Capnogram slope and ventilation dead space parameters: comparison of mainstream and sidestream techniques.

BACKGROUND: Capnography may provide useful non-invasive bedside information concerning heterogeneity in lung ventilation, ventilation-perfusion mismatching and metabolic status. Although the capnogram may be recorded by mainstream and sidestream techniques, the capnogram indices furnished by these approaches have not previously been compared systematically. METHODS: Simultaneous mainstream and sidestream time and volumetric capnography was performed in anaesthetized, mechanically ventilated patients undergoing elective heart surgery. Time capnography was used to assess the phase II (SII,T) and III slopes (SIII,T). The volumetric method was applied to estimate phase II (SII,V) and III slopes (SIII,V), together with the dead space values according to the Fowler (VDF), Bohr (VDB), and Enghoff (VDE) methods and the volume of CO2 eliminated per breath ([Formula: see text]). The partial pressure of end-tidal CO2 ([Formula: see text]) was registered. RESULTS: Excellent correlation and good agreement were observed in SIII,T measured by the mainstream and sidestream techniques [ratio=1.05 (sem 0.16), R(2)=0.92, P<0.0001]. Although the sidestream technique significantly underestimated [Formula: see text] and overestimated SIII,V [1.32 (0.28), R(2)=0.93, P<0.0001], VDF, VDB, and VDE, the agreement between the mainstream and sidestream techniques in the difference between VDE and VDB, reflecting the intrapulmonary shunt, was excellent [0.97 (0.004), R(2)=0.92, P<0.0001]. The [Formula: see text] exhibited good correlation and mild differences between the mainstream and sidestream approaches [0.025 (0.005) kPa]. CONCLUSIONS: Sidestream capnography provides adequate quantitative bedside information about uneven alveolar emptying and ventilation-perfusion mismatching, because it allows reliable assessments of the phase III slope, [Formula: see text] and intrapulmonary shunt. Reliable measurement of volumetric parameters (phase II slope, dead spaces, and eliminated CO2 volumes) requires the application of a mainstream device.

Lung structure and function in elastase-treated rats: A follow-up study.

Structural and functional longitudinal alterations of the lungs were followed in an emphysema model. Rats were treated with porcine pancreatic elastase (PPE, n=21) or saline (controls, C, n=19). Before the treatment and 3, 10, 21 and 105 days thereafter, absolute lung volumes (FRC, TLC and RV) and tissue mechanical parameters (elastance: H; damping: G) were determined. At 3, 21 and 105 days the lungs were fixed in subgroups of rats. From histological samples the equivalent diameter of airspaces (Dalv), elastin (Mec) and collagen densities were assessed. In the PPE group, FRC and RV were higher from 3 days after treatment compared to controls (p<0.001), while TLC exhibited a delayed increase. H and G decreased in the PPE group throughout the study (p<0.001). Higher Mec (p<0.001) and late-phase inflammation were observed at 105 days. We conclude that during the progression of emphysema, septal failures increase Dalv which decreases H; this reveals a strong structure-function relationship.

Functional and morphological assessment of early impairment of airway function in a rat model of emphysema.

The aim of this study was to evaluate airway structure-function relations in elastase-induced emphysema in rats. Sprague-Dawley rats were treated intratracheally with 50 IU porcine pancreatic elastase (PPE, n = 8) or saline (controls, n = 6). Six weeks later, lung volumes [functional residual capacity (FRC), residual volume (RV), and total lung capacity (TLC)] and low-frequency impedance parameters (Newtonian resistance, R(N); tissue damping; tissue elastance, H) were measured, and tracheal sounds were recorded during slow inflation to TLC following in vivo degassing. The lungs were fixed and stained for standard morphometry, elastin, and collagen. In the PPE group, FRC and RV were higher [4.53 ± 0.7 (SD) vs. 3.28 ± 0.45 ml; P = 0.003 and 1.06 ± 0.35 vs. 0.69 ± 0.18 ml; P = 0.036, respectively], and H was smaller in the PPE-treated rats than in the controls (1,344 ± 216 vs. 2,178 ± 305 cmH(2)O/l; P < 0.001), whereas there was no difference in R(N). The average number of crackles per inflation was similar in the two groups; however, the crackle size distributions were different and the lower knee of the pressure-volume curves was higher in the PPE group. Microscopic images revealed different alveolar size distributions but similar bronchial diameters in the two groups. The treatment caused a slight but significant decrease in the numbers of alveolar attachments, no difference in elastin and slightly increased mean level and heterogeneity of collagen in the bronchial walls. These results suggest that tissue destruction did not affect the conventionally assessed airway resistance in this emphysema model, whereas the alterations in the recruitment dynamics can be an early manifestation of impaired airway function.

