Secondary Logo

Journal Logo

Intermittent Hypoxia Causes Inflammation and Injury to Human Adult Cardiac Myocytes

Wu, Jing MD*†; Stefaniak, Joanna MD*; Hafner, Christina MD*; Schramel, Johannes Peter DI, DVM; Kaun, Christoph§; Wojta, Johann PhD§‖¶; Ullrich, Roman MD*; Tretter, Verena Eva DI, PhD*; Markstaller, Klaus MD*; Klein, Klaus Ulrich MD*

doi: 10.1213/ANE.0000000000001048
Ambulatory Anesthesiology and Perioperative Management: Research Report
Free

BACKGROUND: Intermittent hypoxia may occur in a number of clinical scenarios, including interruption of myocardial blood flow or breathing disorders such as obstructive sleep apnea. Although intermittent hypoxia has been linked to cardiovascular and cerebrovascular disease, the effect of intermittent hypoxia on the human heart is not fully understood. Therefore, in the present study, we compared the cellular responses of cultured human adult cardiac myocytes (HACMs) exposed to intermittent hypoxia and different conditions of continuous hypoxia and normoxia.

METHODS: HACMs were exposed to intermittent hypoxia (0%–21% O2), constant mild hypoxia (10% O2), constant severe hypoxia (0% O2), or constant normoxia (21% O2), using a novel cell culture bioreactor with gas-permeable membranes. Cell proliferation, lactate dehydrogenase release, vascular endothelial growth factor release, and cytokine (interleukin [IL] and macrophage migration inhibitory factor) release were assessed at baseline and after 8, 24, and 72 hours of exposure. A signal transduction pathway finder array was performed to determine the changes in gene expression.

RESULTS: In comparison with constant normoxia and constant mild hypoxia, intermittent hypoxia induced earlier and greater inflammatory response and extent of cell injury as evidenced by lower cell numbers and higher lactate dehydrogenase, vascular endothelial growth factor, and proinflammatory cytokine (IL-1β, IL-6, IL-8, and macrophage migration inhibitory factor) release. Constant severe hypoxia showed more detrimental effects on HACMs at later time points. Pathway analysis demonstrated that intermittent hypoxia primarily altered gene expression in oxidative stress, Wnt, Notch, and hypoxia pathways.

CONCLUSIONS: Intermittent and constant severe hypoxia, but not constant mild hypoxia or normoxia, induced inflammation and cell injury in HACMs. Cell injury occurred earliest and was greatest after intermittent hypoxia exposure. Our in vitro findings suggest that intermittent hypoxia exposure may produce rapid and substantial damage to the human heart.

Published ahead of print October 26, 2015

From the *Department of Anesthesia, General Intensive Care and Pain Management, Medical University of Vienna, Vienna, Austria; Department of Anesthesiology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China; Unit of Anesthesiology and Perioperative Intensive Care, University of Veterinary Medicine, Vienna, Austria; §Department of Internal Medicine II and Core Facilities, Medical University of Vienna, Vienna, Austria; and ¶Ludwig Boltzmann Cluster for Cardiovascular Research, Vienna, Austria.

Accepted for publication September 4, 2015.

Published ahead of print October 26, 2015

Funding: The study was supported by a grant from the Mayor of the City of Vienna, Vienna, Austria.

The authors declare no conflicts of interest.

Reprints will not be available from the authors.

Address correspondence to Klaus Ulrich Klein, MD, Department of Anesthesia, General Intensive Care and Pain Management, Medical University of Vienna, Waehringer Guertel 18-20, A-1090 Vienna, Austria. Address e-mail to ulrich.klein@meduniwien.ac.at.

Obstructive sleep apnea (OSA) is a common breathing disorder associated with increased cardiovascular morbidity and mortality, including hypertension, ischemic heart disease, chronic heart failure, arrhythmias, and strokes.1,2 The hallmark of OSA is intermittent hypoxia resulting in periodic hypoxemia, hypercapnia, sleep disturbances, and increased sympathetic activity with potentially deleterious effects on the human body.3,4

Intermittent hypoxia can be considered analogous to repeated ischemia and reperfusion injury, thereby causing high levels of reactive oxygen species and other signaling molecules that can promote myocardial inflammation and injury.3–5 Obviously, these injurious mechanisms are important in the perioperative period.6–9 Although intermittent hypoxia caused by OSA has been linked to endothelial dysfunction and cardiovascular and cerebrovascular disease,3,4,10 no study has investigated the effects of intermittent hypoxia on human adult cardiac myocytes (HACMs).

