Dynamic cardiorespiratory interaction during head-up tilt-mediated presyncope

2004 ◽  
Vol 287 (6) ◽  
pp. H2510-H2517 ◽  
Author(s):  
S. Krishnamurthy ◽  
X. Wang ◽  
D. Bhakta ◽  
E. Bruce ◽  
J. Evans ◽  
...  
Keyword(s):  
Transfer Functions ◽  
Cerebral Blood Flow Velocity ◽  
Cerebral Hemodynamics ◽  
Frequency Region ◽  
Cardiorespiratory Interaction ◽  
Head Up Tilt ◽  
Unexplained Syncope ◽  
End Tidal ◽  
The Relationship ◽  
Reactivity Change

In 28 healthy adults, we compared the dynamic interaction between respiration and cerebral autoregulation in 2 groups of subjects: those who did and did not develop presyncopal symptoms during 70° passive head-up tilt (HUT), i.e., nonpresyncopal (23 subjects) and presyncopal (5 subjects). Airflow, CO2, cerebral blood flow velocity (CBF), ECG, and blood pressure (BP) were recorded. To determine whether influences of mean BP (MBP) and systolic SP (SBP) on CBF were altered in presyncopal subjects, coherencies and transfer functions between these variables and mean and peak CBF (CBFm and CBFp) were estimated. To determine the influence of end-tidal CO2 (ETco2) on CBF, the relative CO2 reactivity (%change in CBFm per mmHg change in ETco2) was calculated. We found that in presyncopal subjects before symptoms during HUT, coherence between SBP and CBFp was higher ( P = 0.02) and gains of transfer functions between BP (MBP and SBP) and CBFm were larger (MBP, P = 0.01; SBP, P = 0.01) in the respiratory frequency region. In the last 3 min before presyncope, presyncopals had a reduced relative CO2 reactivity ( P = 0.005), likely a consequence of the larger decrease in ETco2. We hypothesize that the CO2-mediated increase in resistance attenuates autoregulation such that the relationship between systemic and cerebral hemodynamics is enhanced. Our results suggest that an altered cardiorespiratory interaction involving cerebral hemodynamics may contribute in the cascade of events during tilt that culminate in unexplained syncope.

scholarly journals The cerebrovascular response to lower-body negative pressure vs. head-up tilt

2017 ◽  
Vol 122 (4) ◽  
pp. 877-883 ◽  
Author(s):  
Anne-Sophie G. T. Bronzwaer ◽  
Jasper Verbree ◽  
Wim J. Stok ◽  
Mat J. A. P. Daemen ◽  
Mark A. van Buchem ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Negative Pressure ◽  
Cerebral Blood Flow Velocity ◽  
Lower Body Negative Pressure ◽  
Orthostatic Stress ◽  
Lower Body ◽  
Head Up Tilt ◽  
End Tidal ◽  
Pronounced Reduction

Lower-body negative pressure (LBNP) has been proposed as a MRI-compatible surrogate for orthostatic stress. Although the effects of LBNP on cerebral hemodynamic behavior have been considered to reflect those of orthostatic stress, a direct comparison with actual orthostasis is lacking. We assessed the effects of LBNP (−50 mmHg) vs. head-up tilt (HUT; at 70°) in 10 healthy subjects (5 female) on transcranial Doppler-determined cerebral blood flow velocity (CBF v) in the middle cerebral artery and cerebral perfusion pressure (CPP) as estimated from the blood pressure signal (finger plethysmography). CPP was maintained during LBNP but decreased after 2 min in response to HUT, leading to an ~15% difference in CPP between LBNP and HUT ( P ≤ 0.020). Mean CBF v initially decreased similarly in response to LBNP and for HUT, but, from minute 3 on, the decline became ~50% smaller ( P ≤ 0.029) during LBNP. The reduction in end-tidal Pco2 partial pressure (PetCO2) was comparable but with an earlier return toward baseline values in response to LBNP but not during HUT ( P = 0.008). We consider the larger decrease in CBF v during HUT vs. LBNP attributable to the pronounced reduction in PetCO2 and to gravitational influences on CPP, and this should be taken into account when applying LBNP as an MRI-compatible orthostatic stress modality. NEW & NOTEWORTHY Lower-body negative pressure (LBNP) has the potential to serve as a MRI-compatible surrogate of orthostatic stress but a comparison with actual orthostasis was lacking. This study showed that the pronounced reduction in end-tidal Pco2 together with gravitational effects on the brain circulation lead to a larger decline in cerebral blood flow velocity in response to head-up tilt than during lower-body negative pressure. This should be taken into account when employing lower-body negative pressure as MRI-compatible alternative to orthostatic stress.

