Biomedical subjects

N Claure

Publications and source records attributed to N Claure.

At least 19 recordsLinked to original sources

PubMed2001

Inductance plethysmography: an alternative signal to servocontrol the airway pressure during proportional assist ventilation in small animals.

During proportional assist ventilation (PAV), the ventilator pressure is servocontrolled throughout each spontaneous inspiration such that it instantaneously increases in proportion to the airflow (resistive unloading mode), or inspired volume (elastic unloading mode), or both (combined unloading mode). The PAV pressure changes are generated in a closed-loop feedback circuitry commonly using a pneumotachographic signal. In neonates, however, a pneumotachograph increases dead space ventilation, and its signal may include a substantial endotracheal tube leak component. We hypothesized that respiratory inductive plethysmography (RIP) can replace pneumotachography to drive the ventilator during PAV without untoward effects on ventilation or respiratory gas exchange. Ten piglets and five rabbits were supported for 10-min (normal lungs) or 20-min (meconium injured lungs) periods by each of the three PAV modes. In each mode, three test periods were applied in random order with the ventilator driven by the pneumotachograph signal, or the RIP abdominal band signal, or the RIP sum signal of rib cage and abdomen. Interchanging the three input signals did not affect the regularity of spontaneous breathing, and gas exchange was achieved with similar peak and mean airway pressures (ANOVA). However, the RIP sum signal worked adequately only when the relative gains of rib cage and abdominal band signal were calibrated. We conclude that an RIP abdominal band signal can be used to generate PAV, avoiding increased dead space and endotracheal tube leak problems.

Airway Resistance↗

PubMed2001

Proportional assist ventilation decreases thoracoabdominal asynchrony and chest wall distortion in preterm infants.

Thoracoabdominal asynchrony (TAA) and chest wall distortion (CWD) are commonly seen in preterm infants secondary to a highly compliant rib cage and poor compensation of distorting forces by inspiratory rib cage muscles. Continuous positive airway pressure (CPAP) reduces TAA and CWD by stenting the chest wall. We hypothesized that application of positive airway pressure only during inspiration and in proportion to an infant's inspiratory effort should have a similar but more pronounced effect than CPAP alone. A ventilator providing airway pressure changes in proportion to flow and volume generated by an infant (proportional assist ventilation) was used to unload the respiratory pump during inspiration. Ten preterm infants were studied [birth weight, 745 (635-1175) g; gestational age, 26.5 (24-31) wk; postnatal age 3 (1-7) d; medium (range)]. TAA and CWD were determined by respiratory inductive plethysmography. TAA was expressed as the phase angle between the rib cage and abdominal motion and CWD as the total compartmental displacement ratio. In addition, we measured tidal volume with a pneumotachograph and esophageal and airway pressure deflections with pressure transducers. Measurements were obtained during alternating periods of CPAP and two different degrees of support (Gain 1 = 1.09 +/- 0.68, Gain 2 = 1.84 +/- 0.84 cm H(2)O/mL) that were provided by a proportional assist ventilator. Phase angle and the total compartmental displacement ratio decreased with increasing gain compared with CPAP alone. Peak airway pressure increased from 0.6 to 3.8 to 7.6 cm H(2)O above positive end-expiratory pressure (PEEP) with CPAP, Gain 1, and Gain 2, respectively, as tidal volume increased from 2.8 to 4.1 to 4.7 mL/kg. Esophageal pressure changes decreased only little with increasing gain. Chest wall excursion increased and abdominal movement decreased, indicating a redistribution of tidal volume between chest and abdomen. We conclude that proportional assist ventilation reduces TAA and CWD by generating a small increase in airway pressure that occurs in synchrony and in proportion to each inspiratory effort.

Abdomen↗

PubMed2001

Closed-loop controlled inspired oxygen concentration for mechanically ventilated very low birth weight infants with frequent episodes of hypoxemia.