The present in vitro study compared the effects of intermittent hypoxia (0%–21% O2, average value 10% O2), constant mild hypoxia (10% O2), constant severe hypoxia (0% O2), and constant normoxia (21% O2) on cell count and injurious responses of HACMs. We hypothesized that intermittent hypoxia exposure would have detrimental effects on HACMs as quantified by cell count, lactate dehydrogenase (LDH) release, vascular endothelial growth factor (VEGF) release, and cytokine (interleukin [IL] and macrophage migration inhibitory factor [MIF]) release. A signal transduction pathway finder array for gene expression analysis was performed to unravel the pathomechanisms associated with intermittent hypoxia exposure in HACMs.

Back to Top | Article Outline

METHODS

Isolation and Culture of HACMs

Experiments were performed after obtaining written patient consent and permission of the Ethics Committee of the Medical University of Vienna (approval 151/2008). HACMs were harvested from explanted hearts during heart transplantation and isolated as described previously.11 All experiments were performed with HACMs at passage 3 to 5. The cells were seeded into OptiCell™ (OC) plates (Nunc, Thermo Scientific, Waltham, MA) precoated with 1% gelatin (Sigma-Aldrich, St. Louis, MO) at 5 × 104 cells per plate and cultured under standard growth conditions in M199 medium (Gibco, Invitrogen, Carlsbad, CA) supplemented with 20% fetal bovine serum (Superior, Biochrom, Berlin, Germany) and 1% penicillin/streptomycin (Gibco) for 7 days. After starvation for 24 hours in M199 containing 0.1% bovine serum albumin (Sigma-Aldrich), the cells were exposed to different O2 concentrations.

Back to Top | Article Outline

Experimental Setup

The cell culture system consisted of OC plates stacked in custom-made boxes (Fig. 1A). Each OC plate consists of 2 parallel gas-permeable respiratory active membranes (RAMs) and a chamber for 10 mL of medium. Cells grow on the inside of the RAMs, with nutrients delivered via the medium. O2 exchange is maintained via rapid diffusion through the RAMs. For gas supply, 10 OC plates are surrounded by 11 gas supply frames. The stack of these plates is organized in a custom-made framed metal box. Gas supply tubes connect the gas distributor to premixed gas bottles, forming a unit for exposure of cells to specific O2 conditions.

Figure 1

Figure 1

The intermittent hypoxia unit was connected to an electronic gas flow meter and a computer-controlled valve (EL-Flow Select Series, Bronkhorst, Netherlands) to switch between 95% N2/5% CO2 and 21% O2/5% CO2/74% N2 every 10 minutes, resulting in 3 full O2 oscillation cycles per hour. The constant mild hypoxia, severe hypoxia, and normoxia units were connected to premixed gas bottles of 10% O2/5% CO2/85% N2, 95% N2/5% CO2, and 21% O2/5% CO2/74% N2, respectively. All units and their gas supply tubes were stored in a standard cell incubator (Heratherm, Thermo Fisher Scientific, Waltham, MA) at 37°C. O2 concentrations of the gas supply, inside the boxes, as well as O2 diffusion through the RAMs were measured using precalibrated ultrarapid fluorescence quenching of O2 probes (NeoFox AL300 and RedEye, Ocean Optics, Dunedin, FL). Temperature and humidity in the units were controlled using an electronic sensor (SHT-71; Sensirion, Staefa, Switzerland). A pressure-measuring catheter was inserted into an OC plate and connected to a pressure gauge (Arrow, Reading, PA).

Back to Top | Article Outline

Cell Count and Cytotoxicity Assays

OC plates were removed from the system after 0 (baseline), 8, 24, and 72 hours. To assess plasma membrane damage, the culture medium was collected and LDH activity was measured using a colorimetric enzymatic assay (Cytotoxicity Detection Kit; Roche, Mannheim, Germany). In addition, 100 µL of the cell suspension was lysed in phosphate-buffered saline with 1% Triton X-100 (Sigma-Aldrich) and used for the determination of total LDH. Optical density was measured at 490 nm on a spectrophotometer (Viktor3; PerkinElmer, Waltham, MA). Subsequently, the cells were harvested, centrifuged, and resuspended in 1 mL of phosphate-buffered saline to count the cells using a hemocytometer (Hausser Scientific, Horsham, PA).

