Assessment of airway resistance in preterm infants during incremental inspiratory flow-resistive loading

1991 ◽  
Vol 70 (2) ◽  
pp. 889-894 ◽  
Author(s):  
S. Duara ◽  
T. Gerhardt ◽  
E. Bancalari
Keyword(s):  
Preterm Infants ◽  
Upper Airway ◽  
Inspiratory Flow ◽  
Intraluminal Pressure ◽  
Intrinsic Resistance ◽  
Resistive Loading ◽  
Inspiratory Resistance ◽  
Resistive Loads ◽  
Upper Airway Collapsibility ◽  
Extrathoracic Airway

Extrathoracic airway (ETA) stability was tested by inspiratory flow-resistive loading in 10 preterm infants to determine whether ETA collapsibility was directly related to the size of the added load. A fall in intraluminal pressure was produced by applying two inspiratory flow-resistive loads of lower (L1) and higher (L2) magnitudes. An increase in intrinsic resistance was used as an index of upper airway collapsibility. Total pulmonary resistance did not change from baseline with L1 (73 +/- 26 to 71 +/- 25 cmH2O.l-1.s) but increased significantly with L2 (72 +/- 21 to 99 +/- 34 cmH2O.l-1.s, P less than 0.02) secondary to a rise in inspiratory resistance (55 +/- 21 to 109 +/- 55 cmH2O.l-1.s, P less than 0.05). Expiratory resistance did not change significantly with either load. Proximal airway pressure was more negative with L2 than with L1 in every infant (mean -4.5 +/- 0.6 vs. -3.6 +/- 0.9 cmH2O, P less than 0.05). This study shows that the ETA of preterm infants is pressure passive at high but not at low collapsing pressures, and possible explanations include limited "active" compensation by upper airway dilator muscles and an overwhelming of the “passive” defense offered by the intrinsic rigidity of the ETA to large changes in transmural pressure.

Effect of maturation on the extrathoracic airway stability of infants

1992 ◽  
Vol 73 (6) ◽  
pp. 2368-2372 ◽  
Author(s):  
S. Duara ◽  
G. Silva Neto ◽  
N. Claure ◽  
T. Gerhardt ◽  
E. Bancalari
Keyword(s):  
Preterm Infants ◽  
Full Term ◽  
Intraluminal Pressure ◽  
Pulmonary Resistance ◽  
Intrinsic Resistance ◽  
Quiet Sleep ◽  
Term Infants ◽  
Airway Narrowing ◽  
Extrathoracic Airway ◽  
Age Studies

The influence of maturation on extrathoracic airway (ETA) stability during quiet sleep was determined in 13 normal preterm infants of 1.41 +/- 0.14 (SD) kg birth weight and 32 +/- 2 wk estimated gestational age. Studies began in the first week of life and were performed three times at weekly intervals. A drop in intraluminal pressure within the ETA was produced by external inspiratory flow-resistive loading (60 cmH2O.l-1 x s at 1 l/min); an increase in intrinsic resistance, indicating airway narrowing, was sought as a measure of ETA instability. Baseline total pulmonary resistance was not significantly different between weeks 1, 2, and 3 (88 +/- 35, 65 +/- 24, and 61 +/- 17 cmH2O.l-1 x s, respectively) but increased markedly above baseline with loading to 144 +/- 45 cmH2O.l-1.s during week 1 (P < 0.001), 89 +/- 28 cmH2O.l-1 x s at week 2 (P < 0.01), and 74 +/- 25 cmH2O.l-1 x s at week 3 (n = 10). The increment with loading was significantly greater during week 1 than during weeks 2 or 3 (P < 0.02). Similar studies were also done in seven full-term infants in the first week of life to evaluate the influence of gestational maturity on ETA stability. Despite a relatively greater drop in intraluminal pressure within the ETA of term vs. preterm infants with loading (P < 0.001), total pulmonary resistance failed to increase (68 +/- 21 to 71 +/- 32 cmH2O.l-1.s). These data reveal that ETA instability is present in preterm infants at birth and decreases with increasing postnatal age. Full-term neonates, by comparison, display markedly greater ETA stability in the immediate neonatal period.

