The role of capacitance vessels and blood flow distribution (BFD) in the control of venous return and cardiac output were examined. First, saline infusion during exercise in humans maintained plasma volume, reduced heart rate and core temperature, but did not change endurance time. Second, the vascular mechanics of the skin were studied in dogs. The skin has a large venous compliance (C$ sb{ rm v})$ and a long time constant of venous drainage $( tau sb{ rm v}),$ and may act as a blood reservoir during heat stress. A rise in core or skin temperature increases C$ sb{ rm v}$ and decreases venous resistance (R$ sb{ rm v}),$ but does not change $ tau sb{ rm v}.$ The last three studies were performed in dogs on circulatory bypass. The third study examined the mechanisms of increase in venous return during heat stress. Splanchnic (SPL) unstressed volume (V$ sb{ rm u})$ decreases with no change in R$ sb{ rm v},$ C$ sb{ rm v},$ $ tau sb{ rm v}$ or BFD during heat stress. This decrease in V$ sb{ rm u}$ is abolished by ganglionic blockade but not by $ alpha$ or $ beta$-receptor blockade. The fourth study looked at the effects of the baroreflex on capacitance vessels and BFD. A decreases in carotid sinus pressure from 200 to 50 mm Hg increases SPL blood flow and C$ sb{ rm v},$ and decreases SPL R$ sb{ rm v},$ $ tau sb{ rm v}$ and V$ sb{ rm u}.$ The decrease in V$ sb{ rm u}$ is abolished by ganglionic blockade, but is only partially reversed by $ alpha$-receptor blockade. The last study examined the effects of neuropeptide Y (NPY) on capacitance vessels and BFD. NPY decreases SPL V$ sb{ rm u}$ with no change in R$ sb{ rm v},$ C$ sb{ rm v},$ $ tau sb{ rm v}$ or BFD. Thus, NPY may play a role in the control of venous return.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.74611 |
| Date | January 1990 |
| Creators | Deschamps, Alain |
| 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: 001214645, proquestno: AAINN67626, Theses scanned by UMI/ProQuest. |
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