Orthostatic Challenge Shifts the Hemostatic System of Patients Recovered from Stroke toward Hypercoagulability

The Role of Heparin in Postural Orthostatic Tachycardia Syndrome and Other Post-Acute Sequelae of COVID-19

The therapeutic management and short-term consequences of the coronavirus disease 2019 (COVID-19) are well known. However, COVID-19 post-acute sequelae are less known and represent a public health problem worldwide. Patients with COVID-19 who present post-acute sequelae may display immune dysregulation, a procoagulant state, and persistent microvascular endotheliopathy that could trigger microvascular thrombosis. These elements have also been implicated in the physiopathology of postural orthostatic tachycardia syndrome, a frequent sequela in post-COVID-19 patients. These mechanisms, directly associated with post-acute sequelae, might determine the thrombotic consequences of COVID-19 and the need for early anticoagulation therapy. In this context, heparin has several potential benefits, including immunomodulatory, anticoagulant, antiviral, pro-endothelial, and vascular effects, that could be helpful in the treatment of COVID-19 post-acute sequelae. In this article, we review the evidence surrounding the post-acute sequelae of COVID-19 and the potential benefits of the use of heparin, with a special focus on the treatment of postural orthostatic tachycardia syndrome.

Orthostatic Challenge-Induced Coagulation Activation in Young and Older Persons

The incidence of thrombosis increases with aging. We investigated the coagulatory/haemostatic system across the ages and tested the hypothesis that older persons have a hypercoagulable state compared to younger persons at rest, and that standing up (orthostasis) leads to greater changes in coagulation in older persons. In total, 22 older and 20 young participants performed a 6 min sit-to-stand test (orthostatic challenge). Blood was collected prior to and at the end of standing and haemostatic profiling was performed via thrombelastometry (TEM), calibrated automated thrombogram (CAT) and standard coagulation assays. At baseline, three CAT-derived values indicated enhanced capability to generate thrombin in older participants. However, other measured parameters did not suggest a hypercoagulable state in older participants: prolonged TEM-derived coagulation times (295 vs. 209 s, medians, p = 0.0025) and prothrombin times (103 vs. 114%, medians, p = 0.0087), as well as lower TF levels (440 vs. 672 pg/mL, medians, p = 0.0245) and higher t-PA levels (7.3 vs. 3.8 ng/mL, medians, p = 0.0002), indicative of enhanced fibrinolytic capability, were seen. Younger participants were more sensitive to the orthostatic challenge: CAT-derived endogenous thrombin potentials (ETPs) were only increased in the young (1337 to 1350 nM.min, medians, p = 0.0264) and shortening of PTs was significantly higher in the young vs. older participants (p = 0.0242). Our data suggest that the increased thrombosis propensity in older persons is not primarily attributable to a hyperactive coagulation cascade but may be due to other pathologies associated with aging.

Simulated Hypergravity Activates Hemostasis in Healthy Volunteers

Background

Hypergravity may promote human hemostasis thereby increasing thrombotic risk. Future touristic suborbital spaceflight will expose older individuals with chronic medical conditions, who are at much higher thromboembolic risk compared with professional astronauts, to hypergravity. Therefore, we tested the impact of hypergravity on hemostasis in healthy volunteers undergoing centrifugation.

Methods and Results

We studied 20 healthy seated men before and after 15 minutes under 3 Gz hypergravity on a long‐arm centrifuge. We obtained blood samples for hemostasis testing before, immediately after, and 30 minutes after centrifugation. Tests included viscoelastic thromboelastometry, platelet impedance aggregometry, endothelial activation markers, blood rheology testing, microparticle analyses, and clotting factor analysis. Exposure to hypergravity reduced plasma volume by 12.5% (P=0.002) and increased the red blood cell aggregation index (P<0.05). With hypergravity, thrombelastographic clotting time of native blood shortened from 719±117 seconds to 628±89 seconds (P=0.038) and platetet reactivity increased (P=0.045). Hypergravity shortened partial thromboplastin time from 28 (26–29) seconds to 25 (24–28) seconds (P<0.001) and increased the activity of coagulation factors (eg, factor VIII 117 [93–134] versus 151 [133–175] %, P<0.001). Tissue factor concentration was 188±95 pg/mL before and 298±136 pg/mL after hypergravity exposure (P=0.023). Antithrombin (P=0.005), thrombin‐antithrombin complex (P<0.001), plasmin‐alpha2‐antiplasmin complex (0.002), tissue‐plasminogen activatior (P<0.001), and plasminogen activator inhibitor‐1 (P=0.002) increased with centrifugation. Statistical adjustment for plasma volume attenuated changes in coagulation.

