Recruitment of Lung Diffusing Capacity

Hsia, Connie C. W.

doi:10.1378/chest.122.5.1774

Cited by 127 publications

(44 citation statements)

References 78 publications

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“…This estimate far exceeds observed diffusing capacity values for humans at rest and during exercise, which are approximately 20–60 ml O 2 min −1 mmHg −1 (Hsia, 2002; Hughes and Bates, 2003). Awareness of this discrepancy has motivated a number of modifications to the morphometric method and development of alternative approaches.…”

Section: Introductioncontrasting

confidence: 53%

Theoretical analysis of the determinants of lung oxygen diffusing capacity

Roy

Secomb

2014

Journal of Theoretical Biology

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The process of pulmonary oxygen uptake is analyzed to obtain an explicit equation for lung oxygen diffusing capacity in terms of hematocrit and pulmonary capillary diameter. An axisymmetric model with discrete cylindrical erythrocytes is used to represent radial diffusion of oxygen from alveoli through the alveolar-capillary membrane into pulmonary capillaries, through the plasma, and into erythrocytes. Analysis of unsteady diffusion due to the passage of the erythrocytes shows that transport of oxygen through the alveolar-capillary membrane occurs mainly in the regions adjacent to erythrocytes, and that oxygen transport through regions adjacent to plasma gaps can be neglected. The model leads to an explicit formula for diffusing capacity as a function of geometric and oxygen transport parameters. For normal hematocrit and a capillary diameter of 6.75 µm, the predicted diffusing capacity is 102 ml O2 min−1 mmHg−1. This value is 30–40% lower than values estimated previously by the morphometric method, which considers the total membrane area and the specific uptake rate of erythrocytes. Diffusing capacity is shown to increase with increasing hematocrit and decrease with increasing capillary diameter and increasing thickness of the membrane. Simulations of pulmonary oxygen uptake in humans under conditions of exercise or hypoxia based show closer agreement with experimental data than previous models, but still overestimate oxygen uptake. The remaining discrepancy may reflect effects of heterogeneity of perfusion and ventilation in the lung.

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Section: Introductioncontrasting

confidence: 53%

Theoretical analysis of the determinants of lung oxygen diffusing capacity

Roy

Secomb

2014

Journal of Theoretical Biology

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“…A typical physiological value of DL O2 measured in a healthy adult at rest is ~30 mL O 2 ·min −1 ·torr −1 , considerably less than that based on morphometric estimates. This large difference arises because (i) under resting conditions, O 2 flow required to support metabolism is only one-tenth of what the lungs are capable of transporting under heavy exercise, and (ii) physiological diffusing capacity increases in a linear relationship with respect to pulmonary blood flow from rest to peak exercise (152). Thus, lung structure provides large O 2 transport reserves that are not needed at rest but may be rapidly recruited upon exercise.…”

Section: Structure-function Correlationsmentioning

confidence: 99%

“…The lack of excess DL in dogs explains why maximal DL CO measured physiologically in dogs before and after pneumonectomy is well predicted by morphometric DL CO estimated on the same animals (157). The structure-function correspondence of DL CO in athletic but not sedentary species suggests that the apparent “excess” diffusing capacity in sedentary species is related to a lower capacity in the nonpulmonary steps of the O 2 transport cascade, that is, cardiovascular and skeletal muscle systems, that restrict

{\overset{\cdot}{normalV}}_{normalO 2} \max

before the reserves in pulmonary O 2 uptake are exhausted (152). …”

Section: Structure-function Correlationsmentioning

confidence: 99%

“…Alveolar-capillary recruitment, an essential process that matches pulmonary O 2 uptake to metabolic O 2 demand, is evidenced by a linear increase in DL (~40% in average humans and up to 100% in dogs) with respect to lung expansion (303) and pulmonary perfusion

(\overset{Q}{true})

from rest up to peak exercise (48, 152, 338) (Fig. 71).…”

Section: Matching the Components Of Pulmonary Gas Transport And The Cmentioning

confidence: 99%

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Lung Structure and the Intrinsic Challenges of Gas Exchange

