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.

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.

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.

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.

Effects of nasal CPAP on supraglottic and total pulmonary resistance in preterm infants

1990 ◽  
Vol 68 (1) ◽  
pp. 141-146 ◽  
Author(s):  
M. J. Miller ◽  
J. M. DiFiore ◽  
K. P. Strohl ◽  
R. J. Martin
Keyword(s):  
Continuous Positive Airway Pressure ◽  
Preterm Infants ◽  
Premature Infants ◽  
Airway Pressure ◽  
Positive Airway Pressure ◽  
Nasal Airflow ◽  
Pulmonary Resistance ◽  
Nasal Cpap ◽  
Primary Mechanism ◽  
Postconceptional Age

The effects of continuous positive airway pressure (CPAP) on supraglottic and total pulmonary resistance were determined in 10 healthy premature infants (postconceptional age 34 +/- 2 wk, weight at study 1,628 +/- 250 g). Nasal airflow was measured with a mask pneumotachograph, and pressures in the esophagus and oropharynx were measured with a 5-Fr Millar or fluid-filled catheter. Nasal CPAP between 0 and 5 cmH2O correlated well with oropharyngeal pressure (r = 0.94). Total supraglottic resistance, total pulmonary resistance, and supraglottic resistance in inspiration and expiration were measured on increasing CPAP. Total supraglottic resistance decreased from 46 +/- 29 to 17 +/- 16 cmH2O.l-1.s (P less than 0.005) between 0 and 5 cmH2O CPAP, and a delay in return of resistance to control values was seen as CPAP was reciprocally decreased to 0. CPAP produced a decrease in supraglottic resistance in both inspiration and expiration, from 41 +/- 26 to 14 +/- 9 and from 33 +/- 17 to 10 +/- 6 cmH2O.l-1.s, respectively (P less than 0.01). Total pulmonary resistance also decreased from 161 +/- 40 to 95 +/- 24 cmH2O.l-1.s (P less than 0.01) between 0 and 5 cmH2O CPAP. The decrease in total supraglottic resistance in these infants accounted for 60% of the change in total pulmonary resistance, which occurred on CPAP of 5 cmH2O. We speculate that CPAP may decrease supraglottic resistance directly through mechanical splinting of the airway. This effect of CPAP may be the primary mechanism by which this form of therapy reduces apnea with an obstructive component in premature infants.

Effects of unilateral nasal occlusion on ventilation and pulmonary resistance in infants

1989 ◽  
Vol 66 (6) ◽  
pp. 2522-2526 ◽  
Author(s):  
R. J. Martin ◽  
M. J. Miller ◽  
B. Siner ◽  
J. M. DiFiore ◽  
W. A. Carlo
Keyword(s):  
Tidal Volume ◽  
Preterm Infants ◽  
Nasal Obstruction ◽  
Minute Ventilation ◽  
Blood Gases ◽  
Nasal Passage ◽  
Nasal Mask ◽  
Pulmonary Resistance ◽  
Ventilatory Responses ◽  
Extrathoracic Airway

Because neonates are vulnerable to spontaneous nasal obstruction, this study was designed to evaluate the ventilatory consequences of obstructing a single nasal passage in preterm infants. We employed a nasal pneumotachograph that separately quantified airflow between the two nasal passages and permitted unilateral nasal mask occlusions. Changes in minute ventilation (VI) and total (RT) and inspiratory pulmonary resistance (RI) were measured in response to 30-s unilateral occlusions during quiet and active sleep in 11 subjects. Unilateral nasal obstruction caused VI to fall significantly in both sleep states, because of a fall in both tidal volume and respiratory rate, without alteration in transcutaneous blood gases. RT and RI increased by 27 and 24 cmH2O.1–1.s, respectively, during unilateral nasal occlusion; this increase was greater than would be expected solely from elimination of one nasal passage. In 7 of the 11 infants a single dominant side could be identified as contributing 56–67% to tidal volume. The effect of occlusion on VI, RT, or RI did not differ whether the dominant or nondominant side was occluded. We conclude that unilateral nasal mask occlusion increases RT and RI and decreases VI in preterm infants. The larger than expected increase in resistance suggests that unilateral nasal loading predisposes to narrowing of the extrathoracic airway, and this may explain the comparable ventilatory responses to occluding the dominant and nondominant nasal passage.

