Increased left atrial pressure distorts pulmonary arterial impedance estimates in the low-range of frequency in rats
Authors: Hotta Naoshi , Fukumitsu Masafumi , Kawada Toru , Li Meihua , Nishikawa Takuya , Saku Keita 
Published: May 2024

BACKGROUD: Post-capillary pulmonary hypertension (PH), characterized as increased downstream pressure such as left atrial pressure (LAP), is the most prevalent type of PH and a significant contributor to right heart failure. Accurate estimation of pulmonary arterial characteristics, serving as right ventricular afterload, is crucial for management of PH. These characteristics can be captured comprehensively through pulmonary arterial impedance (PAZ), which elucidates pulmonary arterial pressure-flow relationship within the frequency domain. Although LAP waveforms are potential to affect the contours of pulmonary arterial pressure (PAP) and flow (PAF) waveforms, it remains unknown whether increased LAP affects the accuracy of PAZ measurement. This study aimed to investigate the impact of LAP on the accuracy of PAZ using an acute rodent model. METHODS: We measured pulmonary arterial blood flow (PAF), PAP, and LAP simultaneously in eight male Sprague-Dawley rats. PAZ was calculated as a reciprocal of admittance. Admittance was calculated in the following two ways: 1) one-input (PAP) and one-output (PAF) analysis (I1O1 analysis): the ratio of PAP(f) to PAF(f) at each frequency, where PAP(f) and PAF(f) are frequency spectra of PAP and PAF, respectively, and 2) two-input (PAP and LAP) and one-output (PAF) analysis (I2O1 analysis): excluding the potential effect of LAP from PAP and PAF. We measured PAZ under both normal physiological condition and post-capillary PH condition. To induce acute post-capillary PH by raising LAP >15 mmHg, we ligated aortic arch at the site between brachiocephalic artery and left common carotid artery and performed blood transfusion from a donor rat (TAL/BT). The accuracy of PAZ was examined as the coherence function representing the linearity between the input and output signals. Results: TAL/BT significantly increased LAP from 3 ± 1mmHg to 21 ± 4 mmHg and PAP from 17 ± 3 mmHg to 34 ± 3 mmHg (p<0.01 for both). The I2O1 analysis provided a consistently accurate estimation of PAZ under both normal and elevated LAP conditions with high coherence function (>0.9) in the wide range of frequency between 0.12 and 10.7 Hz. The I1O1 analysis also estimated the PAZ accurately in normal condition with high coherence function (>0.9) in the wide range of frequency, however, the I1O1 analysis overestimated PAZ in the low-range frequency between 0.12 and 1.0 Hz compared with the I2O1 analysis (I1O1: 0.32±0.10 vs. I2O1 0.23±0.06 mmHg/ml/min, p<0.01), with significantly lower coherence function (I1O1: 0.77±0.05 vs. I2O1: 0.96±0.01, p<0.01). CONCLUSION: Increased LAP may have the impact on the accuracy of PAZ estimation in the low-range frequency. The I2O1 analysis can lead to more accurate assessment of right ventricular afterload in post-capillary PH, compared with the I1O1 analysis. Grant-in-Aid for Young Scientists of the Japanese Society of Cardiovascular Anesthesiologists Project Number 2271000048. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.