Contrasting effects of isocapnic and hypocapnic hyperventilation on orthostatic circulatory control

2008 ◽  
Vol 105 (4) ◽  
pp. 1069-1075 ◽  
Author(s):  
Roland D. Thijs ◽  
Joost G. van den Aardweg ◽  
Robert H. A. M. Reijntjes ◽  
J. Gert van Dijk ◽  
Johannes J. van Lieshout
Keyword(s):  
Heart Rate ◽  
Supine Position ◽  
Healthy Subjects ◽  
Cerebral Blood Flow Velocity ◽  
Factors Affecting ◽  
Tilted Position ◽  
Circulatory Control ◽  
Head Up Tilt ◽  
End Tidal ◽  
Normal Ventilation

The effects of hyperventilation (HV) on mean arterial pressure (MAP) are variable. To identify factors affecting the MAP response to HV, we dissected the effects of hypocapnic HV (HHV) and isocapnic HV (IHV) and evaluated the effects of acute vs. prolonged HHV. In 11 healthy subjects the cardio- and cerebrovascular effects of HHV and IHV vs. normal ventilation were examined for 15 min in the supine position and also for 15 min during 60° head-up tilt. The end-tidal CO2 of the HHV condition was set at 15–20 mmHg. With HHV in the supine position, mean cerebral blood flow velocity (mCBFV) declined [95% confidence interval (CI) −43 to −34%], heart rate (HR) increased (95% CI 7 to 16 beats/min), but MAP did not change (95% CI −1 to 6 mmHg). However, an augmentation of the supine MAP was observed in the last 10 min of HHV compared with the first 5 min of HHV (95% CI 2 to 12 mmHg). During HHV in the tilted position mCBFV declined (95% CI −28 to −12%) and MAP increased (95% CI 3 to 11 mmHg) without changes in HR. With supine IHV, mCBFV decreased (95% CI −14 to −4%) and MAP increased (95% CI 1 to 13 mmHg) without changes in HR. During IHV in the tilted position MAP was further augmented (95% CI 11 to 20 mmHg) without changes in CBFV or HR. Preventing hypocapnia during HV resulted in a higher MAP, suggesting two contrasting effects of HV on MAP: hypocapnia causing vasodepression and hyperpnea without hypocapnia acting as a vasopressor.

scholarly journals Cardiorespiratory Functioning in Youth with Persistent Post-Concussion Symptoms: A Pilot Study

2021 ◽  
Vol 10 (4) ◽  
pp. 561
Author(s):  
Aliyah Snyder ◽  
Christopher Sheridan ◽  
Alexandra Tanner ◽  
Kevin Bickart ◽  
Molly Sullan ◽  
...  
Keyword(s):  
Processing Speed ◽  
Mean Value ◽  
Exhaled Breath ◽  
Post Injury ◽  
The Past ◽  
Neurobehavioral Outcomes ◽  
End Tidal ◽  
Relationship Of ◽  
The Relationship ◽  
End Tidal Co2

Dysregulation of the autonomic nervous system (ANS) may play an important role in the development and maintenance of persistent post-concussive symptoms (PPCS). Post-injury breathing dysfunction, which is influenced by the ANS, has not been well-studied in youth. This study evaluated cardiorespiratory functioning at baseline in youth patients with PPCS and examined the relationship of cardiorespiratory variables with neurobehavioral outcomes. Participants were between the ages of 13–25 in two groups: (1) Patients with PPCS (concussion within the past 2–16 months; n = 13) and (2) non-injured controls (n = 12). Capnometry was used to obtain end-tidal CO2 (EtCO2), oxygen saturation (SaO2), respiration rate (RR), and pulse rate (PR) at seated rest. PPCS participants exhibited a reduced mean value of EtCO2 in exhaled breath (M = 36.3 mmHg, SD = 2.86 mmHg) and an altered inter-correlation between EtCO2 and RR compared to controls. Neurobehavioral outcomes including depression, severity of self-reported concussion symptoms, cognitive catastrophizing, and psychomotor processing speed were correlated with cardiorespiratory variables when the groups were combined. Overall, results from this study suggest that breathing dynamics may be altered in youth with PPCS and that cardiorespiratory outcomes could be related to a dimension of neurobehavioral outcomes associated with poorer recovery from concussion.

scholarly journals The Relationship between Resistance Exercise Performance and Ventilatory Efficiency after Beetroot Juice Intake in Well-Trained Athletes

