Ventilatory, cerebrovascular, and cardiovascular interactions in acute hypoxia: regulation by carbon dioxide

2004 ◽  
Vol 97 (1) ◽  
pp. 149-159 ◽  
Author(s):  
Philip N. Ainslie ◽  
Marc J. Poulin
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Cerebral Blood Flow Velocity ◽  
Acute Hypoxia ◽  
Random Order ◽  
Transcranial Doppler Ultrasound ◽  
Individual Variability ◽  
Cerebral Vasoconstriction ◽  
Arterial Blood ◽  
End Tidal

This study examined the effect of high, normal, and uncontrolled end-tidal Pco2 (PetCO2) on the ventilatory, peak cerebral blood flow velocity ( V̄p), and mean arterial blood pressure (MAP) responses to acute hypoxia. Nine healthy subjects undertook, in random order, three hypoxic protocols (end-tidal Po2 was held at eight steps between 300 and 45 Torr) in conditions of hypercapnia, isocapnia, or poikilocapnia (PetCO2 +7.5 Torr, +1.0 Torr, or uncontrolled, respectively). Transcranial Doppler ultrasound was used to measure V̄p in the middle cerebral artery. The slopes of the linear regressions of ventilation, V̄p, and MAP with arterial O2 saturation were significantly greater in hypercapnia than in both isocapnia and poikilocapnia ( P < 0.05). Strong, significant correlations were observed between ventilation, V̄p, and MAP with each PetCO2 condition. These data suggest that 1) a high acute hypoxic ventilatory response (AHVR) decreases the acute hypoxic cerebral blood flow responses during poikilocapnia hypoxia, due to hypocapnic-induced cerebral vasoconstriction; and 2) in hypercapnic hypoxia, a high AHVR is associated with a high acute hypoxic cerebral blood flow response, demonstrating a linkage of individual sensitivities of ventilation and cerebral blood flow to the interaction of PetCO2 and hypoxia. In summary, the between-individual variability in AHVR is shown to be firmly linked to the variability in V̄p and MAP responses to hypoxia. Individuals with a high AHVR are found also to have high V̄p and MAP responses to hypoxia.

Determinants of cerebral blood flow velocity change during squat-stand maneuvers

2021 ◽  
Vol 320 (4) ◽  
pp. R452-R466
Author(s):  
Ronney B. Panerai ◽  
Angus Batterham ◽  
Thompson G. Robinson ◽  
Victoria J. Haunton
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Flow Velocity ◽  
Blood Flow Velocity ◽  
Cerebral Blood Flow Velocity ◽  
Velocity Change ◽  
Arterial Blood ◽  
Autoregulation Index ◽  
End Tidal ◽  
The Right

The large changes in mean arterial blood pressure (MABP) and cerebral blood flow velocity (CBFV) induced by squat-stand maneuvers (SSM) make this approach particularly suited for studying dynamic cerebral autoregulation (CA). However, the role of other systemic determinants of CBFV has not been described and could provide alternative physiological interpretations of SSM results. In 32 healthy subjects (16 female), continuous recordings of MABP (Finometer), bilateral CBFV (transcranial Doppler, MCA), end-tidal CO2 (EtCO2; capnography), and heart rate (HR; electrocardiogram) were performed for 5 min standing at rest, and during 15 SSM at the frequency of 0.05 Hz. A time-domain, multivariate dynamic model estimated the CBFV variance explained by different inputs, corresponding to significant contributions from MABP ( P < 0.00001), EtCO2 ( P < 0.0001), and HR ( P = 0.041). The autoregulation index (ARI; range 0–9) was estimated from the CBFV response to a step change in MABP. At rest, ARI values (typically 5.7) were independent of the number of model inputs, but during SSM, ARI was reduced compared with baseline ( P < 0.0001), and the three input model yielded lower values for the right and left MCA (3.4 ± 1.2, 3.1 ± 1.3) when compared with the single-input MABP–CBFV model (4.1 ± 1.1, 3.9 ± 1.0; P < 0.0001). The high coherence of the MABP–CBFV transfer function at 0.05 Hz (typically 0.98) was considerably reduced (around 0.71–0.73; P < 0.0001) when the contribution of CBFV covariates was taken into account. Not taking into consideration other determinants of CBFV, in addition to MABP, could be misleading and introduce biases in physiological and clinical studies.

