Link between blood pressure and heart rate..hmmm

[riseNshine]

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I came across a TPR passage that got me a little confused. It reads:

"Shock can be divided into three categories: hypovolemic, caused by a decrease in circulatory volume; cardiogenic, due to poor contraction of heart muscle; and distributive, in which blood is abnormally distributed throughout the body. Distributive shock can be either neurogenic, which can result after injury to the sympathetic nervous system, or septic, caused by systemic bacterial infection.

Question: In which shock state might one observe low blood pressure and low heart rate?
1. hypovolemic
2. cardiogenic
3. neurogenic

The answer is only neurogenic, but I thought it would be all 3. Doesn't decreased blood volume mean less blood pressure and hence, lower heart rate? And doesen't poor contraction of the heart muscle mean there's a low heart rate? In the answer explanation, they state that cardiogenic and hypovolemic shock are characterized by low BP along with an increase in heart rate, since loss of sympathetic function does not occur in these instances.

So you can have low BP and a high heart rate?

 

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heart rate and cardiac contractility are 2 different things. You can have an athletic guy who's heart beats 40 bpm and is strong enough to deliver blood to his body, and a person in stage 3 heart failure who's heart beats many times very weakly and can't provide good perfusion.

In cadiogenic shock, the heart can't provide adequate blood pressure, so the brain makes it pump faster to no avail. In hyovolemic shock, the pressure is low (blood loss) so the brain makes the heart pump faster. In both these cases, the BP will be low and the HR will be high. The difference is that in hypo polemic shock the cardiac output will be higher because the heart is able to pump stronger when needed. In cardiogenic shock this is not true so the cardiac output is decreased.

In neurogenic shock, the sympathetic tone is lost leading to vasodilatation and decreased BP and paradoxically, a decreased HR.