Nutrients ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 1094
Author(s):  
Noemí Serra-Payá ◽  
Manuel Vicente Garnacho-Castaño ◽  
Sergio Sánchez-Nuño ◽  
Lluís Albesa-Albiol ◽  
Montserrat Girabent-Farrés ◽  
...  
Keyword(s):  
Resistance Exercise ◽  
Exercise Test ◽  
Exercise Performance ◽  
Beetroot Juice ◽  
Experimental Conditions ◽  
Double Blind ◽  
Ventilatory Efficiency ◽  
End Tidal ◽  
Oxygen Uptake Efficiency Slope ◽  
The Relationship

The assessment of ventilatory efficiency is critical to understanding the matching of ventilation (VE) and perfusion in the lungs during exercise. This study aimed to establish a causal physiological relationship between ventilatory efficiency and resistance exercise performance after beetroot juice (BJ) intake. Eleven well-trained males performed a resistance exercise test after drinking 140 mL of BJ (~12.8 mmol NO3−) or a placebo (PL). Ventilatory efficiency was assessed by the VE•VCO2−1 slope, the oxygen uptake efficiency slope and the partial pressure of end-tidal carbon dioxide (PetCO2). The two experimental conditions were controlled using a randomized, double-blind crossover design. The resistance exercise test involved repeating the same routine twice, which consisted of wall ball shots plus a full squat (FS) with a 3 min rest or without a rest between the two exercises. A higher weight lifted was detected in the FS exercise after BJ intake compared with the PL during the first routine (p = 0.004). BJ improved the VE•VCO2−1 slope and the PetCO2 during the FS exercise in the first routine and at rest (p < 0.05). BJ intake improved the VE•VCO2−1 slope and the PetCO2 coinciding with the resistance exercise performance. The ergogenic effect of BJ could be induced under aerobic conditions at rest.

scholarly journals Improvement of Snowgauge Collection Efficiency through a knowledge of solid precipitation fallspeed

2021 ◽  
Author(s):  
Nicolas R. Leroux ◽  
Julie M. Thériault ◽  
Roy Rasmussen
Keyword(s):  
Wind Speed ◽  
Transfer Function ◽  
Transfer Functions ◽  
Collection Efficiency ◽  
Particle Diameter ◽  
Field Site ◽  
Solid Precipitation ◽  
Gauge Data ◽  
The Relationship ◽  
Measured Particle

AbstractThe collection efficiency (CE) of a typical gauge-shield configuration decreases with increasing wind speed, with a high scatter for a given wind speed. The scatter in the CE for a given wind speed arises in part from the variability in the characteristics of falling snow and atmospheric turbulence. This study uses weighing gauge data collected at the Marshall Field Site near Boulder, Colorado during the WMO Solid Precipitation InterComparison Experiment (SPICE) to show that the scatter in the collection efficiency can be reduced by considering the fallspeed of solid precipitation particle types. Particle diameter and fallspeed data from a laser disdrometer were used to arrive at this conclusion. In particular, the scatter in the CE of an unshielded snow gauge and a single Alter shield snow gauge is shown to be largely produced by the variation in measured particle fallspeed. The CE was divided into two classes depending on the measured mean-event particle fallspeed. Slower-falling particles were associated with a lower CE. A new transfer function (i.e. the relationship between CE and other meteorological variables, such as wind speed or air temperature) that includes the fallspeed of the hydrometeors was developed. The RMSE of the adjusted precipitation with respect to a weighing gauge placed in a Double Fence Intercomparison Reference was lower than using previously developed transfer functions. This shows that the measured fallspeed of solid precipitation with a laser disdrometer accounts for a large amount of the observed scatter in weighing gauge collection efficiency.

scholarly journals Inadequate sympathovagal balance in response to orthostatism in patients with unexplained syncope and a positive head up tilt test

Heart ◽  
1999 ◽  
Vol 82 (3) ◽  
pp. 312-318 ◽  
Author(s):  
C Kouakam ◽  
D Lacroix ◽  
N Zghal ◽  
R Logier ◽  
D Klug ◽  
...  
Keyword(s):  
Tilt Test ◽  
Sympathovagal Balance ◽  
Head Up Tilt ◽  
Unexplained Syncope ◽  
Head Up Tilt Test

scholarly journals Analysis of the time series of waste water quality at the inflow of the wastewater treatment plant and transfer functions

