Permeability of the endothelium and partitioning of the pulmonary blood flow resistance in isolated perfused pig lungs: effects of breed and age.

The right and left lungs of 5 healthy Minipigs and of 13 healthy Landrace piglets were isolated, perfused at constant pressure and maintained in an isogravimetric state under zone III conditions (pulmonary venous pressure greater than alveolar pressure). By applying the double, arterial and venous, occlusion technique, the total blood flow resistance (R) was partitioned into four components: arterial (Ra), pre- (Ra') and post-capillary (Rv') and venous (Rv). The capillary filtration coefficient (Kf,c) was evaluated by measuring the weight gained by the lungs when the arterial and venous pressures were suddenly increased. In the youngest Landrace piglets (5 weeks old), there was an uncontrolled vasoconstriction which sometimes prevented perfusion of the lungs and induced a large increase in Rt. These high values of Rt were decreased by tolazoline administration. The values of Rt recorded in older pigs (12-13 weeks old) were lower in Minipigs (33.66 +/- 3.77 cmH2O min L-1 per 100 g of lungs; n = 5) than in Landrace piglets (55.20 +/- 6.18 cmH2O min L-1 per 100 g; n = 5). This breed difference was due to the differences in Ra' and Rv'. The mean values of Kf,c were 0.193 +/- 0.015 and 0.202 +/- 0.029 ml min (cmH2O)-1 per 100 g of the lungs in Minipigs and Landrace piglets respectively. All these parameters were stable for the 3 hours following the equilibrium period. It was concluded that: (1) There is an age-related maturation of the control of the vasomotor tone in porcine lungs. (2) Pulmonary microvascular haemodynamics are influenced by the breed of the pigs. (3) There was no difference in the Kf,c values between both the breeds. (4) A comparison of the values reported for dogs and rabbits with our data shows that the pre- and post-capillary resistances and, to a lesser extent, the arterial and venous resistances are relatively high in pigs.