Biomedical subjects

A Harf

Publications and source records attributed to A Harf.

At least 37 records · Page 2Linked to original sources

PubMed2000

Nasal obstruction as a risk factor for sleep apnoea syndrome.

Nasal obstruction has frequently been mentioned as a possible risk factor in obstructive sleep apnoea syndrome (OSAS). Over a 2-yr period, 541 unselected consecutive snorers referred for suspected breathing disorders during sleep were included to undergo posterior rhinomanometry. In addition cephalometric landmarks and body mass index (BMI) were obtained. Polysomnography was used to determine the number of abnormal respiratory events that occurred during sleep. OSAS was defined as 15 episodes, or more, of apnoea or hypopnoea per hour of sleep (AHI). Of the 541 consecutive snorers 528 underwent nasal resistance measurement by posterior rhinomanometry (failure rate: 2.4%). Patients with OSAS (259 patients) had higher nasal resistance than patients without OSAS (2.6+/-1.6 hPa x L x s(-1) versus 2.2+/-1.0 hPa x L x s(-1), respectively, p<0.005). A stepwise multiple regression analysis showed that BMI, male sex, nasal resistance, and cephalometric parameters were contributing factors to the AHI. The r2-value of the multiple regression analysis was 0.183. Nasal resistance contributed 2.3% of the variance (p<0.0001), whereas mandibular plane-hyoid distance, BMI, male sex and age contributed 6.2%, 4.6%, 3% and 1.3% of the variance, respectively. To conclude, daytime nasal obstruction is an independent risk factor for OSAS.

Airway Resistance↗

PubMed2000

Airway occlusion pressure to titrate positive end-expiratory pressure in patients with dynamic hyperinflation.

BACKGROUND: Although the use of external positive end-expiratory pressure (PEEP) is recommended for patients with intrinsic PEEP, no simple method exists for bedside titration. We hypothesized that the occlusion pressure, measured from airway pressure during the phase of ventilator triggering (P0.1t), could help to indicate the effects of PEEP on the work of breathing (WOB). METHODS: Twenty patients under assisted ventilation with chronic obstructive pulmonary disease were studied with 0, 5, and 10 cm H2O of PEEP while ventilated with a fixed level of pressure support. RESULTS: PEEP 5 significantly reduced intrinsic PEEP (mean +/- SD, 5.2 +/- 2.4 cm H2O at PEEP 0 to 3.6 +/- 1.9 at PEEP 5; P < 0.001), WOB per min (12. 6 +/- 6.7 J/min to 9.1 +/- 5.9 J/min; P = 0.003), WOB per liter (1.2 +/- 0.4 J/l to 0.8 +/- 0.4 J/l; P < 0.001), pressure time product of the diaphragm (216 +/- 86 cm H2O. s-1. min-1 to 155 +/- 179 cm H2O. s-1. min-1; P = 0.001) and P0.1t (3.3 +/- 1.5 cm H2O to 2.3 +/- 1.4 cm H2O; P = 0.002). At PEEP 10, no further significant reduction in muscle effort nor in P0.1t (2.5 +/- 2.1 cm H2O) occurred, and transpulmonary pressure indicated an increase in end-expiratory lung volume. Significant correlations were found between WOB per min and P0.1t at the three levels of PEEP (P < 0.001), and between the changes in P0.1t versus the changes in WOB per min (P < 0.005), indicating that P0.1t and WOB changed in the same direction. A decrease in P0.1 with PEEP indicated a decrease in intrinsic PEEP with a specificity of 71% and a sensitivity of 88% and a decrease in WOB with a specificity of 86% and a sensitivity of 91%. CONCLUSION: These results show that P0.1t may help to assess the effects of PEEP in patients with intrinsic PEEP.

Adult↗

PubMed2000

Use of the forced oscillation technique to assess airway obstruction and reversibility in children.

