as neurocardiogenic
syncope (ncs).
4. What are the symptoms of ncs?
5. What is the mechanism by which ncs occurs?
6. Discuss how ncs is diagnosed and treated.
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Replies
wrote...
Staff Member
13 years ago
1. End diastolic volume (EDV) is the amount of blood that collects in a ventricle during diastole. End systolic volume (ESV) is the volume of blood remaining in a ventricle after it has contracted. Stroke volume (ml/beat) equals EDV - ESV. Blood flow through the entire vascular system is equivalent to cardiac output. An increase in blood viscosity will cause an increase in peripheral resistance. The influence of blood vessel diameter on peripheral resistance is significant because resistance is inversely proportional to the fourth power of the vessel radius.

2. When there is more blood in the ventricle of the heart, the heart will contract more forcefully and increase stroke volume. This phenomenon is known as the rank-Starling effect. The Frank-Starling effect describes the effect whereby greater filling of the ventricles results in a greater ventricular contraction. It allows the ventricles, effectively, to "autoregulate" stroke volume, so that it can pump effectively. It allows the heart to automatically compensate for increases in the amount of blood returning to the heart. If the Frank-Starling effect didn't exist, and the stroke volume of the heart was always constant, then in a situation in which venous return is increased, there would be "leftover" blood in the heart after each contraction. This extra blood would build up over time, increasing in volume, until the heart was so distended that contraction would be ineffective.
- Master of Science in Biology
- Bachelor of Science
wrote...
Staff Member
13 years ago
3. Dysautonomia is a broad term that describes any disease or malfunction of the autonomic nervous system. This includes postural orthostatic tachycardia syndrome, inappropriate sinus tachycardia, vasovagal syncope, mitral valve prolapse dysautonomia, pure autonomic failure, neurocardiogenic syncope, and a number of lesser-known disorders such as cerebral salt-wasting syndrome. Neurocardiogenic syncope is the medical term for the common faint.

4. Among people with vasovagal episodes, the episodes are typically recurrent, usually happening when the person is exposed to a specific trigger. The initial episode often occurs when the person is a teenager, then recurs in clusters throughout his or her life. Prior to losing consciousness, the individual frequently experiences a prodrome of symptoms such as lightheadedness, nausea, the feeling of being extremely hot (accompanied by sweating), ringing in the ears (tinnitus), uncomfortable feeling in the heart, fuzzy thoughts, a slight inability to speak/form words (sometimes combined with mild stuttering), weakness and visual disturbances such as lights seeming too bright, fuzzy or tunnel vision, and sometimes a feeling of nervousness can occur as well. These last for at least a few seconds before consciousness is lost (if it is lost), which typically happens when the person is sitting up or standing. When sufferers pass out, they fall down (unless this is impeded); and when in this position, effective blood flow to the brain is immediately restored, allowing the person to wake up. Short of fainting a person may experience an almost undescribable weak and tired feeling resulting from a lack of oxygen to the brain due to a sudden drop in blood pressure. Tabor's describes this as the "feeling of impending death" caused by expansion of the aorta, drawing blood from the head and upper body. The autonomic nervous system's physiologic state (see below) leading to loss of consciousness may persist for several minutes, so: If sufferers try to sit or stand when they wake up, they may pass out again;
The person may be nauseated, pale, and sweaty for several minutes.

5. Regardless of the trigger, the mechanism of syncope is similar in the various vasovagal syncope syndromes. In it, the nucleus tractus solitarius of the brainstem is activated directly or indirectly by the triggering stimulus, resulting in simultaneous enhancement of parasympathetic nervous system (vagal) tone and withdrawal of sympathetic nervous system tone.

This results in a spectrum of hemodynamic responses:

Rightwards Arrow On one end of the spectrum is the cardioinhibitory response, characterized by a drop in heart rate (negative chronotropic effect) and in contractility (negative inotropic effect) leading to a decrease in cardiac output that is significant enough to result in a loss of consciousness. It is thought that this response results primarily from enhancement in parasympathetic tone.

Rightwards Arrow On the other end of the spectrum is the vasodepressor response, caused by a drop in blood pressure (to as low as 80/20) without much change in heart rate. This phenomenon occurs due to vasodilation, probably as a result of withdrawal of sympathetic nervous system tone.

Rightwards Arrow The majority of people with vasovagal syncope have a mixed response somewhere between these two ends of the spectrum.
- Master of Science in Biology
- Bachelor of Science
wrote...
13 years ago
i'd thank you but i'd rather thank wikipedia where you copied and pasted it from
wrote...
Staff Member
13 years ago
i'd thank you but i'd rather thank wikipedia where you copied and pasted it from

Perhaps you should attempt to do your own homework and rather than expecting us to be sage on the stage, you tell us exactly what you don't understand so that you don't look like a retard when your teacher looks up where you obtained your answers from on the internet (i.e. plagiarism).
- Master of Science in Biology
- Bachelor of Science
wrote...
Valued Member
Educator
13 years ago
Duddy - your request has been fulfilled Wink Face Sorry buddy.
wrote...
Staff Member
13 years ago
Duddy - your request has been fulfilled Wink Face Sorry buddy.

ha ha, jerk ends up emailing me. I should besmirch her and expose this post to her teacher, but she's not worth the effort. An quintessential definition of an internet loser.
- Master of Science in Biology
- Bachelor of Science
wrote...
Valued Member
Educator
13 years ago
... but she's not worth the effort.

^ Well said.
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