Experimental Orthostasis Elicits Sustained Hypertension, Which Can Be Prevented by Sympathetic Blockade in the Rat

Transient Orthostatic Hypertension During Head-Up Tilt Test in Young Adults: A Phenotype of Blood Pressure Variability

PURPOSE

The mechanisms underlying orthostatic hypertension (OHT) remain poorly understood. The authors evaluated the cardiovascular, cerebrovascular dynamics, and autonomic response to head-up tilt test (HUTT) in young adults with symptoms of orthostatic intolerance and transient OHT.

METHODS

Forty-four female subjects were included (34 ± 13 years old) and categorized in three groups after a 30-minute 70° passive HUTT: symptomatic patients with OHT (surge of systolic blood pressure ≥20 mm Hg for at least 5 minutes at any given time during HUTT), orthostatic intolerance (symptomatic patients without orthostatic blood pressure changes), and healthy asymptomatic control subjects.

RESULTS

At baseline, OHT patients had lower systolic blood pressure than orthostatic intolerance patients (103 ± 8 vs. 116 ± 10 mm Hg, p < 0.01) and lower baroreflex sensitivity than control subjects (15.8 ± 8.3 vs. 27.1 ± 11.7 ms/mm Hg, p = 0.01). On tilt, cardiac output decreased in OHT patients from 6.1 ± 1.4 L/minute during baseline to 5.2 ± 0.8 L/minute after 10 minutes of HUTT (p = 0.01). In OHT patients at 30 minutes of HUTT, sympathetic efferent heart activity was higher (77.4 ± 14.9 normalized units or nu) than orthostatic intolerant patients (63.5 ± 11.8 nu, p = 0.02) and control subjects (65.8 ± 11.2 nu, p = 0.05). Cerebrovascular resistance in OHT was higher than control subjects after 30 minutes (2.2 ± 0.8 vs. 1.6 ± 0.3 cm/second, respectively, p = 0.02).

CONCLUSIONS

This study demonstrates that transient OHT can occur at any given time during HUTT. These patients exhibit a decrease in cardiac output and a hyperadrenergic response to tilt.

Orthostatic Hypertension in Children: An Update

The concept of orthostatic hypertension in children was first proposed in 2012. The pathogenesis is not clear by now. Orthostatic hypertension is one of the important causes of orthostatic intolerance in children and is related to the development of essential hypertension in the future. It is commonly seen in older children, with dizziness and syncope as their main clinical manifestations. Non-drug therapy is the commonly used treatment strategy, which is effective to improve the orthostatic intolerance symptoms. In this paper, we reviewed the clinical studies on the pathogenesis, clinical characteristics, diagnostic criteria, and treatment of orthostatic hypertension in children, aiming to provide new insights for the future studies on pediatric orthostatic hypertension.

Hemodynamic characterization of hypertensive patients with an exaggerated orthostatic blood pressure variation

Exaggerated orthostatic blood pressure variation (EOV) is a poorly understood phenomenon related to high cardiovascular risk. We aimed to determine whether hypertensive patients with EOV have a distinct hemodynamic pattern, assessed through impedance cardiography.

METHODS

In treated hypertensive patients, we measured the cardiac index (CI), systemic vascular resistance index (SVRI), blood pressure (BP), and heart rate (HR) in the supine and standing (after 3 minutes) positions, defining three groups according to BP variation: 1) Normal orthostatic BP variation (NOV): standing systolic BP (stSBP)-supine systolic BP (suSBP) between -20 and 20 mmHg and standing diastolic BP (stDBP)-supine diastolic BP (suDBP) between -10 and 10 mmHg; 2) orthostatic hypotension (OHypo): stSBP-suSBP≤-20 or stDBP-suDBP≤-10 mmHg; 3) orthostatic hypertension (OHyper): stSBP-suSBP≥20 or stDBP-suDBP≥10 mmHg. We performed multivariable analyses to determine the association of hemodynamic variables with EOV.

RESULTS

We included 186 patients. Those with OHyper had lower suDBP and higher orthostatic SVRI variation compared to NOV. In multivariable analyses, orthostatic HR variation (OR = 1.06 (95%CI 1.01-1.13), p = 0.03) and orthostatic SVRI variation (OR = 1.16 (95%CI 1.06-1.28), p = 0.002) were independently related to OHyper. No variables were independently associated with OHypo.

CONCLUSION

Patients with OHyper have a distinct hemodynamic pattern, with an exaggerated increase in SVRI and HR when standing.

Involvement of the paraventricular nucleus (PVN) of hypothalamus in the cardiovascular alterations to head up tilt in conscious rats

We evaluated the involvement of paraventricular nucleus (PVN) in the changes in mean arterial pressure (MAP) and heart rate (HR) during an orthostatic challenge (head up tilt, HUT). Adult male Wistar rats, instrumented with guide cannulas to PVN and artery and vein catheters were submitted to MAP and HR recording in conscious state and induction of HUT. The HUT induced an increase in MAP and HR and the pretreatment with prazosin and atenolol blocked these effects. After inhibition of neurotransmission with cobalt chloride (1 mM/100 nl) into the PVN the HR parameters did not change, however we observed a decrease in MAP during HUT. Our data suggest the involvement of PVN in the brain circuitry involved in cardiovascular adjustment during orthostatic challenges.

