Effect of body posture on spatial distribution of pulmonary blood flow

Single-photon emission-computed tomography (SPECT) on intact dogs and humans suggests that one aspect of regional blood flow in the lung (Qr) is independent of gravity, e.g., the gradient in Qr between the core and the periphery. To further evaluate these findings, six anesthetized healthy dogs (approximately 30 kg), two in the supine posture, two in the prone posture, and two suspended in the upright posture, breathing spontaneously, were injected (iv) at end expiration with 20 mCi99mTc-labeled albumin macroaggregates. The animals were killed, their chests were opened, their lungs were removed and dissected free of other tissue, and the blood was drained. The lungs were dried by blowing warm air (50 degrees C) while they were inflated to full capacity for about 18 h. The fully inflated and dry lungs were placed in the supine position and SPECT was performed to determine the three-dimensional distribution of activity. One hundred and twenty projections of the activity in the entire lungs were obtained at 3 degrees steps with a rotating gamma camera and stored in computer memory. Once SPECT was completed, either a coronal slice or a sagittal slice (1 cm thick) was cut and imaged directly by placing it against the gamma camera collimator for 6 min. The tomographic-reconstructed slices revealed that at isogravity, in all body postures, Qr in the central region of the lungs was up to 10 times that in the periphery. Furthermore, the central-peripheral gradient was discernible within the individual lobes. The direct images of slices also confirmed these findings. Although flow inequalities independent of gravity were present, the central region with the highest flow often was closer to the dependent regions of the lungs, suggesting that gravity had some influence on the final distribution. The results suggest that factors other than gravity also play an important role in the distribution of pulmonary blood flow. These factors may be related to the conductance of the vascular pathways that lead to different regions in the lungs.     

Effect of lung inflation on lung blood volume and pulmonary venous flow

Phasic changes in lung blood volume (LBV) during the respiratory cycle may play an important role in the genesis of the respiratory wave in arterial pressure, or pulsus paradoxus. To better understand the effects of lung inflation on LBV, we studied the effect of changes in transpulmonary pressure (delta Ptp) on pulmonary venous flow (Qv) in eight isolated canine lungs with constant inflow. Inflation when the zone 2 condition was predominant resulted in transient decreases in Qv associated with increases in LBV. In contrast, inflation when the zone 3 condition was predominant resulted in transient increases in Qv associated with decreases in LBV. These findings are consistent with a model of the pulmonary vasculature that consists of alveolar and extra-alveolar vessels. Blood may be expelled from alveolar vessels but is retained in extra-alveolar vessels with each inflation. The net effect on LBV and thus on Qv is dependent on the zone conditions that predominate during inflation, with alveolar or extra-alveolar effects being greater when the zone 3 or zone 2 conditions predominate, respectively. Lung inflation may therefore result in either transiently augmented or diminished Qv. Phasic changes in left ventricular preload may therefore depend on the zone conditions of the lungs during the respiratory cycle. This may be an important modulator of respiratory variations in cardiac output and blood pressure.     

Relative contribution of bronchial flow to subpleural region in dog lung.

The bronchial flow is approximately 1% of the total pulmonary flow. Anastomosis between the bronchial and pulmonary vessels occurs primarily at the microcirculatory level. It is assumed that bronchopulmonary anastomoses are present in a homogeneous manner throughout lung parenchyma. To investigate this issue, an in situ blood-perfused left lower lung lobe (500 ml/min) was prepared in a live dog. The bronchial flow rate in the entire lobe was monitored using the rate of volume gain in the reservoir while the pulmonary and bronchial flow in the subpleural region was monitored using laser-Doppler flowmetry. The results were expressed as ratio of bronchial to pulmonary flow rate for the entire lobe and for the subpleural region. We found that, for the entire lobe, bronchial flow was 1.0% of pulmonary flow, while for the subpleural region this ratio was much higher, with an average of 12%. In two different experimental conditions that were imposed to affect the global bronchial flow, these ratios changed in the same direction as the global bronchial flow. After transfusion of blood into the animal, bronchial flow increased to 1.7%, while the subpleural bronchial flow increased to 18% of the subpleural pulmonary flow. During elevation of venous pressure, bronchial flow decreased to 0.6%, while the subpleural bronchial flow decreased to 10% of the subpleural pulmonary flow. The differences in the ratios between the global and subpleural region may be explained by having low pulmonary blood flow in the periphery compared with the interior regions of the lung.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of furosemide on pulmonary blood flow distribution in resting and exercising horses.

We determined the spatial distribution of pulmonary blood flow (PBF) with 15-micron fluorescent-labeled microspheres during rest and exercise in five Thoroughbred horses before and 4 h after furosemide administration (0.5 mg/kg iv). The primary finding of this study was that PBF redistribution occurred from rest to exercise, both with and without furosemide. However, there was less blood flow to the dorsal portion of the lung during exercise postfurosemide compared with prefurosemide. Furosemide did alter the resting perfusion distribution by increasing the flow to the ventral regions of the lung; however, that increase in flow was abated with exercise. Other findings included 1) unchanged gas exchange and cardiac output during rest and exercise after vs. before furosemide, 2) a decrease in pulmonary arterial pressure after furosemide, 3) an increase in the slope of the relationship of PBF vs. vertical height up the lung during exercise, both with and without furosemide, and 4) a decrease in blood flow to the dorsal region of the lung at rest after furosemide. Pulmonary perfusion variability within the lung may be a function of the anatomy of the pulmonary vessels that results in a predominantly fixed spatial pattern of flow distribution.     

