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Elliott AR, Kizhakke Puliyakote AS, Tedjasaputra V, Pazár B, Wagner H, Sá RC, Orr JE, Prisk GK, Wagner PD, Hopkins SR. Ventilation-perfusion heterogeneity measured by the multiple inert gas elimination technique is minimally affected by intermittent breathing of 100% O 2. Physiol Rep 2020; 8:e14488. [PMID: 32638530 PMCID: PMC7340847 DOI: 10.14814/phy2.14488] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Revised: 05/04/2020] [Accepted: 05/07/2020] [Indexed: 11/24/2022] Open
Abstract
Proton magnetic resonance (MR) imaging to quantify regional ventilation-perfusion ( V ˙ A / Q ˙ ) ratios combines specific ventilation imaging (SVI) and separate proton density and perfusion measures into a composite map. Specific ventilation imaging exploits the paramagnetic properties of O2 , which alters the local MR signal intensity, in an FI O2 -dependent manner. Specific ventilation imaging data are acquired during five wash-in/wash-out cycles of breathing 21% O2 alternating with 100% O2 over ~20 min. This technique assumes that alternating FI O2 does not affect V ˙ A / Q ˙ heterogeneity, but this is unproven. We tested the hypothesis that alternating FI O2 exposure increases V ˙ A / Q ˙ mismatch in nine patients with abnormal pulmonary gas exchange and increased V ˙ A / Q ˙ mismatch using the multiple inert gas elimination technique (MIGET).The following data were acquired (a) breathing air (baseline), (b) breathing alternating air/100% O2 during an emulated-SVI protocol (eSVI), and (c) 20 min after ambient air breathing (recovery). MIGET heterogeneity indices of shunt, deadspace, ventilation versus V ˙ A / Q ˙ ratio, LogSD V ˙ , and perfusion versus V ˙ A / Q ˙ ratio, LogSD Q ˙ were calculated. LogSD V ˙ was not different between eSVI and baseline (1.04 ± 0.39 baseline, 1.05 ± 0.38 eSVI, p = .84); but was reduced compared to baseline during recovery (0.97 ± 0.39, p = .04). There was no significant difference in LogSD Q ˙ across conditions (0.81 ± 0.30 baseline, 0.79 ± 0.15 eSVI, 0.79 ± 0.20 recovery; p = .54); Deadspace was not significantly different (p = .54) but shunt showed a borderline increase during eSVI (1.0% ± 1.0 baseline, 2.6% ± 2.9 eSVI; p = .052) likely from altered hypoxic pulmonary vasoconstriction and/or absorption atelectasis. Intermittent breathing of 100% O2 does not substantially alter V ˙ A / Q ˙ matching and if SVI measurements are made after perfusion measurements, any potential effects will be minimized.
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Affiliation(s)
- Ann R. Elliott
- Department of MedicineUniversity of California San DiegoLa JollaCAUSA
- The Pulmonary Imaging LaboratoryUniversity of California San DiegoLa JollaCAUSA
| | - Abhilash S. Kizhakke Puliyakote
- The Pulmonary Imaging LaboratoryUniversity of California San DiegoLa JollaCAUSA
- Department of RadiologyUniversity of California San DiegoLa JollaCAUSA
| | - Vincent Tedjasaputra
- Department of MedicineUniversity of California San DiegoLa JollaCAUSA
- The Pulmonary Imaging LaboratoryUniversity of California San DiegoLa JollaCAUSA
| | - Beni Pazár
- The Pulmonary Imaging LaboratoryUniversity of California San DiegoLa JollaCAUSA
- Department of RadiologyUniversity of California San DiegoLa JollaCAUSA
| | - Harrieth Wagner
- Department of MedicineUniversity of California San DiegoLa JollaCAUSA
| | - Rui C. Sá
- Department of MedicineUniversity of California San DiegoLa JollaCAUSA
- The Pulmonary Imaging LaboratoryUniversity of California San DiegoLa JollaCAUSA
| | - Jeremy E. Orr
- Department of MedicineUniversity of California San DiegoLa JollaCAUSA
| | - G. Kim Prisk
- Department of MedicineUniversity of California San DiegoLa JollaCAUSA
- The Pulmonary Imaging LaboratoryUniversity of California San DiegoLa JollaCAUSA
- Department of RadiologyUniversity of California San DiegoLa JollaCAUSA
| | - Peter D. Wagner
- Department of MedicineUniversity of California San DiegoLa JollaCAUSA
| | - Susan R. Hopkins
- Department of MedicineUniversity of California San DiegoLa JollaCAUSA
- The Pulmonary Imaging LaboratoryUniversity of California San DiegoLa JollaCAUSA
- Department of RadiologyUniversity of California San DiegoLa JollaCAUSA
