Case Studies in Physiology: Ventilation and perfusion in a giraffe–does size matter?

The trachea in the giraffe is long but narrow, and dead space ventilation is considered to be of approximately the same size as in other mammals. Less is known about the matching between ventilation and lung blood flow. The lungs in the giraffe are large, up to 1 m high and 0.7 m wide, and this may cause considerable ventilation/perfusion (VA/Q) mismatch due to the influence of gravitational forces, which could lead to hypoxemia. We studied a young giraffe under anesthesia using the multiple inert gas elimination technique to analyze the VA/Q distribution and arterial oxygenation and compared the results with those obtained in other species of different sizes, including humans. VA/Q distribution was broad but unimodal, and the shunt of blood flow through nonventilated lung regions was essentially absent, suggesting no lung collapse. The VA/Q match was as good as in the similarly sized horse and was even comparable to that in smaller sized animals, including rabbit and rat. The match was also similar to that in anesthetized humans. Arterial oxygenation was essentially similar in all studied species. The findings suggest that the efficiency of VA/Q matching is independent of lung size in the studied mammals that vary in weight from less than 1 to more than 400 kg.

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Redistribution of pulmonary blood flow in the dog with PEEP ventilation

Journal of Applied Physiology ◽

10.1152/jappl.1979.46.2.278 ◽

1979 ◽

Vol 46 (2) ◽

pp. 278-287 ◽

Cited By ~ 52

Author(s):

G. Hedenstierna ◽

F. C. White ◽

R. Mazzone ◽

P. D. Wagner

Keyword(s):

Blood Flow ◽

Cardiac Output ◽

Pulmonary Blood Flow ◽

Continuous Distribution ◽

Isolated Lung ◽

Flow Through ◽

Peep Ventilation ◽

Isolated Lungs ◽

The Vertical Distribution ◽

Ventilation And Perfusion

The effects of positive end-expiratory pressure (PEEP) at 20 cmH2O on the distribution of pulmonary blood flow was studied in intact dogs and isolated lung preparations. Measurements were made of a) the continuous distribution of ventilation-perfusion ratios (VA/Q), b) the vertical distribution of pulmonary blood flow, and c) the dimensions of the microvasculature. Without PEEP the distributions of ventilation and perfusion were unimodal and centered on a VA/Q close to one. Dependent regions received 5–10 times more of cardiac output than uppermost regions. With PEEP the distribution showed a bimodal character, one mode of normal VA/Q and the other comprising one-third of ventilation, lying between VA/Q of 10 and 100. Cardiac output was reduced two- to threefold and blood flow in the uppermost regions was grossly reduced but not eliminated. Bimodal distributions were also found in isolated lungs with PEEP, and histological examination of rapidly frozen lung tissue showed that alveolar capillaries were closed in the uppermost, poorly perfused regions, whereas alveolar corner vessels remained open. We suggest that the blood flow through these corner vessels is responsible for the additional, high VA/Q mode during PEEP.

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Unsteady blood flow through severe stenosis in an artery under the effects of gravitational forces

10.1063/1.4932445 ◽

2015 ◽

Author(s):

Yan Bin Tan ◽

Norzieha Mustapha

Keyword(s):

Blood Flow ◽

Severe Stenosis ◽

Gravitational Forces ◽

Flow Through ◽

Unsteady Blood Flow

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Factors affecting regional distribution of ventilation and perfusion in the lung

Journal of Applied Physiology ◽

10.1152/jappl.1964.19.3.395 ◽

1964 ◽

Vol 19 (3) ◽

pp. 395-402 ◽

Cited By ~ 160

Author(s):

A. C. Bryan ◽

L. G. Bentivoglio ◽

F. Beerel ◽

H. MacLeish ◽

A. Zidulka ◽

...

