Pulmonary hypertension in patients with chronic obstructive pulmonary disease: recent advances in pathophysiology and management

Comparison of the muscle oxygenation during submaximal and maximal exercise tests in patients post-coronavirus disease 2019 syndrome with pulmonary involvement

INTRODUCTION

Pulmonary involvement is prevalent in patients with coronavirus disease 2019 (COVID-19). Arterial hypoxemia may reduce oxygen transferred to the skeletal muscles, possibly leading to impaired exercise capacity. Oxygen uptake may vary depending on the increased oxygen demand of the muscles during submaximal and maximal exercise.

OBJECTIVE

This study aimed to compare muscle oxygenation during submaximal and maximal exercise tests in patients with post-COVID-19 syndrome with pulmonary involvement.

METHODS

Thirty-nine patients were included. Pulmonary function (spirometry), peripheral muscle strength (dynamometer), quadriceps femoris (QF) muscle oxygenation (Moxy® device), and submaximal exercise capacity (six-minute walk test (6-MWT)) were tested on the first day, maximal exercise capacity (cardiopulmonary exercise test (CPET)) was tested on the second day. Physical activity level was evaluated using an activity monitor worn for five consecutive days. Cardiopulmonary responses and muscle oxygenation were compared during 6-MWT and CPET.

RESULTS

Patients' minimum and recovery muscle oxygen saturation were significantly decreased; maximum total hemoglobin increased, heart rate, blood pressure, breathing frequency, dyspnea, fatigue, and leg fatigue at the end-of-test and recovery increased in CPET compared to 6-MWT (p < .050). Peak oxygen consumption (VO2peak) was 18.15 ± 4.75 ml/min/kg, VO2peak; percent predicted < 80% was measured in 51.28% patients. Six-MWT distance and QF muscle strength were less than 80% predicted in 58.9% and 76.9% patients, respectively.

CONCLUSIONS

In patients with post-COVID-19 syndrome with pulmonary involvement, muscle deoxygenation of QF is greater during maximal exercise than during submaximal exercise. Specifically, patients with lung impairment should be evaluated for deoxygenation and should be taken into consideration during pulmonary rehabilitation.

Pulmonary hypertension and vascular oxidative damage in cigarette smoke exposed eNOS(-/-) mice and human smokers

CONTEXT

Cigarette smoke is known to be associated with pulmonary hypertension in humans and in animal models. Although the etiology of pulmonary hypertension in smokers is not understood, recent work has suggested a role for inducible nitric oxide synthase (iNOS) in inducing oxidative stress.

OBJECTIVE AND METHODS

To further evaluate this question, we assessed eNOS-/- mice exposed to air or cigarette smoke for the presence of pulmonary hypertension and examined vascular remodeling and expression of nitrotyrosine, a marker of reactive nitrogen species-induced oxidative damage, using immunohistochemistry. To ascertain whether oxidants may play a role in humans, we also examined lung tissue from nonsmokers, and patients with chronic obstructive pulmonary disease (COPD) with and without pulmonary hypertension.

RESULTS

We found that eNOS(-/-) mice developed increased pulmonary arterial pressure after six months cigarette smoke exposure, and this was associated with vascular remodeling and increased vascular nitrotyrosine staining. iNOS gene expression was decreased in the pulmonary arteries of the smoke exposed animals, and no protein was detectable by immunohistochemistry. In humans, vascular nitrotyrosine staining intensity was increased in smokers with COPD compared to nonsmokers, and further increased in smokers with combined COPD and pulmonary hypertension.

