G5i: The systemic cardiovascular response to exercise

Definition

Exercise = voluntary activity

  • Associated with extensive changes in cardiovascular system to meet demands of O2 supply + CO2 removal, heart and metabolites from working muscle
  • Heart acts as a demand pump → blood flow is directed from heart to areas of ↑ demand

CV Parameters of Exercise

Parameters

Response

Reason

HR

70 → 200bpm

↑SNS, ↓PNS

SV

70 – 140mL

↑VR, ↑FoC, ↓SVR

SVR

Isotonic = ↓

Isometric = ↑

Peripheral VD

Continuous muscle contraction constricts vessels

CO

5 → 30L/min

CO = SV x HR

MAP

↑

MAP = CO x SVR

O2 consumption

250mL → 10L/min

ODC R) shift

↑demand by myocytes

Skeletal m. BF

1L → 20L/min

Local metabolites → VD

Cardiac BF

250mL → 1L/min

Local metabolites → VD

Splanchnic BF

1.5L → 300mL

SNS/Adrenergic VC

Mechanism of CVS Response

  1. Metabolic
  2. Autonomic
  3. Hormonal
  4. Mechanical

Metabolic

    • ↑CO2, H+, 2,3 DPG → R) shift ODC → unloading of O2 & ↑O2 extraction
    • Skeletal m. & cardiac muscle → ↑metabolites:
      • ↓O2
      • ↑CO2
      • ↑H+
      • Adenosine
      • K+
      • Lactate → vasodilation

 = ↑blood flow

    • Skin → heat from exercise → VD → opening of A-V fistulae → heat loss

Autonomic

  • Sensors: cortex, mechanoR, chemoR
  • Controller: vasomotor centre
  • Effectors: ↑SNS & ↓PNS
  1. Heart → ↑HR, ↑FoC, ↑SV
  2. Resistance vessels → β2 → VD heart & skeletal vessels
  3. Capacitance vessels → α1 → VC → ↑VR → ↑SV
  4. Renal, splanchnic → α1 → VC

Hormonal

    • ↑Adr & NA release from Adrenal Gland
      • β2 → VD
      • β1 → Renal VC → ↓renal BF → directs blood to muscles

Mechanical

  • Skeletal m. pump → contraction/relaxation of skeletal m. → ↑VR
  • Thoracic pump → respiration ↓ITP → ↑VR