The forced oscillation technique (FOT) is particularly attractive in a pediatric setting as it requires only passive cooperation from the child. We assessed the sensitivity and specificity of this method for detecting airway obstruction and its reversibility in 313 children (3 to 16 yr of age) with asthma or chronic nocturnal cough. Baseline and post-bronchodilator (n = 251) resistance were measured (R(0)) with the FOT. Baseline R(0) was normalized for height and weight [R(0)(SD)]. In children able to perform forced expiratory maneuvers (n = 181), R(0)(SD) was independently correlated with FEV(1) (p < 0.02) and maximal expiratory flow at 50% (MEF(50)) (p < 0.004). The optimal R(0)(SD) cutoff value given by receiver operating characteristic (ROC) curves to discriminate between children with baseline FEV(1) < 80% or >/= 80% of predicted values yielded 84% sensitivity and 73% specificity. Post-bronchodilator changes in R(0)(SD) [DeltaR(0)(SD)] were mostly correlated to changes in MEF(50). The optimal DeltaR(0)(SD) cutoff value to discriminate between children with the presence or absence of significant reversibility in FEV(1) yielded 69% sensitivity and 78% specificity. In children unable to perform forced expiratory maneuvers (n = 132), this DeltaR(0)(SD) cutoff clearly identified a subgroup of young children with high R(0) values at baseline, that returned to normal after bronchodilation. We conclude that FOT measurements allow reliable evaluation of bronchial obstruction and its reversibility in asthmatic children over 3 yr old.

Administration, Inhalation↗

PubMed2000

Clinical evaluation of a computer-controlled pressure support mode.

We have designed a computerized system providing closed-loop control of the level of pressure support ventilation (PSV). The system sets itself at the lowest level of PSV that maintains respiratory rate (RR), tidal volume (VT), and end-tidal CO(2) pressure (PET(CO(2))) within predetermined ranges defining acceptable ventilation (i.e., 12 < RR < 28 cycles/min, VT > 300 ml [> 250 if weight < 55 kg], and PET(CO(2)) < 55 mm Hg [< 65 mm Hg if chronic CO(2) retention]). Ten patients received computer-controlled (automatic) PSV and physician-controlled (standard) PSV, in random order, during 24 h for each mode. An estimation of occlusion pressure (P(0.1)) was recorded continuously. The average time spent with acceptable ventilation as previously defined was 66 +/- 24% of the total ventilation time with standard PSV versus 93 +/- 8% with automatic PSV (p < 0.05), whereas the level of PSV was similar during the two periods (17 +/- 4 cm H(2)O versus 19 +/- 6 cm H(2)O). The time spent with an estimated P(0.1) above 4 cm H(2)O was 34 +/- 35% of the standard PSV time versus only 11 +/- 17% of the automatic PSV time (p < 0.01). Automatic PSV increased the time spent within desired ventilation parameter ranges and apparently reduced periods of excessive workload.

Aged↗

PubMed2000

Noninvasive ventilation with helium-oxygen in acute exacerbations of chronic obstructive pulmonary disease.

The use of helium-oxygen (HeO(2)) was tested in combination with noninvasive ventilation (NIV) in 10 patients with acute exacerbation of chronic obstructive pulmonary disease (COPD). Effort to breathe as assessed by the respiratory muscle pressure-time index (PTI), work of breathing (WOB), and gas exchange were the main endpoints. Results of NIV-HeO(2) were compared with those obtained with standard NIV (AirO(2)), at two levels of pressure-support ventilation (PSV), 9 +/- 2 cm H(2)O and 18 +/- 3 cm H(2)O. Significant reductions in PTI were observed between HeO(2) and AirO(2) at both the low PSV level (n = 9; 160 +/- 58 versus 198 +/- 78 cm H(2)O/s/ min; p < 0.05) and the high PSV level (n = 10; 100 +/- 45 versus 150 +/- 82 cm H(2)O/s/min; p < 0.01). WOB also differed significantly between HeO(2) and AirO(2) (7.8 +/- 4.1 versus 10.9 +/- 6.1 J/min at the low PSV level, p < 0.05; and 5.7 +/- 3.3 versus 9.2 +/- 5. J/min, p < 0.01 at the high PSV level). HeO(2) reduced Pa(CO(2)) at both the low PSV level (61 +/- 13 versus 64 +/- 15 mm Hg; p < 0.05) and the high PSV level (56 +/- 13 versus 58 +/- 14 mm Hg; p < 0.05), without significantly changing breathing pattern or oxygenation. We conclude that use of HeO(2) during NIV markedly enhances the ability of NIV to reduce patient effort and to improve gas exchange.

