Vascular Resistance Responses Research Articles

Acute vasoreactivity testing for severe pulmonary hypertension associated with lung disease

Abstract Background Pulmonary hypertension results in clinical deterioration and increases mortality risk in patients with lung disease (LD), including chronic obstructive pulmonary disease, interstitial lung disease and combined pulmonary fibrosis and emphysema. Though acute vasoreactivity testing predicts long term-survival of patients with pulmonary arterial hypertension (PAH), its clinical impact for patients with pulmonary hypertension associated with LD (LD-PH) remains unknown. Purpose The purpose of this study is to clarify the clinical impact of acute vasoreactivity testing using inhaled nitric oxide for severe LD-PH. Methods We retrospectively reviewed 65 consecutive patients with LD-PH between January 2014 and December 2022; 48 patients (73 [68–78] years; males, 81%; median follow-up period 23 [7–35] months) with severe pulmonary hypertension who underwent acute vasoreactivity testing were included. We divided the patients based on a median pulmonary vascular resistance (PVR) response (−15%) in acute vasoreactivity testing into the high-responder (PVR response ≦−15%) and the low-responder (PVR response >−15%) groups. Results Acute vasoreactivity testing significantly decreased mean pulmonary arterial pressure (mPAP) (from 41 [34–48] to 36 [31–40] mmHg, P<0.01) and PVR (from 10.7 [8.3–13.8] to 8.9 [6.6–11.4] Wood units, P<0.01). The high-responder group had better long-term survival than the low-responder group (P = 0.03). Univariate Cox regression analysis showed that the prognostic factors for better survival included younger age, high-responder to acute vasoreactivity testing, and PAH-specific therapy (P <0.01, 0.04, 0.03, respectively). There were correlations between the PVR response at acute vasoreactivity testing and improvement in mPAP (R=0.40, P=0.03) or PVR (R = 0.47, P <0.01) with PAH-specific therapy. Conclusions PVR response at acute vasoreactivity testing was associated with better long-term survival and haemodynamic improvement with PAH-specific therapy. Acute vasoreactivity testing may be useful to predict the responders to PAH-specific therapy and long-term survival in patients with severe LD-PH.

#536 Dedicated patient optimization program delivers effective complex intervention improving the lives of vulnerable HD patients

Abstract Background and Aims Hemodialysis (HD) delivery is failing many patients due to a of lack of available evidence/dialysis-based interventions (previously only studied as single interventions in isolation) to improve outcomes; and the industrialization of institutional-based HD imposing a ‘one size fits all’ approach. To respond to the needs of the most vulnerable patients we have instituted a patient optimization program (POP) to support our Renal Program, fully leveraging our research level assessment tools to provide an individualized appreciation of challenges before delivering an equally individualized complex intervention. The aim was to improve subjective experience [symptoms/health related quality of life (HRQoL) measures] and objective evidence of HD related harm. Method Patients who had suboptimal tolerability to HD were identified and referred by the clinical team (after best efforts to address concern as part of standard care). To understand the patients’ individual challenges, a series of physiological, hemodynamic, and HRQoL assessments were completed. Based on these findings, a series of complex foundational (common to all patients treated) and patient specific interventions were applied, and impact rigorously evaluated. HRQoL/symptoms were measured using the dynamic patient reported outcome measurement tool LEVIL [2-4 weeks leading up to the program (baseline) and continually thereafter]. Comprehensive physiological assessment period was two weeks in length (six HD treatments) and included continuous beat to beat hemodynamic monitoring, intradialytic echocardiography (assess myocardial stunning) and objective volume assessment using ultrasound and bioimpedance. The first session was delivered mirroring routine prescription (establish primary response), subsequent treatments were delivered implementing a variety of foundational, patient/disease specific interventions in a staged manner. Results To date 13 patients have completed the program, referred for a variety of reasons [refractory hypotension (5/13), intradialytic hypotension (2/13) and poor HRQoL [symptoms—cramping, headache, pruritus, insomnia (8/13)]. Complexes of challenges were present in 9/13. All patients had multiple components of dialysis altered. POP was associated with a marked improvement in a range of subjective and objective outcomes. Subjectively, HRQoL improved by 10% [composite LEVIL scores 69.5 ± 15.5 at baseline, 76.5 ± 17 after POP participation (p 0.03)], energy by 18% (64.7 ± 16.2, 76.5 ± 6.4, p 0.01), general wellbeing by 11% (76.5 ± 6.6, 85.2 ± 4.2, p 0.02), and post-dialysis recovery improved from 13.3 ± 16.1 hours to only 2 ± 1.9 hours (p 0.02). Objectively, intradialytic weight gain decreased by 36% (2333.3 ± 1151.8 ml at baseline to 1483.3 ± 591.3 ml, p 0.03), systolic blood pressure improved by 12% [94.9 ± 28.5 mmHg at baseline to 106.2 ± 30 mmHg post optimization p < 0.0001 (despite midodrine being discontinued in 8/13 patients previously dependent on it)]. Tolerability of HD improved (cardiac output 6.4 ± 0.1, 6.5 ± 1, p 0.002 and intradialytic systemic vascular resistance response 15 ± 23.6% at baseline to 48.7 ± 53%, p < 0.0001). Improvement in hemodynamic tolerability led to a reduction in HD induced myocardial stunning larger than reported with any previously applied single intervention; regional wall motion abnormality fell from 5.6 ± 2.4 at baseline (severe stunning) to only 1.2 ± 1.3 (p 0.02) over the two-week program. 2/13 patients who had previously been declined transplantation were accepted and need to repatriate from satellite facilities to in-centre was avoided. Conclusion For the first time, we have created an opportunity for the most challenging patients who have failed conventional best efforts. We have successfully demonstrated the impact of delivering a complex intervention (with a degree of treatment personalization) targeting physiological failure in the most vulnerable HD patients. POP improved HRQoL (principal impact measure), hemodynamic stability and treatment tolerability. Having demonstrated the effectiveness of this approach, we now focus on solutions to up-scale this success.

