Effects of oxygen breathing on pulmonary vascular input impedance in patients with pulmonary hypertension

A computational model of contributors to pulmonary hypertensive disease: impacts of whole lung and focal disease distributions

Pulmonary hypertension has multiple etiologies and so can be difficult to diagnose, prognose, and treat. Diagnosis is typically made via invasive hemodynamic measurements in the main pulmonary artery and is based on observed elevation of mean pulmonary artery pressure. This static mean pressure enables diagnosis, but does not easily allow assessment of the severity of pulmonary hypertension, nor the etiology of the disease, which may impact treatment. Assessment of the dynamic properties of pressure and flow data obtained from catheterization potentially allows more meaningful assessment of the strain on the right heart and may help to distinguish between disease phenotypes. However, mechanistic understanding of how the distribution of disease in the lung leading to pulmonary hypertension impacts the dynamics of blood flow in the main pulmonary artery and/or the pulmonary capillaries is lacking. We present a computational model of the pulmonary vasculature, parameterized to characteristic features of pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension to help understand how the two conditions differ in terms of pulmonary vascular response to disease. Our model incorporates key features known to contribute to pulmonary vascular function in health and disease, including anatomical structure and multiple contributions from gravity. The model suggests that dynamic measurements obtained from catheterization potentially distinguish between distal and proximal vasculopathy typical of pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension. However, the model suggests a non-linear relationship between these data and vascular structural changes typical of pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension which may impede analysis of these metrics to distinguish between cohorts.

Arterial load and right ventricular-vascular coupling in pulmonary hypertension

Right ventricular (RV) functional adaptation to afterload determines outcome in pulmonary hypertension (PH). RV afterload is determined by the dynamic interaction between pulmonary vascular resistance (PVR), characteristic impedance (Z_c), and wave reflection. Pulmonary vascular impedance (PVZ) represents the most comprehensive measure of RV afterload; however, there is an unmet need for an easier bedside measurement of this complex variable. Although a recent study showed that Z_c and wave reflection can be estimated from RV pressure waveform analysis and cardiac output, this has not been validated. Estimations of Z_c and wave reflection coefficient (λ) were validated relative to conventional spectral analysis in an animal model. Z_c, λ, and the single-beat ratio of end-systolic to arterial elastance (E_es/E_a) to estimate RV-pulmonary arterial (PA) coupling were determined from right heart catheterization (RHC) data. The study included 30 pulmonary artery hypertension (PAH) and 40 heart failure with preserved ejection fraction (HFpEF) patients [20 combined pre- and postcapillary PH (Cpc-PH) and 20 isolated postcapillary PH, (Ipc-PH)]. Also included were 10 age- and sex-matched controls. There was good agreement with minimal bias between estimated and spectral analysis-derived Z_c and λ. Z_c in PAH and Cpc-PH groups exceeded that in the Ipc-PH group and controls. λ was increased in Ipc-PH (0.84 ± 0.02), Cpc-PH (0.87 ± 0.05), and PAH groups (0.85 ± 0.04) compared with controls (0.79 ± 0.03); all P values were <0.05. λ was the only afterload parameter associated with RV-PA coupling in PAH. In the PH-HFpEF group, RV-PA uncoupling was independent of RV afterload. Our findings indicate that Z_c and λ derived from an RV pressure curve can be used to improve estimation of RV afterload. λ is the only afterload measure associated with RV-PA uncoupling in PAH, whereas RV-PA uncoupling in PH-HFpEF appears to be independent of afterload consistent with an inherent abnormality of the RV myocardium.NEW & NOTEWORTHY Pulmonary vascular impedance (PVZ) represents the most comprehensive measure of right ventricle (RV) afterload; however, measurement of this variable is complex. We demonstrate that characteristic impedance (Z_c) and a wave reflection coefficient, λ, can be derived from RV pressure waveform analysis. In addition, RV dysfunction in left heart disease is independent of its afterload. The current study provides a platform for future studies to examine the pharmacotherapeutic effects and prognosis of different measures of RV afterload.

Pulmonary hemodynamics and wave reflections in adults with atrial septal defects

Using high-fidelity micromanometers and flow velocity sensors at right heart catheterization, we compared pulmonary hemodynamics and wave reflections in age-matched normal adults and those with atrial septal defects, separated into three subgroups based on levels of mean pulmonary artery pressure: low (<17 mmHg), intermediate (17–26 mmHg), high (>26 mmHg). We made baseline measurements in all groups and after intravenous sodium nitroprusside in the subgroups. All of the subgroups had higher than normal baseline pulmonary flows and corresponding power that did not differ among the subgroups. The pulmonary vascular resistance, input resistance, and characteristic impedance in the subgroups did not differ from normal. Aside from the elevated flow and power, the hemodynamics in the low subgroup did not differ from normal. The intermediate subgroup had significantly higher than normal right ventricular and pulmonary artery pressures, wave reflections, and shorter wave reflection time, which all reverted to normal after nitroprusside. The high subgroup had similar changes as the intermediate subgroup. Unlike that subgroup, however, the pressures, wave reflections, and reflection return time did not revert to normal after nitroprusside. Hence, elevated wave reflections, but not resistance or characteristic impedance, are the hallmark of pulmonary hypertension in adults with atrial septal defects. Our results demonstrate that detailed measurements of hemodynamics and assessment of responsiveness to vasodilators provide important information about the pulmonary circulation in atrial septal defect. Coupled with studies after defect closure, those results may be a better foundation than current ones for clinical decisions.

