Oxygen and pulmonary arterial hypertension: effects, mechanisms, and therapeutic benefits

Epidemiology of supplemental oxygen in patients with pulmonary hypertension

BACKGROUND AND OBJECTIVE

Patients with pulmonary hypertension (PH) may present with hypoxaemia at rest or during daily activities. There is no epidemiological data on the prescription of long-term oxygen therapy (LTOT) in patients with PH. The study sought to analyse the prevalence and incidence of LTOT prescription among patients with pulmonary arterial hypertension (PAH) or chronic thromboembolic pulmonary hypertension (CTEPH) in Spain and to determine predictors for this prescription.

METHODS

A retrospective analysis was performed from the Spanish Registry of Pulmonary Arterial Hypertension (REHAP). Collected data included demographics and anthropometric measurements, functional class (FC), arterial blood gases, pulmonary function tests, haemodynamic measurements, six-minute walking distance (6MWD) and LTOT prescription. In addition, we assessed the prevalence and incidence of LTOT prescription by PH group and subtype and potential predictors for LTOT initiation in the first 5 years after diagnosis.

RESULTS

We analysed 4533 patients (69.9% PAH and 30.1% CTEPH), mostly female (64.5%), with a mean age of 53.0 ± 18.3 years. The prevalence of LTOT was 19.3% for all patients. The incidence of LTOT prescriptions decreased from 5.6% to 1.6% between 2010 and 2019, respectively. Predictors for LTOT prescription, excluding those that represent the indication for oxygen therapy were: FC (HR: 1.813), 6MWD (HR: 1.002), mean pulmonary arterial pressure (mPAP) (HR: 1.014), cardiac index (CI) (HR: 1.253), pulmonary vascular resistance (PVR) (HR: 1.023) and diffusing capacity of carbon monoxide (DLCO) (HR: 1.294).

CONCLUSION

The prevalence of LTOT in PAH and CTEPH patients is close to 20%. FC, 6MWD, mPAP, CI, PVR and DLCO were predictors for LTOT prescription.

Effects of different ventilatory settings on alveolar and pulmonary microvessel dimensions in pigs

Mechanical ventilation with high tidal volume (TV) or positive end-expiratory pressure (PEEP) may induce lung overinflation and increased pulmonary vascular resistance to flow. In 8 healthy mechanically ventilated pigs, we evaluated whether incident dark field (IDF) vital microscopy, applied through a small thoracotomy, could be used to evaluate changes in alveolar and pulmonary microvessel dimensions under different ventilator settings. High TV (12 ml/kg) increased alveolar diameters (from 99 ± 13 to 114 ± 6 μm, p < 0.05 repeated measures one way analysis of variance) and reduced septal capillary diameters (from 12.1 ± 1.7 to 10.5 ± 1.4 μm, p < 0.001) as compared to 8 ml/kg TV. This effect was more pronounced in non-dependent lung. Alveolar and microvessel diameters did not change with high PEEP (12 cmH2O Vs. 5 cmH2O). High FiO2 (100%) led to pulmonary vasodilation (from 12.1 ± 1.7 to 14.7 ± 1.4 μm, p < 0.001), with no change in alveolar dimensions as compared to 50% FiO2. In conclusion, IDF imaging enabled to obtain high-quality images of subpleural alveoli and microvessels. High TV ventilation may induce alveolar distension with compression of septal capillaries, thus potentially increasing dead space ventilation.

Dihydromyricetin treats pulmonary hypertension by modulating CKLF1/CCR5 axis-induced pulmonary vascular cell pyroptosis

Pulmonary hypertension (PH) is a progressive cardiopulmonary disease characterized by elevated pulmonary artery pressure and vascular remodeling, resulting in poor prognosis and increased mortality rates. Chemokine-like factor 1 (CKLF1) plays a significant role in inducing inflammation and cell proliferation, both of which are critical processes in the pathogenesis of various diseases. Dihydromyricetin (DMY) has garnered attention for its potent anti-inflammatory properties. This study evaluated the protective effects of DMY against PH, demonstrating that DMY treatment can mitigate pyroptosis in pulmonary artery endothelial cells (PAECs) and pulmonary artery smooth muscle cells (PASMCs) in vivo via the CKLF1/CCR5 axis. Results indicated significant improvements in hemodynamics, inflammatory responses, fibrosis, vascular remodeling, and right ventricular hypertrophy in PH rats following DMY treatment. Furthermore, the interaction between CKLF1 and CCR5 was investigated in CKLF1-/- rats after PH induction. DMY was found to downregulate CKLF1 expression and the inflammatory response in the lungs, with its therapeutic efficacy diminished following CKLF1 knockdown. This study underscores the therapeutic potential of DMY in the management of PH and lays a foundation for future research and clinical applications.

