Oxygen diffusing capacity estimates derived from measured V̇A/Q̇ distributions in man

Hammond, Michael D.; Hempleman, Steven C.

doi:10.1016/0034-5687(87)90022-3

Cited by 52 publications

(30 citation statements)

References 18 publications

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“…Any comparison of the pulmonary capacity for diffusive O 2 uptake must be gauged to the highest achievable metabolic rate because the structural features determining DL O2 cannot be increased at short notice when demand fluctuates. The estimates of DL O2 in exercising humans are ~100 mL O 2 ·min −1 ·mmHg −1 (129), that is, ~50% lower than the morphometric estimate. The remaining difference likely reflects the deconditioned state of modern humans where the “ true” structural diffusing capacity is not completely exploited even at heavy exercise except perhaps in elite endurance athletes.…”

Section: Structure-function Correlationsmentioning

confidence: 80%

“…The “ideal” value of DL O2 thus obtained estimates the maximal possible conductance for O 2 diffusion and binding. It is therefore not surprising that physiological estimates of DL O2 in humans at heavy exercise are around 100 mL·min −1 ·mmHg −1 (129) compared to 158 mL·min −1 ·mmHg −1 as obtained by the morphometric model (381). Thus, it appears that the pulmonary gas exchanger in humans and sedentary animals possess “excess” DL O2 of which only about 2/3 is utilized at maximal O 2 uptake

({\overset{V}{true}}_{O 2} \max)

, In contrast, athletic mammals, such as dogs or horses, utilize their entire DL O2 at

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

(55,199).…”

Section: Structure-function Correlationsmentioning

confidence: 99%

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Lung Structure and the Intrinsic Challenges of Gas Exchange

Hsia

Hyde

Weibel

2016

Comprehensive Physiology

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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Section: Structure-function Correlationsmentioning

confidence: 80%

({\overset{V}{true}}_{O 2} \max)

, In contrast, athletic mammals, such as dogs or horses, utilize their entire DL O2 at

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

(55,199).…”

Section: Structure-function Correlationsmentioning

confidence: 99%

Lung Structure and the Intrinsic Challenges of Gas Exchange

Hsia

Hyde

Weibel

2016

Comprehensive Physiology

164

137

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“…Geiser et al (1983) approached the heterogeneity influence in D L O 2 on mechanically ventilated dogs in hypoxia through an analytical method. These procedures, by reducing the effect of _ V A = _ Q mismatch with D L O 2 measurements, lead to higher values of D L O 2 than those obtained by traditional methods, as expected from previous theoretical analysis (Hammond & Hempleman, 1987). D L O 2 was then computed considering the existence of the previously calculated _ V A = _ Q distribution.…”

Section: Introductionmentioning

confidence: 92%

“…The rebreathing technique, frequently employing isotopic gases, was a major methodological improvement in the experimental procedures (Meyer et al, 1981). Hammond & Hempleman (1987) devised a method to compute D L O 2 from inert gases that was applied to data of resting and exercising humans. Geiser et al (1983) approached the heterogeneity influence in D L O 2 on mechanically ventilated dogs in hypoxia through an analytical method.…”

Section: Introductionmentioning

confidence: 99%

Estimate of pulmonary diffusing capacity for oxygen during exercise in humans from routine O₂ and CO₂ measurements

Melo

Barazanji

Winga

et al. 2004

Clin Physio Funct Imaging

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A method to estimate pulmonary diffusing capacity for O(2) (D(LO2)) during exercise based on routine O(2) and CO(2) transport variables is presented. It is based on the fitting of a mathematical model to gas exchange data. The model includes heterogeneity (described as two exchanging compartments), diffusion limitation and right-to-left shunt. Mass conservation equations and Bohr integration were solved to calculate partial pressures in each compartment. Diffusion was distributed with perfusion. Two-compartment ventilation and perfusion distributions were estimated at rest during conditions of negligible diffusion limitation. These distributions were used during hypoxic and normoxic exercise to obtain the D(LO2) from the model computations (D(LO2)2C) compatible with experimental data. Three normals, four sarcoid patients and four patients after lung resection were studied. An independent technique for carbon monoxide was used to provide experimental estimates of DLo2 (D(LO2)EXP, rebreathing technique for sarcoid patients and single breath for lung resection). D(LO2)2C was highly correlated with D(LO2)EXP (r2 = 0.95, P<0.001) and the slope of the regression line was not statistically different from 1. The mean (D(LO2)EXP - D(LO2)2C) difference was -1.0 +/- 7.4 ml min-1 mmHg-1. The results suggest that use of a refined analytical procedure allows for assessment of D(LO2) from routine O(2) and CO(2) measurements comparable with those obtained from independent carbon monoxide techniques. The method may be an alternative for estimates of D(LO2) during exercise.

