Marvin S Medow

New York Medical College | NYMC · Department of Pediatrics

We compared standing and upright tilt in patients with postural tachycardia syndrome (POTS) and healthy volunteers to determine whether standing accurately tests for POTS in youngsters < 19 years. POTS in adolescents is defined by orthostatic intolerance plus sustained excessive upright tachycardia, without hypotension during upright tilt. We exami...

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) with orthostatic intolerance (OI) is characterized by neuro-cognitive deficits perhaps related to upright hypocapnia and loss of cerebral autoregulation (CA). We performed N-back neurocognition testing and calculated the phase synchronization index (PhSI) between Arterial Pressure (AP) and...

Pediatric patients with autonomic dysfunction and orthostatic intolerance (OI) often present with co-existing symptoms and signs that might or might not directly relate to the autonomic nervous system. Our objective was to identify validated screening instruments to characterize these comorbidities and their impact on youth functioning. The Pediatr...

50% of POTS patients are hypocapnic during orthostasis related to initial orthostatic hypotension (iOH). We determined whether iOH drives hypocapnia in POTS by low BP or decreased cerebral blood flow velocity (CBFv). We studied 3 groups; healthy volunteers (N=32, 18±3y) were compared to POTS, grouped by presence (POTS-↓ETCO2, N=26, 19±2y) or absenc...

Purpose: Whether evaluating patients clinically, documenting care in the electronic health record, performing research, or communicating with administrative agencies, the use of a common set of terms and definitions is vital to ensure appropriate use of language. At a 2017 meeting of the Pediatric Section of the American Autonomic Society, it was...

Upright postural tachycardia syndrome (POTS) resembles hemorrhage with reduced central blood volume, parasympathetic withdrawal, and sympathetic activation. Baroreflex dysfunction causes low heart rate variability, enhanced blood pressure variability, and decreased maximum baroreflex gain (G max ) putatively measured by spontaneous fluctuation of b...

Introduction The aim of this paper is to describe and demonstrate how a new bioimpedance analytical procedure can be used to monitor cellular hydration of End Stage Renal Disease (ESRD) patients during hemodialysis (HD). Methods A tetra-polar bioimpedance spectroscope (BIS), (UFI Inc., Morro Bay, CA), was used to measure the tissue resistance and r...

Background: Reduced systolic/diastolic blood pressure (BP) by >40/20mmHg defines "Initial orthostatic hypotension" (IOH). Rapid resolution of hypotension and lightheadedness follows but tachycardia may be prolonged. Objectives: To examine IOH in Control and POTS using indices of spontaneous fluctuations of HR and systolic BP as measures of cardi...

Background - Upright posture reduces venous return, stroke volume and cardiac output (CO) while causing reflex sinus rate (HR) increase. Yet, in inappropriate sinus tachycardia (IST), postural tachycardia syndrome (POTS), and vasovagal syncope (VVS) symptomatic excessive HR occurs. We hypothesized CO reaches maximum as function of HR in all. Method...

Objective: To evaluate whether equal volumes of oral rehydration solution (ORS) or intravenous (IV) saline provide similar improvements in cardiovascular status during controlled orthostatic challenge when administered to subjects with postural tachycardia syndrome (POTS) with orthostatic intolerance. Study design: We studied the neurovascular r...

Abstract Upright tilt table testing has been used to test for vasovagal syncope (VVS) but can result in “false positives” in which tilt‐induced fainting (tilt+) occurs in the absence of real‐world fainting. Tilt+ occurs in healthy volunteers and in patients with postural tachycardia syndrome (POTS) and show enhanced susceptibility to orthostatic hy...

Upright hyperventilation occurs in ~25% of our patients with postural tachycardia syndrome (POTS). Poikilocapnic hyperventilation alone causes tachycardia. Here, we examined changes in respiration and hemodynamics comprising cardiac output (CO), systemic vascular resistance (SVR), and blood pressure (BP) measured during head-up tilt (HUT) in three...