Pulmonary Hypertension: Pharmacological and Non-Pharmacological Therapies

Pulmonary hypertension (PH) is a severe and chronic disease characterized by increased pulmonary vascular resistance and remodeling, often precipitating right-sided heart dysfunction and death. Although the condition is progressive and incurable, current therapies for the disease focus on multiple different drugs and general supportive therapies to manage symptoms and prolong survival, ranging from medications more specific to pulmonary arterial hypertension (PAH) to exercise training. Moreover, there are multiple studies exploring novel experimental drugs and therapies including unique neurostimulation, to help better manage the disease. Here, we provide a narrative review focusing on current PH treatments that target multiple underlying biochemical mechanisms, including imbalances in vasoconstrictor-vasodilator and autonomic nervous system function, inflammation, and bone morphogenic protein (BMP) signaling. We also focus on the potential of novel therapies for managing PH, focusing on multiple types of neurostimulation including acupuncture. Lastly, we also touch upon the disease's different subgroups, clinical presentations and prognosis, diagnostics, demographics, and cost.

Long-term oxygen therapy in precapillary pulmonary hypertension - SOPHA study

Current guidelines recommend oxygen (O2) supplementation in patients with pulmonary hypertension (PH), despite scarce data on long-term O2 therapy (LTOT). The aim of this prospective, randomized, controlled trial was to investigate the effect of LTOT in patients with precapillary PH on exercise capacity, clinical parameters and hemodynamics. Patients with precapillary PH under stable therapy and O2 desaturations at rest and/or during exercise were randomized to receive LTOT (≥ 16 h/day) or no O2 (control group) for 12 weeks. The control group was offered LTOT after 12 weeks. The primary endpoint changes of 6-minute walking distance (6MWD) from baseline to 12 weeks was hierarchically tested: (1) pre-post primary and secondary intervention (2) intervention vs. control group. Secondary endpoints included changes in clinical parameters. Twenty patients were randomized (women n = 14, age 67 ± 11.4 years, mean pulmonary arterial pressure 39.7 ± 12.5 mmHg, 70% functional class III). 6MWD significantly improved by 42.2 ± 34.20 m (p = 0.003) within 12 weeks LTOT. The intervention group significantly improved in 6MWD (38.9 ± 33.87 m) compared to the control group (- 12.3 ± 21.83 m, p = 0.015). No consistent between-group differences in other parameters were found. LTOT was well tolerated and led to significant improvement of 6MWD. The effect of LTOT should be investigated in larger controlled-trials.

Low-frequency ultrasound for pulmonary hypertension therapy

BACKGROUND

Currently, there are no reliable clinical tools that allow non-invasive therapeutic support for patients with pulmonary arterial hypertension. This study aims to propose a low-frequency ultrasound device for pulmonary hypertension therapy and to demonstrate its potential.

METHODS

A novel low-frequency ultrasound transducer has been developed. Due to its structural properties, it is excited by higher vibrational modes, which generate a signal capable of deeply penetrating biological tissues. A methodology for the artificial induction of pulmonary hypertension in sheep and for the assessment of lung physiological parameters such as blood oxygen concentration, pulse rate, and pulmonary blood pressure has been proposed.

RESULTS

The results showed that exposure of the lungs to low-frequency ultrasound changed physiological parameters such as blood oxygen concentration, pulse rate and blood pressure. These parameters are most closely related to indicators of pulmonary hypertension (PH). The ultrasound exposure increased blood oxygen concentration over a 7-min period, while pulse rate and pulmonary blood pressure decreased over the same period. In anaesthetised sheep exposed to low-frequency ultrasound, a 10% increase in SpO2, a 10% decrease in pulse rate and an approximate 13% decrease in blood pressure were observed within 7 min.