CONCLUSIONS

We conclude that cigarette smoke-induced pulmonary hypertension is associated with evidence of oxidative vascular damage by reactive nitrogen species, but that iNOS does not appear to be the major contributor to such damage. Most likely the source of reactive nitrogen species is the cigarette smoke itself.

mTOR and vascular remodeling in lung diseases: current challenges and therapeutic prospects

Mammalian target of rapamycin (mTOR) is a major regulator of cellular metabolism, proliferation, and survival that is implicated in various proliferative and metabolic diseases, including obesity, type 2 diabetes, hamartoma syndromes, and cancer. Emerging evidence suggests a potential critical role of mTOR signaling in pulmonary vascular remodeling. Remodeling of small pulmonary arteries due to increased proliferation, resistance to apoptosis, and altered metabolism of cells forming the pulmonary vascular wall is a key currently irreversible pathological feature of pulmonary hypertension, a progressive pulmonary vascular disorder with high morbidity and mortality. In addition to rare familial and idiopathic forms, pulmonary hypertension is also a life-threatening complication of several lung diseases associated with hypoxia. This review aims to summarize our current knowledge and recent advances in understanding the role of the mTOR pathway in pulmonary vascular remodeling, with a specific focus on the hypoxia component, a confirmed shared trigger of pulmonary hypertension in lung diseases. We also discuss the emerging role of mTOR as a promising therapeutic target and mTOR inhibitors as potential pharmacological approaches to treat pulmonary vascular remodeling in pulmonary hypertension.

Haem oxygenase-1 induction protects against tumour necrosis factor alpha impairment of endothelial-dependent relaxation in rat isolated pulmonary artery

BACKGROUND AND PURPOSE

Disturbances in pulmonary vascular reactivity are important components of inflammatory lung disease. Haem oxygenase-1 (HO-1) is an important homeostatic enzyme upregulated in inflammation. Here we have investigated the potentially protective effect of HO-1 against cytokine-induced impairment in pulmonary artery relaxation.

EXPERIMENTAL APPROACH

Haem oxygenase-1 protein levels were assessed by immunofluorescence. HO activity was assessed by conversion of haemin to bilirubin. Rings of rat isolated pulmonary artery in organ baths were used to measure relaxant responses to the endothelium-dependent agent ACh and the endothelium-independent agent sodium nitroprusside (SNP). Production of nitric oxide (NO) and reactive oxygen species (ROS) was assessed by confocal fluorescence microscopy and fluorescent probes.

KEY RESULTS

Haem oxygenase-1 protein expression was strongly induced in pulmonary artery after 24-h incubation with either haemin (5 microM) or curcumin (2 microM), accompanied by a significant increase in HO activity. Incubation with tumour necrosis factor alpha (TNFalpha, 1 ng.mL(-1), 2 h) significantly decreased relaxation of arterial rings to ACh, without affecting responses to SNP. Induction of HO-1 by curcumin or haemin protected against TNFalpha-induced hyporesponsiveness to ACh. The competitive HO inhibitor, tin protoporphyrin (20 microM), abolished the protective effect of haemin. HO-1 induction prevented a TNFalpha-induced increase in NO generation without affecting the TNFalpha-induced increase in ROS generation. HO-1 induction prevented the TNFalpha-induced decrease in ACh-stimulated NO generation.

CONCLUSIONS AND IMPLICATIONS

Induction of HO-1 protected against TNFalpha impairment of endothelium-dependent relaxation in pulmonary artery, by a mechanism involving a reduction in inducible NO synthase-derived NO production.

Pulmonary hypertension in COPD: a review and consideration of the role of arterial vasodilators