Background: Postural tachycardia syndrome (POTS) is a heterogeneous condition. We stratified patients previously evaluated for POTS on the basis of supine resting cardiac output (CO) or with the complaint of platypnea or "shortness of breath" during orthostasis. We hypothesize that postural hyperventilation is one cause of POTS and that hyperventi...

Orthostatic intolerance (OI), having difficulty tolerating an upright posture because of symptoms or signs that abate when returned to supine, is common in pediatrics. For example, ∼40% of people faint during their lives, half of whom faint during adolescence, and the peak age for first faint is 15 years. Because of this, we describe the most commo...

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex disease that affects children and adolescents as well as adults. The etiology has not been established. While many pediatricians and other health-care providers are aware of ME/CFS, they often lack essential knowledge that is necessary for diagnosis and treatment. Many young p...

We measured changes in transcranial Doppler ultrasound (TCD) and near infrared spectroscopy (NIRS) during 70° upright tilt in patients with recurrent vasovagal syncope (VVS, N = 20), postural tachycardia syndrome (POTS, N = 20), and healthy controls (N = 12) aged 15–27 years old. VVS was included if they fainted during testing within 5–15 min of up...

Objective: Syncope is sudden transient loss of consciousness and postural tone with spontaneous recovery; the most common form is vasovagal syncope(VVS). We previously demonstrated impaired post-synaptic adrenergic responsiveness in young VVS patientswas reversed by blocking nitric oxide synthase(NOS). We hypothesised that nitric oxide may account...

Background and objectives: Recurrent postural vasovagal syncope (VVS) is caused by transient cerebral hypoperfusion from episodic hypotension and bradycardia; diagnosis is made by medical history. VVS contrasts with postural tachycardia syndrome (POTS), defined by chronic daily symptoms of orthostatic intolerance with excessive upright tachycardia...

Neurovascular coupling (NVC) describes the link between an increase in task related neural activity and increased cerebral blood flow denoted "functional hyperemia". We previously showed induced cerebral blood flow oscillations suppressed functional hyperemia; conversely functional hyperemia also suppressed cerebral blood flow oscillations. We used...

Background Syncope is a sudden transient loss of consciousness and postural tone caused by cerebral hypoperfusion. The most common form is vasovagal syncope (VVS). Presyncopal progressive early hypotension in older VVS patients is caused by reduced cardiac output (CO); younger patients have reduced systemic vascular resistance (SVR). Using a priori...

Introduction The aim of this paper is to describe and demonstrate how a new bioimpedance analytical procedure can be used to monitor cellular hydration of End Stage Renal Disease (ESRD) patients during hemodialysis (HD). Methods A tetra‐polar bioimpedance spectroscope (BIS), (UFI Inc., Morro Bay, CA), was used to measure the tissue resistance and r...

Background: Syncope is a sudden transient loss of consciousness and postural tone with spontaneous recovery; the most common form is vasovagal syncope (VVS). During VVS, gravitational pooling excessively reduces central blood volume and cardiac output. In VVS, as in hemorrhage, impaired adrenergic vasoconstriction and venoconstriction result in hy...

Neurovascular coupling refers to the link between an increase in neural activity in response to a task, and an increase in cerebral blood flow denoted "functional hyperemia". Recent work on orthostatic intolerance indicated that increased oscillatory cerebral blood flow velocity (CBFv) was associated with reduced functional hyperemia. We hypothesiz...

Objective To study the presentation and treatment in two infants who presented with refractory Sandifer syndrome (SS). Study Design We retrospectively reviewed the cases of two infants who presented to our outpatient clinic with SS who were refractory to conventional treatment. Results We report two patients with refractory SS who responded to tr...

NO, can modulate adrenergic vasoconstriction by central reduction of sympathetic outflow and by peripheral effects in animal models. We investigated whether NO inhibits post–synaptic α‐1‐adrenergic neurotransmission in humans. To accomplish this we performed intravenous phenylephrine dose‐response experiments under three conditions: during a contro...

We hypothesize that upright cognitive impairment in patients with postural tachycardia syndrome (POTS) is caused by reduced cerebral blood flow (CBF). The CBF velocity (CBFv) measured by transcranial Doppler ultrasound decreased excessively during 70° tilt in a minority of patients with intermittent hyperpnea/hypocapnia. Incremental tilt showed no...

