Ventilation‐perfusion ratio: A Mathematical Approach for Gas Exchange in the Lungs

We measured resting pulmonary gas exchange in eight subjects exposed to 9 or 14 days of microgravity (microG) during two Spacelab flights. Compared with preflight standing measurements, microG resulted in a significant reduction in tidal volume (15%) but an increase in respiratory frequency (9%). The increased frequency was caused chiefly by a reduction in expiratory time (10%), with a smaller decrease in inspiratory time (4%). Anatomic dead space (VDa) in microG was between preflight standing and supine values, consistent with the known changes in functional residual capacity. Physiological dead space (VDB) decreased in microG, and alveolar dead space (VDB-VDa) was significantly less in microG than in preflight standing (-30%) or supine (-15%), consistent with a more uniform topographic distribution of blood flow. The net result was that, although total ventilation fell, alveolar ventilation was unchanged in microG compared with standing in normal gravity (1 G). Expired vital capacity was increased (6%) compared with standing but only after the first few days of exposure to microG. There were no significant changes in O2 uptake, CO2 output, or end-tidal PO2 in microG compared with standing in 1 G. End-tidal PCO2 was unchanged on the 9-day flight but increased by 4.5 Torr on the 14-day flight where the PCO2 of the spacecraft atmosphere increased by 1–3 Torr. Cardiogenic oscillations in expired O2 and CO2 demonstrated the presence of residual ventilation-perfusion ratio (VA/Q) inequality. In addition, the change in intrabreath VA/Q during phase III of a long expiration was the same in microG as in preflight standing, indicating persisting VA/Q inequality and suggesting that during this portion of a prolonged exhalation the inequality in 1 G was not predominantly on a gravitationally induced topographic basis. However, the changes in PCO2 and VA/Q at the end of expiration after airway closure were consistent with a more uniform topographic distribution of gas exchange.

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Lung cytokinetics after exposure to hypobaria and/or hypoxia and undernutrition in growing rats

Journal of Applied Physiology ◽

10.1152/jappl.1995.79.4.1299 ◽

1995 ◽

Vol 79 (4) ◽

pp. 1299-1309 ◽

Cited By ~ 5

Author(s):

H. S. Sekhon ◽

W. M. Thurlbeck

Keyword(s):

Gas Exchange ◽

Dead Space ◽

Normal Gravity ◽

Phase Iii ◽

Physiological Dead Space ◽

Co2 Output ◽

Residual Capacity ◽

End Tidal ◽

Ventilation Perfusion Ratio ◽

Topographic Distribution

We measured resting pulmonary gas exchange in eight subjects exposed to 9 or 14 days of microgravity (microG) during two Spacelab flights. Compared with preflight standing measurements, microG resulted in a significant reduction in tidal volume (15%) but an increase in respiratory frequency (9%). The increased frequency was caused chiefly by a reduction in expiratory time (10%), with a smaller decrease in inspiratory time (4%). Anatomic dead space (VDa) in microG was between preflight standing and supine values, consistent with the known changes in functional residual capacity. Physiological dead space (VDB) decreased in microG, and alveolar dead space (VDB-VDa) was significantly less in microG than in preflight standing (-30%) or supine (-15%), consistent with a more uniform topographic distribution of blood flow. The net result was that, although total ventilation fell, alveolar ventilation was unchanged in microG compared with standing in normal gravity (1 G). Expired vital capacity was increased (6%) compared with standing but only after the first few days of exposure to microG. There were no significant changes in O2 uptake, CO2 output, or end-tidal PO2 in microG compared with standing in 1 G. End-tidal PCO2 was unchanged on the 9-day flight but increased by 4.5 Torr on the 14-day flight where the PCO2 of the spacecraft atmosphere increased by 1–3 Torr. Cardiogenic oscillations in expired O2 and CO2 demonstrated the presence of residual ventilation-perfusion ratio (VA/Q) inequality. In addition, the change in intrabreath VA/Q during phase III of a long expiration was the same in microG as in preflight standing, indicating persisting VA/Q inequality and suggesting that during this portion of a prolonged exhalation the inequality in 1 G was not predominantly on a gravitationally induced topographic basis. However, the changes in PCO2 and VA/Q at the end of expiration after airway closure were consistent with a more uniform topographic distribution of gas exchange.

