Effect of hyperinflation on inspiratory function of the diaphragm

Abstract

The inspiratory efficiency of the diaphragm during unilateral and bilateral phrenic stimulation (UEPS and BEPS) with constant stimulus was studied in seven dogs from FRC to 120% TLC. Alveolar pressures (PAl) were recorded during relaxation, BEPS and UEPS at each lung volume in the closed respiratory system. From the PAl-lung volume curves, tidal volume (VT), and pressure developed by the diaphragm (Pmus) were derived. Results are summarized below. a) Hyperinflation impaired the inspiratory efficiency of the diaphragm which behaved as an expiratory muscle beyond the lung volume of 103.7% TLC (Vinef). b) The diaphragm during UEPS became expiratory at the same Vinef as during (BEPS. C) The VT-lung volume relationship was linear during BEPS, allowing simple quantitation of VT loss with hyperinflation and prediction of Vinef. d) With only one phrenic nerve stimulated, the functional loss is less pronounced in VT than in Pmus, as compared to BEPS, indicating that the respiratory system was more compliant during UEPS than BEPS. This compliance difference from UEPS to BEPS diminished with severe hyperinflation.

Developmental Pattern of Maximal Transdiaphragmatic Pressure in Infants during Crying

“…This would place the diaphragm at a better mechanical advantage and may explain some of the developmental pattern observed. The magnitude of our results are greater than one would expect from changes in lung volume alone (7,8,12).…”

“…Diaphragm function has been shown to be dependent on lung volume, and with hyperinflation its ability to generate maximal inspiratory force is compromised (7,8). Although lung volumes were not measured in these infants, none of them demonstrated h y p e m ation on chest roentgenograms.…”

Effect of surgical lung volume reduction on respiratory muscle function in pulmonary emphysema

“…Eur Respir J., 1996Respir J., , 9, 1779 June 11 1996 Severe emphysema of the lung results in detrimental abnormalities in ventilatory mechanics, such as increased airway resistance, diaphragmatic inefficiency, and dynamic hyperinflation [1][2][3][4]. Hyperinflation of the lung impairs the efficiency of the muscles of the chest wall and diaphragm by placing them at mechanical disadvantage [4].…”

“…The relationship between mechanical abnormalities of rib cage and diaphragm and respiratory muscle function has been studied in animals [5], and in patients with pulmonary emphysema [6][7][8][9]. The adverse effects of hyperinflation on diaphragmatic function include foreshortening of diaphragm precontraction length [1,3,6,10,11], decreased area of apposition of the costal part with the chest wall [7,8], increased radius of curvature [1], impaired blood flow and decreased insertional action on the rib cage [12], and increased internal elastic inspiratory load [3,4].…”

“…A series of 100 patients [26] showed significant improvement of lung function, gas exchange, 6 min walking distance, dyspnoea, and quality of life 3 months after bilateral surgical lung reduction. Since the mechanical efficiency of the rib cage and diaphragm is sensitive to changes in lung volume [1,3,9,10,19], LVRS may improve the performance of the respiratory muscles and, thus, reduce dyspnoea.…”