Pulmonary considerations in the older patient

Meryl Cohen

Introduction

Age-related changes in the pulmonary system of a healthy individual are slow and progressive. Often, the decline in pulmonary function is not noticed until the person reaches 60, 70, or even 80 years of age. Unlike the cardiovascular system, the pulmonary system has large ventilatory reserves available to compensate for the structural and physiological consequences of aging. However, in the presence of pulmonary disease, these reserves are often inadequate and can impose severe limitations on the performance of physical activities. In addition, exposure to environmental toxins over a lifetime can contribute to a more rapid decline in pulmonary function in the older person.

The age-related changes that occur in lung tissue and in the ‘musculoskeletal pump’ are discussed in this chapter. A clear distinction among the effects of aging, subclinical disease and prolonged exposure to air pollutants on the pulmonary system is difficult to establish, as all three cause similar structural and physiological abnormalities (Chan & Welsh, 1998; Wu and Shephard, 2011). General observations regarding the senescent lung and the effects of exercise and pulmonary disease on age-related changes in pulmonary function are also discussed. The clinical effects of aging on the pulmonary system and the implications for caregivers of older individuals are identified.

Pulmonary structure

Age-associated changes can be found in the anatomical structures of the pulmonary system. Both the gas-exchanging organ – the lung tissue – and the musculoskeletal pump – the thoracic cage and its muscular attachments – show decline in the older individual when they are compared to the organs of a healthy younger person (see Box 7.1).

Box 7.1

Airways

• ↑ Rigidity of trachea and bronchi (↑ calcification)

• ↓ Elasticity of bronchiolar walls

• ↓ Cilia

• Replacement of smooth muscle fibers in bronchioles with noncontractile tissue

Lungs

• ↑ Mucus layer (thickening) and ↑ mucus glands

• ↑ Thinning of alveolar walls (↓ alveolar collagen)

• ↓ Functional respiratory surface resulting from destruction of alveolar septa (loss of fibrous supporting network)

• ↑ Alveolar diameter with a ↓ in alveolar surface area

• ↓ Alveolar–capillary interface (due to ↑ alveolar size and ↓ capillary bed)

• ↑ Lung compliance

• ↓ Lung parenchymal weight

• Vascular walls stiffen as media and intima thicken

• Probable ↓ surfactant-producing cells

Respiratory Muscles

• ↓ Contractile protein

• ↑ Noncontractile protein

• ↑ Connective tissue

• ↓ Capillary numbers relative to muscle fibers

• ↑ Contraction and relaxation times

• Alteration in diaphragm position and efficiency

Skeleton

• ↓ Loss of bone mineralization

• ↓ Disc spaces

• ↓ Costal movements resulting from reduced sternal and costovertebral motion (↑ stiffness of joints and calcification)

• ↑ Anterior–posterior thorax diameter

• ↑ Kyphosis resulting from a decrease in thoracic length

↑=increase; ↓=decrease.

The lung

Changes in the alveolar membrane, including loss of the alveolar–capillary interface, and increase in alveolar size due to the destruction of the walls of individual alveoli, are the major forms of damage found in the aging lung (Brandstetter & Kasemi, 1983). The general disintegration of the supporting fibrous network of the lung and of the septa of the alveoli is considered a consequence of aging, but these changes can also result from repeated inflammatory injuries caused by life-long exposure to environmental oxidants and cigarette smoke. However, Pelkonen and colleagues have demonstrated that when older individuals stop smoking, the rate of alveolar membrane destruction is slower when alveolar tissue is compared to that of older individuals who continue to smoke (Pelkonen et al., 2001).

The musculokeletal pump

Many of the age-related changes in the thoracic cage result from the loss of mineral and bone matrix and the increased cross-linking of collagen fibers which contribute to the characteristic thoracic kyphosis and barrel chest of the older individual. The decreased mobility of the bony thorax and the less efficient resting position of the muscles of respiration alter lung performance and further contribute to the decline in pulmonary function with age (Polkey et al., 1997; Janssens et al., 1999) (see also Chapter 23, The Aging Bony Thorax).

Pulmonary physiology

The primary functions of the pulmonary system are to exchange gas between the blood and the atmospheric air and to protect the body from airborne invaders. Resting lung function results from a balance of elastic tissue forces pulling inward and musculoskeletal-pump forces pulling outward. This dynamic and mostly involuntary interplay between lung tissue and chest wall musculoskeletal components depends on the compliance of both. Age-related changes in lung tissue compliance result from structural changes in the alveoli. The decrease in efficiency of pulmonary function is not generally perceived in normal elderly people because compromise of other systems with less reserve usually accounts for the alterations in their activity patterns.

The decline in alveolar structure and the pulmonary capillary bed contributes to the changes seen in ventilation (movement of gas to and from the alveoli) and gas distribution. Effective diffusion of oxygen and carbon dioxide into and out of the bloodstream depends on the integrity of the alveolar membrane and on adequate vascularity. Because alveolar membranes and capillary interfaces are compromised in the older individual, the ventilation–perfusion mismatching that is normally found in young individuals worsens with advancing age (Chan & Welsh, 1998; Janssens et al., 1999). As a result, there are larger ventilated areas relative to perfused portions of the lung (physiological dead space) which leads to a noticeable reduction in diffusing capacity (see Box 7.2).

Box 7.2