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Lee JH, Kim Y, Mun J, Lee J, Ko S. Effects of hypercarbia on arterial oxygenation during one-lung ventilation: prospective randomized crossover study. Korean J Anesthesiol 2020; 73:534-541. [PMID: 32460465 PMCID: PMC7714622 DOI: 10.4097/kja.19445] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Accepted: 05/27/2020] [Indexed: 11/12/2022] Open
Abstract
Background This study aimed to evaluate the effects of hypercarbia on arterial oxygenation during one-lung ventilation (OLV). Methods Fifty adult patients undergoing elective video-assisted thoracoscopic lobectomy or pneumonectomy were enrolled. Group I patients (n = 25) were first maintained at normocarbia (PaCO2: 38–42 mmHg) for 30 min and then at hypercarbia (45–50 mmHg). In Group II patients (n = 25), PaCO2 was maintained in the reverse order. Arterial oxygen partial pressure (PaO2), respiratory variables, hemodynamic variables, and hemoglobin concentration were compared during normocarbia and hypercarbia. Arterial O2 content and O2 delivery were calculated. Results PaO2 values during normocarbia and hypercarbia were 66.5 ± 10.6 and 79.7 ± 17.3 mmHg, respectively (mean difference: 13.2 mmHg, 95% CI for difference of means: 17.0 to 9.3, P < 0.001). SaO2 values during normocarbia and hypercarbia were 92.5 ± 4.8% and 94.3 ± 3.1% (P = 0.009), respectively. Static compliance of the lung (33.0 ± 5.4 vs. 30.4 ± 5.3 ml/cmH2O, P < 0.001), arterial O2 content (15.4 ± 1.4 vs. 14.9 ± 1.5 ml/dl, P < 0.001) and O2 delivery (69.9 ± 18.4 vs. 65.1 ± 18.1 ml/min, P < 0.001) were significantly higher during hypercarbia than during normocarbia. Conclusions Hypercarbia increases PaO2 and O2 carrying capacity and improves pulmonary mechanics during OLV, suggesting that it may help manage oxygenation during OLV. Therefore, permissive hypercarbia may be a simple and valuable modality to manage arterial oxygenation during OLV.
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Affiliation(s)
- Jun Ho Lee
- Department of Anesthesiology and Pain Medicine, Jeonbuk National University Medical School and Hospital, Jeonju, Korea
| | - Yesull Kim
- Department of Anesthesiology and Pain Medicine, Jeonbuk National University Medical School and Hospital, Jeonju, Korea
| | - Juhan Mun
- Department of Anesthesiology and Pain Medicine, Jeonbuk National University Medical School and Hospital, Jeonju, Korea
| | - Joseph Lee
- Department of Anesthesiology and Pain Medicine, Jeonbuk National University Medical School and Hospital, Jeonju, Korea
| | - Seonghoon Ko
- Department of Anesthesiology and Pain Medicine, Jeonbuk National University Medical School and Hospital, Jeonju, Korea
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Abstract
Maintenance of intracellular pH is critical for clinical homeostasis. The metabolism of glucose, fatty acids, and amino acids yielding the generation of adenosine triphosphate in the mitochondria is accompanied by the production of acid in the Krebs cycle. Both the nature of this acidosis and the mechanism of its disposal have been argued by two investigators with a long-abiding interest in acid-base physiology. They offer different interpretations and views of the molecular mechanism of this intracellular pH regulation during normal metabolism. Dr. John Severinghaus has posited that hydrogen ion and bicarbonate are the direct end products in the Krebs cycle. In the late 1960s, he showed in brain and brain homogenate experiments that acetazolamide, a carbonic anhydrase inhibitor, reduces intracellular pH. This led him to conclude that hydrogen ion and bicarbonate are the end products, and the role of intracellular carbonic anhydrase is to rapidly generate diffusible carbon dioxide to minimize acidosis. Dr. Erik Swenson posits that carbon dioxide is a direct end product in the Krebs cycle, a more widely accepted view, and that acetazolamide prevents rapid intracellular bicarbonate formation, which can then codiffuse with carbon dioxide to the cell surface and there be reconverted for exit from the cell. Loss of this "facilitated diffusion of carbon dioxide" leads to intracellular acidosis as the still appreciable uncatalyzed rate of carbon dioxide hydration generates more protons. This review summarizes the available evidence and determines that resolution of this question will require more sophisticated measurements of intracellular pH with faster temporal resolution.
