Influence of cardiomegaly on disordered breathing during exercise in chronic heart failure

The clinical associations with cardiomegaly in patients undergoing evaluation for pulmonary hypertension

Background

Chest radiographs can identify important abnormalities in patients undergoing diagnostic evaluation for cardiovascular diseases. Cardiomegaly often reflects cardiac chamber dilation, or cardiac muscle hypertrophy, or both conditions. The clinical implications of cardiomegaly depend on the underlying clinical disorder. Does cardiomegaly have any clinical, laboratory, echocardiographic, and right heart catheterization associations in patients undergoing evaluation for pulmonary hypertension?

Methods

Patients referred to a pulmonary vascular disease clinic for possible pulmonary hypertension underwent a comprehensive evaluation that included right heart catheterization. These patients also had chest radiographs, laboratory studies, and echocardiograms. The patients were divided into two groups based on the presence or absence of cardiomegaly.

Results

This study included 102 patients (63.7% female) with a mean age of 62.3 ± 15.0 years. Patients with cardiomegaly (n = 64) had elevated BNP, BUN, and creatinine levels. They had elevated right atrial pressures, right ventricular pressures, and pulmonary artery pressures and reduced cardiac indices and reduced mixed venous oxygen saturations. There were no differences in echocardiographic parameters between the two groups.

Conclusions

This study demonstrates that the presence of cardiomegaly on chest radiographs has important clinical implications, including increased BNP levels and increased right heart pressures, in patients undergoing evaluation for pulmonary hypertension. Consequently, the presence of cardiomegaly supports the need for additional evaluation, including right heart catheterization, and provides useful information for primary care physicians and specialists.

Ventilatory constraints influence physiological dead space in heart failure

NEW FINDINGS

What is the central question of this study? The goal of this study was to investigate the effect of alterations in tidal volume and alveolar volume on the elevated physiological dead space and the contribution of ventilatory constraints thereof in heart failure patients during submaximal exercise. What is the main finding and its importance? We found that physiological dead space was elevated in heart failure via reduced tidal volume and alveolar volume. Furthermore, the degree of ventilatory constraints was associated with physiological dead space and alveolar volume.

ABSTRACT

Patients who have heart failure with reduced ejection fraction (HFrEF) exhibit impaired ventilatory efficiency [i.e. greater ventilatory equivalent for carbon dioxide ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mi>E</mml:mi></mml:msub> <mml:mo>/</mml:mo> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:mi>C</mml:mi> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ) slope] and elevated physiological dead space (V_D /V_T ). However, the impact of breathing strategy on V_D /V_T during submaximal exercise in HFrEF is unclear. The HFrEF (n = 9) and control (CTL, n = 9) participants performed constant-load cycling exercise at similar ventilation ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mi>E</mml:mi></mml:msub> </mml:math> ). Inspiratory capacity, operating lung volumes and arterial blood gases were measured during submaximal exercise. Arterial blood gases were used to derive V_D /V_T , alveolar volume, dead space volume, alveolar ventilation and dead space ventilation. During submaximal exercise, HFrEF patients had greater <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mi>E</mml:mi></mml:msub> <mml:mo>/</mml:mo> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:mi>C</mml:mi> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> slope and V_D /V_T than CTL subjects (P = 0.01). At similar <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mi>E</mml:mi></mml:msub> </mml:math> , HFrEF patients had smaller tidal volumes and alveolar volumes (HFrEF 1.11 ± 0.33 litres versus CTL 1.66 ± 0.37 litres; both P ≤ 0.01), whereas dead space volume was not different (P = 0.47). The augmented breathing frequency in HFrEF patients resulted in greater dead space ventilation compared with CTL subjects (HFrEF 15 ± 4 l min^-1 versus CTL 10 ± 5 l min^-1 ; P = 0.048). The HFrEF patients exhibited greater increases in expiratory reserve volume and lower inspiratory capacity (as a percentage of predicted) than CTL subjects (both P < 0.05), which were significantly related to V_D /V_T and alveolar volume in HFrEF patients (all P < 0.03). In HFrEF, the reduced tidal volume and alveolar volume elevate physiological dead space during submaximal exercise, which is worsened in those with the greatest ventilatory constraints. These findings highlight the negative consequences of ventilatory constraints on physiological dead space during submaximal exercise in HFrEF.

Exercise on-transition uncoupling of ventilatory, gas exchange and cardiac hemodynamic kinetics accompany pulmonary oxygen stores depletion to impact exercise intolerance in human heart failure

AIM

In contrast to knowledge that heart failure (HF) patients demonstrate peak exercise uncoupling across ventilation, gas exchange and cardiac haemodynamics, whether this dyssynchrony follows that at the exercise on-transition is unclear. This study tested whether exercise on-transition temporal lag for ventilation relative to gas exchange and oxygen pulse (O₂ pulse) couples with effects from abnormal pulmonary gaseous oxygen store (O_2store ) contributions to V˙O₂ to interdependently precipitate persistently elevated ventilatory demand and low oxidative metabolic capacity in HF.