Back to Top | Article Outline

Cytokine Secretion Assays

Cell culture supernatant was collected after 0, 8, 24, and 72 hours of treatment. VEGF, IL-1β, IL-6, IL-8, and MIF concentrations were measured using specific enzyme-linked immunosorbent assay (DuoSet; R&D Systems, Minneapolis, MN). Optical density readings for each protein were compared with standard curves to quantify the amount of protein in the original samples. The values were normalized to cell count and expressed as the percentage of baseline.

Back to Top | Article Outline

Gene Expression

Changes in gene expression were assessed using a human signal transduction pathway finder RT2 Profiler polymerase chain reaction (PCR) array (SA Biosciences, Frederick, MD) composed of 84 primer pairs representing genes from 18 distinct signaling pathways. In brief, total RNA was extracted from cells harvested after 24 hours of exposure to one of the oxygenation protocols using the RNeasy mini plus kit (Qiagen, Valencia, CA). After reverse transcription into cDNA using the RT2 First Strand kit (Qiagen), PCR was performed with Rotor-Gene Q (Qiagen) using the RT2 Profiler PCR array.

Back to Top | Article Outline

Statistical Analysis

All experiments were performed with 3 independent cultures from different hearts and in triplicate for each cell culture. Data are expressed as mean ± SEM. Analyses and graphing were performed with Prism 6.0 software (GraphPad, San Diego, CA). Data were analyzed for Gaussian distribution using the D’Agostino-Pearson omnibus normality test (P < 0.05). Two-way analysis of variance was performed to test for differences between groups, followed by the Bonferroni method for correction of multiple comparisons (P < 0.05). Genomic data were analyzed using the RT2 Profiler PCR array data analysis 3.5 software (SA Biosciences). The P values were calculated based on a Student t test of the replicate 2^(−Delta Ct) values for each gene in the control group (21% O2) and treatment groups.

Back to Top | Article Outline

RESULTS

Confirmation of O2 Concentrations

Three measurements at a low gas flow rate (0.5 L/min) were performed to determine the 10% to 90% time constants (Trise and Tfall) for O2 diffusion through the RAMs. Measurements revealed a Trise of 286 ± 4 seconds and a Tfall of 370 ± 6 seconds (Fig. 1B). Therefore, O2 oscillations were set to a 20-minute cycling frequency (cycle duration) to allow 3 full O2 oscillation cycles per hour (Fig. 1C). The desired O2 oscillations were produced in the intermittent hypoxia unit (O2 oscillation range, 0%–21%; average value, 10%). Constant O2 concentrations were confirmed for normoxia (21% ± 0.5% O2), mild hypoxia (10% ± 0.3% O2), and severe hypoxia (0% ± 0.5% O2). Pressure measurements in OC plates showed no significant increase in pressure (<1 cm H2O) because of cyclically altered or constant gas flow.

Back to Top | Article Outline

Cell Count and Viability

Figure 2

Figure 2

Figure 3

Figure 3

Under phase contrast microscopy, HACMs exposed to 72 hours of intermittent hypoxia or severe hypoxia appeared more flat and spindle shaped than cells incubated under normoxia or mild hypoxia for the same period of time (Fig. 2, A–D). Cultures exposed to intermittent hypoxia for 8 hours showed a reduced cell count to those exposed to mild hypoxia (P < 0.01; Fig. 3A), whereas cultures exposed to mild hypoxia exposed for 8 hours showed an increased cell count (P < 0.05). Furthermore, cultures exposed to intermittent hypoxia for 8 hours released more LDH than cells exposed to mild hypoxia (P < 0.05) or normoxia (P < 0.05), indicating a more rapid cytotoxic response (Fig. 3B). After 24 hours, the cell count was similar in cultures exposed to intermittent hypoxia, mild hypoxia, and normoxia but significantly lower in cultures exposed to severe hypoxia (P < 0.05). Similarly, more LDH was released from cultures exposed to severe hypoxia compared with normoxia or mild hypoxia after 24 hours (P < 0.05). After 72 hours, cell count was reduced in cultures exposed to intermittent hypoxia and severe hypoxia than in cultures exposed to mild hypoxia (P < 0.01) or normoxia (P < 0.0001). Furthermore, intermittent, mild, and severe hypoxia exposure resulted in greater LDH release compared with all other groups after 72 hours (P < 0.01). Thus, intermittent hypoxia resulted in a more rapid and severe cytotoxic response than sustained hypoxia of the same average O2 or normoxia.