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Asadi AK, Sá RC, Arai TJ, Theilmann RJ, Hopkins SR, Buxton RB, Prisk GK. Regional pulmonary perfusion patterns in humans are not significantly altered by inspiratory hypercapnia. J Appl Physiol (1985) 2019; 127:365-375. [PMID: 31169470 DOI: 10.1152/japplphysiol.00254.2018] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
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 FICO2 (P = 0.90). Reanalysis of previously collected data using a similar protocol but with the physiological challenge replaced by decreased FIO2 (FIO2 = 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.
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Affiliation(s)
- Amran K Asadi
- Department of Anesthesiology, Stanford University, Stanford, California
| | - Rui Carlos Sá
- Department of Medicine, University of California, San Diego, La Jolla, California
| | - Tatsuya J Arai
- Department of Medicine, University of California, San Diego, La Jolla, California
| | - Rebecca J Theilmann
- Department of Radiology, University of California, San Diego, La Jolla, California
| | - Susan R Hopkins
- Department of Medicine, University of California, San Diego, La Jolla, California.,Department of Radiology, University of California, San Diego, La Jolla, California
| | - Richard B Buxton
- Department of Radiology, University of California, San Diego, La Jolla, California
| | - G Kim Prisk
- Department of Medicine, University of California, San Diego, La Jolla, California.,Department of Radiology, University of California, San Diego, La Jolla, California
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Abstract
Oxygen delivery and carbon dioxide removal being critical to cell survival, mammals have developed collateral vascular and ventilation systems to ensure tissue viability. Collateral ventilation, defined as ventilation of alveoli via pathways that bypass normal airways, is present in humans and many other species. The presence of collateral ventilation can be beneficial in certain disease states, whereas its relative absence can predispose to other diseases. These well defined anatomical pathways contribute little to ventilation in normal humans, but modulate ventilation perfusion imbalance in a variety of diseases, including obstructive diseases, such as asthma and emphysema. These pathways can be affected by pharmaceuticals and inhaled gas compositions. The middle lobe and lingula, constrained by their isolated, segmental anatomy, have reduced collateral ventilation, which predisposes them to disease. Recently, attempts to improve the quality of life of patients with emphysema, by performing nonsurgical lung volume reduction via use of endobronchial valves, have led to mixed results, because the role of collateral ventilation in the success or failure of the procedure was not initially appreciated. This review describes the anatomical pathways of collateral ventilation, their physiology and relationship to disease states, their modulatory effects on gas exchange, treatment considerations, and their effect on diagnostic procedures.
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Hopkins SR, Elliott AR, Prisk GK, Darquenne C. Ventilation heterogeneity measured by multiple breath inert gas testing is not affected by inspired oxygen concentration in healthy humans. J Appl Physiol (1985) 2017; 122:1379-1387. [PMID: 28280107 DOI: 10.1152/japplphysiol.01013.2016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2016] [Revised: 03/03/2017] [Accepted: 03/08/2017] [Indexed: 11/22/2022] Open
Abstract
Multiple breath washout (MBW) and oxygen-enhanced MRI techniques use acute exposure to 100% oxygen to measure ventilation heterogeneity. Implicit is the assumption that breathing 100% oxygen does not induce changes in ventilation heterogeneity; however, this is untested. We hypothesized that ventilation heterogeneity decreases with increasing inspired oxygen concentration in healthy subjects. We performed MBW in 8 healthy subjects (4 women, 4 men; age = 43 ± 15 yr) with normal pulmonary function (FEV1 = 98 ± 6% predicted) using 10% argon as a tracer gas and oxygen concentrations of 12.5%, 21%, or 90%. MBW was performed in accordance with ERS-ATS guidelines. Subjects initially inspired air followed by a wash-in of test gas. Tests were performed in balanced order in triplicate. Gas concentrations were measured at the mouth, and argon signals rescaled to mimic a N2 washout, and analyzed to determine the distribution of specific ventilation (SV). Heterogeneity was characterized by the width of a log-Gaussian fit of the SV distribution and from Sacin and Scond indexes derived from the phase III slope. There were no significant differences in the ventilation heterogeneity due to altered inspired oxygen: histogram width (hypoxia 0.57 ± 0.11, normoxia 0.60 ± 0.08, hyperoxia 0.59 ± 0.09, P = 0.51), Scond (hypoxia 0.014 ± 0.011, normoxia 0.012 ± 0.015, hyperoxia 0.010 ± 0.011, P = 0.34), or Sacin (hypoxia 0.11 ± 0.04, normoxia 0.10 ± 0.03, hyperoxia 0.12 ± 0.03, P = 0.23). Functional residual capacity was increased in hypoxia (P = 0.04) and dead space increased in hyperoxia (P = 0.0001) compared with the other conditions. The acute use of 100% oxygen in MBW or MRI is unlikely to affect ventilation heterogeneity.NEW & NOTEWORTHY Hyperoxia is used to measure the distribution of ventilation in imaging and MBW but may alter the underlying ventilation distribution. We used MBW to evaluate the effect of inspired oxygen concentration on the ventilation distribution using 10% argon as a tracer. Short-duration exposure to hypoxia (12.5% oxygen) and hyperoxia (90% oxygen) during MBW had no significant effect on ventilation heterogeneity, suggesting that hyperoxia can be used to assess the ventilation distribution.