Pulmonary hypertension: Pathophysiology beyond the lung

Pulmonary hypertension (PH) is classically considered a disease of pulmonary vasculature which has been the predominant target for drug development and PH therapy. Despite significant advancement in recent years in identification of new drug targets and innovative treatment strategies, the prognosis of PH remains poor, with median survival of 5 years. Recent studies have demonstrated involvement of neuroinflammation, altered autonomic and gastrointestinal functions and increased trafficking of bone marrow-derived cells in cardiopulmonary pathophysiology. This has led to the proposal that PH could be considered a systemic disease involving complex interactions among many organs. Our objectives in this review is to summarize evidence for the involvement of the brain, bone marrow and gut in PH pathophysiology. Then, to synthesize all evidence supporting a brain-gut-lung interaction hypothesis for consideration in PH pathophysiology and finally to summarize unanswered questions and future directions to move this novel concept forward. This forward-thinking view, if proven by further experiments, would provide new opportunities and novel targets for the control and treatment of PH.

Pulmonary Vascular Dynamics

The pulmonary circulation carries deoxygenated blood from the systemic veins through the pulmonary arteries to be oxygenated in the capillaries that line the walls of the pulmonary alveoli. The pulmonary circulation carries the cardiac output with a relatively low driving pressure, and so differs considerably in structure and function from the systemic circulation to maintain a low-resistance vascular system. The pulmonary circulation is often considered to be a quasi-static system in both experimental and computational studies of pulmonary perfusion and its matching to ventilation (air flow) for exchange. However, the system is highly dynamic, with cardiac output and regional perfusion changing with posture, exercise, and over time. Here we review this dynamic system, with a focus on understanding the physiology of pulmonary vascular dynamics across spatial and temporal scales, and the changes to these dynamics that are reflective of disease. © 2019 American Physiological Society. Compr Physiol 9:1081-1100, 2019.

alpha1A-adrenoceptor is involved in norepinephrine-induced proliferation of pulmonary artery smooth muscle cells via CaMKII signaling

Pulmonary arterial hypertension (PAH) is a progressive disease of the pulmonary vasculature characterized by excessive proliferation of pulmonary artery smooth muscle cells (PASMCs). Some studies have demonstrated the sympathetic nervous system is activated in PAH and norepinephrine (NE) released is closely linked with its activation. However, the subtypes of adrenoreceptor (AR) and the downstream molecular cascades which are involved in the proliferation of PASMCs are still unclear. In this study, adult male Wistar rats were exposed to chronic hypoxia and PASMCs were cultured in hypoxic condition. Significant upregulation of α_1A -AR was identified by Western blot analysis or immunofluorescence in all of the pulmonary arteries, lung tissues, and cell hypoxic models. Western blot analysis, flow cytometry, and immunofluorescence were applied to detect the roles of α_1A -AR in NE mediated proliferation of PASMCs. We revealed 5-methylurapidil (5-MU) reversed NE-induced upregulation of PCNA, CyclinA and CyclinE, more cells from G₀ /G₁ phase to G₂ /M+S phase, enhancement of the microtubule formation. In addition, we found calcium/calmodulin(CaM)-dependent protein kinase type II (CaMKII) pathway was involved in α_1A -AR-mediated cell proliferation. [Ca²⁺ ]_i measurements showed that an increase of [Ca²⁺ ]_i caused by NE or/and hypoxia could be blocked by 5-MU in PASMCs. Western blot analysis results demonstrated the augmentation of CaMKII phosphorylation level was caused by hypoxia or NE in pulmonary arteries, lung tissues, and PASMCs. KN62 attenuated NE-induced proliferation of PASMCs under normoxia and hypoxia. In conclusion, those results suggested NE which stimulated α_1A -AR-mediated the proliferation of PASMCs, which may be via the CaMKII pathway, and it could be used as a novel treatment strategy in PAH.

Hemodynamic effects of acute hyperoxia: systematic review and meta-analysis

Background

In clinical practice, oxygen is generally administered to patients with the intention of increasing oxygen delivery. Supplemental oxygen may, however, cause arterial hyperoxia, which is associated with hemodynamic alterations. We performed a systematic review and meta-analysis of the literature to determine the effect of hyperoxia on central hemodynamics and oxygen delivery in healthy volunteers and cardiovascular-compromised patients.

Methods

PubMed and EMBASE were searched up to March 2017. Studies with adult humans investigating changes in central hemodynamics or oxygen delivery induced by acute normobaric hyperoxia were included. Studies focusing on lung, retinal, or brain parameters were not included. We extracted subject and oxygen exposure characteristics, indexed and unindexed values for heart rate, stroke volume, cardiac output, mean arterial pressure (MAP), systemic vascular resistance, and oxygen delivery during normoxia and hyperoxia. For quantitative synthesis of the data, a random-effects ratio of means (RoM) model was used.

Results

We identified 33 studies with 42 datasets. Study categories included healthy volunteers (n = 22 datasets), patients with coronary artery disease (CAD; n = 6), heart failure (HF; n = 6), coronary artery bypass graft (CABG; n = 3) and sepsis (n = 5). Hyperoxia (arterial oxygen tension of 234–617 mmHg) reduced cardiac output (CO) by 10–15% in both healthy volunteers (−10.2%, 95% confidence interval (CI) −12.9% to −7.3%) and CAD (−9.6%, 95% CI −12.3% to −6.9%) or HF patients (−15.2%, 95% CI −21.7% to −8.2%). No significant changes in cardiac output were seen in CABG or septic patients (−3%). Systemic vascular resistance increased remarkably in patients with heart failure (24.6%, 95% CI 19.3% to 30.1%). In healthy volunteers, and those with CAD and CABG, the effect was smaller (11–16%) and was virtually absent in patients with sepsis (4.3%, 95% CI −3.2% to 12.3%). No notable effect on MAP was found in any group (2–3%). Oxygen delivery was not altered by hyperoxia. Considerable heterogeneity existed between study results, likely due to methodological differences.

