Gas exchange in dogs in the prone and supine positions

To determine the cause of the difference in gas exchange between the prone and supine postures in dogs, gas exchange was assessed by the multiple inert gas elimination technique (MIGET) and distribution of pulmonary blood flow was determined using radioactively labeled microspheres in seven anesthetized paralyzed dogs. Each animal was studied in the prone and supine positions in random order while tidal volume and respiratory frequency were kept constant with mechanical ventilation. Mean arterial PO2 was significantly lower (P less than 0.01) in the supine [96 +/- 10 (SD) Torr] than in the prone (107 +/- 6 Torr) position, whereas arterial PCO2 was constant (38 Torr). The distribution of blood flow (Q) vs. ventilation-to-perfusion ratio obtained from MIGET was significantly wider (P less than 0.01) in the supine [ln SD(Q) = 0.75 +/- 0.26] than in the prone position [ln SD (Q) = 0.34 +/- 0.05]. Right-to-left pulmonary shunting was not significantly altered. The distribution of microspheres was more heterogeneous in the supine than in the prone position. The larger heterogeneity was due in part to dorsal-to-ventral gradients in Q in the supine position that were not present in the prone position (P less than 0.01). The decreased efficiency of oxygenation in the supine posture is caused by an increased ventilation-to-perfusion mismatch that accompanies an increase in the heterogeneity of Q distribution.

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Mechanisms of improvement in pulmonary gas exchange during isovolemic hemodilution

Journal of Applied Physiology ◽

10.1152/jappl.1999.87.1.132 ◽

1999 ◽

Vol 87 (1) ◽

pp. 132-141 ◽

Cited By ~ 39

Author(s):

Steven Deem ◽

Richard G. Hedges ◽

Steven McKinney ◽

Nayak L. Polissar ◽

Michael K. Alberts ◽

...

Keyword(s):

Blood Flow ◽

Fractal Dimension ◽

Gas Exchange ◽

Spatial Correlation ◽

Pulmonary Blood Flow ◽

Minute Ventilation ◽

Flow Distribution ◽

Pulmonary Gas Exchange ◽

Normal Lung ◽

Blood Flow Distribution

Severe anemia is associated with remarkable stability of pulmonary gas exchange (S. Deem, M. K. Alberts, M. J. Bishop, A. Bidani, and E. R. Swenson. J. Appl. Physiol. 83: 240–246, 1997), although the factors that contribute to this stability have not been studied in detail. In the present study, 10 Flemish Giant rabbits were anesthetized, paralyzed, and mechanically ventilated at a fixed minute ventilation. Serial hemodilution was performed in five rabbits by simultaneous withdrawal of blood and infusion of an equal volume of 6% hetastarch; five rabbits were followed over a comparable time. Ventilation-perfusion (V˙a/Q˙) relationships were studied by using the multiple inert-gas-elimination technique, and pulmonary blood flow distribution was assessed by using fluorescent microspheres. Expired nitric oxide (NO) was measured by chemiluminescence. Hemodilution resulted in a linear fall in hematocrit over time, from 30 ± 1.6 to 11 ± 1%. Anemia was associated with an increase in arterial [Formula: see text] in comparison with controls ( P < 0.01 between groups). The improvement in O2 exchange was associated with reducedV˙a/Q˙heterogeneity, a reduction in the fractal dimension of pulmonary blood flow ( P = 0.04), and a relative increase in the spatial correlation of pulmonary blood flow ( P = 0.04). Expired NO increased with anemia, whereas it remained stable in control animals ( P < 0.0001 between groups). Anemia results in improved gas exchange in the normal lung as a result of an improvement in overallV˙a/Q˙matching. In turn, this may be a result of favorable changes in pulmonary blood flow distribution, as assessed by the fractal dimension and spatial correlation of blood flow and as a result of increased NO availability.

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Effects of Vaporized Perfluorocarbon on Pulmonary Blood Flow and Ventilation/Perfusion Distribution in a Model of Acute Respiratory Distress Syndrome

Anesthesiology ◽

10.1097/00000542-200112000-00021 ◽

2001 ◽

Vol 95 (6) ◽

pp. 1414-1421 ◽

Cited By ~ 12

Author(s):

Matthias Hübler ◽

Jennifer E. Souders ◽

Erin D. Shade ◽

Nayak L. Polissar ◽

Carmel Schimmel ◽

...

