Clinical relevance of autonomic nervous system disturbances in pulmonary arterial hypertension

Excess ventilation and exertional dyspnoea in heart failure and pulmonary hypertension

Increased ventilation relative to metabolic demands, indicating alveolar hyperventilation and/or increased physiological dead space (excess ventilation), is a key cause of exertional dyspnoea. Excess ventilation has assumed a prominent role in the functional assessment of patients with heart failure (HF) with reduced (HFrEF) or preserved (HFpEF) ejection fraction, pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH). We herein provide the key pieces of information to the caring physician to 1) gain unique insights into the seeds of patients' shortness of breath and 2) develop a rationale for therapeutically lessening excess ventilation to mitigate this distressing symptom. Reduced bulk oxygen transfer induced by cardiac output limitation and/or right ventricle-pulmonary arterial uncoupling increase neurochemical afferent stimulation and (largely chemo-) receptor sensitivity, leading to alveolar hyperventilation in HFrEF, PAH and small-vessel, distal CTEPH. As such, interventions geared to improve central haemodynamics and/or reduce chemosensitivity have been particularly effective in lessening their excess ventilation. In contrast, 1) high filling pressures in HFpEF and 2) impaired lung perfusion leading to ventilation/perfusion mismatch in proximal CTEPH conspire to increase physiological dead space. Accordingly, 1) decreasing pulmonary capillary pressures and 2) mechanically unclogging larger pulmonary vessels (pulmonary endarterectomy and balloon pulmonary angioplasty) have been associated with larger decrements in excess ventilation. Exercise training has a strong beneficial effect across diseases. Addressing some major unanswered questions on the link of excess ventilation with exertional dyspnoea under the modulating influence of pharmacological and nonpharmacological interventions might prove instrumental to alleviate the devastating consequences of these prevalent diseases.

Neural respiratory drive in chronic thromboembolic pulmonary hypertension: Effect of balloon pulmonary angioplasty

Excessive ventilation (V̇E) during exercise, ascribed to heightened neural ventilatory drive and/or to increased "wasted" ventilation, is a feature of chronic thromboembolic pulmonary hypertension (CTEPH). In selected CTEPH patients, balloon pulmonary angioplasty (BPA) allows near-normalization of resting haemodynamic parameters but does not allow excess exercise hyperventilation to normalize. Neural ventilatory drive can be estimated by studying how arterial PCO₂ (PaCO₂), end-tidal PCO₂ (PETCO₂), V̇E and CO₂ output (V̇CO₂) change across the exercise-to-recovery transition during a cardiopulmonary exercise test. Increased "wasted" ventilation can be quantified by the physiological dead space fraction of tidal volume (VD/VT) calculated with the Enghoff simplification of the Bohr equation. These measurements were made before and after BPA in 22 CTEPH patients without significant cardiac and/or pulmonary comorbidities. Our observations suggest that before BPA, excessive hyperventilation was secondary to both heightened neural ventilatory drive and increased "wasted" ventilation; after BPA, measurements made across the exercise-to-recovery transition suggest that heightened neural ventilatory drive was no longer present.

Bisoprolol and/or hyperoxic breathing do not reduce hyperventilation in pulmonary arterial hypertension patients

Hyperventilation is common in pulmonary arterial hypertension and may be related to autonomic imbalance. Patients underwent exercise testing and hyperoxic breathing before and after bisoprolol treatment. We found that neither beta blocker treatment nor hyperoxic breathing in patients reduced hyperventilation at rest and during exercise, although it reduced heart rate.

Ventilatory efficiency in pulmonary vascular diseases

Cardiopulmonary exercise testing (CPET) is a frequently used tool in the differential diagnosis of dyspnoea. Ventilatory inefficiency, defined as high minute ventilation (V′_E) relative to carbon dioxide output (V′_CO2), is a hallmark characteristic of pulmonary vascular diseases, which contributes to exercise intolerance and disability in these patients. The mechanisms of ventilatory inefficiency are multiple and include high physiologic dead space, abnormal chemosensitivity and an altered carbon dioxide (CO₂) set-point. A normal V′_E/V′_CO2 makes a pulmonary vascular disease such as pulmonary arterial hypertension (PAH) or chronic thromboembolic pulmonary hypertension (CTEPH) unlikely. The finding of high V′_E/V′_CO2 without an alternative explanation should prompt further diagnostic testing to exclude PAH or CTEPH, particularly in patients with risk factors, such as prior venous thromboembolism, systemic sclerosis or a family history of PAH. In patients with established PAH or CTEPH, the V′_E/V′_CO2 may improve with interventions and is a prognostic marker. However, further studies are needed to clarify the added value of assessing ventilatory inefficiency in the longitudinal follow-up of patients.

Ventilatory inefficiency is a hallmark feature of PH that reflects abnormal ventilation/perfusion matching, chemosensitivity and an altered CO₂ set-point. Minute ventilation/CO₂ production is useful in the diagnosis, management and prognostication of PH.https://bit.ly/3jnNdUG

Oxygen Pathway Limitations in Patients With Chronic Thromboembolic Pulmonary Hypertension

BACKGROUND

Exertional intolerance is a limiting and often crippling symptom in patients with chronic thromboembolic pulmonary hypertension (CTEPH). Traditionally the pathogenesis has been attributed to central factors, including ventilation/perfusion mismatch, increased pulmonary vascular resistance, and right heart dysfunction and uncoupling. Pulmonary endarterectomy and balloon pulmonary angioplasty provide substantial improvement of functional status and hemodynamics. However, despite normalization of pulmonary hemodynamics, exercise capacity often does not return to age-predicted levels. By systematically evaluating the oxygen pathway, we aimed to elucidate the causes of functional limitations in patients with CTEPH before and after pulmonary vascular intervention.

METHODS

Using exercise cardiac magnetic resonance imaging with simultaneous invasive hemodynamic monitoring, we sought to quantify the steps of the O₂ transport cascade from the mouth to the mitochondria in patients with CTEPH (n=20) as compared with healthy participants (n=10). Furthermore, we evaluated the effect of pulmonary vascular intervention (pulmonary endarterectomy or balloon angioplasty) on the individual components of the cascade (n=10).

RESULTS

Peak Vo₂ (oxygen uptake) was significantly reduced in patients with CTEPH relative to controls (56±17 versus 112±20% of predicted; P<0.0001). The difference was attributable to impairments in multiple steps of the O₂ cascade, including O₂ delivery (product of cardiac output and arterial O₂ content), skeletal muscle diffusion capacity, and pulmonary diffusion. The total O₂ extracted in the periphery (ie, ΔAVo₂ [arteriovenous O₂ content difference]) was not different. After pulmonary vascular intervention, peak Vo₂ increased significantly (from 12.5±4.0 to 17.8±7.5 mL/[kg·min]; P=0.036) but remained below age-predicted levels (70±11%). The O₂ delivery was improved owing to an increase in peak cardiac output and lung diffusion capacity. However, peak exercise ΔAVo₂ was unchanged, as was skeletal muscle diffusion capacity.