BACKGROUND: Mechanically ventilated very low birth weight infants often present with frequent episodes of hypoxemia, and maintaining arterial oxygen saturation by pulse oximetry (SpO(2)) within a normal range by manual fraction of inspired oxygen (FIO(2)) adjustments is difficult and time consuming. OBJECTIVES: An algorithm for closed-loop FIO(2) control (cFIO(2)) to maintain SpO(2) within a target range was compared with continuous manual FIO(2) (mFIO(2)) adjustments by a nurse in a group of ventilated infants who presented with frequent episodes of hypoxemia. RESULTS: Fourteen infants (birth weight: 712 +/- 142 g; gestational age: 25 +/- 1.6 weeks; age: 26 +/- 11 days; synchronized intermittent mandatory ventilation rate: 24 +/- 10 b/m; peak inspiratory pressure: 17.5 +/- 2.0 cmH(2)O; positive end-expiratory pressure: 4.3 +/- 0.5 cmH(2)O) were studied for 2 hours on each mode in random sequence. Both modes aimed to maintain SpO(2) between 88% and 96%. There were 15 +/- 7 and 16 +/- 6 hypoxemic episodes/hour (SpO(2) <88%, >5 s) during mFIO(2) and cFIO(2), respectively; episode duration was 41 +/- 23 and 32 +/- 15 s, totaling 19 +/- 16% and 17 +/- 12% of recording time. There were 13 +/- 10 and 10 +/- 8 hyperoxemic episodes/hour (SpO(2)>96%, >5 s) during mFIO(2) and cFIO(2,) respectively; episode duration was 27 +/- 15 and 24 +/- 19 s, totaling 15 +/- 14% and 10 +/- 9% of recording time. Mean SpO(2) and FIO(2) levels were similar during both modes. The nurse made 29 +/- 17 adjustments/hour during mFIO(2). There was a significant increase in the duration of normoxemia (SpO(2) between 88%-96%) during cFIO(2) (75 +/- 13 vs 66 +/- 14% of recording time). CONCLUSION: In this group of infants, cFIO(2) was at least as effective as a fully dedicated nurse in maintaining SpO(2) within the target range, and it may be more effective than a nurse working under routine conditions. We speculate that during long-term use, cFIO(2) may save nursing time and reduce the risks of morbidity associated with supplemental oxygen and episodes of hypo- and hyperoxemia.

Algorithms↗

PubMed1999

Proportional assist ventilation in low birth weight infants with acute respiratory disease: A comparison to assist/control and conventional mechanical ventilation.

OBJECTIVES: To compare the physiologic efficacy and safety aspects of proportional assist (PA), assist/control (A/C), and intermittent mandatory ventilation (IMV) in very low birth weight infants with acute respiratory illness and to test the hypothesis that ventilatory pressure requirements are lower and arterial oxygenation is improved during PA when compared with IMV or A/C at an equivalent inspired oxygen fraction. STUDY DESIGN: Randomized, 3-period, crossover design. METHODS: Thirty-six infants were stratified by birth weight (600 to 750, 751 to 900, and 901 to 1200 g) and exposed to consecutive 45-minute epochs of the 3 modalities in a sequence chosen at random. Tidal volumes of 4 to 6 mL/kg were targeted during A/C and IMV. The IMV rate was matched to the rate during an A/C test period. PA was adjusted to unload the resistance of the endotracheal tube and the disease-related increase in lung elastic recoil. RESULTS: Compared with A/C and IMV, PA maintained similar arterial oxygenation with lower airway and transpulmonary pressures (15% to 44% reduction depending on the index variable). The oxygenation index decreased by 28% during PA. No adverse events were observed. The number and severity of apneic episodes and periods of arterial oxygen desaturations were similar with the 3 modes. Similar results were obtained within each birth weight subgroup. CONCLUSIONS: PA safely maintains gas exchange with smaller transpulmonary pressure changes compared with A/C and IMV. It may therefore offer a way of reducing the incidence of chronic lung disease in low birth weight infants.

Acute Disease↗

PubMed1998

Effects of respiratory mechanical unloading on thoracoabdominal motion in meconium-injured piglets and rabbits.