Keyword(s):

Blood Flow ◽

Oleic Acid ◽

Gas Exchange ◽

Lung Injury ◽

Repeated Measures ◽

Pulmonary Blood Flow ◽

Analysis Of Covariance ◽

Inert Gas ◽

Low Flow ◽

Repeated Measures Analysis

Background Perfluorocarbon (PFC) liquids are known to improve gas exchange and pulmonary function in various models of acute respiratory failure. Vaporization has been recently reported as a new method of delivering PFC to the lung. Our aim was to study the effect of PFC vapor on the ventilation/perfusion (VA/Q) matching and relative pulmonary blood flow (Qrel) distribution. Methods In nine sheep, lung injury was induced using oleic acid. Four sheep were treated with vaporized perfluorohexane (PFX) for 30 min, whereas the remaining sheep served as control animals. Vaporization was achieved using a modified isoflurane vaporizer. The animals were studied for 90 min after vaporization. VA/Q distributions were estimated using the multiple inert gas elimination technique. Change in Qrel distribution was assessed using fluorescent-labeled microspheres. Results Treatment with PFX vapor improved oxygenation significantly and led to significantly lower shunt values (P < 0.05, repeated-measures analysis of covariance). Analysis of the multiple inert gas elimination technique data showed that animals treated with PFX vapor demonstrated a higher VA/Q heterogeneity than the control animals (P < 0.05, repeated-measures analysis of covariance). Microsphere data showed a redistribution of Qrel attributable to oleic acid injury. Qrel shifted from areas that were initially high-flow to areas that were initially low-flow, with no difference in redistribution between the groups. After established injury, Qrel was redistributed to the nondependent lung areas in control animals, whereas Qrel distribution did not change in treatment animals. Conclusion In oleic acid lung injury, treatment with PFX vapor improves gas exchange by increasing VA/Q heterogeneity in the whole lung without a significant change in gravitational gradient.

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Simulation of Gas Exchange and Pulmonary Blood Flow Using a Water-Displacement Model Lung

Advances in Experimental Medicine and Biology - Oxygen Transport to Tissue XVII ◽

10.1007/978-1-4613-0333-6_33 ◽

1996 ◽

pp. 257-264

Author(s):

E. M. Williams

Keyword(s):

Blood Flow ◽

Gas Exchange ◽

Pulmonary Blood Flow ◽

Water Displacement ◽

Model Lung ◽

Displacement Model

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EFFECTIVE PULMONARY BLOOD FLOW IN PRETERM INFANTS WITH AND WITHOUT RESPIRATORY DISTRESS: A SIMPLE BEDSIDE METHOD USING NITROUS OXIDE

PEDIATRICS ◽

10.1542/peds.52.2.179 ◽

1973 ◽

Vol 52 (2) ◽

pp. 179-187

Author(s):

Richard L'E Orme ◽

Elizabeth A. Featherby ◽

Henrique Rigatto ◽

Francisco J. Cervantes ◽

June P. Brady

Keyword(s):

Blood Flow ◽

Nitrous Oxide ◽

Respiratory Distress ◽

Preterm Infants ◽

Pulmonary Blood Flow ◽

Noninvasive Technique ◽

Pulmonary Capillary Blood Flow ◽

Normal Limits ◽

Bedside Method ◽

Arterial Po2

We have devised a method of measuring pulmonary capillary blood flow (Qpc eff) suitable for infants with idiopathic respiratory distress syndrome (IRDS). The uptake of nitrous oxide is measured during a 40-second period of rebreathing 40% nitrous oxide in oxygen from a 40- to 80-ml bag. The rate of uptake of nitrous oxide is divided by the solubility in cord blood and the mean alveolar concentration to give Qpc eff. We studied 14 preterm infants, 7 hours to 14 days of age, on 73 occasions; nine had classical IRDS and five were healthy preterm infants (controls). During the first five days of life Qpc eff was significantly lower in infants with IRDS than in the control infants, 106 ml/kg/min compared with 177 ml/kg/min (P < 0.001). Qpc eff was not related to arterial Po2, Pco2, or pH but was inversely related to the inspired oxygen concentration needed to keep the arterial Po2 within normal limits (P < 0.02). Qpc eff showed a highly significant increase with age in infants with IRDS (P < 0.001). This method provides a reasonably rapid, safe and noninvasive technique for estimating effective pulmonary blood flow in sick infants.