Back to Top | Article Outline

Cytokine Secretion

Figure 4

Figure 4

VEGF release, as estimated by the accumulation in the medium, was higher in HACM cultures exposed to severe hypoxia for 24 hours compared with cultures exposed to normoxia (P < 0.0001; Fig. 3C). Compared with normoxia, extracellular VEGF accumulation was higher after 72 hours of exposure to mild hypoxia (2-fold, P < 0.05), intermittent hypoxia (9-fold, P < 0.0001), or severe hypoxia (12-fold, P < 0.0001). After 8 hours, IL-1β secretion was higher in cultures exposed to intermittent hypoxia compared with mild hypoxia (P < 0.05; Fig. 4A). IL-1β release after 24 hours was highest from cultures exposed to severe hypoxia compared with all other groups (P < 0.05). IL-1β release after 72 hours was greater from cultures exposed to intermittent hypoxia and to severe hypoxia than from those exposed to normoxia (P < 0.0001) or mild hypoxia (P < 0.0001). Similar patterns could be observed for IL-6 and IL-8 secretions, revealing significant increases after 72-hour exposure to intermittent hypoxia compared with mild hypoxia (P < 0.05) or normoxia (P < 0.0001; Fig. 4, B and C). Furthermore, cultures exposed to severe hypoxia showed greater MIF release after 24 hours than cells exposed to normoxia (P < 0.05) or mild hypoxia (P < 0.05). After 72 hours, MIF release was higher in cultures exposed to intermittent hypoxia and severe hypoxia compared with mild hypoxia (P < 0.05) or normoxia (P < 0.05).

Back to Top | Article Outline

Gene Expression

Table 1

Table 1

Nineteen genes showed significant changes in mRNA abundance after 24 hours of hypoxia (Table 1). The expression levels of 4 genes in the hypoxia signaling pathway (lactate dehydrogenase A [LDHA], vascular endothelial growth factor A [VEGFA], carbonic anhydrase IX [CA9], WNT1 inducible signaling pathway protein 1 [WISP1]) were upregulated in cultures exposed to severe hypoxia. In contrast, WISP1 expression was downregulated in cultures exposed to intermittent hypoxia. The expression of 3 genes including the antiapoptotic member of the BCL2 gene family (BCL2L1), the gene encoding glutamate cysteine ligase (GCLC), and the gene encoding plasminogen activator inhibitor-1 (SERPINE1) were selectively downregulated by intermittent hypoxia. Furthermore, the expression levels of Dab, mitogen-responsive phosphoprotein homolog 2 (DAB2), growth arrest and DNA-damage-inducible beta (GADD45B), Hes family BHLH transcription factor 1 (HES1), interferon regulatory factor 1 (IRF1), v-myc avian myelocytomatosis viral oncogene homolog (MYC), wingless-type MMTV integration site family, member 5A (WNT5A) were downregulated in cultures exposed to intermittent hypoxia and severe hypoxia but not in cultures exposed to mild hypoxia.

Back to Top | Article Outline

DISCUSSION

We demonstrated that intermittent hypoxia (0%–21% O2) exerts deleterious effects on HACMs, as evidenced by lower cell count and higher LDH, VEGF, and cytokine (IL-1β, IL-6, IL-8, and MIF) secretion. Moreover, cell inflammation and injury occurred earliest in the intermittent hypoxia group. Severe hypoxia showed more detrimental effects on HACMs at later time points. Pathway analysis showed that intermittent hypoxia exposure activated the oxidative stress, Wnt, Notch, and hypoxia pathways. Our in vitro results suggest that intermittent hypoxia, occurring during OSA or other respiratory-related diseases, may have early injurious effects on human myocardial cells equal to or partially exceeding those induced by constant severe hypoxia.