Impaired pulmonary mechanics can cause chest wall distortion (CWD) so that work of breathing is dissipated in deforming the rib cage. We hypothesized that respiratory mechanical unloading as a technique of assisted mechanical ventilation would reduce CWD in animals with injured lungs. We studied five piglets and five adult rabbits to test across different ages and chest configurations. As a result of intratracheal meconium instillation, lung compliance decreased from 21 (median; range 17-35) to 9.5 (6.7-14) mL/kPa/kg in rabbits and from 26 (18-31) to 7.9 (4.9-11) in piglets. Airway resistance increased from 5.0 (4.6-6.1) to 6.9 (5.8-7.9) kPa/L/s in rabbits only. Respiratory inductive plethysmography was used to measure the phase shift between the rib cage and abdominal compartment movements and the total compartmental displacement ratio. We aimed at unloading at least three-fourths of lung elastance in all animals and 2.0 kPa/L/s of resistance in rabbits. Elastic unloading decreased the phase shift in all but one animal. It reduced the total compartmental displacement ratio from 1.27 (1.14-3.73) to 1.16 (1.02-1.82) in piglets and from 1.77 (1.45-5.24) to 1.37 (1.11-4.78) in rabbits. The inspiratory rib cage expansion increased, whereas abdominal expansion did not. The tidal esophageal pressure deflection decreased. Tidal volume increased, whereas respiratory rate remained unaffected so that the partial pressure of arterial CO2 decreased. Resistive unloading as an adjunct to elastic unloading further reduced CWD and induced a more rapid, shallower breathing. We conclude that respiratory unloading as a mechanical support to spontaneous breathing reduces CWD. We speculate that the decrease in CWD increases ventilatory efficiency for a given diaphragmatic effort.

Abdomen↗

PubMed1997

Increased incidence of sighs (augmented inspiratory efforts) during synchronized intermittent mandatory ventilation (SIMV) in preterm neonates.

A reflex resulting in a deep, sigh-like inspiratory effort (augmented breath) is frequently triggered during synchronized mechanical ventilation in preterm infants. We studied the incidence of augmented inspiratory efforts and their effect on ventilation and lung compliance during conventional IMV and synchronized IMV (SIMV) in 15 preterm neonates (GA 26.7 +/- 1.5 wks (mean +/- SD), BW 925 +/- 222 g, age 1-8 days). Augmentation of spontaneous inspiratory effort was defined as an esophageal pressure deflection occurring coincident with a synchronized mechanical breath and exceeding the previous unassisted spontaneous effort by more than 50%. The incidence of augmented breaths was higher during SIMV (11.1 +/- 7.7%; P < 0.01) than during conventional IMV (5.1 +/- 6.1%). However, when the synchronized breaths were triggered late (200-300 msec) after the onset of inspiration, augmented breaths occurred no more frequently than during conventional IMV (6.0 +/- 4.7%). The incidence of augmented breaths correlated inversely with dynamic lung compliance (P = 0.014), but was not significantly influenced by a change in PEEP. Although inspiratory effort increased nearly three times during the augmented breaths, tidal volume increased only 12%. The change in tidal volume was limited because the augmented effort reached its maximal negativity only approximately 500 ms after the beginning of the synchronized, mechanical breath and at a time when the mechanical breath had already ended. For this reason the augmented effort did not contribute significantly to minute ventilation, but only prolonged inspiration. Dynamic lung compliance did not change significantly after an augmented breath. The results indicate that augmented inspiratory efforts are more common in preterm neonates ventilated with SIMV than with conventional IMV, but do not contribute significantly to ventilation.

Cohort Studies↗

PubMed1997

Computer-controlled minute ventilation in preterm infants undergoing mechanical ventilation.