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Ventilation-perfusion inequality during constant-flow ventilation

Journal of Applied Physiology ◽

10.1152/jappl.1987.62.3.1255 ◽

1987 ◽

Vol 62 (3) ◽

pp. 1255-1263 ◽

Cited By ~ 8

Author(s):

P. T. Schumacker ◽

J. I. Sznajder ◽

A. Nahum ◽

L. D. Wood

Keyword(s):

Blood Flow ◽

Gas Exchange ◽

Lung Volume ◽

Intermittent Positive Pressure Ventilation ◽

Positive Pressure ◽

Asymmetric Distribution ◽

Constant Flow ◽

Arterial Pco2 ◽

Continuous Stream ◽

Anesthetized Dogs

Previous work by Lehnert et al. (J. Appl. Physiol. 53:483–489, 1982) has demonstrated that adequate alveolar ventilation can be maintained during apnea in anesthetized dogs by delivering a continuous stream of inspired ventilation through cannulas aimed down the main-stem bronchi. Because an asymmetric distribution of ventilation might introduce ventilation-perfusion (VA/Q) inequality, we compared gas exchange efficiency in nine anesthetized and paralyzed dogs during constant-flow ventilation (CFV) and conventional ventilation (intermittent positive-pressure ventilation, IPPV). Gas exchange was assessed using the multiple inert gas elimination technique. During CFV at 3 l X kg-1 X min-1, lung volume, retention-excretion differences (R-E*) for low- and medium-solubility gases, and the log standard deviation of blood flow (log SD Q) increased, compared with the findings during IPPV. Reducing CFV flow rate to 1 l X kg-1 X min-1 at constant lung volume improved R-E* and log SD Q, but significant VA/Q inequality compared with that at IPPV remained and arterial PCO2 rose. Comparison of IPPV and CFV at the same mean lung volume showed a similar reversible deterioration in gas exchange efficiency during CFV. We conclude that CFV causes significant VA/Q inequality which may be due to nonuniform ventilation distribution and a redistribution of pulmonary blood flow.

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Effect of acceleration on the distribution of pulmonary blood flow

Journal of Applied Physiology ◽

10.1152/jappl.1965.20.6.1129 ◽

1965 ◽

Vol 20 (6) ◽

pp. 1129-1132 ◽

Cited By ~ 16

Author(s):

A. C. Bryan ◽

W. D. Macnamara ◽

J. Simpson ◽

H. N. Wagner

Keyword(s):

Blood Flow ◽

Gas Exchange ◽

Pulmonary Blood Flow ◽

Lung Perfusion ◽

Centrifugal Acceleration ◽

Vascular Bed ◽

Macroaggregated Albumin ◽

Iodine 131 ◽

Pulmonary Vascular Bed

The distribution of pulmonary blood flow has been measured during increased positive (+Gz) acceleration. Macroaggregated albumin labeled with iodine 131 was injected intravenously during centrifugal acceleration, by the method described by Wagner and co-workers. The particles embolize the pulmonary vascular bed in proportion to flow and can be subsequently detected by scintillation scanning of the lung. One study was done in one subject in one of the five following conditions: supine, seated, +2 Gz, +3 Gz, and +4 Gz. The results show a progressively smaller reduction in upper zone perfusion with increasing acceleration agreeing with hydrostatic principles. Flow increased in the base up to +2 Gz but thereafter becomes fixed, suggesting that the vessels were then maximally dilated. The gas exchange consequences of these changes of perfusion are discussed indicating that there must also be ventilatory changes. lung; perfusion; iodine 131; acceleration Submitted on January 18, 1965

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Hemodilution during Venous Gas Embolization Improves Gas Exchange, without Altering V̇A/Q̇ or Pulmonary Blood Flow Distributions

Anesthesiology ◽

10.1097/00000542-199912000-00041 ◽

1999 ◽

Vol 91 (6) ◽

pp. 1861-1861 ◽

Cited By ~ 12

Author(s):

Steven Deem ◽

Steven McKinney ◽

Nayak L. Polissar ◽

Richard G. Hedges ◽

Erik R. Swenson

Keyword(s):