CONCLUSIONS

The research findings demonstrate the therapeutic efficiency of low-frequency ultrasound on hypertensive lungs, while also revealing insights into the physiological aspects of gas exchange within the pulmonary system.

Effects of High-Flow Nasal Cannula on Right Heart Dysfunction in Patients with Acute-on-Chronic Respiratory Failure and Pulmonary Hypertension

High-flow nasal cannula (HFNC) has several benefits in patients affected by different forms of acute respiratory failure, based on its own mechanisms. We postulated that HFNC may have some advantages over conventional oxygen therapy (COT) on the heart function in patients with acute-on-chronic respiratory failure with concomitant pulmonary hypertension (PH). We therefore designed this retrospective observational study to assess if HFNC improves the right and left ventricle functions and morphologies, arterial blood gases (ABGs), and patients' dyspnea, compared to COT. We enrolled 17 hospitalized patients receiving HFNC, matched with 17 patients receiving COT. Echocardiographic evaluation was performed at the time of admission (baseline) and 10 days after (T10). HFNC showed significant improvements in right ventricular morphology and function, and a reduction in sPAP. However, there were no significant changes in the left heart measurements with HFNC application. Conversely, COT did not lead to any modifications in echocardiographic measurements. In both groups, oxygenation significantly improved from baseline to T10 (in the HFNC group, from 155 ± 47 to 204 ± 61 mmHg while in the COT group, from 157 ± 27 to 207 ± 27 mmHg; p < 0.0001 for both comparisons). In conclusion, these data suggest an improvement of oxygenation with both treatments; however, only HFNC was able to improve the right ventricular morphology and function after 10 days from the beginning of treatment in a small cohort of patients with acute-on-chronic respiratory failure with PH.

Oxygen Therapy in Pulmonary Vascular Disease: A Systematic Review, Meta-Analysis, and Comment

Main pulmonary vascular diseases (PVD) with precapillary pulmonary hypertension (PH) are pulmonary arterial and chronic thromboembolic PH. Guidelines recommend supplemental oxygen therapy (SOT) for severely hypoxemic patients with PH, but evidence is scarce. The authors performed a systematic review and where possible meta-analyses on the effects of SOT on hemodynamics and exercise performance in patients with PVD. In PVD, short-term SOT significantly improved mean pulmonary artery pressure and exercise performance. There is growing evidence on the benefit of long-term SOT for selected patients with PVD regarding exercise capacity and maybe even survival.

Oxygen Supplementation and Hyperoxia in Critically Ill Cardiac Patients: From Pathophysiology to Clinical Practice

Oxygen supplementation has been a mainstay in the management of patients with acute cardiac disease. While hypoxia is known to be detrimental, the adverse effects of artificially high oxygen levels (hyperoxia) have only recently been recognized. Hyperoxia may induce harmful hemodynamic effects, including peripheral and coronary vasoconstriction, and direct cellular toxicity through the production of reactive oxygen species. In addition, emerging evidence has shown that hyperoxia is associated with adverse clinical outcomes. Thus, it is essential for the cardiac intensive care unit (CICU) clinician to understand the available evidence and titrate oxygen therapies to specific goals. This review summarizes the pathophysiology of oxygen within the cardiovascular system and the association between supplemental oxygen and hyperoxia in patients with common CICU diagnoses, including acute myocardial infarction, heart failure, shock, cardiac arrest, pulmonary hypertension, and respiratory failure. Finally, we highlight lessons learned from available trials, gaps in knowledge, and future directions.

The Impact of Breathing Hypoxic Gas and Oxygen on Pulmonary Hemodynamics in Patients With Pulmonary Hypertension

Background

Pure oxygen breathing (hyperoxia) may improve hemodynamics in patients with pulmonary hypertension (PH) and allows to calculate right-to-left shunt fraction (Qs/Qt), whereas breathing normobaric hypoxia may accelerate hypoxic pulmonary vasoconstriction (HPV). This study investigates how hyperoxia and hypoxia affect mean pulmonary artery pressure (mPAP) and pulmonary vascular resistance (PVR) in patients with PH and whether Qs/Qt influences the changes of mPAP and PVR.