INTRODUCTION: Computer-controlled minute ventilation (CCMV) continuously adjusts the ventilator rate to changes in spontaneous respiratory drive and pulmonary mechanics to maintain a preset total minute ventilation. HYPOTHESIS: We hypothesized that CCMV would maintain ventilation and oxygenation with fewer mechanical breaths than conventional intermittent mandatory ventilation in very low birth weight infants. METHODS: Very low birth weight infants in clinically stable condition who were undergoing mechanical ventilation were enrolled. The number of mechanical breaths, total and mechanical expiratory minute ventilation, mean airway pressure, oxygen hemoglobin saturation by pulse oximetry, and transcutaneous partial carbon dioxide and partial oxygen tensions were obtained during intermittent mandatory ventilation and CCMV (45 to 60 minutes) and compared by paired t test. RESULTS: Fifteen infants were studied. Birth weight (median, range) was 700 gm (550 to 1205 gm), gestational age 26 weeks (23 to 34 weeks), age 21 days (3 to 50 days). When switched from intermittent mandatory ventilation to CCMV, the number of mechanical breaths was reduced (15 +/- 2.8 to 8.6 +/- 2.9 breaths per minute, p < 0.001), leading to lower airway pressure (3.97 +/- 1.00 to 3.45 +/- 1.00 cm H2O, p < 0.001) and lower expiratory minute ventilation generated by the mechanical ventilator (116 +/- 31 to 65 +/- 28 ml/min per kilogram, p < 0.001), while total expiratory minute ventilation remained unchanged. Mean transcutaneous partial carbon dioxide and oxygen tensions, oxygen hemoglobin saturation, and the time spent within different oxygen hemoglobin saturation ranges did not differ between both ventilatory modes. CONCLUSION: CCMV maintained adequate ventilation and oxygenation with lower mechanical ventilatory support than IMV. CCMV may reduce barotrauma and chronic lung disease during long-term use.

Down-Regulation↗

PubMed1997

Necrotizing enterocolitis in full-term or near-term infants: risk factors.

A retrospective case-control study of necrotizing enterocolitis (NEC) affecting infants weighing > 2,000 g at birth was performed to determine those factors which could contribute to the development of NEC. Twenty-four infants met the criteria of definite NEC. For each case the next 2 healthy newborns were matched as controls. When compared with the control group, NEC infants had a significantly higher frequency of prolonged rupture of membranes, chorioamnionitis, Apgar score < 7 at 1 and 5 min, respiratory problems, congenital heart disease, hypoglycemia, and exchange transfusions. Only 3 infants with NEC were healthy newborns with an unremarkable perinatal course before NEC. There were no differences in the frequency of preeclampsia, maternal diabetes, maternal drug abuse, meconium-stained amniotic fluid and polycythemia. These results indicate that most of these more mature infants have a predisposing factor before developing NEC.

Case-Control Studies↗

PubMed1996

Effect of leak around the endotracheal tube on measurements of pulmonary compliance and resistance during mechanical ventilation: a lung model study.

We studied the effect of leaks around the endotracheal tube (ETT) on the measurement of pulmonary mechanics during mechanical ventilation. We also evaluated the influence of different ventilator settings on the magnitude of leak. An adjustable leak was created at the end of the ETT in a lung model with constant compliance. Flow, tidal volume, and pressure changes were measured above and below the leak. Compliance (Ci) and resistance (Ri) during inspiration were determined by linear regression analysis (LRA) using the equation of motion and the Mead and Wittenberger method (MWM). The ventilatory change that influenced the degree of leak most was prolongation of inspiratory time (Ti). The presence of a leak around the ETT resulted in an overestimation of the Ci and Ri values, which was proportional to the size of the leak. This overestimation was also influenced by the method used to determine Ci and Ri. Because the contribution of the leak to the fidal volume progressively increases as inspiration continued, methods of analysis that depended mainly on measurement points at the end of inspiration showed a larger deviation from the true Ci and Ri values than methods mainly influenced by measurement points at the beginning of inspiration. Because of this, shortening of inspiration, or analysis of points at the beginning of inspiration reduces the error in the measurements of Ci and Ri when a leak is present. Breaths with a large leak should be excluded from any analysis of pulmonary mechanics.

