Influence of Bifurcations on Forced Oscillations in an Airway Model

1992 ◽  
Vol 114 (2) ◽  
pp. 216-221
Author(s):  
D. A. Bunk ◽  
W. J. Federspiel ◽  
A. C. Jackson

Forced oscillations is a technique to determine respiratory input impedance from small amplitude sinusoidal pressure excursions introduced at the airway opening. Models used to predict respiratory input impedance typically ignore the direct effect of bifurcations on the flow, and treat airway branches as individual straight tubes placed appropriately in parallel and series. The flow within the individual tubes is assumed equivalent to that which would occur in infinitely long tubes. In this study we examined the influence of bifurcations on impedance for conditions of the forced oscillatory technique. We measured input impedance using forced oscillations in straight tubes and in an anatomically-relevant, four generation physical model of a human airway network. The input impedance measured experimentally compared well to that obtained theoretically using model predictions. The predictive scheme was based on appropriate parallel and series combinations of theoretically computed individual tube impedances, which were computed from solutions to oscillatory flow of a compressible gas in an infinitely long rigid tube. The agreement between experimental measurements and predictions indicates that bifurcations play a relatively minor direct role on the flow impedance for conditions of the forced oscillations technique. These results are explained in terms of the small tidal volumes used, whereby the axial distance traveled by a fluid particle during an oscillation cycle is appreciably smaller than branch segment lengths. Accordingly, only a small fraction of fluid particles travel through the bifurcation region, and the remainder experience an environment approaching flow in an infinite straight tube. The relevance of the study to the prediction of impedances in the human lung during forced oscillations is discussed.

1978 ◽  
Vol 100 (2) ◽  
pp. 67-71 ◽  
Author(s):  
J. J. Fredberg ◽  
R. S. Sidell ◽  
M. E. Wohl ◽  
R. G. DeJong

We describe a transient forced oscillation method for measurement of the input impedance of excised canine lungs. The technique employs a single uncalibrated data channel to record short duration pressure transients incident upon and reflected from the airway opening, from which the input impedance up to 10,000 Hz is computed using lossy transmission line theory. Data acquisition time is less than 10 ms. The lung responses exhibit numerous resonances and anti-resonances below 10,000 Hz, and exhibit lung volume dependence. The branching structure of the airways and response of the airway walls appear to be important factors in the lung response.


1992 ◽  
Vol 72 (1) ◽  
pp. 168-178 ◽  
Author(s):  
Z. Hantos ◽  
B. Daroczy ◽  
B. Suki ◽  
S. Nagy ◽  
J. J. Fredberg

Tracheal pressure, central airflow, and alveolar capsule pressures in cardiac lobes were measured in open-chest dogs during 0.1- to 20-Hz pseudorandom forced oscillations applied at the airway opening. In the interval 0.1–4.15 Hz, the input impedance data were fitted by four-parameter models including frequency-independent airway resistance and inertance and tissue parts featuring a marked negative frequency dependence of resistance and a slight elevation of elastance with frequency. The models gave good fits both in the control state and during histamine infusion. At the same time, the regional transfer impedances (alveolar pressure-to-central airflow ratios) showed intralobar and interlobar variabilities of similar degrees, which increased with frequency and were exaggerated during histamine infusion. Results of simulation studies based on a lung model consisting of a central airway and a number of peripheral units with airway and tissue parameters that were given independent wide distributions were in agreement with the experimental findings and showed that even an extremely inhomogeneous lung structure can produce virtually homogeneous mechanical behavior at the input.


1988 ◽  
Vol 64 (2) ◽  
pp. 823-831 ◽  
Author(s):  
H. L. Dorkin ◽  
K. R. Lutchen ◽  
A. C. Jackson