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“…, in terms of alveolar -arterial Po2 differences) may serve to estimate the diffusing capacity. This method has been introduced by Riley and Cournand (1951) in their three-compartment lung analysis, and by Hammond and Hempleman (1987) using the continuous distribution model for analysis of multiple inert gas elimination data according to Wagner et al (1974b). Problems with this method arise from the need to quantify the unequal distribution at a level of accuracy that is not easily achieved.…”

Section: Estimation Of Difising Capacity In Inhomogeneous Lungsmentioning

confidence: 98%

Factors affecting gas transfer in respiratory organs of vertebrates

Piiper¹

1989

Can. J. Zool.

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PIIPER, J. 1989. Factors affecting gas transfer in respiratory organs of vertebrates. Can. J. Zool. 67: [2956][2957][2958][2959][2960].The ability of a gas-exchange organ to transfer respiratory gases (0, and CO,) between the respiratory medium (air or water) and blood is quantitatively characterized by its transfer conductance, usually termed diffusing capacity, D. The problems in defining and determining D are reviewed. In a blood-perfused gas-exchange organ it is useful to consider the ratio Dl(QP) (Q, blood flow; P, effective solubility) which determines the relative role of diffusion limitation. Poor gas transfer may be due to functional inhomogeneities, and not to low D values. Besides the well-known ventilation-perfusion inequality, other types of inhomogeneity involving diffusion resistances in the medium may be operative. Determination of D in functionally inhomogeneous gas-exchange organs is difficult because of both modeling and measurement problems. In blood to medium transfer of CO,, particular features have been noted. First, the equilibration of CO, between medium and blood appears to be slower than expected on the basis of high physical solubility, owing to the slowness of some steps in the CO, exchange process (dehydration of carbonic acid, bicarbonate-chloride exchange of red cells). Second, there is controversial evidence for equilibration of pulmonary capillary blood to a CO, partial pressure lower than that in lung gas. PIIPER, J. 1989. Factors affecting gas transfer in respiratory organs of vertebrates. Can. J. Zool. 67 : 2956-2960.La capacitk d'un organe d'kchanges gazeux de transfkrer les gas respiratoires (0, et CO,) du milieu respiratoire (air ou eau) au sang est quantitativement dkpendante de la conductance de transfert, ordinairement appelke capacitk de diffusion, D. Les problkmes relatifs h la dCfinition et h la mesure de D sont rCvisCs. Dans un organe d'kchanges gazeux en perfusion sanguine, il est important de tenir compte du rapport Dl(QP) (Q, flux sanguin; P, la solubilitk effective) qui dktermine le r6le relatif des contraintes de la diffusion. Un transfert de gaz peu efficace peut &re dO h des inhomogCnCitCs fonctionnelles et pas nkcessairement h une valeur de D faible. Parallklement h l'inkgalitk bien connue ventilation-perfusion, d'autres types d'inhomogCnCites basks sur la rksistance h la diffusion peuvent entrer en jeu. La dktermination de D dans des organes d'Cchange de gaz fonctionnellement inhomogknes est rendue difficile par des problkmes de modklisation et de mesure. Au cours du transfert de CO, du sang au milieu, il se produit des phknomknes particuliers. D'abord 1'Ctablissement de 1'Cquilibre du CO, entre le milieu et le sang semble plus lent que ne permet de le croire la solubilitk physique ClevCe de ce gaz, h cause de la lenteur de certaines Ctapes du processus d'kchange de CO, (dkshydration de l'acide carbonique, Cchange bicarbonates -chlorures des les Crythrocytes). Ensuite, il existe des indices, controversCs il est vrai, de l'existence d'un kquilibre dans les c...

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Oxygen diffusing capacity estimates derived from measured V̇A/Q̇ distributions in man

Cited by 52 publications

References 18 publications

Lung Structure and the Intrinsic Challenges of Gas Exchange

Lung Structure and the Intrinsic Challenges of Gas Exchange

Estimate of pulmonary diffusing capacity for oxygen during exercise in humans from routine O₂ and CO₂ measurements

Factors affecting gas transfer in respiratory organs of vertebrates

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Oxygen diffusing capacity estimates derived from measured V̇A/Q̇ distributions in man

Cited by 52 publications

References 18 publications

Lung Structure and the Intrinsic Challenges of Gas Exchange

Lung Structure and the Intrinsic Challenges of Gas Exchange

Estimate of pulmonary diffusing capacity for oxygen during exercise in humans from routine O2 and CO2 measurements

Factors affecting gas transfer in respiratory organs of vertebrates

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Product

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Estimate of pulmonary diffusing capacity for oxygen during exercise in humans from routine O₂ and CO₂ measurements