Neural, humoral and mechanical factors affecting cardiac function and the peripheral vasculature were examined to assess the relative importance of peripheral vs cardiac factors in the control of cardiac output during exercise. First, I examined neural vs local regulation of humoral vasoconstrictors endothelin-1 (ET) and NPY, in anesthetized dogs, and showed that plasma ET levels, in contrast to NPY, increase in response to systemic hypotension but not carotid sinus baroreceptor activation. This did not occur with intact vagi suggesting an interaction of neural and humoral factors. In the next two studies I separated peripheral vascular and cardiac neural influences on cardiac output (CO) and right atrial pressure (Pra) responses during graded exercise by comparing cardiac denervated heart transplant patients (HT) with normally innervated subjects. The increase in Pra was higher in HT than normals but stabilized as the CO increased at peak effort. Stimulation of the heart with dobutamine in 2 patients did not increase exercise capacity, suggesting that peripheral not cardiac factors limit exercise in HT patients. The rise in central venous pressure at exercise onset was similar in both groups which demonstrates the importance of the mechanical effect of muscle contraction vs reflex changes in mobilizing blood from the peripheral vasculature at exercise onset. In the fourth study I assessed whether large changes in human body mass, induced by isolated gastric bypass surgery, would affect the heart rate (HR)/oxygen consumption (VO2) relationship during exercise. Peak absolute VO2 was significantly lower in the previously obese group vs obese and control groups despite similar normalized 24-hour energy expenditure. HR was higher in the previously obese at a given submaximal VO2 due to the higher relative VO2, suggesting a significant loss of muscle mass and supporting the idea that HR is a function of the relative VO2. In the fifth study I assessed the influence of
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.29098 |
| Date | January 1995 |
| Creators | Notarius, Catherine F. |
| Contributors | Magder, Sheldon (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Physiology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001468313, proquestno: NN08140, Theses scanned by UMI/ProQuest. |
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