CONCLUSIONS

We demonstrated that patients with CTEPH have significant impairment of all steps in the O₂ use cascade, resulting in markedly impaired exercise capacity. Pulmonary vascular intervention increased peak Vo₂ by partly correcting O₂ delivery but had no effect on abnormalities in peripheral O₂ extraction. This suggests that current interventions only partially address patients' limitations and that additional therapies may improve functional capacity.

Residual Exertional Dyspnea in Cardiopulmonary Disease

In cardiopulmonary medicine, residual exertional dyspnea (RED) can be defined by the persistence of limiting breathlessness in a patient who is already under the best available therapy for the underlying heart and/or lung disease. RED is a challenge to the pulmonologist because the patient (and the referring physician) assumes that the "lung doctor" should invariably provide a successful plan to fight the symptom. After presenting a simplified framework to understand the neurobiological underpinnings of dyspnea in cardiorespiratory disease, I discuss the seeds of RED associated with 1) increased metabolic cost of work, 2) increased inspiratory constraints, 3) diaphragm dysfunction, 4) impaired right ventricle preload, 5) increased central and/or peripheral chemosensitivity, 6) increased physiological dead space, 7) increased pulmonary venous and/or high left ventricle filling pressures, 8) impaired chronotropic response to exertion, and 9) increased activation of the cortical-limbic circuits. I finalize by outlining the following two common coexistence of diseases in which these multiple mechanisms interact to produce severe RED: chronic obstructive pulmonary disease-heart failure with reduced ejection fraction and chronic pulmonary fibrosis-emphysema. RED exposes the important limitations of the current reductionist approach focused only on the (over)treatment of the poorly reversible cardiopulmonary disease(s). Conversely, recognizing the existence of RED sets the stage for a more holistic approach toward one of the most devastating symptoms known to man.

Pulmonary Vascular Disease and Cardiopulmonary Exercise Testing

Cardiopulmonary exercise testing (CPET) is of great interest and utility for clinicians dealing Pulmonary Hypertension (PH) in several ways, including: helping with differential diagnosis, evaluating exercise intolerance and its underpinning mechanisms, accurately assessing exertional dyspnea and unmasking its underlying often non-straightforward mechanisms, generating prognostic indicators. Pathophysiologic anomalies in PH can range from reduced cardiac output and aerobic capacity, to inefficient ventilation, dyspnea, dynamic hyperinflation, and locomotor muscle dysfunction. CPET can magnify the PH-related pathophysiologic anomalies and has a major role in the management of PH patients.

Effect of Breathing Oxygen-Enriched Air on Exercise Performance in Patients with Chronic Obstructive Pulmonary Disease: Randomized, Placebo-Controlled, Cross-Over Trial

BACKGROUND

Patients with chronic obstructive pulmonary disease (COPD) experience dyspnea and hypoxemia during exercise.

OBJECTIVE

The aim of this study was to evaluate the effects of breathing oxygen-enriched air on exercise performance and associated physiological changes in patients with COPD.

METHODS

In a randomized, placebo-controlled, single-blind, cross-over trial, 20 patients with COPD (11 women, age 65 ± 6 years, FEV1 64 ± 19% pred., resting SpO2 ≥90%) performed 4 cycle ergospirometries to exhaustion using an incremental exercise test (IET) and a constant work rate (at 75% maximal workload with air) exercise test (CWRET), each with ambient (FiO2 0.21) and oxygen-enriched (FiO2 0.5) air. The main outcomes were the change in maximal workload in the IET and the change in exercise duration in the CWRET with oxygen versus air. Electrocardiogram, pulmonary gas exchange, thoracic volumes by inductance plethysmography, arterial blood gases, and cerebral and quadriceps muscle tissue oxygenation (CTO and MTO) were additionally measured.

RESULTS

In the IET, maximal workload increased from 96 ± 21 to 104 ± 28 W with oxygen. In the CWRET, exercise duration increased from 605 ± 274 to 963 ± 444 s with oxygen. At end-exercise with oxygen, CTO, MTO, PaO2, and PaCO2 were increased, while V'E/V'CO2 was reduced and thoracic volumes were similar. At the corresponding time to end of exercise with ambient air, oxygen decreased heart rate, respiratory rate, minute ventilation, and V'E/V'CO2, while oxygenation was increased.

CONCLUSION

In COPD patients without resting hypoxemia, breathing oxygen-enriched air improves exercise performance. This relates to a higher arterial oxygen saturation promoting oxygen availability to muscle and cerebral tissue and an enhanced ventilatory efficiency. COPD patients may benefit from oxygen therapy during exercise training.

Transcutaneous carbon dioxide monitoring as a predictive tool for all-cause 6-month mortality after acute pulmonary embolism

BACKGROUND

Pulmonary embolism (PE) frequently remains undiagnosed. The partial pressure of carbon dioxide (Pa_CO2)_, a surrogate of dead-space ventilation, is useful in the evaluation of the degree of pulmonary artery occlusion. At present, there is no knowledge about the prognostic role of Pa_CΟ2 variations during the first hours of an acute PE. Transcutaneous measurement of CO₂ (Ptc_CO2) is a simple, non-invasive method that correlates well with Pa_CO2 levels, evaluated in this study for the first time in patients with PE.

PURPOSE

To assess the correlation between Ptc_CO2 and Pa_CO2 levels in the acute phase of PE and the role of Ptc_CO2 in predicting 6-months mortality.

METHODS

This was a pilot study including 53 patients with acute PE who hospitalized in Respiratory Medicine Department at University Hospital of Larissa in central Greece during 15 months. Ptc_CO2 was constantly monitored for four hours after PE diagnosis with the TCM40 monitoring system (SmartCal). Simultaneous arterial blood gas measurements were performed. Each patient was prospectively recorded for six months via standard telephone calls.

RESULTS

Pa_CO2 and Ptc_CO2 values were well-correlated in the acute phase of PE. Decreased Ptc_CO2 levels in the first monitoring hour were associated with a higher risk of mortality. In the PE subgroup who died, the lower Ptc_CO2 level in the first hour of PE was a predictor of shorter survival time independently of gender, age, comorbidities, and smoking status.

CONCLUSION

Ptc_CO2 measurement, especially in the first hour after PE, seemed to be a valid tool in predicting all-cause 6-month mortality.

Value of heart rate recovery in female patients with pulmonary arterial hypertension due to systemic lupus erythematosus

OBJECTIVE

This study intended to explore the relation between heart rate recovery at 1 minutes (HRR1) during the recovery phase of cardiopulmonary exercise test (CPET) and exercise capacity in female systemic lupus erythematosus associated pulmonary arterial hypertension (SLE-PAH) patients.

METHODS

Twenty-one female SLE-PAH patients underwent right heart catheterization (RHC), pulmonary function test (PFT) and CPET. Forty-two healthy subjects matched with SLE-PAH patients in age, sex and BMI were recruited as a control group. The correlations between HRR1 with clinical and CPET parameters were performed.

