scholarly journals Regional pulmonary perfusion patterns in humans are not significantly altered by inspiratory hypercapnia

2019 ◽  
Vol 127 (2) ◽  
pp. 365-375
Author(s):  
Amran K. Asadi ◽  
Rui Carlos Sá ◽  
Tatsuya J. Arai ◽  
Rebecca J. Theilmann ◽  
Susan R. Hopkins ◽  
...  
Keyword(s):  
Blood Flow ◽  
Regional Perfusion ◽  
Spatiotemporal Variability ◽  
Pulmonary Perfusion ◽  
Relative Role ◽  
Alveolar Hypoxia ◽  
Dynamic Measures ◽  
End Tidal ◽  
The Right

Pulmonary vascular tone is known to be sensitive to both local alveolar Po2 and Pco2. Although the effects of hypoxia are well studied, the hypercapnic response is relatively less understood. We assessed changes in regional pulmonary blood flow in humans in response to hypercapnia using previously developed MRI techniques. Dynamic measures of blood flow were made in a single slice of the right lung of seven healthy volunteers following a block-stimulus paradigm (baseline, challenge, recovery), with CO2 added to inspired gas during the challenge block to effect a 7-Torr increase in end-tidal CO2. Effects of hypercapnia on blood flow were evaluated based on changes in spatiotemporal variability (fluctuation dispersion, FD) and in regional perfusion patterns in comparison to hypoxic effects previously studied. Hypercapnia increased FD 2.5% from baseline (relative to control), which was not statistically significant ( P = 0.07). Regional perfusion patterns were not significantly changed as a result of increased [Formula: see text] ( P = 0.90). Reanalysis of previously collected data using a similar protocol but with the physiological challenge replaced by decreased [Formula: see text] ([Formula: see text] = 0.125) showed marked flow redistribution ( P = 0.01) with the suggestion of a gravitational pattern, demonstrating hypoxia has the ability to affect regional change with a global stimulus. Taken together, these data indicate that hypercapnia of this magnitude does not lead to appreciable changes in the distribution of pulmonary perfusion, and that this may represent an interesting distinction between the hypoxic and hypercapnic regulatory response. NEW & NOTEWORTHY Although it is well known that the pulmonary circulation responds to local alveolar hypoxia, and that this mechanism may facilitate ventilation-perfusion matching, the relative role of CO2 is not well appreciated. This study demonstrates that an inspiratory hypercapnic stimulus is significantly less effective at inducing changes in pulmonary perfusion patterns than inspiratory hypoxia, suggesting that in these circumstances hypercapnia is not sufficient to induce substantial integrated feedback control of ventilation-perfusion mismatch across the lung.

Role of collateral ventilation in ventilation-perfusion balance

1984 ◽  
Vol 56 (6) ◽  
pp. 1500-1506 ◽  
Author(s):  
T. Kuriyama ◽  
L. P. Latham ◽  
L. D. Horwitz ◽  
J. T. Reeves ◽  
W. W. Wagner
Keyword(s):  
Blood Flow ◽  
Regional Blood Flow ◽  
Pulmonary Vasoconstriction ◽  
Hypoxic Vasoconstriction ◽  
Alveolar Hypoxia ◽  
Respiratory Mechanism ◽  
End Tidal ◽  
Arterial Po2 ◽  
Collateral Ventilation

Species with collateral ventilation have an auxiliary respiratory mechanism that could protect them, under certain circumstances, from regional alveolar hypoxia. Species without collateral ventilation may have a greater potential for routinely experiencing regional hypoxia; to maintain ventilation-perfusion balance they would have to rely on pulmonary vasoconstriction. We tested these ideas by ventilating a sublobar region of pig lung (no collateral ventilation) with 13% O2 while the rest of the lung was ventilated with 30% O2. Blood flow, as measured by radioactive microsphere distribution to the sublobar region, was reduced 50% during hypoxia. The hypoxia-induced vasoconstriction effectively defended arterial PO2. When a vasodilator was infused, regional blood flow increased to control levels; shunt fraction rose, and arterial PO2 fell. In dogs (collateral ventilation present) the same experimental maneuvers had no significant effect on regional end-tidal gases or on microsphere distribution, indicating that collateral ventilation was able to maintain ventilation-perfusion balance. When regional hypoxia was created in dogs by overcoming collateral ventilation with slightly positive airway pressure in the sublobar region, the dog acted like the pig and used hypoxic vasoconstriction to shift approximately 30% of the blood flow away from the hypoxic alveoli.

scholarly journals The Role of Electrode Size on the Incidence of Spreading Depression and on Cortical Cerebral Blood Flow as Measured by H2 Clearance

