The pulsatile component of left atrial pressure has little effect on pulmonary artery impedance estimation in normal rats

Pulmonary artery impedance (PAZ) that measures the pulsatile properties of the vasculature provides diagnostic and prognostic information in patients with pulmonary vascular diseases. While downstream pressure [i.e., left atrial (LA) pressure] should be considered when calculating static properties of pulmonary vasculature, PAZ is commonly estimated without taking into account the pulsatile component of LA pressure. We examined whether PAZ can be estimated with reasonable accuracy without using LA pressure. Pulmonary artery (PA) flow, PA pressure, and LA pressure were measured under irregular pacing in eight normal Sprague‐Dawley rats. PAZ was estimated by analyzing a one‐input, one‐output system (I1O1 analysis) that does not include LA pressure, and a two‐input, one‐output system (I2O1 analysis) that includes LA pressure. Using a tube and 3‐element Windkessel model, PAZ was parameterized as peripheral resistance (R(P)), arterial compliance (C(P)), characteristic impedance (Z(C)), and transmission time to the reflection site (T(D)). These parameters were not significantly different between the I1O1 and I2O1 analyses (R(P): 0.286 ± 0.040 vs. 0.274 ± 0.038 mmHg·min/mL, C(P): 0.352 ± 0.049 vs. 0.343 ± 0.041 mL/mmHg, Z(C): 0.115 ± 0.005 vs. 0.117 ± 0.005 mmHg·min/mL, T(D): 13.2 ± 1.8 vs. 12.9 ± 1.7 msec). In conclusion, the I1O1 analysis that does not use LA pressure estimates PAZ with reasonable accuracy compared with the I2O1 analysis that uses LA pressure in normal rats. Our finding that the pulsatile component of LA pressure contributes little to PAZ estimation may justify the clinical use of the I1O1 analysis.