2014 ◽  
Vol 62 (1) ◽  
pp. 55-59 ◽  
Author(s):  
Ivan Nesmerak ◽  
Sarka D. Blazkova
Keyword(s):  
Time Series ◽  
Wastewater Treatment ◽  
Wastewater Treatment Plant ◽  
Transfer Functions ◽  
Treatment Plant ◽  
Total Precipitation ◽  
Periodic Components ◽  
The Relationship ◽  
Pollution Loads ◽  
Daily Total

Abstract Time series of the daily total precipitation, daily wastewater discharges and daily concentrations and pollution loads of BOD5, COD, SS, N-NH4, Ntot and Ptot were analyzed at the inflow to the wastewater treatment plant (WWTP) for a larger city in 2004-2009 (WWTP is loaded by pollution from 435,000 equivalent inhabitants). The time series of the outflow from a WWTP was also available for 2007. The time series of daily total precipitation, daily wastewater discharges, concentrations and pollution loads at the inflow and outflow from the WWTP were standardized year by year to exclude a long-term trend, and periodic components with a period of 7 days and 365 days (and potentially also 186.5 days) were excluded from the standardized series. However, these two operations eliminated only a small part of the variance; there was a substantial reduction in the variance only for ammonium nitrogen and total nitrogen at the inflow and outflow from a WWTP. The relationship between the inflow into a WWTP and the outflow from a WWTP for the concentrations and pollution loads was described by simple transfer functions (SISO models) and more complicated transfer functions (MISO models). A simple transfer function (SISO model) was employed to describe the relationship between the daily total precipitation and the wastewater discharge.

Abstract 13216: Initial Survey of Respiratory Mechanics During Prehospital Bag Ventilation

Circulation ◽  
2021 ◽  
Vol 144 (Suppl_2) ◽  
Author(s):  
Betty Y Yang ◽  
Jennifer E Blackwood ◽  
Jenny Shin ◽  
Sally Guan ◽  
Mengqi Gao ◽  
...  
Keyword(s):  
Tidal Volume ◽  
Respiratory Mechanics ◽  
Predicted Body Weight ◽  
Convenience Sample ◽  
Measuring Device ◽  
Respiratory Parameters ◽  
Initial Survey ◽  
Post Intubation ◽  
End Tidal ◽  
The Relationship

Introduction: Respiratory mechanics, such as tidal volume and inspiratory pressures, affect outcome in hospitalized patients with respiratory failure. The ability to accurately measure respiratory mechanics in the prehospital setting is limited, thus the relationship between prehospital respiratory mechanics and clinical outcome is not well understood. In this feasibility study, we examined respiratory mechanics of bag-valve mask (BVM) ventilation by emergency medical services (EMS) using a novel in-line measuring device during a period when agencies switched from larger to smaller ventilation bags. Methods: This prospective cohort study included a convenience sample of adult patients who received BVM ventilation by EMS, from August 2018 to January 2020, in Bellevue, Washington. The airway monitoring device was applied by paramedics after intubation to passively record in black box mode, until termination of efforts or hospital arrival. Respiratory parameters included tidal volume, airway pressure, flow rates, end-tidal carbon dioxide, and respiratory rate. Prehospital agencies transitioned from large (1500 mL) to small (1000 mL) ventilation bags during the study period. Results: 7371 post-intubation breaths were measured in 54 patients, 32 treated for out-of-hospital cardiac arrest (OHCA) and 22 treated for non-arrest conditions, primarily respiratory etiology. EMS ventilated 19 patients with a small bag and 35 patients with a large bag. Ventilation with a smaller bag was characterized by less variability in tidal volumes and higher proportion of breaths delivered within 4-10 mL/kg of predicted body weight (Figure) (p<0.05). Conclusions: Respiratory mechanics can be measured in EMS patients receiving BVM ventilation following intubation. Ventilation with a smaller bag might reduce variation in tidal volume, but further study is needed. These data provide the first evaluation of respiratory mechanics during manual ventilation provided by EMS.

Case 29: Hypocapnic Cerebral Hypoperfusion

2019 ◽  
pp. 185-188
Author(s):  
Peter Novak
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Flow Velocity ◽  
Autonomic Dysfunction ◽  
Blood Flow Velocity ◽  
Cerebral Blood Flow Velocity ◽  
Cerebral Hypoperfusion ◽  
Tilt Test ◽  
Excessive Sleepiness ◽  
End Tidal

This case presents a patient with extreme fatigue and excessive sleepiness. The tilt test provoked decline in cerebral blood flow velocity (CBFv) associated with decline in end tidal CO2, indicative of hypocapnic cerebral hypoperfusion (HYCH). There was also mild small fiber neuropathy affecting predominantly autonomic fibers associated with mild autonomic dysfunction.

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