Theoretical Study of Inspiratory Flow Waveforms during Mechanical Ventilation on Pulmonary Blood Flow and Gas Exchange

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.

Download Full-text

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.

Download Full-text

Gas exchange in dogs in the prone and supine positions

Journal of Applied Physiology ◽

10.1152/jappl.1992.72.6.2292 ◽

1992 ◽

Vol 72 (6) ◽

pp. 2292-2297 ◽

Cited By ~ 49

Author(s):

K. C. Beck ◽

J. Vettermann ◽

K. Rehder

Keyword(s):

Blood Flow ◽

Gas Exchange ◽

Prone Position ◽

Pulmonary Blood Flow ◽

Random Order ◽

Arterial Pco2 ◽

Supine Posture ◽

Pulmonary Shunting ◽

The Difference ◽

Arterial Po2

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.

Download Full-text

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

Download Full-text

Effect of altered gas diffusivity on alveolar gas exchange-a theoretical study

Journal of Applied Physiology ◽

10.1152/jappl.1980.48.1.147 ◽

1980 ◽

Vol 48 (1) ◽

pp. 147-153 ◽

Cited By ~ 14

Author(s):

W. Nixon ◽

A. Pack

Keyword(s):

Blood Flow ◽

Gas Exchange ◽

Theoretical Study ◽

Experimental Studies ◽

Flow Distribution ◽

Molecular Diffusivity ◽

Gas Diffusivity ◽

Experimental Findings ◽

Lung Airways ◽

Alveolar Gas Exchange

Experimental studies have established that alveolar gas exchange is inversely relation to the molecular diffusivity of gas in the lung airways. The mechanism underlying this relationship is, however, unclear. To investigate this phenomenon, the conditions relevant to the experimental studies are simulated using a computational model of pulmonary gas transport. Results from these simulations suggest that the inverse relationship found experimentally can largely be explained on the basis of the intra-acinar stratification of blood flow and gas concentrations. Gas having a relatively low molecular diffusivity is not transported as far into the acinus as gas having a higher diffusivity. When these relative intra-acinar gas distributions interact with the blood flow distribution, which has been shown experimentally to be weighted towards the proximal alveoli, more gas exchange occurs in the low molecular diffusivity mixture. Consideration of the various other mechanisms that have been proposed to explain the experimental findings.he inverse dependence suggests that they are of little significance. In particular, our studies remove the need to invoke Taylor diffusion to explain the experimental findings.

Download Full-text

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

Download Full-text

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.

Download Full-text