Extrathoracic airway stability during resistive loading in preterm infants

1987 ◽  
Vol 63 (4) ◽  
pp. 1539-1543 ◽  
Author(s):  
S. Duara ◽  
T. Gerhardt ◽  
E. Bancalari
Keyword(s):  
Preterm Infants ◽  
Airway Pressure ◽  
Intraluminal Pressure ◽  
Resistive Load ◽  
Simple Test ◽  
Pulmonary Resistance ◽  
Airway Narrowing ◽  
Resistive Loading ◽  
Extrathoracic Airway

Extrathoracic airway (ETA) stability was tested in 10 preterm infants during sleep with a drop in intraluminal pressure produced by the application of an external inspiratory flow-resistive load (IRL, 125 cmH2O.1–1.s at 1 l/min). An increase in total pulmonary resistance was sought as the measure of airway narrowing. The role of the ETA in the increased pulmonary resistance with loading was examined by testing the same infants while endotracheally intubated and after extubation. Total pulmonary resistance decreased with loading during the intubated studies (102.5 +/- 41.2 to 82.4 +/- 33.3 cmH2O.1–1.s, P less than 0.05), whereas a significant increase in pulmonary resistance was seen with loading in the extubated studies (101 +/- 58.1 to 128 +/- 68.6 cmH2O.1–1.s, P less than 0.01). Intraluminal pressure in the ETA, measured by the lowest proximal airway pressure, fell significantly with loading in both conditions, with values changing from -0.7 +/- 0.3 to -4.7 +/- 2.7 cmH2O in the intubated infants and from -0.9 +/- 0.3 to -4.6 +/- 0.9 cmH2O) in the extubated infants (P less than 0.01). The results suggest ETA narrowing with loading in extubated infants despite the absence of overt obstructive apnea. Measurements of total pulmonary resistance with IRL can be used as a simple test of ETA stability.

Thoracoabdominal asynchrony failed to grade airway obstructions in foals

2000 ◽  
Vol 88 (6) ◽  
pp. 2081-2087 ◽  
Author(s):  
Carrie Miller ◽  
Andrew M. Hoffman ◽  
Janice Hunter
Keyword(s):  
Phase Angle ◽  
Upper Airway ◽  
Clinical Feature ◽  
Resistive Load ◽  
Respiratory Inductive Plethysmography ◽  
Resistive Loading ◽  
Airway Obstructions ◽  
Airway Opening ◽  
Resistive Loads ◽  
Thoracoabdominal Asynchrony

Respiratory inductive plethysmography (RIP) can be used to obtain a valid measure of tidal volume in humans. This device also compares the contributions to ventilation of the thorax and abdomen. Although thoracoabdominal asynchrony is a prominent clinical feature for patients with airway obstruction, the accuracy of the RIP device to assess the severity of obstruction is unclear. This study analyzes how well RIP variables reflect the degree of a fixed external inspiratory plus expiratory resistive load in foals. Foals were employed because the species and age group are commonly afflicted with respiratory disease. Eight conscious, sedated (xylazine 1.25 mg/kg body wt) foals were subjected to randomly ordered resistive loads at the airway opening and, on a separate day, to histamine aerosol challenge. During resistive loading, phase angle changed significantly, as did phase relation ( P ≤ 0.05). However, no significant correlation was found between the degree of change in resistive load and the degree to which phase angle or relation was altered ( r s = 0.41 and 0.25, respectively). In addition, neither phase angle nor relation changed significantly with histamine challenge. We conclude that, although RIP variables changed markedly with fixed upper airway resistive loading, the degree to which they changed was erratic and therefore not useful for grading these obstructions. Furthermore, RIP variables were insensitive measures of histamine-induced bronchoconstriction.

