Spontaneous beat-by-beat fluctuations of total peripheral and cerebrovascular resistance in response to tilt

2004 ◽  
Vol 287 (3) ◽  
pp. R670-R679 ◽  
Author(s):  
Deborah D. O'Leary ◽  
J. Kevin Shoemaker ◽  
Michael R. Edwards ◽  
Richard L. Hughson
Keyword(s):  
Blood Pressure ◽  
Transfer Function ◽  
Total Peripheral Resistance ◽  
High Frequency ◽  
Function Analysis ◽  
Peripheral Resistance ◽  
Cerebrovascular Resistance ◽  
Arterial Blood ◽  
Transfer Function Analysis ◽  
Head Up Tilt

Beat-by-beat estimates of total peripheral resistance (TPR) can be obtained from continuous measurements of cardiac output by using Doppler ultrasound and noninvasive mean arterial blood pressure (MAP). We employed transfer function analysis to study the heart rate (HR) and vascular response to spontaneous changes in blood pressure from the relationships of systolic blood pressure (SBP) to HR (SBP→HR), MAP to total peripheral resistance (TPR) and cerebrovascular resistance index (CVRi) (MAP→TPR and MAP→CVRi), as well as stroke volume (SV) to TPR in nine healthy subjects in supine and 45° head-up tilt positions. The gain of the SBP→HR transfer function was reduced with tilt in both the low- (0.03–0.15 Hz) and high-frequency (0.15–0.35 Hz) regions. In contrast, MAP→TPR transfer function gain was not affected by head-up tilt, but it did increase from low- to high-frequency regions. The phase relationships between MAP→TPR were unaffected by head-up tilt, but, consistent with an autoregulatory system, changes in MAP were followed by directionally similar changes in TPR, just as observed for the MAP→CVRi. The SV→TPR had high coherence with a constant phase of 150–160°. Together, these data that showed changes in MAP preceded changes in TPR, as well as a possible link between SV and TPR, are consistent with complex interactions between the vascular component of the arterial and cardiopulmonary baroreflexes and intrinsic properties such as the myogenic response of the resistance arteries.

Effect of head-down-tilt bed rest and hypovolemia on dynamic regulation of heart rate and blood pressure

2000 ◽  
Vol 279 (6) ◽  
pp. R2189-R2199 ◽  
Author(s):  
Ken-Ichi Iwasaki ◽  
Rong Zhang ◽  
Julie H. Zuckerman ◽  
James A. Pawelczyk ◽  
Benjamin D. Levine
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Transfer Function ◽  
Stroke Volume ◽  
Plasma Volume ◽  
High Frequency ◽  
Function Analysis ◽  
Bed Rest ◽  
Baroreflex Control ◽  
Transfer Function Analysis

Adaptation to head-down-tilt bed rest leads to an apparent abnormality of baroreflex regulation of cardiac period. We hypothesized that this “deconditioning response” could primarily be a result of hypovolemia, rather than a unique adaptation of the autonomic nervous system to bed rest. To test this hypothesis, nine healthy subjects underwent 2 wk of −6° head-down bed rest. One year later, five of these same subjects underwent acute hypovolemia with furosemide to produce the same reductions in plasma volume observed after bed rest. We took advantage of power spectral and transfer function analysis to examine the dynamic relationship between blood pressure (BP) and R-R interval. We found that 1) there were no significant differences between these two interventions with respect to changes in numerous cardiovascular indices, including cardiac filling pressures, arterial pressure, cardiac output, or stroke volume; 2) normalized high-frequency (0.15–0.25 Hz) power of R-R interval variability decreased significantly after both conditions, consistent with similar degrees of vagal withdrawal; 3) transfer function gain (BP to R-R interval), used as an index of arterial-cardiac baroreflex sensitivity, decreased significantly to a similar extent after both conditions in the high-frequency range; the gain also decreased similarly when expressed as BP to heart rate × stroke volume, which provides an index of the ability of the baroreflex to alter BP by modifying systemic flow; and 4) however, the low-frequency (0.05–0.15 Hz) power of systolic BP variability decreased after bed rest (−22%) compared with an increase (+155%) after acute hypovolemia, suggesting a differential response for the regulation of vascular resistance (interaction, P < 0.05). The similarity of changes in the reflex control of the circulation under both conditions is consistent with the hypothesis that reductions in plasma volume may be largely responsible for the observed changes in cardiac baroreflex control after bed rest. However, changes in vasomotor function associated with these two conditions may be different and may suggest a cardiovascular remodeling after bed rest.

