[show abstract][hide abstract] ABSTRACT: Changes in pulmonary deadspace are indicators of disease status (e.g. pulmonary embolus, acute respiratory distress syndrome) and they have prognostic usefulness in the intensive care unit. The components of pulmonary deadspace, the alveolar and anatomical deadspaces (VDalv and VDanat), are commonly considered to be independent (i.e. the addition of airway equipment should not alter the measured VDalv). However, VDanat has been shown to affect VDalv in the absence of changes in alveolar ventilation or perfusion. We sought to quantify the variability in measured VDalv induced by changes in VDanat using a cardiorespiratory computational model.
Using the Nottingham Physiology Simulator, we examined three simulated ventilated patients with small, moderate and large ventilation-perfusion (VQ) defects. Each patient received 12.5 bpm x 500 ml. We varied VDanat between 50 and 250 ml, keeping the VQ ratio of each alveolus constant. We calculated VDalv by subtracting VDanat (measured using Fowler's technique) from the physiological deadspace (measured using the Bohr-Enghoff equation). We calculated fresh-gas tidal volume (VTfresh) by subtracting VDanat from the exhaled tidal volume and calculated VDalv/VTfresh. In the simulated patient with the large VQ defect, we performed the same protocol with tidal volumes of 750 and 1000 ml.
When VDanat increased from 50 to 250 ml (500 ml tidal volume) VDalv decreased by 48.3% (mean value across the three VQ defects) and VDalv/VTfresh decreased by 15.1%. These relationships were similar at each tidal volume studied.
Measured VDalv is altered by changes in VDanat despite constant VQ ratios in each alveolus. This has implications for the interpretation of deadspace measured in the clinical setting. The variability is less for the ratio VDalv/VTfresh.
BJA British Journal of Anaesthesia 10/2005; 95(3):400-5. · 4.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: Patients who smoke are at risk of coughing and other adverse airway events during induction of anaesthesia. We have studied the incidence of adverse airway events in smokers under isoflurane or sevoflurane anaesthesia after induction with propofol. Smokers inhaling isoflurane had a 45% incidence of adverse airway events compared to 10% in those inhaling sevoflurane (p = 0.013).
[show abstract][hide abstract] ABSTRACT: We have evaluated a mechanical glottis in healthy volunteers and in patients with bulbar motor neurone disease. In healthy volunteers, the mechanical glottis increased peak flow rate and decreased the time to peak flow during forced expiration, but cough produced even higher flow rates and shorter times to peak flow. In patients, the mechanical glottis increased peak flow rate and decreased the time to peak flow. The mechanical glottis also produced higher peak flow rates when compared to the cough manoeuvres, and the time to peak flow was also significantly shorter with the mechanical glottis. We have shown that the use of a mechanical glottis tends to convert the airflow profile of a peak expiratory flow manoeuvre into that of a cough in both healthy volunteers and patients with motor neurone disease. Its potential role as an aid to clearance of airway secretions in patients with impaired laryngeal function remains to be seen.