The Effect of Increased Pulmonary Blood Flow on the Pulmonary Vascular Bed in Pigs

Abstract

ExtractIncreased pulmonary blood flow was produced in 1-month-old piglets by means of left pneumonectomy, arteriovenous fistulas in the neck, and a combination of both. Physiologic and histologic studies of the pulmonary vascular bed were done 1-9 months after operation.A progressive, moderate increase in pulmonary artery ( P A ) pressure was observed, especially between 1 and 6 months after surgery. This was flow related, 1.e.. the group with the highest flow (pneumonectomy plus fistula) was found to have the most prominent increase in pressure. Mean PA pressure at 6 months was 28.7 ~t 0.07 mm H g in this group, vs 24.4 0.48 mm H g in the group with pneumonectomy alone and 17.2 ~t 0.48 mm H g in controls ( P < 0.01). The pressure response to hypoxia in pigs with high pulmonary blood flow was not different from that found in control animals.Histologic studies revealed that small arteries and arterioles of pigs with high pulmonary blood flow had a decreased relative wall thickness because of dilation up to 6 months follow-up. This was flow related, the group with the highest flow having the lowest wall thickness to vessel diameter ratio; relative wall thickness (in percentage of the vessel diameter) at 6 months was 6.1 s= 0.44% in pigs with pneumonectomy plus fistula. vs 9.6 0.40% in the group with pneumonectomy alone and 11.2 * 0.61% in controls ( P < 0.01). In the group with the highest flow, thick walled arterioles appeared at 9 months follow-up, scattered among dilated ones; mean medial wall thickness in these animals increased significantly between 6 and 9 months after operation, ranging from 6.1 =t 0.44% to 11.3 + 0.73% (P < 0.01).In five animals with high flow, the right PA (main branch) showed patchy intimal thickening, small cystic spaces filled with mucopolysaccharides in the media, and muscular hypertrophy. SpeculationSome changes usually seen in pulmonary hypertension were produced in this model by high pulmonary blood flow in the presence of only mild to moderate elevation of P A pressure. The dilation observed in the pulmonary arteries and arterioles may have been a pathogenetic factor; indeed, it is likely that wall tension rather than intravascular pressure induces vascular changes; wall tension (according to Laplace's law) depends on vessel diameter as well as intravascular pressure. Therefore, in a dilated vascular bed, wall tension will increase considerably with only moderate increase in PA pressure, inducing changes usually seen with more severe degrees of pulmonary hypertension.Pulmonary vascular disease remains a serious complication of congenital heart disease with a left-to-right shunt. Little is known about the pathogenesis of this condition, but three factors are believed to be involved: increased pulmonary blood flow, a raised pulmonary artery pressure, and high left atrial pressure.Experimental models used to study pulmonary vascular disease often involve anastomoses between aorta and pulmonary artery, whereby two if not all three of the above mentioned factors are produced (1, 4).In ...

Changes in pulmonary blood flow affect vascular response to chronic hypoxia in rats.

“…Increased flow to the right lung has been created experimentally in animals by ligating the left pulmonary artery (Leibow et al, 1950;McGrady et al, 1968;Linde et al, 1970;Rosencrantz et al, 1973;Lansimies, 1975;Haworth et al, 1981) or by banding it (Liebow et al, 1950;Cheung, 1976) or by performing a left pneumonectomy (Rudolph et al, 1961;Kato et al, 1971;Freidli et al, 1975). Banding rather than ligating the pulmonary artery avoids the increase in collateral flow associated with the latter procedure (Leibow et al, 1950).…”

“…The series of experiments we report here is unique in that we document the differences in pressures and flows in the two lungs and relate the altered hemodynamic states to a quantitative assessment of the structural remodeling of the Hypoxia TT TT --I I TT Tf TT TT U 11 --Band + Hypoxia TT TT T -T -TTT T TTT T 11 II - Not all species demonstrate a rise in pulmonary artery pressure in response to a chronic increase in flow which we documented in this study in adult rats. For example, after left pneumonectomy, beagle puppies do not show the rise in right pulmonary artery pressure (Freidli et al, 1975) which can be demonstrated in mongrel puppies (Rudolph et al, 1961), in minipigs (Kato et al, 1971), and in piglets (Haworth et al, 1981). The latter study was the first to document that high flow to the right lung is not immediately accompanied by an increase in pressure, but only after the development of structural changes in the peripheral pulmonary arteries.…”

Vascular Responsiveness in Isolated Rat Lungs is Inversely Related to Blood Flow

“…Reductions in vessel wall-to-lumen ratios have been demonstrated in animal prepara tions with High blood flow [4,14]. Further more, pulmonary vessels with a low wall-tolumen ratio require greater smooth muscle contraction or a greater contractile stimulus to produce a similar change in vascular re sistance.…”

“…Left pulmonary artery ligation in dogs has been shown to increase right lung perfusion and increase pulmonary vascular respon siveness to anesthetic agents [10]. However, no change in the pulmonary pressor re sponse to hypoxia was observed after left pneumonectomy in pigs [4,9] and dogs [9], On the other hand, a decrease in pulmonary vascular responsiveness to prostaglandin F2" (PGF2o) and hypoxia has been demon strated in dogs after unilateral pulmonary artery ligation [16]. In all of these studies, however, the ability to make multiple ad justments of blood flow was limited.…”

Pulmonary Hypertension Caused by Pulmonary Venous Hypertension

“…[101][102][103][104] Likewise, in multiple experimental models of increased pulmonary blood flow with or without increased PAP, small PAs are usually of normal or reduced diameter. [105][106][107] Whether smooth muscle mass is normal or increased cannot be determined from the data presented, but reduced vessel diameter (and thickened media) is consistent with eutropic remodeling. Although such remodeling would not directly account for dilation lesions (which are not seen with PVH-PH but are seen with other forms of PH), increased PAP due to narrowed resistance vessels could lead to other microarchitectural abnormalities.…”