Influence of moderate vasoconstriction on the wave reflection properties of the pulmonary arterial bed

Tuning of pulmonary arterial circulation evidenced by MR phase mapping in healthy volunteers

Magnetic resonance (MR) phase mapping was used to noninvasively assess both blood flow and cross-sectional area (CSA) in the main pulmonary artery (MPA) of 12 healthy volunteers. Flow and CSA patterns exhibited two positive peaks: high systolic and small diastolic. This finding can be explained using a simple "distributed" theoretical model that takes into account the role of a reflected pressure wave from pulmonary vascular impedance in generating a diastolic flow. The mean reflection coefficient of pressure wave, MPA input impedance, and pulmonary vascular impedance were assessed. We verified, in this series, that pressure wave velocity appears to be age-dependent. MR phase mapping has been used to observe the tuning (resonance) of the right cardiovascular system at rest under physiological conditions. MR phase mapping could be used to assess pathological modifications of the tuning that occurs in cases of pulmonary arterial hypertension.

Pulmonary arterial impedance after single lung transplantation

Single lung transplantation (SLT) is emerging as definitive therapy for end-stage pulmonary disease of varying etiology, yet a complete description of the hemodynamic properties of the transplanted lung has not been reported. In this study, Fourier analysis was used to calculate the pulmonary arterial (PA) impedance spectrum before and immediately after SLT to define precisely the pulmonary pressure-flow relationship. Median sternotomies were performed in 18 dogs (donors): an ultrasonic flow probe was placed around the PA and micromanometers were placed in the PA and left atrium (LA). Control PA pressure and flow (PAQ) and LA pressure were measured during transient occlusion of the right PA. The lungs were harvested using cold modified Euro-Collins solution for preservation. After thoracotomy and pneumonectomy, left SLT was performed in 18 recipient dogs with a mean ischemic time of 179 +/- 6 min. After reperfusion for 1 hr, PA pressure and flow data were again collected. Characteristic impedance (Z0), a measure of resistance to pulsatile flow, was compared to input resistance (Rin), a measure of resistance to mean flow, and pulmonary vascular resistance (PVR), the conventional index. Rin is defined as the zeroth harmonic of the impedance spectrum and Z0 as the mean of impedance moduli from 2-12 Hz. All recipients survived transplantation. Both PVR and Rin increased significantly after transplantation (11 +/- 1 vs 19 +/- 3 Wood U, P less than 0.05, and 1352 +/- 121 vs 1964 +/- 244 dyne.sec.cm-5, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of vessel distension and myogenic tone on pulmonary arterial input impedance. A study using a computer model of rabbit lung

A computer model of the pulmonary arterial (PA) bed of rabbit lungs was designed in order to test experimental observations of changes in PA input impedance and pulsatile hydraulic power (cap.) during increased PA pressure. The computer model was based on a simple 3-component analog representation of single vessels (i.e. resistance, inertance and compliance). 16 generations of arterial vessels, from PA to 60 mum diameter, were combined to calculate PA input impedance. Input impedance was found to mimic closely that observed experimentally. Both venous pressure elevation and arteriolar constriction was found to reduce input impedance and Wp. By combining arteriolar constriction with increased myogenic tone of the larger arteries, Wp was found to show a minimum level at a certain PA pressure, dependent on the degree of arterial stiffening. Wp was found to follow changes in arterial volume and resistance during stimulated vasoconstriction. Wp dissipation in arterial vessels was calculated to approx. 50% of total imput Wp at physiological pressure conditions, and could be reduced by one half after PA pressure increase from 20 to 50 cm H2O, despite a concurrent halving of arterial compliance. Arterial vessels smaller than 200 mum diameter were found to have negligible direct influence on PA input impedance.

The influence of pulmonary blood flow rate on vascular input impedance and hydraulic power in the sympathetically and noradrenaline stimulated cat lung

This study was designed to evaluate the influence of sympathetic nerve stimulation (SN) and alpha-adrenergic receptor stimulation (alphaS) on the pulmonary vascular input impedance and hydraulic power output of the right heart during variations of cardiac output (CO). An open chest cat preparation was used and pulsatile pressure and flow in the pulmonary artery were measured by high frequency response transducers. Calculations showed that vascular resistance (VR) was inversely dependent on CO, but input impedance of the unstimulated lung was not influenced by CO variations. NS or alphaS increased VR and input impedance significantly, and the relation pulsatile hydraulic power/total hydraulic power (Wp/Wt) increased 40%, indicating that such stimulation has larger relative influence on impedance than on resistance. The reduction of arterial compliance during NS (maximal stimulus) was calculated to be 60%, independent of CO. Input impedance during NS or alphaS was reduced by CO elevations, probably because the concomitant distension of the arterial bed reduced arterial resistance and inertance. The ratio Wp/CO, which expresses the fraction of pulsatile hydraulic power lost per ml mean arterial flow, was found to be flow dependent both in control and stimulated conditions: Wp/CO was positively correlated to CO in control condition and weakly negatively correlated to CO during stimulation. At high CO the arterial vessels could be stimulated and stiffened without much extra load on the right heart.