Hematocrit-corrected Pulmonary Vascular Resistance

Analysis of haemodynamics surrounding blood transfusions after the arterial switch operation: a pilot study utilising real-time telemetry high-frequency data capture

BACKGROUND

Packed red blood cell transfusions occur frequently after congenital heart surgery to augment haemodynamics, with limited understanding of efficacy. The goal of this study was to analyse the hemodynamic response to packed red blood cell transfusions in a single cohort, as "proof-of-concept" utilising high-frequency data capture of real-time telemetry monitoring.

METHODS

Retrospective review of patients after the arterial switch operation receiving packed red blood cell transfusions from 15 July 2020 to 15 July 2021. Hemodynamic parameters were collected from a high-frequency data capture system (SickbayTM) continuously recording vital signs from bedside monitors and analysed in 5-minute intervals up to 6 hours before, 4 hours during, and 6 hours after packed red blood cell transfusions-up to 57,600 vital signs per packed red blood cell transfusions. Variables related to oxygen balance included blood gas co-oximetry, lactate levels, near-infrared spectroscopy, and ventilator settings. Analgesic, sedative, and vasoactive infusions were also collected.

RESULTS

Six patients, at 8.5[IQR:5-22] days old and weighing 3.1[IQR:2.8-3.2]kg, received transfusions following the arterial switch operation. There were 10 packed red blood cell transfusions administered with a median dose of 10[IQR:10-15]mL/kg over 169[IQR:110-190]min; at median post-operative hour 36[IQR:10-40]. Significant increases in systolic and mean arterial blood pressures by 5-12.5% at 3 hours after packed red blood cell transfusions were observed, while renal near-infrared spectroscopy increased by 6.2% post-transfusion. No significant changes in ventilation, vasoactive support, or laboratory values related to oxygen balance were observed.

CONCLUSIONS

Packed red blood cell transfusions given after the arterial switch operation increased arterial blood pressure by 5-12.5% for 3 hours and renal near-infrared spectroscopy by 6.2%. High-frequency data capture systems can be leveraged to provide novel insights into the hemodynamic response to commonly used therapies such as packed red blood cell transfusions after paediatric cardiac surgery.

A novel clinical prediction scoring system of high-altitude pulmonary hypertension

Background

High-altitude pulmonary hypertension (HAPH) is a common disease in regions of high altitude where performing right heart catheterization (RHC) is challenging. The development of a diagnostic scoring system is crucial for effective disease screening.

Methods

A total of 148 individuals were included in a retrospective analysis, and an additional 42 residents were prospectively enrolled. We conducted a multivariable analysis to identify independent predictors of HAPH. Subsequently, we devised a prediction score based on the retrospective training set to anticipate the occurrence and severity of HAPH. This scoring system was further subjected to validation in the prospective cohort, in which all participants underwent RHC.

Results

This scoring system, referred to as the GENTH score model (Glycated hemoglobin [OR = 4.5], Echocardiography sign [OR = 9.1], New York Heart Association-functional class [OR = 12.5], Total bilirubin [OR = 3.3], and Hematocrit [OR = 3.6]), incorporated five independent risk factors and demonstrated strong predictive accuracy. In the training set, the area under the curve (AUC) values for predicting the occurrence and severity of HAPH were 0.851 and 0.832, respectively, while in the validation set, they were 0.841 and 0.893. In the validation set, GENTH score model cutoff values of ≤18 or >18 points were established for excluding or confirming HAPH, and a threshold of >30 points indicated severe HAPH.

Conclusions

The GENTH score model, combining laboratory and echocardiography indicators, represents an effective tool for distinguishing potential HAPH patients and identifying those with severe HAPH. This scoring system improves the clinical screening of HAPH diseases and offers valuable insights into disease diagnosis and management.

Regulation of haemoglobin concentration at high altitude

Lowlanders sojourning for more than 1 day at high altitude (HA) experience a reduction in plasma volume (PV) that increases haemoglobin concentration and thus restores arterial oxygen content. If the sojourn extends over weeks, an expansion of total red cell volume (RCV) occurs and contributes to the haemoconcentration. While the reduction in PV was classically attributed to an increased diuretic fluid loss, recent studies support fluid redistribution, rather than loss, as the underlying mechanism. The fluid redistribution is presumably driven by a disappearance of proteins from the circulation and the resulting reduction in oncotic pressure exerted by the plasma, although the fate of the disappearing proteins remains unclear. The RCV expansion is the result of an accelerated erythropoietic activity secondary to enhanced renal erythropoietin release, but a contribution of other mechanisms cannot be excluded. After return from HA, intravascular volumes return to normal values and the normalisation of RCV might involve selective destruction of newly formed erythrocytes, although this explanation has been strongly challenged by recent studies. In contrast to acclimatised lowlanders, native highlanders originating from the Tibetan and the Ethiopian plateaus present with a normal or only mildly elevated haemoglobin concentration. Genetic adaptations blunting the erythropoietic response to HA exposure have been proposed as an explanation for the absence of more pronounced haemoconcentration in these populations, but new evidence also supports a contribution of a larger than expected PV. The functional significance of the relatively low haemoglobin concentration in Tibetan and Ethiopian highlanders is incompletely understood and warrants further investigation.