RESULTS

Peak HR, ΔHR, HRR1, Peak HR-warm HR_1min , Peak HR-warm HR_2min and CR were significantly lower in SLE-PAH than in controls (P < .01). Increased incidence of CRI was seen in SLE-PAH. Except for the Peak P_ET O₂ , which was higher in controls, all other CPET parameters were lower in SLE-PAH. SLE-PAH patients with HRR1 ≥ 16 had longer 6MWD, lower NT-proBNP, better percent of predicted gas transfer index or diffusing capacity for carbon monoxide (DLco% pred) as well as better CO and CI. Peak HR, ΔHR, HRR1, Peak HR-warm HR_1min , Peak HR-warm HR_2min , CR, Peak Load, Peak VO₂ , Peak P_ET CO₂ , OUEP and OUES were lower and duration of exercise was shorter in patients with HRR1 < 16. HRR1 had positive correlation with 6MWD, DLco% pred, CO, CI and some key CPET parameters.

CONCLUSIONS

HRR1 is an easily obtained auxiliary parameter in SLE-PAH patients to reflect an altered autonomic tone. SLE-PAH patients with HRR1 < 16 have more severe hemodynamics, worse clinical findings and marked oxygen uptake inefficiency than those with HRR1 ≥ 16.

Right heart dysfunction: from pathophysiologic insights to therapeutic options: a translational overview

: The right ventricle has become increasingly studied in cardiovascular research. In this article, we describe specific pathophysiological characteristics of the right ventricle, with special focus on functional and molecular modifications as well as therapeutic strategies in right ventricular dysfunction, underlining the differences with the left ventricle. Then we analyze the main imaging modalities to assess right ventricular function in different clinical settings. Finally, we acknowledge main therapeutic advances for treatment of right heart diseases.

Ventilatory response to exercise in cardiopulmonary disease: the role of chemosensitivity and dead space

The lungs and heart are irrevocably linked in their oxygen (O₂) and carbon dioxide (CO₂) transport functions. Functional impairment of the lungs often affects heart function and vice versa The steepness with which ventilation (V'_E) rises with respect to CO₂ production (V'_CO2 ) (i.e. the V'_E/V'_CO2 slope) is a measure of ventilatory efficiency and can be used to identify an abnormal ventilatory response to exercise. The V'_E/V'_CO2 slope is a prognostic marker in several chronic cardiopulmonary diseases independent of other exercise-related variables such as peak O₂ uptake (V'_O2 ). The V'_E/V'_CO2 slope is determined by two factors: 1) the arterial CO₂ partial pressure (P_aCO2 ) during exercise and 2) the fraction of the tidal volume (V_T) that goes to dead space (V_D) (i.e. the physiological dead space ratio (V_D/V_T)). An altered P_aCO2 set-point and chemosensitivity are present in many cardiopulmonary diseases, which influence V'_E/V'_CO2 by affecting P_aCO2 Increased ventilation-perfusion heterogeneity, causing inefficient gas exchange, also contributes to the abnormal V'_E/V'_CO2 observed in cardiopulmonary diseases by increasing V_D/V_T During cardiopulmonary exercise testing, the P_aCO2 during exercise is often not measured and V_D/V_T is only estimated by taking into account the end-tidal CO₂ partial pressure (P_ETCO2 ); however, P_aCO2 is not accurately estimated from P_ETCO2 in patients with cardiopulmonary disease. Measuring arterial gases (P_aO2 and P_aCO2 ) before and during exercise provides information on the real (and not "estimated") V_D/V_T coupled with a true measure of gas exchange efficiency such as the difference between alveolar and arterial O₂ partial pressure and the difference between arterial and end-tidal CO₂ partial pressure during exercise.

Autonomic nervous system involvement in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a chronic pulmonary vascular disease characterized by increased pulmonary vascular resistance (PVR) leading to right ventricular (RV) failure. Autonomic nervous system involvement in the pathogenesis of PAH has been demonstrated several years ago, however the extent of this involvement is not fully understood. PAH is associated with increased sympathetic nervous system (SNS) activation, decreased heart rate variability, and presence of cardiac arrhythmias. There is also evidence for increased renin-angiotensin-aldosterone system (RAAS) activation in PAH patients associated with clinical worsening. Reduction of neurohormonal activation could be an effective therapeutic strategy for PAH. Although therapies targeting adrenergic receptors or RAAS signaling pathways have been shown to reverse cardiac remodeling and improve outcomes in experimental pulmonary hypertension (PH)-models, the effectiveness and safety of such treatments in clinical settings have been uncertain. Recently, novel direct methods such as cervical ganglion block, pulmonary artery denervation (PADN), and renal denervation have been employed to attenuate SNS activation in PAH. In this review, we intend to summarize the multiple aspects of autonomic nervous system involvement in PAH and overview the different pharmacological and invasive strategies used to target autonomic nervous system for the treatment of PAH.

A prescribed walking regimen plus arginine supplementation improves function and quality of life for patients with pulmonary arterial hypertension: a pilot study

Current evidence suggests that exercise training is beneficial in pulmonary arterial hypertension (PAH). Unfortunately, the standard supervised, hospital-based programs limit patient accessibility to this important intervention. Our proof-of-concept study aimed to provide insight into the usefulness of a prescribed walking regimen along with arginine supplementation to improve outcomes for patients with PAH. Twelve PAH patients (all women) in New York Heart Association (NYHA) functional class (FC) II (n = 7) or III (n = 5) and in stable condition for ≥ 3 months were enrolled. Patients performed home- and fitness-center- based walking at 65-75% heart rate (HR) reserve for 45 min, six sessions/week for 12 weeks. Concomitant L-arginine supplementation (6000 mg/day) was provided to maximize beneficial endothelial training adaptations. Cardiopulmonary exercise testing, 6-min walk testing (6MWT), echocardiography, laboratory studies, and quality of life (QoL) survey (SF-36) were performed at baseline and 12 weeks. Eleven patients completed the study (72 session adherence rate = 96 ± 3%). Objective improvement was demonstrated by the 6MWT distance (increased by 40 ± 13 m, P = 0.01), VO₂max (increased by 2 ± 0.7 mL/kg/min, P = 0.02), time-to-VO₂max (increased by 2.5 ± 0.6 min, P = 0.001), VO₂ at anaerobic threshold (increased by 1.3 ± 0.5 mL/kg/min, P = 0.04), HR recovery (reduced by 68 ± 23% in slope, P = 0.01), and SF-36 subscales of Physical Functioning and Energy/Fatigue (increased by 70 ± 34% and 74 ± 34%, respectively, P < 0.05). No adverse events occurred, and right ventricular function and brain natriuretic peptide levels remained stable, suggesting safety of the intervention. This proof-of-concept study indicates that a simple walking regimen with arginine supplementation is a safe and efficacious intervention for clinically stable PAH patients, with gains in objective function and QoL measures. Further investigation in a randomized controlled trial is warranted.