Airway Resistance↗

PubMed1996

Influence of different methods of synchronized mechanical ventilation on ventilation, gas exchange, patient effort, and blood pressure fluctuations in premature neonates.

We studied the effects of two methods of synchronized mechanical ventilation [synchronized intermittent mandatory ventilation (SIMV) and assist/control (A/C)] on ventilation, gas exchange, patient effort, and arterial blood pressure (ABP) fluctuations. SIMV and A/C were applied in random order in 12 preterm neonates (gestational age, 29.7 +/- 2.3 weeks; birth weight, 1,217 +/- 402 g). We measured total (Vetot) and mechanical (Vemech) minute ventilation, spontaneous (Vtspont) and ventilator supported (Vtmech) tidal volume, transcutaneous oxygen saturation (SpO2), transcutaneous PO2 (TcPO2), and PCO2, (TcPCO2), mean airway pressure (Paw), phasic esophageal pressure deflections (Pe) as an estimate of inspiratory effort, mean arterial blood pressure (ABP), and beat-to-beat ABP fluctuations. The measurements obtained during conventional intermittent mandatory ventilation (IMV) were compared with the recordings during SIMV and A/C. To make the measurement conditions comparable and to prevent hyperventilation, peak inspiratory pressure was reduced during the A/C mode so that Vetot remained in the same range as during the IMV mode. Whereas Vetot was similar in all three conditions by study design, Vemech was larger during SIMV and A/C than during IMV. Vtmech increased during SIMV and by study design was smaller during A/C than during IMV. Pe decreased during SIMV and A/C compared with IMV, and Paw was higher during A/C than during IMV or SIMV. Beat-to-beat ABP fluctuations were reduced during SIMV and A/C compared with IMV and showed a close positive correlation with Pe changes. We conclude that SIMV increases Vemech and reduces Pe compared with IMV, resulting in smaller intrathoracic and ABP fluctuations. During A/C, a substantial portion of the spontaneous respiratory effort is shifted to the ventilator, resulting in a further decrease in Pe and ABP fluctuations.

Blood Pressure↗

PubMed1996

Influence of infection on patent ductus arteriosus and chronic lung disease in premature infants weighing 1000 grams or less.

OBJECTIVES: To test the hypotheses that (1) infection increases ductal dilatory prostaglandins and inflammatory mediators that may influence the closure of a patent ductus arteriosus (PDA), increasing the incidence of late episodes of PDA (after 7 days) and the rate of closure failures, and (2) the concurrence of PDA and infection increases the risk of chronic lung disease (CLD). METHODS: One hundred fourteen premature infants (birth weight, 500 to 1000 gm) were prospectively assessed for PDA and infection. Serum levels of 6-ketoprostaglandin F1 alpha and tumor necrosis factor alpha were measured routinely in all infants and when PDA or infection was present. Multivariate assessment of risk factors for PDA closure failure and for CLD was done by logistic regression, and expressed as an odds ratio and as 95% confidence intervals. RESULTS: Late PDA episodes were more frequent in infants with infection than in those without infection. A temporally related infection (<5 days between both diagnoses) was associated with an increased risk of PDA closure failure (odds ratio, 19.1 (confidence interval, 4 to 90)). In addition to birth weight and the severity of initial respiratory failure, PDA and infection increased the risk of CLD (odds ratio, 11.7 (confidence interval, 1.7 to 81) for PDA; odds ration, 3.1 (confidence interval, 1 to 11) for infection). Furthermore, when both factors were temporally related, they further increased the risk of CLD (odds ratio, 29.6 (confidence interval, 4.5 to >100)). Infants with infection and those with PDA had higher levels of 6-ketoprostaglandin F1 alpha than did control subjects. Levels of tumor necrosis factor alpha were also elevated in infants with infection and in those with late PDA. CONCLUSIONS: Infection adversely influences PDA outcome by increasing the risk of late ductal reopening and PDA closure failures. Increased levels of prostaglandins and tumor necrosis factor alpha in infants with infection may explain the poor PDA outcome. The concurrence of PDA and infection potentiates their negative effects on the risk of CLD.