Dynamic modulation of cerebrovascular resistance as an index of autoregulation under tilt and controlled Pet CO2

2002 ◽  
Vol 283 (3) ◽  
pp. R653-R662 ◽  
Author(s):  
Michael R. Edwards ◽  
J. Kevin Shoemaker ◽  
Richard L. Hughson
Keyword(s):  
Transfer Function ◽  
Function Analysis ◽  
Low Frequency ◽  
Mean Flow ◽  
Low Frequencies ◽  
Cerebrovascular Autoregulation ◽  
Cerebrovascular Resistance ◽  
Arterial Blood ◽  
Transfer Function Analysis ◽  
Frequency Changes

Transfer function analysis of the arterial blood pressure (BP)-mean flow velocity (MFV) relationship describes an aspect of cerebrovascular autoregulation. We hypothesized that the transfer function relating BP to cerebrovascular resistance (CVRi) would be sensitive to low-frequency changes in autoregulation induced by head-up tilt (HUT) and altered arterial Pco 2. Nine subjects were studied in supine and HUT positions with end-tidal Pco 2(Pet CO2 ) kept constant at normal levels: +5 and −5 mmHg. The BP-MFV relationship had low coherence at low frequencies, and there were significant effects of HUT on gain only at high frequencies and of Pco 2 on phase only at low frequencies. BP → CVRi had coherence >0.5 from very low to low frequencies. There was a significant reduction of gain with increased Pco 2 in the very low and low frequencies and with HUT at the low frequency. Phase was affected by Pco 2 in the very low frequencies. Transfer function analysis of BP → CVRi provides direct evidence of altered cerebrovascular autoregulation under HUT and higher levels of Pco 2.

Influence of controlled breathing patterns on cerebrovascular autoregulation and cardiac baroreceptor sensitivity

2004 ◽  
Vol 106 (2) ◽  
pp. 155-162 ◽  
Author(s):  
Penelope J. EAMES ◽  
John F. POTTER ◽  
Ronney B. PANERAI
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Transfer Function ◽  
Respiratory Rate ◽  
Function Analysis ◽  
Step Response ◽  
Arterial Blood ◽  
Transfer Function Analysis ◽  
Controlled Breathing

Transfer function analysis has become one of the main techniques to study the dynamic relationship between cerebral blood flow and arterial blood pressure, but the influence of different respiratory rates on cerebral blood flow has not been fully investigated. In 14 healthy volunteers, middle cerebral artery blood flow velocity, recorded using transcranial Doppler ultrasound, non-invasive beat-to-beat Finapres blood pressure, ECG and end-tidal CO2 (PETCO2) levels were recorded with subjects resting supine and breathing spontaneously or at controlled rates of 6, 10 and 15 breaths/min. Transfer function analysis and impulse and step responses were computed at each respiratory rate. PETCO2 levels tended to fall slightly during paced respiration, especially at 15 breaths/min. Controlled breathing rates did not alter transfer function analysis in the frequency range below 0.08 Hz but, above this frequency, the coherence function contained significant peaks corresponding to the respiratory frequencies. The impulse response was similar at all breathing rates, but the step response was characteristic of more efficient autoregulation with reduced PETCO2 levels associated with increasing respiratory rate. The effects of breathing rate and rhythmicity and PETCO2 must be considered in studies of cerebral autoregulation.