The possibility that pulmonary hypertension (PH) may develop in patients with chronic obstructive pulmonary disease (COPD) is well established, but prevalence data vary. The current World Health Organization clinical classification includes COPD in diagnostic group III: PH associated with disorders of the respiratory system or hypoxemia. The National Institute of Health defines PH as a mean pulmonary artery pressure of greater than 25 mmHg. Approximately 10% of the patients seen over the last decade in the PH Clinic at Mayo Clinic in Jacksonville, Florida, have PH due to COPD. The pathophysiology is likely complex and involves hypoxic pulmonary vasoconstriction. Ultimately, chronic hypoxia results in vascular remodeling with narrowing of the vascular lumen. The right heart is forced to generate increased driving pressures to overcome the increased vascular resistance. As the disease progresses, cor pulmonale may develop. The mortality in this setting is increased with five-year survival of 20% to 36% and seems to correlate with worsening PH and age. Fortunately, the PH in most cases is mild and occurs primarily in those with severe hypoxemia. Only 1% to 4% of patients have PH seemingly out of proportion to the severity of the COPD. This disproportionate subgroup may represent an important phenotype that requires a different therapeutic approach. Although supplemental oxygen remains the primary treatment for all PH in association with chronic hypoxia, pulmonary arterial vasodilators may have a therapeutic role in this subgroup. Vasodilators may worsen gas exchange, however, and to date, have no proven benefit. Rigorous future study will be required to determine whether there is a role for using pulmonary arterial vasodilators in this setting.

Pulmonary hypertension associated with COPD

Although the prevalence of pulmonary hypertension (PH) in individuals with chronic obstructive pulmonary disease (COPD) is not known precisely, approximately 10%–30% of patients with moderate to severe COPD have elevated pulmonary pressures. The vast majority of PH associated with COPD is mild to moderate and severe PH occurs in <5% of patients. When COPD is associated with PH, both mortality and morbidity are increased. There are no clinical or physical examination findings that accurately identify patients with underlying PH. Radiographic imaging findings are specific but not sensitive indicators of PH. Echocardiography is the principle noninvasive diagnostic test but may be technically limited in a significant proportion of patients with COPD. Right heart catheterization is required for accurate measurement of pulmonary pressures. The combined effects of inflammation, endothelial cell dysfunction, and angiogenesis appear to contribute to the development of PH associated with COPD. Systemic vasodilators have not been found to be effective therapy. Selective pulmonary vasodilators including inhaled nitric oxide and phosphodiesterase inhibitors are promising treatments for patients with COPD associated PH but further evaluation of these medications is needed prior to their routine use.

Chronic hypoxia-hypercapnia influences cognitive function: a possible new model of cognitive dysfunction in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a slowly progressive lung disease that results in several complications, including cognitive dysfunction. Some evidences support that cognitive impairment is common and clinically important in COPD, but the exact mechanism is still unclear. It has been confirmed that chronic hypoxia-hypercapnia contributes a lot to the development in pathophysiology of COPD. Data from some pilot studies indicated that chronic hypoxia-hypercapnia influences cognitive functions both in patients and in animals, which includes some distinctive pattern of cognitive dysfunction in human being or impairment of spatial learning-memory in rat. Therefore, we propose that cognitive impairment is strongly related to combination of chronic hypoxia and hypercapnia, and chronic hypoxia-hypercapnia-induced animal models may mimic the cognitive dysfunction of COPD. Attempts to confirm this hypothesis may lead to new model of cognitive dysfunction in COPD.

Comparison of oxygenation in peripheral muscle during submaximal aerobic exercise, in persons with COPD and healthy, matched-control persons

OBJECTIVE

The purpose of this study was to compare peripheral muscle oxygenation in persons with chronic obstructive pulmonary disease (COPD) to healthy control persons, during submaximal exercise.

METHODS

Eight persons with COPD (forced expiratory volume in one second [FEV1] = 1.00 +/- 0.27 L) and eight healthy control persons (FEV, = 1.88 +/- 0.55L) performed a submaximal graded exercise test (GXT), and completed 4 min of constant load exercise (CON) at 50% of peak GXT. Measurements included oxygen uptake, heart rate, arterial oxygen saturation and peripheral muscle oxygenation (%StO2) at rest, during exercise, and recovery.