Conclusions

Hyperoxia may considerably decrease cardiac output and increase systemic vascular resistance, but effects differ between patient categories. Heart failure patients were the most sensitive while no hemodynamic effects were seen in septic patients. There is currently no evidence supporting the notion that oxygen supplementation increases oxygen delivery.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-1968-2) contains supplementary material, which is available to authorized users.

Pulmonary artery wave propagation and reservoir function in conscious man: impact of pulmonary vascular disease, respiration and dynamic stress tests

KEY POINTS

Wave travel plays an important role in cardiovascular physiology. However, many aspects of pulmonary arterial wave behaviour remain unclear. Wave intensity and reservoir-excess pressure analyses were applied in the pulmonary artery in subjects with and without pulmonary hypertension during spontaneous respiration and dynamic stress tests. Arterial wave energy decreased during expiration and Valsalva manoeuvre due to decreased ventricular preload. Wave energy also decreased during handgrip exercise due to increased heart rate. In pulmonary hypertension patients, the asymptotic pressure at which the microvascular flow ceases, the reservoir pressure related to arterial compliance and the excess pressure caused by waves increased. The reservoir and excess pressures decreased during Valsalva manoeuvre but remained unchanged during handgrip exercise. This study provides insights into the influence of pulmonary vascular disease, spontaneous respiration and dynamic stress tests on pulmonary artery wave propagation and reservoir function.

ABSTRACT

Detailed haemodynamic analysis may provide novel insights into the pulmonary circulation. Therefore, wave intensity and reservoir-excess pressure analyses were applied in the pulmonary artery to characterize changes in wave propagation and reservoir function during spontaneous respiration and dynamic stress tests. Right heart catheterization was performed using a pressure and Doppler flow sensor tipped guidewire to obtain simultaneous pressure and flow velocity measurements in the pulmonary artery in control subjects and patients with pulmonary arterial hypertension (PAH) at rest. In controls, recordings were also obtained during Valsalva manoeuvre and handgrip exercise. The asymptotic pressure at which the flow through the microcirculation ceases, the reservoir pressure related to arterial compliance and the excess pressure caused by arterial waves increased in PAH patients compared to controls. The systolic and diastolic rate constants also increased, while the diastolic time constant decreased. The forward compression wave energy decreased by ∼8% in controls and ∼6% in PAH patients during expiration compared to inspiration, while the wave speed remained unchanged throughout the respiratory cycle. Wave energy decreased during Valsalva manoeuvre (by ∼45%) and handgrip exercise (by ∼27%) with unaffected wave speed. Moreover, the reservoir and excess pressures decreased during Valsalva manoeuvre but remained unaltered during handgrip exercise. In conclusion, reservoir-excess pressure analysis applied to the pulmonary artery revealed distinctive differences between controls and PAH patients. Variations in the ventricular preload and afterload influence pulmonary arterial wave propagation as demonstrated by changes in wave energy during spontaneous respiration and dynamic stress tests.

Determinants of right ventricular afterload (2013 Grover Conference series)

Right ventricular (RV) afterload consists of both resistive and capacitive (pulsatile) components. Total afterload can be measured directly with pulmonary artery input impedance spectra or estimated, either with lumped-parameter modeling or by pressure-volume analysis. However, the inverse, hyperbolic relationship between resistance and compliance in the lung would suggest that the pulsatile components are a predictable and constant proportion of the resistive load in most situations, meaning that total RV load can be estimated from mean resistive load alone. Exceptions include elevations in left atrial pressures and, to a lesser extent, chronic thromboembolic disease. The pulsatile components may also play a more significant role at normal or near-normal pulmonary artery pressures. Measures of coupling between RV afterload and RV contractility may provide important information not apparent by other clinical and hemodynamic measures. Future research should be aimed at development of noninvasive measures of coupling.

Cardiac sympathetic activation in patients with pulmonary arterial hypertension

Patients with congestive heart failure (CHF) due to left ventricular (LV) dysfunction have sympathetic activation specifically directed to the myocardium. Although pulmonary arterial hypertension (PAH) is associated with increased systemic sympathetic activity, its impact on sympathetic drive to ventricular myocardium is unknown. Fifteen patients with PAH (9 women; 54 ± 12 years) were studied: 10 with idiopathic PAH and 5 with a connective tissue disorder. We measured hemodynamics, as well as radiolabeled and endogenous concentrations of arterial and coronary sinus norepinephrine (NE). These measures were repeated after inhaled nitric oxide (NO). Measurement of transcardiac NE concentrations and the cardiac extraction of radiolabeled NE allowed calculation of the corrected transcardiac gradient of NE (CTCG of NE). Comparative data were collected from 15 patients (9 women: 55 ± 12 yr) with normal LV function and 15 patients with CHF (10 women; 53 ± 12 yr). PAH patients had elevated arterial NE concentrations compared with those with normal LV function but were similar to those with CHF. The CTCG of NE was higher in those with PAH than in the normal LV group (3.6 ± 2.2 vs. 1.5 ± 0.9 pmol/ml; P < 0.01) but similar to that seen in those with CHF (3.3 ± 1.4; P = NS). Inhaled NO, which reduced pulmonary artery pressure and increased cardiac output, had no effect on cardiac sympathetic activity. Therefore, cardiac sympathetic activation occurs in PAH. The mechanism of this activation remains uncertain but does not involve elevations in left heart filling pressure.