Back to Top | Article Outline

Clinical Relevance

Intermittent hypoxia may occur in a number of clinical scenarios, including the interruption of myocardial blood flow and disorders such as OSA, chronic obstructive lung disease, smoking, sickle cell anemia, or immaturity of newborns.3,4 In addition, cyclic recruitment and derecruitment of atelectasis during mechanical ventilation can result in intermittent hypoxia.12–18 This phenomenon occurs because of repetitive opening and closing of atelectasis (cyclic atelectasis), thereby causing varying pulmonary shunt fraction. In subjects with lung disease, cyclic atelectasis can cause within-breath arterial partial pressure of O2 oscillations that are transmitted with the circulation to organs, exposing them to intermittent hypoxia.19–21

The underlying mechanisms by which OSA-related intermittent hypoxia causes injury to the myocardium have been partially investigated. OSA has been described to be an independent risk factor for heart failure, arrhythmias, and myocardial infarction.3–5 In contrast, the effect of intermittent hypoxia caused by cyclic atelectasis on the myocardium presently remains unknown. Although cyclic atelectasis has not been demonstrated in clinical settings, some evidence hints toward its existence in patients undergoing high-risk surgery because arterial partial pressure of O2 levels can fluctuate, despite hemodynamic steady-state conditions.22,23 Importantly, intermittent hypoxia caused by either OSA or cyclic atelectasis may largely differ in frequency, amplitude, or range and therefore may exhibit different effects on the cardiovascular system and organs. As an example, brief periods of intermittent hypoxia can promote protection by hypoxic preconditioning, whereas long-term intermittent hypoxia such as during OSA can exhibit harmful cardiovascular and cerebrovascular effects.3,4,24 These associations of intermittent hypoxia are complex; therefore, research needs to identify the detailed characteristics of intermittent hypoxia in more detail.

Back to Top | Article Outline

Cell Count and Viability

Numerous studies have investigated the effects of constant hypoxia on murine cardiac myocytes. However, few studies have examined HACMs, and no previous investigation has compared the cytotoxicity of sustained versus intermittent hypoxia in HACMs. The present study reveals that exposure of HACMs to intermittent hypoxia resulted in more injury than exposure to constant hypoxia of the same average O2, irrespective of the duration. Moreover, intermittent hypoxia induced the greatest injury within the first 8 hours. Consistent with our findings, previous studies have reported chronic intermittent hypoxia-induced myocardial injury in rodents.25–27 However, other preclinical studies reported growth-promoting effects by intermittent hypoxia and protection against subsequent severe hypoxia.28–30 As highlighted earlier, discrepancies may result from differences in the severity, frequency, and/or duration of intermittent hypoxia exposure, and intermittent hypoxia can exert dichotomous (harm or benefit) effects on the human body.31

Back to Top | Article Outline

Cytokine Secretion

The secretion rates of IL-1β, IL-6, IL-8, and MIF, which are widely accepted mediators of myocardial inflammation and injury, were higher under intermittent and severe hypoxia than under mild hypoxia. This finding may account, in part, for enhanced cytotoxicity.3,4,32 Notably, an increase in IL-1β, promoting inflammation, occurred earliest in intermittent hypoxia-treated HACMs. Although the effects of IL-6 and IL-8 on cardiac myocytes remain poorly understood, it is widely accepted that IL-8 promotes chemotaxis, which could enhance the infiltration of other inflammatory cells into the myocardium.33,34 Alternatively, IL-6 reduces cardiac myocyte apoptosis, suggesting that its activation is an adaptive mechanism to promote survival under intermittent hypoxia.35 MIF has been shown to be expressed by myocardial cells in response to redox stress.36 Furthermore, an increase in MIF serum levels has been discussed as playing a role in the pathogenesis of myocardial ischemia.36,37

Back to Top | Article Outline

Gene Expression

The expression levels of LDHA, CA9, and VEGFA, 3 well-described genes of the hypoxia pathway, were upregulated by mild and severe hypoxia but not by intermittent hypoxia.29 Furthermore, WISP1, a member of the CYR61/CTGF/Nov family of growth factors mediating cell proliferation, transformation, and survival, was upregulated by severe hypoxia but downregulated by intermittent hypoxia. Thus, cytoprotective factors induced by sustained hypoxia may not be induced by intermittent hypoxia. In fact, WISP1 has antiapoptotic effects on cardiac myocytes and regulates postinfarction heart remodeling.38,39 The BCL2 family members are key regulators of mitochondrial apoptosis.40 The BCL2 family members BAX and BCL2 were downregulated by severe hypoxia, whereas BCL2L1 was downregulated selectively by intermittent hypoxia, indicating that the activation of these apoptotic regulators is sensitive to the magnitude and kinetics of hypoxia. These differential gene expression patterns may also account for the observed differences in cell count and cytotoxicity among the treatment groups.

