Work of breathing

Most CF patients have an increased caloric need due to increased energy expenditure through increased work of breathing and increased basal metabolism. Prevention of malnutrition requires early nutritional intervention. In patients with mild lung disease and well-controlled absorption, required caloric intake is approximately 100% to 120% of the recommended daily allowance (RDA) for age.15 As lung disease progresses, caloric requirements increase. 

More physiologically, it can be shown that work is given by pressure x volume. This enables indices such as work of breathing to be calculated simply by studying the pressure-volume curve. 

The power required to sustain physiological processes can be calculated by using the above equation. If a pressure-volume loop for a respiratory cycle is plotted, the work of breathing may be found. If the respiratory rate is now measured then the power may be calculated. The power required for respiration is only approximately 700-1000 mW, compared with approximately 80 W needed at basal metabolic rate. 

When administered in sufficient quantities by an appropriate route, bronchodilators will usually reduce the work of breathing, relieve asthmatic symptoms, and improve ventilation. Bronchodilators can produce a substantial increase in pulmonary function by relaxing bronchial smooth muscle, thus dilating the airways. Commonly used bronchodilators are discussed next. 

Postexposure survival remains a perplexing problem. In the early work, death was probably due to many factors such as exhaustion from the work of breathing, contamination of lungs by urine, feces, and skin oils, atelectasis due to loss of pulmonary surfactant, hyaline membrane, and possibly electrolyte imbalances, especially in the lung parenchyma. However, Kylstra and Lanphier devised techniques to obviate the difficulties en-... 

Undernourished patients have demonstrated a blunted response to hypercapnia that improves after as little as 1 week of adequate nutritional support. This response is thought to result from protein administration, as evidenced by decreased partial CO2 pressure, increased minute ventilation, and improved breathing patterns after the start of PN. F rotein administration also may influence ventilatory demand by increased ventilatory response to hypoxia and hypercapnia. This stimulation may be altered by the amino acid composition of the protein source, with increased amounts of BCAAs having a greater effect compared with standard amino acids." Although this protein effect is potentially beneficial in some patients, excessive protein administration could theoretically lead to increased work of breathing and fatigue." ... 

The second class of models is exemplified by the work of Priban and associates who use the work of breathing as a performance criteria in a self-adaptive control scheme. However, these workers do not include the representation of the central receptors whose physiological importance is now widely recognized. In addition, no information about the response... 

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