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Affiliation(s)
- Susan R Hopkins
- Department of Medicine, University of California, San Diego, La Jolla, California; and .,Department of Radiology, University of California, San Diego, La Jolla, California
| | - Ann R Elliott
- Department of Medicine, University of California, San Diego, La Jolla, California; and
| | - G Kim Prisk
- Department of Medicine, University of California, San Diego, La Jolla, California; and.,Department of Radiology, University of California, San Diego, La Jolla, California
| | - Chantal Darquenne
- Department of Medicine, University of California, San Diego, La Jolla, California; and
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Tsang JYC, Hogg JC. Gas exchange and pulmonary hypertension following acute pulmonary thromboembolism: has the emperor got some new clothes yet? Pulm Circ 2014; 4:220-36. [PMID: 25006441 DOI: 10.1086/675985] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/25/2013] [Accepted: 02/17/2014] [Indexed: 01/09/2023] Open
Abstract
Patients present with a wide range of hypoxemia after acute pulmonary thromboembolism (APTE). Recent studies using fluorescent microspheres demonstrated that the scattering of regional blood flows after APTE, created by the embolic obstruction unique in each patient, significantly worsened regional ventilation/perfusion (V/Q) heterogeneity and explained the variability in gas exchange. Furthermore, earlier investigators suggested the roles of released vasoactive mediators in affecting pulmonary hypertension after APTE, but their quantification remained challenging. The latest study reported that mechanical obstruction by clots accounted for most of the increase in pulmonary vascular resistance, but that endothelin-mediated vasoconstriction also persisted at significant level during the early phase.
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Affiliation(s)
- John Y C Tsang
- Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
| | - James C Hogg
- Department of Pathology, University of British Columbia, Vancouver, British Columbia, Canada
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Glenny RW, Robertson HT. Spatial distribution of ventilation and perfusion: mechanisms and regulation. Compr Physiol 2013; 1:375-95. [PMID: 23737178 DOI: 10.1002/cphy.c100002] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
With increasing spatial resolution of regional ventilation and perfusion, it has become more apparent that ventilation and blood flow are quite heterogeneous in the lung. A number of mechanisms contribute to this regional variability, including hydrostatic gradients, pleural pressure gradients, lung compressibility, and the geometry of the airway and vascular trees. Despite this marked heterogeneity in both ventilation and perfusion, efficient gas exchange is possible through the close regional matching of the two. Passive mechanisms, such as the shared effect of gravity and the matched branching of vascular and airway trees, create efficient gas exchange through the strong correlation between ventilation and perfusion. Active mechanisms that match local ventilation and perfusion play little if no role in the normal healthy lung but are important under pathologic conditions.
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Affiliation(s)
- Robb W Glenny
- Department of Medicine, University of Washington, USA.