An Emerging Role for Understanding Orthostatic Hyp'er'tension in the Cardiorenal Syndrome

Orthostatic hypertension (OHT) is a clinically important problem increasingly recognized in persons with borderline hypertension, diabetes mellitus, and autonomic neuropathies, and in the elderly. Moreover, the association of OHT with progression of target end-organ damage, especially coronary heart disease and chronic kidney disease (CKD), and the attendant increased cardiovascular disease (CVD) and CKD risk, is gaining attention but is still underappreciated. There are various mechanisms that contribute to the development of OHT: excessive vascular adrenergic sensitivity, baroreceptor reflex abnormalities, and inappropriate activation of the renin-angiotensin-aldosterone system, which are also mechanisms that lead to cardiorenal metabolic disease (CRS). While the evidence is compelling for the clinical importance of OHT, more investigation is needed to evaluate the effects of OHT on CKD and CVD. The notion that the development of OHT is a risk factor for the development of CRS raises the need for further clinical and investigational attention to this clinical dilemma.

Orthostatic hypertension: when pressor reflexes overcompensate

Orthostatic hypertension--a rise in blood pressure upon assuming upright posture-is an underappreciated and understudied clinical phenomenon. There is currently no widely agreed-upon definition of clinical orthostatic hypertension, the current definitions being operational within the context of particular studies. The underlying pathophysiology is thought to involve activation of the sympathetic nervous system, but the actual etiology is poorly understood. Orthostatic hypertension is observed in association with a variety of other clinical conditions, including essential hypertension, dysautonomias, and type 2 diabetes mellitus. Orthostatic hypertension has been associated with increased occurrence of silent cerebrovascular ischemia and possibly with neuropathy in type 2 diabetes. So, appreciation of the true incidence of orthostatic hypertension, elucidation of the underlying pathophysiology, and an understanding of potentially effective treatment approaches and their associated risks and benefits might all have major clinical significance. Orthostatic hypertension is an aspect of hypertension that is in need of further focused investigation.

Effects of nine antihypertensive drugs on blood pressure variability in sinoaortic-denervated rats

AIM

The present work was designed to investigate the effects of nine commonly used antihypertensive drugs on blood pressure (BP) and blood pressure variability (BPV) in conscious sinoaortic-denervated (SAD) rats.

METHODS

Seventy-two SAD rats were randomly divided into nine groups. They were respectively given nifedipine 3 mg/kg, nitrendipine 5 mg/kg, amlodipine 1 mg/kg, clonidine 10 mug/kg, prazosin 0.5 mg/kg, atenolol 20 mg/kg, telmisartan 20 mg/kg, hydrochlorothiazide 40 mg/kg or captopril 50 mg/kg. The drugs were given via a catheter previously implanted into the stomach. BP was recorded for 5 h from 1 h before drug administration to 4 h after drug administration in conscious, freely moving rats.

RESULTS

It was found that all these nine drugs significantly decreased BP in SAD rats. Six of these drugs (nifedipine, nitrendipine, amlodipine, clonidine, prazosin and atenolol) significantly decreased BPV in SAD rats, but the remaining three drugs did not. Clonidine and atenolol increased the heart period and the others did not. No drugs affected the heart period variability.

CONCLUSION

Among nine antihypertensive drugs from different classes, calcium antagonists and sympathetic inhibitors decreased BPV in SAD rats.

Inverse-Orthostasis May Induce Elevation of Blood Pressure due to Sympathetic Activation

Microgravity and simulated microgravity may cause cardiovascular deconditioning, but mechanisms of instantaneous responses to inverse-orthostasis are not studied. Hence, we investigated transient and steady state cardiovascular changes by combining the tilt technique with cardiovascular telemetry. Normotensive and NO-deprived hypertensive Wistar rats were used to analyze responses of mean arterial blood pressure, heart rate, contractility, spontaneous baroreflex sensitivity (sBRS), and autonomic balance. Inverse-orthostasis tests were carried out by 45 degrees head-down tilting (repeated 3 x 5 mins "R", or sustained for 120 mins "S"). In normotensive rats, horizontal control blood pressure was R111.3 +/- 1.7/S110.4 +/- 2.3 mm Hg and heart rate was R385.2 +/- 5.9/S371.1 +/- 6.1 BPM. Head-down tilt induced an increase in blood pressure by R5.9/S10.6 mm Hg, while heart rate, contractility, sBRS, and autonomic balance did not change. The hypertensive response was sustained, could be prevented by prazosin (10 mg/kgbw), and augmented by subanesthetic doses of chloralose (26 and 43 mg/kgbw). In NO-suppressed hypertension, control blood pressure and heart rate were R132.4 +/- 2.9/S130.0 +/- 4.1 mm Hg and R339.2 +/- 7.9/S307.2 +/- 23.6 BPM, respectively. Head-down tilt further increased blood pressure by R5.1/S10.5 mm Hg. These data demonstrate that conscious rats respond to inverse-orthostasis by sustained elevation of blood pressure independent of NO synthesis. This response is neither due to increased contractility and altered sBRS, nor due to non-specific stress, but probably due to sympathetic activation elicited by gravity-related reflexes, which increase peripheral resistance.