Solitary Functioning Kidneys Attenuate Renal Hemodynamics Responses to Angiotensin II in Male But Not in Female Rats.

People with solitary functioning kidneys (SFK) are prone to renal failure with time. Accordingly, local renin angiotensin system (RAS) and renal functions in subjects with SFK may act differently compared to normal condition. This study was designed to determine the renal hemodynamics responses to angiotensin II (Ang. II) in SFK male and female rats. Fifty to sixty-day-old male and female Wistar rats were subjected to unilateral renal artery obstruction, and 28 days later basal renal hemodynamic responses to Ang. II were examined in SFK groups compared to sham groups. The findings indicated lower renal vascular resistance (RVR) and renal blood flow (RBF) responses to Ang. II in male SFK compared to sham group. Such observation was not seen in female animals. An increase in renal metabolism due to hyperfunction, especially in SFK male rats, may cause a decrease in RVR. Moreover, the lower RBF response to Ang. II may be related to alteration to Ang. II receptors in the remnant kidneys in SFK rats.

Hormonal Control of Blood Viscosity.

The hemodynamic milieu differs throughout the vascular tree because of varying vascular geometry and blood velocities.Accordingly, the risk of turbulence, which is dictated by the Reynolds and Dean numbers, also varies. Relatively high blood viscosity is needed to prevent turbulence in the left ventricle and aorta, where high-velocity blood changes direction several times. Low blood viscosity is needed in the capillaries, where erythrocytes pass through vessels with a diameter smaller than their own. In addition, higher blood viscosity is necessary when the cardiac output and peak blood velocity increase as a part of a sympathetic response or anemia, which occurs following significant hemorrhage. Blood viscosity, as reflected in systemic vascular resistance and vascular wall shear stress, is sensed, respectively, by cardiomyocyte stretching in the left ventricle and mechanoreceptors for wall shear stress in the carotid sinus.By controlling blood volume and red blood cell mass, the renin-aldosterone-angiotensin system and the systemic vascular resistance response control the hematocrit, the strongest intrinsic determinant of blood viscosity. These responses provide gross control of blood viscosity. Fine-tuning of blood viscosity in transient conditions is provided by hormonal control of erythrocyte deformability. The short half-life of some of these hormones limits their activity to specific vascular beds. Hormones that modulate blood viscosity include erythropoietin, angiotensin II, brain natriuretic factor, epinephrine, prostacyclin E2, antidiuretic hormone, and nitric oxide.

Calcineurin inhibition, cardiovascular consequences, vascular resistance, and potential responses.

To place the consequences of calcineurin inhibition in a cardiovascular context. Literature review coupled with personal encounters. Calcineurin is a calcium-binding and calmodulin-binding protein that is conserved across evolution from yeast to mammals. The enzyme functions as a calcium-dependent, calmodulin-stimulated protein phosphatase. Its role in regulating physiology has largely been elucidated by observing calcineurin inhibition. Calcineurin inhibition transformed organ transplantation from an experiment into a therapy and made much of general immunotherapy possible. The function of this phosphatase and how its inhibition leads to toxicity concern us to this date. Initial research from patients and animal models implicated a panoply of factors contributing to hypertension and vasculopathy. Subsequently, the role of calcineurin in regulating the effective fluid volume, sodium reabsorption, and potassium and hydrogen ion excretion was elucidated by investigating calcineurin inhibition. Understanding the regulatory effects of calcineurin on endothelial and vascular smooth muscle cell function has also made substantial progress. However, precisely how the increase in systemic vascular resistance arises requires further mechanistic research. Calcineurin inhibition continues to save lives; however, options to counteract the negative effects of calcineurin inhibition should be vigorously pursued.

