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The Journal of physiology1987; 387; 425-440; doi: 10.1113/jphysiol.1987.sp016582

Transmural coronary vasodilator reserve and flow distribution during maximal exercise in normal and splenectomized ponies.

Abstract: 1. Transmural distribution of myocardial blood flow was studied using 15 micron diameter radionuclide-labelled microspheres in six normal ponies and nine splenectomized ponies at rest, and during maximal exercise performed without as well as with adenosine infusion (3 microM kg-1 min-1). The splenectomized ponies were also studied during submaximal exercise performed at 75% of the workload. 2. Maximal exertion in normal ponies increased heart rate (348%), mean arterial blood pressure (40.9%), rate-pressure product (563%), arterial O2 content (43.2%), and mean pulmonary artery pressure (247%). Accompanying these changes, the left ventricular, septal and right ventricular myocardial blood flows increased 419, 500, and 921% above control values, respectively, and the perfusion in all regions became nearly homogeneous. 3. Adenosine infusion during maximal exercise in normal ponies caused further significant increments in transmural myocardial blood flow in all regions as coronary vascular resistance decreased, thereby demonstrating considerable unutilized coronary vasodilator capacity. 4. In splenectomized ponies, with maximal exercise heart rate rose to a similar value as in normal ponies but mean aortic pressure, rate pressure product, pulmonary artery pressure and arterial O2 content were significantly less than in normal ponies (P less than 0.01). 5. Transmural myocardial perfusion in the splenectomized ponies also increased markedly with both exercise intensities and no significant differences were observed. 6. In the left ventricle and the septum of splenectomized ponies, transmural blood flow levels during maximal exertion were significantly higher (P less than 0.05) than in normal ponies. Adenosine infusion during maximal exercise in splenectomized ponies failed to cause further increments in blood flow to the inner layers of the left ventricle and the septum. 7. It is concluded that marked augmentation of arterial O2 content in normal ponies helped limit the increment in left ventricular myocardial perfusion required during maximal exertion, and thereby helped preservation of considerable unutilized coronary vasodilator capacity.
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Publication Date: 1987-06-01 PubMed ID: 3116213PubMed Central: PMC1192513DOI: 10.1113/jphysiol.1987.sp016582Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This study examines the effect of extreme exertion on heart function, specifically blood flow, in both normal and spleen-removed ponies. It discovered variances in blood flow and cardiovascular responses between the two types of ponies during extreme exertion and recognized a considerable unused coronary vasodilator capacity.

Study Design and Methodology

  • The team undertook a comparative study of transmural myocardial blood flow — the blood flow through the wall of the heart — in both normal and splenectomized (spleen-removed) ponies.
  • The investigation involved resting conditions and during maximal exercise, which is the most intense level of exercise an individual pony can undertake. Adenosine, a drug commonly used to simulate the effects of intense exercise on the heart, was also administered.
  • The researchers used radionuclide-labelled microspheres, small particles that are radioactive, to track the blood flow inside the heart.

Findings in Normal Ponies

  • In normal ponies, performing at maximal exertion resulted in significant changes in various heart-related measures, such as heart rate, arterial blood pressure, arterial oxygen content, and average pulmonary artery pressure.
  • Furthermore, the blood flow in the heart’s left ventricle, septal (the wall separating the chambers of the heart), and right ventricle increased significantly too.
  • However, when adenosine was introduced during maximal exercise, the blood flow through the heart substantially increased as the coronary vascular resistance fell. This indicated a significant unutilized coronary vasodilator capacity, meaning the coronary arteries could still expand further to allow more blood flow.

Findings in Splenectomized Ponies

  • In ponies without a spleen, maximal exercise caused an increase in heart rate similar to the normal ponies.
  • However, observations like mean aortic pressure, pressure product rate, arterial oxygen content, and pulmonary artery pressure were significantly lower than those recorded in normal ponies.
  • Moreover, the splenectomized ponies’ blood flow in the left ventricle and septum was significantly higher during maximal exertion compared to normal ponies. However, introducing adenosine did not result in further increase in blood flow.

Conclusions

  • The researchers concluded that the increased arterial oxygen content in normal ponies helped limit the increase in left ventricular myocardial perfusion required during maximal exertion.
  • This mechanism thus allowed a considerable unutilized coronary vasodilator capacity to be preserved. In other words, there was still room for the coronary arteries to dilate further and allow more blood flow if needed.

Cite This Article

APA
Manohar M. (1987). Transmural coronary vasodilator reserve and flow distribution during maximal exercise in normal and splenectomized ponies. J Physiol, 387, 425-440. https://doi.org/10.1113/jphysiol.1987.sp016582

Publication

The Journal of physiology
ISSN: 0022-3751
NlmUniqueID: 0266262
Country: England
Language: English
Volume: 387
Pages: 425-440

Researcher Affiliations

Manohar, M
  • Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois, Urbana-Champaign 61801.

MeSH Terms

  • Animals
  • Carbon Dioxide / blood
  • Coronary Circulation
  • Hemodynamics
  • Hemoglobins / metabolism
  • Horses / physiology
  • Oxygen / blood
  • Physical Exertion
  • Regional Blood Flow
  • Vasodilation

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Citations

This article has been cited 3 times.
  1. Goodwill AG, Dick GM, Kiel AM, Tune JD. Regulation of Coronary Blood Flow. Compr Physiol 2017 Mar 16;7(2):321-382.
    doi: 10.1002/cphy.c160016pubmed: 28333376google scholar: lookup
  2. Joyner MJ, Casey DP. Regulation of increased blood flow (hyperemia) to muscles during exercise: a hierarchy of competing physiological needs. Physiol Rev 2015 Apr;95(2):549-601.
    doi: 10.1152/physrev.00035.2013pubmed: 25834232google scholar: lookup
  3. Fan L, Wang H, Kassab GS, Lee LC. Review of cardiac-coronary interaction and insights from mathematical modeling. WIREs Mech Dis 2024 May-Jun;16(3):e1642.
    doi: 10.1002/wsbm.1642pubmed: 38316634google scholar: lookup
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