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.

Age dependency of cardiovascular autonomic responses to head-up tilt in healthy subjects

2004 ◽  
Vol 96 (6) ◽  
pp. 2333-2340 ◽  
Author(s):  
Tomi Laitinen ◽  
Leo Niskanen ◽  
Ghislaine Geelen ◽  
Esko Länsimies ◽  
Juha Hartikainen
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
High Frequency ◽  
Healthy Subjects ◽  
Baroreflex Sensitivity ◽  
Low Frequency ◽  
Upright Position ◽  
Vascular Responses ◽  
Autonomic Responses ◽  
Head Up Tilt

In elderly subjects, heart rate responses to postural change are attenuated, whereas their vascular responses are augmented. Altered strategy in maintaining blood pressure homeostasis during upright position may result from various cardiovascular changes, including age-related cardiovascular autonomic dysfunction. This exploratory study was conducted to evaluate impact of age on cardiovascular autonomic responses to head-up tilt (HUT) in healthy subjects covering a wide age range. The study population consisted of 63 healthy, normal-weight, nonsmoking subjects aged 23–77 yr. Five-minute electrocardiogram and finger blood pressure recordings were performed in the supine position and in the upright position 5 min after 70° HUT. Stroke volume was assessed from noninvasive blood pressure signals by the arterial pulse contour method. Heart rate variability (HRV) and systolic blood pressure variability (SBPV) were analyzed by using spectral analysis, and baroreflex sensitivity (BRS) was assessed by using sequence and cross-spectral methods. Cardiovascular autonomic activation during HUT consisted of decreases in HRV and BRS and an increase in SBPV. These changes became attenuated with aging. Age correlated significantly with amplitude of HUT-stimulated response of the high-frequency component ( r = -0.61, P < 0.001) and the ratio of low-frequency to high-frequency power of HRV ( r = -0.31, P < 0.05) and indexes of BRS (local BRS: r = -0.62, P < 0.001; cross-spectral baroreflex sensitivity in the low-frequency range: r = -0.38, P < 0.01). Blood pressure in the upright position was maintained well irrespective of age. However, the HUT-induced increase in heart rate was more pronounced in the younger subjects, whereas the increase in peripheral resistance was predominantly observed in the older subjects. Thus it is likely that whereas the dynamic capacity of cardiac autonomic regulation decreases, vascular responses related to vasoactive mechanisms and vascular sympathetic regulation become augmented with increasing age.

Pet CO2 inversely affects MSNA response to orthostatic stress

2001 ◽  
Vol 281 (3) ◽  
pp. H1040-H1046 ◽  
Author(s):  
J. Kevin Shoemaker ◽  
Debbie D. O'Leary ◽  
Richard L. Hughson
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Cardiac Output ◽  
Orthostatic Intolerance ◽  
Muscle Sympathetic Nerve Activity ◽  
Peripheral Resistance ◽  
Burst Frequency ◽  
Head Up Tilt ◽  
End Tidal ◽  
Combined Data

Arterial hypocapnia has been associated with orthostatic intolerance. Therefore, we tested the hypothesis that hypocapnia may be detrimental to increases in muscle sympathetic nerve activity (MSNA) and total peripheral resistance (TPR) during head-up tilt (HUT). Ventilation was increased ∼1.5 times above baseline for each of three conditions, whereas end-tidal Pco 2 (Pet CO2 ) was clamped at normocapnic (Normo), hypercapnic (Hyper; +5 mmHg relative to Normo), and hypocapnic (Hypo; −5 mmHg relative to Normo) conditions. MSNA (microneurography), heart rate, blood pressure (BP, Finapres), and cardiac output (Q, Doppler) were measured continuously during supine rest and 45° HUT. The increase in heart rate when changing from supine to HUT ( P < 0.001) was not different across Pet CO2 conditions. MSNA burst frequency increased similarly with HUT in all conditions ( P < 0.05). However, total MSNA and the increase in total amplitude relative to baseline (%ΔMSNA) increased more when changing to HUT during Hypo compared with Hyper ( P < 0.05). Both BP and Q were higher during Hyper than both Normo and Hypo (main effect; P < 0.05). Therefore, the MSNA response to HUT varied inversely with levels of Pet CO2 . The combined data suggest that augmented cardiac output with hypercapnia sustained blood pressure during HUT leading to a diminished sympathetic response.