The ventilatory component of the muscle metaboreflex is overstimulated in transthyretin cardiac amyloidosis patients with poor aerobic capacity.

Background: The exercise pressor reflex, i.e., metabo- and mechano-reflex, partially regulates the control of ventilation and cardiovascular function during exercise. Abnormal exercise pressor reflex response has been associated with exaggerated ventilatory drive, sympathovagal imbalance and exercise limitation in chronic heart failure patients. Whether metaboreflex is over-activated and participate to poor aerobic capacity in patients with hereditary transthyretin cardiac amyloidosis (CA-TTR) is unknown. Methods: Twenty-two CA-TTR patients (aged 76 ± 7, 68% male) with the V122I (p.Val142Ile) transthyretin underwent a thorough evaluation including heart rate variability metrics, electrochemical skin conductance (ESC), physical function cardiopulmonary exercise testing, and muscle metaboreflex assessment. Eleven control subjects were chosen for muscle metaboreflex assessment. Results: Age-matched controls (n = 11) and CA-TTR patients (n = 22) had similar metaboreflex sensitivity for heart rate, stroke volume, cardiac index and mean systemic arterial pressure. Compared with age-matched controls, metaboreflex sensitivity for systemic vascular resistance (-18.64% ± 6.91% vs 3.14% ± 23.35%) and minute-ventilation responses (-9.65% ± 14.83% vs 11.84% ± 23.1%) was markedly increased in CA-TTR patients. Values of ESC displayed positive correlations with stroke volume (r = 0.53, p = 0.011) and cardiac index (r = 0.51, p = 0.015) components of metaboreflex sensitivity, an inverse correlation with systemic vascular resistance (r = -0.55, p = 0.008) and a trend with mean arterial (r = -0.42, p = 0.052) components of metaboreflex sensitivity. Peak aerobic capacity (peak VO2%) displayed an inverse correlation with the ventilation component of metaboreflex sensitivity (r = -0.62, p = 0.015). Conclusion: Consistent with the "muscle hypothesis" in heart failure, it is proposed that deterioration of skeletal muscle function in hereditary CA-TTR patients may activate muscle metaboreflex, leading to an increase in ventilation and sensation of breathlessness, the perception of fatigue, and overall sympathetic activation.

Differential central integration of left versus right baroreceptor afferent input in spontaneously hypertensive rats.

The blood pressure (BP) regulatory impact of the arterial baroreflex has been well established in health and disease. Under normotensive conditions, we have previously demonstrated functional differences in the central processing of the left versus right aortic baroreceptor afferent input. However, it is unknown if lateralization in aortic baroreflex function remains evident during hypertension. We therefore, investigated the effects of laterality on the expression of baroreflex-driven cardiovascular reflexes in a genetic model of essential hypertension, the spontaneously hypertensive rat (SHR). Anesthetized male SHRs (total n = 9) were instrumented for left, right, and bilateral aortic depressor nerve (ADN) stimulation (1-40 Hz, 0.2 ms, and 0.4 mA for 20 s) and measurement of mean arterial pressure (MAP), heart rate (HR), mesenteric vascular resistance (MVR), and femoral vascular resistance (FVR). Left right, and bilateral ADN stimulation evoked frequency-dependent decreases in MAP, HR, MVR, and FVR. Left and bilateral ADN stimulation evoked greater reflex reductions in MAP, HR, MVR, and FVR compared with right-sided stimulation. Reflex bradycardia to bilateral stimulation was larger relative to both left-sided and right-sided stimulation. Reflex depressor and vascular resistance responses to bilateral stimulation mimicked those of the left-sided stimulation. These data indicate a left-side dominance in the central integration of aortic baroreceptor afferent input. Furthermore, reflex summation due to bilateral stimulation is only evident on the reflex bradycardic response, and does not drive further reductions in BP, suggesting that reflex depressor responses in the SHRs are primarily driven by changes in vascular resistance. Together, these results indicate that lateralization in aortic baroreflex function is not only evident under normotensive conditions but also extends to hypertensive conditions.

S-18-1: THE USUAL HEMODYNAMIC MECHANISM CAUSING SALT-INDUCED HYPERTENSION: ABNORMALLY INCREASED CARDIAC OUTPUT OR VASCULAR RESISTANCE?