Chronic Fatigue Syndrome (CFS), with orthostatic intolerance is characterized by neurocognitive deficits, impaired working memory, concentration, and information processing. In CFS, upright tilting (HUT) caused decreased cerebral blood flow velocity (CBFv) related to hyperpnea/hypocapnia and impaired cerebral autoregulation; increasing orthostatic...

Decreased upright cerebral blood flow (CBF) with hyperpnea and hypocapnia is seen in a minority of patients with postural tachycardia syndrome (POTS). More often, CBF is not decreased despite upright neurocognitive dysfunction. This may result from time-dependent changes in CBF. We hypothesized that increased oscillations in CBF occurs in POTS (N =...

Cognitive deficits are characteristic of postural tachycardia syndrome (POTS). Intact nitrergic nitric oxide (NO) is important to cerebral blood flow (CBF) regulation, to neurovascular coupling, and to cognitive efficacy. POTS patients often experience defective (NO) mediated vasodilation caused by oxidative stress. We previously showed dilation of...

Hyperventilation and reduced cerebral blood flow velocity can occur in postural tachycardia syndrome (POTS). We studied orthostatically intolerant patients, with suspected POTS, with a chief complaint of upright dyspnea. On the basis of our observations of an immediate reduction of cerebral blood flow velocity with orthostasis, we hypothesize that...

Cognitive deficits are characteristic of postural tachycardia syndrome (POTS). Intact nitrergic nitric oxide (NO) is important to cerebral blood flow (CBF) regulation, to neurovascular coupling, and to cognitive efficacy. POTS patients often experience defective (NO) mediated vasodilation caused by oxidative stress. We used combined transcranial Do...

Measureable upright cognitive loss occurs in postural tachycardia syndrome (POTS). Some POTS patients have impaired cognition associated with an excessive decrease in mean cerebral blood flow (CBF) equivalent to a loss of static autoregulation. More often, however, CBF is not decreased but a demonstrable loss of neurovascular coupling occurs and ma...

Adolescents with postural tachycardia syndrome (POTS) often experience ill-defined cognitive impairment referred to by patients as "brain fog." The objective of this study was to evaluate the symptom of brain fog as a means of gaining further insight into its etiology and potential palliative interventions. Eligible subjects who reported having bee...

Postural tachycardia syndrome (POTS) is a chronic form of orthostatic intolerance. Neuropathic POTS is characterized by decreased adrenergic vasoconstriction, while hyperadrenergic POTS exhibits increased adrenergic vasoconstriction. We hypothesized that midodrine, an α1-adrenergic receptor agonist, would increase calf vascular resistance (CVR), de...

Withdrawal of muscle sympathetic nerve activity (MSNA) may not be necessary for the precipitous fall of peripheral arterial resistance and arterial pressure (AP) during vasovagal syncope (VVS). We tested the hypothesis that the MSNA-AP baroreflex entrainment is disrupted prior to VVS regardless of MSNA withdrawal using the phase synchronization bet...

Spontaneous fluctuation indices of cardiovagal baroreflex have been suggested to be inaccurate measures of baroreflex function during orthostatic stress when compared to alternate open-loop methods (eg. neck pressure/suction, modified Oxford). We therefore tested the hypothesis that spontaneous fluctuation measurements accurately reflect local baro...

The modified Oxford maneuver is the reference standard for assessing arterial baroreflex function. The maneuver comprises systemic bolus injection of 100µg sodium nitroprusside (SNP) followed by 150µg phenylephrine. On the one hand, this results in an increase in oxyhemoglobin and total hemoglobin followed by a decrease within the cerebral sample v...

Individuals with orthostatic intolerance (OI) often experience ill‐defined neurocognitive impairment, typically referred to by patients as brain fog. The objective of this study was to evaluate brain fog to further insight on its mechanism and potential treatments. Eligible subjects, 14–29 yrs diagnosed with OI, were recruited through ads on online...

