2008B15 Describe the changes that occur with ageing that can affect
oxygen delivery to the tissues during moderate exercise.

 

List:

·       Intro

·       Ageing and cardiac output

·       Ageing and oxygen content

 

Intro:

Ageing

·  Gradual time-dependent loss of cellular function and physiological reserve, resulting in death

Moderate exercise

·  3-6 METs = VO2 750-1500mL/min

·  e.g. walking up stairs

·  Predominantly aerobic metabolism

·  Dependent upon oxygen delivery

Oxygen delivery

·  DO2 = CO x CaO2

·  Where CaO2 = [Hb] x 1.34 x SaO2 + 0.03 x PaO2 (per L)

Summary

·  ↓Cardiac output

o Resting CO: ↓1% per year with age

o Max CO: more substantial decrease

o Decline attenuated with training

·  ↓Oxygen content

·  Hence decreased reserve

 

Factors decreasing cardiac output:

↓Preload (PL)

·  ↓Blood volume (↓lean mass)

·  ↓Skeletal muscle pump (sarcopaenia)

·  ↓LV compliance (LVH)

↑Afterload (AL)

·  ↓Aortic compliance, ↓Windkessel effect

o Media thickened, less elastin

o Intima thickened, fibrotic

↓Rate (HR)

·  ≈ 220 – (age x 0.7)

·  Decreased sympathetic response

o ↓β1 Adrenoceptors

o ↓Post-adrenoceptor signalling

o ↓SNS response to exercise, ↓baroreceptor reflex

o Partly offset by ↑circulating noradrenaline and ↓noradrenaline reuptake

·  Impaired conduction

o ↓Conduction velocity

o ↓Pacemaker cells in SA and AV nodes (50% age 20, 10% age 75)

o Fatty, fibrous infiltration of conduction system

↓Contractility (CY)

·  ↓Myocyte number

o 2° to apoptosis, necrosis

·  Partly offset by concentric hypertrophy

o 2° to ↑afterload

Comorbidities

·  Hypertension: ↑SVR -> ↑AL

·  Coronary artery disease ->↓O2 supply -> ↓work

·  Cardiomyopathy: ↓contractility

·  Severe valvular disease (e.g. aortic stenosis) -> fixed stroke volume

·  Atrial fibrillation -> ↓preload (especially important with poorly compliant LV)

 

Factors decreasing oxygen content:

↓Haemoglobin

·  Senile anaemia

o ↓Bone marrow function

·  ↓Renal function

o ↓EPO production in response to anaemia

↓VA max

·  ↓Respiratory muscle strength

o Respiratory muscle sarcopaenia

·  ↑Work of breathing

o Senile emphysema -> ↓radial traction -> ↑dynamic compression

o Ossification of costal cartilage -> ↓chest wall compliance

↑V/Q mismatch

·  Emphysema -> ↑lung compliance/↓radial traction -> ↑alveolar collapse

·  Closing capacity exceeds FRC when upright at age 66

↓Diffusion rate

·  ↑Thickness (fibrosis)

·  ↓Area (senile emphysema)

 

 

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