Exercise Stress Echocardiography of the Right Ventricle and Pulmonary Circulation

BACKGROUND

Exercise echocardiography is used for assessment of pulmonary circulation and right ventricular function, but limits of normal and disease-specific changes remain insufficiently established.

OBJECTIVES

The objective of this study was to explore the physiological vs pathologic response of the right ventricle and pulmonary circulation to exercise.

METHODS

A total of 2,228 subjects were enrolled: 375 healthy controls, 40 athletes, 516 patients with cardiovascular risk factors, 17 with pulmonary arterial hypertension, 872 with connective tissue diseases without overt pulmonary hypertension, 113 with left-sided heart disease, 30 with lung disease, and 265 with chronic exposure to high altitude. All subjects underwent resting and exercise echocardiography on a semirecumbent cycle ergometer. All-cause mortality was recorded at follow-up.

RESULTS

The 5th and 95th percentile of the mean pulmonary artery pressure-cardiac output relationships were 0.2 to 3.5 mm Hg.min/L in healthy subjects without cardiovascular risk factors, and were increased in all patient categories and in high altitude residents. The 5th and 95th percentile of the tricuspid annular plane systolic excursion to systolic pulmonary artery pressure ratio at rest were 0.7 to 2.0 mm/mm Hg at rest and 0.5 to 1.5 mm/mm Hg at peak exercise, and were decreased at rest and exercise in all disease categories and in high-altitude residents. An increased all-cause mortality was predicted by a resting tricuspid annular plane systolic excursion to systolic pulmonary artery pressure <0.7 mm/mm Hg and mean pulmonary artery pressure-cardiac output >5 mm Hg.min/L.

CONCLUSIONS

Exercise echocardiography of the pulmonary circulation and the right ventricle discloses prognostically relevant differences between healthy subjects, athletes, high-altitude residents, and patients with various cardio-respiratory conditions. (Right Heart International NETwork During Exercise in Different Clinical Conditions; NCT03041337).

Risk Factors for Thirty-Day Readmission Following Lumbar Surgery: A Meta-Analysis

OBJECTIVE

Thirty-day readmission is one of the common complications after lumbar surgery. More 30-day readmission increases the total hospitalization, economic burden, and physical pain of patients, delays the progress of postoperative rehabilitation, and even lead to die. Therefore, it is necessary to analyze the risk factors of 30-day readmission following lumbar surgery.

METHODS

We searched for all the clinical trials published from the establishment of the database to May 1, 2022 through the Cochrane Library, Web of Science, Embase, and PubMed. Data including age, American Society of Anesthesiology physical status class, preoperative hematocrit (Hct), diabetes mellitus (DM), current smoker, chronic obstructive pulmonary disease (COPD), length of hospital stay (LHS), operation time, and surgical site infection (SSI) were extracted. We used Review Manager 5.4 for data analysis.

RESULTS

Six studies with 30,989 participants were eligible for this meta-analysis. The analysis revealed that there were statistically significant differences in the age (95% confidence interval [CI]: -3.35-2.90, P < 0.001), preoperative Hct (95% CI: 0.75-1.33, P < 0.001), DM (95% CI: 0.56-0.74, P < 0.001), COPD (95% CI: 0.38-0.58, P < 0.001), operation time (95% CI: -35.54-16.18, P < 0.001), LHS (95% CI: -0.54-0.50, P < 0.001), and SSI (95% CI: 0.02-0.03, P < 0.001) between no readmission and readmission groups. In terms of the American Society of Anesthesiology physical status class and current smoker, there was no significant effect on the 30-day readmission (P = 0.16 and P = 0.35 respectively).

CONCLUSIONS

Age, preoperative Hct, DM, COPD, operation time, LHS, and SSI are the danger factors of 30-day readmission following lumbar surgery.

Sotatercept for the treatment of pulmonary arterial hypertension: PULSAR open-label extension

BACKGROUND

In participants with pulmonary arterial hypertension, 24 weeks of sotatercept resulted in a significantly greater reduction from baseline in pulmonary vascular resistance than placebo. This report characterises the longer-term safety and efficacy of sotatercept in the PULSAR open-label extension. We report cumulative safety, and efficacy at months 18-24, for all participants treated with sotatercept.