Effects of bronchoconstriction and external resistive loading on the sensation of dyspnea

1991 ◽  
Vol 71 (6) ◽  
pp. 2183-2190 ◽  
Author(s):  
O. Taguchi ◽  
Y. Kikuchi ◽  
W. Hida ◽  
N. Iwase ◽  
M. Satoh ◽  
...  
Keyword(s):  
Normal Subjects ◽  
Vagal Afferents ◽  
Vagal Activity ◽  
Resistive Load ◽  
Occlusion Pressure ◽  
Analog Scale ◽  
External Resistance ◽  
Resistive Loading ◽  
Afferent Vagal

To determine whether the intensity of dyspnea at a given level of respiratory motor output differs between bronchoconstriction and the presence of an external resistance, we compared the sensation of difficulty in breathing during isocapnic voluntary hyperventilation in six normal subjects. An external resistance of 1.9 cmH2O.1–1.s was applied during both inspiration and expiration. To induce bronchoconstriction, histamine aerosol (5 mg/ml) was inhaled until airway resistance (Raw) increased to a level approximately equal to the subject's control Raw plus the added external resistance. To clarify the role of vagal afferents on the genesis of dyspnea during both forms of obstruction to airflow, the effect of airway anesthesia by lidocaine aerosol inhalation was also examined after histamine and during external resistive loading. The sensation of difficulty in breathing was rated at 30-s intervals on a visual analog scale during isocapnic voluntary hyperpnea, in which the subjects were asked to copy an oscilloscope volume trace obtained previously during progressive hypercapnia. Histamine inhalation significantly increased the intensity of the dyspneic sensation over the equivalent external resistive load at the same levels of ventilation and occlusion pressure during voluntary hyperpnea. Inhaled lidocaine decreased the sensation of dyspnea during bronchoconstriction with no change in Raw, but it did not significantly change the sensation during external resistive loading. These results suggest that afferent vagal activity plays a role in the genesis of dyspnea during bronchoconstriction.

Changes in total pulmonary resistance and PCO2 between wakefulness and sleep in normal human subjects

1995 ◽  
Vol 78 (4) ◽  
pp. 1339-1349 ◽  
Author(s):  
M. J. Morrell ◽  
H. R. Harty ◽  
L. Adams ◽  
A. Guz
Keyword(s):  
Continuous Positive Airway Pressure ◽  
Airway Pressure ◽  
Positive Airway Pressure ◽  
Human Subjects ◽  
Stage Iv ◽  
Pulmonary Resistance ◽  
Inspiratory Resistance ◽  
Normal Human ◽  
End Tidal

We investigated the possible role of an increase in total pulmonary resistance in the sleep-related hypoventilation that occurs in healthy subjects. Eight nonsnoring volunteers were studied during quiet wakefulness and stage IV sleep. Airflow was measured via a nasal mask with a low dead space, and breathing pattern, end-tidal PCO2 (PETCO2), and a continuous estimate of total pulmonary resistance were estimated. From wakefulness to sleep, mean inspiratory resistance increased from 5.5 +/- 2.4 (SD) to 8.1 +/- 4.3 cmH2O.l–1.s, PETCO2 increase from 38.7 +/- 3.0 to 40.7 +/- 3.5 Torr, and ventilation decreased from 7.12 +/- 1.15 to 6.47 +/- 1.68 l/min. In five of the eight subjects, low levels of continuous positive airway pressure were applied during stage IV sleep to reverse any increase in resistance. In these subjects, continuous positive airway pressure reduced mean inspiratory resistance from 9.3 +/- 4.3 +/- 3.0 cmH2O.l–1.s but had little effect on mean PETCO2 (from 39.8 +/- 4.0 to 39.6 +/- 4.0 Torr) and mean ventilation (from 6.79 +/- 1.93 to 6.91 +/- 1.80 l/min). These findings suggest that in nonsnoring subjects reductions in alveolar ventilation cannot be accounted for by an increase in airway resistance.