Chronic Disease↗

PubMed1996

Patient-triggered ventilation in neonates: comparison of a flow-and an impedance-triggered system.

We conducted a study with the objective of comparing the performance of two different systems for patient-triggered ventilation in neonates (impedance versus flow/volume-triggered) by measuring response time, autotrigger and trigger failure rates, ventilation, and gas exchange. The two ventilator systems were applied in random order in 10 preterm neonates (median gestational age: 30.5 wk; range: 27 to 34 wk; body weight: 1,266 g; range: 840 to 2,240 g) using identical ventilator settings. The median (range) response time was 169 (98 to 305) ms for the impedance system and 115 (79 to 184) ms for the flow/volume system (p < 0.01). The longer and more variable response time of the impedance system was secondary to a phase lag of the impedance signal caused by chest wall distortion. Although 13.1 (0.2 to 29.4)% of mechanical breaths were autotriggered with the impedance system, there were no autotriggered breaths using the flow/volume system (p < 0.01). The rate of trigger failures was not significantly different with the two systems, at 1.2 (0 to 4.4)% (impedance) versus 3.1 (0 to 6.4)% (flow/volume). Minute ventilation was smaller with the impedance system (p < 0.001), because of the larger number of breaths triggered late in inspiration or during expiration. We conclude that the flow/volume-triggered system is less prone to autotriggering and has a shorter and more consistent response time than the impedance-triggered system. The impedance-triggered system is more susceptible to artifacts and chest wall distortion.

Female↗

PubMed1995

Effect of chestwall distortion on the measurement of pulmonary mechanics in preterm infants.

The purpose of this study was to determine the effect of chestwall distortion (CWD) on the measurement of pulmonary compliance (CL) and resistance (RL). Inductance plethysmography was used in 15 preterm infants to determine CWD as total compartmental displacement ratio (TCDR) and out of phase movement between ribcage and abdomen as phase shift (PS). Flow was measured by pneumotachography and esophageal pressure change (Pe) with a water-filled catheter. CL and RL were calculated by linear regression analysis. Seven infants (mean +/- SD: BW, 1,484 +/- 186 g, GA 32.4 +/- 2.2 weeks, age 8.7 +/- 4.7 days) had a breathing pattern characterized by episodes with a high degree of CWD, followed by periods with minimal CWD (distortion group). In this group lung function measurements were analyzed separately during periods with and without CWD. The remaining 8 infants (BW, 1,244 +/- 233 g, GA 30.4 +/- 2.4 weeks, age 7.4 +/- 3.1 days) always breathed with minimal CWD, and the measurements in this group (non-distortion group) were used as a reference for the values obtained in the distortion group. Measurements of TCDR, PS, CL, RL, and tidal volume (VT) obtained in the absence of CWD were not significantly different between distortion and non-distortion groups. The measurements obtained in the presence of CWD showed a significantly higher TCDR and PS, but CL and RL were not significantly different from the CL and RL measurements obtained in the distortion and non-distortion groups in the absence of CWD. The only significant effect of CWD was a reduction in VT.(ABSTRACT TRUNCATED AT 250 WORDS)

Birth Weight↗

PubMed1995

Mechanisms for episodes of hypoxemia in preterm infants undergoing mechanical ventilation.