Lung volumes and respiratory mechanics in elastase-induced emphysema in mice.

Absolute lung volumes such as functional residual capacity, residual volume (RV), and total lung capacity (TLC) are used to characterize emphysema in patients, whereas in animal models of emphysema, the mechanical parameters are invariably obtained as a function of transrespiratory pressure (Prs). The aim of the present study was to establish a link between the mechanical parameters including tissue elastance (H) and airway resistance (Raw), and thoracic gas volume (TGV) in addition to Prs in a mouse model of emphysema. Using low-frequency forced oscillations during slow deep inflation, we tracked H and Raw as functions of TGV and Prs in normal mice and mice treated with porcine pancreatic elastase. The presence of emphysema was confirmed by morphometric analysis of histological slices. The treatment resulted in an increase in TGV by 51 and 44% and a decrease in H by 57 and 27%, respectively, at 0 and 20 cmH(2)O of Prs. The Raw did not differ between the groups at any value of Prs, but it was significantly higher in the treated mice at comparable TGV values. In further groups of mice, tracheal sounds were recorded during inflations from RV to TLC. All lung volumes but RV were significantly elevated in the treated mice, whereas the numbers and size distributions of inspiratory crackles were not different, suggesting that the airways were not affected by the elastase treatment. These findings emphasize the importance of absolute lung volumes and indicate that tissue destruction was not associated with airway dysfunction in this mouse model of emphysema.

Crackle-sound recording to monitor airway closure and recruitment in ventilated pigs.

It was hypothesised that the recruitment of atelectatic lung areas is signified by changes in the airway and tissue mechanics, and by the appearance of crackle activity attributed to the sudden reopening of collapsed airways. The authors also assumed that the acoustic activity is an earlier indicator of lung recruitment than the change in the overall mechanical state of the lungs. Six thoracotomised and mechanically ventilated mini-pigs were studied. Low-frequency pulmonary impedance was measured at end-expiratory pauses at transpulmonary pressures of 4 and 1 hPa to estimate airway resistance (Raw) and the coefficient of lung tissue elastance (H), and tracheal sounds were recorded during subsequent slow inflations to 30 hPa, in the control state and following increasing doses of i.v. methacholine (Mch). Raw and H were higher at baseline and increased more in response to Mch at 1 hPa than at 4 hPa. The crackles detected during the subsequent inflations were concentrated around and associated with the development of the lower knee of the pressure-volume curve. The number of crackles increased faster following the Mch doses and reached statistical significance earlier than Raw and H. Crackle recording during mechanical ventilation can be employed as a simple method with which to monitor lung recruitment-derecruitment.

Acoustic evidence of airway opening during recruitment in excised dog lungs.

The aim of this study was to test the hypothesis that the mechanism of recruitment and the lower knee of the pressure-volume curve in the normal lung are primarily determined by airway reopenings via avalanches rather than simple alveolar recruitments. In isolated dog lung lobes, the pressure-volume loops were measured, and crackle sounds were recorded intrabronchially during both the first inflation from the collapsed state to total lobe capacity and a second inflation without prior degassing. The inflation flow contained transients that were accompanied by a series of crackles. Discrete volume increments were estimated from the flow transients, and the energy levels of the corresponding crackles were calculated from the sound recordings. Crackles were concentrated in the early phase of inflation, with the cumulative energy exceeding 90% of its final value by the lower knee of the pressure-volume curve. The values of volume increments were correlated with crackle energy during the flow transient for both the first and the second inflations (r(2) = 0.29-0.73 and 0.68-0.82, respectively). Because the distribution of volume increments followed a power law, the correlation between crackle energy and discrete volume increments suggests that an avalanche-like airway opening process governs the recruitment of collapsed normal lungs.

Implementation, management and continuous quality improvement of point-of-care testing in an academic health care setting.