METHODS

Beat-to-beat HR and breath-to-breath ventilation and gas exchange were continuously acquired in HF (N = 9, ejection fraction = 30 ± 9%) and matched controls (N = 10) during square-wave ergometry at 60% V˙O_2peak (46 ± 14 vs 125 ± 54-W, P < .001). Temporal responses across V˙_E , V˙O₂ and O₂ pulse were assessed for the exercise on-transition using single exponential model Phase II on-kinetic time constants (τ = time to reach 63% steady-state rise). Breath-to-breath gas fractions and respiratory flows were used to determine O_2stores .

RESULTS

HF vs controls: τ for V˙_E (137 ± 93 vs 74 ± 40-seconds, P = .03), V˙O₂ (60 ± 40 vs 23 ± 5-seconds, P = .03) and O₂ pulse (28 ± 18 vs 23 ± 15-seconds, P = .59). Within HF, τ for V˙_E differed from O₂ pulse (P < .02), but not V˙O₂ . Exercise V˙_E rise (workload indexed) differed in HF vs controls (545 ± 139 vs 309 ± 88-mL min^-1 W^-1 , P < .001). Exercise on-transition O_2store depletion in HF exceeded controls, generally persisting to end-exercise.

CONCLUSION

These data suggest HF demonstrated exercise on-transition O_2store depletion (high O_2store contribution to V˙O₂ ) coupled with dyssynchronous V˙_E , V˙O₂ and O₂ pulse kinetics-not attributable to prolonged cardiac haemodynamics. Persistent high ventilatory demand and low oxidative metabolic capacity in HF may be precipitated by physiological uncoupling occurring within the exercise on-transition.

Streamlining cardiopulmonary exercise testing for use as a screening and tracking tool in primary care

Cardiopulmonary exercise testing (CPET) using a spectrum of different approaches demonstrates usefulness for objectively assessing patient disease severity in clinical and research settings. Still, an absence of trained specialists and/or improper data interpretation techniques can pose major limitations to the effective use of CPET for the clinical classification of patients. This study aimed to test an automated disease likelihood scoring algorithm system based on cardiopulmonary responses during a simplified step-test protocol. For patients with heart failure (HF), pulmonary hypertension (PAH), obstructive lung disease (OLD), or restrictive lung disease (RLD), we compared patient scores stratified into one of four "silos" generated from our novel algorithm system against patient evaluations provided by expert clinicians. Patients with HF (n = 12), PAH (n = 9), OLD (n = 16), or RLD (n = 10) performed baseline pulmonary function testing followed by submaximal step-testing. Breath-by-breath measures of ventilation and gas exchange, in addition to oxygen saturation and heart rate were collected continuously throughout testing. The algorithm demonstrated close alignment with patient assessments provided by clinical specialists: HF (r = 0.89, P < 0.01); PAH (r = 0.88, P < 0.01); OLD (r = 0.70, P < 0.01); and RLD (r = 0.88, P < 0.01). Furthermore, the algorithm was capable of differentiating major disease from other disease pathologies. Thus, in a clinically relevant manner, these data suggest this simplified automated disease algorithm scoring system used during step-testing to identify the likelihood that patients have HF, PAH, OLD, or RLD closely correlates with patient assessments conducted by trained clinicians.

Use of 'ideal' alveolar air equations and corrected end-tidal PCO2 to estimate arterial PCO2 and physiological dead space during exercise in patients with heart failure

BACKGROUND

Arterial CO₂ tension (PaCO₂) and physiological dead space (V_D) are not routinely measured during clinical cardiopulmonary exercise testing (CPET). Abnormal changes in PaCO₂ accompanied by increased V_D directly contribute to impaired exercise ventilatory function in heart failure (HF). Because arterial catheterization is not standard practice during CPET, this study tested the construct validity of PaCO₂ and V_D prediction models using 'ideal' alveolar air equations and basic ventilation and gas-exchangegas exchange measurements during CPET in HF.

METHODS

Forty-seven NYHA class II/III HF (LVEF=21±7%; age=55±9years; male=89%; BMI=28±5kg/m²) performed step-wise cycle ergometry CPET to volitional fatigue. Breath-by-breath ventilation and gas exchange were measured continuously. Steady-state PaCO₂ was measured at rest and peak exercise via radial arterial catheterization. Criterion V_D was calculated via 'ideal' alveolar equations, whereas PaCO₂ or V_D models were based on end-tidal CO₂ tension (P_ETCO₂), tidal volume (V_T), and/or weight.