Conclusions

Hypergravity triggers low‐level hemostasis activation through endothelial cell activation, increased viscoelasticity, and augmented platelet reactivity, albeit partly counteracted through endogenous coagulation inhibitors release. Hemoconcentration may contribute to the response.

Menstrual Phase Affects Coagulation and Hematological Parameters during Central Hypovolemia

Background: It has been reported that women have a higher number of heart attacks in the “follicular phase” of the menstrual cycle. We, therefore, tested the hypothesis that women in the follicular phase exhibit higher coagulability. As lower body negative pressure (LBNP) has been used previously to assess coagulation changes in whole blood (WB) samples in men and women, effects of menstrual phase on coagulation was assessed during LBNP. Methods: Seven women, all healthy young participants, with no histories of thrombotic disorders and not on medications, were tested in two phases of the menstrual cycle (early follicular (EF) and mid-luteal (ML)). LBNP was commenced at −10 mmHg and increased by −10 mmHg every 5 min until a maximum of −40 mmHg. Recovery up to 10 min was also monitored. Blood samples were collected at baseline, at end of LBNP, and at end of recovery. Hemostatic profiling included comparing the effects of LBNP on coagulation values in both phases of the menstrual cycle using standard coagulation tests, calibrated automated thrombogram, thrombelastometry, impedance aggregometry, and markers of thrombin formation. Results: LBNP led to coagulation activation determined in both plasma and WB samples. During both phases, coagulation was affected during LBNP, as reflected in their decreased partial thromboplastin time (PTT) and elevated coagulation factor VIII FVIII, F1 + 2, and thrombin-antithrombin (TAT) levels. Additionally, during the ML phase, greater PT [%] and shorter time to peak (ttPeak) values (implying faster maximum thrombin formation) suggest that women in the ML phase are relatively hypercoagulable compared to the early follicular phase. Conclusions: These results suggest that thrombosis occurs more during the midluteal phase, a finding with substantial medical implications.

Postural hemodynamic parameters in older persons have a seasonal dependency : A pilot study

Aims

It is known that blood pressure regulation differs seasonally. It is unknown, however, how the cardiovascular system in patients with a stroke reacts to postural changes in different seasons. The aim was therefore to investigate how different temperatures in cold and warm seasons influence the reactions of haemodynamic mechanisms as well as heart rate variability during a sit-to-stand test in patients with stroke and a control group.

Methods

Hemodynamic responses were assessed in both groups during a sit-to-stand test (5 min sitting followed by 5 min standing) beat to beat within two different seasons. Systolic blood pressure (SBP), diastolic blood pressure (DBP), mean blood pressure (MBP), heart rate (HR), stroke index (SI), cardiac index (CI) and heart rate variability (HRV) were continuously monitored.

Results

During the sitting baseline period delta values of DBP (+15.1 [Standard error (SE) 3.75] mmHg, p < 0.05) and MBP (+14.35 [SE 4.18] mmHg, p < 0.05) were significantly higher in colder months compared to warmer months whereas SI (−3.86 [SE 1.43] ml/beat/m², p < 0.05) and CI (−0.4 [SE 0.11] l/min/m², p < 0.05) were lower in colder months compared to warmer months in non-stroke participants. In patients with stroke during sitting, baseline period delta values of DBP (+19.92 [SE 8.03] mmHg, p < 0.05) and MBP (+19.29 [SE 8.6] mmHg, p < 0.05) were significantly higher in colder months compared to warmer months but SI (−5.43 [SE 1.96] ml/beat/m², p < 0.05) was significantly lower in colder months compared to warmer months. After standing, there was a significant decrease in SBP in warmer months (−16.84 [SE 4.38] mmHg, p < 0.05) and a decrease in DBP in warmer months (−7.8 [SE 2.3] mmHg, p < 0.05) and colder months (−6.73 [SE 1.5] mmHg, p < 0.05) in non-stroke participants and a decrease in MBP in warmer months (−12.5 [SE 2.8] mmHg, p < 0.05) and colder months (−8.93 [SE 1.8] mmHg, p < 0.05) in non-stroke participants and in warmer months (−14.54 [SE 4.1] mmHg, p < 0.05) in patients with stroke.