We investigated whether the nitric oxide donor sodium nitroprusside (SNP) dilates and phenylephrine constricts the MCA in 10 supine young healthy volunteers. We combined transcranial Doppler (TCD) measurements of the MCA with near infrared spectroscopy (NIRS) over the frontal cortex. Cerebral oxyhemoglobin and total hemoglobin increased by 14±1 and...

Withdrawal of muscle sympathetic nerve activity (MSNA) may not be necessary for the precipitous fall of peripheral arterial resistance and blood pressure (BP) during vasovagal syncope (VVS). We tested the hypothesis that the MSNA‐BP baroreflex entrainment is disrupted prior to VVS regardless if MSNA is withdrawn. We measured phase synchronization d...

Electrical impedance spectroscopic (EIS) technique is a novel method to non-invasively measure the fluid volume in the Vc, Vi, and Vb compartments in humans. The aim is to use EIS technology to measure Vc, Vi, and Vb volume change during HD in end-stage renal disease (ESRD) patients in the outpatient or chronic unit (CU) and in the inpatient or acu...

Local cutaneous heating causes vasodilation as an initial first peak, a nadir, and increase to plateau. Reactive oxygen species (ROS) modulate the heat plateau in healthy controls. The initial peak, due to C-fibre nociceptor-mediated axon reflexes, is blunted with local anesthetics, and may serve as a surrogate for the cutaneous response to periphe...

Chronic fatigue syndrome (CFS) is a complex illness, which is often misdiagnosed as a psychiatric illness. In two previous reports, using (1)H MRSI, we found significantly higher levels of ventricular cerebrospinal fluid (CSF) lactate in patients with CFS relative to those with generalized anxiety disorder and healthy volunteers (HV), but not relat...

Local cutaneous heating causes vasodilation as an initial peak, a nadir, and increase to plateau. We showed reactive oxygen species (ROS) produced by Ang‐II via NADPH and xanthine oxidase, modulates this response in healthy controls. The initial peak, due to C‐fibre nociceptor‐mediated axon reflex and local release of calcitonin gene‐related peptid...

Thoracic hypovolemia and hyperpnea contribute to the nonlinear time‐dependent hemodynamic instability of vasovagal syncope. We used a phase synchronization index (PhSI) to describe coupling between systolic BP (SBP), RR‐interval (RR), and ventilation, and a directional index (DI) of coupling. We hypothesized normal AP‐RR PhSI during early 70° head‐...

Measurement of cardiovagal baroreflex gain is often evaluated using spontaneous fluctuations in blood pressure (BP) and R‐R interval. However, spontaneous indices (SI) only provide a slope of the baroreflex curve at operating points (OP) and may not adequately identify changes in sensitivity and range of reflex function produced by the reference st...

Neurocognition is impaired in chronic fatigue syndrome (CFS). We propose that the impairment relates to postural cerebral hemodynamics. Twenty-five CFS subjects and twenty control subjects underwent incremental upright tilt at 0, 15, 30, 45, 60, and 75° with continuous measurement of arterial blood pressure and cerebral blood flow velocity (CBFV)....

CFS (chronic fatigue syndrome) is commonly co-morbid with POTS (postural tachycardia syndrome). Individuals with CFS/POTS experience unrelenting fatigue, tachycardia during orthostatic stress and ill-defined neurocognitive impairment, often described as 'mental fog'. We hypothesized that orthostatic stress causes neurocognitive impairment in CFS/PO...

Models of microgravity are linked to excessive constitutive nitric oxide (NO) synthase (NOS), splanchnic vasodilation, and orthostatic intolerance. Normal-flow postural tachycardia syndrome (POTS) is a form of chronic orthostatic intolerance associated with splanchnic hyperemia. To test the hypothesis that there is excessive constitutive NOS in POT...

Low flow postural tachycardia syndrome (LFP) is associated with vasoconstriction, reduced cardiac output, increased plasma angiotensin II, reduced bioavailable nitric oxide (NO), and oxidative stress. We tested whether ascorbate would improve cutaneous NO and reduce vasoconstriction when delivered systemically. We used local cutaneous heating to 42...

