In Transgenic Erythropoietin Deficient Mice, an Increase in Respiratory Response to Hypercapnia Parallels Abnormal Distribution of CO2/H+-Activated Cells in the Medulla Oblongata

Survival benefit of CPAP therapy among dialysis patients with obstructive sleep apnea

BACKGROUND AND HYPOTHESIS

We observed lower risk of all-cause mortally among continuous positive airway pressure (CPAP) users compared to those non-users using a large polysomnography (PSG) registry. However, the effect of CPAP on mortality risk has not been examined in dialysis patents.

METHODS

We studied 9841 patients with PSG performed from September 1990 to 2010 in Nakamura clinic, Okinawa. Among them, we found 195 dialysis patients: 16 (1.0%) dialysis patients with apnea hypopnea index (AHI) < 5/hour in 1665 subjects and 179 (2.2%) in 8176 obstructive sleep apnea (OSA) patients. CPAP users were defined as patients who had been on CPAP for more than one month. Patients qualified and eligible for CPAP but refused were assigned as CPAP non-users. The median observation was 6.6 years. Mortality rates were compared between CPAP users and non-users using multivariate logistic analysis adjusted for age, sex, body mass index (BMI), AHI and medical history.

RESULTS

Among OSA dialysis patients (men 127, women 37), 116 (2.6%) were CPAP users and 48 (2.3%) were CPAP non-users. The number of deaths was 52 (29 CPAP users and 23 (CPAP non-users) during follow-up. The death rate was 25.0% for CPAP users and 47.9% for non-users. CPAP users showed better survival; hazard ratio (HR) 0.47 and 95% confidence interval (CI) of 0.27-0.81 (P = 0.007).

CONCLUSION

Dialysis patients with OSA showed better survival rates with the use of CPAP. Screening for OSA is recommended if patients complain of sleep problems, such as insomnia, daytime sleepiness, headache, and fatigue.

Fos expression in A1/C1 neurons of rats exposed to hypoxia, hypercapnia, or hypercapnic hypoxia

The distribution of Fos expression in catecholaminergic neurons with immunoreactivity for dopamine β-hydroxylase (DBH) of the ventrolateral medulla was compared between rats exposed to hypoxia (10 % O2), hypercapnia (8 % CO2), and hypercapnic hypoxia (8 % CO2 and 10 % O2) for 2 h. Among the experimental groups, hypoxia-exposed rats had more Fos/DBH double-immunoreactive neurons than the control group (20 % O2) in the rostral area of the ventrolateral medulla, specifically in the range of + 150 μm to + 2,400 μm from the caudal end of the facial nerve nucleus. On the other hand, Fos/DBH double-immunoreactive neurons were scarcely observed in the ventrolateral medullary region of hypercapnia-exposed rats. The number of double-immunoreactive neurons in hypercapnic hypoxia-exposed rats was comparable to that in the control group. The present results suggest that adrenergic C1 neurons are specifically activated by hypoxia and are involved in the regulation of respiratory and circulatory functions.

Establishment of a Diamond-Blackfan anemia like model in zebrafish

BACKGROUND

Anemia is defined as a lack of erythrocytes, low hemoglobin levels, or abnormal erythrocyte morphology. Diamond-Blackfan anemia (DBA) is a rare and severe congenital hypoplastic anemia that occurs due to the dominant inheritance of a ribosomal protein gene mutation. Even rarer is a case described as Diamond-Blackfan anemia like (DBAL), which occurs due to a loss-of-function EPO mutation recessive inheritance. The effective cures for DBAL are bone marrow transfusion and treatment with erythropoiesis-stimulating agents (ESAs). To effectively manage the condition, construction of DBAL models to identify new medical methods or screen drugs are necessary.

RESULTS

Here, an epoa-deficient mutant zebrafish called epoaszy8 was generated to model DBAL. The epoa-deficiency in zebrafish caused developmental defects in erythroid cells, leading to severe congenital anemia. Using the DBAL model, we validated a loss-of-function EPO mutation using an in vivo functional analysis and explored the ability of ESAs to alleviate congenital anemia.