scholarly journals Cerebral blood flow regulation in women across menstrual phase: differential contribution of cyclooxygenase to basal, hypoxic, and hypercapnic vascular tone

2016 ◽  
Vol 311 (2) ◽  
pp. R222-R231 ◽  
Author(s):  
Garrett L. Peltonen ◽  
John W. Harrell ◽  
Benjamin P. Aleckson ◽  
Kaylie M. LaPlante ◽  
Meghan K. Crain ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Menstrual Cycle ◽  
Transcranial Doppler Ultrasound ◽  
Follicular Phase ◽  
Cerebrovascular Reactivity ◽  
Menstrual Phase ◽  
Arterial Blood ◽  
End Tidal ◽  
Late Follicular Phase

In healthy young women, basal cerebral blood flow (CBF) and cerebrovascular reactivity may change across the menstrual cycle, but mechanisms remain untested. When compared with the early follicular phase of the menstrual cycle, we hypothesized women in late follicular phase would exhibit: 1) greater basal CBF, 2) greater hypercapnic increases in CBF, 3) greater hypoxic increases in CBF, and 4) increased cyclooxygenase (COX) signaling. We measured middle cerebral artery velocity (MCAv, transcranial Doppler ultrasound) in 11 healthy women (23 ± 1 yr) during rest, hypoxia, and hypercapnia. Subjects completed four visits: two during the early follicular (∼ day 3) and two during the late follicular (∼ day 14) phases of the menstrual cycle, with and without COX inhibition (oral indomethacin). Isocapnic hypoxia elicited an SPO2 = 90% and SPO2 = 80% for 5 min each. Separately, hypercapnia increased end-tidal CO2 10 mmHg above baseline. Cerebral vascular conductance index (CVCi = MCAv/MABP·100, where MABP is mean arterial blood pressure) was calculated and a positive change reflected vasodilation (ΔCVCi). Basal CVCi was greater in the late follicular phase ( P < 0.001). Indomethacin decreased basal CVCi (∼37%) and abolished the phase difference ( P < 0.001). Hypoxic ΔCVCi was similar between phases and unaffected by indomethacin. Hypercapnic ΔCVCi was similar between phases, and indomethacin decreased hypercapnic ΔCVCi (∼68%; P < 0.001) similarly between phases. In summary, while neither hypercapnic nor hypoxic vasodilation is altered by menstrual phase, increased basal CBF in the late follicular phase is fully explained by a greater contribution of COX. These data provide new mechanistic insight into anterior CBF regulation across menstrual phases and contribute to our understanding of CBF regulation in women.

Case 84: Intermittent Confusion

2019 ◽  
pp. 423-426
Author(s):  
Peter Novak
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Orthostatic Hypotension ◽  
Flow Velocity ◽  
Blood Flow Velocity ◽  
Cerebral Blood Flow Velocity ◽  
Cerebral Hypoperfusion ◽  
Shortness Of Breath ◽  
Cerebral Vasoconstriction ◽  
End Tidal

Short episodes confusion, dizziness, and shortness of breath can be associated with intermittent declines in cerebral blood flow velocity (CBFv). CBFv decline without orthostatic hypotension or decline in end tidal CO2 can be seen in orthostatic cerebral hypoperfusion syndrome (OCHOS) associate with abnormal cerebral vasoconstriction due to cerebral autoregulatory failure.

Cerebral blood flow responses to changes in oxygen and carbon dioxide in humans

2002 ◽  
Vol 80 (8) ◽  
pp. 819-827 ◽  
Author(s):  
Andrea Vovk ◽  
David A Cunningham ◽  
John M Kowalchuk ◽  
Donald H Paterson ◽  
James Duffin
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Middle Cerebral Artery ◽  
Arterial Blood Pressure ◽  
Cerebral Artery ◽  
Mean Arterial Blood Pressure ◽  
Transcranial Doppler Ultrasound ◽  
Arterial Blood ◽  
End Tidal