Recent studies on respiratory impedance (Zrs) have predicted that at frequencies greater than 64 Hz a second resonance will occur. Furthermore, if one intends to fit a model more complicated than the simple series combination of a resistance, inertance, and compliance to Zrs data, the only way to ensure statistically reliable parameter estimates is to include data surrounding this second resonance. An additional question, however, is whether the resulting parameters are physiologically meaningful. We obtained input impedance data from eight healthy adult humans using discrete frequency forced oscillations from 4 to 200 Hz. Three resonant frequencies were seen: 8 +/- 2, 151 +/- 10, and 182 +/- 16 Hz. A seven-parameter lumped element model provided an excellent fit to the data in all subjects. This model consists of an airway resistance (Raw), which is linearly dependent on frequency, and airway inertance separated from a tissue resistance, inertance, and compliance by a shunt compliance (Cg) thought to represent gas compressibility. Model estimates of Raw and Cg were compared with those suggested by measurement of Raw and thoracic gas volume using a plethysmograph. In all subjects the model Raw and Cg were significantly lower than and not correlated with the corresponding plethysmographic measurement. We hypothesize that the statistically reliable but physiologically inconsistent parameters are a consequence of the distorting influence of airway wall compliance and/or airway quarter-wave resonance. Such factors are not inherent to the seven-parameter model.


Author(s):  
Donald J. Munro

Chinese Marxism is a mixture of elements from Confucianism, German Marxism, Soviet Leninism and China’s own guerrilla experience. Because Mao Zedong (1893–1976) was in power longer than any other Chinese communist, the phrase ‘Chinese Marxism’ is commonly used to refer to Mao’s own evolving mixture of ideas from these sources. However, the advocates of Chinese Marxism have come from many different factional backgrounds and have tended to emphasize different aspects in their own thinking. Even Maoism reflects many minds. For example, Mao’s two most famous essays, ‘Shijianlun’ (‘On Practice’) and ‘Maodunlun’ (‘On Contradiction’) (1937) drew heavily from Ai Siqi, the author of the popular philosophical work Dazhong zhexue (Philosophy for the Masses) (1934). The goals of the Chinese Marxists included the salvation of China from its foreign enemies and the strengthening of the country through modernization. Accordingly, they selected from other systematic theories those doctrines that appeared to facilitate those goals, and then paired these doctrines with others from theories that were sometimes incompatible. One should not, therefore, look for logical consistency in the relations between the ideas that the Chinese Marxists drew from these various sources. The foundation of Chinese Marxism was undoubtedly Marx’s materialist conception of history, and the concepts of class struggle and control of the forces of production shaped the thinking of many early Marxists. However, faced with the need to accelerate social change through class struggle rather than waiting for the full flowering of capitalism, Marxists such as Li Dazhao began focusing less on materialism or determinism and more on voluntarism. There also arose a doctrine, based on the ideas of Lenin and Trotsky, that right-minded people could ‘telescope’ the phases of the revolution and hasten the transition through the historical stages. This ultimately led to the doctrine of permanent revolution. First promulgated in China in the late 1920s, it reappeared in the 1950s. After Mao’s death, the ‘subjectivity’ movement within Chinese Marxism sought to move the focus away from classes or groups and onto the individual subject as an active agent. Throughout the evolution of Chinese Marxism, political struggles played a direct role in the formulation and discussion of philosophical positions. Mao’s epistemological essay ‘Shijianlun’ clearly reflects the experience of leaders during the guerrilla period, and his theories of knowledge are analogous to the ‘democracy’ practised by the guerrilla leaders: the people were consulted for their knowledge and opinions, decisions were then made from the centre, and the resulting policies were taken back to the masses through teaching. In the same way, Mao believed, individuals perceive through their senses, form theories in their brains (the centre), and test the resulting theories in a manner analogous to teaching. In China, right minds among the people were thought to arise through officials teaching the people. Here pre-modern Confucian legacy becomes important. It helps to explain the endurance of teaching as an official function in the Chinese Marxist discussion of democratic centralism. In Confucianism, the primary function of government was education, although it certainly had other tasks, such as the collection of taxes. All officials, including the emperor, had the task of transforming the character of the people. The education in which the state involved itself, through control of the curriculum and national examinations for the civil service, was moral education. The ultimate aim of state-controlled Confucian education was a one-minded, hierarchical society, meaning that people of all different strata would think the same on important matters. Maoists also sought to create a one-minded people through officially controlled teaching. If the focus of teaching is on right ideas, which are supposed to motivate people towards socialism, one such idea in later Maoist writing is egalitarianism of social status. This was challenged by others, notably Liu Shaoqi, and following Deng Xiaoping’s assumption of power in 1978 it suffered a further blow with the switch in economic policy from central planning to market forces. An example of the relevance of political struggle to the formulation of ideas was the heightening of the campaign against the philosophy called ‘humanism’, following a dispute in 1957 between Mao and President Liu Shaoqi. Liu made a speech in April of that year saying that capitalists had changed and so class struggle against them could be minimized; this was followed by a Maoist-inspired attack on humanism as a philosophy. The humanism that the Maoists attacked was a Confucian-inspired belief in a class-transcending humaneness or compassion for humankind or humaneness. In contrast, in the post-Mao years, the content of humanism has altered, and the term has come to refer to a doctrine inspired by both the early Marx and by the Western psychologist Maslow, namely that the goal of society is the individual’s self-realization. This form of humanism is one of several competing positions that claim to carry on the Marxist tradition in new directions, and has been reinforced by one form of the subjectivity movement in the Deng Xiaoping era.