Administration, Inhalation↗

PubMed2000

Detection of positional airway obstruction in neonates by acoustic reflection.

In neonates intubated with an uncuffed endotracheal tube (ETT), positional changes of the head may induce obstruction (side position-related ETT obstruction [SPRO]) due to abutment of the beveled distal ETT orifice against the tracheal wall. We studied whether the acoustic reflection (ACR) method, a 4-s measurement that maps cross-sectional area as a function of the distance along the ETT and the airways, could detect SPRO. Eleven preterm newborns intubated with 2.5-mm ETTs and clinically suspected of having SPRO were studied with the head oriented to the left and to the right. In all patients there was a marked decrease in the ACR-measured area beyond the distal tip of the ETT in the presence of obstruction (decrease = 38 +/- 22% [mean +/- SD] of the ETT inside area), while the ACR-measured area increased markedly in the absence of obstruction (increase = 49 +/- 17%). For six of the 11 infants, we also recorded the maximal flow produced by a set mechanical inflation pressure. This maximal flow decreased in the presence of obstruction (decrease = 47 +/- 18%), and was constantly associated with a decrease in ACR-measured area beyond the ETT. In conclusion, ACR measurement is an efficient method for diagnosing positional ETT obstruction in intubated newborns.

Acoustics↗

PubMed2000

Predictive value of pulmonary function parameters for sleep apnea syndrome.

Nocturnal polysomnography is the standard diagnostic test for sleep apnea syndrome (SAS) but is both expensive and time-consuming. We developed a predictive index for SAS based on pulmonary function data, including respiratory resistance determined by the forced oscillation technique, from 168 obese snorers with suspected SAS. Our model used logistic regression to obtain case-by-case predictions of the probability of SAS, defined as an apnea-hypopnea index (AHI) > or = 15 during overnight polysomnography. We then tested our model in a prospective group of 101 similar patients. Specific respiratory conductance and daytime oxygen saturation contributed significantly to the model. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the index computed from these parameters were 98%, 86%, 90%, and 97%, respectively. In the prospective group, the model proved repeatable, with 100% sensitivity, 84% specificity, 86% PPV, and 100% NPV. The high NPV may help to identify obese snorers with a SAS risk that is so low as to make polysomnography unnecessary. Based on the 50% prevalence of SAS in our study and on the fact that polysomnography is required in all patients with daytime somnolence, we calculated that using our model would have obviated the need for polysomnography in 38% of our patients.

Female↗

PubMed2000

Optimization of aerosol deposition by pressure support in children with cystic fibrosis: an experimental and clinical study.