Mechanics and Function of the Pulmonary Vasculature: Implications for Pulmonary Vascular Disease and Right Ventricular Function

The relationship between cardiac function and the afterload against which the heart muscle must work to circulate blood throughout the pulmonary circulation is defined by a complex interaction between many coupled system parameters. These parameters range broadly and incorporate system effects originating primarily from three distinct locations: input power from the heart, hydraulic impedance from the large conduit pulmonary arteries, and hydraulic resistance from the more distal microcirculation. These organ systems are not independent, but rather, form a coupled system in which a change to any individual parameter affects all other system parameters. The result is a highly nonlinear system which requires not only detailed study of each specific component and the effect of disease on their specific function, but also requires study of the interconnected relationship between the microcirculation, the conduit arteries, and the heart in response to age and disease. Here, we investigate systems-level changes associated with pulmonary hypertensive disease progression in an effort to better understand this coupled relationship.

Pulmonary vascular stiffness: measurement, modeling, and implications in normal and hypertensive pulmonary circulations

This article introduces the concept of pulmonary vascular stiffness, discusses its increasingly recognized importance as a diagnostic marker in the evaluation of pulmonary vascular disease, and describes methods to measure and model it clinically, experimentally, and computationally. It begins with a description of systems-level methods to evaluate pulmonary vascular compliance and recent clinical efforts in applying such techniques to better predict patient outcomes in pulmonary arterial hypertension. It then progresses from the systems-level to the local level, discusses proposed methods by which upstream pulmonary vessels increase in stiffness, introduces concepts around vascular mechanics, and concludes by describing recent work incorporating advanced numerical methods to more thoroughly evaluate changes in local mechanical properties of pulmonary arteries.

Prognostic significance of sympathetic nervous system activation in pulmonary arterial hypertension

RATIONALE

The sympathetic nervous system has been reported to be activated in pulmonary arterial hypertension (PAH).

OBJECTIVES

We investigated the prognostic significance of muscle sympathetic nervous system activity (MSNA) in PAH.

METHODS

Thirty-two patients with PAH were included in the study and underwent a measurement of MSNA over a 6-year period of time. They had undergone a concomitant evaluation of New York Heart Association (NYHA) functional class, a 6-minute walk distance (6MWD), an echocardiographic examination, and a right heart catheterization for diagnostic or reevaluation purposes. The median follow-up time was 20.6 months (interquartile range, 45.8 mo). Clinical deterioration was defined by listing for transplantation or death.

MEASUREMENTS AND MAIN RESULTS

Seventeen patients presented with clinical deterioration. As compared with the 15 others, they had an increased MSNA (80 +/- 12 vs. 52 +/- 18 bursts/min; P < 0.001) and heart rate (88 +/- 17 vs. 74 +/- 12 bpm; P = 0.01), a lower 6MWD (324 +/- 119 vs. 434 +/- 88 m; P < 0.01) and a deteriorated NYHA functional class (3.6 +/- 0.5 vs. 2.9 +/- 0.8; P < 0.001). The hemodynamic variables were not different. MSNA was directly related to heart rate and inversely to 6MWD. A univariate analysis revealed that increased MSNA and heart rate, NYHA class IV, lower 6MWD, and pericardial effusion were associated with subsequent clinical deterioration. A multivariate analysis showed that MSNA was an independent predictor of clinical deterioration. For every increase of 1 burst/minute, the risk of clinical deterioration during follow-up increased by 6%.

CONCLUSIONS

Sympathetic nervous system activation is an independent predictor of clinical deterioration in pulmonary arterial hypertension.

Right heart function and haemodynamics in pulmonary hypertension

The primary challenge in the care of the patient with advanced pulmonary arterial hypertension (PAH) is right ventricular dysfunction with concomitant right heart failure. Right heart function is closely tied to survival in this disease, and there is a growing interest in the study of this unique structure. While echocardiography and cardiac magnetic resonance (CMR) have augmented our ability to image the right ventricle (RV), the primary means of assessing right heart function remains right heart catheterisation. Several of the currently available treatments for PAH have been shown to have effects on the RV, not just the pulmonary vasculature, and, in future, therapies aimed at optimizing right ventricular function may allow better outcomes in this challenging disease. New directions in right ventricular assessment including measurement of pulmonary vascular impedance and more widespread availability of CMR may allow greater knowledge about this little studied, yet highly important, right side of the heart.

Increased sympathetic nerve activity in pulmonary artery hypertension

BACKGROUND

This study tested the hypothesis that sympathetic nerve activity is increased in pulmonary artery hypertension (PAH), a rare disease of poor prognosis and incompletely understood pathophysiology. We subsequently explored whether chemoreflex activation contributes to sympathoexcitation in PAH.