We hypothesize that, after a sudden decrease in cerebral blood flow velocity (CBFV) in adolescents, a faint, rapid hyperemic pulsatile CBFV occurs upon the patient's return to the supine position and is associated with postsyncopal headache. This case-control study involved 16 adolescent subjects with a history of fainting and headaches. We induced...

While orthostatic tachycardia is the hallmark of postural tachycardia syndrome (POTS), orthostasis also initiates increased minute ventilation (Ve) and decreased end-tidal CO(2) in many patients. We hypothesized that chemoreflex sensitivity would be increased in patients with POTS. We therefore measured chemoreceptor sensitivity in 20 POTS (16 wome...

Local cutaneous heating produces vasodilation that is largely nitric oxide (NO) dependent. We showed that angiotensin II (ANG II) attenuates this by an ANG II receptor, type 1 (AT1R)-dependent mechanism that is reversible with the antioxidant ascorbate, indicating oxidative stress. Reactive oxygen species (ROS) produced by ANG II employ NADPH and x...

To evaluate the response to rectal distension in children with chronic constipation and children with chronic constipation and encopresis. We studied 27 children, aged 3 to 16 years, with chronic constipation; 12 had encopresis. Anorectal motility was measured with a solid state catheter. When the catheter was located in the internal sphincter, the...

Increasing arterial blood pressure (AP) decreases ventilation, whereas decreasing AP increases ventilation in experimental animals. To determine whether a "ventilatory baroreflex" exists in humans, we studied 12 healthy subjects aged 18-26 yr. Subjects underwent baroreflex unloading and reloading using intravenous bolus sodium nitroprusside (SNP) f...

Loss of the cardiovagal baroreflex (CVB), thoracic hypovolemia, and hyperpnea contribute to the nonlinear time-dependent hemodynamic instability of vasovagal syncope. We used a nonlinear phase synchronization index (PhSI) to describe the extent of coupling between cardiorespiratory parameters, systolic blood pressure (SBP) or arterial pressure (AP)...

POTS have increased minute ventilation (V E ) and decreased end tidal carbon dioxide (ETCO 2 ) compared to healthy subjects. Chemoreceptor sensitivity was measured in 18 POTS (14F, 4M), 10 healthy controls (6F, 4M) 16–35 years old by exposing them to eucapneic hyperoxia‐30%oxygen, eucapneic hypoxia (10%oxygen) and hypercapnia 30%oxygen+5%carbon dio...

Nonlinear phase synchronization (PhS) between systolic BP (SBP) and R‐R interval (R‐R) can measure cardiovagal baroreflex. We hypothesized that desynchronization (loss of baroreflex) occurs prior to fainting. 15 fainters (F) and 15 control subjects (C) aged 15–25 underwent 70° head‐up tilt. Hilbert transform followed by bandpass filter (0.005–0.5 H...

Initial orthostatic hypotension is common in children. Isometric handgrip increases arterial pressure, central blood volume, cardiac output, and total peripheral resistance. We show that in 14 subjects with initial orthostatic hypotension, isometric handgrip coupled with standing abolished symptoms of initial orthostatic hypotension and minimized d...

We used breath-holding during inspiration as a model to study the effect of pulmonary stretch on sympathetic nerve activity. Twelve healthy subjects (7 females, 5 males; 19-27 years) were tested while they performed an inspiratory breath-hold, both supine and during a 60 degrees head-up tilt (HUT 60). Heart rate (HR), mean arterial blood pressure (...

Vasovagal syncope may be due to a transient cerebral hypoperfusion that accompanies frequency entrainment between arterial pressure (AP) and cerebral blood flow velocity (CBFV). We hypothesized that cerebral autoregulation fails during fainting; a phase synchronization index (PhSI) between AP and CBFV was used as a nonlinear, nonstationary, time-de...

We report here that exposure of large vessel EC to clinically relevant, atherogenic levels of native LDL (240 mg cholesterol/dL) increases the incidence and severity of shear-induced EC plasma membrane wound injury in vitro. The proportion of LDL-treated EC that survived mechanical shearing in suspension was significantly less (20%; p < 0.005) than...