1992 ◽  
Vol 12 (2) ◽  
pp. 230-237 ◽  
Author(s):  
Marleen J. Verhaegen ◽  
Michael M. Todd ◽  
David S. Warner ◽  
Bruce James ◽  
Julie B. Weeks
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Gray Matter ◽  
Spreading Depression ◽  
Insertion Depth ◽  
Flow Measurements ◽  
Electrode Size ◽  
Cortical Gray Matter ◽  
The Right

Cerebral blood flow was measured by the H2 clearance method 30 and 60 min after the implantation of 300, 250, 125, or 50 μm diameter platinum–iridium electrodes 2 mm deep into the right parietal cortex of normothermic, normocarbic halothane-anesthetized rats. Another group of animals had 50 μm electrodes inserted 1 mm. In all animals, the presence or absence of a wave of spreading depression (SD) was noted at the time of implantation, with recordings made with glass micropipettes. H2 flow values were compared with those measured in gray matter from the same anatomical region (but from different rats), using [3H]nicotine. The incidence of SD ranged from 60% following insertion of 300 μm electrodes to 0% with 50 μm electrodes. H2 clearance flows also varied with electrode size, from 77 ± 21 ml 100 g−1 min−1 (mean ± standard deviation) with 300 μm electrodes to 110 ± 31 and 111 ± 16 ml 100 g−1 min−1 with 125 and 50 μm electrodes, respectively (insertion depth of 2 mm). A CBF value of 155 ± 60 ml 100 g−1 min−1 was obtained with 50 μm electrodes inserted only 1 mm. Cortical gray matter blood flow measured with [3H]nicotine was 154 ± 35 ml 100 g−1 min−1. When the role of SD in subsequent flow measurements was examined, there was a gradual increase in CBF between 30 and 60 min after electrode insertion in those animals with SD, while no such change was seen in rats without SD. These results indicate that the choice of electrode size and implantation depth influences the measurement of CBF by H2 clearance. CBF values equivalent to those obtained with isotopic techniques can be acutely obtained with small (50 μm diameter) electrodes inserted 1 mm into the cortex. While the occurrence of SD does influence CBF in the period immediately after implantation, a relationship between electrode size and measured flow is present that is independent of SD.

Role of tracheal and bronchial circulation in respiratory heat exchange

1985 ◽  
Vol 58 (1) ◽  
pp. 217-222 ◽  
Author(s):  
E. M. Baile ◽  
R. W. Dahlby ◽  
B. R. Wiggs ◽  
P. D. Pare
Keyword(s):  
Blood Flow ◽  
Blood Gases ◽  
Lung Parenchyma ◽  
Arterial Blood ◽  
Respiratory Heat Loss ◽  
Reference Flow ◽  
Pulmonary Arterial ◽  
End Tidal ◽  
Humidified Air

Due to their anatomic configuration, the vessels supplying the central airways may be ideally suited for regulation of respiratory heat loss. We have measured blood flow to the trachea, bronchi, and lung parenchyma in 10 anesthetized supine open-chest dogs. They were hyperventilated (frequency, 40; tidal volume 30–35 ml/kg) for 30 min or 1) warm humidified air, 2) cold (-20 degrees C dry air, and 3) warm humidified air. End-tidal CO2 was kept constant by adding CO2 to the inspired ventilator line. Five minutes before the end of each period of hyperventilation, measurements of vascular pressures (pulmonary arterial, left atrial, and systemic), cardiac output (CO), arterial blood gases, and inspired, expired, and tracheal gas temperatures were made. Then, using a modification of the reference flow technique, 113Sn-, 153Gd-, and 103Ru-labeled microspheres were injected into the left atrium to make separate measurements of airway blood flow at each intervention. After the last measurements had been made, the dogs were killed and the lungs, including the trachea, were excised. Blood flow to the trachea, bronchi, and lung parenchyma was calculated. Results showed that there was no change in parenchymal blood flow, but there was an increase in tracheal and bronchial blood flow in all dogs (P less than 0.01) from 4.48 +/- 0.69 ml/min (0.22 +/- 0.01% CO) during warm air hyperventilation to 7.06 +/- 0.97 ml/min (0.37 +/- 0.05% CO) during cold air hyperventilation.

