Respiratory System Impedance Research Articles

Modeling of respiratory system impedances in dogs.

Mechanical impedances between 4 and 64 Hz of the respiratory system in dogs have been reported (A.C. Jackson et al. J. Appl. Physiol. 57: 34-39, 1984) previously by this laboratory. It was observed that resistance (the real part of impedance) decreased slightly with frequency between 4 and 22 Hz then increased considerably with frequency above 22 Hz. In the current study, these impedance data were analyzed using nonlinear regression analysis incorporating several different lumped linear element models. The five-element model of Eyles and Pimmel (IEEE Trans. Biomed. Eng. 28: 313-317, 1981) could only fit data where resistance decreased with frequency. However, when the model was applied to these data the returned parameter estimates were not physiologically realistic. Over the entire frequency range, a significantly improved fit was obtained with the six-element model of DuBois et al. (J. Appl. Physiol. 8: 587-594, 1956), since it could follow the predominate frequency-dependent characteristic that was the increase in resistance. The resulting parameter estimates suggested that the shunt compliance represents alveolar gas compressibility, the central branch represents airways, and the peripheral branch represents lung and chest wall tissues. This six-element model could not fit, with the same set of parameter values, both the frequency-dependent decrease in Rrs and the frequency-dependent increase in resistance. A nine-element model recently proposed by Peslin et al. (J. Appl. Physiol. 39: 523-534, 1975) was capable of fitting both the frequency-dependent decrease and the frequency-dependent increase in resistance. However, the data only between 4 and 64 Hz was not sufficient to consistently determine unique values for all nine parameters.

Effects of mean airway pressure on gas transport during high-frequency ventilation in dogs.

In 10 anesthetized, paralyzed, supine dogs, arterial blood gases and CO2 production (VCO2) were measured after 10-min runs of high-frequency ventilation (HFV) at three levels of mean airway pressure (Paw) (0, 5, and 10 cmH2O). HFV was delivered at frequencies (f) of 3, 6, and 9 Hz with a ventilator that generated known tidal volumes (VT) independent of respiratory system impedance. At each f, VT was adjusted at Paw of 0 cmH2O to obtain a eucapnia. As Paw was increased to 5 and 10 cmH2O, arterial PCO2 (PaCO2) increased and arterial PO2 (PaO2) decreased monotonically and significantly. The effect of Paw on PaCO2 and PaO2 was the same at 3, 6, and 9 Hz. Alveolar ventilation (VA), calculated from VCO2 and PaCO2, significantly decreased by 22.7 +/- 2.6 and 40.1 +/- 2.6% after Paw was increased to 5 and 10 cmH2O, respectively. By taking into account the changes in anatomic dead space (VD) with lung volume, VA at different levels of Paw fits the gas transport relationship for HFV derived previously: VA = 0.13 (VT/VD)1.2 VTf (J. Appl. Physiol. 60: 1025-1030, 1986). We conclude that increasing Paw and lung volume significantly decreases gas transport during HFV and that this effect is due to the concomitant increase of the volume of conducting airways.

Respiratory system impedance in patients with acute left ventricular failure: pathophysiology and clinical interest.

To investigate the relationship between alterations in lung mechanics and acute pulmonary vascular congestion, repeated measurements of the respiratory system impedance (Zrs) were performed in 11 patients with and in seven without acute left ventricular failure. Indexes of Zrs were obtained by calculating the average and slope of the resistance and reactance in low (10 to 20 Hz) and high (20 to 50 Hz) frequency intervals. Zrs indexes in patients with ventricular failure differ significantly from those in patients without failure. Pulmonary vascular congestion is regularly associated with an abnormal frequency dependence of resistance at low frequencies and with an increased resonant frequency. Discriminant analysis of Zrs indexes allows 92% correct classification of pulmonary capillary wedge pressures lower than and those equal to or higher than 18 mm Hg. Zrs differences between patients with and without left ventricular failure are consistent with the presence of a small airways obstruction even in patients with mild left ventricular failure. Furthermore, use of Zrs indexes permits moderate and severe pulmonary vascular congestion to be distinguished from one another and this is probably due to a significant narrowing of the large airways during severe left ventricular failure.