scholarly journals Relation of body mass index (BMI) with cardiovascular response to head up tilt in healthy subjects

2020 ◽  
Vol 15 (1) ◽  
pp. 6-10
Author(s):  
Sadia Afrin Rimi ◽  
Shamima Sultana ◽  
Iffat Rezwana ◽  
Sultana Ferdousi
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Systolic Blood Pressure ◽  
Healthy Subjects ◽  
Cardiovascular Response ◽  
Tilt Test ◽  
Tilt Table ◽  
Chi Square ◽  
Female Head ◽  
Head Up Tilt

Background: Tilt table test is used for the last few decades to detect cause in unexplained syncope. The response to tilting may vary physiologically with obesity. Objective: To assess the relationship of BMI to cardiovascular response to tilting. Methods: This experimental study was conducted from March 2019 to Feb 2020 on 90 healthy subjects with different BMI. Fifty one subjects of both gender with BMI 18.5-24.9 kg/m2 were included in the non-obese group and 39 subjects of both gender with BMI of 25-29.9 kg/m2 were included in overweight group and they were further subdivided into male and female. Head up tilting was done for 10 minutes at 600 by using a motorized tilt table. Systolic blood pressure (SBP), diastolic blood pressure (DBP) were recorded by an automatic sphygmomanometer. Heart rate (HR) and peripheral capillary oxygen saturation (SpO2) were measured by a pulse oximeter. For statistical analysis, Independent sample ‘t’ test, Pearson’s correlation test and Chi square tests were applied. Results: Significantly smaller rise of heart rate was observed in overweight males and greater fall of systolic blood pressure was observed in overweight females. Conclusion: This study concluded that over weight is associated with reduced orthostatic tolerance to head up tilt test in both genders. J Bangladesh Soc Physiol. 2020, June; 15(1): 6-10

Circulatory adaptation to orthostatic stress in healthy 10–14-year-old children investigated in a general practice

1991 ◽  
Vol 81 (1) ◽  
pp. 51-58 ◽  
Author(s):  
J. H. A. Dambrink ◽  
B. P. M. Imholz ◽  
J. M. Karemaker ◽  
W. Wieling
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Steady State ◽  
Initial Phase ◽  
Time Course ◽  
Free Standing ◽  
Postural Tachycardia ◽  
Circulatory Control ◽  
Head Up Tilt ◽  
Blood Pressures

1. The magnitude and time course of circulatory adaptation to active standing were investigated in healthy premenarchic girls and boys (n = 24; 10–14 years old) by non-invasive measurement of heart rate and continuous finger blood pressure (Finapres). 2. Four subjects (two girls, two boys) showed presyncopal symptoms after 4–9 min of free standing. 3. In the 20 non-fainting subjects, changes in blood pressure and heart rate upon standing did not differ between girls (n = 10) and boys (n = 10). In the initial phase of standing (first 30 s) systolic and diastolic blood pressures dropped by 22 ± 14 (mean ± sd) and 16 ± 7 mmHg, respectively, at 8 ± 2 s. Blood pressure subsequently recovered and showed an overshoot in all subjects. The transient drop in blood pressure was accompanied by an increase in heart rate of 40 ± 7 beats/min. These characteristic transient changes were not observed with passive head-up tilt. During the early steady-state phase (2 min), systolic blood pressure was similar to the supine value and diastolic blood pressure rose by 11 ± 5 mmHg. Heart rate increased by 25 ± 11 beats/min. In six of the subjects (three girls, three boys) the increase in heart rate exceeded 30 beats/min (postural tachycardia). Little further changes were observed during prolonged (10 min) standing. 4. Typical findings in the four near-fainting subjects were higher supine heart rates, no blood pressure overshoot in the initial phase (in three out of four subjects), postural tachycardia in the early steady-state phase and progressive decreases in blood pressure and heart rate afterwards. 5. In conclusion, for investigation of orthostatic circulatory adaptation in childhood it is important to pay attention to the dynamics of the circulatory response. No important differences appear to exist in orthostatic circulatory control between premenarchic girls and boys: orthostatic tachycardia and fainting appear to be common in both.