The role of the geophysical template and environmental regimes in controlling stream-living trout populations

2015 ◽  
Vol 72 (6) ◽  
pp. 893-901 ◽  
Author(s):  
Brooke E. Penaluna ◽  
Steve F. Railsback ◽  
Jason B. Dunham ◽  
Sherri Johnson ◽  
Robert E. Bilby ◽  
...  
Keyword(s):  
Fish Habitat ◽  
Spatiotemporal Variability ◽  
Sensitivity Analyses ◽  
Low Flow ◽  
Aquatic Biota ◽  
Relative Role ◽  
Oncorhynchus Clarkii ◽  
Environmental Regimes ◽  
Multiple Processes

The importance of multiple processes and instream factors to aquatic biota has been explored extensively, but questions remain about how local spatiotemporal variability of aquatic biota is tied to environmental regimes and the geophysical template of streams. We used an individual-based trout model to explore the relative role of the geophysical template versus environmental regimes on biomass of trout (Oncorhynchus clarkii clarkii). We parameterized the model with observed data from each of the four headwater streams (their local geophysical template and environmental regime) and then ran 12 simulations where we replaced environmental regimes (stream temperature, flow, turbidity) of a given stream with values from each neighboring stream while keeping the geophysical template fixed. We also performed single-parameter sensitivity analyses on the model results from each of the four streams. Although our modeled findings show that trout biomass is most responsive to changes in the geophysical template of streams, they also reveal that biomass is restricted by available habitat during seasonal low flow, which is a product of both the stream’s geophysical template and flow regime. Our modeled results suggest that differences in the geophysical template among streams render trout more or less sensitive to environmental change, emphasizing the importance of local fish–habitat relationships in streams.

scholarly journals Role of CO2 in the cerebral hyperemic response to incremental normoxic and hyperoxic exercise

2016 ◽  
Vol 120 (8) ◽  
pp. 843-854 ◽  
Author(s):  
K. J. Smith ◽  
K. W. Wildfong ◽  
R. L. Hoiland ◽  
M. Harper ◽  
N. C. Lewis ◽  
...  
Keyword(s):  
Blood Flow ◽  
Posterior Cerebral Artery ◽  
Submaximal Exercise ◽  
Maximum Workload ◽  
Exercise Induced ◽  
End Tidal ◽  
Induced Changes ◽  
Isocapnic Hyperpnea ◽  
Hyperemic Response

Cerebral blood flow (CBF) is temporally related to exercise-induced changes in partial pressure of end-tidal carbon dioxide (PetCO2); hyperoxia is known to enhance this relationship. We examined the hypothesis that preventing PetCO2 from rising (isocapnia) during submaximal exercise with and without hyperoxia [end-tidal Po2 (PetO2) = 300 mmHg] would attenuate the increases in CBF. Additionally, we aimed to identify the magnitude that breathing, per se, influences the CBF response to normoxic and hyperoxic exercise. In 14 participants, CBF (intra- and extracranial) measurements were measured during exercise [20, 40, 60, and 80% of maximum workload (Wmax)] and during rest while ventilation (V̇e) was volitionally increased to mimic volumes achieved during exercise (isocapnic hyperpnea). While V̇e was uncontrolled during poikilocapnic exercise, during isocapnic exercise and isocapnic hyperpnea, V̇e was increased to prevent PetCO2 from rising above resting values (∼40 mmHg). Although PetCO2 differed by 2 ± 3 mmHg during normoxic poikilocapnic and isocapnic exercise, except for a greater poikilocapnic compared with isocapnic increase in blood velocity in the posterior cerebral artery at 60% Wmax, the between condition increases in intracranial (∼12-15%) and extracranial (15–20%) blood flow were similar at each workload. The poikilocapnic hyperoxic increases in both intra- and extracranial blood-flow (∼17–29%) were greater compared with poikilocapnic normoxia (∼8–20%) at intensities >40% Wmax ( P < 0.01). During both normoxic and hyperoxic conditions, isocapnia normalized both the intracranial and extracranial blood-flow differences. Isocapnic hyperpnea did not alter CBF. Our findings demonstrate a differential effect of PetCO2 on CBF during exercise influenced by the prevailing PetO2.

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 Role of terminal and anastomotic circulation in the patency of arteries jailed by flow-diverting stents: animal flow model evaluation and preliminary results

2016 ◽  
Vol 125 (4) ◽  
pp. 898-908 ◽  
Author(s):  
Christina Iosif ◽  
Philipp Berg ◽  
Sebastien Ponsonnard ◽  
Pierre Carles ◽  
Suzana Saleme ◽  
...  
Keyword(s):  
Blood Flow ◽  
Flow Rate ◽  
Blood Flow Rate ◽  
Large White ◽  
Flow Modification ◽  
Group A ◽  
Group B ◽  
The Right ◽  
Anastomotic Circulation