Effect of breathing oxygen-enriched air on exercise performance in patients with precapillary pulmonary hypertension: randomized, sham-controlled cross-over trial

Aims

The purpose of the current trial was to test the hypothesis that breathing oxygen-enriched air increases exercise performance of patients with pulmonary arterial or chronic thrombo-embolic pulmonary hypertension (PAH/CTEPH) and to investigate involved mechanisms.

Methods and results

Twenty-two patients with PAH/CTEPH, eight women, means ± SD 61 ± 14 years, resting mPAP 35 ± 9mmHg, PaO2 ambient air >7.3 kPa, underwent four bicycle ergospirometries to exhaustion on different days, while breathing oxygen-enriched (FiO2 0.50, hyperoxia) or ambient air (FiO2 0.21, normoxia) using progressively increased or constant load protocols (with 75% maximal work rate under FiO2 0.21), according to a randomized, sham-controlled, single-blind, cross-over design. ECG, pulmonary gas-exchange, arterial blood gases, cerebral and quadriceps muscle tissue oxygenation (CTO and QMTO) by near-infrared spectroscopy were measured. In ramp exercise, maximal work rate increased from 113 ± 38 W with normoxia to 132 ± 48 W with hyperoxia, mean difference 19.7 (95% CI 10.5-28.9) W, P < 0.001. Constant load exercise endurance increased from 571 ± 443 to 1242 ± 514 s, mean difference 671 (95% CI 392-951) s, P < 0.001. At end-exercise with hyperoxia PaO2, CTO, QMTO, and PaCO2 were increased, and ventilatory equivalents for CO2 were reduced while the physiological dead space/tidal volume ratio remained unchanged.

Conclusion

In patients with PAH/CTEPH, breathing oxygen-enriched air provides major increases in exercise performance. This is related to an improved arterial oxygenation that promotes oxygen availability in muscles and brain and to a reduction of the excessive ventilatory response to exercise thereby enhancing ventilatory efficiency. Patients with PAH/CTEPH may therefore benefit from oxygen therapy during daily physical activities and training.

Trial registration

clinicaltrials.gov Identifier: NCT01748474.

Compromised Cerebrovascular Regulation and Cerebral Oxygenation in Pulmonary Arterial Hypertension

Background

Functional cerebrovascular regulatory mechanisms are important for maintaining constant cerebral blood flow and oxygen supply in heathy individuals and are altered in heart failure. We aim to examine whether pulmonary arterial hypertension (PAH) is associated with abnormal cerebrovascular regulation and lower cerebral oxygenation and their physiological and clinical consequences.

Methods and Results

Resting mean flow velocity in the middle cerebral artery mean flow velocity in the middle cerebral artery (MCAv_mean); transcranial Doppler), cerebral pressure‐flow relationship (assessed at rest and during squat‐stand maneuvers; analyzed using transfer function analysis), cerebrovascular reactivity to CO₂, and central chemoreflex were assessed in 11 patients with PAH and 11 matched healthy controls. Both groups also completed an incremental ramp exercise protocol until exhaustion, during which MCAv_mean, mean arterial pressure, cardiac output (photoplethysmography), end‐tidal partial pressure of CO₂, and cerebral oxygenation (near‐infrared spectroscopy) were measured. Patients were characterized by a significant decrease in resting MCAv_mean (P<0.01) and higher transfer function gain at rest and during squat‐stand maneuvers (both P<0.05). Cerebrovascular reactivity to CO₂ was reduced (P=0.03), whereas central chemoreceptor sensitivity was increased in PAH (P<0.01), the latter correlating with increased resting ventilation (R²=0.47; P<0.05) and the exercise ventilation/CO₂ production slope (V˙E/V˙CO2 slope; R²=0.62; P<0.05) during exercise for patients. Exercise‐induced increases in MCAv_mean were limited in PAH (P<0.05). Reduced MCAv_mean contributed to impaired cerebral oxygen delivery and oxygenation (both P<0.05), the latter correlating with exercise capacity in patients with PAH (R²=0.52; P=0.01).

Conclusions

These findings provide comprehensive evidence for physiologically and clinically relevant impairments in cerebral hemodynamic regulation and oxygenation in PAH.

Functional impact of exercise pulmonary hypertension in patients with borderline resting pulmonary arterial pressure

Borderline resting mean pulmonary arterial pressure (mPAP) is associated with adverse outcomes and affects the exercise pulmonary vascular response. However, the pathophysiological mechanisms underlying exertional intolerance in borderline mPAP remain incompletely characterized. In the current study, we sought to evaluate the prevalence and functional impact of exercise pulmonary hypertension (ePH) across a spectrum of resting mPAP’s in consecutive patients with contemporary resting right heart catheterization (RHC) and invasive cardiopulmonary exercise testing. Patients with resting mPAP <25 mmHg and pulmonary arterial wedge pressure ≤15 mmHg (n = 312) were stratified by mPAP < 13, 13–16, 17–20, and 21–24 mmHg. Those with ePH (n = 35) were compared with resting precapillary pulmonary hypertension (rPH; n = 16) and to those with normal hemodynamics (non-PH; n = 224). ePH prevalence was 6%, 8%, and 27% for resting mPAP 13–16, 17–20, and 21–24 mmHg, respectively. Within each of these resting mPAP epochs, ePH negatively impacted exercise capacity compared with non-PH (peak oxygen uptake 70 ± 16% versus 92 ± 19% predicted, P < 0.01; 72 ± 13% versus 86 ± 17% predicted, P < 0.05; and 64 ± 15% versus 82 ± 19% predicted, P < 0.001, respectively). Overall, ePH and rPH had similar functional limitation (peak oxygen uptake 67 ± 15% versus 68 ± 17% predicted, P > 0.05) and similar underlying mechanisms of exercise intolerance compared with non-PH (peak oxygen delivery 1868 ± 599 mL/min versus 1756 ± 720 mL/min versus 2482 ± 875 mL/min, respectively; P < 0.05), associated with chronotropic incompetence, increased right ventricular afterload and signs of right ventricular/pulmonary vascular uncoupling. In conclusion, ePH is most frequently found in borderline mPAP, reducing exercise capacity in a manner similar to rPH. When borderline mPAP is identified at RHC, evaluation of the pulmonary circulation under the stress of exercise is warranted.

