Time varying loading of the pulmonary circulation: a model to describe hemodynamic observations in the stiff left atrial syndrome.
OBJECTIVE
To develop a mathematical model that could explain the following observations: that right heart failure can develop in association with no other cardiac abnormality than a severe reduction in the compliance of the left atrium; and that patients with this syndrome have systolic pulmonary hypertension with left atrial v waves in the absence of either mitral regurgitation or left ventricular dysfunction.


METHODS
A model of the pulmonary circulation was designed with a time varying terminal hydraulic load, which was varied between a noncompliant left atrium during systole and a compliant left ventricle/left atrium combination during diastole. Using representative parameters and a pulmonary arterial flow wave as input, pressures in the pulmonary artery and left atrium and right ventricular power output were calculated.


RESULTS
Pulmonary arterial and left atrial systolic pressures are increased as left atrial compliance is reduced. The time varying change in terminal load results in an increase in systolic pressures, whereas diastolic pressures remain normal. A decrease in left atrial compliance increases both the nonpulsatile and pulsatile components of pulmonary input impedance, whereas only the nonpulsatile component of right ventricular power output is increased.


CONCLUSIONS
The time varying pulmonary load model of the pulmonary circulation, in the presence of a reduced left atrial compliance results in pulmonary, and left atrial pressures similar to those observed in patients with the stiff left atrial syndrome. The resulting increase in right ventricular power output could be an important factor in the development of right heart failure.
Division of Cardiology, Royal Victoria Hospital, McGill University, Montreal, Quebec.
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DH
Fitchett
D000368:Aged; D016279:Atrial Function, Left / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology*; D001794:Blood Pressure; D002303:Cardiac Output, Low / Q000503:physiopathology*; D003187:Compliance; D005260:Female; D006325:Heart Atria / Q000503:physiopathology*; D006801:Humans; D008433:Mathematics; D008962:Models, Theoretical; D011651:Pulmonary Artery / Q000503:physiopathology*; D011652:Pulmonary Circulation / Q000502:physiology*; D011673:Pulsatile Flow; D013577:Syndrome; D013997:Time Factors; D014655:Vascular Resistance; D016277:Ventricular Function, Left