Geriatric MedicineTier 2Topic

Changes associated with ageing in major organ systems

Overview

Physiological ageing produces measurable, predictable changes across major organ systems, distinct from disease - understanding these changes is essential to distinguish normal ageing from pathology and to anticipate altered physiological reserve
These changes are universal (occurring in everyone who ages) but highly variable in rate and severity between individuals - chronological age is a poor proxy for physiological/biological age

Changes by organ system

System	Key age-related change
Cardiovascular	Arterial stiffening (raised systolic BP, pulse pressure), reduced maximal heart rate response, diastolic dysfunction
Renal	Progressive GFR decline (~1mL/min/year from age ~40), reduced concentrating ability
Respiratory	Reduced chest wall compliance, reduced elastic recoil, reduced FEV1/vital capacity
Musculoskeletal	Sarcopenia (progressive muscle mass/strength loss), reduced bone density
Immune	Immunosenescence (blunted vaccine response, increased "inflammaging")
CNS	Reduced brain volume, slower processing speed (though most cognitive domains are well preserved in healthy ageing)

Ageing vs disease

Distinguishing normal ageing from early disease requires comparing against age-adjusted norms, not a single fixed "normal" range derived from younger populations - a mildly reduced eGFR or FEV1 may simply reflect expected ageing rather than a new pathological process

Clinical implications

These physiological changes explain reduced tolerance to physiological stress (illness, surgery, dehydration) in older patients even without overt organ disease - reduced reserve, not necessarily disease, is often what limits resilience
Anticipating these changes (rather than treating an older patient as a "smaller, older version" of a younger patient) informs dosing, fluid management, and risk assessment

Associated syndromes

Sarcopenia, presbycusis/presbyopia, immunosenescence, age-related GFR decline and drug dosing

Key point

Normal ageing changes compound with, but are distinct from, disease - a frail 85-year-old's reduced reserve reflects both normal ageing and any superimposed pathology, and management should account for both rather than assuming all deficits are disease-driven and therefore reversible

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