RESULTS

Criterion measurements of PaCO₂ (38±5 vs. 33±5mmHg, P<0.01) and V_D (0.26±0.07 vs. 0.41±0.15L, P<0.01) differed at rest vs. peak exercise, respectively. The equation, 5.5+0.90×P_ETCO₂-0.0021×V_T, was the strongest predictor of PaCO₂ at rest and peak exercise (bias±95%LOA=-3.24±6.63 and -0.98±5.76mmHg; R²=0.57 and 0.75, P<0.001, respectively). This equation closely predicted V_D at rest and peak exercise (bias±95%LOA=-0.03±0.06 and -0.02±0.13L; R²=0.86 and 0.83, P<0.001, respectively).

CONCLUSIONS

These data suggest predicted PaCO₂ and V_D based on breath-by-breath gas exchange and ventilatory responses demonstrate acceptable agreement with criterion measurements at peak exercise in HF patients. Routine assessment of PaCO₂ and V_D can be used to improve interpretability of exercise ventilatory responses in HF.

Algorithm for Predicting Disease Likelihood From a Submaximal Exercise Test

We developed a simplified automated algorithm to interpret noninvasive gas exchange in healthy subjects and patients with heart failure (HF, n = 12), pulmonary arterial hypertension (PAH, n = 11), chronic obstructive lung disease (OLD, n = 16), and restrictive lung disease (RLD, n = 12). They underwent spirometry and thereafter an incremental 3-minute step test where heart rate and SpO2 respiratory gas exchange were obtained. A custom-developed algorithm for each disease pathology was used to interpret outcomes. Each algorithm for HF, PAH, OLD, and RLD was capable of differentiating disease groups (P < .05) as well as healthy cohorts (n = 19, P < .05). In addition, this algorithm identified referral pathology and coexisting disease. Our primary finding was that the ranking algorithm worked well to identify the primary referral pathology; however, coexisting disease in many of these pathologies in some cases equally contributed to the cardiorespiratory abnormalities. Automated algorithms will help guide decision making and simplify a traditionally complex and often time-consuming process.

Obstructive Ventilatory Disorder in Heart Failure-Caused by the Heart or the Lung?

Heart failure (HF) is a clinical syndrome frequently associated with airway obstruction, either as a respiratory comorbidity or as a direct consequence of HF pathophysiology. Recognizing the relative contribution of an underlying airway disease as opposed to airway obstruction due to volume overload and left atrial pressure elevation is of importance for the appropriate management of patients affected by HF. This review focuses on "les liaisons dangereuses" between the heart and the lungs, outlying recent advances linking in a vicious circle of chronic obstructive lung disease (COPD) and obstructive sleep apnea (OSA) on one side and HF on the other side. It also discusses the role of pivotal diagnostic tools such as pulmonary function tests and cardiopulmonary exercise test to determine the contribution of HF and COPD to symptoms and clinical status. Treatment implications are discussed as well.

Submaximal Exercise Pulmonary Gas Exchange in Left Heart Disease Patients With Different Forms of Pulmonary Hypertension

BACKGROUND

We determined whether pulmonary gas exchange indices during submaximal exercise are different in heart failure (HF) patients with combined post- and pre-capillary pulmonary hypertension (PPC-PH) versus HF patients with isolated post-capillary PH (IPC-PH) or no PH.

METHODS AND RESULTS

Pulmonary hemodynamics and pulmonary gas exchange were assessed during rest and submaximal exercise in 39 HF patients undergoing right heart catheterization. After hemodynamic evaluation, patients were classified as having no PH (n = 11), IPC-PH (n = 12), or PPC-PH (n = 16). At an equivalent oxygen consumption, end-tidal CO2 (PETCO2) and arterial oxygen saturation (SaO2) were greater in no-PH and IPC-PH versus PPC-PH patients (36.1 ± 3.2 vs. 31.7 ± 4.5 vs. 26.2 ± 4.7 mm Hg and 97 ± 2 vs. 96 ± 3 vs. 91 ± 1%, respectively). Conversely, dead-space ventilation (VD/VT) and the ventilatory equivalent for carbon dioxide (V˙(E)/V˙CO2 ratio) were lower in no-PH and IPC-PH versus PPC-PH patients (0.37 ± 0.05 vs. 0.38 ± 0.04 vs. 0.47 ± 0.03 and 38 ± 5 vs. 42 ± 8 vs. 51 ± 8, respectively). The exercise-induced change in V(D)/V(T), V˙(E)/V˙CO2 ratio, and PETCO2 correlated significantly with the change in mean pulmonary arterial pressure, diastolic pressure difference, and transpulmonary pressure gradient in PPC-PH patients only.

CONCLUSIONS

Noninvasive pulmonary gas exchange indices during submaximal exercise are different in HF patients with combined post- and pre-capillary PH compared with patients with isolated post-capillary PH or no PH.