Aaron R Casha1,2, Liberato Camilleri3, Alexander Manché2, Ruben Gatt4, Marilyn Gauci5, Marie-Therese Camilleri-Podesta1, Joseph N Grima4, Marco Scarci6, Stanley Chetcuti7. 1. Biomedical Sciences, Faculty of Medicine, University of Malta, Msida, Malta. 2. Department of Cardiac Services, Mater Dei Hospital, Msida, Malta. 3. Department of Statistics and Operational Research, University of Malta, Msida, Malta. 4. Metamaterials Unit, Faculty of Science, University of Malta, Msida, Malta. 5. Department of Anaesthesia, Mater Dei Hospital, Msida, Malta. 6. Department of Thoracic Surgery, University College London Hospital, London, UK. 7. Cardiovascular Center, University of Michigan, Ann Arbor, Michigan, USA.
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.
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.
Authors: V Cavallaro; M Petretta; S Betocchi; C Salvatore; G Morgano; V Bianchi; R Breglio; D Bonaduce Journal: Eur Heart J Date: 1993-07 Impact factor: 29.983