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A Mathematical Approach for Gas Exchange in the Lungs; Balance Between Ventilation and Perfusion

The FASEB Journal ◽

10.1096/fasebj.2018.32.1_supplement.627.2 ◽

2018 ◽

Vol 32 (S1) ◽

Author(s):

ALEJANDRO PIZANO ◽

PAOLA CALVACHI ◽

FELIPE GIRÓN ◽

JUAN MANUEL CORDOVEZ

Keyword(s):

Gas Exchange ◽

Mathematical Approach ◽

Ventilation And Perfusion

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Regional differences in gas exchange in the lung of erect man

Journal of Applied Physiology ◽

10.1152/jappl.1962.17.6.893 ◽

1962 ◽

Vol 17 (6) ◽

pp. 893-898 ◽

Cited By ~ 193

Author(s):

J. B. West

Keyword(s):

Blood Flow ◽

Gas Exchange ◽

Lung Volume ◽

Regional Differences ◽

Capillary Blood ◽

O2 Uptake ◽

Regional Ventilation ◽

Ventilation Perfusion Ratio ◽

Ph Variations

Measurements of regional ventilation and blood flow using radioactive CO2 show that both increase from apex to base of the lung; the results are used to build an integrated picture of gas exchange. Ventilation-perfusion ratios at nine levels of the lung have been calculated and differences in local gas exchange deduced. In the resulting model, alveolar O2 tension changes by more than 40 mm Hg from apex to base while CO2 and N2 tensions change by about 14 and 29 mm Hg, respectively. Maximal differences in O2 saturation of end-capillary blood are 4% but differences in CO2 contents of 7 vol % and pH variations of 0.12 units occur. The O2 uptake per unit lung volume increases eightfold down the lung while corresponding variations in CO2 output are less than threefold. N2 passes out of the blood in upper parts of the lung but into the blood in basal regions (net exchange is zero). Over-all O2 uptake and CO2 outputs are reduced by only 2–3% by the ventilation-perfusion ratio inequality, causing alveolar-arterial differences of 4, 1, and 3 mm Hg for O2, CO2, and N2, respectively. Submitted on April 6, 1962

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Identification of functional lung unit in the dog by graded vascular embolization

Journal of Applied Physiology ◽

10.1152/jappl.1980.49.1.132 ◽

1980 ◽

Vol 49 (1) ◽

pp. 132-141 ◽

Cited By ~ 42

Author(s):

I. Young ◽

R. W. Mazzone ◽

P. D. Wagner

Keyword(s):

Gas Exchange ◽

Histological Examination ◽

Inert Gas ◽

Polystyrene Beads ◽

Lung Unit ◽

Bead Size ◽

Exchange Unit ◽

Ventilation Perfusion Ratio

To study the dimensions of the functional gas exchange unit, spherical polystyrene beads (diam 50-500 micrometers) were injected intravenously into 12 normal anesthetized paralyzed dogs (15-24 kg wt). We argued that beads small enough to lodge within gas exchange units would not give rise to a population of high ventilation-perfusion ratio (VA/Q) areas, whereas embolization of larger vessels supplying these units would. Each dog received only one bead size in cumulative 0.25-g doses up to a maximum of 2.25 g. Multiple inert gas elimination data were obtained after each dose to monitor the development of high VA/Q regions. Injection of 50- and 100-micrometers beads never gave rise to high VA/Q regions, whereas 150-, 250-, and 500-micrometers beads consistently induced a high VA/Q mode comprising up to 45% of the ventilation. Histological examination of lungs from five additional dogs injected with small (approximately 0.5 g) doses revealed that beads rarely formed clusters and appeared in vessels of their own diameter in over 90% of instances. By the above criterion, the functional gas exchange unit in these lungs is that volume of tissue subtended by 150- micrometers-diam arteries (vessels associated with respiratory bronchioles).