CONCLUSIONS

Together, our study demonstrated that epoa deficiency in zebrafish leads to a phenotype resembling DBAL. The DBAL zebrafish model was found to be beneficial for the in vivo assessment of patient-derived EPO variants with unclear implications and for devising potential therapeutic approaches for DBAL.

KCNK3 channel is important for the ventilatory response to hypoxia in rats

To clarify the contribution of KCNK3/TASK-1 channel chemoreflex in response to hypoxia and hypercapnia, we used a unique Kcnk3-deficient rat. We assessed ventilatory variables using plethysmography in Kcnk3-deficient and wild-type rats at rest in response to hypoxia (10% O2) and hypercapnia (4% CO2). Immunostaining for C-Fos, a marker of neuronal activity, was performed to identify the regions of the respiratory neuronal network involved in the observed response.Under basal conditions, we observed increased minute ventilation in Kcnk3-deficient rats, which was associated with increased c-Fos positive cells in the ventrolateral region of the medulla oblongata. Kcnk3-deficient rats show an increase in ventilatory response to hypoxia without changes in response to hypercapnia. In Kcnk3-deficient rats, linked to an increased hypoxia response, we observed a greater increase in c-Fos-positive cells in the first central relay of peripheral chemoreceptors and Raphe Obscurus. This study reports that KCNK3/TASK-1 deficiency in rats induces an inadequate peripheral chemoreflex, alternating respiratory rhythmogenesis, and hypoxic chemoreflex.

Does fetal growth restriction induce neuropathology within the developing brainstem?

Fetal growth restriction (FGR) is a complex obstetric issue describing a fetus that does not reach its genetic growth potential. The primary cause of FGR is placental dysfunction resulting in chronic fetal hypoxaemia, which in turn causes altered neurological, cardiovascular and respiratory development, some of which may be pathophysiological, particularly for neonatal life. The brainstem is the critical site of cardiovascular, respiratory and autonomic control, but there is little information describing how chronic hypoxaemia and the resulting FGR may affect brainstem neurodevelopment. This review provides an overview of the brainstem-specific consequences of acute and chronic hypoxia, and what is known in FGR. In addition, we discuss how brainstem structural alterations may impair functional control of the cardiovascular and respiratory systems. Finally, we highlight the clinical and translational findings of the potential roles of the brainstem in maintaining cardiorespiratory adaptation in the transition from fetal to neonatal life under normal conditions and in response to the pathological environment that arises during development in growth-restricted infants. This review emphasises the crucial role that the brainstem plays in mediating cardiovascular and respiratory responses during fetal and neonatal life. We assess whether chronic fetal hypoxaemia might alter structure and function of the brainstem, but this also serves to highlight knowledge gaps regarding FGR and brainstem development.

Chronic pulmonary fibrosis alters the functioning of the respiratory neural network

Some patients with idiopathic pulmonary fibrosis present impaired ventilatory variables characterised by low forced vital capacity values associated with an increase in respiratory rate and a decrease in tidal volume which could be related to the increased pulmonary stiffness. The lung stiffness observed in pulmonary fibrosis may also have an effect on the functioning of the brainstem respiratory neural network, which could ultimately reinforce or accentuate ventilatory alterations. To this end, we sought to uncover the consequences of pulmonary fibrosis on ventilatory variables and how the modification of pulmonary rigidity could influence the functioning of the respiratory neuronal network. In a mouse model of pulmonary fibrosis obtained by 6 repeated intratracheal instillations of bleomycin (BLM), we first observed an increase in minute ventilation characterised by an increase in respiratory rate and tidal volume, a desaturation and a decrease in lung compliance. The changes in these ventilatory variables were correlated with the severity of the lung injury. The impact of lung fibrosis was also evaluated on the functioning of the medullary areas involved in the elaboration of the central respiratory drive. Thus, BLM-induced pulmonary fibrosis led to a change in the long-term activity of the medullary neuronal respiratory network, especially at the level of the nucleus of the solitary tract, the first central relay of the peripheral afferents, and the Pre-Bötzinger complex, the inspiratory rhythm generator. Our results showed that pulmonary fibrosis induced modifications not only of pulmonary architecture but also of central control of the respiratory neural network.