Dead-space ventilation as a determinant in the ventilation-perfusion concept

1960 ◽  
Vol 15 (3) ◽  
pp. 363-371 ◽  
Author(s):  
Benjamin B. Ross ◽  
Leon E. Farhi
Keyword(s):  
Dead Space ◽  
Alveolar Ventilation ◽  
Gas Composition ◽  
New Concepts ◽  
Straight Line ◽  
Variable Quantity ◽  
Line Passing ◽  
Ventilation Perfusion Ratio ◽  
Actual Ratio ◽  
Additional Area

Gas exchange in an alveolus is affected by the redistribution of dead-space gas during inspiration. Theoretical analysis of the total ventilation of an alveolus permits the description of several new concepts. a) The gas inspired by an alveolus may be identified on a PCO2-PO2 diagram as any point within an area formed by the alveolar ventilation-perfusion curve and a straight line drawn through the environmental and mixed venous points. b) The composition of gas in an alveolus may lie anywhere within this area and an additional area above the conventional curve. c) The actual ratio of exchange in an alveolus is identified by the blood R line passing through the alveolar point. The ratio of exchange between alveolus and environment is not necessarily the same as the blood R. d) The total ventilation-perfusion ratio compatible with a given alveolar gas composition is a variable quantity. e) The rebreathing of dead-space gas has a buffering action in limiting the range of gas compositions possible in alveoli. Submitted on November 30, 1959

scholarly journals Dead space: the physiology of wasted ventilation

2014 ◽  
Vol 45 (6) ◽  
pp. 1704-1716 ◽  
Author(s):  
H. Thomas Robertson
Keyword(s):  
Dead Space ◽  
Distress Syndrome ◽  
Severe Heart Failure ◽  
Alveolar Ventilation ◽  
Pathophysiological Mechanism ◽  
Physiological Dead Space ◽  
Disease Condition ◽  
Physiological Abnormalities ◽  
Ventilation Perfusion Ratio ◽  
Space Measurement

An elevated physiological dead space, calculated from measurements of arterial CO2 and mixed expired CO2, has proven to be a useful clinical marker of prognosis both for patients with acute respiratory distress syndrome and for patients with severe heart failure. Although a frequently cited explanation for an elevated dead space measurement has been the development of alveolar regions receiving no perfusion, evidence for this mechanism is lacking in both of these disease settings. For the range of physiological abnormalities associated with an increased physiological dead space measurement, increased alveolar ventilation/perfusion ratio (V′A/Q′) heterogeneity has been the most important pathophysiological mechanism. Depending on the disease condition, additional mechanisms that can contribute to an elevated physiological dead space measurement include shunt, a substantial increase in overall V′A/Q′ ratio, diffusion impairment, and ventilation delivered to unperfused alveolar spaces.

scholarly journals Physical properties of surfaces. II—Viscous flow of liquid films. The range of action of surface forces

1935 ◽  
Vol 151 (872) ◽  
pp. 220-233 ◽  
Author(s):  
S. H. Bastow ◽  
Frank Philip Bowden ◽  
Thomas Martin Lowry
Keyword(s):  
Viscous Flow ◽  
Freezing Point ◽  
Applied Pressure ◽  
Liquid Films ◽  
Appreciable Effect ◽  
Straight Line Passing ◽  
Straight Line ◽  
Fluid Properties ◽  
Line Passing ◽  
Induced Structure

The present paper describes experiments which were carried out in order to determine the extent to which the fluid properties of water and other liquids may be modified by the presence of a solid surface. For this purpose, measurements of the viscous flow of a liquid very near to a surface are particularly suitable, since they provide a sensitive test for the existence of any induced structure in the liquid. If the surface has no appreciable effect, the smallest applied pressure will cause the liquid to flow and the rate of flow plotted against pressure will give a straight line passing through the origin, see fig. 3. If, however, as many authors have suggested, long chains of oriented liquid molecules with a definite rigidity are formed by the influence of the surface, the liquid will show a resistance to shear, which will be specially evident at low pressures; Poiseuille’s law will not hold and the pressure-flow curve will be of the form shown in fig. 4. A method has been developed for measuring the viscosity of thin liquid films enclosed between flat polished surfaces of glass and steel. The film thickness can be varied from about 10 -5 cm to any desired distance and can be accurately determined. The experiments show that films of a liquid, known to possess a bulk structure (liquid crystal), possess a high rigidity, but there is no sign of induced structure in normal liquids even with very thin films and at temperatures near the freezing point.