Two competing theories have been proposed for the hemodynamic mechanism that usually mediates salt sensitivity and the initiation of salt-induced hypertension. The historical natriuretic dysfunction theory holds that impaired renal excretion of sodium initiates hypertension by causing abnormally large increases in cardiac output secondary to abnormally large increases in salt and water retention. In contrast, the contemporary vasodysfunction theory holds that abnormal vascular resistance responses to salt, not abnormal increases in cardiac output, mediate salt sensitivity and the initiation of salt-induced hypertension. Primary aldosteronism is one of the most common causes of salt sensitivity and salt-dependent hypertension. This presentation will discuss new studies showing that hyperaldosteronism promotes salt sensitivity and initiation of salt-dependent hypertension by amplifying salt-induced increases in systemic vascular resistance, not cardiac output. The findings are consistent with the results of other studies showing that an abnormal vascular resistance response to salt (vasodysfunction) is also usually responsible for the initiation of salt-induced hypertension in humans and animals without hyperaldosteronism. The vasodysfunction framework for the pathogenesis of salt sensitivity and salt-induced hypertension has implications for: 1) understanding how various genetic and non-genetic factors influence BP responses to high salt diets, and 2) development of new methods for preventing and treating salt-dependent hypertension.

Glomerular filtration rate reserve is reduced during mild passive heat stress in healthy young adults.

We tested the hypothesis that, compared with normothermia, the increase in glomerular filtration rate (GFR) after an oral protein load (defined as the GFR reserve) is attenuated during moderate passive heat stress in young healthy adults. Sixteen participants (5 women; 26 ± 2 yr) completed two experimental visits, heat stress or a normothermic time-control, assigned in a block-randomized crossover design. During the heat stress trial, core temperature was increased by 0.6°C in the first hour before commencing a 2-min cold pressor test (CPT) to assess renal vasoconstrictor responses. One-hour post-CPT, subjects ingested a whey protein shake (1.2 g of protein/kg body wt), and measurements were taken pre-, 75, and 150 min postprotein. Segmental artery vascular resistance was calculated as the quotient of Doppler ultrasound-derived segmental artery blood velocity and mean arterial pressure and provided an estimate of renal vascular tone. GFR was estimated from creatinine clearance. The increase in segmental artery vascular resistance during the CPT was attenuated during heat stress (end CPT: 5.6 ± 0.9 vs. 4.7 ± 1.1 mmHg/cm/s, P = 0.024). However, the reduction in segmental artery vascular resistance in response to an oral protein load did not differ between heat stress (at 150 min: 1.9 ± 0.4 mmHg/cm/s) and normothermia (at 150 min: 1.8 ± 0.5 mmHg/cm/s; P = 0.979). The peak increase in creatinine clearance postprotein, independent of time, was attenuated during heat stress (+26 ± 19 vs. +16 ± 20 mL/min, P = 0.013, n = 13). GFR reserve is diminished by mild passive heat stress. Moreover, renal vasoconstrictor responses are attenuated by mild passive heat stress, but renal vasodilator responses are maintained.

Maladaptation of renal hemodynamics contributes to kidney dysfunction resulting from thoracic spinal cord injury in mice.

Renal dysfunction is a hallmark of spinal cord injury (SCI). Several SCI sequalae are implicated; however, the exact pathogenic mechanism of renal dysfunction is unclear. Herein, we found that T3 (T3Tx) or T10 (T10Tx) complete thoracic spinal cord transection induced hypotension, bradycardia, and hypothermia immediately after injury. T3Tx-induced hypotension but not bradycardia or hypothermia slowly recovered to levels in T10Tx SCI and uninjured mice ∼16 h after injury as determined by continuous radiotelemetry monitoring. Both types of thoracic SCI led to a marked decrease in albuminuria and proteinuria in all phases of SCI, whereas the kidney injury marker neutrophil gelatinase-associated lipocalin rapidly increased in the acute phase, remaining elevated in the chronic phase of T3Tx SCI. Renal interstitial and vascular elastin fragmentation after SCI were worsened during chronic T3Tx SCI. In the chronic phase, renal vascular resistance response to a step increase in renal perfusion pressure or a bolus injection of angiotensin II or norepinephrine was almost completely abolished after T3Tx SCI. Bulk RNA-sequencing analysis showed enrichment of genes involved in extracellular matrix remodeling and chemokine signaling in the kidney from T3Tx SCI mice. The serum level of interleukin-6 was elevated in the acute but not chronic phase of T3Tx and T10Tx SCI, whereas the serum amyloid A1 level was elevated in both acute and chronic phases. We conclude that tissue fibrosis and hemodynamic impairment are involved in renal dysfunction resulting from thoracic SCI; these pathological alterations, exacerbated by high thoracic-level injury, is mediated at least partly by renal microvascular extracellular matrix remodeling.NEW & NOTEWORTHY Urinary complications resulting from thoracic spinal cord injury (SCI) greatly affects quality of life and contributes to morbidity and mortality in patients with SCI. Herein, we showed that thoracic SCI initiates changes in the structure and function of the renal microvasculature that leads to autoregulation failure in the chronic phase of high thoracic-level injury. Our study identified extracellular matrix regulators and cytokine/chemokine signaling as potential targets for developing novel therapeutics for restoring renal function following SCI.

