Non-linear response of descriptors of myocardial oxygenation balance to pharmacologically induced blood pressure changes.

A. Response of oxygen delivery (ΔDO2, red, n = 88) and myocardial oxygen consumption (ΔMVO2, dark blue, n = 74) relative to their baseline (arbitrarily set at a MAP of 70mmHg). Both, ΔDO2 and ΔMVO2 reveal an autoregulatory plateau and steep slopes beyond autoregulatory limits. Within the autoregulation zone, DO2 consistently surpasses MVO2, whereas there is mismatch between DO2 and MVO2 outside autoregulatory limits. At hypotension, ΔMVO2 is no more matched by ΔDO2, while there is redundant oxygen supply at hypertensive MAP beyond 130 mmHg. B. Curvilinear response to MAP variation of arterio-venous difference (ΔDO2 - ΔMVO2; purple n = 74) and myocardial oxygenation response (%OS-SI; green, n = 94). Note upslope beyond autoregulatory limits. C. Curvilinear response to MAP of coronary sinus oxygen saturation (ScsO2, purple, n = 75) and D. oxygen excess Ω (blue, n = 75). E. MAP-associated OS-SI rise is accompanied by falling coronary blood oxygen extraction ratio (O2eER, black, n = 75), due to improving DO2. x-axis intercept of fitted curves is at a MAP of 50-60mmHg. This indicates the lower limit of autoregulation and is consistent with calculated limits (see S1 File). Line: fitted mean of non-linear regression; shaded area: 95% confidence interval.