Proportional assist versus pressure support ventilation: effects on breathing pattern and respiratory work of patients with chronic obstructive pulmonary disease.

OBJECTIVE: To investigate the breathing pattern and the inspiratory work of breathing (WOB(I)) in patients with chronic obstructive pulmonary disease (COPD) assisted with proportional assist ventilation (PAV) and conventional pressure support ventilation (PSV). DESIGN: Prospective controlled study. SETTING: Intensive care unit of a university hospital. PATIENTS: Thirteen COPD patients being weaned from mechanical ventilation. INTERVENTIONS: All patients were breathing PSV and two different levels of PAV. MEASUREMENTS AND MAIN RESULTS: During PAV (EVITA 2 prototype, Dräger, Germany), the resistance of the endotracheal tube (R(et)) was completely compensated while the patients' resistive and elastic loads were compensated for by approximately 80 % and 50 % (PAV(80) and PAV(50)), respectively. PSV was adjusted to match the same mean inspiratory pressure (Pinsp(mean)) as during PAV(80). Airway pressure, esophageal pressure and gas flow were measured over a period of 5 min during each mode. Neuromuscular drive (P(0.1)) was determined by inspiratory occlusions. Mean tidal volume (V(T)) was not significantly different between the modes. However, the coefficient of variation of V(T) was 10 +/- 4.%, 20 +/- 13 % and 15 +/- 8 % during PSV, PAV(80) and PAV(50), respectively. Respiratory rate (RR) and minute ventilation (V(E)) were significantly lower during PAV(80) as compared with both other modes, but the differences did not exceed 10 %. PAV(80) and PSV had comparable effects on WOB(I) and P(0.1), whereas WOB(I) and P(0.1) increased during PAV(50) compared with both other modes. CONCLUSION: Mean values of breathing pattern did not differ by a large amount between the investigated modes. However, the higher variability of V(T) during PAV indicates an increased ability of the patients to control V(T) in response to alterations in respiratory demand. A reduction in assist during PAV(50) resulted in an increase in WOB and indices of patient effort.

Monitoring perioperative changes in distribution of pulmonary ventilation by functional electrical impedance tomography.

BACKGROUND: Electrical impedance tomography (EIT) is a noninvasive technique providing cross-sectional images of the thorax. We have tested an extended evaluation procedure, the functional EIT (f-EIT), to identify the local shifts of ventilation known to occur during the transition between spontaneous, controlled and assisted ventilation modes. METHODS: Ten patients scheduled for elective laparotomy were studied in the surgical ward, operating theatre and ICU during spontaneous and different modes of mechanical ventilation. Sixteen ECG electrodes were placed on the circumference of the thorax and connected with an EIT device (APT System Mark I, IBEES, Sheffield, UK). Measurements lasting 180 s were performed and f-EIT images of regional ventilation computed. The geometrical centre of ventilation was determined to quantify the regional distribution of lung ventilation during individual modes of ventilation. RESULTS: F-EIT confirmed the differences in the distribution of ventilation associated with various modes of artificial ventilation. Accentuated ventilation of the dependent lung regions was observed during spontaneous breathing, whereas a shift of the centre of ventilation to the nondependent regions was found during controlled ventilation. In the course of assisted ventilation a continuous displacement of the centre of ventilation back towards the dependent lung regions, consistent with an increased proportion of spontaneous breathing, was detected. Unassisted spontaneous breathing after weaning from mechanical ventilation resulted in a similar ventilation distribution as during tidal breathing prior to surgery. CONCLUSION: F-EIT determined the redistribution of lung ventilation during different modes of mechanical ventilation. We expect that f-EIT will become a useful noninvasive bedside monitoring technique for imaging regional ventilation in pulmonary diseased patients during mechanical ventilation.

[Variation in inspiratory gas flow in pressure support ventilation. The effect on respiratory mechanics and respiratory work]. / Variation des inspiratorischen Gasflusses unter druck-unterstützter Spontanatmung. Einfluss auf Atemmechanik und Atemarbeit.