METHODS AND RESULTS

We measured muscle sympathetic nerve activity (MSNA) by microneurography, heart rate (HR), and arterial oxygen saturation (Sao(2)) in 17 patients with PAH and 12 control subjects. The patients also underwent cardiac echography, right heart catheterization, and a 6-minute walk test with dyspnea scoring. Circulating catecholamines were determined in 8 of the patients. Chemoreflex deactivation by 100% O(2) was assessed in 14 patients with the use of a randomized, double-blind, placebo-controlled, crossover study design. Compared with the controls, the PAH patients had increased MSNA (67+/-4 versus 40+/-3 bursts per minute; P<0.0001) and HR (82+/-4 versus 68+/-3 bpm; P=0.02). MSNA in the PAH patients was correlated with HR (r=0.64, P=0.006), Sao(2) (r=-0.53, P=0.03), the presence of pericardial effusion (r=0.51, P=0.046), and NYHA class (r=0.52, P=0.033). The PAH patients treated with prostacyclin derivatives had higher MSNA (P=0.009), lower Sao(2) (P=0.01), faster HR (P=0.003), and worse NYHA class (P=0.04). Plasma catecholamines were normal. Peripheral chemoreflex deactivation with hyperoxia increased Sao(2) (91.7+/-1% to 98.4+/-0.2%; P<0.0001) and decreased MSNA (67+/-5 to 60+/-4 bursts per minute; P=0.0015), thereby correcting approximately one fourth of the difference between PAH patients and controls.

CONCLUSIONS

We report for the first time direct evidence of increased sympathetic nerve traffic in advanced PAH. Sympathetic hyperactivity in PAH is partially chemoreflex mediated and may be related to disease severity.

Feasibility of Routine Pulmonary Arterial Impedance Measurements in Pulmonary Hypertension

OBJECTIVES

Right ventricular (RV) afterload is best described by a pulmonary arterial impedance (PVZ) spectrum, which integrates pulmonary vascular resistance (PVR), elastance, and wave reflection. We evaluated the feasibility of PVZ determinations in patients with pulmonary arterial hypertension (PAH) during routine right heart catheterization and Doppler echocardiography.

DESIGN

Prospective study.

SETTING

Academic hospital.

PATIENTS

Twenty-two patients with PAH.

INTERVENTIONS

Right heart catheterization with a fluid-filled Swan-Ganz catheter, Doppler echocardiography, and administration of inhaled nitric oxide (NO) [10 to 20 ppm; 17 patients], maximum tolerated dose of IV epoprostenol (average, 8.5 ng/kg/min; 5 patients), and IV dobutamine (8 micro g/kg/min; 8 patients).

MEASUREMENTS AND RESULTS

PVZ was calculated from the spectral analysis of synchronized pulmonary artery pressure (Ppa) and flow waves. The mean (+/- SE) Ppa was 63 +/- 3 mm Hg, and the mean PVR was 16 +/- 2 Wood units. The PVZ spectrum was markedly shifted to higher than normal pressures and frequencies, with a mean 0-Hz impedance (Z(0)) of 1,506 +/- 138 dyne. s. cm(-5), and a mean characteristic impedance (Zc) of 124 +/- 11 dyne. s. cm(-5), which are in keeping with data from previous studies. Inhaled NO levels decreased Ppa, PVR, Z(0), and Zc without a change in cardiac output. Epoprostenol administration did not affect Ppa, increased cardiac output, and decreased Z(0) and Zc. Dobutamine administration increased cardiac output and Ppa, and decreased PVR and Z(0), without changing Zc.

CONCLUSIONS

The determination of PVZ to quantify RV afterload is feasible during routine right heart catheterization and Doppler echocardiography. The measurement is sensitive to pharmacologic interventions.

Primary pulmonary hypertension and cor pulmonale

Primary pulmonary hypertension and cor pulmonale represent forms of precapillary pulmonary hypertension due to intrinsic lung disease. In the case of primary pulmonary hypertension, this is due to disease of the pulmonary vasculature while cor pulmonale is related to diseases of the pulmonary vasculature, airways, or interstitium. Patients present with signs and symptoms of right ventricular dysfunction and low cardiac output including dyspnea, chest pain and peripheral edema. Therapy is directed at the underlying disease and may include supplemental oxygen for diseases causing chronic hypoxemia and anticoagulation for thrombotic disease. Vasodilator therapy has variable efficacy for pulmonary vascular disorders. Postacyclin by continuous infusion has been a major advance in the therapy of primary pulmonary hypertension and has prolonged survival and delayed the need for lung transplantation. Bosentan, an endothelin receptor blocking agent is the first oral medication approved for the therapy of pulmonary hypertension.

Hemodynamic response to oxygen administration in chronic heart failure: role of chemoreflexes

The aim of this study was to assess whether arterial chemoreceptors are activated in chronic heart failure and to appreciate whether this activation is related to the degree of cardiac dysfunction. We examined whether administration of pure oxygen for 30 min to 35 patients with chronic heart failure was followed by hemodynamic modifications that would suggest a negative feedback (inactivation) of such chemoregulation. A decrease in heart rate and cardiac output was observed in all patients. The decrease in cardiac output and stroke volume was inversely correlated to the left ventricular ejection fraction. We observed that the lower the left ventricular ejection fraction, the smaller the decrease in heart rate and the greater the increase in systemic vascular resistance. The variation of stroke volume was related to the variation of systemic vascular resistance. In 12 patients, keeping heart rate constant during oxygen inhalation by adequate right atrial pacing prevented the decrease of cardiac output. These results suggest that chemoregulation remains generally effective in chronic heart failure: increase in Pao2 resulted in a reduction of cardiac output mainly related to the decrease of heart rate. However, when the left ventricular function is very poor, the central chemomediated regulation is impaired, and the direct peripheral effect of oxygen on systemic circulation appears to play a leading part.