OBJECTIVE: To ascertain possible mechanisms implicated in the development of transient episodes of hypoxemia (oxygen saturation < 85%) frequently observed in preterm infants undergoing mechanical ventilation, even after the acute phase of respiratory failure has passed. STUDY DESIGN: Tidal flow, airway and esophageal pressure, and oxygen saturation were continuously recorded in 10 infants (mean +/- SD, birth weight 733 +/- 149 gm, gestational age 25.5 +/- 2.2 weeks, age 26.3 +/- 11.9 days) who had repeated episodes of hypoxemia without any evident cause. Measurements of minute ventilation (VE) inspiratory compliance (Ci), and inspiratory resistance (Ri) were compared before and during episodes of hypoxemia. RESULTS: All episodes of hypoxemia were preceded by an active exhalation that produced a mean decrease in end-expiratory lung volume of 6.4 +/- 2.8 ml/kg. The reduction in lung volume was immediately followed by a sudden decrease in tidal flow and volume, despite continuation of mechanical ventilation at the same rate and peak pressure. The resulting hypoventilation was associated with a drop in Ci to approximately one half and an increase in Ri to more than double the baseline values. Approximately 30 seconds after the beginning of hypoventilation, the arterial oxygen saturation reached a hypoxemic level (oxygen saturation < 85%)> CONCLUSION: Most hypoxemic episodes were triggered by an expiratory effort that produced a large decrease in lung volume. This reduction in lung volume probably leads to closure of small airways and the development of intrapulmonary shunts, which would explain the rapid development of hypoxemia.

Analysis of Variance↗

PubMed1995

Changing trends in the epidemiology and pathogenesis of neonatal chronic lung disease.

OBJECTIVE: To assess the role of specific risk factors that may predispose preterm infants with mild or no initial respiratory distress syndrome to the development of chronic lung disease (CLD). STUDY DESIGN: Clinical data were collected prospectively from 119 ventilator-supported preterm infants with birth weights between 500 and 1000 gm, who survived more than 28 days and required fewer than 3 days of treatment with fraction of inspired oxygen > 25% during the first 5 days of life. Logistic regression analysis was used in a multivariate assessment of risk factors for CLD. RESULTS: Chronic lung disease occurred in 44 of the patients (37%). The analysis showed that low birth weight, patent ductus arteriosus (PDA), and sepsis were significant risk factors for CLD. The corresponding odds ratios for CLD and their 95% confidence intervals (CI) were as follows: 2.9 per 100 gm birth weight decrement (CI, 1.7 to 4.8); 6.2 (CI, 2.1 to 18.4) for PDA; and 4.4 (CI, 1.3 to 14.5) for sepsis. When sepsis and PDA occurred simultaneously, the odds ratio for CLD increased to 48.3 (CI, 6.3 to > 100) in comparison with infants without these conditions. Episodes of PDA were categorized as either early (occurring during the first week of life) or late (after the first week), and the respective odds ratios for CLD were 2.8 (CI, 0.8 to 9.4) and 21.1 (CI, 5.6 to 80) in comparison with infants without PDA. For the duration of symptomatic PDA, the odds ratio for CLD was 3.5 per week that the PDA remained open (CI, 1.9 to 6.5). CONCLUSION: CLD is a frequent sequela in very low birth weight infants with mild or no respiratory distress syndrome. In this population, the development of late episodes of PDA, usually in association with a nosocomial infection, seems to play a primary role in the pathogenesis of CLD.

Chronic Disease↗

PubMed1995

Influence of chest wall distortion and esophageal catheter position on esophageal manometry in preterm infants.

The purpose of this study was to determine the effect of chest wall distortion on esophageal manometry by measuring simultaneous esophageal pressure changes at two sites in preterm infants. Fourteen infants were studied (mean +/- SD; birth weight, 1340 +/- 260 g; age, 8.5 +/- 4 d). Esophageal pressure was measured through two water-filled catheters, one placed just above the cardia (Pes1) and the other at the level of the carina (Pes2). Chest wall distortion was measured by inductance plethysmography, and inspiratory and expiratory flow by pneumotachography. No significant differences were found between the peak to peak esophageal pressure changes measured through the lower and higher catheters during both airway occlusion (18.7 +/- 4.4 versus 18.3 +/- 2.6 cm H2O) and spontaneous breathing (9.4 +/- 1.8 versus 9.0 +/- 1.8 cm H2O), although half of the infants had significant chest wall distortion. Mean pulmonary compliance and resistance measures calculated from the two pressures for individual infants showed small differences consistent with the difference between Pes1 and Pes2. For the whole group of 14 infants, however, these differences were not significant. The pressure changes from the lower and higher measuring sites for each breath were analyzed using linear regression. The weighted average of the mean slopes of the 14 infants was significantly different from 1.0 (mean +/- SD: 0.92 +/- 0.10, range: 0.75-1.10; p < 0.05). In some of the infants, the slopes for different breaths were not consistent, but varied from breath to breath.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗

PubMed1994

Role of respiratory muscles in upper airway narrowing induced by inspiratory loading in preterm infants.