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9
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Emery MJ, Eveland RL, Min JH, Hildebrandt J, Swenson ER. CO2 relaxation of the rat lung parenchymal strip. Respir Physiol Neurobiol 2013; 186:33-9. [PMID: 23305910 DOI: 10.1016/j.resp.2012.12.014] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2012] [Revised: 12/29/2012] [Accepted: 12/29/2012] [Indexed: 01/13/2023]
Abstract
Evidence from liquid-filled rat lungs supported the presence of CO2-dependent, active relaxation of parenchyma under normoxia by unknown mechanisms (Emery et al., 2007). This response may improve matching of alveolar ventilation (V˙A) to perfusion (Q˙) by increasing compliance and V˙A in overperfused (high CO2) regions, and decrease V˙A in underperfused regions. Here, we have more directly studied CO2-dependent parenchymal relaxation and tested a hypothesized role for actin-myosin interaction in this effect. Lung parenchymal strips (∼1.5mm×1.5mm×15mm) from 16 rats were alternately exposed to normoxic hypocapnia ( [Formula: see text] ) or hypercapnia ( [Formula: see text] ). Seven specimens were used to construct length-tension curves, and nine were tested with and without the myosin blocker 2,3-butanedione monoxime (BDM). The results demonstrate substantial, reversible CO2-dependent changes in parenchyma strip recoil (up to 23%) and BDM eliminates this effect, supporting a potentially important role for parenchymal myosin in V˙A/Q˙ matching.
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Affiliation(s)
- Michael J Emery
- Pulmonary and Critical Care Medicine (S-111-PULM), VA Puget Sound Health Care System, 1660 South Columbian Way, Seattle, WA 98108, USA.
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Kim YS, An SJ, Lee HJ, Choi HJ. Change in the electroencephalogram delta wave in the frontal cranial region of rats with the hyperventilation. Respir Physiol Neurobiol 2012; 181:177-82. [PMID: 22406840 DOI: 10.1016/j.resp.2012.02.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2011] [Revised: 02/28/2012] [Accepted: 02/29/2012] [Indexed: 10/28/2022]
Abstract
Hyperventilation is one way to cause activation on the electroencephalogram (EEG) to diagnose brain disorders. The hyperventilation is also known to affect on the delta power in EEG. This study divided the total delta wave into low, middle, and high bands corresponding to the wave frequency. The power in these three delta wave bands was examined in the frontal cranial region of adult male Sprague-Dawley rats hyperventilated with ventilation (VE) of 360, 540, and 720 ml/min for 5 min. The control group was ventilated normally with a volume of 160 ml/min. The results show that the relative power of the low delta band in the rats hyperventilated at 360 ml/min VE was significantly increased compared with powers of pre-hyperventilation (p<0.05). The relative power of the middle delta band was not significantly affected by hyperventilation at any VE, and in the high delta band, all of the relative powers were decreased significantly in all hyperventilated rats compared with powers of pre-hyperventilation (p<0.05). We concluded that hyperventilation affects the frontal cranial region, by increasing the low delta band and decreasing the high delta band.
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Affiliation(s)
- Young Sik Kim
- Department of Smart Foods and Drugs, Inje University, Gimhae 621-749, Republic of Korea.
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Swenson ER. CON: Most Climbers Do Not Develop Subclinical Interstitial Pulmonary Edema. High Alt Med Biol 2011; 12:125-8; discussion 129-30. [DOI: 10.1089/ham.2011.0005] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Erik R. Swenson
- VA Puget Sound Health Care System, University of Wasington, Seattle, Washington
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12
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Abstract
Carbon dioxide is a waste product of aerobic cellular respiration in all aerobic life forms. PaCO2 represents the balance between the carbon dioxide produced and that eliminated. Hypocapnia remains a common - and generally underappreciated - component of many disease states, including early asthma, high-altitude pulmonary edema, and acute lung injury. Induction of hypocapnia remains a common, if controversial, practice in both adults and children with acute brain injury. In contrast, hypercapnia has traditionally been avoided in order to keep parameters normal. More recently, advances in our understanding of the role of excessive tidal volume has prompted clinicians to use ventilation strategies that result in hypercapnia. Consequently, hypercapnia has become increasingly prevalent in the critically ill patient. Hypercapnia may play a beneficial role in the pathogenesis of inflammation and tissue injury, but may hinder the host response to sepsis and reduce repair. In contrast, hypocapnia may be a pathogenic entity in the setting of critical illness. The present paper reviews the current clinical status of low and high PaCO2 in the critically ill patient, discusses the insights gained to date from studies of carbon dioxide, identifies key concerns regarding hypocapnia and hypercapnia, and considers the potential clinical implications for the management of patients with acute lung injury.
