Lung volumes

TABLE 5.7 Predictive Equations for Static Lung Volumes and Dynamic Puimonary Function ... 

Forced expiration is commonly used to assess pulmonary function in both healthy and impaired individuals. Static measures of lung volumes (TLC, Vj, FRC) fail to detect dynamic changes in pulmonary function that are attributable to disease (e.g., asthmatic airway constriction). Obtaining maximum expiratory flow-volume (MEFV) curves (Fig. 5.21) permits derivation of key parameters in detecting changes in lung function. 

Lung volume reduction surgery is a rarely performed treatment option for heterogeneous emphysema patients with high hyperinflation. Novel semi-invasive and invasive alternatives are being developed, such as bronchial valves for heterogeneous emphysema treatment, and bronchial stents for homogeneous emphysema to reduce counteiproductive collateral ventilation. 

A suspected diagnosis of COPD should be based on the patient s symptoms and/or history of exposure to risk factors. Spirometry is required to confirm the diagnosis. The presence of a postbronchodilator FEV,/FVC ratio less than 70% [the ratio of FEV, to forced vital capacity (FVC)] confirms the presence of airflow limitation that is not fully reversible.1,2 Spirometry results can further be used to classify COPD severity (Table 12-1). Full pulmonary function tests (PFTs) with lung volumes and diffusion capacity and arterial blood gases are not necessary to establish the diagnosis or severity of COPD. 

Bullectomy, lung volume reduction surgery, and lung transplantation are surgical options for very severe COPD. These procedures may result in improved spirometry, lung volumes, exercise capacity, dyspnea, health-related quality of life, and possibly survival. Patient selection is critical because not all patients benefit. Refer to the ATS/ERS COPD standards for a detailed discussion of appropriate selection of surgical candidates.1... 

Atelectasis Decreased or absent air in a partial or entire lung, with resulting loss of lung volume. 

Pulmonary pressures. Changes in thoracic volume and lung volume cause pressures within the airways and the pleural cavity to change. These pressure changes create the pressure gradients responsible for airflow in and out of the lungs. Four pressures must be considered (see Figure 17.1) ... 

Ventilation is the exchange of air between the external atmosphere and the alveoli. It is typically defined as the volume of air entering the alveoli per minute. A complete understanding of ventilation requires the consideration of lung volumes. 

The four standard lung capacities consist of two or more lung volumes in combination (see Figure 17.4) ... 

Species Body Weight (kg) Lung Volume (ml) Minute Volume (ml min-1) Alveolar Surface Area (m2) Lung Volume % Surface Area Minute Volume % Lung Volume Minute Volume % Surface area... 

The curve crosses the y axis at a value of a. It declines exponentially as t increases. The line is asymptotic to the x axis. This curve is seen in physiological processes such as drug elimination and lung volume during passive expiration. ... 

Most lung volumes can be measured with a spirometer except total lung capacity (TLC), functional residual capacity (FRC) and residual volume (RV). The FRC can be measured by helium dilution or body plethysmography. 

High or low lung volume Volatile anaesthetic agents... 

The point to demonstrate is that resistance is lowest around the FRC. The curve rises at low lung volumes as there is direct compression of the vessels. At high lung volumes, the vessels are overstretched, which alters the flow dynamics and increases resistance further. The curve will be moved up or down by those other factors (above) which increase or decrease PVR. 

Expiration The expiratory limb is a smooth curve. At high lung volumes, the compliance is again low and the curve flat. The steep part of the curve is around FRC as pressure returns to baseline. 

The lung volume level for measurement of MEF40% and MEF40%(P) is shown by the dashed vertical line. Point of maximum inspiration is indicated by the zero point on volume axis. The v shaped pen deflection near full expiration on MEFV curve is the one second time marker for measurement of FEV, . The entire expiration-inspiration-expiration maneuver was recorded uninterrupted. 

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