METHODS

PULSAR was a phase 2, randomised, double-blind, placebo-controlled study followed by an open-label extension, which evaluated sotatercept on top of background pulmonary arterial hypertension therapy in adults. Participants originally randomised to placebo were re-randomised 1:1 to sotatercept 0.3 or 0.7 mg·kg^-1 (placebo-crossed group); those initially randomised to sotatercept continued the same sotatercept dose (continued-sotatercept group). Safety was evaluated in all participants who received ≥1 dose of sotatercept. The primary efficacy endpoint was change from baseline to months 18-24 in pulmonary vascular resistance. Secondary endpoints included 6-min walk distance and functional class. Two prespecified analyses, placebo-crossed and delayed-start, evaluated efficacy irrespective of dose.

RESULTS

Of 106 participants enrolled in the PULSAR study, 97 continued into the extension period. Serious treatment-emergent adverse events were reported in 32 (30.8%) participants; 10 (9.6%) reported treatment-emergent adverse events leading to study discontinuation. Three (2.9%) participants died, none considered related to study drug. The placebo-crossed group demonstrated significant improvement across primary and secondary endpoints and clinical efficacy was maintained in the continued-sotatercept group.

CONCLUSION

These results support the longer-term safety and durability of clinical benefit of sotatercept for pulmonary arterial hypertension.

Cardiac remodelling in the highest city in the world: effects of altitude and chronic mountain sickness

AIMS

A unique Andean population lives in the highest city of the world (La Rinconada, 5100 m, Peru) and frequently develops a maladaptive syndrome, termed chronic mountain sickness (CMS). Both extreme altitude and CMS are a challenge for the cardiovascular system. This study aims to evaluate cardiac remodelling and pulmonary circulation at rest and during exercise in healthy and CMS highlanders.

METHODS AND RESULTS

Highlanders living permanently at 3800 m (n = 23) and 5100 m (n = 55) with (n = 38) or without CMS (n = 17) were compared with 18 healthy lowlanders. Rest and exercise echocardiography were performed to describe cardiac remodelling, pulmonary artery pressure (PAP), and pulmonary vascular resistance (PVR). Total blood volume (BV) and haemoglobin mass were determined in all people. With the increase in the altitude of residency, the right heart dilated with an impairment in right ventricle systolic function, while the left heart exhibited a progressive concentric remodelling with Grade I diastolic dysfunction but without systolic dysfunction. Those modifications were greater in moderate-severe CMS patients. The mean PAP was higher both at rest and during exercise in healthy highlanders at 5100 m. The moderate-severe CMS subjects had a higher PVR at rest and a larger increase in PAP during exercise. The right heart remodelling was correlated with PAP, total BV, and SpO2.

CONCLUSION

Healthy dwellers at 5100 m exhibit both right heart dilatation and left ventricle concentric remodelling with diastolic dysfunction. Those modifications are even more pronounced in moderate-severe CMS subjects and could represent the limit of the heart's adaptability before progression to heart failure.

A change of heart: mechanisms of cardiac adaptation to acute and chronic hypoxia

Over the last 100 years, high‐altitude researchers have amassed a comprehensive understanding of the global cardiac responses to acute, prolonged and lifelong hypoxia. When lowlanders are exposed to hypoxia, the drop in arterial oxygen content demands an increase in cardiac output, which is facilitated by an elevated heart rate at the same time as ventricular volumes are maintained. As exposure is prolonged, haemoconcentration restores arterial oxygen content, whereas left ventricular filling and stroke volume are lowered as a result of a combination of reduced blood volume and hypoxic pulmonary vasoconstriction. Populations native to high‐altitude, such as the Sherpa in Asia, exhibit unique lifelong or generational adaptations to hypoxia. For example, they have smaller left ventricular volumes compared to lowlanders despite having larger total blood volume. More recent investigations have begun to explore the mechanisms underlying such adaptive responses by combining novel imaging techniques with interventions that manipulate cardiac preload, afterload, and/or contractility. This work has revealed the contributions and interactions of (i) plasma volume constriction; (ii) sympathoexcitation; and (iii) hypoxic pulmonary vasoconstriction with respect to altering cardiac loading, or otherwise preserving or enhancing biventricular systolic and diastolic function even amongst high altitude natives with excessive erythrocytosis. Despite these advances, various areas of investigation remain understudied, including potential sex‐related differences in response to high altitude. Collectively, the available evidence supports the conclusion that the human heart successfully adapts to hypoxia over the short‐ and long‐term, without signs of myocardial dysfunction in healthy humans, except in very rare cases of maladaptation.