Sleep and the ventilatory response to resistive loading in normal men

1988 ◽  
Vol 64 (3) ◽  
pp. 1186-1195 ◽  
Author(s):  
L. Wiegand ◽  
C. W. Zwillich ◽  
D. P. White
Keyword(s):  
Eye Movement ◽  
Rem Sleep ◽  
Airway Resistance ◽  
Ventilatory Response ◽  
Upper Airway ◽  
Resistive Load ◽  
Load Compensation ◽  
Resistive Loading ◽  
Resistive Loads ◽  
Normal Men

Since upper airway resistance is known to increase during sleep, inadequate resistive load compensation may contribute to the normal decline in sleeping ventilation. We determined the acute and sustained (4 min) ventilatory response to a range of external inspiratory resistive loads (4, 8, 12, and 25 cmH2O.l-1.s) during wakefulness and non-rapid-eye-movement (NREM) and rapid-eye-movement (REM) sleep in seven normal men. We found that minute ventilation (VI) was well maintained with acute and sustained resistive loading during wakefulness. Immediate adjustments in ventilatory timing (prolongation of inspiratory duration) provided full compensation for airflow reduction. In marked contrast, resistive load application during NREM sleep invariably produced a significant (P less than 0.05) reduction in VI with progressively larger resistive loads producing progressively greater ventilatory decrements. This decline in ventilation was a product of a falling inspiratory flow rate with inadequate prolongation of inspiratory duration (TI). The largest decrements in ventilation occurred immediately after load application followed by partial ventilatory recovery, which occurred over time in concert with rising PCO2 and augmented ventilatory effort (as reflected by P0.1 or mouth occlusion pressure). Similar observations were made during REM sleep, although the responses were less consistent and fewer data were obtained. These observations support the hypothesis that poor load compensation for increased upper airway resistance contributes to the hypoventilation characteristic of normal sleep.

Collapsibility of the Upper Airway at Different Concentrations of Propofol Anesthesia

2005 ◽  
Vol 103 (3) ◽  
pp. 470-477 ◽  
Author(s):  
Peter R. Eastwood ◽  
Peter R. Platt ◽  
Kelly Shepherd ◽  
Kathy Maddison ◽  
David R. Hillman
Keyword(s):  
Upper Airway ◽  
Inspiratory Flow ◽  
Electromyographic Activity ◽  
Flow Limitation ◽  
Genioglossus Muscle ◽  
Airway Collapsibility ◽  
Effect Site Concentration ◽  
Intramuscular Electrodes ◽  
Upper Airway Collapsibility ◽  
Spontaneously Breathing

Background This study investigated the effect of varying concentrations of propofol on upper airway collapsibility and the mechanisms responsible for it. Methods Upper airway collapsibility was determined from pressure-flow relations at three concentrations of propofol anesthesia (effect site concentration = 2.5, 4.0, and 6.0 mug/ml) in 12 subjects spontaneously breathing on continuous positive airway pressure. At each level of anesthesia, mask pressure was transiently reduced from a pressure sufficient to abolish inspiratory flow limitation (maintenance pressure = 12 +/- 1 cm H2O) to pressures resulting in variable degrees of flow limitation. The relation between mask pressure and maximal inspiratory flow was determined, and the critical pressure at which the airway occluded was recorded. Electromyographic activity of the genioglossus muscle (EMGgg) was obtained via intramuscular electrodes in 8 subjects. Results With increasing depth of anesthesia, (1) critical closing pressure progressively increased (-0.3 +/- 3.5, 0.5 +/- 3.7, and 1.4 +/- 3.5 cm H2O at propofol concentrations of 2.5, 4.0, and 6.0 microg/ml respectively; P &lt; 0.05 between each level), indicating a more collapsible upper airway; (2) inspiratory flow at the maintenance pressure significantly decreased; and (3) respiration-related phasic changes in EMGgg at the maintenance pressure decreased from 7.3 +/- 9.9% of maximum at 2.5 microg/ml to 0.8 +/- 0.5% of maximum at 6.0 microg/ml, whereas tonic EMGgg was unchanged. Relative to the levels of phasic and tonic EMGgg at the maintenance pressure immediately before a decrease in mask pressure, tonic activity tended to increase over the course of five flow-limited breaths at a propofol concentration of 2.5 microg/ml but not at propofol concentrations of 4.0 and 6.0 microg/ml, whereas phasic EMGgg was unchanged. Conclusions Increasing depth of propofol anesthesia is associated with increased collapsibility of the upper airway. This was associated with profound inhibition of genioglossus muscle activity. This dose-related inhibition seems to be the combined result of depression of central respiratory output to upper airway dilator muscles and of upper airway reflexes.