UNLABELLED: During pressure support ventilation (PSV), the timing of the breathing cycle is mainly controlled by the patient. Therefore, the delivered flow pattern during PSV might be better synchronised with the patient's demands than during volume-assisted ventilation. In several modern ventilators, inspiration is terminated when the inspiratory flow decreases to 25% of the initial peak value. However, this timing algorithm might cause premature inspiration termination if the initial peak flow is high. This could result not only in an increased risk of dyssynchronization between the patient and the ventilator, but also in reduced ventilatory support. On the other hand, a decreased peak flow might inappropriately increase the patient's inspiratory effort. The aim of our study was to evaluate the influence of the variation of the initial peak-flow rate during PSV on respiratory pattern and mechanical work of breathing. PATIENTS: Six patients with chronic obstructive pulmonary disease (COPD) and six patients with no or minor nonobstructive lung pathology (control) were studied during PSV with different inspiratory flow rates by variations of the pressurisation time (Evita I, Drägerwerke, Lübeck, Germany). During the study period all patients were in stable circulatory conditions and in the weaning phase. METHOD: Patients were studied in a 45 degrees semirecumbent position. Using the medium pressurization time (l s) during PSV the inspiratory pressure was individually adjusted to obtain a tidal volume of about 8 ml/kg body weight. Thereafter, measurements were performed during five pressurization times (< 0.1, 0.5, 1, 1.5, 2 s defined as T 0.1, T 0.5, T 1, T 1.5 and T 2) in random order, while maintaining the pressure support setting at the ventilator. Between each measurement steady-state was attained. Positive end-exspiratory pressure (PEEP) and FIO2 were maintained at prestudy levels and remained constant during the study period. Informed consent was obtained from each patient or his next of kin. The study protocol was approved by the ethics committee of our medical faculty. Gas flow was measured at the proximal end of the endotracheal tube with a pneumotachometer (Fleisch no. 2, Fleisch, Lausanne, Switzerland) and a differential pressure transducer. Tracheal pressure (Paw) was determined in the same position with a second differential pressure transducer (Dr. Fenyves & Gut, Basel, Switzerland). Esophageal pressure (Pes) was obtained by a nasogastric balloon-catheter (Mallinckrodt, Argyle, NY, USA) connected to a further differential pressure transducer of the same type as described above. The balloon was positioned 2-3 cm above the dome of the diaphragm. The correct balloon position was verified by an occlusion test as described elsewhere. The data were sampled after A/D conversion with a frequency of 20 Hz and processed on an IBM-compatible PC. Software for data collection and processing was self-programmed using a commercially available software program (Asyst 4.0, Asyst Software Technologies, Rochester, NY, USA). Patient's inspiratory work of breathing Wpi (mJ/l) was calculated from Pes/ volume plots according to the modified Campbell's diagram. Dynamic intrinsic PEEP (PEEPidyn) was obtained from esophageal pressure tracings relative to airway pressure as the deflection in Pes before the initiation of inspiratory flow Patient's additive work of breathing (Wadd) against ventilator system resistance was calculated directly from Paw/V tracings when Paw was lower than the pressure on the compliance curve. Two-way analysis of variance (ANOVA) was used for statistical analysis, followed by post hoc testing of the least significant difference between means for multiple comparisons. Probability values less than 0.05 were considered as significant. RESULTS: COPD patients had significantly higher pressure support than control patients. With decreasing inspiratory flow, Wpi increased significantly in COPD patients.(ABSTRACT TRUNCATED)

Earth-Based Observations of the Galileo Probe Entry Site

Earth-based observations of Jupiter indicate that the Galileo probe probably entered Jupiter's atmosphere just inside a region that has less cloud cover and drier conditions than more than 99 percent of the rest of the planet. The visual appearance of the clouds at the site was generally dark at longer wavelengths. The tropospheric and stratospheric temperature fields have a strong longitudinal wave structure that is expected to manifest itself in the vertical temperature profile.

Effect of low-level PEEP on inspiratory work of breathing in intubated patients, both with healthy lungs and with COPD.

OBJECTIVE: Evaluation of low-level PEEP (5 cm H2O) and the two different CPAP trigger modes in the Bennett 7200a ventilator (demand-valve and flow-by trigger modes) on inspiratory work of breathing (Wi) during the weaning phase. DESIGN: Prospective controlled study. SETTING: The intensive care unit of a university hospital. PATIENTS: Six intubated patients with normal lung function (NL), ventilated because of non-pulmonary trauma or post-operative stay in the ICU, and six patients recovering from acute respiratory failure due to exacerbation of chronic obstructive pulmonary disease (COPD), breathing either FB-CPAP or DV-CPAP with the Bennett 7200a ventilator. INTERVENTIONS: The patients studied were breathing with zero end-expiratory pressure (ZEEP), as well as CPAP of 5 cm H2O (PEEP), with the following respiratory modes: the demand-valve trigger mode, pressure support of 5 cm H2O, and the flow-by trigger mode (base flow of 20 l/min and flow trigger of 2 l/min). Furthermore, Wi during T-piece breathing was evaluated. MEASUREMENTS AND RESULTS: Wi was determined using a modified Campbell's diagram. Total inspiratory work (Wi), work against flow-resistive resistance (W(ires)), work against elastic resistance (Wiel), work imposed by the ventilator system (W(imp)), dynamic intrinsic positive end-expiratory pressure (PEEPidyn), airway pressure decrease during beginning inspiration (P(aw)) and spirometric parameters were measured. In the NL group, only minor, clinically irrelevant changes in the measured variables were detected. In the COPD group, in contrast, PEEP reduced Wi and its components W(ires) and Wiel significantly compared to the corresponding ZEEP settings. This was due mainly to a significant decrease in PEEPidyn when external PEEP was applied. Flow-by imposed less Wi on the COPD patients during PEEP than did demand-valve CPAP. Differences in W(imp) between the flow-by and demand-valve trigger models were significant for both groups. However, in relation to Wi these differences were small. CONCLUSION: We conclude that the application of low-level external PEEP benefits COPD patients because it reduces inspiratory work, mainly by lowering the inspiratory threshold represented by PEEPidyn. Differences between the trigger modes of the ventilator used in this study were small and can be compensated for by the application of a small amount of pressure support.

