Different formulas to calculate mean blood pressure entail significantly different results

Abstract

Purpose: Mean ocular perfusion pressure (MOPP) is calculated as the difference between mean brachial arterial pressure (MBP; with a correction factor to compensate for differences in flow resistance and hydrostatic pressure between the arm and eye) and intraocular pressure (IOP). The main aim was to evaluate differences between the most used formulas to calculate MOPP and the effects that physical exercise may have in this parameter. Methods: Fifteen physically active, healthy subjects (6 female, 24.07 ± 3.65 years) voluntarily performed a 15‐minute protocol consisting of combined exercise including, mobility, bodyweight exercises, running, dynamic stretching, and three sets of barbell back squat at low intensities. Five different formulas retrieved from the scientific literature were used to calculate MBP. Formulas used to calculate MOPP pressure were 1) 2/3*(MBP)–IOP; 2) 2/3*(MBP–IOP); 3) 95/140*(MBP)–IOP. A three‐way analysis of variance evaluated the effect of the exercise, the formula used to calculate MBP, and the formula used to calculate the mean ocular perfusion pressure. Results: Significant effects of the exercise (F(1, 14) = 135.21, p < 0.001, η2 = 0.91), formula used to calculate mean blood pressure (F(1.06, 14.87) = 250.37, p < 0.001, η2 = 0.95), formula used to calculate mean ocular perfusion pressure (F(1.01, 14.14) = 163.98, p < 0.001, η2 = 0.92) and their interaction (F(1.48, 20.68) = 47.35, p < 0.001, η2 = 0.77) were observed. The post‐hoc results showed significant differences between most of the formulas both preexercise and postexercise. Conclusions: The results presented suggest that caution should be applied when using indirect formulas to estimate mean ocular perfusion pressure. Future research should objectively evaluate ocular perfusion pressure with a direct method to find the most reliable formula. Meanwhile, this study is published to raise awareness on the importance of choosing one or other methods when aiming to estimate physiological parameters with formulas.