Mechanism-based strategies to prevent salt sensitivity and salt-induced hypertension.

High-salt diets are a major cause of hypertension and cardiovascular (CV) disease. Many governments are interested in using food salt reduction programs to reduce the risk for salt-induced increases in blood pressure and CV events. It is assumed that reducing the salt concentration of processed foods will substantially reduce mean salt intake in the general population. However, contrary to expectations, reducing the sodium density of nearly all foods consumed in England by 21% had little or no effect on salt intake in the general population. This may be due to the fact that in England, as in other countries including the U.S.A., mean salt intake is already close to the lower normal physiologic limit for mean salt intake of free-living populations. Thus, mechanism-based strategies for preventing salt-induced increases in blood pressure that do not solely depend on reducing salt intake merit attention. It is now recognized that the initiation of salt-induced increases in blood pressure often involves a combination of normal increases in sodium balance, blood volume and cardiac output together with abnormal vascular resistance responses to increased salt intake. Therefore, preventing either the normal increases in sodium balance and cardiac output, or the abnormal vascular resistance responses to salt, can prevent salt-induced increases in blood pressure. Suboptimal nutrient intake is a common cause of the hemodynamic disturbances mediating salt-induced hypertension. Accordingly, efforts to identify and correct the nutrient deficiencies that promote salt sensitivity hold promise for decreasing population risk of salt-induced hypertension without requiring reductions in salt intake.

The effect of water temperature on orthostatic tolerance: a randomised crossover trial

PurposeBolus water drinking, at room temperature, has been shown to improve orthostatic tolerance (OT), probably via sympathetic activation; however, it is not clear whether the temperature of the water bolus modifies the effect on OT or the cardiovascular responses to orthostatic stress. The aim of this study was to assess whether differing water temperature of the water bolus would alter time to presyncope and/or cardiovascular parameters during incremental orthostatic stress.MethodsFourteen participants underwent three head-up tilt (HUT) tests with graded lower body negative pressure (LBNP) continued until presyncope. Fifteen minutes prior to each HUT, participants drank a 500 mL bolus of water which was randomised, in single-blind crossover fashion, to either room temperature water (20 °C) (ROOM), ice-cold water (0–3 °C) (COLD) or warm water (45 °C) (WARM). Cardiovascular parameters were monitored continuously.ResultsThere was no significant difference in OT in the COLD (33 ± 3 min; p = 0.3321) and WARM (32 ± 3 min; p = 0.6764) conditions in comparison to the ROOM condition (31 ± 3 min). During the HUT tests, heart rate and cardiac output were significantly reduced (p < 0.0073), with significantly increased systolic blood pressure, stroke volume, cerebral blood flow velocity and total peripheral resistance (p < 0.0054), in the COLD compared to ROOM conditions.ConclusionsIn healthy controls, bolus cold water drinking results in favourable orthostatic cardiovascular responses during HUT/LBNP without significantly altering OT. Using a cold water bolus may result in additional benefits in patients with orthostatic intolerance above those conferred by bolus water at room temperature (by ameliorating orthostatic tachycardia and enhancing vascular resistance responses). Further research in patients with orthostatic intolerance is warranted.

Is the Pannexin-1 Channel a Mechanism Underlying Hypertension in Humans? a Translational Study of Human Hypertension

