Pulmonary blood flow distribution in standing horses is not dominated by gravity.
Abstract: Recent studies using microspheres in dogs, pigs and goats have demonstrated considerable heterogeneity of pulmonary perfusion within isogravitational planes. These studies demonstrate a minimal role of gravity in determining pulmonary blood flow distribution. To test whether a gravitational gradient would be more apparent in an animal with large vertical lung height, we measured perfusion heterogeneity in horses (vertical lung height = approximately 55 cm). Four unanesthetized Thoroughbred geldings (422-500 kg) were studied awake in the standing position with fluorescent microspheres injected into a central vein. Between 1,621 and 2,503 pieces (1.3 cm3 in volume) were obtained from the lungs of each horse with spatial coordinates, and blood flow was determined for each piece. The coefficient of variation of blood flow throughout the lungs ranged between 22 and 57% among the horses. Considerable heterogeneity was seen in each isogravitational plane. The relationship between blood flow and vertical height up the lung was characterized by the slope and correlation coefficient of a least squares regression analysis. The slopes within each horse ranged from -0.052 to +0.021 relative flow units/cm height up the lung, and the correlation coefficients varied from 0.12 to 0.75. A positive slope, indicating that flow increased with vertical distance up the lung (opposite to gravity), was observed in three of the four horses. In addition, blood flow was uniformly low in three of the four horses in the most cranial portions of the lungs. We conclude that in lungs of resting unanesthetized horses, animals with a large lung height, there is no consistent vertical gradient to pulmonary blood flow and there is a considerable degree of perfusion heterogeneity, indicating that gravity alone does not play the major role in determining blood flow distribution.
Publication Date: 1996-09-01 PubMed ID: 8889734DOI: 10.1152/jappl.1996.81.3.1051Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
- Research Support
- U.S. Gov't
- P.H.S.
Summary
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The research looked into how gravity influences the distribution of blood flow in the lungs of standing horses. It concluded that gravity doesn’t primarily determine this pattern, as the blood flow distribution profile showed considerable variability.
Methods and Subjects
The study involved four Thoroughbred geldings (uncastrated male horses) which weighed between 422 to 500 kilograms. The animals were examined in an awake and standing position, ensuring a natural scenario. The researchers chose horses as their subjects because they have large lungs with a vertical height of roughly 55 centimeters. They hypothesized that the effects of gravity on pulmonary blood flow would be more visible in such animals.
- Fluorescent microspheres were injected into a central vein of each horse. These microspheres were used as markers to track and measure the distribution of blood flow within the lungs.
- Between 1,621 and 2,503 small pieces of lung tissue, representing a volume of approximately 1.3 cubic centimeters, were collected from each horse. The spatial coordinates of each piece were noted to identify their relative positions in the lung.
Findings
The researchers assessed the variability of the blood flow throughout the horses’ lungs and found the coefficient of variation ranging from 22% to 57%. This demonstrated significant differences in blood flow across various parts of the lungs for each horse. Remarkably, this heterogeneity was observed within each isogravitational plane, challenging the intuitive expectation that gravity would simply direct more blood to the lower parts of the lungs.
- The relationship between the blood flow and the vertical height up the lung was determined using a least squares regression analysis. The slopes for each horse varied from -0.052 to +0.021 relative flow units per centimeter of lung height, and the correlation coefficients ranged from 0.12 to 0.75. Remarkably, three of four horses showed a positive slope, suggesting that the blood flow increased with vertical distance up the lung, contrary to what would be expected if gravity were the dominant factor.
- Blood flow was consistently low in the uppermost parts of the lungs in three out of four horses. This, again, was unexpected if gravity were the key driver in blood distribution within the lungs.
Conclusion
The study concluded that there is no consistent vertical gradient to pulmonary blood flow in horses with large lung height. Instead, there was a high degree of perfusion heterogeneity or variable blood flow across different regions of the lungs, suggesting that gravity does not play a dominating role in determining this distribution.
Cite This Article
APA
Hlastala MP, Bernard SL, Erickson HH, Fedde MR, Gaughan EM, McMurphy R, Emery MJ, Polissar N, Glenny RW.
(1996).
Pulmonary blood flow distribution in standing horses is not dominated by gravity.
J Appl Physiol (1985), 81(3), 1051-1061.
https://doi.org/10.1152/jappl.1996.81.3.1051 Publication
Researcher Affiliations
- Department of Physiology and Biophysics, University of Washington, Seattle 98195-6522, USA.
MeSH Terms
- Animals
- Blood Flow Velocity / physiology
- Gravitation
- Horses
- Posture / physiology
- Pulmonary Circulation / physiology
Grant Funding
- HL-02625 / NHLBI NIH HHS
- HL-12174 / NHLBI NIH HHS
- HL-24163 / NHLBI NIH HHS
Citations
This article has been cited 18 times.- Ferretti G, Fagoni N, Taboni A, Vinetti G, di Prampero PE. A century of exercise physiology: key concepts on coupling respiratory oxygen flow to muscle energy demand during exercise. Eur J Appl Physiol 2022 Jun;122(6):1317-1365.
- Berg RMG, Hartmann JP, Iepsen UW, Christensen RH, Ronit A, Andreasen AS, Bailey DM, Mortensen J, Moseley PL, Plovsing RR. Therapeutic benefits of proning to improve pulmonary gas exchange in severe respiratory failure: focus on fundamentals of physiology. Exp Physiol 2022 Jul;107(7):759-770.
- Ceriotti S, Bullone M, Leclere M, Ferrucci F, Lavoie JP. Severe asthma is associated with a remodeling of the pulmonary arteries in horses. PLoS One 2020;15(10):e0239561.
- Lindahl SGE. Using the prone position could help to combat the development of fast hypoxia in some patients with COVID-19. Acta Paediatr 2020 Aug;109(8):1539-1544.
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- Frlic O, Seliškar A, Domanjko Petrič A, Blagus R, Heigenhauser G, Vengust M. Pulmonary Circulation Transvascular Fluid Fluxes Do Not Change during General Anesthesia in Dogs. Front Physiol 2018;9:124.
- Guérin C. Prone positioning acute respiratory distress syndrome patients. Ann Transl Med 2017 Jul;5(14):289.
- Aref MW, Akans E, Allen MR. Assessment of regional bone tissue perfusion in rats using fluorescent microspheres. Bone Rep 2017 Jun;6:140-144.
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- Hall ET, Sá RC, Holverda S, Arai TJ, Dubowitz DJ, Theilmann RJ, Prisk GK, Hopkins SR. The effect of supine exercise on the distribution of regional pulmonary blood flow measured using proton MRI. J Appl Physiol (1985) 2014 Feb 15;116(4):451-61.
- Harvey BG, Strulovici-Barel Y, Vincent TL, Mezey JG, Raviram R, Gordon C, Salit J, Tilley AE, Chung A, Sanders A, Crystal RG. High correlation of the response of upper and lower lobe small airway epithelium to smoking. PLoS One 2013;8(9):e72669.
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