Resonant and notch behavior in intracranial pressure dynamics

2009 ◽  
Vol 3 (5) ◽  
pp. 354-364 ◽  
Author(s):  
Mark E. Wagshul ◽  
Erin J. Kelly ◽  
Hui Jing Yu ◽  
Barbara Garlick ◽  
Tom Zimmerman ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Intracranial Pressure ◽  
Transfer Function ◽  
Arterial Blood Pressure ◽  
Pulse Pressure ◽  
Function Analysis ◽  
Isotonic Saline ◽  
Pressure Amplitude ◽  
Arterial Blood ◽  
Transfer Function Analysis

Object The intracranial pulse pressure is often increased when neuropathology is present, particularly in cases of increased intracranial pressure (ICP) such as occurs in hydrocephalus. This pulse pressure is assumed to originate from arterial blood pressure oscillations entering the cranium; the fact that there is a coupling between the arterial blood pressure and the ICP is undisputed. In this study, the nature of this coupling and how it changes under conditions of increased ICP are investigated. Methods In 12 normal dogs, intracarotid and parenchymal pulse pressure were measured and their coupling was characterized using amplitude and phase transfer function analysis. Mean intracranial ICP was manipulated via infusions of isotonic saline into the spinal subarachnoid space, and changes in transfer function were monitored. Results Under normal conditions, the ICP wave led the arterial wave, and there was a minimum in the pulse pressure amplitude near the frequency of the heart rate. Under conditions of decreased intracranial compliance, the ICP wave began to lag behind the arterial wave and increased significantly in amplitude. Most interestingly, in many animals the pulse pressure exhibited a minimum in amplitude at a mean pressure that coincided with the transition from a leading to lagging ICP wave. Conclusions This transfer function behavior is characteristic of a resonant notch system. This may represent a component of the intracranial Windkessel mechanism, which protects the microvasculature from arterial pulsatility. The impairment of this resonant notch system may play a role in the altered pulse pressure in conditions such as hydrocephalus and traumatic brain swelling. New models of intracranial dynamics are needed for understanding the frequency-sensitive behavior elucidated in these studies and could open a path for development of new therapies that are geared toward addressing the pulsation dysfunction in pathological conditions, such as hydrocephalus and traumatic brain injury, affecting ICP and flow dynamics.

Cerebrovascular reactivity and dynamic autoregulation in tetraplegia

2010 ◽  
Vol 298 (4) ◽  
pp. R1035-R1042 ◽  
Author(s):  
Luke C. Wilson ◽  
James D. Cotter ◽  
Jui-Lin Fan ◽  
Rebekah A. I. Lucas ◽  
Kate N. Thomas ◽  
...  
Keyword(s):  
Transfer Function ◽  
Cerebral Oxygenation ◽  
Function Analysis ◽  
Plasma Catecholamines ◽  
Peripheral Resistance ◽  
Cardiovascular Function ◽  
Cerebrovascular Reactivity ◽  
Arterial Blood ◽  
Transfer Function Analysis ◽  
Cord Injury

Humans with spinal cord injury have impaired cardiovascular function proportional to the level and completeness of the lesion. The effect on cerebrovascular function is unclear, especially for high-level lesions. The purpose of this study was to evaluate the integrity of dynamic cerebral autoregulation (CA) and the cerebrovascular reactivity in chronic tetraplegia (Tetra). After baseline, steady-state hypercapnia (5% CO2) and hypocapnia (controlled hyperventilation) were used to assess cerebrovascular reactivity in 6 men with Tetra (C5–C7 lesion) and 14 men without [able-bodied (AB)]. Middle cerebral artery blood flow velocity (MCAv), cerebral oxygenation, arterial blood pressure (BP), heart rate (HR), cardiac output (Q̇; model flow), partial pressure of end-tidal CO2 (PetCO2), and plasma catecholamines were measured. Dynamic CA was assessed by transfer function analysis of spontaneous fluctuations in BP and MCAv. MCAv pulsatility index (MCAv PI) was calculated as (MCAvsystolic − MCAvdiastolic)/MCAvmean and standardized by dividing by mean arterial pressure (MAP). Resting BP, total peripheral resistance, and catecholamines were lower in Tetra ( P < 0.05), and standardized MCAv PI was ∼36% higher in Tetra ( P = 0.003). Resting MCAv, cerebral oxygenation, HR, and PetCO2 were similar between groups ( P > 0.05). Although phase and transfer function gain relationships in dynamic CA were maintained with Tetra ( P > 0.05), coherence in the very low-frequency range (0.02–0.07 Hz) was ∼21% lower in Tetra ( P = 0.006). Full (hypo- and hypercapnic) cerebrovascular reactivity to CO2 was unchanged with Tetra ( P > 0.05). During hypercapnia, standardized MCAv PI reactivity was enhanced by ∼78% in Tetra ( P = 0.016). Despite impaired cardiovascular function, chronic Tetra involves subtle changes in dynamic CA and cerebrovascular reactivity to CO2. Changes are evident in coherence at baseline and MCAv PI during baseline and hypercapnic states in chronic Tetra, which may be indicative of cerebrovascular adaptation.