Rapid, shallow breathing after Ascaris suum antigen inhalation: role of vagus nerves

1977 ◽  
Vol 42 (1) ◽  
pp. 101-106 ◽  
Author(s):  
D. J. Cotton ◽  
E. R. Bleecker ◽  
S. P. Fischer ◽  
P. D. Graf ◽  
W. M. Gold ◽  
...  
Keyword(s):  
Ventilatory Response ◽  
Ascaris Suum ◽  
Minute Volume ◽  
Vagus Nerves ◽  
Pulmonary Resistance ◽  
Afferent Pathways ◽  
Airway Narrowing ◽  
Shallow Breathing ◽  
Vagal Afferent

In five treadmill-exercising, unsedated dogs, we studied the effect of inhaled Ascaris suum antigen aerosols on minute volume of ventilation (VE), respiratory frequency (f), tidal volume (VT), total pulmonary resistance (RL), and dynamic pulmonary compliance (CLdyn), before and during cooling of the vagus nerves. With the vagi warm, inhaled antigen increased VE (mean + 62%; P less than 0.01)by increasing f (mean + 180%; P less than 0.01), despite a decrease in VT (mean - 42%; P less than 0.01). RL increased (mean + 170%; P less than 0.001) and CLdyn decreased (mean - 43%; P less than 0.005). With the vagi cool, inhaled antigen no longer affected VE, f, or VT (P greater than 0.5), although RL still increased and CLdyn still decreased. Inhalation of a bronchodilator, terbutaline, prevented the broncho-constriction induced by antigen but did not prevent the ventilatory response. We conclude that vagal afferent pathways mediate the ventilatory response to inhaled antigen and suggest that the primary stimulus for this response is not airway narrowing.

Methacholine-induced bronchoconstriction and airway smooth muscle in the guinea pig

1996 ◽  
Vol 80 (2) ◽  
pp. 437-444 ◽  
Author(s):  
A. Opazo Saez ◽  
T. Du ◽  
N. S. Wang ◽  
J. G. Martin
Keyword(s):  
Smooth Muscle ◽  
Airway Smooth Muscle ◽  
Guinea Pigs ◽  
Pulmonary Resistance ◽  
Mechanically Ventilated ◽  
Airway Narrowing ◽  
Luminal Area ◽  
Lung Resistance ◽  
The Relationship

We examined the role of airway smooth muscle (ASM) as a determinant of the site and extent of methacholine (MCh)-induced airway narrowing in anesthetized and mechanically ventilated guinea pigs. The sites of airway narrowing and ASM were determined in animals (n = 4) bronchoconstricted to 75, 60, 40, or 15% of the maximal lung resistance (RL,max) induced by aerosolized MCh and compared with a saline-challenged animal. The median luminal area of each animal was significantly inversely correlated to the percentage of RL,max (r = -0.95; P < 0.01). However, there was no correlation between the degree of narrowing of any given airway and the quantity of ASM of any given airway. The relationship between the amount of ASM and responsiveness to MCh was studied in different animals (n = 13). The range of the concentration of MCh required to reach 50% of RL,max (EC50) varied by 254-fold, but the RL,max had only a 3.6-fold range. There was no correlation between RL,max and ASM. However, there was a correlation between the log EC50 and ASM (r = -0.541; P<0.05) in intraparenchymal cartilaginous airways. In conclusion, morphometric measurements of airway narrowing are correlated with pulmonary resistance. Variability in the quantity of ASM does not appear to be a determinant of the heterogeneity of airway narrowing or of maximal bronchoconstriction among normal guinea pigs. However, the sensitivity to MCh is associated with differences in the amount of ASM in intraparenchymal cartilaginous airways.

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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