Golden Ratio and the Proportionality Between Pulmonary Pressure Components in Pulmonary Arterial Hypertension

BACKGROUND: The golden ratio (phi, Phi = 1.618) is a proportion that has been found in many phenomena in nature, including the cardiovascular field. We tested the hypothesis that the systolic over mean pulmonary artery pressure ratio (sPAP/mPAP) and the mean over diastolic pressure ratio (mPAP/dPAP) may match Phi in patients with pulmonary arterial hypertension (PAH) and in control patients. METHODS: In the first, theoretical part of the study, we discuss why our hypothesis is consistent with three known hemodynamic features of the pulmonary circulation: (1) the 0.61 slope of the mPAP vs sPAP relationship, (2) pulmonary artery pulse pressure and mPAP have an almost 1:1 ratio, and (3) the proportional relationship among sPAP, mPAP, and dPAP. In the second part of the study, fluid-filled pressures were analyzed in 981 incident, untreated PAH and high-fidelity pressures were also analyzed in 44 historical control patients (mPAP range, 9-113 mm Hg). RESULTS: In PAH (non-normal distribution), median values of sPAP/mPAP and mPAP/dPAP were 1.591 (98%Phi) and 1.559 (96%Phi), respectively. In control patients (normal distribution), mean sPAP/mPAP and mPAP/dPAP were 1.572 (97%Phi) and 1.470 (91%Phi), respectively. In both PAH and control patients, this was consistent with the Phi hypothesis, assuming < 1 mm Hg error in estimation of sPAP, mPAP, and dPAP on average. CONCLUSIONS: In PAH and in control patients, the fluctuations in sPAP and dPAP around mPAP exhibited a constant scaling factor matched to Phi. This remarkable property allows linkage of various empirical observations on pulmonary hemodynamics that were hitherto apparently unrelated. These findings warrant further confirmation in other types of pulmonary hypertension and warrant explanation.