[Difficult intubation due to facial malformations in a child. The laryngeal mask as an aid]. / Schwierige Intubationen bei Gesichtsfehlbildungen im Kindesalter. Die Kehlkopfmaske als Hilfsmittel.

Variations in anatomy of the bony and soft-tissue structures of the neck and facial cranium due to trauma, disease, or dysmorphic syndromes may lead to severe intubation problems. These patients are admitted for mandibulofacial and otolaryngologic surgery. It is important to inspect the patient's outer and inner pharyngeal structures carefully during preoperative assessment, as suggested by Mallampati. The observer estimates the facility of intubation by inspection of the faucial pillars, soft palate, and uvula. Unfortunately, even careful examination does not predict every case of difficult intubation, so that unexpected problems may occur. There may also be difficulties in ventilating these patients with a face mask. Safe intubation is possible in these cases using the laryngeal mask airway (LMA), laryngoscopy with a rigid optical aid, and the fibreoptic bronchoscope. Case report. We report a 14-month-old girl with Goldenhar's syndrome (oculo-auricular dysplasia) who presented for soft-palate surgery. This syndrome belongs to the group of cranio-mandibular-facial malformations; the main symptoms are congenital unilateral malformations in the area of the 1st and 2nd branchial arches. The patient's jaw was hypoplastic with aplasia of the temporo-mandibular joint, which led to asymmetry of the lower face and an extremely short mandible. Additionally, we observed a large tongue in relation to the small jaw. Macrostomia is part of the syndrome, and may lead to underestimation of intubation problems.(ABSTRACT TRUNCATED AT 250 WORDS)

Spatial Organization and Time Dependence of Jupiter's Tropospheric Temperatures, 1980-1993.

The spatial organization and time dependence of Jupiter's temperatures near 250-millibar pressure were measured through a jovian year by imaging thermal emission at 18 micrometers. The temperature field is influenced by seasonal radiative forcing, and its banded organization is closely correlated with the visible cloud field. Evidence was found for a quasi-periodic oscillation of temperatures in the Equatorial Zone, a correlation between tropospheric and stratospheric waves in the North Equatorial Belt, and slowly moving thermal features in the North and South Equatorial Belts. There appears to be no common relation between temporal changes of temperature and changes in the visual albedo of the various axisymmetric bands.

Thermal maps of jupiter: spatial organization and time dependence of stratospheric temperatures, 1980 to 1990.

The spatial organization and time dependence of Jupiter's stratospheric temperatures have been measured by observing thermal emission from the 7.8-micrometer CH(4) band. These temperatures, observed through the greater part of a Jovian year, exhibit the influence of seasonal radiative forcing. Distinct bands of high temperature are located at the poles and mid-latitudes, while the equator alternates between warm and cold with a period of approximately 4 years. Substantial longitudinal variability is often observed within the warm mid-latitude bands, and occasionally elsewhere on the planet. This variability includes small, localized structures, as well as large-scale waves with wavelengths longer than approximately 30,000 kilometers. The amplitudes of the waves vary on a time scale of approximately 1 month; structures on a smaller scale may have lifetimes of only days. Waves observed in 1985, 1987, and 1988 propagated with group velocities less than +/-30 meters per second.

Infrared emission from P/Halley's dust coma during March 1986.

2 to 20 micrometers photometry of the inner dust coma of comet Halley was obtained at the NASA IRTF on Mar 6.85, 12.8, 13.75, 17.7, and 24.8. Positions offset 10" were measured as well as the central brightness. The strength of the 10 micrometers emission feature was observed to vary with location in the coma. The infrared emission is in general agreement with the dust size distribution measured from the Vega and Giotto spacecraft. Mar 6.8, 17.7, and 24.8 corresponded to strong dust jet activity. The strength of the 10 micrometers silicate emission is shown to be a sensitive indicator of grain size and thus of jet activity. Dust production rate on March 13.75, 6 h before Giotto encounter, was approximately 10(7) gm s-1.