Author(s):  
Constance M. Dahlin ◽  
Elaine Wittenberg

Communication, a learned skill that establishes the nurse-patient relationship, is composed of 20% verbal and 80% nonverbal characteristics. The art of nursing communication includes listening, silence, presence, and therapeutic use of self to facilitate a patient- and family-centered process. Nursing communication includes gathering and imparting information and providing support and reassurance as dictated by the individual needs of patients and families. Nurses have a direct role in difficult conversations such as advance care planning, delivery of bad news, poor prognosis, or transition to hospice and palliative care.


1984 ◽  
Vol 57 (2) ◽  
pp. 596-600 ◽  
Author(s):  
R. Peslin ◽  
C. Duvivier ◽  
P. Jardin

Respiratory input impedance (Zrs) measured by forced oscillations needs to be corrected for the motion of extrathoracic airway walls. Two methods of obtaining the impedance of this shunt pathway [upper airway impedance (Zuaw)] were compared in six normal subjects. In the first, flow was measured at the airway opening during Valsalva maneuvers, as described by Michaelson et al. (10). In the second, motions of upper airway walls were directly assessed during respiratory impedance measurements by use of a head plethysmograph. Larger upper airway impedance values were found during Valsalva maneuvers, corresponding to a larger upper airway resistance (Ruaw) (at 20 Hz, Ruaw = 9.1 +/- 4.7 compared with 7.0 +/- 2.1 cmH2O X 1–1 X s with the second method) and inertance (Iuaw) (Iuaw = 0.053 +/- 0.036 vs. 0.025 +/- 0.008 cmH2O X 1–1 X s2, P less than 0.05) and a lower upper airway compliance (Cuaw) (Cuaw = 0.78 +/- 0.33 vs. 1.15 +/- 0.15 ml X cmH2O–1, P less than 0.05). Active contraction of facial muscles during Valsalva maneuvers may be responsible for this finding. As a consequence, respiratory impedance values are undercorrected when using the Valsalva method, leading in normal subjects to an overestimation of respiratory compliance by 30% and an underestimation of inertance by 16% (P less than 0.05) and promoting positive frequency dependence of respiratory resistance. Substantial errors may be avoided by using a head plethysmograph, which permits measuring Zrs and Zuaw simultaneously.


2001 ◽  
Vol 90 (2) ◽  
pp. 630-637 ◽  
Author(s):  
Bruno Louis ◽  
Redouane Fodil ◽  
Samir Jaber ◽  
Jérôme Pigeot ◽  
Pierre-Henri Jarreau ◽  
...  

This report concerns the inference of geometric and mechanical airway characteristics based on information derived from a single transient planar wave recorded at the airway opening. We describe a new method to simultaneously measure upper airway area and respiratory input impedance by performing dual analysis of a single pressure wave. The algorithms required to reconstruct airway dimensions and mechanical characteristics were developed, implemented, and tested with reference to known physical models. Our method appears suitable to estimate, even under severe intensive care unit conditions, the respiratory system frequency response (above 10 Hz) in intubated patients and the patency of the endotracheal tube used to connect the patients to the ventilator.


