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· Most of the pulmonary function indices reach their maximum levels between 20 and 25 years of age, and then progressively decline. Static mechanical properties · Elastic recoil of the lungs decreases, causing lung compliance to increase. Due to the alveoli progressively deteriorate and enlarge after age 30 · The costal cartilages progressively calcify, causing the ribs to slant downward thus causing the thorax to become less compliant · Transpulmonary pressure difference, which is responsible for holding the airways open, is diminished with age · Reduction in chest wall compliance is slightly greater than the increase in lung compliance, resulting in an overall moderate decline in total compliance of the respiratory system. · Work expenditure of a 60 year old to overcome static mechanical forces during normal breathing is 20% greater than that of a 20 year old · The decreased compliance with age is offset by increased RR
Lung volumes and capacities · TLC typically remains the same, however, a decrease in TLC is probably due to the decreased height that typically occurs with age · RV increases with age due to alveoli enlargement and small airway closure · RV/TLC ratio increases from approx 20% at age 20 to about 35% at age 60 · As RV increases, ERV decreases · FRC typically increases · IC decreases · VC decreases about 40 to 50% by age 70
Dynamic maneuvers of ventilation The following dynamic lung functions progressively decrease with age: · Forced vital capacity (FVC) · Peak expiratory flow rate (PEFR) · Forced expiratory flow25-75% (FEF25-75%) · Forced expiratory volume in 1 second (FEV1) · Forced expiratory volume in 1 second/forced vital capacity ratio (FEV1/FVC ratio) · Maximum voluntary ventilation (MVV) It is estimated these functions decrease approx 20 to 30% throughout life. Pulmonary diffusing capacity DLCO progressively decreases with age. · Estimated to fall about 20% over the adult’s life. · Due to decreased alveolar surface area · Decreased pulmonary capillary blood flow Alveolar dead space ventilation Alveolar dead space ventilation increases with advancing age · Decreased cardiac index · Structural alterations of the pulmonary capillaries · Increases about 1 mL/year
Pulmonary Gas Exchange P(A-a)O2 progressively increases with age · Physiologic shunt · Decreased diffusing capacity Arterial Blood Gases PaO2 progressively decreases with age · Lung degeneration and hypoxemia are a normal part of aging · Acceptable PaO2 ranges for adults 60 to 90 years can be calculated by subtracting 1 mm Hg from the minimal 80 mm Hg level for every year over 60 PaCO2 remains constant throughout life · Greater diffusion ability of CO2 through the alveolar-capillary barrier Arterial-venous oxygen content difference The maximum arterial-venous oxygen content difference C(a-v)O2 tends to decrease with age · Decline in physical fitness · Less efficient peripheral blood distribution · Reduction in tissue enzyme activity Hemoglobin Concentration Anemia is a common finding in the elderly · Red bone marrow replaced by fatty marrow · Gastrointestinal atrophy, slows absorption of iron and vitamin B12 · Gastrointestinal bleeding · Insufficient income to purchase food · Decreased interest in cooking and eating adequate meals
Control of Ventilation The ventilatory response to both hypoxia and hypercapnia diminishes with age. · Reduced sensitivity of the peripheral and central chemoreceptors Snoring and OSA also increases with age Exercise Tolerance VO2max – maximal oxygen uptake · Used to evaluate an individuals aerobic exercise tolerance · Peaks at age 20 · Progressively and linearly decreases with age · From 20 to 60 years of age, decreases about 35% · Regular physical conditioning throughout life increases oxygen uptake
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