Effects of acetone in heparin on the multiple inert gas elimination technique

1985 ◽  
Vol 58 (4) ◽  
pp. 1143-1147 ◽  
Author(s):  
F. L. Powell ◽  
F. A. Lopez ◽  
P. D. Wagner
Keyword(s):  
Partial Pressure ◽  
Dead Space ◽  
Room Temperature ◽  
Inert Gas ◽  
Published Data ◽  
Physiological Mechanisms ◽  
Heparinized Saline ◽  
Partial Pressures ◽  
Ventilation Perfusion Ratio ◽  
Mixed Venous

We have detected acetone in several brands of heparin. If uncorrected, this leads to errors in measuring acetone in blood collected in heparinized syringes, as in the multiple inert gas elimination technique for measuring ventilation-perfusion ratio (VA/Q) distributions. Error for acetone retention [R = arterial partial pressure-to-mixed venous partial pressure (P-V) ratio] is usually small, because R is normally near 1.0, and the error is similar in arterial and mixed venous samples. However, acetone excretion [E = mixed expired partial pressure (P-E)-to-P-V ratio] will appear erroneously low, because P-E is accurately measured in dry syringes, but P-V is overestimated. A physical model of a homogeneous alveolar lung at room temperature and without dead space shows: the magnitude of acetone E error depends upon the ratio of blood sample to heparinized saline volumes and acetone partial pressures, without correction, acetone E can be less than that of less soluble gases like ether, a situation incompatible with conventional gas exchange theory, and acetone R and E can be correctly calculated using the principle of mass balance if the acetone partial pressure in heparinized saline is known. Published data from multiple inert gas elimination experiments with acetone-free heparin, in our labs and others, are within the limits of experimental error. Thus the hypothesis that acetone E is anomalously low because of physiological mechanisms involving dead space tissue capacitance for acetone remains to be tested.

Spinor-Based Attitude Determination with Star Sensor Considering Depth

2021 ◽  
Vol 87 (8) ◽  
pp. 551-556
Author(s):  
Qinghong Sheng ◽  
Rui Ren ◽  
Weilan Xu ◽  
Hui Xiao ◽  
Bo Wang ◽  
...  
Keyword(s):  
Attitude Determination ◽  
Geometric Condition ◽  
Depth Information ◽  
Star Sensor ◽  
Imaging Geometry ◽  
Straight Line Passing ◽  
Geometry Model ◽  
Straight Line ◽  
Order Of Magnitude ◽  
Line Passing

A star sensor is a high-precision satellite attitude measurement device. Since its observation information has only two-dimensional direction vectors, when a star sensor is used for attitude determination the dimension of the observation information is less than the number of attitude angles determined, so mainstream algorithms usually only guarantee the accuracy of the pitch angle and the roll angle. In view of the lack of depth information in the observation's imaging geometric condition, this article proposes a spinor-based attitude determination model, which describes a straight line passing through two stars with the spinor and maps the depth information of the straight line with the pitch, to establish an imaging geometry model of the spinor coplanar condition. Experiments show that the yaw-angle attitude accuracy of the method is an order of magnitude better than that of mainstream algorithms, and the accuracy of the three attitude angles reaches the arc-second level.

scholarly journals Horizontal Cervix as a Novel Sign for Predicting Adhesions on the Posterior Extrauterine Wall in Cases of Placenta Previa

2019 ◽  
Vol 8 (12) ◽  
pp. 2141 ◽  
Author(s):  
Shinya Matsuzaki ◽  
Aiko Okada ◽  
Masayuki Endo ◽  
Yoshikazu Nagase ◽  
Satoshi Nakagawa ◽  
...  
Keyword(s):  
Placenta Accreta ◽  
Placenta Previa ◽  
Area Under The Curve ◽  
Cervical Canal ◽  
Perpendicular Line ◽  
Straight Line ◽  
Line Passing ◽  
Adhesion Rate ◽  
Placenta Accreta Spectrum ◽  
Magnetic Resonance Imaging Mri