This study characterized cerebral blood flow (CBF) responses in the middle cerebral artery to PCO2ranging from 30 to 60 mmHg (1 mmHg = 133.322 Pa) during hypoxia (50 mmHg) and hyperoxia (200 mmHg). Eight subjects (25 ± 3 years) underwent modified Read rebreathing tests in a background of constant hypoxia or hyperoxia. Mean cerebral blood velocity was measured using a transcranial Doppler ultrasound. Ventilation (VE), end-tidal PCO2 (PETCO2), and mean arterial blood pressure (MAP) data were also collected. CBF increased with rising PETCO2 at two rates, 1.63 ± 0.21 and 2.75 ± 0.27 cm·s–1·mmHg–1 (p < 0.05) during hypoxic and 1.69 ± 0.17 and 2.80 ± 0.14 cm·s–1·mmHg–1 (p < 0.05) during hyperoxic rebreathing. VE also increased at two rates (5.08 ± 0.67 and 10.89 ± 2.55 L·min–1·mmHg–1 and 3.31 ± 0.50 and 7.86 ± 1.43 L·min–1·mmHg–1) during hypoxic and hyperoxic rebreathing. MAP and PETCO2 increased linearly during both hypoxic and hyperoxic rebreathing. The breakpoint separating the two-component rise in CBF (42.92 ± 1.29 and 49.00 ± 1.56 mmHg CO2 during hypoxic and hyperoxic rebreathing) was likely not due to PCO2 or perfusion pressure, since PETCO2 and MAP increased linearly, but it may be related to VE, since both CBF and VE exhibited similar responses, suggesting that the two responses may be regulated by a common neural linkage. Key words: brain blood flow, middle cerebral artery, ventilation, mean arterial blood pressure.

scholarly journals Cerebral blood flow autoregulation in ischemic heart failure

2017 ◽  
Vol 312 (1) ◽  
pp. R108-R113 ◽  
Author(s):  
J. R. Caldas ◽  
R. B. Panerai ◽  
V. J. Haunton ◽  
J. P. Almeida ◽  
G. S. R. Ferreira ◽  
...  
Keyword(s):  
Heart Failure ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Healthy Volunteers ◽  
Neurological Complications ◽  
Ischemic Heart ◽  
Step Response ◽  
Ischemic Heart Failure ◽  
Arterial Blood ◽  
End Tidal

Patients with ischemic heart failure (iHF) have a high risk of neurological complications such as cognitive impairment and stroke. We hypothesized that iHF patients have a higher incidence of impaired dynamic cerebral autoregulation (dCA). Adult patients with iHF and healthy volunteers were included. Cerebral blood flow velocity (CBFV, transcranial Doppler, middle cerebral artery), end-tidal CO2 (capnography), and arterial blood pressure (Finometer) were continuously recorded supine for 5 min at rest. Autoregulation index (ARI) was estimated from the CBFV step response derived by transfer function analysis using standard template curves. Fifty-two iHF patients and 54 age-, gender-, and BP-matched healthy volunteers were studied. Echocardiogram ejection fraction was 40 (20–45) % in iHF group. iHF patients compared with control subjects had reduced end-tidal CO2 (34.1 ± 3.7 vs. 38.3 ± 4.0 mmHg, P < 0.001) and lower ARI values (5.1 ± 1.6 vs. 5.9 ± 1.0, P = 0.012). ARI <4, suggestive of impaired CA, was more common in iHF patients (28.8 vs. 7.4%, P = 0.004). These results confirm that iHF patients are more likely to have impaired dCA compared with age-matched controls. The relationship between impaired dCA and neurological complications in iHF patients deserves further investigation.

Diurnal variation in time to presyncope and associated circulatory changes during a controlled orthostatic challenge

2010 ◽  
Vol 299 (1) ◽  
pp. R55-R61 ◽  
Author(s):  
N. C. S. Lewis ◽  
G. Atkinson ◽  
S. J. E. Lucas ◽  
E. J. M. Grant ◽  
H. Jones ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Diurnal Variation ◽  
Flow Velocity ◽  
Blood Flow Velocity ◽  
Cerebral Blood Flow Velocity ◽  
Orthostatic Challenge ◽  
Arterial Blood ◽  
Neurally Mediated Syncope

