Smaller is better—but not too small: A physical scale for the design of the mammalian pulmonary acinus

Sapoval, B.; Filoche, Marcel; Weibel, Ewald R.

doi:10.1073/pnas.122352499

Cited by 194 publications

(200 citation statements)

References 22 publications

Supporting

Mentioning

187

Contrasting

Order By: Relevance

“…However, considering also the structure of the pulmonary acinar airways that distribute O 2 to the alveolar surface, one finds that the scaling of the membrane conductance is tightly associated with that of V O ∑ max , both with exponents of 0.9. The effect of O 2 screening in the acinar airways reduces the effective conductance at rest to scale with 0.735, similar to the scaling of basal metabolic rate (Sapoval et al, 2002).…”

Section: The Scaling Of the O 2 Supply Cascadementioning

confidence: 68%

Exercise-induced maximal metabolic rate scales with muscle aerobic capacity

Weibel

Hoppeler

2005

Journal of Experimental Biology

263

279

View full text Add to dashboard Cite

Maximal metabolic rate (MMR) is elicited by a welldefined dominant process: the energy needs of locomotor activity at its sustainable maximum during a run. In contrast, other forms of MR have a more complex origin. Basal metabolic rate (BMR) reflects the lowest need of energy at rest in a postprandial state under thermoneutral conditions. It is the energy used to run basic cell functions in a large variety of organs, such as maintaining cell potentials, driving the heart and circulation, synthetic and housekeeping functions of all sorts, and maintenance of body temperature. BMR and MMR thus define the span over which the metabolic rate of the organism can vary. Their definitions are unambiguous and, as such, they are reproducible. They reflect the performance of the organism under these specific test conditions, but are not conditions that occur usually in life. Natural forms of MR are intermediate. Field metabolic rate (FMR) reflects the timeaveraged MR elicited by all possible organismic functions at variable levels of activity, such as foraging or hunting for food, or digestion, and is commonly found to be about 4 times BMR. What is termed sustained MR refers to the metabolic rate that allows for maintaining body mass over longer time; it is a form of FMR mostly related to nutrient supply.Whereas BMR appears to depend essentially on body mass, MMR shows large inter-individual and inter-species variability, related to the degree of work or exercise capacity. It is typically about tenfold higher than BMR. Well-trained human athletes can achieve MMR up to 20 times higher than their BMR. Even greater variation is found in animals. Athletic species such as dogs or horses increase their MR by 30-fold from rest to maximal exercise, and in race horses this factor can rise to 50, as in the pronghorn antelope, the world's top athletic mammal.MMR reflects the limitation of oxidative metabolism of muscle cells. It is not sustainable for more than a few minutes because, under these limiting conditions, the incipient aerobic energy deficit must be covered by anaerobic glycolysis, which leads to lactate accumulation in the blood and thus to cessation of exercise.All forms of MR in mammals and other taxa show some scaling with body mass M b according to the allometric The logarithmic nature of the allometric equation suggests that metabolic rate scaling is related to some fractal properties of the organism. Two universal models have been proposed, based on (1) the fractal design of the vasculature and (2) the fractal nature of the 'total effective surface' of mitochondria and capillaries. According to these models, basal and maximal metabolic rates must scale as M 3/4 . This is not what we find. In 34 eutherian mammalian species (body mass M b ranging from 7·g to 500·kg) we found V O ∑ max to scale with the 0.872 (±0.029) power of body mass, which is significantly different from 3/4 power scaling. Integrated structure-function studies on a subset of eleven species (M b 20·g to 450·kg) show that the variation of V O ∑ max wit...

