What do normal pulmonary artery (PA) and central aortic pressure (CAP) waveforms look like?

Normal Pulmonary Artery (PA) and Central Aortic Pressure (CAP) Waveforms

Normal pulmonary artery and central aortic pressure waveforms have distinct characteristics that reflect their physiological functions, with the PA waveform showing lower pressures and a more rounded contour compared to the aortic waveform which displays a sharper systolic upstroke and a clear dicrotic notch. 1

Normal Central Aortic Pressure (CAP) Waveform Characteristics

• A normal central aortic pressure waveform has a rapid, steep systolic upstroke representing left ventricular ejection, with the first shoulder occurring at peak blood flow velocity 1
• The waveform displays a visible dicrotic notch representing aortic valve closure, which is a key characteristic of a good arterial waveform 1
• Two visible demarcations are present on the central aortic pressure wave:
  • The first (early) shoulder generated by LV ejection
  • The second shoulder representing the reflected pressure wave, typically occurring in mid-to-late systole 1, 2
• Normal central aortic systolic pressure is typically lower than peripheral (brachial) systolic pressure due to pressure amplification that occurs as the pressure wave travels peripherally 2, 3
• Mean arterial pressure falls by only 1-2 mmHg between the aorta and peripheral arteries, while systolic pressure increases and diastolic pressure decreases in more distal arteries 3

Normal Pulmonary Artery (PA) Waveform Characteristics

• Normal mean pulmonary arterial pressure (mPAP) at rest is 14.0 ± 3.3 mmHg in healthy individuals, rarely exceeding 20 mmHg 4
• The PA waveform has a more gradual upstroke compared to the aortic waveform, reflecting the lower pressure and more compliant pulmonary vasculature 5
• Normal pulmonary artery pulse pressure (systolic minus diastolic PA pressure) is proportionally higher relative to mean pressure than in the systemic circulation 5
• The PA waveform typically shows:
  • A systolic peak
  • A dicrotic notch (less pronounced than in aortic waveform)
  • A diastolic decay 5
• Wave reflection can be quantified in the PA waveform by measuring:
  • Time to inflection point (Ti) - the time between pressure upstroke and systolic inflection point
  • Pressure augmentation (ΔP) - the difference between systolic PA pressure and pressure at inflection point
  • Augmentation index (ΔP/PPAP) 5

Clinical Significance of Waveform Patterns

• Increased wave reflection amplitude in the aortic waveform predicts all-cause 15-year mortality, making accurate waveform assessment critical 1, 2
• Abnormal wave reflection patterns affect left ventricular loading and can cause myocardial hypertrophy, fibrosis, and dysfunction 1, 2
• In pulmonary hypertension, the PA waveform shows:
  • Increased mean pressure (>25 mmHg at rest)
  • Higher pulse pressure
  • Earlier wave reflections, particularly in chronic pulmonary thromboembolism compared to primary pulmonary hypertension 5
• The ratio of early transmitral velocity to early diastolic velocity of the mitral annulus (E/Ea) is the major determinant of pulmonary artery systolic pressure in conditions like moderate to severe aortic stenosis 6

Technical Considerations for Waveform Measurement

• Proper positioning of the arterial transducer at heart level is critical, as hydrostatic pressure differences can cause errors of approximately 2 mmHg for every inch above or below heart level 3
• Central aortic pressure can be measured invasively with a pressure sensing catheter or wire, or estimated non-invasively via radial arterial tonometry and a general transfer function 2, 7
• For non-invasive assessments of central aortic pressure, calibration should be performed using peripheral diastolic and mean arterial pressures, which remain relatively constant throughout the arterial tree 2
• Novel methods for deriving aortic pressure from aortic flow velocity have been developed, showing good agreement with directly measured pressure (mean RMS error 2.4 ± 1.0 mmHg) 8