Norepinephrine stimulation of alpha1D-adrenoceptor promotes proliferation of pulmonary artery smooth muscle cells via ERK-1/2 signaling

It has been shown that the sympathetic nervous system is activated in pulmonary arterial hypertension (PAH). Norepinephrine (NE) levels are increased by chemoreflex-dependent sympathetic overactivation and involved in pulmonary vascular remodeling. However, the underlying mechanisms of the remodeling induced by NE are poorly understood. In this study, we found that, in vivo, the expression of tyrosine hydroxylase and the concentration of plasma NE were increased in PAH rats compared with normal rats. Increases in ventricular hypertrophy and medial width of the pulmonary arteries were reversed by prazosin, α₁-adrenoceptor (α₁-AR) antagonists, in PAH rats. Elevated expression of α_1D-AR was detected in PAH rats. In addition, prazosin reduced the increasing expression of PCNA, CyclinA and CyclinE induced by hypoxia. In vitro, MTT assay, flow cytometry, Western blotting and immunofluorescence were performed to investigate the effects of NE on proliferation of pulmonary artery smooth muscle cells (PASMCs). We revealed that NE promoted PASMCs viability, increased the expression of PCNA, CyclinA and CyclinE, made more cells from G₀/G₁ phase to G₂/M+S phase and enhanced the microtubule formation. Above NE-induced changes could be suppressed by BMY 7378, an inhibitor of α_1D-AR. Furthermore, ERK-1/2 pathway was activated by NE. U0126, a specific inhibitor for ERK-1/2, attenuated the NE-induced proliferation of PASMCs under normoxia and hypoxia. Taken together, our results suggest that NE which stimulates α_1D-AR promotes proliferation of PASMCs and the effect is, at least in part, mediated via the ERK-1/2 pathway.

Cerebral microvascular blood flow and CO2 reactivity in pulmonary arterial hypertension

Hypocapnia and endothelial dysfunction might impair microvascular cerebral blood flow (CBF_micr) and cerebrovascular reactivity to CO₂ (CVR_CO2). Pulmonary arterial hypertension (PAH) is characteristically associated with chronic alveolar hyperventilation and microvascular endothelial dysfunction. We therefore determined CBF_micr (pre-frontal blood flow index (BFI) by the indocyanine green-near infrared spectroscopy methodology) during hypocapnia and hypercapnia in 25 PAH patients and 10 gender- and age-matched controls. Cerebral BFI was lower in patients than controls at similar transcutaneous PCO₂ (PtcCO₂) levels in both testing conditions. In fact, while BFI increased from hypocapnia to hypercapnia in all controls, it failed to increase in 17/25 (68%) patients. Thus, BFI increased to a lesser extent from hypo to hypercapnia ("Δ") in patients, i.e., they showed lower Δ BFI/Δ PtcCO₂ ratios than controls. In conclusion, CBF_micr and CVR_CO2 are lessened in clinically stable, mildly-impaired patients with PAH. These abnormalities might be associated with relevant clinical outcomes (hyperventilation and dyspnea, cognition, cerebrovascular disease) being potentially amenable to pharmacological treatment.

Are transcutaneous oxygen and carbon dioxide determinations of value in pulmonary arterial hypertension?

BACKGROUND

We hypothesized that transcutaneous gas determinations of O2 and CO2 (TcPO2 and TcPCO2 ) are associated with the severity of PAH.

METHODS

In this cross-sectional study, we included consecutive patients with PAH (group 1 PH; n = 34). Transcutaneous gas determinations were compared to those of age- and gender-matched healthy controls (n = 14), nongroup 1 PH (n = 19) or patients with high estimated RVSP on echocardiography but without hemodynamic evidence of PH (n = 12).

RESULTS

In patients with PAH, TcPO2 , and TcPCO2 were significantly associated with PaO2 (R = 0.44, p = 0.03) and PaCO2 (R = 0.77, p < 0.001), respectively. TcPO2 /FiO2 (mean difference: -65.0 [95% CI: -121.3, -8.7]) and TcPCO2 (mean difference: -7.4 [95% CI: -11.6, -3.1]) were significantly lower in patients with PAH than healthy controls. TcPCO2 was useful in discriminating PAH patients from other individuals (AUC: 0.74 [95% CI: 0.62, 0.83]). TcPO2 /FiO2 ratio was significantly associated with mean PAP, TPG, PVR, CI, SVI, DLCO, six-minute walk distance and components of the CAMPHOR questionnaire.

CONCLUSIONS

Transcutaneous pressure of CO2 was lower in patients with PAH. Transcutaneous pressure of O2 over inspired fraction of O2 ratio was inversely associated with severity of disease in patients with PAH.

Heart rate recovery is an important predictor of outcomes in patients with connective tissue disease-associated pulmonary hypertension

Reduced heart rate recovery (HRR) after exercise is associated with increased mortality in cardiac and pulmonary diseases. We sought to evaluate the association between HRR after the 6-minute walk test (6MWT) and outcomes in patients with connective tissue disease-associated pulmonary hypertension (CTD-PH). Data were obtained by review of the medical records. HRR was defined as the difference in heart rate at the end of the 6MWT and after 1 minute (HRR1), 2 minutes (HRR2), and 3 minutes (HRR3) of rest. All patients with pulmonary hypertension and a diagnosis of systemic sclerosis, systemic lupus erythematosus, or mixed connective tissue disease who underwent the 6MWT between August 1, 2009, and October 30, 2011, were included (n = 66). By Kaplan-Meier analysis, HRR1, HRR2, and HRR3 at different cutoff points were all good predictors, with HRR1 of <16 being the best predictor of time to clinical worsening (log-rank P < 0.0001), hospitalization (log-rank P = 0.0001), and survival (log-rank P < 0.003). By proportional hazards regression, patients with HRR1 of <16 were at increased risk of clinical worsening (hazard ratio [HR]: 6.4 [95% confidence interval (CI): 2.6-19.2]; P < 0.0001], hospitalization (HR: 6.6 [95% CI: 2.4-23]; P < 0.0001), and death (HR: 4.5 [95% CI: 1.6-15.7]; P = 0.003). Patients in the highest tercile (HRR1 of ≥19) were unlikely to have a clinical worsening event (HR: 0.1 [95% CI: 0.04-0.5]; P = 0.001], to be hospitalized (HR: 0.1 [95% CI: 0.02-0.5]; P = 0.001), or to die (HR: 0.3 [95% CI: 0.07-0.9]; P = 0.04]. In conclusion, in patients with CTD-PH, abnormal HRR1 (defined as HRR1 of <16) after the 6MWT is a strong predictor of clinical worsening, time to clinical worsening, survival, and hospitalization.

Effects of Intrinsic and Extrinsic Cardiac Nerves on Atrial Arrhythmia in Experimental Pulmonary Artery Hypertension

Atrial arrhythmia, which includes atrial fibrillation (AF) and atrial flutter (AFL), is common in patients with pulmonary arterial hypertension (PAH), who often have increased sympathetic nerve activity. Here, we tested the hypothesis that autonomic nerves play important roles in vulnerability to AF/AFL in PAH. The atrial effective refractory period and AF/AFL inducibility at baseline and after anterior right ganglionated plexi ablation were determined during left stellate ganglion stimulation or left renal sympathetic nerve stimulation in beagle dogs with or without PAH. Then, sympathetic nerve, β-adrenergic receptor densities and connexin 43 expression in atrial tissues were assessed. The sum of the window of vulnerability to AF/AFL was increased in the right atrium compared with the left atrium at baseline in the PAH dogs but not in the controls. The atrial effective refractory period dispersion was increased in the control dogs, but not in the PAH dogs, during left stellate ganglion stimulation. The voltage thresholds for inducing AF/AFL during anterior right ganglionated plexi stimulation were lower in the PAH dogs than in the controls. The AF/AFL inducibility was suppressed after ablation of the anterior right ganglionated plexi in the PAH dogs. The PAH dogs had higher sympathetic nerve and β1-adrenergic receptor densities, increased levels of nonphosphorylated connexin 43, and heterogeneous connexin 43 expression in the right atrium when compared with the control dogs. The anterior right ganglionated plexi play important roles in the induction of AF/AFL. AF/AFL induction was associated with right atrium substrate remodeling in dogs with PAH.