[Right ventricular function: physiological and physiopathological features]

Sinus and conus constitute the two cavities of the right ventricle. They are anatomically and functionally different. The sinus is a flow-generator and the conus a pressure-regulator. The coronary circulation of the right ventricle is provided by the right coronary artery and the left anterior descending artery. The right ventricle is perfused during systole and diastole. When oxygen demand increases, coronary arteries dilate and oxygen extraction rises. As for the left ventricle, right ventricular performance depends upon heart rate, rhythm, contractility and loading conditions. Ventricular interactions are very important for right ventricular function. Loading conditions and contractility of the left ventricle are of major significance for right ventricular performance. For the right ventricle, the end of the ejection is different from the end of the active contraction. The time between them allows to achieve ventricular emptying. This duration is linked to afterload. Presently, it is impossible to accurately and simply assess these conditions. Pressure and volume overloadings result in right ventricular failure. They are responsible for ventricular dilation and ischaemia with a decrease in cardiac output, generating a vicious circle. Treatment includes the removal of the cause, and the maintenance of systemic arterial pressure and biventricular contractility. It is difficult to assess the effects of intravenous vasodilators on right ventricular afterload.

Pulmonary arterial impedance analysis by the use of the oscillated assist flow

Pulmonary arterial impedance is an important and interesting characteristic that can be used to evaluate the physiological properties of the pulmonary vessel. However, power spectrum analysis of the pulmonary artery pressure and flow pattern have suggested that peak power in the relatively high frequency range (> 10 Hz) is significantly low; thus, we cannot analyze the vessel properties in the high frequency range. In this study, we used the newly developed vibrating flow pump (VFP), which can generate oscillated blood flow with a relatively high frequency (10-50 Hz) for right heart bypass, to evaluate the pulmonary arterial impedance pattern in the high frequency range. Acute animal experiments of the right heart bypass from the right atrium to the pulmonary artery using 6 healthy adult goats were performed. The flow pattern and pressure of the pulmonary artery, electrocardiograms (ECGs), and arterial and right atrial pressures were continuously monitored during the experiments. Spectral analysis of the hemodynamic parameters using the fast Fourier transform (FFT) method was performed to evaluate the spectral properties. The coherence function, transfer function, and phase patterns were calculated to analyze the impedance pattern in the relatively high frequency area. Previously, various investigators had tried to analyze the impedance patterns of the pulmonary artery; however, they could not analyze the impedance patterns over 10 Hz because the spectral patterns of the pulmonary flow do not have high power at high frequencies. These physiological analyses may be useful in designing the optimal pulmonary circulation.

Pulmonary artery hemodynamics in primary pulmonary hypertension

OBJECTIVES

The present investigation compared and contrasted steady and pulsatile pulmonary hemodynamics at rest and during exercise in patients with primary pulmonary hypertension and normal control subjects.

BACKGROUND

A complete description of the relation between pressure and flow in the pulmonary circulation includes both steady and pulsatile hemodynamic behavior. Patients with primary pulmonary hypertension provide a unique opportunity to study the effects of primary alterations in pulmonary vasculature on pulmonary artery vascular hydraulic load.

METHODS

Catheter tip pressure and velocity recordings from the main pulmonary artery in 8 patients with primary pulmonary hypertension and 10 control subjects were used to derive the pulmonary artery input impedance spectrum and the extent of pulse wave reflection at rest and during exercise.

RESULTS

As expected, in patients with primary pulmonary hypertension, mean pulmonary artery pressure (50 +/- 10 mm Hg) and pulmonary vascular resistance (880 +/- 446 dynes.s.cm-5) were markedly elevated at rest and remained so during exercise (mean pressure 71 +/- 15 mm Hg, mean resistance 750 +/- 530 dynes.s.cm-5). Pulmonary artery characteristic impedance was elevated at rest and did not change with exercise (rest 55 +/- 25 dynes.s.cm-5; exercise 66 +/- 33 dynes.s.cm-5). Measures of arterial wave reflection indicated that the extent of wave reflection in the pulmonary bed in those with primary pulmonary hypertension is large at rest (reflection coefficient 0.89 +/- 0.09) and that the composite reflected wave arrived during the midportion of right ventricular ejection. Although the extent of wave reflection decreased with exercise (reflection coefficient 0.81 +/- 0.10, p < 0.05), the magnitude and timing of these reflections remained adverse. Furthermore, in patients with primary pulmonary hypertension, the stroke volume response to exercise was strongly related to rest levels of pulmonary artery diastolic pressure, pulmonary vascular resistance and the reflection factor, whereas no such relation was found in the control subjects.

CONCLUSIONS

In addition to the expected abnormalities in steady measures of pulmonary artery hemodynamics at rest in patients with primary pulmonary hypertension, rest and exercise measures of oscillatory behavior (characteristic impedance and pulse wave reflection) are perturbed. Measures of steady and pulsatile behavior, particularly wave reflection, appear to have an important role in the exercise response of these patients.

Effects of pacing tachycardia and balloon valvuloplasty on pulmonary artery impedance and hydraulic power in mitral stenosis

BACKGROUND

Mitral stenosis is characterized by progressive pulmonary hypertension and eventual right ventricular failure. However, the correlation between right ventricular failure and the level of pulmonary hypertension is poor, suggesting that factors other than those recognized from nonpulsatile hemodynamic parameters may contribute to impaired right ventricular performance in this condition.

