The Effect of Acute Alterations in Left Atrial Pressure on Rc Time in the Pulmonary Circulation

PurposeThe product of pulmonary vascular resistance (PVR) and pulmonary artery compliance (PAC) describes the time constant (RC time) of the pulmonary circulation. RC time integrates parameters which describe the steady and pulsatile afterload of the right ventricle. This study investigated the effects of acute changes in left atrial pressure (LAP) on RC-time using hi-fidelity pulmonary artery (PA) pressure waveform analysis.MethodsPatients with left ventricular assist devices (LVADs) were recruited during right heart catheterization (RHC) and clinical ramp study was performed to assess change in left atrial pressure on RC time and PAC. Pulmonary arterial waveform was recorded at highest and lowest LVAD speeds using Mikrocath pressure catheter sample at 1000Hz. Phase plane analysis was then performed on 10 consecutive diastolic decay waveforms at each speed to calculate RC-time.Results5 patients underwent ramp studies with simultaneous RHC. Mean pulmonary arterial wedge pressure (mPAWP) was altered acutely by a mean of 5mmHg (range 4-6). Mean pulmonary arterial pressure (mPAP) changed by 3 mmHg (range 0-5) and pulmonary vascular resistance (PVR) by 0.02 WU (range -1.3-2.0). RC time derived from waveform analysis deviated significantly from RC time estimated by the PVR and volume (SV)/pulse pressure (PP) product. Consequently, PAC also deviated significantly from SV/PP. Acute increase in PAWP resulted in shortening of the RC-time.ConclusionMeasuring RC time using direct pressure waveform analysis produces significantly different results from PVR*SV/PP. RC time reliably shortens with acute elevations in PAWP, suggesting that PAWP can augment pulsatile RV afterload without intrinsic pulmonary vascular remodelling. Further studies are needed to investigate whether direct of analyses of PA waveform provides more meaningful assessment of the pulsatile load. The product of pulmonary vascular resistance (PVR) and pulmonary artery compliance (PAC) describes the time constant (RC time) of the pulmonary circulation. RC time integrates parameters which describe the steady and pulsatile afterload of the right ventricle. This study investigated the effects of acute changes in left atrial pressure (LAP) on RC-time using hi-fidelity pulmonary artery (PA) pressure waveform analysis. Patients with left ventricular assist devices (LVADs) were recruited during right heart catheterization (RHC) and clinical ramp study was performed to assess change in left atrial pressure on RC time and PAC. Pulmonary arterial waveform was recorded at highest and lowest LVAD speeds using Mikrocath pressure catheter sample at 1000Hz. Phase plane analysis was then performed on 10 consecutive diastolic decay waveforms at each speed to calculate RC-time. 5 patients underwent ramp studies with simultaneous RHC. Mean pulmonary arterial wedge pressure (mPAWP) was altered acutely by a mean of 5mmHg (range 4-6). Mean pulmonary arterial pressure (mPAP) changed by 3 mmHg (range 0-5) and pulmonary vascular resistance (PVR) by 0.02 WU (range -1.3-2.0). RC time derived from waveform analysis deviated significantly from RC time estimated by the PVR and volume (SV)/pulse pressure (PP) product. Consequently, PAC also deviated significantly from SV/PP. Acute increase in PAWP resulted in shortening of the RC-time. Measuring RC time using direct pressure waveform analysis produces significantly different results from PVR*SV/PP. RC time reliably shortens with acute elevations in PAWP, suggesting that PAWP can augment pulsatile RV afterload without intrinsic pulmonary vascular remodelling. Further studies are needed to investigate whether direct of analyses of PA waveform provides more meaningful assessment of the pulsatile load.