What determines perfusion: diastolic blood pressure, systolic blood pressure, arterial pressure, pulse pressure, or ejection fraction (EF)?

Determinants of Coronary Perfusion

Diastolic blood pressure is the primary determinant of coronary perfusion, as coronary perfusion pressure is calculated as the difference between diastolic blood pressure and left ventricular end-diastolic pressure. 1

Understanding Coronary Perfusion Pressure

Coronary perfusion occurs primarily during diastole when the heart muscle relaxes. This physiological process is governed by several key factors:

Primary Determinant: Diastolic Blood Pressure

• Coronary flow is normally autoregulated so that within wide limits of changes in perfusion pressure (which approximate to diastolic BP), blood flow to the heart remains constant 1
• Population-based studies have provided evidence that low diastolic perfusion pressure (<50 mmHg) is associated with a higher prevalence of primary open-angle glaucoma, demonstrating the importance of diastolic pressure for tissue perfusion throughout the body 2
• Myocardial perfusion pressure is defined as the aortic diastolic pressure minus the right atrial diastolic pressure, which correlates with coronary blood flow 3

Secondary Determinants

1. Mean Arterial Pressure

   • Ocular perfusion pressure is calculated as the difference between blood pressure (at systole or diastole) and intraocular pressure 2
   • Nocturnal mean arterial pressure 10 mmHg lower than daytime mean arterial pressure may predict progression of normal-tension glaucoma and increased risk of visual field loss 2

2. Pulse Pressure

   • Pulse pressure (difference between systolic and diastolic blood pressure) represents the force that the heart generates each time it contracts 4
   • Widened pulse pressure is associated with increased risk of cardiovascular events, particularly coronary disease, in patients with hypertension 4
   • In middle-aged and elderly patients, pulse pressure shows strong predictive value for cardiovascular events 4

3. Ejection Fraction

   • While ejection fraction influences cardiac output, it is not a direct determinant of coronary perfusion pressure
   • Ejection fraction is defined as the stroke volume divided by the end-diastolic volume for the relevant ventricular chamber of the heart 2
   • In heart failure with preserved ejection fraction, LV wall thickness and mass index increased with higher systolic blood pressure, but functional measures reflecting diastolic LV function decreased with higher diastolic blood pressure 5

Clinical Implications

• In patients with coronary artery disease and left ventricular hypertrophy, lowering the diastolic blood pressure below the low-mid 80s results in an increased frequency of myocardial infarction (the J-curve relationship) 1
• Fractional flow reserve (FFR) measures the maximum achievable myocardial blood flow in the presence of a coronary artery stenosis as a percentage of the maximum blood flow in a completely normal artery 2
• A myocardial perfusion pressure at 10 min of CPR of 20 mmHg or less is an excellent predictor of poor survival (negative predictive value = 96%) 3

Common Pitfalls and Caveats

• Relying solely on systolic blood pressure measurements when assessing coronary perfusion risk
• Failing to consider the J-curve relationship between diastolic blood pressure and myocardial infarction in high-risk patients
• Not accounting for coronary flow reserve impairment in the presence of severe coronary artery stenosis and/or left ventricular hypertrophy
• Overlooking the importance of diastolic blood pressure in patients with coronary artery disease

In summary, while multiple hemodynamic parameters influence overall cardiovascular function, diastolic blood pressure stands as the primary determinant of coronary perfusion, with mean arterial pressure and pulse pressure playing important secondary roles.