RESULTS

Significantly greater workloads were attained for controls compared with COPD for peak GXT and CON. No significant differences in %StO2 were observed between groups at: rest (GXT: 29.5 +/- 22.8 vs 30.4 +/- 17.3%; CON: 33.3 +/- 15.4 vs 35.1 +/- 17.2%); peak GXT (29.4 +/- 19.4 vs 26.5 +/- 15.9%); 4 min of CON (25.9 +/- 13.5 vs 34.5 +/- 21.8%); and recovery (GXT: 46.6 +/- 29.1 vs 44.3 +/- 21.7%; CON: 40.9 +/- 21.5 vs 44.5 +/- 23.2%).

CONCLUSION

These results suggest that peripheral skeletal muscle oxygenation is not compromised in COPD during submaximal exercise, and limitations in exercise capacity are most likely a result of muscle disuse and poor lung function.

Hypoxia-induced mitogenic factor has proangiogenic and proinflammatory effects in the lung via VEGF and VEGF receptor-2

From a mouse model of hypoxia-induced pulmonary hypertension, we previously found a highly upregulated protein in the lung that we named hypoxia-induced mitogenic factor (HIMF), also known as found in inflammatory zone 1 (FIZZ1), and resistin-like molecule alpha (RELMalpha). However, the mechanisms of HIMF in the pulmonary vascular remodeling remain unknown. We now demonstrate that HIMF promoted cell proliferation, migration, and the production of vascular endothelial growth factor (VEGF) and monocyte chemotactic protein-1 (MCP-1) in pulmonary endothelial cells as well as the production of reactive oxygen species in murine monocyte/macrophage cells. HIMF-induced CD31-positive cell infiltrate in in vivo Matrigel plugs was significantly suppressed by VEGF receptor-2 (VEGFR2) blockade. In ex vivo studies, HIMF stimulated the production of VEGF, MCP-1, and stromal cell-derived factor-1 (SDF-1) in the lung resident cells, and VEGFR2 neutralization significantly suppressed HIMF-induced MCP-1 and SDF-1 production. Furthermore, intravenous injection of HIMF showed marked increase of CD68-positive inflammatory cells in the lungs, and these events were attenuated by VEGFR2 neutralization. Intravenous injection of HIMF also downregulated the expression of VEGFR2 in the lung. These results suggest that HIMF plays critical roles in pulmonary inflammation as well as angiogenesis.

Hemodynamic effects of bupropion in anesthetized dogs

Bupropion is a non-nicotinic drug used in smoking cessation therapy. However, its acute effects remain unclear. In this study, we investigated the effects of bupropion on hemodynamic parameters in pentobarbital-anesthetized mongrel dogs. Bupropion administered either in bolus injections (3 or 6 mg/kg, i.v.) or in cumulative doses of 0.01, 0.1, 1, 3 and 10 mg/kg showed, in both studies, a significant increase of mean pulmonary arterial pressure and pulmonary vascular resistance index. These results show that bupropion can elevate the pulmonary pressure. Further investigations should be done to test this effect in smokers with chronic obstructive pulmonary disease.

Prevalence of chronic obstructive pulmonary disease in Japanese people on medical check-up

In Japan, spirometry has not been included as an item in medical check-ups for all persons. The purpose of this study was to show evidence to recommend spirometry routinely on medical check-up for the early detection of chronic obstructive pulmonary disease (COPD). There were 12,760 enrolled persons who underwent medical check-up. COPD was defined as a ratio of forced expiratory volume in one second to slow vital capacity of 70% or less. We investigated the prevalence and its characteristics of COPD in people on medical check-up. The prevalence of COPD was 3.6% in all subjects, 4.5% in males, and 1.8% in females. In the comparison between males and females, the prevalence of COPD in males of most age groups was higher than that of females, and this difference was greater with aging. Males in their 50s and over 60 years old and females over 60 years old showed remarkably high prevalences. Occupations associated with a high smoking rate such as transportation-related occupations showed a higher prevalence of COPD. These results suggest that spirometry for all persons in medical check-ups can identify many COPD patients not aware of this disease. Spirometry should be carried out routinely on medical check-up.

