2004B10 List the physiological factors which affect left atrial pressure and explain their effects.

 

List:

·         Intro: LAP

·         LAP trace

·         LAP determinants

 

Intro:

Definitions

·   Mean LA pressure throughout the cardiac cycle

·   End-diastolic LA pressure (prior to ‘a’ wave)

Normal

·   6-12mmHg

Measurement

·   Direct: Swann-Ganz catheter with pressure transduction

·   Indirect: echocardiography (E:A and E:e’ ratios)

Significance

·   Key determinant of preload hence cardiac output

 

LAP trace:

 

Note: a and c waves are often fused

 

LAP determinants:

Venous return

VR = (mean systemic pressure – right atrial pressure / resistance to venous return

·   ↑Blood volume -> ↓MSFP -> ↓VR -> ↓LAP

·   Venoconstriction -> ↑MSFP ->

·   Head up -> pooling -> ↓MSFP -> ↓VR -> ↓LAP

·   Limb muscle pumps: ↑MSFP -> ↑VR -> ↑LAP

o Absent under GA

·   Diaphragm pump: contraction -> ↑abdo pressure + dilated IVC -> ↑VR

o Absent if IPPV

LA filling

·   RV output: e.g. primary RV failure -> ↓LA filling -> ↓LAP

·   Intrathoracic pressure: e.g. PPV -> obstruction to LA filling -> ↓LAP

·   Intrapericardial pressure: e.g. tamponade -> obstruction to LA filling -> ↓LAP

LA emptying

·   Atrial function: e.g. AF -> ↓emptying -> ↑LAP

·   Mitral valve function: e.g. mitral stenosis -> ↓emptying -> ↑LAP

LV filling

·   LV relaxation: LV ischaemia -> ↓relaxation -> ↑LAP

·   LV stiffness: LV hypertrophy, fibrosis, infiltration -> ↓compliance ->↑LAP

·   LV volume: e.g. AR -> ↑LVESV -> ↓compliance -> ↑LAP

LV emptying

·   Contractility: LV failure -> ↓emptying -> ↑LAP

·   Afterload: ↑afterload (e.g. ↑SVR) -> ↓emptying -> ↑LAP

 

 

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