Total respiratory impedance in healthy children.

Impedance of the total respiratory system was measured in 121 healthy children aged 4-16 years during spontaneous breathing by pseudo-random forced oscillations between 3 and 10 Hz. Total respiratory resistance (Rrs), inertance (Irs) and compliance (Crs) were determined by least-mean-squares fitting. Estimates for inertance were reliable only for the larger children, where the values of Irs (0.0127 +/- 0.0034 SD) were similar to those reported for normal adults. Rrs correlated significantly (P less than 0.001) with height (r = -0.868), age (r = -0.865), and, in a subpopulation of the 6- to 16-year-old children, with forced vital capacity (r = -0.803). The corresponding correlation coefficients for Crs were 0.873, 0.844, and 0.853, respectively. Crs amounted to about a third of the static total compliance values of Sharp et al. (J Appl Physiol 1970; 29: 775-779) over the same interval of heights. In these relationships no significant difference was found between boys and girls.

Airway pressures in an asymmetrically branched airway model of the dog respiratory system.

A computer model of the mechanical properties of the dog respiratory system based on the asymmetrically branching airway model of Horsfield et al. (11) is described. The peripheral ends of this airway model were terminated by a lumped-parameter impedance representing gas compression in the alveoli, and lung and chest wall tissue properties were derived from measurements made in this laboratory. Using this model we predicted the respiratory system impedance and the distribution of pressures along the airways in the dog lung. Predicted total respiratory system impedances for frequencies between 4 and 64 Hz at three lung volumes were found to compare quite closely to measured impedances in dogs. Serial pressure distributions were found to be frequency-dependent and to result in higher pressures in the lung periphery than at the airway opening at some frequencies. The implications of this finding for high-frequency ventilation are discussed.

Breathing pattern and occlusion pressure during moderate and heavy exercise.

We studied changes in breathing pattern and mouth occlusion pressure (P0.1) in 11 healthy subjects performing graded steady-state exercise on a cycle ergometer up to the maximal load sustainable for 4 min. With increasing work intensity both the tidal volume (VT) and end-inspiratory volume relations to inspiratory (TI) and expiratory (TE) durations were linear in the moderate work load range; in the high load range VT and end-inspiratory volume tended to plateau with further decreases in TI and TE. The ratio of TI to total breath duration (TI/Ttot) increased with work intensity. Intraindividual coefficients of variation for VT, breathing frequency (f), mean inspiratory flow (VT/TI), and other respiratory variables decreased with increasing work intensity, indicating that breath-to-breath variations in breathing pattern became smaller as the level of ventilation increased. P0.1 rose with VT/TI as a power function with an exponent averaging 1.5 (range 1.3-1.9), indicating that the ratio P0.1/(VT/TI), an index of respiratory system impedance, increased with VT/TI and work intensity. We conclude that in moderate and heavy exercise the work of inspiration at a given ventilation is reduced because of the increase in TI/Ttot, the impedance of the respiratory system increases with work intensity because of both an increase in f and a flow-dependent rise in airway resistance, and the neuromuscular inspiratory activity is reflexly augmented because of internal flow-resistive loading.

Respiratory system, lung, and chest wall impedances in anesthetized dogs.

