X hits on this document

PDF document

Common Congenital Heart Lesions - page 62 / 126

296 views

0 shares

0 downloads

0 comments

62 / 126

62 of 126

  • Endothelial factors

    • o

      Vasoactive substances are produced by endothelial cells

      • o

        Nitric Oxide

        • vasodilator

        • Released under normal conditions in response to ACh or sheer stress of blood flow

        • Utilizes a cGMP mechanism

      • o

        Prostacyclin

        • vasodilator

        • Released from endothelial cells in response to hypoxia, ACh, sheer stress

        • Utilizes a cAMP mechanism

      • o

        Endothelium-derived hyperpolarizing factor

        • Vasodilator

        • Does NOT involve a cGMP or cAMP mechanism

      • o

        Endothelin-1

        • VASOCONSTRICTOR

        • Stimulated by Ang II, EPI, sheer stress of blood flow

Normally there is a balance between these factors, where the vasodilators predominate. In sick endothelium, the balance can be shifted towards the constrictors.

  • Neural Factors

    • o

      Recall both beta 2 and alpha receptors are on the coronary vessels

      • o

        Beta 2 dilates, and alphas constrict.

The way all these factors work together determines the net coronary tone.

OXYGEN DEMAND DEPENDS ON

  • 1.

    ventricular wall stress: increased wall stress increases O2 needs

      • definition: tangential force acting on the myocardial fibers tending to pull them apart; energy is needed to oppose that force.

      • Wall stress = intraventricular pressure (P) times the radius of the vent. (r) divided by 2 times the vent. wall thickness (h).

      • Wall stress = P x r / (2h)

      • Wall stress is increased with more LV filling (mitral or aortic regurg)

      • Wall stress also increases with increased systolic pressure in the LV (aortic stenosis or HTN)

      • Increased thickness of the vent. wall will decrease wall stress (hypertrophy)

  • 2.

    heart rate

    • increasing HR consumes more ATP and O2 requirement increases

  • 3.

    contractility

    • increasing force of contraction increases O2 utilization

3

Document info
Document views296
Page views296
Page last viewedMon Dec 05 16:55:44 UTC 2016
Pages126
Paragraphs5002
Words33792

Comments