Effect of pulmonary blood flow on leukocyte uptake and release by dog lung

The effect of pulmonary blood flow on leukocyte uptake and release by the lung was examined in 10 anesthetized spontaneously breathing dogs. Pulmonary arterial and pulmonary venous blood was sampled with catheters placed into the right ventricle and aorta, respectively. Pulmonary blood flow was lowered by inflating a balloon catheter located in the inferior vena cava. In five experiments simultaneous blood samples were drawn from the right ventricle and aorta at 10-s intervals during a control period, a 2- to 3-min period of low flow, and a recovery period. In five additional experiments, less frequent samples were taken over periods of 15-60 min. Total leukocyte concentrations and differential counts were determined for each blood sample. The study shows that large numbers of leukocytes become sequestered within the lung when pulmonary blood flow is low and that an equivalent number of cells are released from the lung after deflation of the balloon catheter. Both the polymorphonuclear leukocytes and the lymphocytes were taken up by the lung when pulmonary blood flow was reduced. We conclude that pulmonary blood flow has a marked effect on the uptake and release of leukocytes by the dog lung.     

Effect of regional pulmonary blood flow on extravascular lung water measurements with PET

We examined the effect of regional pulmonary blood flow (PBF) on lung water measurements made with a blood-borne label (15O-water) and positron emission tomography (PET) in five dogs. The total lung water (TLW) content of a lung region obtained at equilibrium after intravenous injection of 15O-water (TLW-water) was compared with calculations made from lung density measurements (TLW-density) also obtained with PET. These latter measurements are proportional to the tissue attenuation of radioactivity originating from an external source encircling the animal and are independent of PBF. Comparisons were made before and 60 min after oleic acid-induced injury confined to the left caudal lobe (LCL). PBF fell 61% in regions from the dorsal half of the LCL after lung injury and was unchanged on the right side. Both before and after injury, TLW-density was 10-15% higher than TLW-water. This systematic difference is probably due to overestimates of TLW-density resulting from partial volume and scattered radiation effects. When TLW-water and TLW-density were compared in 151 3-ml regions from both normal and injured lung, the disparity between the two methods of calculating TLW increased in regions with a PBF less than 0.5 ml.min-1.ml lung-1 (less than 20% of base line). However, this represented only 22% of the injured regions analyzed. Thus lung water measurements made with PET and 15O-water are accurate until regional PBF is severely reduced. With PET, such areas can be eliminated from analysis or regions can be made sufficiently large so the overall effect on the TLW measurement is minimized.     

Role of pulmonary blood flow in postpneumonectomy lung growth.

To study the influence of blood flow on postpneumonectomy lung growth, we banded the left caudal lobe pulmonary artery of eight ferrets in such a way that blood flow to the caudal lobe did not increase when the right lung was excised 1 wk later. The fraction of the cardiac output received by the right lung before pneumonectomy was therefore directed entirely to the left cranial lobe. Three weeks after pneumonectomy the weight, volume, and protein and DNA contents of the two lobes of the left lung were measured and compared with those of five unoperated animals and eight animals after right pneumonectomy alone. Although its perfusion did not increase after pneumonectomy, the left caudal lobe of banded animals participated in compensatory growth, increasing in weight and protein and DNA contents. Although the cranial lobe of banded animals received 25% more of the cardiac output than the same lobe in pneumonectomized animals, cranial lobe volume and protein and DNA contents in the two groups were similar. Caudal lobes were smaller in banded than in simple pneumonectomized animals and tended to contain less protein, whereas the cranial lobes tended to be heavier. We conclude that increased pulmonary perfusion is not necessary for compensatory lung growth in adult ferrets, but it may modify this response.     

Effect of gravity and posture on lung mechanics.

The volume-pressure relationship of the lung was studied in six subjects on changing the gravity vector during parabolic flights and body posture. Lung recoil pressure decreased by approximately 2.7 cmH(2)O going from 1 to 0 vertical acceleration (G(z)), whereas it increased by approximately 3.5 cmH(2)O in 30 degrees tilted head-up and supine postures. No substantial change was found going from 1 to 1.8 G(z). Matching the changes in volume-pressure relationships of the lung and chest wall (previous data), results in a decrease in functional respiratory capacity of approximately 580 ml at 0 G(z) relative to 1 G(z) and of approximately 1,200 ml going to supine posture. Microgravity causes a decrease in lung and chest wall recoil pressures as it removes most of the distortion of lung parenchyma and thorax induced by changing gravity field and/or posture. Hypergravity does not greatly affect respiratory mechanics, suggesting that mechanical distortion is close to maximum already at 1 G(z). The end-expiratory volume during quiet breathing corresponds to the mechanical functional residual capacity in each condition.