Nebulized aerosols are commonly used to deliver drugs into the lungs of patients with cystic fibrosis (CF). The aim of this study was to assess the effectiveness of pressure-support (PS) ventilation in increasing aerosol deposition within the lungs of children with CF. An in vitro study demonstrated the feasibility of coupling a breath-actuated nebulizer to a PS device. An in vivo study was done with 18 children (ages 6 to 21 yr) with clinically stable CF, each of whom underwent both a standard and a PS-driven ventilation scan (control session and PS session, respectively). In addition, a perfusion scan was used to determine lung outlines and to construct a geometric model for quantifying aerosol deposition by radioactivity counting in MBq. Homogeneity of nebulization was evaluated from the four first-order moments of aerosol distribution in the peripheral and central lung regions. The time-activity nebulization curve was linear in all patients, with higher slopes during the PS than during the control session (0.43 +/- 0.07 [mean +/- SD] MBq/min and 0.32 +/- 0.23 MBq/min, respectively; p < 0.018). Quantitatively, aerosol deposition was about 30% greater after the PS session (4.4 +/- 2.7 MBq) than after the control session (3.4 +/- 2.1 MBq; p < 0.05). Similarly, deposition efficacy (as a percentage of nebulizer output) was significantly better during the PS session than during the control session (15.3 +/- 8.3% versus 11.5 +/- 5.7%, p < 0.05). No differences in the regional deposition pattern or in homogeneity of uptake were observed. In conclusion, our data show that driving the delivery of a nebulized aerosol by noninvasive PS ventilation enhances total lung aerosol deposition without increasing particle impaction in the proximal airways.

Adolescent↗

PubMed2000

Effects of mandibular advancement on respiratory resistance.

Mandibular advancing devices are proposed as nonsurgical treatment for certain patients with an obstructive sleep apnoea syndrome. Since they act by increasing the upper airway calibre, the aim of the present study was to investigate the changes in respiratory resistance (Rrs) resulting from mandibular advancement. Rrs was measured at the nose by the forced oscillation technique (4-32 Hz). Ten normal subjects were studied under three conditions: resting mandibular position, passive mandibular advancement steadied by a wax bite, and voluntary advancement, in random order. Respiratory resistance was extrapolated to 0 Hz (R0) and estimated at 16 Hz (R16) by linear regression analysis of respiratory resistive impedance versus frequency. R0 (mean+/-SEM=3.5+/-0.2 cmH2O x L(-1) x s in the resting position) decreased significantly with passive advancement (2.9+/-0.2 cmH2O x L(-1) x s, p<0.001), but remained unchanged with voluntary mandibular advancement (3.6+/-0.2 cmH2O x L(-1) s). Similar results were obtained for R16. The results of this study demonstrate that the effects of mandibular advancement on upper airway resistance differ, depending on whether advancement is passive or active, and suggest that in order to simulate the actual effects of therapeutic devices, mandibular advancement should be passive.

Adult↗

PubMed2000

Effects of nasal prongs on nasal airflow resistance.

STUDY OBJECTIVES: The aim of this study was to investigate whether nasal prongs, which have been proposed to assess nasal flow during sleep, affect nasal airflow resistance (NR). DESIGN: NR was estimated by posterior rhinomanometry at a 0.5 L/s flow, under eight conditions: in the basal state, and with seven different nasal prongs. PARTICIPANTS: The study was performed in 17 healthy supine subjects, 8 of whom had basal NR values within the normal range (< or = 2 cm H(2)O.L(-1).s, group 1), and 9 had increased basal NR values (> 2.5 cm H(2)O.L(-1).s, group 2), because of nare narrowness and/or deviated nasal septum. MEASUREMENTS AND RESULTS: NR increased significantly while breathing with nasal prongs (p < 0.0001 in both groups). The changes in NR (DeltaNR) induced by the different nasal prongs were characterized by large intersubject and intrasubject variability, with a maximum DeltaNR of 24.2 cm H(2)O.L(-1).s. Significant differences were found between the DeltaNR induced by the different nasal prongs (p < 0.001 in group 1, and p < 0.0003 in group 2), and for six of them, DeltaNR was significantly higher in group 1 than in group 2 (p < 0.02). CONCLUSIONS: This study demonstrates that nasal prongs can markedly increase NR in subjects presenting with nare narrowness and/or deviated nasal septum. Further investigations that would include nocturnal polysomnography are still required to evaluate the possible influence of nasal prongs on the diagnosis of obstructive sleep apnea syndrome and its severity.

Adult↗

PubMed2000

Constant vs. automatic continuous positive airway pressure therapy: home evaluation.