Study Design and Methods

Adults with pulmonary arterial or chronic thromboembolic PH (PAH/CTEPH) underwent repetitive hemodynamic and blood gas measurements during right heart catheterization (RHC) under normoxia [fractions of inspiratory oxygen (FiO2) 0.21], hypoxia (FiO2 0.15), and hyperoxia (FiO2 1.0) for at least 10 min.

Results

We included 149 patients (79/70 PAH/CTEPH, 59% women, mean ± SD 60 ± 17 years). Multivariable regressions (mean change, CI) showed that hypoxia did not affect mPAP and cardiac index, but increased PVR [0.4 (0.1–0.7) WU, p = 0.021] due to decreased pulmonary artery wedge pressure [−0.54 (−0.92 to −0.162), p = 0.005]. Hyperoxia significantly decreased mPAP [−4.4 (−5.5 to −3.3) mmHg, p &lt; 0.001] and PVR [−0.4 (−0.7 to −0.1) WU, p = 0.006] compared with normoxia. The Qs/Qt (14 ± 6%) was &gt;10 in 75% of subjects but changes of mPAP and PVR under hyperoxia and hypoxia were independent of Qs/Qt.

Conclusion

Acute exposure to hypoxia did not relevantly alter pulmonary hemodynamics indicating a blunted HPV-response in PH. In contrast, hyperoxia remarkably reduced mPAP and PVR, indicating a preserved vasodilator response to oxygen and possibly supporting the oxygen therapy in patients with PH. A high proportion of patients with PH showed increased Qs/Qt, which, however, was not associated with changes in pulmonary hemodynamics in response to changes in FiO2.

Oxygen Therapy Lowers Right Ventricular Afterload in Experimental Acute Pulmonary Embolism

OBJECTIVES

To investigate if oxygen could unload the right ventricle and improve right ventricle function in a porcine model mimicking intermediate-high risk acute pulmonary embolism.

DESIGN

Controlled, blinded, animal study.

SETTING

Tertiary university hospital, animal research laboratory.

SUBJECTS

Female, Danish pigs (n = 16, approximately 60 kg).

INTERVENTIONS

Acute autologous pulmonary embolism was induced until doubling of baseline mean pulmonary arterial pressure. Group 1 animals (n = 8) received increasing Fio2 (40%, 60%, and 100%) for time intervals of 15 minutes returning to atmospheric air between each level of Fio2. In group 2 (n = 8), the effects of Fio2 40% maintained over 75 minutes were studied. In both groups, pulmonary vasodilatation from inhaled nitric oxide (40 parts per million) was used as a positive control.

MEASUREMENTS AND MAIN RESULTS

Effects were evaluated by biventricular pressure-volume loop recordings, right heart catheterization, and arterial and mixed venous blood gasses. Pulmonary embolism increased mean pulmonary arterial pressure from 15 ± 4 to 33 ± 6 mm Hg (p = 0.0002) and caused right ventricle dysfunction (p < 0.05) with troponin release (p < 0.0001). In group 1, increasing Fio2 lowered mean pulmonary arterial pressure (p < 0.0001) and pulmonary vascular resistance (p = 0.0056) and decreased right ventricle volumes (p = 0.0018) and right ventricle mechanical work (p = 0.034). Oxygenation was improved and pulmonary shunt was lowered (p < 0.0001). Maximal hemodynamic effects were seen at Fio2 40% with no additional benefit from higher fractions of oxygen. In group 2, the effects of Fio2 40% were persistent over 75 minutes. Supplemental oxygen showed the same pulmonary vasodilator efficacy as inhaled nitric oxide (40 parts per million). No adverse effects were observed.

CONCLUSIONS

In a porcine model mimicking intermediate-high risk pulmonary embolism, oxygen therapy reduced right ventricle afterload and lowered right ventricle mechanical work. The effects were immediately present and persistent and were similar to inhaled nitric oxide. The intervention is easy and safe. The study motivates extended clinical evaluation of supplemental oxygen in acute pulmonary embolism.