Point-of-care testing (POCT) has economic and medical benefits in the areas of immediate medical management, resource utilization and time management. Starting with bedside glucose, the Mount Sinai Medical Center has, over the past 11 years, implemented 23 POC tests, spanning complexity from blood gas/electrolyte testing to occult blood, in compliance with all regulatory and accreditation requirements. QC data are reviewed on a daily and weekly basis and all patient results are in the electronic medical record. A variety of healthcare workers; nurses, physicians, respiratory therapists and technologists, perform testing. Since POCT impacts on a variety of hospital departments, proper implementation and management requires a multi-disciplinary team approach with focus on the financial, regulatory, quality assurance and data integration issues. Established in 1996, the institutional committee, with laboratory leadership, handles the establishment, compliance review and future direction setting of the program. In 1999, over 1300 individuals performed over 440,000 POC tests within the institution. A formalized continuous quality improvement (CQI) program for the POCT program was developed in the fall of 1999. All testing sites are reviewed on a monthly basis for various quality indicators that cover QC performance, maintenance performance, proficiency testing, patient identification, and alert value confirmations.

Size distribution of recruited alveolar volumes in airway reopening.

In 11 isolated dog lung lobes, we studied the size distribution of recruited alveolar volumes that become available for gas exchange during inflation from the collapsed state. Three catheters were wedged into 2-mm-diameter airways at total lung capacity. Small-amplitude pseudorandom pressure oscillations between 1 and 47 Hz were led into the catheters, and the input impedances of the regions subtended by the catheters were continuously recorded using a wave tube technique during inflation from -5 cm H(2)O transpulmonary pressure to total lung capacity. The impedance data were fit with a model to obtain regional tissue elastance (Eti) as a function of inflation. First, Eti was high and decreased in discrete jumps as more groups of alveoli were recruited. By assuming that the number of opened alveoli is inversely proportional to Eti, we calculated from the jumps in Eti the distribution of the discrete increments in the number of opened alveoli. This distribution was in good agreement with model simulations in which airways open in cascade or avalanches. Implications for mechanical ventilation may be found in these results.

Scaling behavior in crackle sound during lung inflation.

During slow inflation of lung lobes, we measure a sequence of short explosive transient sound waves called "crackles," each consisting of an initial spike followed by ringing. The crackle time series is irregular and intermittent, with the number of spikes of size s following a power law, n(s) proportional, variants(-alpha), with alpha=2.77+/-0.05. We develop a model of crackle wave generation and propagation in a tree structure that combines the avalanchelike opening of airway segments with the wave propagation of crackles in a tree structure. The agreement between experiments and simulations suggests that (i) the irregularities are a consequence of structural heterogeneity in the lung, (ii) the intermittent behavior is due to the avalanchelike opening, and (iii) the scaling is a result of successive attenuations acting on the sound spikes as they propagate through a cascade of bifurcations along the airway tree.

Mechanical impedance of the lung periphery.

The mechanics of the regional airways and tissues was studied in isolated dog lobes by means of a modified wave-tube technique. Small-amplitude pseudorandom forced oscillations between 0.1 and 48 Hz were applied through catheters wedged in 2-mm-diameter bronchi in three regions of each lobe at translobar pressures (PL) of 10, 7, 5, 3, 2, and 1 cmH2O. The measured regional input impedances were fitted by a model containing the resistance (R1) and inertance (I) of the regular (segmental) airways, the resistance of the collateral channels (R2), and the damping (G) and elastance (H) of the local tissues. This model gave far better fits to the data on impedance of the lung periphery than when G and H were replaced by a single tissue compliance, which explains why interruption of segmental flow did not lead to monoexponential pressure decay in previous studies. The interlobar and intralobar variances of the parameters were equally significant, and poor correlations were found between the airway parameters R1 and R2 and between any airway and tissue parameter (e.g., R1 and H). R2 was on average approximately 10 times higher than R1, although the R2-to-R1 ratios and their dependencies on PL were regionally highly variable. However, for the total of 33 regions studied, the PL dependence was the same for R1 and R2, which may reflect similar morphological structures for the regular and collateral airways. The dependencies of G and H on PL showed high interregional variations; generally, however, they assumed their minima at medium PL values (approximately 5 cmH2O).