Outcomes of β-blocker use in pulmonary arterial hypertension: a propensity-matched analysis

The utility and safety of β-blockers in pulmonary hypertension is controversial. Anecdotal reports suggest that β-blockers may be harmful in these patients. The aim of our study was to evaluate outcomes of β-blocker use in pulmonary hypertension.We reviewed patients from our pulmonary hypertension registry between 2000 and 2011. Patients who continued to use β-blockers were compared to those who never used β-blockers for all-cause mortality, time to clinical worsening events, defined as death, lung transplantation and hospitalisation due to pulmonary hypertension. We also evaluated the effect of β-blockers on 6-min walking distance and New York Heart Association (NYHA) functional class.133 patients used β-blockers and 375 patients never used β-blockers. Mean±sd age was 57±16 years and the median follow-up period was 78 months. Propensity-matched analysis showed that the adjusted odds ratio (95% CI) for mortality with β-blocker use was 1.13 (0.69-1.82) and for clinical worsening events was 0.96 (0.55-1.68). No significant difference was noted in probability of survival and time to clinical worsening events. Patients on β-blockers walked a shorter distance on follow-up 6 min walk test; follow-up NYHA class was similar between groups.Pulmonary hypertension patients receiving β-blockers had a similar survival and time to clinical worsening events compared to patients not receiving them. Functional outcomes were similar, although β-blocker use was associated with a tendency towards shorter walking distance.

Beneficial Effects of Renal Denervation on Pulmonary Vascular Remodeling in Experimental Pulmonary Artery Hypertension

INTRODUCTION AND OBJECTIVES

Activation of both the sympathetic nervous system and the renin-angiotensin-aldosterone system is closely associated with pulmonary arterial hypertension. We hypothesized that renal denervation decreases renin-angiotensin-aldosterone activity and inhibits the progression of pulmonary arterial hypertension.

METHODS

Twenty-two beagles were randomized into 3 groups. The dogs' pulmonary dynamics were measured before and 8 weeks after injection of 0.1mL/kg dimethylformamide (control dogs) or 2mg/kg dehydromonocrotaline (pulmonary arterial hypertension and pulmonary arterial hypertension + renal denervation dogs). Eight weeks after injection, neurohormone levels and pulmonary tissue morphology were measured.

RESULTS

Levels of plasma angiotensin II and endothelin-1 were significantly increased after 8 weeks in the pulmonary arterial hypertension dogs and were higher in the lung tissues of these dogs than in those of the control and renal denervation dogs (mean [standard deviation] angiotensin II: 65 [9.8] vs 38 [6.7], 46 [8.1]; endothelin-1: 96 [10.3] vs 54 [6.2], 67 [9.4]; P < .01). Dehydromonocrotaline increased the mean pulmonary arterial pressure (16 [3.4] mmHg vs 33 [7.3] mmHg; P < .01), and renal denervation prevented this increase. Pulmonary smooth muscle cell proliferation was higher in the pulmonary arterial hypertension dogs than in the control and pulmonary arterial hypertension + renal denervation dogs.

CONCLUSIONS

Renal denervation attenuates pulmonary vascular remodeling and decreases pulmonary arterial pressure in experimental pulmonary arterial hypertension. The effect of renal denervation may contribute to decreased neurohormone levels.

Capillary pCO2 helps distinguishing idiopathic pulmonary arterial hypertension from pulmonary hypertension due to heart failure with preserved ejection fraction

RATIONALE

The demographics of patients with idiopathic pulmonary arterial hypertension (IPAH) are changing and this diagnosis is increasingly being made in older patients. However, diagnostic misclassifications are common as it may be difficult to differentiate between IPAH and pulmonary hypertension due to heart failure with preserved ejection fraction (PH-HFpEF). We investigated the hypothesis that the capillary pCO2 (pcCO2) may help distinguishing between idiopathic pulmonary arterial hypertension (IPAH) and pulmonary hypertension due to heart failure with preserved ejection fraction (PH-HFpEF).

METHODS

In a cross-sectional study, we retrospectively assessed pcCO2 levels (obtained from arterialized capillary blood at the time of diagnosis) from patients with IPAH or PH-HFpEF, respectively. Receiver operated characteristics (ROC) were used to determine the pcCO2 level providing the best discrimination between these two conditions. PcCO2 values were considered helpful if they were associated with a negative predictive value >0.9 to excluded either IPAH or PH-HFpEF.

RESULTS

The study enrolled 185 patients, 99 with IPAH (74% female; age 47 ± 17 years; body mass index 26 ± 5 kg/m2, PAPm 53 ± 12 mmHg, PAWP 8 ± 3 mmHg), and 86 with PH-HFpEF (64% female; age 69 ± 10 years; body mass index 30 ± 6 kg/m2, PAPm 47 ± 10 mmHg, PAWP 21 ± 5 mmHg). PcCO2 at time of diagnosis was 33 ± 4 mmHg in the IPAH group and 40 ± 5 mmHg in the PH-HFpEF group (p < 0.001), respectively. According to ROC analysis, a pcCO2 of 36 mmHg was the best discriminator between both entities with an area under curve of 0.87 (p < 0.001). The likelihood of PH-HFpEF was <10% in patients with a PcCO2 < 34 mmHg, whereas the likelihood of IPAH was <10% in patients with a PcCO2 > 41 mmHg.

CONCLUSIONS

PcCO2 levels were significantly lower in IPAH compared to PH-HFpEF and may provide useful information in differentiating between both conditions.

Exercise pathophysiology and sildenafil effects in chronic thromboembolic pulmonary hypertension

OBJECTIVES

Symptoms in patients with chronic thromboembolic pulmonary hypertension (CTEPH) predominantly occur during exercise, while haemodynamic assessment is generally performed at rest. We hypothesised that exercise imaging of RV function would better explain exercise limitation and the acute effects of pulmonary vasodilator administration than resting measurements.

METHODS

Fourteen patients with CTEPH and seven healthy control subjects underwent cardiopulmonary testing to determine peak exercise oxygen consumption (VO2peak) and ventilatory equivalent for carbon dioxide (VE/VCO2) at the anaerobic threshold. Subsequently, cardiac MRI was performed at rest and during supine bicycle exercise with simultaneous invasive measurement of mean pulmonary arterial pressure (mPAP) before and after sildenafil.