We aimed to identify a magnetic resonance imaging (MRI) feature that can predict posterior extrauterine adhesion (posterior adhesion) antenatally, in patients with placenta previa. We retrospectively reviewed patients with placenta previa who underwent a preoperative MRI examination of placenta accreta spectrum. We categorized the patients into two groups based on whether the cervix was anterior or posterior to a line perpendicular to the anatomical conjugate on the MRI. We projected the perpendicular line toward a straight line through the broad of the back on T2-weighted sagittal MRI images and measured the angle between this line and the line passing through the cervical canal. We analyzed the correlation of the cervical canal angle with the presence of posterior adhesions. Of the 96 patients analyzed, 71 patients had an anteverted cervix and 25 patients had a retroverted cervix. There were 21 posterior adhesions. The adhesion rate was significantly higher in patients with a retroverted cervix than those with an anteverted cervix (8.5% vs. 60%; p = 0.00). The cervical canal angle was ≤10° in 25 patients; of these 17 had adhesions (sensitivity, 81.0%; specificity, 89.3%; area under the curve, 0.887; 95% confidence interval, 0.792–0.981). This finding, labeled “positive horizontal cervix sign,” may be a promising indicator of posterior adhesions in patients with placenta previa.

Effects of altering ventilation on steady-state diffusing capacity for carbon monoxide

1963 ◽  
Vol 18 (1) ◽  
pp. 89-96 ◽  
Author(s):  
Kaye H. Kilburn ◽  
Harry A. Miller ◽  
John E. Burton ◽  
Ronald Rhodes
Keyword(s):  
Carbon Monoxide ◽  
Steady State ◽  
Tidal Volume ◽  
Lung Volume ◽  
Dead Space ◽  
Control Level ◽  
Alveolar Ventilation ◽  
Positive Pressure ◽  
Diffusing Capacity ◽  
Fixed Rate

Alterations in the steady-state diffusing capacity for carbon monoxide (Dco) by the method of Filley, MacIntosh, and Wright, produced by sequential changes in the pattern of breathing were studied in anesthetized, paralyzed, artificially ventilated dogs. The Dco of paralyzed, artificially ventilated control dogs did not differ significantly during 3 hr from values found in conscious and anesthetized controls. A fivefold increase in tidal volume without changing frequency of breathing raised alveolar ventilation and CO uptake 500% and Dco 186%. A high correlation between tidal volume and Dco was noted during reciprocal alterations of tidal volume and rate which maintained minute volume. The Dco appeared to fall when alveolar ventilation was tripled by increments of rate with a fixed-tidal volume, despite a 63% increase in CO uptake. Doubling end-expiratory lung volume by positive pressure breathing without altering tidal volume or rate did not affect Dco. The addition of 100 ml of external dead space with rate and tidal volume constant decreased Dco to 42% of control level, however, stepwise reduction of dead space from 100 ml to 0 in two dogs failed to change Dco. Added dead space equal to frac12 tidal volume (170 ml) reduced Dco to 25% of control in two dogs with a return to control with removal of dead space. Thus, in paralyzed artificially ventilated dogs, tidal volume appears to be the principal ventilatory determinant of steady-state Dco. Dco is minimally affected by increases in alveolar ventilation with a constant tidal volume effected by increasing the frequency of breathing. Prolonged ventilation, at fixed rate and volume, and increased dead space either did not effect, or they reduced Dco, perhaps by rendering less uniform the distribution of gas, and blood in the lungs. Although lung volume was doubled by positive-pressure breathing, pulmonary capillary blood volume was probably reduced to produce opposing effects on diffusing capacity and no net change. Submitted on March 14, 1962

Effects of forward acceleration on anatomical dead space

1965 ◽  
Vol 20 (6) ◽  
pp. 1205-1210 ◽  
Author(s):  
Charles Jacquemin ◽  
Jean Demange ◽  
Jean Timbal ◽  
Pierre Varene
Keyword(s):  
Mass Spectrometer ◽  
Dead Space ◽  
Human Subjects ◽  
Alveolar Plateau ◽  
Anatomical Dead Space ◽  
Ventilation Perfusion Ratio