Response to inspiratory resistive loading during sleep in normal children and children with obstructive apnea

1999 ◽  
Vol 87 (4) ◽  
pp. 1448-1454 ◽  
Author(s):  
Carole L. Marcus ◽  
Gustavo A. Moreira ◽  
Owen Bamford ◽  
Janita Lutz
Keyword(s):  
Marked Decrease ◽  
Minute Ventilation ◽  
Sleep Apnea Syndrome ◽  
Upper Airway ◽  
Normal Subjects ◽  
Normal Children ◽  
Ventilatory Responses ◽  
Obstructive Sleep ◽  
Resistive Loading ◽  
Inspiratory Resistance

The response to inspiratory resistance loading (IRL) of the upper airway during sleep in children is not known. We, therefore, evaluated the arousal responses to IRL during sleep in children with the obstructive sleep apnea syndrome (OSAS) compared with controls. Children with OSAS aroused at a higher load than did controls (23 ± 8 vs. 15 ± 7 cmH2O ⋅ l−1 ⋅ s; P < 0.05). Patients with OSAS had higher arousal thresholds during rapid eye movement (REM) vs. non-REM sleep ( P < 0.001), whereas normal subjects had lower arousal thresholds during REM ( P < 0.005). Ventilatory responses to IRL were evaluated in the controls. There was a marked decrease in tidal volume both immediately (56 ± 17% of baseline at an IRL of 15 cmH2O ⋅ l−1 ⋅ min; P < 0.001) and after 3 min of IRL (67 ± 23%, P < 0.005). The duty cycle increased. We conclude that children with OSAS have impaired arousal responses to IRL. Despite compensatory changes in respiratory timing, normal children have a decrease in minute ventilation in response to IRL during sleep. However, arousal occurs before gas-exchange abnormalities.

Oxygen cost of breathing during fatiguing inspiratory resistive loads

1989 ◽  
Vol 66 (5) ◽  
pp. 2045-2055 ◽  
Author(s):  
F. D. McCool ◽  
G. E. Tzelepis ◽  
D. E. Leith ◽  
F. G. Hoppin
Keyword(s):  
Lung Volume ◽  
Normal Subjects ◽  
Esophageal Pressure ◽  
Inspiratory Flow ◽  
Energy Utilization ◽  
Whole Body ◽  
Inspiratory Flow Rate ◽  
Inspiratory Muscles ◽  
Inspiratory Resistance ◽  
Resistive Loads

When a subject breathes against an inspiratory resistance, the inspiratory pressure, the inspiratory flow, and the lung volume at which the breathing task takes place all interact to determine the length of time the task can be sustained (Tlim). We hypothesized that the mechanism actually limiting tasks in which these parameters were varied involved the rate of energy utilization by the inspiratory muscles. To test this hypothesis, we studied four experienced normal subjects during fatiguing breathing tasks performed over a range of pressures and flows and at two different lung volumes. We assessed energy utilization by measuring the increment in the rate of whole body O2 consumption due to the breathing task (VO2 resp). Power and mean esophageal pressure correlated with Tlim but depended also on lung volume and inspiratory flow rate. In contrast, VO2 resp closely correlated with Tlim, and this relationship was not systematically altered by inspiratory flow or lung volume. The shape of the VO2 resp vs. Tlim curve was approximately hyperbolic, with high rates of VO2 resp associated with short endurance times and lower rates of VO2 resp approaching an asymptotic value at high Tlim. These findings are consistent with a mechanism whereby a critical rate of energy utilization determines the endurance of the inspiratory pump, and that rate varies with pressure, flow, and lung volume.