In preclinical models, the pannexin-1 channel has been shown to be involved in blood pressure regulation through an effect on peripheral vascular resistance. Pannexin-1 releases ATP, which can activate constrictive purinergic receptors on the smooth muscle cells. Pannexin-1 opening is proposed to be mediated by α-adrenergic receptors to potentiate sympathetic constriction. This positions pannexin-1 as a putative pharmacological target in blood pressure regulation in humans. The aim was to provide the first translational evidence for a role of pannexin-1 in essential hypertension in humans by use of an advanced invasive mechanistic approach. Middle-aged stage-1 hypertensive (n=13; 135.7±6.4 over 83.7±3.7 mm Hg) and normotensive men (n=12; 117.3±5.7 over 72.2±3.5 mm Hg) were included. Blood pressure and leg vascular resistance were determined during femoral arterial infusion of tyramine (α-adrenergic receptor stimulation), sodium nitroprusside, and acetylcholine. Measurements were made during control conditions and with pannexin-1 blockade (3000 mg probenecid). Expression of Pannexin-1, purinergic- and α-adrenergic receptors in skeletal muscle biopsies was determined by Western blot. The changes in leg vascular resistance in response to tyramine (+289% versus +222%), sodium nitroprusside (-82% versus -78%) and acetylcholine (-40% versus -44%) infusion were not different between the 2 groups (P>0.05) and pannexin-1 blockade did not alter these variables (P>0.05). Expression of pannexin-1 and of purinergic- and α-adrenergic receptors was not different between the 2 groups (P>0.05). Contrary to our hypothesis, the data demonstrate that pannexin-1 does not contribute to the elevated blood pressure in essential hypertension, a finding, which also opposes that reported in preclinical models.

Estradiol Supplement or Induced Hypertension May Attenuate the Angiotensin II Type 1 Receptor Antagonist-Promoted Renal Blood Flow Response to Graded Angiotensin II Administration in Ovariectomized Rats.

Backgrounds Estrogen replacement therapy (ERT) and hypertension may influence females' renin-angiotensin system (RAS) and its components. The angiotensin II (Ang II) type 1 receptor (AT1R) antagonist (losartan) may promote renal blood flow (RBF), and it is widely used in the clinic to control hypertension. The main objective of this study was the effects of estradiol or induced hypertension on RBF response to Ang II in losartan-treated ovariectomized (OVX) rats. Methods Two groups of OVX rats were treated with placebo (group 1) and estradiol (group 2) for period of four weeks, and another group of OVX rats was subjected to induce hypertension by two-kidney one clip (2K1C) model (group 3). All the groups were subjected to the surgical procedure under anesthesia, and AT1R was blocked by losartan. RBF and renal vascular resistance (RVR) responses to Ang II administration were determined and compared. Results Mean arterial (MAP) and renal perfusion (RPP) pressures in group 3 and uterus weight (UT) in group 2 were significantly more than other groups (P < 0.05). Ang II infusion resulted in dose-related percentage change increase in RBF and decrease in RVR. However, these responses in the OVX-estradiol and OVX-hypertensive rats were significantly lower than in the OVX-control group (P < 0.05). For instance, at the dose of 1000 ng/kg/min of Ang II administration, the percentage change of RBF was 45.1 ± 10.4%, 17.9 ± 2.3%, and 16.7 ± 4.7% in the groups of 1 to 3, respectively. Conclusion Losartan prescription in some conditions such as hypertension or ERT could worsen RBF and RVR responses to Ang II.

Reliance on vascular responses for the maintenance of blood pressure in healthy older adults - Insights from the Valsalva maneuver.

Effective baroreflex-mediated cardiac and vascular resistance responses are crucial for homeostatic blood pressure control. We investigated the impacts of age and sex on arterial blood pressure regulation during a standard supine Valsalva maneuver (40mmHg, 20s) in 46 healthy young and 25 healthy older adults. Noninvasive, continuous cardiovascular parameters were recorded. In older adults, cardiac output (older: -58.4±2.4%; young: -40.8±1.4%; p<0.001) and stroke volume (older: -63.6±2.6%; young: -48.7±1.9%; p<0.001) fell more than in young adults and was compensated by augmented vascular resistance responses (older: +189.8±17.6%; young: +105.8±6.7; p<0.001); heart rate responses were attenuated in older adults. Male and female responses were comparable in their respective age groups.

Abstract 6991: Impaired Systemic Oxygen Extraction Relates to Reduced Exercise Capacity in Post-COVID-19 Long Hauler Syndrome

