Nocturnal hypercapnia with daytime normocapnia in patients with advanced pulmonary arterial hypertension awaiting lung transplantation.

Background: Pulmonary arterial hypertension (PAH) is frequently complicated by sleep disordered breathing (SDB), and previous studies have largely focused on hypoxemic SDB. Even though nocturnal hypercapnia was shown to exacerbate pulmonary hypertension, the clinical significance of nocturnal hypercapnia among PAH patients has been scarcely investigated.
Method: Seventeen patients with PAH were identified from 246 consecutive patients referred to Kyoto University Hospital for the evaluation of lung transplant registration from January 2010 to December 2017. Included in this study were 13 patients whose nocturnal transcutaneous carbon dioxide partial pressure (PtcCO2) monitoring data were available. Nocturnal hypercapnia was diagnosed according to the guidelines of the American Academy of Sleep Medicine. Associations of nocturnal PtcCO2 measurements with clinical features, the findings of right heart catheterization and pulmonary function parameters were evaluated.
Results: Nocturnal hypercapnia was diagnosed in six patients (46.2%), while no patient had daytime hypercapnia. Of note, nocturnal hypercapnia was found for 5 out of 6 patients with idiopathic PAH (83.3%). Mean nocturnal PtcCO2 levels correlated negatively with the percentage of predicted total lung capacity (TLC), and positively with cardiac output and cardiac index.
Conclusion: Nocturnal hypercapnia was prevalent among advanced PAH patients who were waiting for lung transplantation, and associated with %TLC. Nocturnal hypercapnia was associated with the increase in cardiac output, which might potentially worsen pulmonary hypertension especially during sleep. Further studies are needed to investigate hemodynamics during sleep and to clarify whether nocturnal hypercapnia can be a therapeutic target for PAH patients.
Competing Interests: I have read the journal's policy and the authors of this manuscript have the following competing interests: Yoshinari Nakatsuka and Naomi Takahashi reports grants from Philips-Respironics, grants from ResMed Japan, grants from Fukuda Denshi, grants from Fukuda Lifetec Keiji. Kimihiko Murase and Hirofumi Takeyama reports grants from Philips-Respironics, grants from Teijin Pharma, grants from Fukuda Denshi, grants from Fukuda Lifetec Keiji. Kazuo Chin reports grants and personal fees from Philips-Respironics, grants and personal fees from Teijin Pharma, grants and personal fees from Fukuda Denshi, grants and personal fees from Fukuda Lifetec Keiji, grants from KYORIN Pharmaceutical Co., Ltd, grants from Nippon Boehringer Ingelheim Co., Ltd, grants and personal fees from GlaxoSmithKline, personal fees from MSD, personal fees from ResMed, personal fees from Astellas Pharma, personal fees from Eisai Co., Ltd. Hideyuki Kinoshita reports personal fees from Actelion Pharmaceuticals Japan Ltd., Nippon Shinyaku Co., Ltd, Bayer Yakuhin, Ltd., and research grant from Bayer Yakuhin, Ltd. Toyofumi Chen-Yoshikawa, Akihiro Aoyama, Hiroyasu Kubo, Satoshi Hamada, Takuma Minami, Kiminobu Tanizawa, Tomohiro Handa, Toyohiro Hirai and Hiroshi Date declare no potential conflict of interests. The Department of Respiratory Care and Sleep Control Medicine is funded by endowments from Philips-Respironics, ResMed, Fukuda Denshi and Fukuda Lifetec-Keiji to Kyoto University. These competing interests do not alter our adherence to PLOS ONE policies on sharing data and materials.