3'UTR shortening of HAS2 promotes hyaluronan hyper-synthesis and bioenergetic dysfunction in pulmonary hypertension

Pulmonary hypertension (PH) comprises a diverse group of disorders that share a common pathway of pulmonary vascular remodeling leading to right ventricular failure. Development of anti-remodeling strategies is an emerging frontier in PH therapeutics that requires a greater understanding of the interactions between vascular wall cells and their extracellular matrices. The ubiquitous matrix glycan, hyaluronan (HA), is markedly elevated in lungs from patients and experimental models with PH. Herein, we identified HA synthase-2 (HAS2) in the pulmonary artery smooth muscle cell (PASMC) layer as a predominant locus of HA dysregulation. HA upregulation involves depletion of NUDT21, a master regulator of alternative polyadenylation, resulting in 3'UTR shortening and hyper-expression of HAS2. The ensuing increase of HAS2 and hyper-synthesis of HA promoted bioenergetic dysfunction of PASMC characterized by impaired mitochondrial oxidative capacity and a glycolytic shift. The resulting HA accumulation stimulated pro-remodeling phenotypes such as cell proliferation, migration, apoptosis-resistance, and stimulated pulmonary artery contractility. Transgenic mice, mimicking HAS2 hyper-synthesis in smooth muscle cells, developed spontaneous PH, whereas targeted deletion of HAS2 prevented experimental PH. Pharmacological blockade of HAS2 restored normal bioenergetics in PASMC, ameliorated cell remodeling phenotypes, and reversed experimental PH in vivo. In summary, our results uncover a novel mechanism of HA hyper-synthesis and downstream effects on pulmonary vascular cell metabolism and remodeling.

Sex Differences in Pulmonary Hypertension

Pulmonary hypertension (PH) includes multiple diseases that share as common characteristic an elevated pulmonary artery pressure and right ventricular involvement. Sex differences are observed in practically all causes of PH. The most studied type is pulmonary arterial hypertension (PAH) which presents a gender bias regarding its prevalence, prognosis, and response to treatment. Although this disease is more frequent in women, once affected they present a better prognosis compared to men. Even if estrogens seem to be the key to understand these differences, animal models have shown contradictory results leading to the birth of the estrogen paradox. In this review we will summarize the evidence regarding sex differences in experimental animal models and, very specially, in patients suffering from PAH or PH from other etiologies.

The physiologic basis of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare dyspnea-fatigue syndrome caused by a progressive increase in pulmonary vascular resistance (PVR) and eventual right ventricular (RV) failure. In spite of extensive pulmonary vascular remodeling, lung function in PAH is generally well preserved, with hyperventilation and increased physiologic dead space, but minimal changes in lung mechanics and only mild to moderate hypoxemia and hypocapnia. Hypoxemia is mainly caused by a low mixed venous PO₂ from a decreased cardiac output. Hypocapnia is mainly caused by an increased chemosensitivity. Exercise limitation in PAH is cardiovascular rather than ventilatory or muscular. The extent of pulmonary vascular disease in PAH is defined by multipoint pulmonary vascular pressure-flow relationships with a correction for hematocrit. Pulsatile pulmonary vascular pressure-flow relationships in PAH allow for the assessment of RV hydraulic load. This analysis is possible either in the frequency-domain or in the time-domain. The RV in PAH adapts to increased afterload by an increased contractility to preserve its coupling to the pulmonary circulation. When this homeometric mechanism is exhausted, the RV dilates to preserve flow output by an additional heterometric mechanism. Right heart failure is then diagnosed by imaging of increased right heart dimensions and clinical systemic congestion signs and symptoms. The coupling of the RV to the pulmonary circulation is assessed by the ratio of end-systolic to arterial elastances, but these measurements are difficult. Simplified estimates of RV-PA coupling can be obtained by magnetic resonance or echocardiographic imaging of ejection fraction.

The influence of hemoconcentration on hypoxic pulmonary vasoconstriction in acute, prolonged, and lifelong hypoxemia

Hemoconcentration can influence hypoxic pulmonary vasoconstriction (HPV) via increased frictional force and vasoactive signaling from erythrocytes, but whether the balance of these mechanism is modified by the duration of hypoxia remains to be determined. We performed three sequential studies: 1) at sea level, in normoxia and isocapnic hypoxia with and without isovolumic hemodilution (n = 10, aged 29 ± 7 yr); 2) at altitude (6 ± 2 days acclimatization at 5,050 m), before and during hypervolumic hemodilution (n = 11, aged 27 ± 5 yr) with room air and additional hypoxia [fraction of inspired oxygen ([Formula: see text])= 0.15]; and 3) at altitude (4,340 m) in Andean high-altitude natives with excessive erythrocytosis (EE; n = 6, aged 39 ± 17 yr), before and during isovolumic hemodilution with room air and hyperoxia (end-tidal Po₂ = 100 mmHg). At sea level, hemodilution mildly increased pulmonary artery systolic pressure (PASP; +1.6 ± 1.5 mmHg, P = 0.01) and pulmonary vascular resistance (PVR; +0.7 ± 0.8 wu, P = 0.04). In contrast, after acclimation to 5,050 m, hemodilution did not significantly alter PASP (22.7 ± 5.2 vs. 24.5 ± 5.2 mmHg, P = 0.14) or PVR (2.2 ± 0.9 vs. 2.3 ± 1.2 wu, P = 0.77), although both remained sensitive to additional acute hypoxia. In Andeans with EE at 4,340 m, hemodilution lowered PVR in room air (2.9 ± 0.9 vs. 2.3 ± 0.8 wu, P = 0.03), but PASP remained unchanged (31.3 ± 6.7 vs. 30.9 ± 6.9 mmHg, P = 0.80) due to an increase in cardiac output. Collectively, our series of studies reveal that HPV is modified by the duration of exposure and the prevailing hematocrit level. In application, these findings emphasize the importance of accounting for hematocrit and duration of exposure when interpreting the pulmonary vascular responses to hypoxemia.NEW & NOTEWORTHY Red blood cell concentration influences the pulmonary vasculature via direct frictional force and vasoactive signaling, but whether the magnitude of the response is modified with duration of exposure is not known. By assessing the pulmonary vascular response to hemodilution in acute normobaric and prolonged hypobaric hypoxia in lowlanders and lifelong hypobaric hypoxemia in Andean natives, we demonstrated that a reduction in red cell concentration augments the vasoconstrictive effects of hypoxia in lowlanders. In high-altitude natives, hemodilution lowered pulmonary vascular resistance, but a compensatory increase in cardiac output following hemodilution rendered PASP unchanged.