OBJECTIVE The authors describe herein the creation of an animal model capable of producing quantifiable data regarding blood flow rate and velocity modifications in terminal and anastomotic types of cerebrofacial circulation. They also present the preliminary results of a translational study aimed at investigating the role of terminal and anastomotic types of circulation in arterial branches jailed by flow-diverting stents as factors contributing to arterial patency or occlusion. METHODS Two Large White swine were used to validate a terminal-type arterial model at the level of the right ascending pharyngeal artery (APhA), created exclusively by endovascular means. Subsequently 4 Large White swine, allocated to 2 groups corresponding to the presence (Group B) or absence (Group A) of terminal-type flow modification, underwent placement of flow-diverting stents. Blood flow rates and velocities were quantified using a dedicated time-resolved 3D phase-contrast MRA sequence before and after stenting. Three months after stent placement, the stented arteries were evaluated with digital subtraction angiography (DSA) and scanning electron microscopy (SEM). Patent (circulating) ostia quantification was performed on the SEM images. RESULTS Terminal-type flow modification was feasible; an increase of 75.8% in mean blood velocities was observed in the right APhAs. The mean blood flow rate for Group A was 0.31 ± 0.19 ml/sec (95% CI −1.39 to 2.01) before stenting and 0.21 ± 0.07 ml/sec (95% CI −0.45 to 0.87) after stenting. The mean blood flow rate for Group B was 0.87 ± 0.32 ml/sec (95% CI −1.98 to 3.73) before stenting and 0.76 ± 0.13 ml/sec (95% CI −0.41 to 1.93) after stenting. Mean flow rates after stenting showed a statistically significant difference between Groups A and B (Welch test). Mean and maximal blood velocities were reduced in Group A cases and did not decrease in Group B cases. Control DSA and SEM findings showed near occlusion of the jailed APhAs in both cases of anastomotic circulation (mean patent ostium surface 32,776 μm2) and patency in both cases of terminal-type circulation (mean patent ostium surface 422,334 μm2). CONCLUSIONS Terminal-type arterial modification in swine APhAs is feasible. Sufficient data were acquired to perform an a priori analysis for further research. Flow diversion at the level of the APhA ostium resulted in significant stenosis in cases of anastomotic circulation, while sufficient patency was observed in terminal-type circulation.

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.

Role of pulmonary blood flow in postpneumonectomy lung growth

1992 ◽  
Vol 73 (6) ◽  
pp. 2448-2451 ◽  
Author(s):  
J. T. McBride ◽  
K. K. Kirchner ◽  
G. Russ ◽  
J. Finkelstein
Keyword(s):  
Blood Flow ◽  
Cardiac Output ◽  
Pulmonary Blood Flow ◽  
Compensatory Growth ◽  
Left Lung ◽  
Lung Growth ◽  
Caudal Lobe ◽  
Dna Contents ◽  
The Right

To study the influence of blood flow on postpneumonectomy lung growth, we banded the left caudal lobe pulmonary artery of eight ferrets in such a way that blood flow to the caudal lobe did not increase when the right lung was excised 1 wk later. The fraction of the cardiac output received by the right lung before pneumonectomy was therefore directed entirely to the left cranial lobe. Three weeks after pneumonectomy the weight, volume, and protein and DNA contents of the two lobes of the left lung were measured and compared with those of five unoperated animals and eight animals after right pneumonectomy alone. Although its perfusion did not increase after pneumonectomy, the left caudal lobe of banded animals participated in compensatory growth, increasing in weight and protein and DNA contents. Although the cranial lobe of banded animals received 25% more of the cardiac output than the same lobe in pneumonectomized animals, cranial lobe volume and protein and DNA contents in the two groups were similar. Caudal lobes were smaller in banded than in simple pneumonectomized animals and tended to contain less protein, whereas the cranial lobes tended to be heavier. We conclude that increased pulmonary perfusion is not necessary for compensatory lung growth in adult ferrets, but it may modify this response.

scholarly journals Differences in cerebrovascular regulation and ventilatory responses during ramp incremental cycling in children, adolescents, and adults

2021 ◽  
Vol 131 (4) ◽  
pp. 1200-1210
Author(s):  
Max E. Weston ◽  
Alan R. Barker ◽  
Owen W. Tomlinson ◽  
Jeff S. Coombes ◽  
Tom G. Bailey ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Incremental Exercise ◽  
Regulatory Role ◽  
Progressive Development ◽  
Ventilatory Responses ◽  
Adolescents And Adults ◽  
End Tidal ◽  
Cerebrovascular Regulation

This is the first study to observe similar increases in cerebral blood flow during incremental exercise in adolescents and adults. Increases in cerebral blood flow during exercise were smaller in children compared with adolescents and adults and were associated with a greater V̇E/V̇co2 slope. This study also provides the first evidence on the progressive development of the regulatory role of end-tidal CO2 on cerebral blood flow during exercise during the transition from childhood to adulthood.

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