We measured impedances of the respiratory system (Zrs) and lung (ZL) in anesthetized and paralyzed dogs at frequencies between 4 and 64 Hz. Zrs was measured at functional residual capacity (FRC) and with mean transpulmonary pressures (Ptp) of 12 and 30 cmH2O; ZL was measured with the chest wall open at FRC and Ptp = 12 cmH2O. From these data we derived chest wall impedances at FRC and 12 cmH2O. Effective resistances of the respiratory system, lung, and chest wall were all frequency dependent. At frequencies below 22 Hz frequency dependence of respiratory system resistance was due to the frequency dependence of the chest wall, whereas at higher frequencies it was due to frequency dependence of the lung. Analysis of the impedance data between 4 and 32 Hz provided estimates of resistance, inertance, and compliance of the lung, chest wall, and respiratory system. At FRC, 41% of the respiratory system resistance was due to the lung and 59% was associated with the chest wall. Nearly all of the respiratory inertance (98%) was due to the lung. Lung compliance was approximately twice that of the chest wall, the former accounting for approximately one-third of respiratory elasticity. As lung volume was increased, respiratory resistance and compliance decreased; inertance also decreased, although this change was not significant.

ALVEOLAR PRESSURE AND TIDAL VOLUME DURING HIGH FEEQUENCY VENTILATION

Alveolar pressures and tidal volumes have not been quantified during high frequency ventilation. We have measured dynamic and mean pressures at the airway opening, trachea, and alveoli as well as delivered volumes and blood gases in vivo in closed-chest adult rabbits ventilated at rates of 2-37.5 Hz with the Emerson flow-interrupting high frequency ventilator. Alveolar pressure was measured by opening the chest, gluing an adapter to the visceral pleural surface, puncturing the pleura and lung surface through the adapter, closing the chest, and attaching a pressure transducer. Delivered volume was measured with a pressure plethysmograph. As frequency increased, alveolar pressure swings decreased from 26 to 8% of pressure swings at the airway opening, and 100 to 42% of those in the trachea. Delivered volume decreased from 5.3±0.5 to 0.6±0.1 ml/kg as frequency increased. Respiratory system impedance fell initially with increasing frequency, then tended to remain relatively stable with no resonance seen. Lung tissue plus chest wall impedance behaved as an elastance and fell as frequency increased. Muscle paralysis had no effect on alveolar pressure swings, but excision of the rib cage resulted in a decrease. Mean pressures were equal at the airway opening, trachea and alveoli at all frequencies. The clinical implication of these results is that if gas exchange can be maintained with constant tracheal pressure swings, alveolar barotrauma may be minimized by choosing the highest possible frequency for ventilation. (Supported in part by HL 27372.)

Oscillatory mechanics of the respiratory system in ozone-exposed rats.

The respiratory system impedance of tracheostomized cardiorespiratory disease-free Sprague-Dawley rats was measured from 20 to 90 Hz at constant flow amplitudes in 10 rats exposed to 0.64 ppm (UV) ozone for 7 days, and eight rats exposed to the same level of ozone for 20 days. This data was compared with respiratory system impedence spectra of 24 normal rats obtained in the same manner. When compared with control, the real part (effective resistance) was significantly different at several frequencies in the 7-day group (P less than 0.05), and group means were higher at all frequencies. The 20-day group showed no significant differences in effective resistance. The imaginary part (effective reactance) was significantly lower at higher frequencies (f greater than 36) in both exposure groups (P less than 0.05). When the impedance curves for each individual were fit to a lumped six-parameter model, and the parameters were compared, only the peripheral resistance parameter of the 7-day group was significantly different from control (P less than 0.05). We conclude that ozone exposure at this level causes changes in respiratory system impedance, that these changes consist primarily of decreased reactances at higher frequencies, and that at 7 days these changes can be modeled by an increase in peripheral resistance.

Active impedance of respiratory system in anesthetized cats.

We have assessed the validity of the method of Siafakas et al. (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 51: 109-121, 1981) for determining active elastance (E'rs) and flow resistance (R'rs) of the respiratory system. In six cats anesthetized with pentobarbital sodium we have measured flow, volume, and tracheal occlusion pressure during spontaneous breathing. This allowed us to compute E'rs and R'rs. From these data and the occlusion pressure wave we predicted the time course of volume during inspirations with added linear flow resistances (delta R). These were compared to the actual loaded inspirograms. The agreement was generally good, except for small predictable discrepancies with the highest delta R values, which could be attributed to decompression of thoracic gas. These results indicate that the approach of Siakafas et al. to determine E'rs and R'rs is valid. In addition, we have quantified the "terminal inhibition" of inspiratory activity, which occurs toward the end of unoccluded breaths (both loaded and unloaded).