Effect of sympathetic blockade on diurnal variation of hemodynamic patterns

1989 ◽  
Vol 256 (3) ◽  
pp. R778-R785 ◽  
Author(s):  
M. I. Talan ◽  
B. T. Engel
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Cardiac Output ◽  
Stroke Volume ◽  
Total Peripheral Resistance ◽  
Peripheral Resistance ◽  
Base Line ◽  
Sympathetic Blockade ◽  
Selective Blockade ◽  
Arterial Blood

Heart rate, stroke volume, and intra-arterial blood pressure were monitored continuously in each of four monkeys, 18 consecutive h/day for several weeks. The mean heart rate, stroke volume, cardiac output, systolic and diastolic blood pressure, and total peripheral resistance were calculated for each minute and reduced to hourly means. After base-line data were collected for approximately 20 days, observation was continued for equal periods of time under conditions of alpha-sympathetic blockade, beta-sympathetic blockade, and double sympathetic blockade. This was achieved by intra-arterial infusion of prazosin, atenolol, or a combination of both in concentration sufficient for at least 75% reduction of response to injection of agonists. The results confirmed previous findings of a diurnal pattern characterized by a fall in cardiac output and a rise in total peripheral resistance throughout the night. This pattern was not eliminated by selective blockade, of alpha- or beta-sympathetic receptors or by double sympathetic blockade; in fact, it was exacerbated by sympathetic blockade, indicating that the sympathetic nervous system attenuates these events. Because these findings indicate that blood volume redistribution is probably not the mechanism mediating the observed effects, we have hypothesized that a diurnal loss in plasma volume may mediate the fall in cardiac output and that the rise in total peripheral resistance reflects a homeostatic regulation of arterial pressure.

Carotid baroreceptor control of liver and spleen volume in cats

1991 ◽  
Vol 260 (1) ◽  
pp. H254-H259
Author(s):  
R. Maass-Moreno ◽  
C. F. Rothe
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Cardiac Output ◽  
Arterial Blood Pressure ◽  
Total Peripheral Resistance ◽  
Venous Pressure ◽  
Peripheral Resistance ◽  
Normal Brain ◽  
Spleen Volume ◽  
Arterial Blood

We tested the hypothesis that the blood volumes of the spleen and liver of cats are reflexly controlled by the carotid sinus (CS) baroreceptors. In pentobarbital-anesthetized cats the CS area was isolated and perfused so that intracarotid pressure (Pcs) could be controlled while maintaining a normal brain blood perfusion. The volume changes of the liver and spleen were estimated by measuring their thickness using ultrasonic techniques. Cardiac output, systemic arterial blood pressure (Psa), central venous pressure, central blood volume, total peripheral resistance, and heart rate were also measured. In vagotomized cats, increasing Pcs by 100 mmHg caused a significant reduction in Psa (-67.8%), cardiac output (-26.6%), total peripheral resistance (-49.5%), and heart rate (-15%) and significantly increased spleen volume (9.7%, corresponding to a 2.1 +/- 0.5 mm increase in thickness). The liver volume decreased, but only by 1.6% (0.6 +/- 0.2 mm decrease in thickness), a change opposite that observed in the spleen. The changes in cardiovascular variables and in spleen volume suggest that the animals had functioning reflexes. These results indicate that in pentobarbital-anesthetized cats the carotid baroreceptors affect the volume of the spleen but not the liver and suggest that, although the spleen has an active role in the control of arterial blood pressure in the cat, the liver does not.

