The local matching of blood flow with ventilation is ________. Robb Glenny, MD 2019-02-18
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packet 22 chapter 22 Flashcards
Definition Transpulmonary pressure is a term used to describe the difference between the alveolar pressure and the intrapleural pressure in the lungs. Modern bronchodilators cause less hypoxemia than shown in Figure 4-26 and also less deterioration in the ventilation-perfusion ratio distribution. What are the effects of gravity? C The inspired oxygen concentration relative to the inspired ratio that is critical for absorption collapse. However, the findings suggest that susceptibility to pulmonary hypertension may be genetically determined, even in very young infants. Am Rev Respir Dis 116:919, 1977.
Distribution of blood flow and ventilation in the lung: gravity is not the only factor
Indeed, voluntary changes in breathing movements and diaphragm activity clearly affect regional ventilation and reduce the differences between lung regions. The large air spaces mean that some of the air breathed in gets nowhere close to a blood cell, while the loss of capillaries means that some areas of the lung are not getting much blood, while others are getting too much blood. Selected contribution: redistribution of pulmonary perfusion during weightlessness and increased gravity. Sixteen patients with chronic bronchitis and airways obstruction were given radioactive nitrogen 13N by intravenous injection and by inhalation, while breathing air and after 10-20 min breathing 30% oxygen. However, it is interesting that these patients generally do not show much shunting blood flow to unventilated alveoli , and a possible explanation is collateral ventilation. The left lung is composed of only two lobes, separated midway by an interlobular fissure.
Calculation of the standard deviation of pulmonary blood flow provides a quantitative index of dispersion of about the mean value, separate from shunt and dead space. The arrow on the abscissa indicates solubility that is numerically equal to mean in the lung. Each quantity is measured in litres per minute and taking the lungs as a whole, typical resting values might be 4 l. Right: Vascular tree with asymmetrical branching that leads to neighboring regions having similar flows. However, it should be noted that the confidence limits of these relationships not shown are very large. If ventilation and perfusion of all alveoli were the same, then would be 0. They found variations in perfusion in all three conditions, at the same gravitational plane, and this heterogeneity is the most convincing argument against gravity being responsible for blood flow variation.
The local matching of blood flow with ventilation is ________. the local matching of blood flow with
The alveolar and are thus determined by the relationship between alveolar ventilation and pulmonary capillary perfusion. Gravity is a minor determinant of pulmonary blood flow distribution. Therefore, the right ventricle has time to adapt to the modest increase in afterload. The results suggest that local hypoxic vasoconstriction is present in some patients on breathing air and that this is relieved by 30% oxygen, resulting in a diversion of local blood flow from well-ventilated to more poorly ventilated areas. However, evidence shows that neonatal lambs have an already fully recruited microvasculature, at least as assessed by direct vital microscopy during hypoxia. The lower diagram indicates the orientation of the lung in relation to gravity.
In addition, the most dominant respiratory stimulus for breathing in a healthy person is upsurge of carbon dioxide and with the bohr effect more oxygen is unconfined because reduction in ph or acidosis deteriorates the hemoglobin oxygen bond. Teleologically, hypoxic vasoconstriction plays a fundamental role in matching pulmonary blood flow to alveolar ventilation. Alveoli with no perfusion ratio of infinity will have P o 2 and P co 2 values that are the same as those of the inspired gas, because there is no gas exchange to alter the composition of the inspired gas that is drawn into these alveoli. Distribution of blood flow and ventilation in the lung: gravity is not the only factor. The suggestion has been made that this term should be abandoned in favor of a more precise definition based on objective evidence of right ventricular hypertrophy, enlargement, functional abnormality, or failure.
In the lungs, mucus functions to smooth the airways linings and traps foreign substances that invade the respiratory system. Three-compartment Riley model of gas exchange. Studies in animals have also found more uniform distribution of alveolar ventilation in the prone position. Pulmonary changes in these conditions mimic those seen in acute lung injury, and hypergravity has been used by several authors as a model of acute lung injury. Hyperoxia-treated animals demonstrated diminished hemodynamic response and deterioration in matching during exposure to acute vasoconstrictive stimuli, including alveolar hypoxia.
Early studies used radioactive gases with collimated scintillation counters over the chest wall to detect the inhaled gases. In the lung, it provides an efficient mechanism to yield a vast surface area of approximately 130 m within a limited volume of 5—6 litres. Down to the scale of the acinus, there is considerable heterogeneity in the distribution of both ventilation and blood flow. Trace quantities of inert gases can be used to quantitate the continuous distribution of ventilation-perfusion ratios from shunt to dead space of 0 to to infinity. A intrapleural pressure is lower than transpulmonary pressure B intrapleural pressure is higher than intrapulmonary pressure C intrapulmonary pressure is lower than transpulmonary pressure D intrapulmonary pressure is higher than atmospheric pressure Answer B intrapleural pressure is higher than intrapulmonary pressure A internal intercostals and abdominal muscles would contract B diaphragm contracts, internal intercostals would relax C diaphragm would contract, external intercostals would relax D external intercostals would contract and diaphragm would relax Answer A internal intercostals and abdominal muscles would contract A increase in pH alkalosis strengthens the hemoglobin-oxygen bond B decrease in pH acidosis strengthens the hemoglobin-oxygen bond C increase in pH alkalosis weakens the hemoglobin-oxygen bond D decrease in pH acidosis weakens the hemoglobin-oxygen bond Answer D decrease in pH acidosis weakens the hemoglobin-oxygen bond.
Distribution of blood flow and ventilation in the lung: gravity is not the only factor
The effects of dry inhaled gases, positive-pressure ventilation, and high inspired oxygen content also contribute to ciliary impairment. There was a marked increase in the amount of blood flow to low ventilation-perfusion ratio units, and this was associated with a corresponding decrease in arterial P o 2 from 81 to 70 mm Hg. The flow dependence found in the upright position was more marked than when the subjects were supine. This is crucial because it can add to the alterations in blood gases produced directly by the pathology. This suggests that there are differences in pleural pressure swings between the different regions, and such differences can affect regional ventilation and its dependence on the inspiratory flow. These concentration differences must be maintained by ventilation of the alveoli and perfusion of the pulmonary capillaries. Gas exchange between the alveoli and the pulmonary capillary blood occurs by diffusion, as will be discussed in the next chapter.