RESULTS

During exercise, patients with CTEPH had a greater increase in the ratio of mPAP relative to cardiac output (CO) than controls (6.7 (5.1-8.7) vs 0.94 (0.86-1.8) mm Hg/L/min; p < 0.001). Stroke volume index (SVi) and RVEF increased during exercise in controls, but not in patients with CTEPH (interaction p < 0.001). Sildenafil decreased the mPAP/CO slope and increased SVi and RVEF in patients with CTEPH (p < 0.05) but not in controls. In patients with CTEPH, RVEF reserve correlated moderately with VO2peak (r = 0.60; p = 0.030) and VE/VCO2 (r = -0.67; p = 0.012). By contrast, neither VO2peak nor VE/VCO2 correlated with resting RVEF.

CONCLUSIONS

Exercise measures of RV function explain much of the variance in the exercise capacity of patients with CTEPH while resting measures do not. Sildenafil increases SVi during exercise in patients with CTEPH, but not in healthy subjects.

Modulation of ventilatory reflex control by cardiac resynchronization therapy

BACKGROUND

Heart failure (HF) is characterized by heightened sensitivities of the CO2 chemoreflex and the ergoreflex which promote increased ventilatory drive manifested as increased minute ventilation per volume of expired CO2 (VE/VCO2). The aims of this study were to evaluate the effects of cardiac resynchronization therapy (CRT) on carbon dioxide (CO2) chemosensitivity and the arterial CO2 setpoint.

METHODS AND RESULTS

Consecutive HF patients (n = 35) who underwent clinically indicated CRT were investigated by means of cardiopulmonary exercise testing and CO2 chemosensitivity evaluation with the use of a rebreathe method before and 4-6 months after CRT. Pre- and post-CRT measures were compared with the use of either paired t test or Wilcoxon test. Decreased peak VE/VCO2 (44 ± 10 vs 40 ± 8; P < .01), CO2 chemosensitivity (2.2 ± 1.1 vs 1.7 ± 0.8 L min(-1) mm Hg(-1); P = .04), and increased peak end-tidal CO2 (29 ± 5 vs 31 ± 5 mm Hg; P < .01) were also observed after CRT. Multivariate analysis adjusted for age and sex showed the decrease of peak VE/VCO2 from before to after CRT to be most strongly associated with the increase of peak end-tidal CO2 (β = -0.84; F = 21.5; P < .0001).

CONCLUSIONS

Decrease of VE/VCO2 after CRT is associated with decreased CO2 chemosensitivity and increase of the arterial CO2 setpoint, which is consistent with decreased activation of both the CO2 chemoreflex and the ergoreflex.

ESC Working Group on Myocardial Function Position Paper: how to study the right ventricle in experimental models

The right ventricle has become an increasing focus in cardiovascular research. In this position paper, we give a brief overview of the specific pathophysiological features of the right ventricle, with particular emphasis on functional and molecular modifications as well as therapeutic strategies in chronic overload, highlighting the differences from the left ventricle. Importantly, we put together recommendations on promising topics of research in the field, experimental study design, and functional evaluation of the right ventricle in experimental models, from non-invasive methodologies to haemodynamic evaluation and ex vivo set-ups.

Pulmonary vascular diseases

Diseases of the pulmonary vasculature are a cause of increased pulmonary vascular resistance (PVR) in pulmonary embolism, chronic thromboembolic pulmonary hypertension (CTEPH), and pulmonary arterial hypertension or decreased PVR in pulmonary arteriovenous malformations on hereditary hemorrhagic telangiectasia, portal hypertension, or cavopulmonary anastomosis. All these conditions are associated with a decrease in both arterial PO2 and PCO2. Gas exchange in pulmonary vascular diseases with increased PVR is characterized by a shift of ventilation and perfusion to high ventilation-perfusion ratios, a mild to moderate increase in perfusion to low ventilation-perfusion ratios, and an increased physiologic dead space. Hypoxemia in these patients is essentially explained by altered ventilation-perfusion matching amplified by a decreased mixed venous PO2 caused by a low cardiac output. Hypocapnia is accounted for by hyperventilation, which is essentially related to an increased chemosensitivity. A cardiac shunt on a patent foramen ovale may be a cause of severe hypoxemia in a proportion of patients with pulmonary hypertension and an increase in right atrial pressure. Gas exchange in pulmonary arteriovenous malformations is characterized by variable degree of pulmonary shunting and/or diffusion-perfusion imbalance. Hypocapnia is caused by an increased ventilation in relation to an increased pulmonary blood flow with direct peripheral chemoreceptor stimulation by shunted mixed venous blood flow.

Optimizing the evaluation of excess exercise ventilation for prognosis assessment in pulmonary arterial hypertension

BACKGROUND

Increased ventilatory (.VE) response to carbon dioxide output (.VCO2) is a key finding of incremental cardiopulmonary exercise testing in both heart failure and pulmonary arterial hypertension (PAH). As with heart failure, measures of excessive exercise ventilation considering high-to-peak exercise .VE-VCO2 might have higher prognostic relevance than those restrained to sub-maximal exercise in PAH.

DESIGN

Cross-sectional and observational study on a tertiary center.

METHODS

Eighty-four patients (36 idiopathic and 48 with associated conditions) were followed up for up to five years. Excessive exercise ventilation was calculated as a slope (Δ .VE/Δ .VCO2 to the respiratory compensation point (RCP) and to exercise cessation (PEAK)) and as a ratio (.VE-VCO2 at the anaerobic threshold (AT) and at PEAK).

RESULTS

Thirteen patients died and three had atrial septostomy. Multivariable regression analyses revealed that Δ .VE/Δ .VCO2(PEAK) <55 and .VE/.VCO2(PEAK) <57 were better related to prognosis than Δ .VE/Δ .VCO2(RCP) and .VE/.VCO2(AT) (p < 0.01). Δ oxygen uptake (.VO2)/Δ work rate >5.5 ml/min per W was the only other independent prognostic index. According to a Kaplan-Meier survival analysis, 96.9% (90.8% to 100%) of patients showing Δ .VE/Δ .VCO2(PEAK) <55 and Δ .VO2/Δ work rate >5.5 ml/min per W were free from a PAH-related event. In contrast, 74.7% (70.1% to 78.2%) with both parameters outside these ranges had a negative outcome.

CONCLUSION

Measurements of excessive exercise ventilation which consider all data points maximize the usefulness of incremental cardiopulmonary exercise testing in the prognosis evaluation of PAH.

