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Gravitational Lung Gradients
Jud W. Gurney, MD, FACR
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KEY FACTS

  • Terminology

    • Imaging Findings

      TERMINOLOGY

      • Definitions

        • Perfusion (Q) upright lung
          • Normal 18 fold difference from the top to bottom of the lung due to effect of gravity on low pressure pulmonary arterial system
            • Main pulmonary artery inclined towards the left upper lung, the jet effect across the pulmonic valve increases blood flow 10% above similar regions in the right upper lobe
          • Zonal blood flow
            • Blood flow determined by pulmonary arterial (pa), pulmonary venous (pv), and alveolar pressure (pA)
            • Zone 1: pA > pa > pv, capillaries collapsed, no blood flow, does not occur in normal lung but in hypotensive patient on mechanical ventilation and PEEP may develop zone 1 conditions in the nondependent lung
            • Zone 2: pa > pA > pv, blood flow not determined by gradient between arterial and venous pressure but gradient between arterial and alveolar pressure and may produce erroneous clinical pressure readings from a wedged Swan-Ganz catheter
            • Zone 3: pa > pv > pA, blood flow determined by arterial venous pressure gradient
          • Pathophysiology
            • Determines the distribution of hydrostatic (cardiogenic edema) and blood borne insults (hematogenous metastases)
        • Ventilation (V) upright lung
          • Normal 3 fold difference from the top to the bottom of the lung due to effect of gravity on intrapleural pressure, transpulmonary gradients and alveolar size
          • Branching pattern of the airways important in distribution of particulate material suspended in the inhaled air
            • Turbulent airflow in the large upper airways (1st 6 generations) directs particles > 5μ in diameter against the ciliated airways where they can be removed from the lung
            • Particles < 5μ in diameter can deposit in the respiratory bronchioles within the centrilobular portion of the lobule
            • Particles tend to follow the straightest pathway through the lung which is to the lung periphery
          • Pathophysiology
            • Determines the distribution of inhaled insults which acutely affect the lung
        • Ventilation to perfusion ratio (V/Q) upright lung
          • Normal ratio decreases from the top (3.3) to the bottom of the lung (0.6)
          • Pathophysiology
            • Determines the concentration of inhaled gas
          • Alveolar oxygen concentration upright lung
            • Apex lung: 132 mmHg and base lung: 89 mmHg
        • pH upright lung
          • Normal pH decreases from apex lung (7.51) to base (7.39)
          • Upper lobes relatively alkalotic: Environment also shared by gastric wall and medulla of kidney
          • Pathophysiology
            • Affects the distribution of calcium which is less soluble in alkalotic environment
        • Intrapleural pressure upright lung
          • Normal pleural pressure increases down the lung from apex (-10 cm water) to base (-2.5 cm water)
          • Large transpulmonary pressure in upper lung zones expand alveoli which are 4x larger at the top than at the bottom
            • 50% of total change in alveolar volume occurs over the top 4 cm of the lung
            • Müller maneuver (inspire against a closed glottis) can generate pressures down to -80 mmHg
            • Valsalva maneuver (forced expiration against a closed glottis) can generate pressures > 100 mmHg
          • Pathophysiology
            • Determines the distribution of stress, (blebs, bullae and cavities all more common in upper lung zone)
        • Lymphatic flow upright lung
          • Flow 10-50 ml/hr
          • Linearly increase down the lung due to gravitational increase in pulmonary arterial pressure
          • Aided by kinetics of respiratory motion
            • Diaphragmatic motion and excursion of anterior and lateral chest wall
          • Regions with slowest lymphatic flow
            • Upper lobes, especially the right due to slightly higher pulmonary blood flow in the left upper lung
            • Dorsal lung due to relatively decreased respiratory motion posteriorly
          • Pathophysiology
            • Determines the distribution of disease due to chronic clearance of particulate material

      IMAGING FINDINGS

      • General Features

        • Radiographic Findings

          • CT Findings

            • Nuclear Medicine Findings

              • Imaging Recommendations

                DIFFERENTIAL DIAGNOSIS

                  PATHOLOGY

                  • General Features

                    • Gross Pathologic & Surgical Features

                      CLINICAL ISSUES

                      • Presentation

                        DIAGNOSTIC CHECKLIST

                        • Image Interpretation Pearls

                          Selected References

                          1. Murray JF: Bill Dock and the location of pulmonary tuberculosis: how bed rest might have helped consumption. Am J Respir Crit Care Med. 168(9):1029-33, 2003
                          2. Gurney JW: Cross-sectional physiology of the lung. Radiology. 178(1):1-10, 1991
                          3. Gurney JW et al: Upper lobe lung disease: physiologic correlates. Review. Radiology. 167(2):359-66, 1988
                          Related Anatomy
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                          Related Differential Diagnoses
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                          References
                          Tables