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 Mathematical modeling of the cardiovascular autonomic control in healthy subjects during a passive head-up tilt test

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Yurii M. Ishbulatov ◽  
Anatoly S. Karavaev ◽  
Anton R. Kiselev ◽  
Margarita A. Simonyan ◽  
Mikhail D. Prokhorov ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Cardiovascular System ◽  
Healthy Subjects ◽  
Low Frequency ◽  
Tilt Test ◽  
Peripheral Vascular ◽  
Control Loops ◽  
Head Up Tilt ◽  
Head Up Tilt Test

Abstract A mathematical model is proposed for the autonomic control of cardiovascular system, which takes into account two separated self-exciting sympathetic control loops of heart rate and peripheral vascular tone. The control loops are represented by self-exciting time-delay systems and their tone depends on activity of the aortic, carotid, and lower-body baroreceptors. The model is used to study the dynamics of the adaptive processes that manifest in a healthy cardiovascular system during the passive head-up tilt test. Computer simulation provides continuous observation of the dynamics of the indexes and variables that cannot be measured in the direct experiment, including the noradrenaline concentration in vessel wall and heart muscle, tone of the sympathetic and parasympathetic control, peripheral vascular resistance, and blood pressure. In the supine and upright positions, we estimated the spectral characteristics of the model variables, especially in the low-frequency band, and the original index of total percent of phase synchronization between the low-frequency oscillations in heart rate and blood pressure signals. The model demonstrates good quantitative agreement with the dynamics of the experimentally observed indexes of cardiovascular system that were averaged for 50 healthy subjects.

scholarly journals Cardiovascular dynamics in healthy subjects with differing heart rate responses to tilt

2008 ◽  
Vol 105 (5) ◽  
pp. 1448-1453 ◽  
Author(s):  
Farah A. Ramirez-Marrero ◽  
Nisha Charkoudian ◽  
Emma C. Hart ◽  
Darrell Schroeder ◽  
Liu Zhong ◽  
...  
Keyword(s):  
Heart Rate ◽  
Pulse Pressure ◽  
Healthy Subjects ◽  
Systolic Pressure ◽  
Plasma Norepinephrine ◽  
Sex Distribution ◽  
Cardiovascular Dynamics ◽  
Fundamental Part ◽  
Wide Range ◽  
Head Up Tilt

Orthostatic stress such as head-up tilt (HUT) elicits a wide range of heart rate (HR) and arterial pressure (AP) responses among healthy individuals. In this study, we evaluated cardiovascular dynamics in healthy subjects with different HR responses to HUT, but without autonomic dysfunction. We measured AP (brachial artery) and HR (ECG) during 5 min of 60° HUT in 76 healthy normotensive individuals. We then chose individuals on the basis of the extremes of HR responses to HUT (high = ΔHR ≥ 20 beats/min, and low = ΔHR ≤ 10 beats/min; n = 15 per group). Peak HR during HUT was 87 ± 10 beats/min in the high and 69 ± 14 beats/min in the low group ( P < 0.05). High HR responders had lower systolic pressure at baseline (121 ± 9 vs. 129 ± 11 mmHg, P < 0.05) and during HUT (120 ± 10 vs. 131 ± 13 mmHg, P < 0.05), and higher plasma norepinephrine (NE) response to HUT (ΔNE: 156.9 ± 17.8 vs. 89.0 ± 17.2 pg/ml; P < 0.05). ΔNE during HUT was also significantly correlated with ΔHR when all 76 subjects were included in a regression analysis ( r = 0.39; P < 0.001). Pulse pressure was lower during HUT in high HR responders compared with low HR responders (45 ± 1 vs. 55 ± 2 mmHg, P < 0.05). High HR responders also had larger fluctuations in systolic and pulse pressure during HUT (coefficient of variation = 10.7 ± 0.7 vs. 5.7 ± 0.3%; 7.9 ± 0.5 vs. 4.1 ± 0.4%, respectively, P < 0.05). Sex distribution was different between groups (high: 5 women, 10 men; low: 10 women, 5 men). Higher HR with lower AP during HUT is consistent with normal baroreflex mechanisms of integration. Although interindividual variability appears to be a fundamental part of cardiovascular regulation, the mechanisms of these differences and the sex discrepancy requires further investigation.

