Integrating concepts in Cardiovascular Physiology

Examples of normal physiology and pathophysiology:ExerciseHeart failureHypovolemic shock

compensatory/decompensatory responses

Mohrman and Heller

NEJM 2003 May

Law of LaPlace T = PD x r

PD = distending pressure (or transmural pressure)T = wall tensionr = radius of circle

PDPD

T

Smaller vessel radius results in less distending pressure, thus requires less wall tension

Normal Hypertrophic Dilated

Dilated hearts must do more work to generate same pressure as normal heart

radius

Law of Laplace

Mechanically bad for dilated heartsWhy?

Hypertrophic/dilated hearts are also compromised electrically

Hypertrophic and dilated cardiomyopathies present with prolonged action potential durations.

What are the consequences on heart rate, relaxation (diastole) time, potential for arrhythmias?

Your patient presents with shortness of breath upon exertion (dyspnea) and lying down (orthopnea) and has severe ankle swelling. Her heart and respiratory rates are elevated, her skin is pale, cold and sweaty.

Explain each symptom as it relates to congestive heart failure.

1

2

3

4

Explain why each of the following result from reduced cardiac output

1

2

3

4 Distinguish the sequence of effects between LV versus RV failure

LV failure tissue perfusion… pulmonary congestion RV failure

RV failure venous volume/pressure arterial-venous pressure gradient venous return vascular edema and congestion…

During your first day of clinical rotations in the ER a patient comes in with severe femoral lacerations due to a motorcycle accident. The paramedics were unable to stop the bleeding, but you were able to do so upon admission (~1 hour after the accident).

What consequences would you anticipate on the following prior to cessation of bleeding?

Heart rateCardiac outputBlood pressureUrinary production

What reflexes would be involved in these responses?

What would you do to stabilize this patient?

Mohrman and Heller

Boron and Boulpaep Fig 24-8A

• If 10-20% total blood loss comes from large vein, significant decrease in intravascular volume, venous return, cardiac output…

• If blood loss comes from peripheral artery, MAP does not fall until venous return is compromised