METHODS AND RESULTS

We studied 16 patients with severe mitral stenosis (mean valve area, 1.0 +/- 0.2 cm2) at supine rest and during pacing tachycardia using high-fidelity catheter recordings of pulmonary artery (PA) pressure and flow velocity. Pulmonary impedance spectra, wave reflection properties, and hydraulic power data were derived from Fourier analysis of signal-averaged data. Pacing tachycardia (baseline heart rate, 81 +/- 11 beats per minute; pacing, 132 +/- 11 beats per minute) significantly raised pulmonary wedge and mean PA pressures. There was no change in pulmonary vascular resistance (209 +/- 144 to 232 +/- 164 dyne-sec/cm5) or PA characteristic impedance (62 +/- 25 to 55 +/- 28 dyne-sec/cm5). However, first harmonic impedance (Z1) significantly decreased (134 +/- 71 to 100 +/- 68 dyne-sec/cm5; p < 0.001). Accordingly, oscillatory and total dissipated hydraulic power per unit forward flow (WT/CO) fell during tachycardia (2.6 +/- 1.6 to 2.3 +/- 1.4 mW/ml.sec-1; p = 0.06) despite acute pulmonary hypertension. Reflected pressure waves returned earlier to the proximal PA, suggesting increased vessel stiffness. Immediately after percutaneous balloon mitral valvuloplasty (PBV) in eight of the patients, baseline and pacing data were again recorded. Compared with the pre-PBV baseline state, post-PBV resting data demonstrated no change in resistance or characteristic impedance, but there was a significant fall in Z1 (166 +/- 75 to 103 +/- 45 dyne-sec/cm5; p < 0.05) and in the magnitude of pulmonary wave reflections. WT/CO tended to decrease after PBV, and pacing after PBV produced a further decrease in WT/CO, again in association with lower Z1.

CONCLUSIONS

These data demonstrate that 1) increased pulmonary characteristic impedance, although a feature of mitral stenosis, is not exacerbated by the acute effects of increased distending pressure; 2) pacing tachycardia in mitral stenosis causes little change in the pulmonary impedance spectrum except at low frequencies, where decreased impedance lowers power requirements per unit flow; and 3) relief of mitral stenosis produces immediate improvement in low-frequency impedance and in hydraulic power requirements. These findings suggest that although characteristic impedance may be a measure of the long-term effects of pulmonary hypertension on the pulmonary circulation, acute increases and decreases in PA pressure produce effects on right ventricular load that are best described in terms of the low-frequency properties of the PA system. Improvement in low-frequency impedance diminishes hydraulic power requirements and thus reflects improved ventricular-vascular coupling, irrespective of distending PA pressure. Efforts to treat or prevent right heart failure in the presence of pulmonary hypertension should take account of the potential benefit of changes in low-frequency impedance characteristics of the pulmonary vascular bed.

Right ventricular-pulmonary arterial interactions

The application of pulsatile models to hemodynamic data has made possible a more complete understanding of the relationship of pulmonary pressure and flow. To review the genesis of these concepts, the unique characteristics of the pulmonary artery and right ventricle are outlined as a basis for understanding why differences in their pulsatile properties from the systemic circuit must exist. The pulmonary impedance spectrum is introduced and the concept of optimal right ventricular-pulmonary artery coupling is explored based on a review of extensive experimental data. Finally, available studies of normal pulmonary impedance in man and abnormal impedance in human disease states are reviewed, with emphasis on disturbances in optimal ventricular-vascular coupling. The important implications of these concepts for understanding and treatment of cardiovascular disease are developed.

Cardiopulmonary response to oxygen therapy in hypoxaemic chronic airflow obstruction

The acute change in pulmonary artery pressure in response to oxygen may have prognostic value for patients with chronic obstructive pulmonary disease treated with long term domiciliary oxygen. A study was carried out to elucidate the mechanism of the acute cardio-respiratory response to oxygen in such patients and to determine whether it can be quantified non-invasively. The effects of acute oxygen administration (100% for 20 minutes and 28% oxygen for 24 hours) were assessed by non-invasive means and right heart catheterisation in 17 patients with severe stable hypoxaemic chronic obstructive pulmonary disease. Measurements included change in the ratio of dead space to tidal volume (VD/VT), effective pulmonary capillary blood flow (by rebreathing and single breath soluble gas uptake: QRB, QSB), left ventricular ejection fraction (radionuclide ventriculography), and M mode echocardiographic estimates of ventricular diameters and fractional shortening. These values were compared with those obtained from right heart catheter measurements of pulmonary artery pressure, cardiac index (thermodilution and direct carbon dioxide Fick: QTD, QFICK), and pulmonary vascular resistance. Oxygen administration resulted in a significant fall in pulmonary artery pressure, QTD, and QRB and a significant increase in VD/VT. The fall in QRB after 100% oxygen breathing for 20 minutes correlated strongly with the fall in pulmonary artery pressure (r = 0.86). There was no correlation between the fall in pulmonary artery pressure and the fall in QSB or the risen in VD/VT. Left ventricular ejection fraction did not change significantly. Echocardiography was technically unsatisfactory because of lung hyperinflation. Apart from a possible relation between VO2max and fall in pulmonary artery pressure after 24 hours of 28% oxygen breathing (r = 0.49, p less than 0.1) none of the baseline respiratory function measurements predicted the fall in pulmonary artery pressure or QRB. It is concluded that the cardiopulmonary response to acute oxygen breathing in patients with hypoxic chronic obstructive pulmonary disease includes a reduction in pulmonary artery pressure and cardiac output and a redistribution of pulmonary blood flow, and that rebreathing measurements of effective pulmonary blood flow can be used to quantify this response non-invasively.

