Cardiovascular performance of modern swine does not comply with allometric scaling laws

Abstract Text: In view of long-standing concerns about possible consequences regarding the cardiovascular capacity and adaptability of modern pigs we investigated the proportionality and performance of porcine hearts over a wide range of body weights (25 – 225 kg), according to allometric scaling laws. Specifically, we tested the hypothesis that both heart mass (HM) and cardiac output (CO) scale with body mass (M) to the power of 0.75 (HM or CO= a.M0.75), stroke volume (SV) and left ventricular end-diastolic volume (LVEDV) to the power of 1.00. For this purpose, 21 Yorkshire x Landrace pigs were instrumented under anesthesia to measure CO and SV and LVEDV. Subsequently, animals were sacrificed and hearts were excised and weighed and tissue samples of the LV anterior myocardial wall analysed for collagen content. Using a linear mixed model, the scaling coefficients of the relations between M and CO, SV, HM, and LVEDLV were determined. The 95% confidence intervals of the power-coefficient b for HM were 0.67 – 0.88, encompassing the predicted value of 0.75, indicating that HM increased proportionally to M. In contrast, the 95% confidence intervals of power-coefficient b for CO amounted 0.40-0.65, thus failing to encompass the predicted value of 0.75. This was principally due to the lack of proper scaling of SV as the confidence interval of 0.52-0.83 failed to encompass the predicted value of 1.0, which in turn appeared to be due to a lack of scaling of LVEDV as its confidence interval of b values amounted 0.57-0.99, thus failing to encompass the predicted value of 1.0. The increase of HM without a proportional increase of LV volume, was accompanied by a doubling of collagen content in the LV of swine >150 kg compared to swine <75 kg (p<0.05). In conclusion, cardiac geometry and function of modern swine fail to obey allometric scaling laws, likely due to an increased extracellular matrix deposition preventing physiological remodelling during growth.

Keywords: allometric scaling laws, cardiovascular system, swine