Keyword(s):

Blood Flow ◽

Regional Distribution ◽

Normal Subjects ◽

Bicycle Ergometer ◽

Upright Posture ◽

Progressive Decrease ◽

Factors Affecting ◽

Flow Through ◽

Xenon 133 ◽

Ventilation And Perfusion

Regional distribution of ventilation and perfusion in the lung has been studied using Xe133 in normal subjects. In 31 subjects seated upright at rest the previous findings of a gradient of ventilation and perfusion distribution from apex to base of the lung, have been confirmed. The results agree well with those obtained using C15O2. In seven normal subjects lying supine, the V/Q distribution from apex to base of the lung is much more uniform, though a perfusion gradient can be shown to exist from front to back. Five normal subjects exercising on a bicycle ergometer in the upright posture were found to have a proportionately much greater blood flow through the upper zone of the lung than when in the same position at rest. One study during induced syncope on standing indicated that this state is accompanied by a progressive decrease in perfusion to the upper zones of the lung. No change in distribution occurred breathing 100% oxygen. xenon 133; posture; exercise; syncope; oxygen Submitted on August 30, 1963

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Effects of common dead space on inert gas exchange in mathematical models of the lung

Journal of Applied Physiology ◽

10.1152/jappl.1979.47.4.896 ◽

1979 ◽

Vol 47 (4) ◽

pp. 896-906 ◽

Cited By ~ 14

Author(s):

J. B. Fortune ◽

P. D. Wagner

Keyword(s):

Blood Flow ◽

Gas Exchange ◽

Dead Space ◽

The Other ◽

Inert Gas ◽

Mixed Gas ◽

Space Model ◽

Different Types ◽

The Dead ◽

Ventilation And Perfusion

Theoretical gas exchange is compared in lung models having two different types of dead space. In one, the dead space of a lung unit is “personal” and contains gas equivalent in composition to its own alveolar gas; in the other, the dead space is “common” and contains mixed gas from all gas-exchanging units. Formal algebraic analysis of tracer inert gas exchange in two-compartment models shows that values of compartmental ventilation and perfusion can be found that establish one and only one personal dead-space model equivalent for every common dead-space model. When the total dead space and distribution of blood flow and ventilation in the two models are the same, common dead space will always result in improved inert gas elimination. Under these conditions, the amount of improvement is usually greatest when the partition coefficient of the inert gas is between 0.1 and 1.0 and when there is greatest disparity in the ventilation-perfusion ratios (VA/Q). In the inert gas elimination technique that analyzes all dead space as personal, the presence of common dead space consistently causes the recovered VA/Q distributions to be narrower than the actual distributions, but the resultant error is small.

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Ventilation-perfusion relationships after hemorrhage and resuscitation: an inert gas analysis

Journal of Applied Physiology ◽

10.1152/jappl.1983.54.4.1131 ◽

1983 ◽

Vol 54 (4) ◽

pp. 1131-1140 ◽

Cited By ~ 3

Author(s):

N. B. Robinson ◽

E. Y. Chi ◽

H. T. Robertson

Keyword(s):

Blood Flow ◽

Hemorrhagic Shock ◽

Dead Space ◽

Pulmonary Blood Flow ◽

Autologous Blood ◽

Regional Distribution ◽

Gas Analysis ◽

Inert Gas ◽

Base Line ◽

Dead Space Ventilation

Previous investigations suggest that ventilation-perfusion (VA/Q) relationships after hemorrhagic shock are primarily dependent on regional distribution of pulmonary blood flow and implicated early VA/Q heterogeneity secondary to disproportionate redistribution of pulmonary blood flow to dependent lung regions. Multiple inert gas elimination analysis, as described by Wagner et al. (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 36: 588–599, 1974), was applied to a standard hemorrhagic shock preparation to test this hypothesis. Soon after hemorrhage, VA/Q distributions shifted homogeneously into high VA/Q compartments, preserving base-line VA/Q relationships around a new mean VA/Q ratio. Although the mean VA/Q and VA/Q distribution returned to base line after resuscitation with autologous blood, absolute dead space ventilation persisted. Gas exchange defects included increased Bohr dead space ventilation, which could be attributed to 1) a homogeneous shift of VA/Q distributions into high VA/Q compartments, and 2) new absolute dead space ventilation associated with observed intravascular leukostasis and vascular occlusion. In contrast to previous investigations, these data suggest that VA/Q heterogeneity does not occur after hemorrhage, but rather pulmonary blood flow decreases proportionately throughout all lung regions, preserving base-line VA/Q patterns around a new mean VA/Q ratio.

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