Enhanced left ventricular contractility in autonomic failure: assessment using pressure-volume relations

Area of Science:

• Cardiology
• Autonomic Neuroscience
• Physiology

Background:

• Severe autonomic failure often presents with both supine hypertension and orthostatic hypotension.
• Mechanisms contributing to hypotension include inadequate preload, insufficient arterial resistance, and abnormal cardiac performance.

Purpose of the Study:

• To clarify the mechanisms underlying autonomic failure by assessing left ventricular performance and contractility.
• To compare cardiac function in patients with autonomic failure to normal subjects under varying conditions.

Main Methods:

• Radionuclide ventriculography and systolic pressure-volume relations were used to assess left ventricular performance.
• Measurements were taken in the supine position and during graded head-up tilt in 11 patients with autonomic failure and 12 normal subjects.
• Phenylephrine infusion was used for pharmacologic afterload augmentation after autonomic blockade.

Main Results:

• Patients with autonomic failure showed decreased end-diastolic volume, end-systolic volume, and stroke volume with increasing tilt.
• Supine ejection fraction and cardiac output were similar between autonomic failure patients and normal subjects.
• Autonomic failure patients exhibited significantly greater slopes of pressure-volume relations and supine pressure/volume ratios, indicating hypercontractility.

Conclusions:

• Patients with autonomic failure demonstrate hypercontractile left ventricular performance.
• The heart in autonomic failure is well-matched to elevated peripheral resistance, contributing to the characteristic blood pressure abnormalities.