Introduction: Following acute coronavirus 2019 (COVID-19) disease, at least 10% of patients report some form of residual limitation, most commonly dyspnea and fatigue. These COVID-19 “long haulers” experience symptoms that are largely unexplained by pulmonary function testing (PFT), echocardiogram and chest computed tomography (CT). Using invasive cardiopulmonary exercise testing, this pilot study characterized exercise limitation in 5 patients with persistent symptoms 1 year following mild COVID-19 illness. Methods: Following written informed consent, data were obtained in accordance with an IRB-approved protocol entailing placement of radial and pulmonary arterial catheters for pressure monitoring and blood sampling prior to and during maximum upright incremental exercise. Rest and exercise pulmonary hemodynamics, ventilation and gas exchange were recorded. Aerobic exercise capacity was estimated by peak O 2 consumption (VO 2 ). Results: All patients had normal biventricular and valvular function on resting echocardiogram, no evident parenchymal lung disease on CT, and normal PFTs. Resting mean pulmonary arterial pressure was ≤20 mmHg for all patients with pulmonary vascular resistance &lt;3 Woods units. At maximum exercise, all patients exhibited normal respiratory, cardiac output (% predicted), and total pulmonary vascular resistance responses, but demonstrated clearly depressed aerobic capacity (peak VO 2 &lt;80% predicted). Reduced peak VO 2 was associated with impaired systemic O 2 extraction as indicated by an arterial-venous O 2 content difference (adjusted for hemoglobin) of &lt;80% ( Figure 1 ). Conclusion: This case series provides preliminary evidence that reduced peak aerobic capacity among long haulers is primarily attributable to a peripheral (i.e., impaired systemic O 2 extraction), rather than central cardiopulmonary, limitation. These results suggest that systemic microcirculatory dysfunction contributes to exercise limitation.

Acute hyperoxia reveals tonic influence of peripheral chemoreceptors on systemic vascular resistance in heart failure patients

Peripheral chemoreceptors’ (PCh) hyperactivity increases sympathetic tone. An augmented acute ventilatory response to hypoxia, being a marker of PCh oversensitivity, was also identified as a marker of poor prognosis in HF. However, not much is known about the tonic (chronic) influence of PCh on cardio-respiratory parameters. In our study 30 HF patients and 30 healthy individuals were exposed to 100% oxygen for 1 min during which minute ventilation and hemodynamic parameters were non-invasively recorded. Systemic vascular resistance (SVR) and mean arterial pressure (MAP) responses to acute hyperoxia differed substantially between HF and control. In HF hyperoxia caused a significant drop in SVR in early stages with subsequent normalization, while increase in SVR was observed in controls. MAP increased in controls, but remained unchanged in HF. Bilateral carotid bodies excision performed in two HF subjects changed the response to hyperoxia towards the course seen in healthy individuals. These differences may be explained by the domination of early vascular reaction to hyperoxia in HF by vasodilation due to the inhibition of augmented tonic activity of PCh. Otherwise, in healthy subjects the vasoconstrictive action of oxygen remains unopposed. The magnitude of SVR change during acute hyperoxia may be used as a novel method for tonic PCh activity assessment.

Maternal cardiovascular dysfunction in women with early onset preeclampsia: a cross-sectional study

Background Cardiac remodeling and diastolic dysfunction may occur, in women with early-onset preeclampsia, following raised total vascular resistance in response to the impaired placentation. These changes can increase the risk of premature cardiac morbidity and mortality later in life. According to updated guidelines by the American and European Societies of Echocardiography (ASE/ESE) to diagnose diastolic dysfunction, using a simpler criterion is not yet used in pregnant women. Objective To compare the maternal cardiovascular changes and the variation in the diastolic dysfunction using the 2009 and 2016 criteria by ASE/ESE among women with early onset preeclampsia and gestational age-matched normotensive controls. Methods A prospective matched cross-sectional study conducted in a tertiary hospital in South India, involving 40 women with early and 40 women with gestational age-matched normotensive controls. Cardiac function and remodeling were assessed by conventional 2D, M-mode, and Doppler echocardiography. Results Compared to the controls, women with early-onset preeclampsia had significantly higher. Total vascular resistance index (2867.6 vs. 2277.2 dynes/s/cm5/m2, p = .035) and median end-systolic stress index (5.2 vs. 9.2 dyne/cm2/m2), suggesting a higher afterload. Cases had a significant rate of left ventricular diastolic dysfunction using the 2009 criteria (grade II/III: 21 (52%) vs. 0 (0%), p<.001) whereas the rates were much lower when the updated 2016 guidelines were used (grade II/III: 9 (22.5%) vs. 1 (2.5%), p<.001). Conclusions In women with early-onset preeclampsia, cardiovascular adaption occurs to minimize wall stress and myocardial oxygenation. The prevalence of diastolic dysfunction was observed to be lower with the 2016 criteria. Further studies involving pregnant women are required to assess the impact of newer guidelines on association with short- and long-term cardiovascular outcomes in high-risk women.

Forearm vascular resistance responses to the Valsalva maneuver in healthy young and older adults.