STUDY OBJECTIVES: To compare the efficacy and patient tolerance, compliance, and preference between auto-continuous positive airway pressure (CPAP) and constant CPAP. DESIGN: Single-blinded, crossover, cohort study of consecutive patients with obstructive sleep apnea syndrome, with two treatment periods of 2 months each. PATIENTS: Twenty-five patients (22 men, 3 women) with sleep apnea syndrome confirmed by ambulatory polysomnography. MEASUREMENTS AND INTERVENTIONS: After baseline polysomnography, patients underwent in-laboratory polysomnography for titration of constant CPAP. The order of treatment was randomly allocated, either auto-CPAP and then constant CPAP, or vice versa. The auto-CPAP pressure range was 6 to 16 cm H(2)O. At the end of each 2-month period, patients underwent a control ambulatory polysomnography and received a questionnaire on subjective well-being and device evaluation. Duration of use was checked through CPAP device monitoring. RESULTS: No differences were found in apnea/hypopnea index (constant CPAP, 9.7+/-1.9 events/h vs auto-CPAP, 10.6+/-9.3 events/h), awakening/arousal index (constant CPAP, 13.7 +/- 8.0 events/h vs auto-CPAP, 15.5 +/- 8.9 events/h), slow-wave sleep duration, nocturnal saturation, or complaint of daytime sleepiness. The mean pressure required was significantly lower during auto-CPAP than during constant CPAP (8.8+/-1.8 cm H(2)O vs. 9.7+/-2.6 cm H(2)O, respectively). Patient tolerance, compliance, and duration of use were similar with both treatments. CONCLUSIONS: Auto-CPAP is as effective as constant CPAP. A wide pressure range for auto-CPAP can be used in all patients, suggesting that, in the future, use of a broad pressure range in the auto-CPAP mode could obviate the need for the titration night.

Circadian Rhythm↗

PubMed2000

Costs for acute myocardial infarction in a tertiary care centre and nationwide in France.

OBJECTIVE: We compared the estimated costs of coronary interventions from our hospital's cost accounting system with data from the French Diagnosis Related Group (DRG) cost database, taking the perspective of our hospital. DESIGN: Cost data on hospital resources used by patients hospitalised for acute myocardial infarction (MI), with and without complications, including deceased patients, were collected in a tertiary care university hospital located in Paris, France. The data were collected using the hospital's cost accounting system and then compared with the estimates provided by the DRG reimbursement schedule for similar conditions. MAIN OUTCOME MEASURES AND RESULTS: The estimated costs were 849 euro (EUR) for coronary angiography, EUR4762 for coronary angioplasty with stenting, and EUR4978 to 8067 for MI. The DRG reimbursement schedule provided for acute MI was EUR3920 to 5709. CONCLUSIONS: Although the current cost of treating acute MI in a teaching hospital is reasonably close to that in the current reimbursement schedule, rapid technological changes regarding both drugs and devices renders necessary a close monitoring of costs associated with the management of these acute care patients.

Angioplasty, Balloon, Coronary↗

PubMed1999

Altered balance between matrix gelatinases (MMP-2 and MMP-9) and their tissue inhibitors in human dilated cardiomyopathy: potential role of MMP-9 in myosin-heavy chain degradation.