GLOBAL REACH 2018: Iron infusion at high altitude reduces hypoxic pulmonary vasoconstriction equally in both lowlanders and healthy Andean highlanders

BACKGROUND

Increasing iron bioavailability attenuates hypoxic pulmonary vasoconstriction in both lowlanders and Sherpa at high altitude. In contrast, the pulmonary vasculature of Andeans suffering with chronic mountain sickness is resistant to iron administration. While pulmonary vascular remodeling and hypertension are characteristic features of chronic mountain sickness, the impact of iron administration in healthy Andeans has not been investigated. If the interplay between iron status and pulmonary vascular tone in healthy Andeans remains intact, this could provide valuable clinical insight into the role of iron regulation at high altitude.

RESEARCH QUESTION

Is the pulmonary vasculature in healthy Andeans responsive to iron infusion?

STUDY DESIGN AND METHODS

In a double-blinded, block-randomized design, 24 healthy high-altitude Andeans and 22 partially acclimatized lowlanders at 4300 m (Cerro de Pasco, Peru), received an i.v. infusion of either iron [iron (III)-hydroxide sucrose; 200mg] or saline. Markers of iron status were collected at baseline and 4 hours after infusion. Echocardiography was performed during room-air breathing (P_IO₂=∼96 mmHg) and during exaggerated hypoxia (P_IO₂=∼73 mmHg), at baseline, and at 2 and 4 hours following the infusion.

RESULTS

Iron infusion reduced pulmonary artery systolic pressure (PASP) by ∼2.5 mmHg in room air (main effect P<0.001), and by ∼7 mmHg during exaggerated hypoxia (main effect P<0.001) in both lowlanders and healthy Andean highlanders. There was no change in PASP following the infusion of saline. Iron metrics were comparable between groups, except for serum ferritin, which was 1.8-fold higher at baseline in the Andeans when compared to lowlanders [95% confidence interval (CI) 74-121 ng/ml vs. 37-70 ng/ml, respectively; P=0.003].

INTERPRETATION

The pulmonary vasculature of healthy Andeans and lowlanders remains sensitive to iron infusion and this response seems to differ from the pathological characteristics of chronic mountain sickness.

The different facets of sickle cell disease-related pulmonary hypertension

PURPOSE OF REVIEW

Sickle cell disease (SCD), one of the most common genetic diseases in the world, is characterized by repeated episodes of hemolysis and vaso-occlusion. Hemolytic anemia is a risk factor for the development of pulmonary hypertension, and currently SCD-related pulmonary hypertension is classified as World Health Organization group 5 pulmonary hypertension. Patients with SCD-related pulmonary hypertension have unique hemodynamics, multiple comorbidities, and distinct phenotypes that may contribute to the development of pulmonary hypertension.

RECENT FINDINGS

SCD-related pulmonary hypertension is defined as a mean pulmonary artery pressure >20 mmHg, a pulmonary artery occlusion pressure ≤15 mmHg and relatively low pulmonary vascular resistance (>2 Wood units) rather than the traditional definition of ≥3 Wood units, an important distinction due to a baseline high-cardiac output state in the setting of chronic anemia and low vascular resistance. Diastolic dysfunction is frequently identified in this patient population and right heart catheterization is essential to determine if combined pre- and postcapillary pulmonary hypertension is present. Thromboembolism is common among patients with SCD, and screening for chronic thromboembolic pulmonary hypertension is essential. Data regarding advanced therapies are limited. Primary treatment options include targeting correction of their primary hemoglobinopathy as well as aggressive management of underlying comorbid conditions.