                          Tables

                          KEY FACTS

                          • Terminology

                            • Imaging Findings

                              TERMINOLOGY

                              • Definitions

                                • Perfusion (Q) upright lung
                                  • Normal 18 fold difference from the top to bottom of the lung due to effect of gravity on low pressure pulmonary arterial system
                                    • Main pulmonary artery inclined towards the left upper lung, the jet effect across the pulmonic valve increases blood flow 10% above similar regions in the right upper lobe
                                  • Zonal blood flow
                                    • Blood flow determined by pulmonary arterial (pa), pulmonary venous (pv), and alveolar pressure (pA)
                                    • Zone 1: pA > pa > pv, capillaries collapsed, no blood flow, does not occur in normal lung but in hypotensive patient on mechanical ventilation and PEEP may develop zone 1 conditions in the nondependent lung
                                    • Zone 2: pa > pA > pv, blood flow not determined by gradient between arterial and venous pressure but gradient between arterial and alveolar pressure and may produce erroneous clinical pressure readings from a wedged Swan-Ganz catheter
                                    • Zone 3: pa > pv > pA, blood flow determined by arterial venous pressure gradient
                                  • Pathophysiology
                                    • Determines the distribution of hydrostatic (cardiogenic edema) and blood borne insults (hematogenous metastases)
                                • Ventilation (V) upright lung
                                  • Normal 3 fold difference from the top to the bottom of the lung due to effect of gravity on intrapleural pressure, transpulmonary gradients and alveolar size
                                  • Branching pattern of the airways important in distribution of particulate material suspended in the inhaled air
                                    • Turbulent airflow in the large upper airways (1st 6 generations) directs particles > 5μ in diameter against the ciliated airways where they can be removed from the lung
                                    • Particles < 5μ in diameter can deposit in the respiratory bronchioles within the centrilobular portion of the lobule
                                    • Particles tend to follow the straightest pathway through the lung which is to the lung periphery
                                  • Pathophysiology
                                    • Determines the distribution of inhaled insults which acutely affect the lung
                                • Ventilation to perfusion ratio (V/Q) upright lung
                                  • Normal ratio decreases from the top (3.3) to the bottom of the lung (0.6)
                                  • Pathophysiology
                                    • Determines the concentration of inhaled gas
                                  • Alveolar oxygen concentration upright lung
                                    • Apex lung: 132 mmHg and base lung: 89 mmHg
                                • pH upright lung
                                  • Normal pH decreases from apex lung (7.51) to base (7.39)
                                  • Upper lobes relatively alkalotic: Environment also shared by gastric wall and medulla of kidney
                                  • Pathophysiology
                                    • Affects the distribution of calcium which is less soluble in alkalotic environment
                                • Intrapleural pressure upright lung
                                  • Normal pleural pressure increases down the lung from apex (-10 cm water) to base (-2.5 cm water)
                                  • Large transpulmonary pressure in upper lung zones expand alveoli which are 4x larger at the top than at the bottom
                                    • 50% of total change in alveolar volume occurs over the top 4 cm of the lung
                                    • Müller maneuver (inspire against a closed glottis) can generate pressures down to -80 mmHg
                                    • Valsalva maneuver (forced expiration against a closed glottis) can generate pressures > 100 mmHg
                                  • Pathophysiology
                                    • Determines the distribution of stress, (blebs, bullae and cavities all more common in upper lung zone)
                                • Lymphatic flow upright lung
                                  • Flow 10-50 ml/hr
                                  • Linearly increase down the lung due to gravitational increase in pulmonary arterial pressure
                                  • Aided by kinetics of respiratory motion
                                    • Diaphragmatic motion and excursion of anterior and lateral chest wall
                                  • Regions with slowest lymphatic flow
                                    • Upper lobes, especially the right due to slightly higher pulmonary blood flow in the left upper lung
                                    • Dorsal lung due to relatively decreased respiratory motion posteriorly
                                  • Pathophysiology
                                    • Determines the distribution of disease due to chronic clearance of particulate material

                              IMAGING FINDINGS

                              • General Features

                                • Radiographic Findings

                                  • CT Findings

                                    • Nuclear Medicine Findings

                                      • Imaging Recommendations

                                        DIFFERENTIAL DIAGNOSIS

                                          PATHOLOGY

                                          • General Features

                                            • Gross Pathologic & Surgical Features

                                              CLINICAL ISSUES

                                              • Presentation

                                                DIAGNOSTIC CHECKLIST

                                                • Image Interpretation Pearls

                                                  Selected References

                                                  1. Murray JF: Bill Dock and the location of pulmonary tuberculosis: how bed rest might have helped consumption. Am J Respir Crit Care Med. 168(9):1029-33, 2003
                                                  2. Gurney JW: Cross-sectional physiology of the lung. Radiology. 178(1):1-10, 1991
                                                  3. Gurney JW et al: Upper lobe lung disease: physiologic correlates. Review. Radiology. 167(2):359-66, 1988