Blood Flow ◽

Gas Exchange ◽

Lung Injury ◽

Partial Pressure ◽

Pulmonary Blood Flow ◽

Flow Distribution ◽

Arterial Oxygen ◽

Control Group ◽

Blood Flow Distribution ◽

Over Time

Background Isovolemic anemia results in improved gas exchange in rabbits with normal lungs but in relatively poorer gas exchange in rabbits with whole-lung atelectasis. In the current study, the authors characterized the effects of hemodilution on gas exchange in a distinct model of diffuse lung injury: venous gas embolization. Methods Twelve anesthetized rabbits were mechanically ventilated at a fixed rate and volume. Gas embolization was induced by continuous infusion of nitrogen via an internal jugular venous catheter. Serial hemodilution was performed in six rabbits by simultaneous withdrawal of blood and infusion of an equal volume of 6% hetastarch; six rabbits were followed as controls over time. Measurements included hemodynamic parameters and blood gases, ventilation-perfusion (V(A)/Q) distribution (multiple inert gas elimination technique), pulmonary blood flow distribution (fluorescent microspheres), and expired nitric oxide (NO; chemoluminescence). Results Venous gas embolization resulted in a decrease in partial pressure of arterial oxygen (PaO2) and an increase in partial pressure of arterial carbon dioxide (PaCO2), with markedly abnormal overall V(A)/Q distribution and a predominance of high V(A)/Q areas. Pulmonary blood flow distribution was markedly left-skewed, with low-flow areas predominating. Hematocrit decreased from 30+/-1% to 11+/-1% (mean +/- SE) with hemodilution. The alveolar-arterial PO2 (A-aPO2) difference decreased from 375+/-61 mmHg at 30% hematocrit to 218+/-12.8 mmHg at 15% hematocrit, but increased again (301+/-33 mmHg) at 11% hematocrit. In contrast, the A-aPO2 difference increased over time in the control group (P < 0.05 between groups over time). Changes in PaO2 in both groups could be explained in large part by variations in intrapulmonary shunt and mixed venous oxygen saturation (SvO2); however, the improvement in gas exchange with hemodilution was not fully explained by significant changes in V(A)/Q or pulmonary blood flow distributions, as quantitated by the coefficient of variation (CV), fractal dimension, and spatial correlation of blood flow. Expired NO increased with with gas embolization but did not change significantly with time or hemodilution. Conclusions Isovolemic hemodilution results in improved oxygen exchange in rabbits with lung injury induced by gas embolization. The mechanism for this improvement is not clear.

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Mechanisms of gas exchange with different gases during constant-flow ventilation

Journal of Applied Physiology ◽

10.1152/jappl.1990.68.1.88 ◽

1990 ◽

Vol 68 (1) ◽

pp. 88-93 ◽

Cited By ~ 3

Author(s):

F. J. Chen ◽

A. S. Menon ◽

S. V. Lichtenstein ◽

N. Zamel ◽

A. S. Slutsky

Keyword(s):

Gas Exchange ◽

Physical Properties ◽

Flow Rate ◽

Constant Flow ◽

Catheter Position ◽

Arterial Pco2 ◽

The Mean ◽

The Difference ◽

The Individual ◽

Different Gases

To investigate the mechanisms responsible for the difference in gas exchange during constant-flow ventilation (CFV) when using gases with different physical properties, we used mixtures of 70% N2-30% O2 (N2-O2) and 70% He-30% O2 (He-O2) as the insufflating gases in 12 dogs. All dogs but one had higher arterial PCO2 (PaCO2) with He-O2 compared with N2-O2. At a flow of 0.37 +/- 0.12 l/s, the mean PaCO2's with N2-O2 and He-O2 were 41.3 +/- 13.9 and 53.7 +/- 20.3 Torr, respectively (P less than 0.01); at a flow rate of 0.84 +/- 0.17 l/s, the mean PaCO2's were 29.1 +/- 11.3 and 35.3 +/- 13.6 Torr, respectively (P less than 0.01). The chest was then opened to alter the apposition between heart and the lungs, thereby reducing the extent of cardiogenic oscillations by 58.4 +/- 18.4%. This intervention did not significantly alter the difference in PaCO2 between N2-O2 and He-O2 from that observed in the intact animals, although the individual PaCO2 values for each gas mixture did increase. When the PaCO2 was plotted against stagnation pressure (rho V2), the difference in PaCO2 between N2-O2 and He-O2 was nearly abolished in both the closed- and open-chest animals. These findings suggest that the different PaCO2's obtained by insufflating gases with different physical properties at a fixed flow rate, catheter position, and lung volume result mainly from a difference in the properties of the jet.

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