Acute and chronic hypoxic regulation of recombinant hNa(v)1.5 alpha subunits

Acute and chronic hypoxic regulation of ion channels is involved in both cell physiology and pathology. Voltage-dependent Na(+) channels play a dominant role in the upstroke of the action potential in excitable cells, while non-inactivating (persistent or sustained) Na(+) currents contribute to action potential shape and duration. In cardiac myocytes, hypoxic augmentation of persistent Na(+) currents has been proposed to underlie cardiac arrhythmias via prolonging action potential duration. Here, we demonstrate that acute hypoxia (P(O2), 20mm Hg) augmented persistent Na(+) currents in HEK293 cells stably expressing human Na(v)1.5 alpha subunits. Hypoxia also inhibited peak Na(+) currents in a voltage-dependent manner, and the kinetics of activation and inactivation of Na(+) currents were significantly slowed during hypoxia. We further demonstrate that exposure to chronic hypoxia (6% O(2) for 24h) augmented peak Na(+) channel current, which given the exogenous promoter driving expression of the channel occurs most probably via a post-transcriptional mechanism. These effects of acute and chronic hypoxia likely play an arrhythmogenic role during both short- and long-term hypoxic/ischaemic episodes. The HEK293 expression system provides a useful paradigm in which to examine the mechanisms of O(2) sensing by the Na(+) channel.

Ion channel regulation by chronic hypoxia in models of acute oxygen sensing

Several potentially life-threatening cardiovascular and respiratory disorders result in prolonged deprivation of oxygen, which in turn results in significant cellular adaptation, or remodelling. An important component of this functional adaptation arises as a direct consequence of altered ion channel expression by chronic hypoxia. In this review, we discuss current understanding of this hypoxic remodelling process, with particular reference to regulation of L-type Ca2+ channels and high-conductance, Ca2+-sensitive K+ (BK) channels. In systems where this remodelling occurs, changes in functional expression of these particular channels evokes marked alteration in, or responses to, Ca2+-dependent events. Evidence to date indicates that channel expression can be modulated at the transcriptional level but, additionally, that crucial post-transcriptional events are also regulated by chronic hypoxia. Importantly, such remodelling is, in some cases, strongly associated with production of amyloid peptides of Alzheimer's disease, implicating chronic hypoxia as a causative factor in the progression of specific pathology. Moreover, subtle changes in functional expression of BK channels implicates chronic hypoxia as an important regulator of cell excitability.

Heterozygous deficiency of hypoxia-inducible factor-2alpha protects mice against pulmonary hypertension and right ventricular dysfunction during prolonged hypoxia

Chronic hypoxia induces pulmonary vascular remodeling, leading to pulmonary hypertension, right ventricular hypertrophy, and heart failure. Heterozygous deficiency of hypoxia-inducible factor-1alpha (HIF-1alpha), which mediates the cellular response to hypoxia by increasing expression of genes involved in erythropoiesis and angiogenesis, has been previously shown to delay hypoxia-induced pulmonary hypertension. HIF-2alpha is a homologue of HIF-1alpha and is abundantly expressed in the lung, but its role in pulmonary hypertension remains unknown. Therefore, we analyzed the pulmonary response of WT and viable heterozygous HIF-2alpha-deficient (Hif2alpha(+/-)) mice after exposure to 10% O(2) for 4 weeks. In contrast to WT mice, Hif2alpha(+/-) mice were fully protected against pulmonary hypertension and right ventricular hypertrophy, unveiling a critical role of HIF-2alpha in hypoxia-induced pulmonary vascular remodeling. Pulmonary expression levels of endothelin-1 and plasma catecholamine levels were increased threefold and 12-fold respectively in WT but not in Hif2alpha(+/-) mice after hypoxia, suggesting that HIF-2alpha-mediated upregulation of these vasoconstrictors contributes to the development of hypoxic pulmonary vascular remodeling.