Comparison of baseline predictors of prognosis in pulmonary arterial hypertension in patients surviving ≤2 years and those surviving ≥5 years after baseline right-sided cardiac catheterization

Idiopathic pulmonary arterial hypertension (PAH) is usually associated with a poor outcome but the prognosis with other forms of PAH is not well-described. Advances in therapy have furthered clouded the disease course. We sought to determine the baseline indicators of prognosis in patients with PAH. We reviewed the records of patients with PAH followed up at our institution to identify those who died within 2 years (reduced survival group; n = 21) and those who survived >5 years (long survival group; n = 60). The groups were compared for prognostic significance of the baseline clinical parameters. The reduced survival group were older (p = 0.001) and more likely to have scleroderma-associated PAH (p = 0.01), have pericardial effusion (p = 0.01), have a shorter 6-minute walk test (6MWT) distance (p = 0.001), to require oxygen during 6MWT (p = 0.02), have a worse World Health Organization functional class (p <0.001), and have greater serum brain natriuretic peptide levels (p = 0.01). Regression analysis showed age, World Health Organization functional class, 6MWT distance, the need for oxygen during the 6MWT, and renal disease to be independently associated with a poor prognosis. In conclusion, age, PAH etiology, World Health Organization functional class, pericardial effusion, 6MWT distance, the need for oxygen during the 6MWT, and brain natriuretic peptide are predictors of prognosis in patients PAH receiving specific therapy and might help identify a group that could benefit from aggressive upfront therapy.

[The cardiopulmonary exercise test in the management of patients with pulmonary hypertension]

The main symptom of patients with pulmonary hypertension (PH) is exercise intolerance. The gold standard for evaluation of exercise capacity is the incremental cardio-pulmonary exercise test (ICPET) on a bicycle ergometer. Exercise tolerance in patients with PH is mainly determined by the capacity to increase cardiac output to meet metabolic demands, which depends on right ventricular function. Therefore, right ventricular dysfunction is the main factor limiting exercise tolerance in PH. Patients with PH also show hypoxemia during exercise and hyperventilation is also common, both at rest and during exercise, which can be attributed to greater chemosensitivity. The present review analyzes the physiological mechanisms determining exercise tolerance, exercise response in patients with PH, the variables of greatest interest in the study of this disorder, the similarities and differences between ICPET and other, simpler tests such as the 6-minute walk test, and the prognostic value of exercise testing in these patients. Evaluation of exercise tolerance is an essential element in the clinical assessment of patients with PH. Consequently, detailed knowledge of the information provided by exercise testing and its limitation is of undoubted interest in the clinical management of this complex disease.

Diaphragm muscle fiber weakness in pulmonary hypertension

RATIONALE

Recently it was suggested that patients with pulmonary hypertension (PH) suffer from inspiratory muscle dysfunction. However, the nature of inspiratory muscle weakness in PH remains unclear.

OBJECTIVES

To assess whether alterations in contractile performance and in morphology of the diaphragm underlie inspiratory muscle weakness in PH.

METHODS

PH was induced in Wistar rats by a single injection of monocrotaline (60 mg/kg). Diaphragm (PH n = 8; controls n = 7) and extensor digitorum longus (PH n = 5; controls n = 7) muscles were excised for determination of in vitro contractile properties and cross-sectional area (CSA) of the muscle fibers. In addition, important determinants of protein synthesis and degradation were determined. Finally, muscle fiber CSA was determined in diaphragm and quadriceps of patients with PH, and the contractile performance of single fibers of the diaphragm.

MEASUREMENTS AND MAIN RESULTS

In rats with PH, twitch and maximal tetanic force generation of diaphragm strips were significantly lower, and the force-frequency relation was shifted to the right (i.e., impaired relative force generation) compared with control subjects. Diaphragm fiber CSA was significantly smaller in rats with PH compared with controls, and was associated with increased expression of E3-ligases MAFbx and MuRF-1. No significant differences in contractility and morphology of extensor digitorum longus muscle fibers were found between rats with PH and controls. In line with the rat data, studies on patients with PH revealed significantly reduced CSA and impaired contractility of diaphragm muscle fibers compared with control subjects, with no changes in quadriceps muscle.

CONCLUSIONS

PH induces selective diaphragm muscle fiber weakness and atrophy.

Submaximal exercise gas exchange is an important prognostic tool to predict adverse outcomes in heart failure

AIMS

Traditionally, VO(2peak) has been used to determine prognosis in heart failure; however, this measure has limitations. Hence, other exercise and gas exchange parameters measured submaximally, e.g. breathing efficiency (V(E)/VCO(2)), end-tidal CO(2) (P(ET)CO(2)), oxygen uptake efficiency slope (OUES), and circulatory power [ systolic blood pressure (SBP)], have been investigated. The aim of this study was to investigate the prognostic relevance of submaximal exercise gas exchange in heart failure patients. Method and results One hundred and thirty-two consecutive heart failure patients (mean age 56 ± 12 years, ejection fraction 29 ± 11%) performed peak treadmill testing. Gas exchange and haemodynamic variables were measured continuously. Gas exchange data obtained from the first 2 min of exercise and at a respiratory exchange ratio (RER) of 0.9 were the measurements of interest. Over a median follow-up period of 62.4 (range 0-114) months, there were 44 endpoints (death or transplant). Univariate analysis demonstrated submaximal predictors of survival, which included V(E)/VCO(2) slope and ratio, P(ET)CO(2), OUES, and circulatory power (P ≤ 0.01). When these and additional submaximal variables were included together in the multivariable analysis, the strongest submaximal exercise predictive model (C-statistic 0.75) comprised data from the first stage of exercise (V(E) and circulatory power) and at an RER of 0.9 (V(E)/VCO(2) ratio). The inclusion of VO(2 peak) and demographic data, with submaximal data (V(E)/VCO(2) ratio at an RER = 0.9), increased the predictiveness of the model (C-statistic 0.78).

CONCLUSION

Submaximal exercise measures provide useful prognostic information for predicting survival in heart failure. This form of testing is logistically easier, cheaper, and safer for patients compared with maximal exercise.

Causes of breathing inefficiency during exercise in heart failure

BACKGROUND

Patients with heart failure (HF) develop abnormal pulmonary gas exchange; specifically, they have abnormal ventilation relative to metabolic demand (ventilatory efficiency/minute ventilation in relation to carbon dioxide production [V(E)/VCO₂]) during exercise. The purpose of this investigation was to examine the factors that underlie the abnormal breathing efficiency in this population.

METHODS AND RESULTS

Fourteen controls and 33 moderate-severe HF patients, ages 52 ± 12 and 54 ± 8 years, respectively, performed submaximal exercise (∼65% of maximum) on a cycle ergometer. Gas exchange and blood gas measurements were made at rest and during exercise. Submaximal exercise data were used to quantify the influence of hyperventilation (PaCO₂) and dead space ventilation (V(D)) on V(E)/VCO₂. The V(E)/VCO₂ relationship was lower in controls (30 ± 4) than HF (45 ± 9, P < .01). This was the result of hyperventilation (lower PaCO₂) and higher V(D)/V(T) that contributed 40% and 47%, respectively, to the increased V(E)/VCO₂ (P < .01). The elevated V(D)/V(T) in the HF patients was the result of a tachypneic breathing pattern (lower V(T), 1086 ± 366 versus 2003 ± 504 mL, P < .01) in the presence of a normal V(D) (11.5 ± 4.0 versus 11.9 ± 5.7 L/min, P = .095).

CONCLUSIONS

The abnormal ventilation in relation to metabolic demand in HF patients during exercise was due primarily to alterations in breathing pattern (reduced V(T)) and excessive hyperventilation.