SUMMARY

SCD-related pulmonary hypertension is common among patients with SCD and is associated with increased mortality. A high index of suspicion is warranted during evaluation to identify all potential factors that may be contributing to disease.

Global REACH 2018: Volume regulation in high-altitude Andeans with and without chronic mountain sickness

The high-altitude maladaptation syndrome known as chronic mountain sickness (CMS) is characterized by polycythemia and is associated with proteinuria despite unaltered glomerular filtration rate. However, it remains unclear if indigenous highlanders with CMS have altered volume regulatory hormones. We assessed N-terminal pro-B-type natriuretic peptide (NT pro-BNP), plasma aldosterone concentration, plasma renin activity, kidney function (urinary microalbumin, glomerular filtration rate), blood volume, and estimated pulmonary artery systolic pressure (ePASP), in Andean males without (n=14; age=39±11) and with (n=10; age=40±12) CMS at 4330 meters (Cerro de Pasco, Peru). Plasma renin activity (non-CMS: 15.8±7.9 vs. CMS: 8.7±5.4 ng/ml; p=0.025) and plasma aldosterone concentration (non-CMS: 77.5±35.5 vs. CMS: 54.2±28.9 pg/ml; p=0.018) were lower in highlanders with CMS compared to non-CMS, while NT pro-BNP was not different between groups (non-CMS: 1394.9±214.3 vs. CMS: 1451.1±327.8 pg/ml; p=0.15). Highlanders had similar total blood volume (non-CMS: 90±15 vs. CMS: 103±18 ml • kg^-1; p=0.071), but Andeans with CMS had greater total red blood cell volume (non-CMS: 46±10 vs. CMS 66±14 ml • kg^-1; p<0.01) and smaller plasma volume (non-CMS 43±7 vs. CMS 35±5 ml • kg^-1; p=0.03) compared to non-CMS. There were no differences in ePASP between groups (non-CMS 32±9 vs. CMS 31±8 mmHg; p=0.6). A negative correlation was found between plasma renin activity and glomerular filtration rate in both groups (group: r=-0.66; p<0.01; non-CMS: r=-0.60; p=0.022; CMS: r=-0.63; p=0.049). A smaller plasma volume in Andeans with CMS may indicate an additional CMS maladaptation to high-altitude, causing potentially greater polycythemia and clinical symptoms.

Influence of iron manipulation on hypoxic pulmonary vasoconstriction and pulmonary reactivity during ascent and acclimatization to 5050 m

KEY POINTS

Iron acts as a cofactor in the stabilization of the hypoxic-inducible factor family, and plays an influential role in the modulation of hypoxic pulmonary vasoconstriction. It is uncertain whether iron regulation is altered in lowlanders during either (1) ascent to high altitude, or (2) following partial acclimatization, when compared to high-altitude adapted Sherpa. During ascent to 5050 m, the rise in pulmonary artery systolic pressure (PASP) was blunted in Sherpa, compared to lowlanders; however, upon arrival to 5050 m, PASP levels were comparable in both groups, but the reduction in iron bioavailability was more prevalent in lowlanders compared to Sherpa. Following partial acclimatization to 5050 m, there were differential influences of iron status manipulation (via iron infusion or chelation) at rest and during exercise between lowlanders and Sherpa on the pulmonary vasculature.

ABSTRACT

To examine the adaptational role of iron bioavailability on the pulmonary vascular responses to acute and chronic hypobaric hypoxia, the haematological and cardiopulmonary profile of lowlanders and Sherpa were determined during: (1) a 9-day ascent to 5050 m (20 lowlanders; 12 Sherpa), and (2) following partial acclimatization (11 ± 4 days) to 5050 m (18 lowlanders; 20 Sherpa), where both groups received an i.v. infusion of either iron (iron (iii)-hydroxide sucrose) or an iron chelator (desferrioxamine). During ascent, there were reductions in iron status in both lowlanders and Sherpa; however, Sherpa appeared to demonstrate a more efficient capacity to mobilize stored iron, compared to lowlanders, when expressed as a Δhepcidin per unit change in either body iron or the soluble transferrin receptor index, between 3400-5050 m (P = 0.016 and P = 0.029, respectively). The rise in pulmonary artery systolic pressure (PASP) was blunted in Sherpa, compared to lowlanders during ascent; however, PASP was comparable in both groups upon arrival to 5050 m. Following partial acclimatization, despite Sherpa demonstrating a blunted hypoxic ventilatory response and greater resting hypoxaemia, they had similar hypoxic pulmonary vasoconstriction when compared to lowlanders at rest. Iron-infusion attenuated PASP in both groups at rest (P = 0.005), while chelation did not exaggerate PASP in either group at rest or during exaggerated hypoxaemia ( P I O 2  = 67 mmHg). During exercise at 25% peak wattage, PASP was only consistently elevated in Sherpa, which persisted following both iron infusion or chelation. These findings provide new evidence on the complex interplay of iron regulation on pulmonary vascular regulation during acclimatization and adaptation to high altitude.