1985 ◽  
Vol 58 (6) ◽  
pp. 1914-1922 ◽  
Author(s):  
J. J. Fredberg ◽  
R. H. Ingram ◽  
R. G. Castile ◽  
G. M. Glass ◽  
J. M. Drazen

To assess the homogeneity of airway responses to inhaled histamine we examined regional alveolar pressure excursions (PA) arising from small-amplitude oscillations applied at the airway opening (Pao). In five anesthetized and vagotomized dogs the sternum was split and the anterior right lung field exposed. PA was sampled using four capsules affixed to the right apical and middle lobes while lung impedance (ZL) and airway impedances (Zaw) were measured during conventional tidal breathing and during forced oscillations (2–60 HZ at 10 cmH2O distending pressure). During tidal breathing after exposure to aerosol histamine regional PA's could be separated into three groups by plotting Lissajous figures of PA vs. Pao: PA in phase with Pao (no looping), PA lagging Pao (moderate looping), and PA decreasing while Pao was increasing and vice versa (paradoxical looping), suggesting unresponsive, responsive, and closed pathways, respectively, between the airway opening and specific alveolar zones. During high-frequency oscillation the corresponding PA spectra were markedly different from control spectra and revealed resonant amplification, overdamped resonance, and marked attenuation, respectively. With induced bronchospasm resonant amplification of PA was damped on average. However, the more obstructed and closed pathways were protected from resonant amplification, and the more open (nonlooping) pathways were subjected to resonant amplification greater than in the control state. In spite of this markedly nonhomogeneous behavior, frequency dependence of ZL was consistent with the model by Mead (J. Appl. Physiol. 26: 670–673, 1969), which ignores nonhomogeneity of peripheral compartments. These data demonstrate that the response of airways to inhaled histamine is nonhomogeneous but that frequency dependence of ZL above 2 Hz is not sufficient to characterize this nonhomogeneity.


Geophysics ◽  
2016 ◽  
Vol 81 (1) ◽  
pp. WA159-WA167 ◽  
Author(s):  
Thomas Ingeman-Nielsen ◽  
Soňa Tomaškovičová ◽  
Torleif Dahlin

Electrode grounding resistance is a major factor affecting measurement quality in electric resistivity tomography (ERT) measurements for cryospheric applications. Still, little information is available on grounding resistances in the geophysical literature, mainly because it is difficult to measure. The focus-one protocol is a new method for estimating single electrode grounding resistances by measuring the resistance between a single electrode in an ERT array and all the remaining electrodes connected in parallel. For large arrays, the measured resistance is dominated by the grounding resistance of the electrode under test, the focus electrode. We have developed an equivalent circuit model formulation for the resistance measured when applying the focus-one protocol. Our model depends on the individual grounding resistances of the electrodes of the array, the mutual resistances between electrodes, and the instrument input impedance. Using analytical formulations for the potentials around prolate and oblate spheroidal electrode models (as approximations for rod and plate electrodes), we have investigated the performance and accuracy of the focus-one protocol in estimating single-electrode grounding resistances. We also found that the focus-one protocol provided accurate estimations of electrode grounding resistances to within [Formula: see text] for arrays of 30 electrodes or more when the ratio of instrument input impedance to the half-space resistivity was [Formula: see text] or more. The focus-one protocol was of high practical value in field operations because it helped to optimize array installation, electrode design, and placement. The measured grounding resistances may also be included in future inversion schemes to improve data interpretation under difficult environmental conditions such as those encountered in cryospheric applications.


2019 ◽  
Vol 286 (1916) ◽  
pp. 20192153 ◽  
Author(s):  
Michelle Achlatis ◽  
Mathieu Pernice ◽  
Kathryn Green ◽  
Jasper M. de Goeij ◽  
Paul Guagliardo ◽  
...  

Marine sponges are set to become more abundant in many near-future oligotrophic environments, where they play crucial roles in nutrient cycling. Of high importance is their mass turnover of dissolved organic matter (DOM), a heterogeneous mixture that constitutes the largest fraction of organic matter in the ocean and is recycled primarily by bacterial mediation. Little is known, however, about the mechanism that enables sponges to incorporate large quantities of DOM in their nutrition, unlike most other invertebrates. Here, we examine the cellular capacity for direct processing of DOM, and the fate of the processed matter, inside a dinoflagellate-hosting bioeroding sponge that is prominent on Indo-Pacific coral reefs. Integrating transmission electron microscopy with nanoscale secondary ion mass spectrometry, we track 15 N- and 13 C-enriched DOM over time at the individual cell level of an intact sponge holobiont. We show initial high enrichment in the filter-feeding cells of the sponge, providing visual evidence of their capacity to process DOM through pinocytosis without mediation of resident bacteria. Subsequent enrichment of the endosymbiotic dinoflagellates also suggests sharing of host nitrogenous wastes. Our results shed light on the physiological mechanism behind the ecologically important ability of sponges to cycle DOM via the recently described sponge loop.


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