show abstract

Section: The Scaling Of the O 2 Supply Cascadementioning

confidence: 68%

Exercise-induced maximal metabolic rate scales with muscle aerobic capacity

Weibel

Hoppeler

2005

Journal of Experimental Biology

263

279

View full text Add to dashboard Cite

show abstract

“…As was pointed out by SAPOVAL et al [39], efficient gas exchange depends crucially on ensuring adequate oxygen supply to all capillary gas exchange units within the acinus, whether they are centrally located near the entrance or deep at the periphery of the acinus. As oxygen diffuses along the acinar airways, it is progressively extracted at the gas exchange surface along the longitudinal diffusion path, resulting in a progressive decrease of the oxygen partial pressure in a process referred to as screening [39]. Addition of new alveoli at the lung periphery increases the fraction of gas exchange area exposed to low oxygen partial pressure.…”

Section: Discussionmentioning

confidence: 98%

Neoalveolarisation contributes to compensatory lung growth following pneumonectomy in mice

Fehrenbach¹,

Voswinckel²,

Michl³

et al. 2008

European Respiratory Journal

View full text Add to dashboard Cite

Regeneration of the gas exchange area by induction of neoalveolarisation would greatly improve therapeutic options in destructive pulmonary diseases. Unilateral pneumonectomy is an established model to remove defined portions of gas exchange area and study mechanisms of compensatory lung growth. The question of whether new alveoli are added to the residual lung after pneumonectomy in mice was addressed.Left-sided pneumonectomy was performed in 11 adult C57BL/6 mice. Alveolar numbers were analysed in lungs fixed at days 6 and 20 after pneumonectomy and in 10 age-matched controls using design-based stereology based on a physical fractionator. Post-fixation lung volume was determined by fluid displacement.Complete restoration of lung volume was observed 20 days after pneumonectomy. Alveolar numbers were significantly increased by 33% in residual right lungs at day 20 in comparison with control right lungs. In control left lungs, an average of 471¡162610 3 alveoli was estimated, 49% of which were regenerated by residual lungs at day 20. Of the newly formed alveoli seen at day 20, 74% were already present at day 6. The present data demonstrate that, in addition to growth in size of existing alveoli, neoalveolarisation contributes to restoration of the gas exchange area in adult mice and is induced early after pneumonectomy.

show abstract

“…In particular, low Reynolds alveolar flows can be extremely complex due to the unique alveolated duct structures and their time dependent motion. While convective acinar flows may not affect diffusive gas (oxygen) transport [9], alveolar flow patterns are, however, of significant relevance for aerosol kinematics and deposition of inhaled particles [10,11].…”

Section: Introductionmentioning

confidence: 99%

CFD investigation of respiratory flows in a space-filling pulmonary acinus model

Sznitman¹,

Schmuki²,

Sutter³

et al. 2007

Modelling in Medicine and Biology VII

View full text Add to dashboard Cite

Due to the sub-millimetre dimensions and accessibility of the distal regions of the lung, respiratory flows in the pulmonary acinus are often difficult to assess. However, a realistic description of acinar flows is needed to understand aerosol transport and deposition for medical applications such as aerosol inhalation. In an effort to develop more realistic computational fluid dynamics (CFD) models of the pulmonary acinus, we have simulated convective flows under rhythmic breathing motion in a space-filling model of an acinar branching tree. Our model captures well the variety of 3D flow patterns present along the tree and confirms the existence of complex recirculating alveolar flows. Our results emphasize the role of the alveolar to ductal flow ratio in characterizing acinar flows. Lagrangian particle trajectories suggest that massless particles, not influenced by sedimentation or diffusion, stay principally confined within acinar ducts without entering into alveoli. The inherent modularity of the present model is well suited to create more complete geometries of acinar trees and investigate the influence of convective acinar flows on realistic sedimenting and/or diffusing particles.

show abstract

Smaller is better—but not too small: A physical scale for the design of the mammalian pulmonary acinus

Cited by 194 publications

References 22 publications

Exercise-induced maximal metabolic rate scales with muscle aerobic capacity

Exercise-induced maximal metabolic rate scales with muscle aerobic capacity

Neoalveolarisation contributes to compensatory lung growth following pneumonectomy in mice

CFD investigation of respiratory flows in a space-filling pulmonary acinus model

Contact Info

Product

Resources

About