Extrathoracic airway (ETA) narrowing is induced in preterm infants by inspiratory flow-resistive loading (IRL), which reduces intraluminal pressure within the region. Neuromuscular load compensation was evaluated over time in 10 infants [body wt 1.5 +/- 0.17 (SD) kg, gestational age 33 +/- 2.3 wk, age 12 +/- 5.2 days] during quiet sleep. Baseline (BL) studies were followed by IRL (125 cmH2O.l-1.s at 1 l/min). Minute ventilation, changes in esophageal pressure (Pes) and proximal airway pressure, and moving time averages of posterior cricoarytenoid (PCA), submental genioglossus (SM), and diaphragm (DIA) electromyograms were obtained during BL and 1 and 5 min of IRL. Total respiratory resistance was calculated from pressure and flow changes and was used to estimate ETA narrowing: there was an increase in total respiratory resistance from 90 +/- 15 to 120 +/- 34 and 151 +/- 86 cmH2O.l-1.s after 1 and 5 min of IRL, respectively (P < 0.05, 1-min IRL vs. BL), in association with a sustained decline in minute ventilation (P < 0.05) and increases in Pes and proximal airway pressure (P < 0.05). Phasic PCA activity was always present, but its duration was only transiently prolonged with IRL (P < 0.05, 1-min IRL vs. BL). SM activity was present in only one infant during BL and was recruited in two additional infants during IRL. The decline in Pes from 1 to 5 min of IRL occurred despite continuing increases in peak and average activities of the DIA moving time average, which may reflect an onset of DIA fatigue. The transient prolongation of phasic PCA activity and occasional recruitment of SM activity with sustained loading explain, in part, the ETA instability detectable by moderate IRL in sleeping preterm infants.

Airway Resistance↗

PubMed1994

Upper airway stability and respiratory muscle activity during inspiratory loading in full-term neonates.

To investigate the role of genioglossus and posterior cricoarytenoid (PCA) activity in stabilizing the extrathoracic airway (ETA) of full-term infants during inspiratory flow-resistive loading (IRL), 10 unsedated full-term infants were evaluated in quiet sleep. IRLs were randomly imposed (L2, 125 cmH2O.l-1.s; L3, 250 cmH2O.l-1.s). Ventilation, total respiratory resistance (a correlate of ETA resistance), and moving time averages of PCA, submental activity of the genioglossus (SM), and diaphragm electromyogram were obtained. Results revealed no phasic activity in the SM during baseline breathing or with either IRL. Phasic PCA activity was always observed; burst duration increased with L2 and L3 (P < 0.01) and commenced earlier in relation to the onset of inspiratory airflow with both loads (P < 0.05). PCA activity always preceded that of the diaphragm and invariably outlasted it other than with L3. The upper airway negative pressure changes induced by IRL were insufficient to recruit SM activity; other potential stimuli such as transcutaneous PO2, transcutaneous PCO2, and pulmonary stretch receptor activation (increase in tidal volume) remained unchanged. Ventilation decreased with both loads (L3: P < 0.01), esophageal and mouth pressures increased (P < 0.01), and inspiratory time and inspiratory time divided by total time were both prolonged (P < 0.01). Total respiratory resistance remained unchanged with L2 but increased with L3 (P < 0.01). We concluded that ETA narrowing may be induced in full-term infants during quiet sleep with moderately large-sized IRL and that it is not entirely ameliorated by activation of the SM or PCA or by arousal.

Airway Resistance↗