Decreased Contractility and Stroke Volume in Acidosis? - USMLE Forums
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Old 04-22-2011
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Heart Decreased Contractility and Stroke Volume in Acidosis?

I am trying to understand why there is decreased contractility and SV with

1. Acidosis
2. Hypoxia/Hypercapnea


Is it because as the increased extracellular H+ rises, intracellular H+ rises to compensate. To maintain electrical neutrality K+ leaves increasing the resting membrane potential. Increasing the RMP decreases cell's excitability.

Can someone please elaborate and help! thanks!!!

Also any extra explanations or advice on acid base balance would be appreciated as well!!
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Old 04-22-2011
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I would say that decreased stroke volume is just a product of increased heart rate since there will be less filling time (shorter diastole)

As for decreased contractility, not sure.
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Cautie Pie (04-22-2011)
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Old 04-22-2011
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hey Cautie

you have answered the Q ...

hyperK cause RMP to be more negative hence less excitable plus the increased H+ inactivates Na channels....So decreases contractility and hence SV
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Old 04-23-2011
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Hi Cautie,
I read in one of the banks (and I actually have it jotted down in my FA that acidosis decreases contractility and SV because it produces decreased affinity of Troponin C for Ca++.
Hope this helps.
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Old 04-23-2011
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Triquetrum



How does acidosis produce decreased affinity for troponin??
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