Cardiac Output by the Dye Dilution Technique Under Thiopental Sodium-Oxygen and Ether Anesthesia

1956 ◽  
Vol 186 (1) ◽  
pp. 101-104 ◽  
Author(s):  
Esther M. Greisheimer ◽  
Dorothy W. Ellis ◽  
George Stewart ◽  
Lydia Makarenko ◽  
Nadia Oleksyshyn ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Cardiac Output ◽  
Arterial Blood Pressure ◽  
Total Peripheral Resistance ◽  
Peripheral Resistance ◽  
Stroke Index ◽  
Ether Anesthesia ◽  
Dye Dilution ◽  
Arterial Blood ◽  
Thiopental Sodium

One hundred-twenty determinations of cardiac output by the dye dilution technic utilizing the cuvette oximeter were made on 20 dogs. Of these, 60 were done under thiopental sodium-oxygen analgesia and 60 were done after supplementing with ether. Arterial blood pressure was recorded by strain gauge. Electrocardiograms were taken periodically. Concentrations of thiopental and ether in arterial blood were determined. Cardiac output began to increase under thiopental analgesia and continued to increase when ether was administered. Arterial blood pressure and heart rate decreased slightly when ether was administered. Stroke index increased when ether was administered. Total peripheral resistance decreased markedly under thiopental analgesia, and continued to decrease when ether was administered. When compared with an earlier study in which cyclopropane was used as the supplementing agent, it was found that cyclopropane and ether exert opposite effects on cardiac output and peripheral resistance despite the fact that the effect on arterial blood pressure is similar under the two agents. Increase in cardiac output was found to be parallel with decrease in total peripheral resistance in this study. Amount of dye injected did not influence cardiac output. Under the conditions of this study, cardiac output was in no way dependent on the concentration of thiopental in the blood nor on the amount injected. Level of ether in the blood did not show much effect, if any, on cardiac output. It is probable that the changes observed in this study are comparable with those which obtain clinically when thiopental-oxygen analgesia is supplemented with ether. Systolic blood pressure is not an infallible guide to other cardiovascular functions since it may remain fairly steady while cardiac output and peripheral resistance undergo marked changes under anesthesia.

Dynamic cerebral autoregulation during brain activation paradigms

2005 ◽  
Vol 289 (3) ◽  
pp. H1202-H1208 ◽  
Author(s):  
Ronney B. Panerai ◽  
Michelle Moody ◽  
Penelope J. Eames ◽  
John F. Potter
Keyword(s):  
Transfer Function ◽  
Cerebral Autoregulation ◽  
Function Analysis ◽  
Brain Activation ◽  
Hemispheric Lateralization ◽  
Step Response ◽  
Arterial Blood ◽  
Transfer Function Analysis ◽  
The Right ◽  
Dynamic Cerebral Autoregulation

