Gas exchange abnormalities after pneumonectomy in conditioned foxhounds

Abstract

Loss of a major portion of lung tissue has been associated with impaired exercise capacity, but the underlying mechanisms are not well defined. We studied the alterations in gas exchange during exercise before and after left pneumonectomy in three conditioned foxhounds. After pneumonectomy, minute ventilation and O2 consumption at comparable submaximal work loads were unchanged but arterial PCO2 at any work load was higher, implying that ventilatory response to CO2 was impaired. Arterial hypoxemia and an elevated alveolar-arterial O2 tension difference (AaDO2) developed during heavy exercise. Using the multiple inert gas elimination technique, we determined the distributions of ventilation-perfusion (VA/Q) ratios postpneumonectomy. Significant increase in VA/Q inequality developed during exercise while the foxhounds were breathing room air, accounting for an average of 42% of the total increase in AaDO2 while diffusion limitation accounted for 58%. While the animals were breathing hypoxic gas mixture, diffusion limitation accounted for an average of 88% of the total increase AaDO2. Cardiac output and O2 delivery were reduced at a given O2 consumption after pneumonectomy. After pneumonectomy, the animals reached O2 consumptions close to the maximum expected for normal dogs. Compensation for the impairment in O2 delivery post-pneumonectomy occurred mainly by an increase in hemoglobin concentration. Training probably played an important role in returning exercise capacity toward prepneumonectomy levels. We conclude that significant abnormalities in gas exchange develop during exercise after loss of 42% of lung tissue, but the animals demonstrate a remarkable ability to compensate for these changes.

Structural changes underlying compensatory increase of diffusing capacity after left pneumonectomy in adult dogs.

“…This is particularly important in dogs that appear to have a small amount of redundancy in their gas exchanger for meeting oxygen demands at heavy exercise (3). However, in previous studies on dogs, we have oW served that exercise performance is not significantly impaired by left pneumonectomy (4). Diffusing capacity for carbon have increased by some 30% above that ofthe same lung before pneumonectomy (5).…”

“…Although no clear plateau in the linear rise of DLco is observed up to peak exercise equivalent to a cardiac output of 35 liters. min-' through two lungs, functional reserves in the remaining lung are insufficient to meet the demands for 02 transport, evidenced by arterial 02 desaturation due to diffusion limitation at moderate and heavy workloads after pneumonectomy (4). Furthermore, the pattern of decline in arterial 02 saturation after pneumonectoiny could be predicted from physiologically measured DLco ( 12).…”

“…DLCo was calculated using the same model described above (Eqs. [1][2][3][4] substituting CO for 02. Again, for the purpose of comparison with previous data, we used the same 0co as in the study by Weibel et al (19), calculated from the equation given by Holland (20,21) for dog blood at 40'C, the core temperature expected of exercising dogs: Data analysis.…”

Compensatory lung growth occurs in adult dogs after right pneumonectomy.

“…However, there were marked changes in the existing structures of the remaining lung, including hyperinflation, enlargement of the alveolar spaces, and thinning of the alveolar-capillary membrane. These structural changes were associated with a remarkable degree of functional compensation (4)(5)(6); no significant reduction in exercise capacity was found 1 yr after left pneumonectomy compared with before. We expected that if the larger right lung is resected, functional reserves in the remaining lung would be smaller, and exercise limitation would become more apparent.…”

Avaliação hemogasométrica em cães submetidos à pneumonectomia esquerda

“…Durante a anestesia, procurou-se empregar uma FIO 2 de 80% pois quando se emprega 100% de oxigênio, a chance de atelectasia pós-operatória é muito maior (Galiatsou et al 2006). Durante a avaliação de todos os momentos pós-operató-rios, foi mantido o equilíbrio ácido-básico, vale dizer que nenhum animal dos Grupos A e B desenvolveu alcalose ou acidose após a exérese do pulmão esquerdo, à semelhança ao observado por Wilcox et al (1979), Hsia et al (1990), Hjaimarsen et al (1995) e Miyazawa et al (1999) em seus estudos.…”