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Results for “Respiratory Dead Space”

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At least 19 recordsLinked to original sources
PubMed2005

Respiratory dead space measurement in the investigation of pulmonary embolism in outpatients with pleuritic chest pain.

STUDY OBJECTIVES: Pleuritic chest pain is a common presenting condition in the emergency department. A noninvasive bedside rule out test for pulmonary embolism would aid investigating this patient group. Our study aimed to compare the clinical utility of three methods for calculating respiratory dead space in the diagnosis of pulmonary embolism in outpatients with pleuritic chest pain. DESIGN: Prospective diagnostic study. SETTING: Large city-center emergency department. PATIENTS: Between February 2002 and June 2003, 425 patients presenting to the emergency department with pleuritic chest pain were prospectively recruited. INTERVENTION: Data collection for respiratory dead space was performed in the emergency department by two researchers. The respiratory dead space fraction was calculated independently using three different methods. All patients underwent an independent reference standard diagnostic algorithm to establish the presence or absence of pulmonary embolism. Those with a low modified Wells clinical probability and a normal quantitative d-dimer finding were discharged home. All others followed a reference standard protocol using Prospective Investigation of Pulmonary Embolism Diagnosis-interpreted ventilation/perfusion scanning, CT pulmonary angiography, and digital subtraction pulmonary angiography. All patients were followed up clinically for 3 months. MEASUREMENTS AND RESULTS: For the Bohr calculation, the area under the receiver operating characteristic curve was 0.62 (95% confidence interval [CI], 0.51 to 0.73), the Enghoff calculation was 0.66 (95% CI, 0.55 to 0.77), and the capillary sample Enghoff was 0.62 (95% CI, 0.49 to 0.65). The optimum Bohr cutoff value gave 100.0% sensitivity (95% CI, 84.5 to 100%) but a low specificity of 22.7% (95% CI, 18.8 to 27.2%). The optimum cutoff points for Enghoff and capillary Enghoff calculations gave sensitivities of 95.3% (95% CI, 77.3 to 99.2%) and 94.4% (95% CI, 74.2 to 99.0%), respectively, with poor specificity. CONCLUSIONS: Respiratory dead space analysis does not perform well as a stand-alone diagnostic test for pulmonary embolism in outpatients presenting with pleuritic chest pain.

Adult↗
PubMed1990

Ventilatory control during exercise with increased respiratory dead space in goats.

Our objectives were to determine 1) the effects of increased respiratory dead space (VD) on the ventilatory response to exercise and 2) whether changes in the ventilatory response are due to changes in chemoreceptor feedback (rest to exercise) vs. changes in the feedforward exercise stimulus. Steady-state ventilation (VI) and arterial blood gas responses to mild or moderate hyperoxic exercise in goats were compared with and without increased VD. Responses were compared using a simple mathematical model with the following assumptions: 1) steady state, 2) linear CO2 chemoreceptor feedback, 3) linear feedforward exercise stimulus proportional to CO2 production (VCO2) and characterized by an exercise gain (Gex), and 4) additive exercise stimulus and CO2 feedback producing the system gain (Gsys = delta VI/delta VCO2). Model predictions at constant Gex [assuming VD-to-tidal volume (VT) ratio independent of VCO2] are that increased VD/VT will 1) increase arterial PCO2 (PaCO2) and VI at rest and 2) increase Gsys via changes in chemoreceptor feedback due to a small increase in the PaCO2 vs. VCO2 slope. Experimental results indicate that increased VD increased VD/VT, PaCO2, and VI at rest and increased Gsys during exercise. However, measurable changes in the PaCO2 vs. VCO2 slope occurred only at high VD/VT or running speeds. Gex was estimated at each VD for each goat by using the model in conjunction with experimental measurements. With 0.2 liter VD, Gex increased 40% (P less than 0.01); with 0.6 liter VD, Gex increased 110% between 0 and 2.4 km/h and 5% grade (P less than 0.01) but not between 2.4 and 4.8 km/h. Thus, Gex is increased by VD through a limited range. In goats, increases in Gsys with increased VD result from increases in both Gex and CO2 chemoreceptor feedback. These results are consistent with other experimental treatments that increase the exercise ventilatory response, maintaining constant relative PaCO2 regulation, and suggest that a common mechanism linked to resting ventilatory drive modulates Gex.

Animals↗
PubMed2004

Reproducibility of the respiratory dead space measurements in mechanically ventilated children using the CO2SMO monitor.

OBJECTIVES: To assess the reproducibility of respiratory dead space measurements in ventilated children. DESIGN: Prospective study. SETTING: University pediatric intensive care unit. PATIENTS: Thirty-two mechanically ventilated children (0.13-15.4 years) who were clinically stable. METHODS: The single-breath CO(2) test (SBT-CO(2)) was recorded using the CO(2)SMO Plus from the mean of 30 ventilatory cycles during 1 h (at T0, T15, T30, T45, and T60). Airway dead space was determined automatically (Novametrix Medical Systems, USA), and manually by Bohr- Enghoff equations using data obtained by SBT-CO(2). At the end of the study period, arterial blood gas was sampled in order to calculate alveolar and physiologic dead space. Intrasubject reproducibility of measurements was evaluated by the intraclass correlation coefficient. Two-way analysis of variance was used to evaluate the relationships between time and measurements. The two methods for calculating airway dead space were compared by using two-tailed Student's t-test and Bland-Altman analysis. RESULTS: Airway dead space measurement had a good reproducibility during the 1-h period, whatever the method used (intraclass correlation coefficient: 0.84 to 0.87). No significant difference was observed with time. Airway dead space values from the SBT-CO(2) method were smaller than those from Bohr-Enghoff equations. Physiologic dead space values from the SBT-CO2 method were similar to those from Bohr-Enghoff equations. CONCLUSION: The measurement of airway dead space by the CO(2)SMO Plus was reproducible over a 1-h period in children requiring mechanical ventilation, provided ventilatory parameters were constant throughout the study. SBT-CO(2) analysis may provide a bedside non-invasive monitoring of volumetric capnography.

Adolescent↗
PubMed1991

Effect of increased inspired CO2 on respiratory dead space in ponies.

The objective of the present study was to determine the effect of elevated inspired CO2 on respiratory dead space (VD) of 12 normal, 8 carotid body-denervated (CBD), 7 hilar nerve-denervated (HND), and 6 CBD+HND ponies. The Fowler technique was used to determine VD on a breath-by-breath basis while the ponies breathed room air and inspired CO2 at 3 and 6%. During room air breathing, tidal volume (VT) and VD were greater in HND ponies than in normal and CBD ponies (P less than 0.05), and VT was less and VD/VT was greater after CBD than before CBD. For all groups. VD, VT, and breathing frequency (f) increased and VD/VT decreased significantly (P less than 0.01) with increasing inspired CO2. During CO2 breathing, VT and VD were higher (P less than 0.05) in the HND ponies than in all other groups, the decrease (P less than 0.05) in VD/VT was greatest in the CBD+HND group, and f was lower in the HND and HND+CBD than in the normal and CBD ponies. In addition, when inspired CO2 was increased from 0 to 6%, the decrease in VD/VT was greater and the increase in arterial PCO2 was less (P less than 0.05) after CBD than before CBD. For 70% of the ponies in all groups, VD increased linearly with increases in VT; for most of the remainder, VD tended to plateau at higher values of VT.

Animals↗