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Affiliation(s)
- Gerard Curley
- Department of Anaesthesia, Clinical Sciences Institute, National University of Ireland, Galway, Ireland
- Lung Biology Group, National Centre of Biomedical Engineering Sciences, National University of Ireland, Galway, Ireland
| | - John G Laffey
- Department of Anaesthesia, Clinical Sciences Institute, National University of Ireland, Galway, Ireland
- Lung Biology Group, National Centre of Biomedical Engineering Sciences, National University of Ireland, Galway, Ireland
| | - Brian P Kavanagh
- Departments of Critical Care Medicine and Anesthesia and the Program in Physiology and Experimental Medicine, The Hospital for Sick Children, University of Toronto, 555 university Avenue, Toronto, ON M5G 1X8, Canada
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Dorrington KL, Balanos GM, Talbot NP, Robbins PA. Extent to which pulmonary vascular responses to PCO2 and PO2 play a functional role within the healthy human lung. J Appl Physiol (1985) 2010; 108:1084-96. [PMID: 20185627 PMCID: PMC2867535 DOI: 10.1152/japplphysiol.90963.2008] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Regional blood flow in the lung is known to be influenced by the alveolar Pco2 and alveolar Po2. For the healthy lung, the extent to which this influence is of functional importance in limiting heterogeneity in alveolar gas composition by matching regional perfusion (q̇) to regional ventilation (v̇) remains unclear. To address this issue, the efficiency of regulation (E) was defined as the percent correction to an initial perturbation in regional alveolar gas composition generated by the pulmonary vascular response to the disturbance. This study develops the theory to calculate E from global measurements of vascular reactivity to CO2 and O2 in human volunteers. For O2, these data were available from the literature. For CO2, an experimental component of the present study used Doppler echocardiography to evaluate the magnitude of the global vascular response to hypercapnia and hypocapnia in 12 volunteers over a timescale of ∼0.5 h. The results suggest a value for E of ∼60% over a wide range of values for v̇-to-q̇ ratio (∼0.1–10) encompassing those found in normal lung. At low v̇/q̇ (<0.65), the vascular response to O2 forms the dominant mechanism; however, at higher v̇/q̇ (>0.65), the response to CO2 dominates. The values for E suggest that the pulmonary vascular responses to both CO2 and O2 play a significant role in ventilation-perfusion matching in the healthy human lung.
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Affiliation(s)
- Keith L Dorrington
- Department of Physiology, Anatomy & Genetics, Sherrington Bldg., Parks Road, University of Oxford, Oxford, OX1 3PT, UK
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Tsang JYC, Lamm WJE, Swenson ER. Regional CO2 tension quantitatively mediates homeostatic redistribution of ventilation following acute pulmonary thromboembolism in pigs. J Appl Physiol (1985) 2009; 107:755-62. [PMID: 19608933 DOI: 10.1152/japplphysiol.00245.2009] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Previous studies reported that regional CO(2) tension might affect regional ventilation (V) following acute pulmonary thromboembolism (APTE). We investigated the pathophysiology and magnitude of these changes. Eight anesthetized and ventilated piglets received autologous clots at time = 0 min until mean pulmonary artery pressure was 2.5 times baseline. The distribution of V and perfusion (Q) at four different times (-5, 30, 60, 120 min) was mapped by fluorescent microspheres. Regional V and Q were examined postmortem by sectioning the air-dried lung into 900-1,000 samples of approximately 2 cm(3) each. After the redistribution of regional Q by APTE, but in the scenario assuming that no V shift had yet occurred, CO(2) tension in different lung regions at 30 min post-APTE (P(X)CO(2)) was estimated from the V/Q data and divided into four distinct clusters: i.e., P(X)CO(2) < 10 Torr; 10 < P(X)CO(2) < 25 Torr; 25 < P(X)CO(2) < 50 Torr; P(X)CO(2) > 50 Torr. Our data showed that the clusters in higher V/Q regions (with a P(X)CO(2) < 25 Torr) received approximately 35% less V when measured within 30 min of APTE, whereas, in contrast, the lower V/Q regions showed no statistically significant increases in their V. However, after 30 min, there was minimal further redistribution of V. We conclude that there are significant compensatory V shifts out of regions of low CO(2) tension soon following APTE, and that these variations in regional CO(2) tension, which initiate CO(2)-dependent changes in airway resistance and lung parenchymal compliance, can lead to improved gas exchange.
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Affiliation(s)
- John Y C Tsang
- James Hogg iCAPTURE Research Laboratory, Division of Critical Care Medicine, Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada V6Z 1Y6
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