Cardiorespiratory: Vascular (MEDI221/EXSC221) PDF

Cardiorespiratory: Vascular MEDI221/EXSC221 Lecture objectives Describe the intrinsic and extrinsic control of vascular tone Describe regulation of blood flow and pressure during exercise Compare physiological mechanisms for the differing blood pressure responses to aerobic...

Cardiorespiratory: Vascular MEDI221/EXSC221 Lecture objectives Describe the intrinsic and extrinsic control of vascular tone Describe regulation of blood flow and pressure during exercise Compare physiological mechanisms for the differing blood pressure responses to aerobic vs resistance exercise in terms of blood pressure  Reading Chapter 15. The Cardiovascular System McArdle, W.D., Katch, F.I. and Katch, V.L. Exercise Physiology: Nutrition, Energy and Human Performance. Lippingcott, Williams and Wilkins, Sydney, NSW, 2014. ISBN/ISSN: 9781451191554.  Active muscle needs more oxygen during exercise Four ways that this happens: 1. Local vessels dilate to increased metabolites –Lecture 6 2. Cardiac output  (linear with work rate)- Lecture 5 3. Blood flow redistributed in favour of active muscle- Lecture 6 4.  oxygen extraction from each unit of blood(mainly intrinsic) - lecture 3 & 4  proportion going to active muscle  PO2 gradient blood to muscle  offloading from Hb (Bohr effect) Active muscle needs more oxygen during exercise Four ways that this happens: 1. Local vessels dilate to increased metabolites Lec 6 2. Cardiac output  (linear with work rate) 3. Blood flow redistributed in favour of active muscle Lec 6 4.  Oxygen extraction from each unit of blood (mainly intrinsic)  proportion going to active muscle  PO2 gradient blood to muscle  offloading from Hb (Bohr effect)  Oxygen extraction greatly ↑ with exercise intensity ↑ Oxygen extraction (a-vO2 difference) From ~25% at rest To 90% in max exercise Due to: Redistribute blood ↓ away from gut (substantially ↓), liver, kidney etc NOT from brain and heart ↑ to active skeletal muscle ↑ Metabolic activity of the muscle Bohr effect ↑ PO2 gradient to muscle Muscle gets a much larger share of cardiac output Blood generally flows to tissues in proportion to their metabolic demands Blood flow is changed by vasoconstriction in some tissues and vasodilation in others (intrinsic and extrinsic control) Medicated by hormonal control and local metabolite control. Blood flow in skeletal muscle is highly regulated Most flows to oxidative fibers over the glycolytic fibers Figure 17.3  Vasoconstriction and vasodilation Small change in radius = large change in flow (Ohms law) Local (= intrinsic) control of arteriolar tone Local factors are released by the tissue to ensure perfusion (flow) meets metabolic demands 1. Temperature: Dilate with increased temp. 2. Blood flow: Dilate with pressure/stretch 3. Metabolites: ↑CO2, ↑ H+, ↑ K+, ↑ Adenosine (Heart), ↑ ATP, ↓ PO2 , ↑ Nitric Oxide Physiol Rev. 2015 Apr; 95(2): 549–601. doi: 10.1152/physrev.00035.2013 Local muscle factors strongly determine its perfusion (flow) Metabolites – Dilate with ↑ CO2, H+, K+, Adenosine, ATP, ↓ PO2 (esp. in striated muscle), Nitric Oxide Overrides some of SNS vasoconstriction ‘Functional sympatholysis’ Blocks effect of NorAd.  More about the local vasodilation in active muscle: Nitric oxide (NO) – released from the endothelium Released in response to an ↑ in blood flow (shear stress on the arterial wall) Dilates upstream arteries to promote more flow to capillaries Extrinsic control of arteriolar tone Intrinsic control – Purpose = ensure local blood flow matches tissues demand Extrinsic control- Main Purpose = Ensure maintenance of Mean arterial BP (MAP) How? Neural (Hormonal) : SNS – release of Noradrenaline  Blood Pressure BP = cardiac output X Total Peripheral Resistance (Q x TPR) Systolic BP (SBP) estimates: Work of the heart Strain against arterial walls Appropriate cardiovascular function Diastolic BP (DBP) estimates peripheral resistance (TPR) Mean arterial pressure = 2/3 DBP + 1/3 SBP Blood pressure Learning how to correctly take blood pressure at rest and during exercise is an important skill for an Exercise Physiologist. You need to show competence in this skill in labs. Please watch the BP Video (link on Moodle) explaining how blood pressure is taken correctly. Read page 310 of your text book Blood Pressure responses in aerobic exercise ↑SBP reflects increased work of the heart Delivery of blood to large muscle mass Myocardial workload can be calculated by: Rate pressure product (RPP) = HR x SBP ↓DBP reflects decreased TPR Local muscle dilation Figure 15.12 The rise in BP with resistance exercise Depends on: Muscle mass contracted Duration of contraction Relative force of contraction Dramatically ↑ the work of the heart ↑ SBP and RPP The SBP response is attenuated with regular training Figure 15.11 Blood Pressure responses to Exercise Aerobic exercise  Resistance exercise For interest: Check out Pg. 319 of textbook for study comparing peak BP at different % MVC