Vasomotor tone in the pulmonary vascular bed in patients with left-to-right shunts

Pulmonary blood flow and pulmonary hypertension: Is the pulmonary circulation flowophobic or flowophilic?

Increased pulmonary blood flow (PBF) is widely thought to provoke pulmonary vascular obstructive disease (PVO), but the impact of wall shear stress in the lung is actually poorly defined. We examined information from patients having cardiac lesions which impact the pulmonary circulation in distinct ways, as well as experimental studies, asking how altered hemodynamics impact the risk of developing PVO. Our results are as follows: (1) with atrial septal defect (ASD; increased PBF but low PAP), shear stress may be increased but there is little tendency to develop PVO; (2) with normal PBF but increased pulmonary vascular resistance (PVR; mitral valve disease) shear stress may also be increased but risk of PVO still low; (3) with high PVR and PBF (e.g., large ventricular septal defect), wall shear stress is markedly increased and the likelihood of developing PVO is much higher than with high PBF or PAP only; and (4) with ASD, experimental and clinical observations suggest that increased PBF plus another stimulus (e.g., endothelial inflammation) may be required for PVO. We conclude that modestly increased wall shear stress (e.g., ASD) infrequently provokes PVO, and likely requires other factors to be harmful. Likewise, increased PAP seldom causes PVO. Markedly increased wall shear stress may greatly increase the likelihood of PVO, but we cannot discriminate its effect from the combined effects of increased PAP and PBF. Finally, the age of onset of increased PAP may critically impact the risk of PVO. Some implications of these observations for future investigations are discussed.

The pulmonary vascular response to oxygen and its influence on operative results in children with ventricular septal defect

The ratio of pulmonary vascular resistance to systemic resistance was determined before and after oxygen administration in 25 children with an isolated large ventricular septal defect and elevated pulmonary vascular resistance (pulmonary/systemic resistance ratio, Rp/Rs greater than 0.25). A fall of 30% or more in the Rp/Rs, after 20 minutes of oxygen inhalation (FiO2 greater than 0.90), was considered a positive response to oxygen. In the 6 children with Down's syndrome, the Rp/Rs fell significantly more in oxygen (52%) than it did in the 19 children without Down's syndrome (31%, p less than 0.05). No other clinical or baseline hemodynamic finding was predictive of vascular responsiveness. Seventeen children underwent closure of the ventricular septal defect. Three of 11 children who responded to O2 expired shortly after operation; each of the 6 children who did not respond to O2 survived operation. Two of the deaths (occurring less than 12 hours after closure) were from low cardiac output; a third child died suddenly 5 days postoperatively. Thirteen children, 7 who responded to oxygen and 6 who did not, were restudied by cardiac catheterization an average of 2.0 years following successful closure of the ventricular septal defect. While the Rp/Rs in room air fell following closure of the defect in both groups, the decrease was 22% in responders and 28% in nonresponders. The results of this study, unlike similar studies performed at higher altitudes, suggest that the preoperative responsiveness of the pulmonary vasculature to oxygen does not predict either operative survival or postoperative pulmonary vascular resistance.

Haemodynamic studies after repair of ventricular septal defect

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