Cardiac Pressure- Volume Curve

• In severe aortic stenosis , the left ventricle functions at the steep portion of the pressure-volume curve.

• In aortic stenosis, there is pressure overload leading to concentric hypertrophy of the left ventricle. This causes increased contractility and decreased compliance of the chamber. More pressure is thus exerted to eject the same volume of blood. The pressure–volume curve therefore shifts to the left.

• In aortic and mitral regurgitation, volume overload occurs leading to a dilated left ventricle. This causes decreased contractility and increased compliance and shifts the pressure–volume curve to the right.
  
• In mitral and tricuspid stenosis, there is pressure overload in the left atrium and not the left ventricle. There would thus be no change in the pressure–volume curve of the left ventricle. MAP = diastolic blood pressure + [(systolic BP – diastolic BP)/3]. Even in the presence of heart failure or hypertensive encephalopathy, a controlled reduction, to a level of about 150/90 mmHg, over a period of 24–36 hours is ideal. In most patients, blood pressure can be brought down with bed rest and oral medication.
• Intravenous labetalol (2 mg/min to a maximum of 200 mg), intravenous glyceryl trinitrate (0.6–1.2 mg/h), intravenous sodium nitroprusside (0.3–1.0 mg/kg per min) or intramuscular hydralazine (5 or 10 mg repeated at half-hourly intervals) are all effective but require close monitoring.

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