Nocturnal home oxygen in the treatment of hypoxemic cystic fibrosis patients

The effect of nocturnal oxygen therapy on mortality and morbidity rates and on progression of disease was tested in a double-blind, randomized trial of 28 subjects with advanced cystic fibrosis. Patients were selected on the basis that their awake arterial oxygen tension was less than 65 mm Hg when they were clinically stable. Oxygen was prescribed in 1 L/min increments to obtain an awake arterial oxygen tension of greater than or equal to 70 mm Hg. Subjects received humidified oxygen or room air from modified concentrators. They were enrolled over a 3-year period and followed for an average (+/- SD) of 26 +/- 9 months. The average number of hours per night of concentrator use was 5.3 +/- 3.2 hours in the air group and 7.0 +/- 1.9 hours in the oxygen group. Over the follow-up period there were four deaths in each group, and oxygen therapy had no significant effect on the frequency of hospitalizations. Progression of disease was ascertained from nutritional status, pulmonary function, blood gas values, exercise ability, and right ventricular ejection fraction response to exercise (as measured by equilibrium-gated radionuclide angiocardiography), and psychologic status was measured by standardized tests of mood, self-esteem, and cognitive function; group comparisons for the first year revealed no significant differences; however, school or work attendance was maintained in the oxygen group but deteriorated in the air group. Clinical signs of cor pulmonale were documented during follow-up in 10 patients in toto, and all lived at least 9 months from the onset of these signs. The lack of association between the onset of these signs and imminent death, or the usefulness of measurements of the maximal oxygen uptake during progressive exercise and the right ventricular ejection fraction response to exercise as prognostic indicators, suggest that death may not be the result of cor pulmonale. We conclude that nocturnal oxygen treatment in patients with cystic fibrosis did not appear to affect mortality rates, the frequency of hospitalizations, or the progression of disease; oxygen use should be instituted only after the development of symptoms related to hypoxemia.

The degree of increment in plasma catecholamines in patients with mitral stenosis by mild exercise

Although sympathetic excitation during mild exercise may readily occur in patients with mitral stenosis (MS), the degree of increment in plasma catecholamines has not been fully investigated. We imposed mild ergometric exercise (50 watts, 300 kg/min for 5 minutes) on five patients with mild MS (mitral valve area greater than or equal to 1.0 cm2) and eight with severe MS (mitral valve area less than 1.0 cm2) while they were undergoing cardiac catheterization. In patients with severe MS, total plasma catecholamine levels during exercise were remarkably higher (2821 +/- 783 [SEM] pg/ml) than in those with mild MS (957 +/- 113 pg/ml, p less than 0.05) and in seven control subjects (612 +/- 75 pg/ml, p less than 0.05). This marked increment could not be predicted by heart rate response, which did not differ between severe and mild MS (166 +/- 5 vs 153 +/- 10 bpm). In contrast with catecholamine change, the cardiac index in severe MS showed a very small increment. Results suggest that mild daily exercise can remarkably increase plasma catecholamine levels in severe MS, and this may accelerate various complications of this disorder.

Maturation of pulmonary input impedance spectrum in infants and children with ventricular septal defect

To determine whether pulmonary vascular disease can be detected in infants with ventricular septal defect (VSD) by the presence of an increase in the frequency of the impedance modulus minimum of the pulmonary input impedance spectrum, as has been implied for older children, spectra of 25 infants (2 years or younger) (group 1) were compared with spectra of 20 children (ages 2 to 7 years) (group 2). Groups were subdivided according to mean pulmonary artery (PA) pressure: those with moderate pressure levels (35 mm Hg or less, groups 1A and 2A) and those with high pressure levels (at least 40 mm Hg, groups 1B and 2B). Pulmonary vascular resistance, characteristic impedance and frequency of the modulus minimum were significantly lower in group 2A than in group 1A. The decrease in pulmonary vascular resistance and characteristic impedance with increasing age was consistent with body surface area increases; however, the shift in frequency of the modulus minimum could be more easily related to a decrease in the pulse wave velocity than to a shift in the primary reflection site. Pulmonary vascular resistance, characteristic impedance and the frequency of the first modulus minimum were comparable in groups 1B and 2B; however, none of the patients in group 1B had evidence of pulmonary damage, whereas 3 of 4 group 2B patients had microscopically apparent pulmonary vascular disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Systemic vasoconstrictor effects of oxygen administration in obliterative pulmonary vascular disorders

Although oxygen is frequently administered to patients with obliterative pulmonary vascular disorders (OPVD) for diagnostic and therapeutic purposes, its hemodynamic effects in these patients have not been systematically evaluated. The response to administration of 50 to 70% oxygen was studied in 14 patients with pulmonary hypertension secondary to OPVD. Mean pulmonary artery pressure decreased (from 62 +/- 5 to 57 +/- 5 mm Hg, p less than 0.01) after oxygen inhalation secondary to a decrease in cardiac index (1.9 +/- 0.2 to 1.8 +/- 0.2 liters/min/m2, p less than 0.01), without changes in pulmonary arteriolar resistance. This decline in forward output appeared to result from a systemic vasoconstrictor effect of oxygen (change in systemic vascular resistance from 1,965 +/- 275 to 2,297 +/- 336 dynes s cm-5, p less than 0.01), which decreased heart rate (from 93 +/- 3 to 89 +/- 2 beats/min, p less than 0.01) by stimulation of baroreceptor reflexes and decreased stroke volume (from 22 +/- 3 to 21 +/- 2 ml/beat/m2, p less than 0.05) by increasing impedance to left ventricular ejection. The decrease in left-sided cardiac output likely led to a decline in venous return to the right side of the heart and, consequently, to a decrease in right atrial and pulmonary arterial pressures. Accordingly, the percent decrease in mean pulmonary artery pressure varied linearly and directly with the percent increase in systemic vascular resistance (r = 0.84), but not with changes in pulmonary arteriolar resistance (r = 0.15).(ABSTRACT TRUNCATED AT 250 WORDS)