Cardiopulmonary System in Exercise and Aging

How do aging and exercise interact with life expectancy?

• Aging effects + exercise effects discussed

• Exercise slows aging → synergistic benefit

How has the fraction of population >65 changed?

• 1900: 4%

• 2000: 12.4%

• Now: 18%

• Expected 2050s: 25%

What are the major mechanisms of aging?

• Oxidative stress

• Inadequate repair of damage

• DNA theory: ↑ DNA damage with age

• Telomere theory: limits cell division

• Dysregulation of cell number

• Clinical examples: AMD, presbycusis, NAFLD

How does aging affect the cardiovascular system?

• ↓ Max HR

• ↓ Max stroke volume (↓ preload, contractility, plasma volume)

• ↑ TPR

• ↓ Max cardiac output (~30%)

• Qc = HR × SV

What changes occur with aging in HR and SV?

• ↓ Max HR

• ↓ Peak SV

• ↓ Peak CO → ↓ VO₂max

• ↑ Afterload → ↑ cardiac work

• PCWP ~ LA pressure

What vascular changes occur with aging?

• ↓ Arterial compliance → ↑ BP, ↑ afterload

• ↓ CO → LV hypertrophy (eccentric)

• ↑ wall thickness, ↓ cavity volume

How do vascular changes reduce O₂ delivery/utilization?

• ↓ Vasodilation (ROS ↓ eNOS/NO)

• ↓ Capillary density

• ↓ Blood flow distribution

• ↓ Mitochondrial volume → ↓ O₂ consumption

How does aging affect the pulmonary system?

• Rib cage stiffer → ↓ max ventilation

• ↑ FRC → limits tidal volume during exercise

• Abdominal weight worsens diaphragm descent

What are pulmonary aging effects?

• ↑ Pulmonary compliance

• ↓ Chest wall compliance

• ↓ Elastic recoil

• ↓ Mucociliary clearance

• Larger alveoli/ducts (↑ FRC breathing)

How does aging affect compliance curves?

• ↑ Pulmonary compliance → ↑ FRC

• ↓ Elastic recoil → ↑ air trapping, ↑ RV

How do PFTs change with aging?

• Most measures ↓ with age

• TLC unchanged (anatomic size)

What are skeletal muscle changes with aging?

• Sarcopenia: ↓ muscle mass, ↓ fiber number/size (esp. type II)

• ↓ Capillary density, ↓ mitochondria → ↓ O₂ consumption

• Loss of type II motor neurons → ↓ strength

How is energy expenditure measured?

• Determination of VO₂ max

• Direct calorimetry: heat production

• Indirect calorimetry: O₂ consumption (1 L O₂ ≈ 5 kcal)

What is mass‑specific metabolic rate and why does it matter?

• Smaller animals → larger surface area/body mass ratio → require more energy per gram to maintain temperature.

• Must correct for body mass/muscle mass when comparing metabolic rates across species.

What is BMR and what factors affect it?

• Definition: Minimum rate of energy production to sustain vital functions in waking state (~60–75% daily expenditure).

• Factors: Age (↓ muscle mass), Gender (muscle mass differences), Weight (body mass correction), Hormonal status (thyroid hormone).

• Hyperthyroid → ↑ BMR.

How does physical activity affect energy expenditure?

• Accounts for 15–30% of daily expenditure.

• Can ↑ metabolic rate 10× resting during large muscle exercise (walking, running, swimming, cycling).

• Influences body composition and alters BMR.

How is metabolic rate related to energy metabolism?

• Metabolic rate = energy expenditure → heat production.

• Calories: 1 kcal = energy to raise 1 L water by 1°C.

• O₂ consumption: indirect measure (1 L O₂ ≈ 5 kcal).

• Direct calorimetry: measure body heat.

• Indirect calorimetry: measure O₂ consumption.

How is energy expenditure measured in practice?

• Indirect calorimetry: VO₂ uptake proportional to energy production.

• Example: 250 ml O₂/min → ~1800 kcal/day (5 kcal/L × 0.25 L/min × 1440 min/day).

What is VO₂ max and what factors affect it?

• Gold standard for endurance performance.

• Factors: exercise mode, % muscle mass engaged, heredity, training level, age.

• VO₂max falls with age.

• Tight linear relationship between O₂ delivery and O₂ uptake.

What systems determine VO₂ max?

• Lung function: brings O₂ in.

• Cardiac function: transports O₂.

• Vascular function: shunts O₂ to exercising tissues.

• Muscle function: mitochondria consume O₂.

• VO₂max = Qc max × max O₂ extraction.

What limits VO₂ max during exercise?

• Equation: VO₂max = (HRmax × SVmax) × (max a‑vO₂ diff).

• Perfusion limitation (cardiac output): most common (67–95%).

• Diffusion limitation (O₂ extraction): more common in highly trained (~33%).

How does cardiac output change with exercise?

• ↑ CO parallels ↑ VO₂.

• ↑ a‑vO₂ diff also contributes.

• Fick’s law: VO₂ = Q × a‑vO₂ diff.

How does aging affect exercise performance?

• ↓ CV capacity

• ↓ Pulmonary capacity

• ↓ Neuromuscular capacity

• Orthopedic challenges

• Overall performance ↓ with age.

How does VO₂ max decline with age?

• Decline inevitable, but endurance training maintains higher values.

• Sedentary vs trained older individuals show differences.

• VO₂max ↓ 5–15% per decade after 25.

What causes VO₂ max decline with aging?

• ↓ Physical activity

• Physiological aging

• Pathological conditions

• ↓ Max CO, HR, SV, a‑vO₂ diff

• ↓ O₂ utilization (↓ mitochondria, ↓ capillary density)

How does training impact health and fitness?

• Improves CV, pulmonary, skeletal muscle function.

• ↓ ROS generation.

• Counters aging effects.

How does exercise training improve cardiopulmonary fitness?

• ↑ Max stroke volume

• ↑ Max CO (HR unchanged)

• ↑ O₂ delivery

• Vascular: ↑ vasodilatory capacity, ↑ capillary density, ↑ NO‑mediated dilation

• Slows age‑induced decline.

How does training affect pulmonary system?

• Training does not change lung tissue or flow rates.

• Improves respiratory muscle strength/endurance → ↑ ventilation capacity.

How does training affect skeletal muscle?

• ↑ Angiogenesis (capillarity)

• ↑ Mitochondrial biogenesis

• ↑ Protein synthesis, hypertrophy

• ↑ Satellite cell activation → repair/regeneration

How does training impact aging process?

• Aging ↓ CV, pulmonary, skeletal muscle capacity.

• Training ↑ capacity of these systems.

• Older individuals can still ↑ aerobic capacity (Tufts studies).

• “Cap” lower, but adaptation intact.

How does VO₂ max vary across fitness levels and age?

• VO₂ max falls with age regardless of fitness.

• Equation: VO₂max = (HR × SV) × % O₂ extraction.

• Aging ↓ HR, SV, O₂ extraction (↓ capillary density, ↓ muscle blood flow).