Epidemiological data indicate that the risk of neurally mediated syncope is substantially higher in the morning. Syncope is precipitated by cerebral hypoperfusion, yet no chronobiological experiment has been undertaken to examine whether the major circulatory factors, which influence perfusion, show diurnal variation during a controlled orthostatic challenge. Therefore, we examined the diurnal variation in orthostatic tolerance and circulatory function measured at baseline and at presyncope. In a repeated-measures experiment, conducted at 0600 and 1600, 17 normotensive volunteers, aged 26 ± 4 yr (mean ± SD), rested supine at baseline and then underwent a 60° head-up tilt with 5-min incremental stages of lower body negative pressure until standardized symptoms of presyncope were apparent. Pretest hydration status was similar at both times of day. Continuous beat-to-beat measurements of cerebral blood flow velocity, blood pressure, heart rate, stroke volume, cardiac output, and end-tidal Pco2 were obtained. At baseline, mean cerebral blood flow velocity was 9 ± 2 cm/s (15%) lower in the morning than the afternoon ( P < 0.0001). The mean time to presyncope was shorter in the morning than in the afternoon (27.2 ± 10.5 min vs. 33.1 ± 7.9 min; 95% CI: 0.4 to 11.4 min, P = 0.01). All measurements made at presyncope did not show diurnal variation ( P > 0.05), but the changes over time (from baseline to presyncope time) in arterial blood pressure, estimated peripheral vascular resistance, and α-index baroreflex sensitivity were greater during the morning tests ( P < 0.05). These data indicate that tolerance to an incremental orthostatic challenge is markedly reduced in the morning due to diurnal variations in the time-based decline in blood pressure and the initial cerebral blood flow velocity “reserve” rather than the circulatory status at eventual presyncope. Such information may be used to help identify individuals who are particularly prone to orthostatic intolerance in the morning.

Suctioning and Cerebral Blood Flow

PEDIATRICS ◽  
1984 ◽  
Vol 73 (5) ◽  
pp. 737-737
Author(s):  
JEFFREY M. PERLMAN ◽  
JOSEPH J. VOLPE
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Intracranial Pressure ◽  
Flow Velocity ◽  
Arterial Blood Pressure ◽  
Blood Flow Velocity ◽  
Cerebral Blood Flow Velocity ◽  
Base Line ◽  
Arterial Blood

In Reply.— Marshall misread a critical piece of information in the text. His interpretation of the data would be correct, if the intracranial pressure, arterial blood pressure, and cerebral blood flow velocity changes occurred simultaneously. However, as we stated in the text (see section on "Temporal Features of Changes with Suctioning"), the intracranial pressure fell to base-line values immediately following suctioning, whereas the changes in arterial blood pressure and cerebral blood flow velocity occurred more slowly over an approximately two-minute period.

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.

Cerebral blood flow velocity response to induced and spontaneous sudden changes in arterial blood pressure

2001 ◽  
Vol 280 (5) ◽  
pp. H2162-H2174 ◽  
Author(s):  
Ronney B. Panerai ◽  
Suzanne L. Dawson ◽  
Penelope J. Eames ◽  
John F. Potter
Keyword(s):  
Blood Pressure ◽  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Flow Velocity ◽  
Arterial Blood Pressure ◽  
Blood Flow Velocity ◽  
Cerebral Blood Flow Velocity ◽  
Step Response ◽  
Arterial Blood ◽  
Step Responses

The influence of different types of maneuvers that can induce sudden changes of arterial blood pressure (ABP) on the cerebral blood flow velocity (CBFV) response was studied in 56 normal subjects (mean age 62 yr, range 23–80). ABP was recorded in the finger with a Finapres device, and bilateral recordings of CBFV were performed with Doppler ultrasound of the middle cerebral arteries. Recordings were performed at rest (baseline) and during the thigh cuff test, lower body negative pressure, cold pressor test, hand grip, and Valsalva maneuver. From baseline recordings, positive and negative spontaneous transients were also selected. Stability of Pco 2 was monitored with transcutaneous measurements. Dynamic autoregulatory index (ARI), impulse, and step responses were obtained for 1-min segments of data for the eight conditions by fitting a mathematical model to the ABP-CBFV baseline and transient data (Aaslid's model) and by the Wiener-Laguerre moving-average method. Impulse responses were similar for the right- and left-side recordings, and their temporal pattern was not influenced by type of maneuver. Step responses showed a sudden rise at time 0 and then started to fall back to their original level, indicating an active autoregulation. ARI was also independent of the type of maneuver, giving an overall mean of 4.7 ± 2.9 ( n = 602 recordings). Amplitudes of the impulse and step responses, however, were significantly influenced by type of maneuver and were highly correlated with the resistance-area product before the sudden change in ABP ( r = −0.93, P < 0.0004). These results suggest that amplitude of the CBFV step response is sensitive to the point of operation of the instantaneous ABP-CBFV relationship, which can be shifted by different maneuvers. Various degrees of sympathetic nervous system activation resulting from different ABP-stimulating maneuvers were not reflected by CBFV dynamic autoregulatory responses within the physiological range of ABP.

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