Improved Methodology for Threshold Detection Studies in Asthmatic Children

2001 ◽  
Vol 15 (3) ◽  
pp. 190-197 ◽  
Author(s):  
Gregory K. Fritz ◽  
Keren Rosenblum ◽  
Robert B. Klein ◽  
Elizabeth L. McQuaid ◽  
Jack H. Nassau ◽  
...  
Keyword(s):  
First Generation ◽  
Second Generation ◽  
Asthma Severity ◽  
Intrinsic Resistance ◽  
Threshold Detection ◽  
Asthmatic Children ◽  
Resistive Loading ◽  
Children With Asthma ◽  
The Mean ◽  
Resistive Loads

Abstract This paper reports the differences between two methodologies for threshold detection of added resistive loads in children and adolescents. The first-generation apparatus utilized a series of laminar flow screens to present various total resistances, while in the second generation the apparatus utilized a servo-controlled cone that occluded an aperture to varying degrees. Protocol modifications in the second generation methodology included forced choice, attentional enhancements, and larger increments of added resistance. Two studies conducted 2 years apart provided data on the first and second generations of methodology. All participants in Study 1 (N = 33) and Study 2 (N = 33) were children with asthma. Subjects were matched for both age and asthma severity. Results showed the methodologic improvements in the second generation to be significant. Tracking and random thresholds were achieved by 85% and 82% of the subjects in Study 2 compared to 76% and 42% in Study 1, respectively. The correlation between the mean tracking and random thresholds was .40 in Study 2 compared to a statistically insignificant result in Study 1, indicating improved reliability. Raw thresholds were correlated with intrinsic resistance in both studies (r = .29-.88), supporting the use of Weber's Law in resistive loading studies of children. Results using the second generation methodologic improvements demonstrate that children as young as age 7 can complete resistance loading protocols. Standard methodology will enhance the comparability between studies.

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

1994 ◽  
Vol 77 (1) ◽  
pp. 30-36 ◽  
Author(s):  
S. Duara ◽  
G. Silva Neto ◽  
N. Claure
Keyword(s):  
Preterm Infants ◽  
Airway Pressure ◽  
Minute Ventilation ◽  
Respiratory Muscles ◽  
Upper Airway ◽  
Esophageal Pressure ◽  
Intraluminal Pressure ◽  
Respiratory Resistance ◽  
Quiet Sleep ◽  
Airway Narrowing

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.

Metabolic and respiratory effects of flow-resistive loading in preterm infants

1991 ◽  
Vol 70 (2) ◽  
pp. 895-899 ◽  
Author(s):  
S. Duara ◽  
G. Silva Neto ◽  
T. Gerhardt ◽  
C. Suguihara ◽  
E. Bancalari
Keyword(s):  
Carbon Dioxide ◽  
Preterm Infants ◽  
Minute Ventilation ◽  
Carbon Dioxide Tension ◽  
Resistive Load ◽  
Intrinsic Resistance ◽  
Transcutaneous Oxygen ◽  
Resistive Loading ◽  
Before And After ◽  
Transcutaneous Carbon Dioxide Tension

Oxygen consumption (VO2) was measured during hypoventilation induced by moderate-sized flow-resistive loading in 12 preterm infants, and the results were compared with those obtained under basal conditions immediately before and after the loaded run, each of which lasted for 7-10 min. Loading was performed with a continuous flow-resistive load (inspiratory and expiratory), which was approximately threefold greater in magnitude than the intrinsic resistance of preterm infants. VO2, minute ventilation (VE), transcutaneous oxygen tension (PtCO2), and transcutaneous carbon dioxide tension (PtcCO2) were continuously monitored. Results revealed that VE decreased significantly with loading, from 336 +/- 103 to 231 +/- 58 (SD) ml.min-1.kg-1 (P less than 0.001), while returning to basal levels of 342 +/- 59 ml.min-1.kg-1 after discontinuation of the load. VO2 decreased from 7.2 +/- 1.2 to 5.9 +/- 0.9 ml.min-1.kg-1 with loading (P less than 0.001) and returned to 7.2 +/- 1.2 ml.min-1.kg-1 at the second basal measurement. PtcCO2 remained unchanged with loading, and PtcCO2 only increased from 39 +/- 8 to 41 +/- 9 Torr (P less than 0.05) with loading, while returning to 40 +/- 9 Torr at the second basal measurement. Results indicate a decrease in the metabolic rate and ventilation with loading, with relatively little increase in PtcCO2. These data can explain prior observations that minimal disturbances in oxygen and carbon dioxide tensions occur with hypoventilation during flow-resistive loading in neonates, although the precise mechanism for this reduction remains to be determined.

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