BACKGROUND: End-stage of human dilated cardiomyopathy (DCM) is characterized by myocyte loss and fibrosis, and associated with ventricular dilatation and reduced cardiac function. Matrix metalloproteinases (MMPs) and their natural tissue inhibitors (TIMPs) have been involved in the myocardial remodeling. AIMS: To evaluate the potential role of matrix gelatinases (MMP-2 and MMP-9) in DCM, the balance between gelatinases and TIMPs and the gelatinase localization were investigated in left free wall ventricles from six normal donors and six patients with DCM at the transplantation time. METHODS: TIMP-(1, 2, 3 and 4) mRNAs were analyzed by quantitative reverse transcription-polymerase chain reaction (RT-PCR). TIMP-1 and -2 protein content was assessed by ELISA. MMP-2 and MMP-9 expression were examined by zymography and immunological techniques. RESULTS: All TIMPs were down-regulated in DCM hearts, especially TIMP-1 (reduced by 80%). Gel zymography revealed similar activity of MMP-2 and MMP-9 in both tissues. By in situ zymography and immunohistochemistry, active and immunoreactive gelatinases were pericardiomyocyte in control hearts and intracardiomyocyte in DCM hearts. Intracellular MMPs were associated with sarcomeric structure in DCM. To estimate a putative role of these gelatinases, several sarcomeric contractile proteins were digested in vitro by purified active MMP-9. Only myosin-heavy chain was cleaved in vitro giving 180-, 120-, 80- and 20-kDa proteolytic fragments. In vivo, two major myosin-heavy chain proteolytic fragments (80 and 20 kDa) were detected by specific monoclonal antibody against myosin-heavy chain in DCM left ventricular homogenates, only. CONCLUSIONS: Taken together, these data highly suggest that MMP-2 and MMP-9 may be involved in the disorganization of the contractile apparatus in DCM hearts.

Adult↗

PubMed1999

Effect of increased pressure on tracheal ciliary beat frequency.

Effects of increased ambient pressure on mucociliary clearance have been poorly investigated. The effects of increasing pressures on ciliary beat frequency (CBF) of guinea-pig tracheal rings were studied in vitro. Increased pressures of 25 and 100 kPa induced a significant and equivalent enhancement of CBF from 30 min after the pressure increase. The increase in CBF observed after a pressure increase of 50 kPa (inspiratory oxygen fraction = 21%), was significantly greater than that observed with an equivalent oxygen tension at atmospheric pressure, i.e. with a gas mixture containing 30% oxygen. Addition of N(G)-nitro-L-arginine methylester (L-NAME) inhibited the enhancement in CBF observed after the 25 kPa pressure increase. Addition of L-arginine reversed the effect of L-NAME. These results demonstrate that a pressure increase applied to tracheal rings, in vitro, induces an enhancement of ciliary beat frequency and that generation of nitric oxide may be involved in this ciliary stimulation.

Animals↗

PubMed1999

Accuracy of the i-STAT bedside blood gas analyser.

The performance of the i-STAT portable clinical analyser for measuring blood gases and pH was evaluated with reference to a conventional blood gas analyser (ABL520 Radiometer). Ninety-two samples from the routine blood gas analysis laboratory were chosen according to a wide distribution of partial pressure of carbon dioxide (Pa,CO2), partial pressure oxygen (Pa,O2) and pH and then analysed. All measurements were performed in duplicate by trained technicians from the central hospital laboratory. Differences between duplicate measurements were computed for Pa,CO2: (1.2 versus 0.4%), Pa,O2 (1.7 versus 1.1%) and pH (0.06 versus 0.02%), for the i-STAT and ABL520, respectively. pH and Pa,CO2 values measured with the i-STAT were very close to those obtained with the ABL520, the difference (mean+/-SD) being 0.006+/-0.018 and -0.13+/-0.17 kPa, respectively. Statistical analysis showed that the differences between analysers did not depend on values of pH or Pa,CO2. The performance of the analysers depended on the level of PO2. Below 15 kPa (n=48), the two systems gave nearly identical values, the mean difference was 0.01+/-0.37 kPa. Between 16 and 55 kPa (n=44), there was a systematic but small (-0.69+/-0.67 kPa) underestimation of Pa,O2 measured with the i-STAT (p<10(-8)). In conclusion, this study shows that blood gas analysis using the i-STAT portable device is comparable with that performed by a conventional laboratory blood gas analyser.

Blood Gas Analysis↗

PubMed1999

Matrix metalloproteinase gelatinases in sulfur mustard-induced acute airway injury in guinea pigs.

