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 · Hypovolaemia -> ↓MSFP -> ↓VR -> ↓LAP · Venodilatation -> ↓MSFP -> ↓VR -> ↓LAP · Head up -> pooling -> ↓MSFP -> ↓VR -> ↓LAP · Limb muscle relaxation: ↓MSFP -> ↓VR -> ↓LAP · Diaphragm relaxation: loss of negative intrathoracic pressure -> ↓VR -> ↓LAP (Above the above may occur under GA)
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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