Hsia

Hyde

Weibel

2016

Comprehensive Physiology

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164

137

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Structural and functional complexities of the mammalian lung evolved to meet a unique set of challenges, namely, the provision of efficient delivery of inspired air to all lung units within a confined thoracic space, to build a large gas exchange surface associated with minimal barrier thickness and a microvascular network to accommodate the entire right ventricular cardiac output while withstanding cyclic mechanical stresses that increase several folds from rest to exercise. Intricate regulatory mechanisms at every level ensure that the dynamic capacities of ventilation, perfusion, diffusion, and chemical binding to hemoglobin are commensurate with usual metabolic demands and periodic extreme needs for activity and survival. This article reviews the structural design of mammalian and human lung, its functional challenges, limitations, and potential for adaptation. We discuss (i) the evolutionary origin of alveolar lungs and its advantages and compromises, (ii) structural determinants of alveolar gas exchange, including architecture of conducting bronchovascular trees that converge in gas exchange units, (iii) the challenges of matching ventilation, perfusion, and diffusion and tissue-erythrocyte and thoracopulmonary interactions. The notion of erythrocytes as an integral component of the gas exchanger is emphasized. We further discuss the signals, sources, and limits of structural plasticity of the lung in alveolar hypoxia and following a loss of lung units, and the promise and caveats of interventions aimed at augmenting endogenous adaptive responses. Our objective is to understand how individual components are matched at multiple levels to optimize organ function in the face of physiological demands or pathological constraints.

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“…These results are consistent with those of Hsia et al 34 , who found only a mild decline in arterial O 2 saturation during exercise after pneumonectomy, indicating high functional reserves for diffusion capacity in the lungs during exercise. As cardiac output rises during incremental exercise in healthy participants, a twofold increase in diffusion capacity in the lungs is observed in order to maintain oxygenation, 35 indicating a higher diffusion capacity reserve compared with cardiac output. This may explain why the majority of patients undergoing lung resection are able to maintain their SpO 2 after surgery, even during maximal exercise.…”

Section: Cardiorespiratory Fitnessmentioning

confidence: 99%

Reduction in cardiorespiratory fitness after lung resection is not related to the number of lung segments removed

Edvardsen

Anderssen

Borchsenius

et al. 2015

BMJ Open Sport Exerc Med

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AimTo evaluate the effect of lung cancer surgery on cardiorespiratory fitness (CRF), and to assess the agreement between the predicted postoperative (ppo) V̇O2peak and actually measured postoperative peak oxygen uptake (V̇O2peak).MethodsBefore and 4–6 weeks after lung cancer surgery, 70 patients (35 women) underwent measurements of pulmonary function and CRF via a cardiopulmonary exercise test. In addition, the 23 non-exercising patients underwent measurements after 6 months. The ppo V̇O2peak calculated from the number of functional segments removed was compared with the actually measured postoperative values of V̇O2peak for accuracy and precision.ResultsAfter surgery, the V̇O2peak decreased from 23.9±5.8 to 19.2±5.5 mL/kg/min (−19.6±15.7%) (p<0.001). The breathing reserve increased by 5% (p=0.001); the oxygen saturation remained unchanged (p=0.30); the oxygen pulse decreased by −1.9 mL/beat (p<0.001); the haemoglobin concentration decreased by 0.7 g/dL (p=0.001). The oxygen pulse was the strongest predictor for change in V̇O2peak; adjusted linear squared: r2=0.77. Six months after surgery, the V̇O2peak remained unchanged (−3±15%, p=0.27). The ppo V̇O2peak (mL/kg/min) was 18.6±5.4, and the actually measured V̇O2peak was 19.2±5.5 (p=0.24). However, the limits of agreement were large (CI −7.4 to 8.2). The segment method miscalculated the ppo V̇O2peak by more than ±10 and ±20% in 54% and 25% of the patients, respectively.ConclusionsThe reduction in V̇O2peak and lack of improvement 6 months after lung cancer surgery cannot be explained by the loss of functional lung tissue. Predicting postoperative V̇O2peak based on the amount of lung tissue removed is not recommendable due to poor precision.Trial registration numberNCT01748981.

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Recruitment of Lung Diffusing Capacity

Cited by 127 publications

References 78 publications

Theoretical analysis of the determinants of lung oxygen diffusing capacity

Theoretical analysis of the determinants of lung oxygen diffusing capacity

Lung Structure and the Intrinsic Challenges of Gas Exchange

Reduction in cardiorespiratory fitness after lung resection is not related to the number of lung segments removed

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