Respiratory tract lesions induced by sulfur mustard (SM), a chemical warfare agent, are characterized by epithelial damage associated with inflammatory cell infiltration. To test the potential role of matrix metalloproteinase gelatinases in these lesions, we evaluated gelatinase activity, albumin content, and total cell count in bronchoalveolar lavage fluid of guinea pigs 24 h after an intratracheal injection of 0.2 mg/kg of SM. The bronchial lavage and alveolar lavage fluids were analyzed separately. The increase in inflammatory cell content of the bronchial lavage fluid, mainly macrophages, observed in SM-intoxicated guinea pigs was accompanied by an increase in albumin and in 92-kDa gelatinase activity. There was a significant correlation between albumin content and 92-kDa gelatinase activity (r = 0.67) and between 92-kDa gelatinase and the number of macrophages. Immunohistochemistry performed on tracheal sections showed the presence of 92-kDa gelatinase at the site of intraepithelial cleavages. Zymography analysis of culture medium conditioned by guinea pig tracheal epithelial cells demonstrated that these cells produced in vitro 92-kDa gelatinase on stimulation. Culture of human bronchial epithelial cells obtained by the explant technique showed a marked increase in 92-kDa gelatinase after exposure to 5 x 10(-5) M SM that reinforced the relevance of our animal results to human exposure to SM. These results suggest that in SM respiratory intoxication, 92-kDa gelatinase of both inflammatory and epithelial cell origins could be involved in epithelial cell detachment.

Albumins↗

PubMed1999

Estimation of inspiratory pressure drop in neonatal and pediatric endotracheal tubes.

Endotracheal tubes (ETTs) constitute a resistive extra load for intubated patients. The ETT pressure drop (DeltaP(ETT)) is usually described by empirical equations that are specific to one ETT only. Our laboratory previously showed that, in adult ETTs, DeltaP(ETT) is given by the Blasius formula (F. Lofaso, B. Louis, L. Brochard, A. Harf, and D. Isabey. Am. Rev. Respir. Dis. 146: 974-979, 1992). Here, we also propose a general formulation for neonatal and pediatric ETTs on the basis of adimensional analysis of the pressure-flow relationship. Pressure and flow were directly measured in seven ETTs (internal diameter: 2.5-7.0 mm). The measured pressure drop was compared with the predicted drop given by general laws for a curved tube. In neonatal ETTs (2.5-3.5 mm) the flow regime is laminar. The DeltaP(ETT) can be estimated by the Ito formula, which replaces Poiseuille's law for curved tubes. For pediatric ETTs (4.0-7.0 mm), DeltaP(ETT) depends on the following flow regime: for laminar flow, it must be calculated by the Ito formula, and for turbulent flow, by the Blasius formula. Both formulas allow for ETT geometry and gas properties.

Adult↗

PubMed1999

Physiological effects of alveolar, tracheal, and "standard" pressure supports.

Pressure support (PS) is characterized by a pressure plateau, which is usually generated at the ventilator level (PS(vent)). We have built a PS device in which the pressure plateau can be obtained at the upper airway level (PS(aw)) or at the alveolar level (PS(A)). The effect of these different PS modes was evaluated in seven healthy men during air breathing and 5% CO(2) breathing. Minute ventilation during air breathing was higher with PS(A) than with PS(aw) and lower with PS(vent) (16 +/- 3, 14 +/- 3, and 11 +/- 2 l/min, respectively). By contrast, there were no significant differences in minute ventilation during 5% CO(2) breathing (25 +/- 5, 27 +/- 7, and 23 +/- 5 l/min, respectively). The esophageal pressure-time product per minute was lower with PS(A) than with PS(aw) and PS(vent) during air breathing (29 +/- 26, 44 +/- 44, and 48 +/- 30 cmH(2)O. s, respectively) and 5% CO(2) breathing (97 +/- 40, 145 +/- 62, and 220 +/- 41 cmH(2)O. s, respectively). In conclusion, during PS, moving the inspiratory pressure plateau from the ventilator to the alveolar level reduces pressure output, particularly at high ventilation levels.

Adult↗