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Effects of an open lung ventilatory strategy on lung gas exchange during laparoscopic surgery

Anaesthesia and Intensive Care ◽

10.1177/0310057x211047602 ◽

2021 ◽

pp. 0310057X2110476

Author(s):

Philip J Peyton ◽

Sarah Aitken ◽

Mats Wallin

Keyword(s):

Laparoscopic Surgery ◽

Gas Exchange ◽

Partial Pressure ◽

Intervention Group ◽

Lung Ventilation ◽

Alveolar Ventilation ◽

Control Group ◽

Positive End Expiratory Pressure ◽

Open Lung ◽

Ventilation Perfusion Ratio

In general anaesthesia, early collapse of poorly ventilated lung segments with low alveolar ventilation–perfusion ratios occurs and may lead to postoperative pulmonary complications after abdominal surgery. An ‘open lung’ ventilation strategy involves lung recruitment followed by ‘individualised’ positive end-expiratory pressure titrated to maintain recruitment of low alveolar ventilation–perfusion ratio lung segments. There are limited data in laparoscopic surgery on the effects of this on pulmonary gas exchange. Forty laparoscopic bowel surgery patients were randomly assigned to standard ventilation or an ‘open lung’ ventilation intervention, with end-tidal target sevoflurane of 1% supplemented by propofol infusion. After peritoneal insufflation, stepped lung recruitment was performed in the intervention group followed by maintenance positive end-expiratory pressure of 12–15 cmH2O adjusted to maintain dynamic lung compliance at post-recruitment levels. Baseline gas and blood samples were taken and repeated after a minimum of 30 minutes for oxygen and carbon dioxide and for sevoflurane partial pressures using headspace equilibration. The sevoflurane arterial/alveolar partial pressure ratio and alveolar deadspace fraction were unchanged from baseline and remained similar between groups (mean (standard deviation) control group = 0.754 (0.086) versus intervention group = 0.785 (0.099), P = 0.319), while the arterial oxygen partial pressure/fractional inspired oxygen concentration ratio was significantly higher in the intervention group at the second timepoint (control group median (interquartile range) 288 (234–372) versus 376 (297–470) mmHg in the intervention group, P = 0.011). There was no difference between groups in the sevoflurane consumption rate. The efficiency of sevoflurane uptake is not improved by open lung ventilation in laparoscopy, despite improved arterial oxygenation associated with effective and sustained recruitment of low alveolar ventilation–perfusion ratio lung segments.

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Ventilation-perfusion lines and gas exchange in liquid breathing: theory

Journal of Applied Physiology ◽

10.1152/jappl.1980.49.2.262 ◽

1980 ◽

Vol 49 (2) ◽

pp. 262-269 ◽

Cited By ~ 2

Author(s):

S. V. Matalon ◽

L. E. Farhi

Keyword(s):

Gas Exchange ◽

Partition Coefficient ◽

Dissociation Curve ◽

Co2 Solubility ◽

Solubility Coefficients ◽

Ventilation Perfusion Ratio ◽

Ostwald Coefficients ◽

Mixed Venous ◽

Q Values ◽

Co2 Elimination

Alveolar exchange of a gas is governed by the ventilation-perfusion ratio (VA/Q) and the Ostwald partition coefficient for that species. We altered the Ostwald coefficients for O2 and CO2 by considering an animal breathing water or a fluorocarbon (FC-80) and studied the effects on gas exchange. Among our conclusions are the following. 1) When the ratio of the CO2 to O2 solubility in the inspirate exceeds the ratio of the O2 to the CO2 slope of the blood dissociation curve, as in water breathing, the VA/Q line becomes concave upward, and elements having a low VA/Q differ from each other more in terms of CO2 than of O2. 2) As the ratio of the CO2 to O2 solubility in the inspired medium increases, CO2 elimination becomes more dependent on perfusion. 3) At times, the same R will prevail in areas having different VA/Q values. 4) The alveolar-to-arterial O2 and CO2 differences resulting from a given VA/Q distribution do not depend on the O2 and CO2 solubility coefficients of the inspired medium, but on the inspired and mixed venous concentrations necessary to maintain adequate arterial gas levels in the presence of different inspired media.

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