scholarly journals Multiple-input nonlinear modelling of cerebral haemodynamics using spontaneous arterial blood pressure, end-tidal CO 2  and heart rate measurements

2016 ◽  
Vol 374 (2067) ◽  
pp. 20150180 ◽  
Author(s):  
V. Z. Marmarelis ◽  
G. D. Mitsis ◽  
D. C. Shin ◽  
R. Zhang
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Arterial Blood Pressure ◽  
Prediction Error ◽  
Cerebral Blood Flow Velocity ◽  
Cerebral Arteries ◽  
Cerebral Haemodynamics ◽  
Functional Connection ◽  
Arterial Blood ◽  
End Tidal

In order to examine the effect of changes in heart rate (HR) upon cerebral perfusion and autoregulation, we include the HR signal recorded from 18 control subjects as a third input in a two-input model of cerebral haemodynamics that has been used previously to quantify the dynamic effects of changes in arterial blood pressure and end-tidal CO 2 upon cerebral blood flow velocity (CBFV) measured at the middle cerebral arteries via transcranial Doppler ultrasound. It is shown that the inclusion of HR as a third input reduces the output prediction error in a statistically significant manner, which implies that there is a functional connection between HR changes and CBFV. The inclusion of nonlinearities in the model causes further statistically significant reduction of the output prediction error. To achieve this task, we employ the concept of principal dynamic modes (PDMs) that yields dynamic nonlinear models of multi-input systems using relatively short data records. The obtained PDMs suggest model-driven quantitative hypotheses for the role of sympathetic and parasympathetic activity (corresponding to distinct PDMs) in the underlying physiological mechanisms by virtue of their relative contributions to the model output. These relative PDM contributions are subject-specific and, therefore, may be used to assess personalized characteristics for diagnostic purposes.

Cerebral blood flow during orthostasis: role of arterial CO2

2006 ◽  
Vol 290 (4) ◽  
pp. R1087-R1093 ◽  
Author(s):  
J. M. Serrador ◽  
R. L. Hughson ◽  
J. M. Kowalchuk ◽  
R. L. Bondar ◽  
A. W. Gelb
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Healthy Subjects ◽  
Cerebral Arteries ◽  
Alveolar Ventilation ◽  
Orthostatic Stress ◽  
Upright Posture ◽  
Head Up Tilt ◽  
End Tidal

Reductions in end-tidal Pco2 (PetCO2) during upright posture have been suggested to be the result of hyperventilation and the cause of decreases in cerebral blood flow (CBF). The goal of this study was to determine whether decreases in PetCO2 reflected decreases in arterial Pco2 (PaCO2) and their relation to increases in alveolar ventilation (V̇a) and decreases in CBF. Fifteen healthy subjects (10 women and 5 men) were subjected to a 10-min head-up tilt (HUT) protocol. PaCO2, V̇a, and cerebral flow velocity (CFV) in the middle and anterior cerebral arteries were examined. In 12 subjects who completed the protocol, reductions in PetCO2 and PaCO2 (−1.7 ± 0.5 and −1.1 ± 0.4 mmHg, P < 0.05) during minute 1 of HUT were associated with a significant increase in V̇a (+0.7 ± 0.3 l/min, P < 0.05). However, further decreases in PaCO2 (−0.5 ± 0.5 mmHg, P < 0.05), from minute 1 to the last minute of HUT, occurred even though V̇a did not change significantly (−0.2 ± 0.3 l/min, P = not significant). Similarly, CFV in the middle and anterior cerebral arteries decreased (−7 ± 2 and −8 ± 2%, P < 0.05) from minute 1 to the last minute of HUT, despite minimal changes in PaCO2. These data suggest that decreases in PetCO2 and PaCO2 during upright posture are not solely due to increased V̇a but could be due to ventilation-perfusion mismatch or a redistribution of CO2 stores. Furthermore, the reduction in PaCO2 did not fully explain the decrease in CFV throughout HUT. These data suggest that factors in addition to a reduction in PaCO2 play a role in the CBF response to orthostatic stress.

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.

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