Residence at moderately high altitude and its relationship with WHO Group 1 pulmonary arterial hypertension symptom severity and clinical characteristics: the Pulmonary Hypertension Association Registry

BACKGROUND

WHO Group 1 pulmonary arterial hypertension is a progressive and potentially fatal disease. Individuals living at higher altitude are exposed to lower barometric pressure and hypobaric hypoxemia. This may result in pulmonary vasoconstriction and contribute to disease progression. We sought to examine the relationship between living at moderately high altitude and pulmonary arterial hypertension characteristics.

METHODS

Forty-two US centers participating in the Pulmonary Hypertension Association Registry enrolled patients who met the definition of WHO Group 1 pulmonary arterial hypertension. We utilized baseline data and patient questionnaire responses. Patients were divided into two groups: moderately high altitude residence (home ≥4000 ft) and low altitude residence (home <4000 ft) based on zip-code. Clinical characteristics, hemodynamic data, patient demographics, and patient reported quality of life metrics were compared.

RESULTS

Controlling for potential confounders (age, sex at birth, body mass index, supplemental oxygen use, race, 100-day cigarette use, alcohol use, and pulmonary arterial hypertension medication use), subjects residing at moderately high altitude had a 6-min walk distance 32 m greater than those at low altitude, despite having a pulmonary vascular resistance that was 2.2 Wood units higher. Additionally, those residing at moderately high altitude had 3.7 times greater odds of using supplemental oxygen.

CONCLUSION

Patients with pulmonary arterial hypertension who live at moderately high altitude have a higher pulmonary vascular resistance and are more likely to need supplemental oxygen. Despite these findings, moderately high altitude Pulmonary Hypertension Association Registry patients have better functional tolerance as measured by 6-min walk distance. It is possible that a "high-altitude phenotype" of pulmonary arterial hypertension may exist. These findings warrant further study.

Sex, Gender, and Sex Hormones in Pulmonary Hypertension and Right Ventricular Failure

Pulmonary hypertension (PH) encompasses a syndrome of diseases that are characterized by elevated pulmonary artery pressure and pulmonary vascular remodeling and that frequently lead to right ventricular (RV) failure and death. Several types of PH exhibit sexually dimorphic features in disease penetrance, presentation, and progression. Most sexually dimorphic features in PH have been described in pulmonary arterial hypertension (PAH), a devastating and progressive pulmonary vasculopathy with a 3-year survival rate <60%. While patient registries show that women are more susceptible to development of PAH, female PAH patients display better RV function and increased survival compared to their male counterparts, a phenomenon referred to as the "estrogen paradox" or "estrogen puzzle" of PAH. Recent advances in the field have demonstrated that multiple sex hormones, receptors, and metabolites play a role in the estrogen puzzle and that the effects of hormone signaling may be time and compartment specific. While the underlying physiological mechanisms are complex, unraveling the estrogen puzzle may reveal novel therapeutic strategies to treat and reverse the effects of PAH/PH. In this article, we (i) review PH classification and pathophysiology; (ii) discuss sex/gender differences observed in patients and animal models; (iii) review sex hormone synthesis and metabolism; (iv) review in detail the scientific literature of sex hormone signaling in PAH/PH, particularly estrogen-, testosterone-, progesterone-, and dehydroepiandrosterone (DHEA)-mediated effects in the pulmonary vasculature and RV; (v) discuss hormone-independent variables contributing to sexually dimorphic disease presentation; and (vi) identify knowledge gaps and pathways forward. © 2020 American Physiological Society. Compr Physiol 10:125-170, 2020.

Clinical phenotypes and outcomes of precapillary pulmonary hypertension of sickle cell disease

Rationale

Precapillary pulmonary hypertension (PH) is a devastating complication of sickle cell disease (SCD). Little is known about the influence of the SCD genotype on PH characteristics.

Objectives

To describe clinical phenotypes and outcomes of precapillary PH due to SCD according to disease genotype.

Methods

A nationwide multicentre retrospective study including all patients with SCD-related precapillary PH from the French PH Registry was conducted. Clinical characteristics and outcomes according to SCD genotype were analysed.