Oscillatory mechanics of the respiratory system in normal rats

Respiratory system impedances were measured by a modified forced oscillatory technique in 30 normal male CRD-free Sprague-Dawley rats at frequencies between 20 and 90 Hz. A resonance frequency was found (mean = 39 Hz) below which reactances were negative and above which reactances were positive. Resistances were generally found to be frequency dependent, increasing with increasing frequencies. Frequency dependent behavior in resistance has been ascribed to inhomogeneities in parallel airway pathways and to the effects of airways wall compliance. Optimization techniques were used to estimate the values of parameters in a variety of lumped-parameter mechanical networks incorporating parallel pathways and/or airway wall compliance. The model whose response compared the best with the data and that resulted in the most consistent parameter values was found to be one where the airways are separated into central and peripheral components by a shunt pathway containing an airway wall compliance. The mean values for each of the parameters within the model were central airway resistance (54 cm H 2O/L/sec), peripheral airway resistance (53 cm H 2O/L/sec), central airway inertance (0.058 cm H 2O/L/sec 2), peripheral airway inertance (0.116 cm H 2O/L/sec 2), airway wall compliance (0.182 × 10 −4 L/cm H 2O), and respiratory system compliance (1.267 × 10 −4 L/cm H 2O).

Pathogenesis of respiratory insufficiency in myotonic dystrophy: the mechanical factors.

We have previously shown that the chemosensitivity of the respiratory centers is well preserved in myotonic dystrophy but that the ventilatory output is reduced. The present study was designed to determine at which degree of ventilatory performance weakness and fatigability of the respiratory muscles are interfering with ventilation and which mechanical factors contribute to the tachypnea of patients with myotonic dystrophy at rest and during low ventilatory output. We studied 10 patients with the disease and 10 normal control subjects. The strength of respiratory muscles was assessed by measurements of maximal pressure-volume diagrams generated against airway occlusion. Performance was evaluated during 1-min maximal voluntary ventilation (1-min MVV) test, during 7-min 7% CO2 breathing and during quiet breathing. Occlusion pressure (P0.1) in patients at rest was slightly higher than in control subjects, and during CO2 breathing, it was similar to that of control subjects. Maximal static pressure was reduced in patients to an average of 35% of that of control subjects. During the 1-min MVV test, there was a 50% reduction in esophageal and transdiaphragmatic pressure output (Pes, Pdi) in patients, resulting in similar reduction in ventilation (VE) and patients had rapid cycles of alternating dominant thoracic and abdominal volume displacements (Vrc/Vabd) suggesting respiratory muscle fatigue. During the 3- to 4-fold increase in breathing drive induced by hypercapnia, pressure output and the Vrc/Vabd were identical in both groups. However, ventilation was reduced in patients who had tachypneic respiration. In patients, tachypnea was also observed during quiet breathing. This tachypnea was associated with higher impedance of the respiratory system (Zrs) in patients and identical impedance of the lung (ZL) in both groups. In addition, Pdi during tidal volume was significantly higher in patients. These data demonstrate that the ventilatory output in out patients was altered predominantly by weakness and fatigability of the respiratory muscles during high ventilatory performance and by increased impedance of the respiratory system at lower degrees of ventilation.