While higher frequency oscillations (0.021-0.6 Hz) in cutaneous blood flow measured by laser Doppler flowmetry (LDF) relate to oscillations in blood pressure and sympathetic nerve activity, very low-frequency oscillations (VLF, 0.0095-0.021 Hz) do not. The authors investigated whether VLF LDF power is nitric oxide (NO) specific. LDF combined with i...

Postural tachycardia syndrome (POTS), a chronic form of orthostatic intolerance, has signs and symptoms of lightheadedness, loss of vision, headache, fatigue, and neurocognitive deficits consistent with reductions in cerebrovascular perfusion. We hypothesized that young, normocapnic POTS patients exhibit abnormal cerebral autoregulation (CA) that r...

Postural tachycardia syndrome (POTS) is associated with increased plasma angiotensin II (Ang II). Ang II administered in the presence of NO synthase inhibition with nitro-L-arginine (NLA) and Ang II type 1 receptor blockade with losartan produces vasodilation during local heating in controls. We tested whether this angiotensin-mediated vasodilation...

Prior studies indicate that fainting relates to thoracic hypovolemia and increased vascular resistance until late during head‐up tilt (HUT). Splanchnic resistance, cardiac output and BP decreased throughout HUT. We investigated alterations of baroreflex activity that occur with time dependent changes in HR, BP and TPR, using BP Mayer waves to estim...

Previous studies indicate pulmonary stretch reflex produces bradycardia and hypotension. We used deep inspiratory apnea (IA) as a model to study pulmonary stretch reflex. Twelve healthy subjects (9 females, 3 males; 19‐27 yrs) performed a maximal inspiratory apnea both supine and after 10 min of head up tilt to 70 degrees (HUT). Heart rate (HR), bl...

Orthostatic intolerance (OI) is defined by symptoms and signs while upright, relieved by recumbency. Included are symptoms of CNS malperfusion. Chronic OI, also known as postural tachycardia syndrome (POTS), is associated with excessive upright tachycardia. We hypothesized that CNS symptoms are due to defects of dynamic and static cerebral autoregu...

Our prior studies indicated that postural fainting relates to thoracic hypovolemia. A supranormal increase in initial vascular resistance was sustained by increased peripheral resistance until late during head-up tilt (HUT), whereas splanchnic resistance, cardiac output, and blood pressure (BP) decreased throughout HUT. Our aim in the present study...

We determined the occurrence of fructose malabsorption in pediatric patients with previous diagnoses of abdominal pain caused by a functional bowel disorder, whether the restriction of fructose intake changes the reporting of symptoms, the role of fructose dosage, and the severity of resultant symptoms. We administered a fructose breath test to chi...

Acetylcholine-induced endothelium-dependent vasodilation in conduit arteries primarily depends on nitric oxide (NO). However, the biochemical mediators in the microvasculature remain less well defined. We tested whether prostaglandins and NO are responsible for cutaneous acetylcholine-mediated vasodilation and if they interact to modulate vasodilat...

The vasodilation response to local cutaneous heating is nitric oxide (NO) dependent and blunted in postural tachycardia but reversed by angiotensin II (ANG II) type 1 receptor (AT(1)R) blockade. We tested the hypothesis that a localized infusion of ANG II attenuates vasodilation to local heating in healthy volunteers. We heated the skin of a calf t...

Our prior studies indicated that postural fainting relates to splanchnic hypervolemia and thoracic hypovolemia during orthostasis. We hypothesized that thoracic hypovolemia causes excessive sympathetic activation, increased respiratory tidal volume, and fainting involving the pulmonary stretch reflex. We studied 18 patients 13-21 yr old, 11 who fai...

Low-flow postural tachycardia syndrome (POTS) is associated with increased plasma angiotensin II (ANG II) and reduced neuronal nitric oxide (NO), which decreases NO-dependent vasodilation. We tested whether the ANG II type 1 receptor (AT(1)R) antagonist losartan would improve NO-dependent vasodilation in POTS patients. Furthermore, if the action of...