Conclusion

Elderly with and without stroke respond to orthostatic stress with a greater drop in blood pressure in the warmer seasons.

Aerobic Training and Mobilization Early Post-stroke: Cautions and Considerations

Knowledge gaps exist in how we implement aerobic exercise programs during the early phases post-stroke. Therefore, the objective of this review was to provide evidence-based guidelines for pre-participation screening, mobilization, and aerobic exercise training in the hyper-acute and acute phases post-stroke. In reviewing the literature to determine safe timelines of when to initiate exercise and mobilization we considered the following factors: arterial blood pressure dysregulation, cardiac complications, blood-brain barrier disruption, hemorrhagic stroke transformation, and ischemic penumbra viability. These stroke-related impairments could intensify with inappropriate mobilization/aerobic exercise, hence we deemed the integrity of cerebral autoregulation to be an essential physiological consideration to protect the brain when progressing exercise intensity. Pre-participation screening criteria are proposed and countermeasures to protect the brain from potentially adverse circulatory effects before, during, and following mobilization/exercise sessions are introduced. For example, prolonged periods of standing and static postures before and after mobilization/aerobic exercise may elicit blood pooling and/or trigger coagulation cascades and/or cerebral hypoperfusion. Countermeasures such as avoiding prolonged standing or incorporating periodic lower limb movement to activate the venous muscle pump could counteract blood pooling after an exercise session, minimize activation of the coagulation cascade, and mitigate potential cerebral hypoperfusion. We discuss patient safety in light of the complex nature of stroke presentations (i.e., type, severity, and etiology), medical history, comorbidities such as diabetes, cardiac manifestations, medications, and complications such as anemia and dehydration. The guidelines are easily incorporated into the care model, are low-risk, and use minimal resources. These and other strategies represent opportunities for improving the safety of the activity regimen offered to those in the early phases post-stroke. The timeline for initiating and progressing exercise/mobilization parameters are contingent on recovery stages both from neurobiological and cardiovascular perspectives, which to this point have not been specifically considered in practice. This review includes tailored exercise and mobilization prescription strategies and precautions that are not resource intensive and prioritize safety in stroke recovery.

Coagulation changes induced by lower-body negative pressure in men and women

We investigated whether lower-body negative pressure (LBNP) application leads to coagulation activation in whole blood (WB) samples in healthy men and women. Twenty-four women and 21 men, all healthy young participants, with no histories of thrombotic disorders and not on medications, were included. LBNP was commenced at −10 mmHg and increased by −10 mmHg every 5 min until a maximum of −40 mmHg. Recovery up to 10 min was also monitored. Blood samples were collected at baseline, at end of LBNP, and end of recovery. Hemostatic profiling included comparing the effects of LBNP on coagulation values in both men and women using standard coagulation tests, calibrated automated thrombogram, thrombelastometry, impedance aggregometry, and markers of thrombin formation. LBNP led to coagulation activation determined in both plasma and WB samples. At baseline, women were hypercoagulable compared with men, as evidenced by their shorter “lag times” and higher thrombin peaks and by shorter “coagulation times” and “clot formation times.” Moreover, men were more susceptible to LBNP, as reflected in their elevated factor VIII levels and decreased lag times following LBNP. LBNP-induced coagulation activation was not accompanied by endothelial activation. Women appear to be relatively hypercoagulable compared with men, but men are more susceptible to coagulation changes during LBNP. The application of LBNP might be a useful future tool to identify individuals with an elevated risk for thrombosis, in subjects with or without history of thrombosis.

NEW & NOTEWORTHY LBNP led to coagulation activation determined in both plasma and whole blood samples. At baseline, women were hypercoagulable compared with men. Men were, however, more susceptible to coagulation changes during LBNP. LBNP-induced coagulation activation was not accompanied by endothelial activation. The application of LBNP might be a useful future tool to identify individuals with an elevated risk for thrombosis, in subjects with or without history of thrombosis.