Results

58 consecutive SCD patients with precapillary PH were identified, of whom 41 had homozygous for haemoglobin S (SS) SCD, three had S-β0 thalassaemia (S-β0 thal) and 14 had haemoglobin SC disease (SC). Compared to SC patients, SS/S-β0 thal patients were characterised by lower 6-min walk distance (p=0.01) and lower pulmonary vascular resistance (p=0.04). Mismatched segmental perfusion defects on lung scintigraphy were detected in 85% of SC patients and 9% of SS/S-β0 thal patients, respectively, and 50% of SS/S-β0 thal patients had heterogeneous lung perfusion without segmental defects. After PH diagnosis, 31 patients (53%) received medical therapies approved for pulmonary arterial hypertension, and chronic red blood cell exchange was initiated in 23 patients (40%). Four patients were managed for chronic thromboembolic PH by pulmonary endarterectomy (n=1) or balloon pulmonary angioplasty (n=3). Overall survival was 91%, 80% and 60% at 1, 3 and 5 years, respectively, without influence of genotype on prognosis.

Conclusions

Patients with precapillary PH related to SCD have a poor prognosis. Thrombotic lesions appear as a major component of PH related to SCD, more frequently in SC patients.

Pulmonary arterial pressure at rest and during exercise in chronic mountain sickness: a meta-analysis

Up to 10% of the more than 140 million high-altitude dwellers worldwide suffer from chronic mountain sickness (CMS). Patients suffering from this debilitating problem often display increased pulmonary arterial pressure (PAP), which may contribute to exercise intolerance and right heart failure. However, there is little information on the usual PAP in these patients.We systematically reviewed and meta-analysed all data published in English or Spanish until June 2018 on echocardiographic estimations of PAP at rest and during mild exercise in CMS patients.Nine studies comprising 287 participants fulfilled the inclusion criteria. At rest, the point estimate from meta-analysis of the mean systolic PAP was 27.9 mmHg (95% CI 26.3-29.6 mmHg). These values are 11% (+2.7 mmHg) higher than those previously meta-analysed in apparently healthy high-altitude dwellers. During mild exercise (50 W) the difference in mean systolic PAP between patients and high-altitude dwellers was markedly more accentuated (48.3 versus 36.3 mmHg) than at rest.These findings indicate that in patients with CMS PAP is moderately increased at rest, but markedly increased during mild exercise, which will be common with activities of daily living.

Pulmonary Vascular Distensibility and Early Pulmonary Vascular Remodeling in Pulmonary Hypertension

BACKGROUND

Exercise stress testing of the pulmonary circulation may uncover decreased pulmonary vascular (PV) distensibility as a cause of impaired aerobic exercise capacity and right ventricular (RV)-pulmonary arterial (PA) uncoupling. As such, it may help in the differential diagnosis of unexplained dyspnea, including pulmonary hypertension (PH) and/or heart failure with preserved ejection fraction (HFpEF). We investigated rest and exercise invasive pulmonary hemodynamics, ventilation, and gas exchange in patients with unexplained dyspnea, including 44 patients with HFpEF (of whom 20 had a normal pulmonary vascular resistance [PVR] during exercise [ie, passive HFpEF] and 24 had a higher than normal exercise PVR), 22 patients with exercise PH, 19 patients with pulmonary arterial hypertension (PAH), and 24 age- and sex-matched normal control subjects.

METHODS

A PV distensibility coefficient α (%/mm Hg) was determined from multipoint PV pressure-flow plots. RV-PA coupling was quantified from the analysis of RV pressure curves to determine ratios of end-systolic to arterial elastances (Ees/Ea). Aerobic exercise capacity was estimated by peak oxygen consumption.

RESULTS

The α coefficient decreased from 1.35 ± 0.58%/mm Hg in control subjects and 1.1 ± 0.48%/mm Hg in patients with passive HFpEF to 0.62 ± 0.32%/mm Hg in exercise PH, 0.54 ± 0.27%/mm Hg in HFpEF with high exercise PVR, and 0.18 ± 0.16%/mm Hg in PAH. On multivariate analysis, PV distensibility was associated with decreased Ees/Ea and maximal volume of oxygen consumed.

CONCLUSIONS

PV distensibility is an early and sensitive hemodynamic marker of PV disease that is associated with RV-PA uncoupling and decreased aerobic exercise capacity.

Thin Air, Thick Vessels: Historical and Current Perspectives on Hypoxic Pulmonary Hypertension

The association between pulmonary hypertension (PH) and hypoxia is well-established, with two key mechanistic processes, hypoxic pulmonary vasoconstriction and hypoxia-induced vascular remodeling, driving changes in pulmonary arterial pressure. In contrast to other forms of pulmonary hypertension, the vascular changes induced by hypoxia are reversible, both in humans returning to sea-level from high altitude and in animal models. This raises the intriguing possibility that the molecular drivers of these hypoxic processes could be targeted to modify pulmonary vascular remodeling in other contexts. In this review, we outline the history of research into PH and hypoxia, before discussing recent advances in our understanding of this relationship at the molecular level, focussing on the role of the oxygen-sensing transcription factors, hypoxia inducible factors (HIFs). Emerging links between HIF and vascular remodeling highlight the potential utility in inhibiting this pathway in pulmonary hypertension and raise possible risks of activating this pathway using HIF-stabilizing medications.