The European respiratory journal : official journal of the European Society for Clinical Respiratory Physiology
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We studied 80 subjects (63 M, 17 F; 23-82 yrs) and related lung computerized tomography (CT) density with age, height, spirometry, lung volumes, diffusing capacity and arterial blood gas tensions. These subjects demonstrated a wide range of physiological impairment (forced expiratory volume in one second (FEV1) 8-116% predicted; diffusing capacity (Kco) 15-139% predicted; arterial oxygen tension (Pao2) 38-91 mmHg). They ranged from normal subjects to patients with chronic respiratory failure. ⋯ Lung CT density correlated most strongly with airflow obstruction (EMI 5th percentile versus FEV1/forced vital capacity (FVC) % predicted, r = 0.73, p less than 0.001) and diffusing capacity (EMI 5th percentile versus Kco, r = 0.77, p less than 0.001). This suggests that reduction in lung density, which reflects loss of the surface area of the distal airspaces, is a major index of respiratory function in patients with smoking related chronic obstructive pulmonary disease (COPD). These data provide no indication of other factors such as small and large airways disease, and loss of elastic recoil, which may contribute to airflow limitation, or disruption of the pulmonary vascular bed which may also affect CT lung density.
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Two sets of seven pulse oximeters (Criticare CSI-502; Nellcor-N200; Datex-Satlite; Physio-Control-Lifestat 1600; Critikon-Oxyshuttle; Ohmeda-Biox 3700; Ohmeda-Biox 3740; Radiometer-Oxi; Spectramed-Pulsat; Kontron-7840; Biochem-Ox2000; Invivo-4500; Engström-EOS; Novametrix-505) were studied in two groups of eight healthy subjects, aged 26-50 yrs. The transcutaneous oxygen saturation (SpO2) was compared with arterial oxygen saturation (SaO2) measured in simultaneously with drawn blood samples (OSM2 Radiometer) at four 20 min steady-state levels of inspired oxygen fraction (FIO2) (0.21, 0.10, 0.08 and 0.07; SaO2 99-55%) in a conditioned chamber. ⋯ An instrumental systematic bias affected accuracy in particular. We concluded that a good agreement between SpO2 and SaO2, as reflected by the Bartko's intraclass coefficient, was observed in nine instruments.
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Review
The role of PEEP in patients with chronic obstructive pulmonary disease during assisted ventilation.
In patients with acute respiratory failure (ARF) due to acute exacerbation of chronic obstructive pulmonary disease (COPD), the intrinsic positive end-expiratory pressure (PEEPi) can significantly increase workload for ventilation. It has been suggested that, in the presence of expiratory flow limitation, application of low levels of PEEP by the ventilator can be used to reduce PEEPi and therefore the magnitude of the inspiratory effort during assisted mechanical ventilation (or pressure support) and weaning. Clearly, pulmonary hyperinflation should not be further enhanced in order not to counteract the beneficial effect of removing PEEPi by decreasing respiratory muscle length and force. ⋯ Therefore, application of PEEP in COPD patients requires close monitoring of the end-expiratory lung volume. This can be accomplished, among other noninvasive ways (e.g. the inductive plethysmography), by inspection of flow/volume curves during application of increasing levels of PEEP. The shape of the expiratory limb of the flow/volume curve can also suggest the presence of dynamic hyperinflation and expiratory flow limitation.
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Long-term oxygen therapy requires a practical regulated oxygen delivery system which works in the home. Although face-masks are cheap and efficient, they are awkward and need removal for talking and eating. Few patients would comply with this for 15 h her day. ⋯ Permanent tracheostomy is not indicated in most cases of hypoxic chronic obstructive airways disease (COAD). Nasal prongs would seem the most reasonable method of oxygen delivery. Their use with oxygen concentrators lessens the need for oxygen conservation.
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To examine the relationship between end-expiratory lung volume and respiratory muscle work during acute bronchoconstriction, we measured the work of breathing in nine asthmatic subjects, in whom bronchoconstriction was induced with histamine aerosol. When the forced expiratory volume in one second (FEV1) fell below 60% of the control value, work was measured at the spontaneously hyperinflated lung volume (VLS), at a volume equivalent to the control functional residual capacity (FRC) and at a volume 30% of vital capacity (VC) above the control FRC. ⋯ Breathing above VLS did not alter the total positive muscle work, but did increase the negative work of the inspiratory muscles from 0.4 +/- 0.1 to 0.8 +/- 0.1 J.breath. We conclude that during induced asthma spontaneous hyperinflation minimizes the total respiratory muscle work and may constitute a mechanism for minimizing energy expenditure.