Physiological rules for the heart, lungs and other pressure-based organs

Abstract

Background: The adherence of the heart to physical laws, such as Laplace's Law, may act as a measure of the organ's relative efficiency. Allometric relationships were investigated to assess the heart's efficiency concerning end-diastolic and end-systolic volumes, cardiac pressurization energy, cardiac output and mass.Methods: Data to generate allometric relationships was obtained using a literature search, identifying heart and lung data across different mammalian and bird species. Statistical analysis was carried out using ordinary least squares (OLS) estimation.Results: Near isometric relationships exist between body mass and seven parameters indicating no "efficiency of size" with scaling of the heart, and size-matching of the heart to the lungs and whole body.Even though there was equal efficiency in pressurization energy generation, cardiac output was maximally efficient in small mammals <10 kg and birds; the human heart reached only 71% efficiency. This loss in cardiac efficiency with increasing body mass can be explained by the aortic cross-section that scales following the three-quarter allometry law, compared to end-systolic and end-diastolic volumes that scale isometrically.The heart is therefore throttled by a relatively small aorta at large body size.Conclusions: Mammalian and avian hearts operate at similar efficiencies, demonstrating a high degree of symmorphosis, however cardiac output efficiency decreases in larger animals due to a relatively negative aortic cross-section allometry. This work has a myriad of potential applications including explaining cardiac dysfunction in athletes, patient-prosthesis mismatch in aortic valve replacement and why heavy exercise is associated with a worse prognosis than mild or moderate exercise.

Ultrasound images of the ascending aorta of anesthetized northern fur seals and Steller sea lions confirm that the aortic bulb maintains continuous blood flow

“…Using the median body mass of each species, the predicted SV was 34.4 mL in the northern fur seals and 212.4 mL in the Steller sea lions using SV = 0.776·BW 1.06 (Stahl, 1967) and 33.2 mL for northern fur seals and 166.5 mL for Steller sea lions using SV = 1.149·BW 0.94 (Casha et al, 2017; Mortola, 2015). For the fur seals, the predicted values are very similar to the value we measured from the anesthetized fur seals of 33.5 mL.…”

“…(Mortola, 2015; Casha et al, 2017), $$$\mathrm{Cardiac}\hspace{0.17em}\mathrm{output}\,({\rm{L}}/\min )=0.187\cdot {\mathrm{BW}}^{0.81}$$$…”

“…(Casha et al, 2017), where BW is expressed in kilograms. We calculated the equation for CO from Casha and colleagues (2017) by substituting the equation they provided relating heart mass and body mass $$(\mathrm{log}\mathrm{heart}\mathrm{mass}=1.0663\cdot \mathrm{log}\mathrm{BW}+0.5955)$$ into the equation they provided relating CO and heart mass in similarly sized mammals $$(\mathrm{log}\mathrm{cardiac}\mathrm{output}=0.7127\cdot \mathrm{log}\mathrm{heart}\mathrm{mass}+1.9168)$$. Paired t tests were run to evaluate the effects of atropine on HR and SV after excluding outliers.…”

Common Pathophysiological Pathways for Apical and Upper Lobe Lung Disease

“…In an antero-posteriorly flattened chest there is a further fourfold increase; when combined this results in a forty-fold increase in pleural stress [10,12,73,74]. A tall, unsupported apex is therefore prone to increased stress leading to apical TB and spontaneous pneumothorax; this geometrical shape may also explain the occurrence of both TB and pneumothorax in the apex of the lower lobe where ventilation-perfusion ratios and blood flow are optimal, lymphatic clearance is normal and ventilation is average [54,55].…”

Relações entre mecânica respiratória e medidas morfológicas em camundongos BALB/c.

“…No que tange ao sistema respiratório, diversos estudos realizados durante décadas, notaram que variáveis respiratórias como a resistência, a complacência, o volume e a massa pulmonar de mamíferos de diferentes dimensões seguem leis alométricas (CASHA et al, 2017;GOMES et al, 2000;STAHL, 1967), como a apresentada pela equação 2.6:…”