Effective end-organ peripheral vascular resistance responses are critical to blood pressure control while upright, and prevention of syncope (fainting). The Valsalva maneuver (VM) induces blood pressure decreases that evoke baroreflex-mediated vasoconstriction. We characterized beat-to-beat forearm vascular resistance (FVR) responses to the VM in healthy adults, evaluated the impact of age and sex on these responses, and investigated their association with orthostatic tolerance (OT; susceptibility to syncope). We hypothesized that individuals with smaller FVR responses would be more susceptible to syncope. Healthy young (N = 36; 19 women; age 25.4 ± 4.6years) and older (N = 21; 12 women; age 62.4 ± 9.6years) adults performed a supine 40mmHg, 20s VM. Graded 60° head-up-tilt with combined lower body negative pressure continued to presyncope was used to determine OT. Non-invasive beat-to-beat blood pressure and heart rate (finger plethysmography) were recorded continuously. FVR was calculated as mean arterial pressure (MAP) divided by brachial blood flow velocity (Doppler ultrasound) relative to baseline. The VM produces a distinctive FVR pattern that peaks (+137.1 ± 11.6%) in phase 2B (17.5 ± 0.3s) as the baroreflex responds to low-pressure perturbations. This response increased with age overall (p < 0.001) and within male (p = 0.030) and female subgroups (p < 0.001). Maximum FVR during the VM was significantly correlated with maximal tilt FVR (r = 0.364; p = 0.0153) and with OT when expressed relative to the MAP decrease in phase 2A (Max FVR (%)/MAP2A-1; r = 0.337; p = 0.0206). This is the first characterization of FVR responses to the VM. The VM elicits large baroreflex-mediated increases in FVR; small FVR responses to the VM may indicate susceptibility to syncope.

Sex Differences in Vascular Reactivity with Acute and Chronic Hypoxia

Objective Males and females may respond differently to hypoxic exposure at high altitude. Females have reduced vascular resistance in response to hypoxia, possibly due to differences in adrenergic control. We investigated the role of sex in vascular control during hypoxia. We hypothesized females have reduced vasoreactivity to sympathetic stressors compared to males during acute and prolonged hypoxia exposure. Methods We studied a convenient sample of 7 males and 6 females at three time points: 1) low altitude (Calgary AB, 1100m) breathing room air (normoxia; LOW) and acute isocapnic hypoxia (PETO2~50mmHg; PETCO2~32mmHg; ACUTE); 2) during early (day 2-3; EARLY) and 3) late (day 8-10; LATE) acclimatization at high altitude (White Mountain, CA; 3800m) breathing room air (PETO2~50mmHg) and hyperoxia (100% O2). Heart rate (HR), mean arterial pressure (MAP), and blood oxygen saturation (SpO2) were collected beat-by-beat. Participants performed a cold pressor test (CPT) to assess integrated cardiovascular reactivity to a sympathetic stressor. To isolate α1-adrenergic receptor sensitivity, we delivered a graded series of phenylephrine hydrochloride (PE) injections. Statistical analysis included a mixed model ANOVA, and Holm-Sidak post hoc tests when we identified main effects (α<0.05). Results In response to CPT, peak change in MAP decreased with hypoxia duration (p<0.001). There was also a significant interaction between condition and sex (p=0.038). While LOW (+17.0±5.9mmHg) and ACUTE (+15.3±4.7mmHg) responses were not different (p=0.565), males showed a marked decrease in peak MAP response to CPT at EARLY (+10.2±4.9mmHg) and LATE (+9.8±5.4mmHg) compared to LOW (both p<0.001). Similarly, LOW (+11.8±8.4mmHg) and ACUTE (+8.2±3.8mmHg) peak MAP responses to CPT were not different in females (p=0.137). Though female responses decreased between LOW and EARLY (+6.3±3.3mmHg; p=0.042), they returned to similar values by LATE (+9.7±7.5mmHg; p=0.479). Adrenergic sensitivity slope was decreased at altitude (p=0.025) independent of sex (p=0.977). LOW (0.33±0.21) and ACUTE (0.22±0.10) sensitivity were not different (p=0.309). Notably, sensitivity was reduced at altitude at LATE (0.14±0.16; p=0.043), but not significantly at EARLY (0.16±0.18; p=0.051) compared to LOW. Hyperoxia did not correct CPT responses or PE adrenergic sensitivity to low altitude values at EARLY (p<0.001; p=0.01, respectively) nor LATE (p=0.013; p=0.042, respectively). Conclusions Our data indicate decreased α1-adrenergic responsiveness with acclimatization underlies blunted vascular reactivity in both sexes. However, female responses to CPT returned to low altitude values following 8 days at altitude, indicating differential adaptation. Additional mechanisms influencing the vascular response to stress (e.g. less neuropeptide mediated constriction, higher β-adrenergic dilation) may account for lower responsiveness in females compared to males. Our results have implications for understanding vascular function at high altitude and in clinical conditions characterized by hypoxemia.