Dynamic cerebral autoregulation (CA) describes the transient response of cerebral blood flow (CBF) to rapid changes in arterial blood pressure (ABP). We tested the hypothesis that the efficiency of dynamic CA is increased by brain activation paradigms designed to induce hemispheric lateralization. CBF velocity [CBFV; bilateral, middle cerebral artery (MCA)], ABP, ECG, and end-tidal Pco2 were continuously recorded in 14 right-handed healthy subjects (21–43 yr of age), in the seated position, at rest and during 10 repeated presentations (30 s on-off) of a word generation test and a constructional puzzle. Nonstationarities were not found during rest or activation. Transfer function analysis of the ABP-CBFV (i.e., input-output) relation was performed for the 10 separate 51.2-s segments of data during activation and compared with baseline data. During activation, the coherence function below 0.05 Hz was significantly increased for the right MCA recordings for the puzzle tasks compared with baseline values (0.36 ± 0.16 vs. 0.26 ± 0.13, P < 0.05) and for the left MCA recordings for the word paradigm (0.48 ± 0.23 vs. 0.29 ± 0.16, P < 0.05). In the same frequency range, significant increases in gain were observed during the puzzle paradigm for the right (0.69 ± 0.37 vs. 0.46 ± 0.32 cm·s−1·mmHg−1, P < 0.05) and left (0.61 ± 0.29 vs. 0.45 ± 0.24 cm·s−1·mmHg−1, P < 0.05) hemispheres and during the word tasks for the left hemisphere (0.66 ± 0.31 vs. 0.39 ± 0.15 cm·s−1·mmHg−1, P < 0.01). Significant reductions in phase were observed during activation with the puzzle task for the right (−0.04 ± 1.01 vs. 0.80 ± 0.86 rad, P < 0.01) and left (0.11 ± 0.81 vs. 0.57 ± 0.51 rad, P < 0.05) hemispheres and with the word paradigm for the right hemisphere (0.05 ± 0.87 vs. 0.64 ± 0.59 rad, P < 0.05). Brain activation also led to changes in the temporal pattern of the CBFV step response. We conclude that transfer function analysis suggests important changes in dynamic CA during mental activation tasks.

scholarly journals Methodological comparison of active- and passive-driven oscillations in blood pressure; implications for the assessment of cerebral pressure-flow relationships

2015 ◽  
Vol 119 (5) ◽  
pp. 487-501 ◽  
Author(s):  
Jonathan D. Smirl ◽  
Keegan Hoffman ◽  
Yu-Chieh Tzeng ◽  
Alex Hansen ◽  
Philip N. Ainslie
Keyword(s):  
Blood Pressure ◽  
Transfer Function ◽  
Lower Body Negative Pressure ◽  
Function Analysis ◽  
Flow Dynamics ◽  
Pressure Flow ◽  
Reliable Assessment ◽  
Transfer Function Analysis ◽  
End Tidal ◽  
Normalized Gain

We examined the between-day reproducibility of active (squat-stand maneuvers)- and passive [oscillatory lower-body negative pressure (OLBNP) maneuvers]-driven oscillations in blood pressure. These relationships were examined in both younger ( n = 10; 25 ± 3 yr) and older ( n = 9; 66 ± 4 yr) adults. Each testing protocol incorporated rest (5 min), followed by driven maneuvers at 0.05 (5 min) and 0.10 (5 min) Hz to increase blood-pressure variability and improve assessment of the pressure-flow dynamics using linear transfer function analysis. Beat-to-beat blood pressure, middle cerebral artery velocity, and end-tidal partial pressure of CO2 were monitored. The pressure-flow relationship was quantified in the very low (0.02-0.07 Hz) and low (0.07–0.20 Hz) frequencies (LF; spontaneous data) and at 0.05 and 0.10 Hz (driven maneuvers point estimates). Although there were no between-age differences, very few spontaneous and OLBNP transfer function metrics met the criteria for acceptable reproducibility, as reflected in a between-day, within-subject coefficient of variation (CoV) of <20%. Combined CoV data consist of LF coherence (15.1 ± 12.2%), LF gain (15.1 ± 12.2%), and LF normalized gain (18.5 ± 10.9%); OLBNP data consist of 0.05 (12.1 ± 15.%) and 0.10 (4.7 ± 7.8%) Hz coherence. In contrast, the squat-stand maneuvers revealed that all metrics (coherence: 0.6 ± 0.5 and 0.3 ± 0.5%; gain: 17.4 ± 12.3 and 12.7 ± 11.0%; normalized gain: 16.7 ± 10.9 and 15.7 ± 11.0%; and phase: 11.6 ± 10.2 and 17.3 ± 10.8%) at 0.05 and 0.10 Hz, respectively, were considered biologically acceptable for reproducibility. These findings have important implications for the reliable assessment and interpretation of cerebral pressure-flow dynamics in humans.

Sign in / Sign up

Export Citation Format

Share Document