Impedance of the lower respiratory system in ducks measured by forced oscillations during normal breathing

The lower respiratory system of 10 conscious Pekin ducks breathing normally was subjected to superimposed oscillations of 1.3 to 16 Hz by a small volume piston pump. Induced sinusoidal flow (V̇ O) and pressure (P O) signals were measured in late expiration, when the gas flow ventilated by the animal was minimum. The modulus of the respiratory impedance was calculated as the ratio P O/V̇. The values obtained at the various oscillatory frequencies were compared to those predicted on the basis of a series mechanical network model consisting of resistive, inertial and compliant elements (RIC) using a least squares non linear regression method. The experimental data fitted well the frequency response of a simple RIC mathematical model. After correcting for the effects of the endotracheal tube, the mean values ±SE of the optimized parameters were: resistance 4.8±0.4 cm H 2O·L −1·sec; inertance: 0.05±0.01 cm H 2O·L −1·sec 2; compliance: 7.7±0.5 ml·cm H 2O −1; natural frequency: 8.0±0.4 Hz. It is concluded that: (1) the lower respiratory system in ducks can be closely modeled by a RIC mechanical series network model; (2) the forced oscillation method can be used to investigate avian mechanics of breathing, with the birds awake and breathing spontaneously.

Bronchial response to methacholine and histamine in monkeys with beta adrenergic blockade

The possibility has been investigated that propranolol administration could alter bronchial reactivity to methacholine and histamine in monkeys ( Macaca fuscata and Macaca fascicularis). The impedance of the total respiratory system was measured by the forced 3-Hz oscillation method through an endotracheal tube. Methacholine and histamine dose-dependently increased the impedance in monkeys irrespective of the route of administration (inhalation of aerosol or intravenous injection). Propranolol treatment increased the bronchial response to intravenously injected methacholine and caused no significant change in the bronchial response to aerosolized methacholine. No marked difference was observed in the bronchial response to histamine due to treatment with propranolol regardless of whether administered by intravenous injection or aerosol challenge.

Effect of hypoxia on airway smooth muscle mechanics and electrophysiology.

ArticleEffect of hypoxia on airway smooth muscle mechanics and electrophysiology.N L Stephens, and E KroegerN L Stephens, and E KroegerPublished Online:01 May 1970https://doi.org/10.1152/jappl.1970.28.5.630MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByEditorial Focus: Oxygen sensors and mediators of the contractile responses of smooth muscle to hypoxia. Focus on: “Hydrogen sulfide mediates hypoxic vasoconstriction through a production of mitochondrial ROS in trout gills”Jose F. Perez-Zoghbi1 September 2012 | American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, Vol. 303, No. 5Interaction Between Volatile Anesthetics and Hypoxia in Porcine Tracheal Smooth MuscleAnesthesia & Analgesia, Vol. 91, No. 4Effect of hypoxia on respiratory system impedance in dogsB. A. Simon, P. B. Zanaboni, and D. P. Nyhan1 August 1997 | Journal of Applied Physiology, Vol. 83, No. 2Hypoxia modulates mediator responses and neurotransmission in guinea-pig trachea in vitroPulmonary Pharmacology, Vol. 5, No. 1Time course of pulmonary vasoconstriction with repeated hypoxia and glucose depletionRespiration Physiology, Vol. 63, No. 2Angiotensin inhibits gastric and tracheal contractile responses to peripheral parasympathetic stimulationJournal of the Autonomic Nervous System, Vol. 14, No. 1Pulmonary mechanics during hypoxia in spontaneously breathing anesthetized rabbitsJournal of the Autonomic Nervous System, Vol. 2, No. 4Aleration of electrophysiological properties of airways smooth muscle from sensitized guinea-pigsRespiration Physiology, Vol. 41, No. 1Effect of antigen challenge on sensitized guinea pig tracheaRespiration Physiology, Vol. 27, No. 2Mechanical properties of diaphragm of three-toed slothComparative Biochemistry and Physiology Part A: Physiology, Vol. 55, No. 4 More from this issue > Volume 28Issue 5May 1970Pages 630-5 https://doi.org/10.1152/jappl.1970.28.5.630PubMed5442259History Published online 1 May 1970 Published in print 1 May 1970 Metrics