The effects of transverse acceleration (1–5 G) on anatomical dead space have been studied on four human subjects. Instantaneous analysis of expired gases has been done by mass spectrometer. Half deflection between inspired gases and alveolar plateau levels is considered as the signal for the end of dead-space sweep. It is confirmed that no obstructive syndrome occurs during these accelerations. The airway size is not reduced; on the contrary, the anatomical dead space increases with the level of accelerations. Furthermore, a decreasing slope of the CO2 alveolar plateau has been noted on two subjects. These facts can be interpreted admitting a passive displacement of the pulmonary blood mass under influence of forward acceleration and the adjustment of ventilation to perfusion. transverse acceleration; mass spectrometer; ventilation-perfusion ratio Submitted on February 8, 1965

scholarly journals A mathematical model of odor dispersion from a wastewater treatment plant

2019 ◽  
Vol 138 ◽  
pp. 01029
Author(s):  
Valerii Azarov ◽  
Tat’yana Solov’eva ◽  
Sergei Svitskov
Keyword(s):  
Mathematical Model ◽  
Wind Direction ◽  
Treatment Plant ◽  
Straight Line Passing ◽  
Straight Line ◽  
Odor Character ◽  
Line Passing ◽  
Kaliningrad Region ◽  
Odor Dispersion

Smell is an important criterion of the quality of atmospheric air. The paper looks at quantitative and qualitative methods of odor assessment and describes the method of field olfactometry. Studies were carried out on the spread of odor from the WWTP OAO OKOS in the Kaliningrad region of Russia which resulted in 817 measurements. For each measurement, the following parameters were recorded: odor strength (D/T), odor character, atmospheric pressure (mmHg), temperature (°C), relative humidity (%), wind speed (m/s), wind direction and the the point where a measurement was taken. A mathematical model is given of the dependence of odor strength on the distance to two sources s1 (m) and s2 (m) and the wind direction from a straight line passing through a given point and a source 1 — a1 or a source 2 — a2.

scholarly journals THE RELATION BETWEEN CHLOROPHYLL CONTENT AND RATE OF PHOTOSYNTHESIS

1935 ◽  
Vol 18 (4) ◽  
pp. 573-597 ◽  
Author(s):  
Walter E. Fleischer
Keyword(s):  
Chlorophyll Content ◽  
Similar Data ◽  
Straight Line Passing ◽  
Iron Supply ◽  
Similar Relation ◽  
Straight Line ◽  
Rate Of Photosynthesis ◽  
Line Passing

1. Data are presented which support the conclusion of Emerson (1929) that the rate of photosynthesis is proportional to the chlorophyll content when the latter is varied by varying the iron supply. These data give a straight line passing through the origin, which is not true of Emerson's results. 2. Similar data are presented which show that a similar relation exists when nitrogen controls the chlorophyll content. 3. Evidence is given which indicates that magnesium plays a part in the process of photosynthesis in addition to its effect upon the chlorophyll content.

Physiological dead space during high-frequency ventilation in dogs

1984 ◽  
Vol 57 (3) ◽  
pp. 881-887 ◽  
Author(s):  
G. G. Weinmann ◽  
W. Mitzner ◽  
S. Permutt
Keyword(s):  
Gas Exchange ◽  
Tidal Volume ◽  
Dead Space ◽  
High Frequency ◽  
Minute Ventilation ◽  
Alveolar Ventilation ◽  
High Frequency Ventilation ◽  
Physiological Dead Space ◽  
Frequency Ventilation ◽  
Normal Ventilation

Tidal volumes used in high-frequency ventilation (HFV) may be smaller than anatomic dead space, but since gas exchange does take place, physiological dead space (VD) must be smaller than tidal volume (VT). We quantified changes in VD in three dogs at constant alveolar ventilation using the Bohr equation as VT was varied from 3 to 15 ml/kg and frequency (f) from 0.2 to 8 Hz, ranges that include normal as well as HFV. We found that VD was relatively constant at tidal volumes associated with normal ventilation (7–15 ml/kg) but fell sharply as VT was reduced further to tidal volumes associated with HFV (less than 7 ml/kg). The frequency required to maintain constant alveolar ventilation increased slowly as tidal volume was decreased from 15 to 7 ml/kg but rose sharply with attendant rapid increases in minute ventilation as tidal volumes were decreased to less than 7 ml/kg. At tidal volumes less than 7 ml/kg, the data deviated substantially from the conventional alveolar ventilation equation [f(VT - VD) = constant] but fit well a model derived previously for HFV. This model predicts that gas exchange with volumes smaller than dead space should vary approximately as the product of f and VT2.

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