Comprehensive Hemodynamic Assessments for Pulmonary Hypertension: Pulmonary Vascular Resistance, Capacitance, and Impedance

Abstract

Therapeutic strategies must be based on appropriate evaluation in pediatric pulmonary hypertension because of the diversity of its pathophysiology. Pulmonary arterial pressure is expressed as the product of pulmonary blood flow and pulmonary vascular resistance (R); however, pulmonary circulation exhibits high arterial capacitance (C), so circulatory resistance is the impedance defined as the combined resistance of R and C. Typically, C is expressed as the pulmonary stroke volume divided by the pulmonary artery pulse pressure, and the product of R and C is the time constant τ, which reflects the temporal changes in the pulmonary blood capacity. The time constant τ depends on age, heart rate, and left-atrial pressure. When the hyperbolic curve-plotting RC (RC coupling) is assessed, alterations in the C value in response to the R value are non-negligible in practical clinical settings. Therefore, C more sensitively reflects alterations in the pulmonary vascular beds. The pathophysiological factors of pediatric pulmonary hypertension are classified into left-to-right shunt due to congenital heart disease, left-heart obstructive disease, or left-heart diastolic dysfunction, alveolar hypoxemia, pulmonary vascular obstructive disease, and pulmonary vascular maldevelopment. The extent to which these five pathological factors contribute to pulmonary hypertension must be known. Consequently, it will be helpful to observe alterations in pulmonary arterial pressure as well as RC couplings while modifying each pathological factor during the appropriate evaluations in pediatric pulmonary hypertension.