Furthermore, we measured the changes in the expression of genes related to oxidative stress signaling. The gene encoding thioredoxin reductase-1 was downregulated under all 3 hypoxic conditions, whereas the gene encoding GCLC was downregulated selectively by intermittent hypoxia. Glutamate cysteine ligase is a rate-limiting enzyme for the synthesis of glutathione, a crucial antioxidant in mammalian cells. Weakness in this antioxidant defense mechanism exposes cells to greater oxidative stress and increases the risk of myocardial infarction.41 Furthermore, we observed selective downregulation of SERPINE1, the gene encoding plasminogen activator inhibitor-1, after exposure to intermittent hypoxia, suggesting that intermittent hypoxia may also influence plasmatic coagulation.11

Back to Top | Article Outline

Study Limitations

We acknowledge several limitations of our study. O2 was delivered via diffusion through RAMs, which limited the number of O2 oscillation cycles to 3 per hour that is slower than respiration but near the frequency of OSA. Classical cell culture models have investigated key mechanisms associated with intermittent hypoxia by O2 diffusion through the medium.29,42,43 This approach, however, likely requires longer to achieve full O2 equilibrium in the medium than O2 diffusion via RAMs. Therefore, higher intermittent hypoxia cycling frequencies cannot be easily achieved in in vitro models without changing the medium, which also has disadvantages such as mechanical stress on cells and dilution of the medium.44,45 Another important confounder is the O2 concentration used. To produce a measureable effect in vitro, we selected a range of O2 (0%–21%) causing a level of transient hypoxia. Previous investigations revealed that it is very difficult to reduce O2 solitarily by diffusion.46 Therefore, we doubt that real cellular anoxia was induced in the present model. This idea might be supported by our results because we measured 0% ± 0.5% O2 and not true anoxia in the severe hypoxia group. In addition, not all cells died in the severe hypoxia group even after 72 hours, indicating that cells still had enough O2 for survival. Nonetheless, our model provides a foundation for testing specific hypotheses regarding the differential impacts of continuous versus intermittent hypoxia on HACMs.

Back to Top | Article Outline

CONCLUSIONS

In HACMs, intermittent hypoxia (0%–21% O2) and constant severe hypoxia (0% O2) resulted in inflammation and injury, as revealed by reduced cell numbers and elevated LDH, VEGF, IL-1β, IL-6, IL-8, and MIF secretion. Cell inflammation and injury occurred earlier in HACMs exposed to intermittent hypoxia than in cultures exposed to the same average O2 (10% O2) or normoxia (21% O2). Severe hypoxia showed more detrimental effects on HACMs at later time points. Furthermore, intermittent hypoxia resulted in a distinct gene activation pattern that included members of the oxidative stress, Wnt, Notch, and hypoxia pathways. Our in vitro findings suggest that intermittent hypoxia exposure, as occurring during OSA or other respiratory-related diseases, may produce rapid and substantial damage to the human heart.

Back to Top | Article Outline

DISCLOSURES

Name: Jing Wu, MD.

Contribution: This author helped conduct the study, analyze the data, and prepare the manuscript and also contributed equally to the work.

Attestation: Jing Wu approved the final manuscript.

Name: Joanna Stefaniak, MD.

Contribution: This author helped conduct the study, analyze the data, and prepare the manuscript and also contributed equally to the work.

Attestation: Joanna Stefaniak approved the final manuscript.

Name: Christina Hafner, MD.

Contribution: This author helped conduct the study, analyze the data, and prepare the manuscript.

Attestation: Christina Hafner approved the final manuscript.

Name: Johannes Peter Schramel, DI, DVM.

Contribution: This author helped design the study and equipment, prepare the manuscript, and in technical assistance.

Attestation: Johannes Peter Schramel approved the final manuscript.

Name: Christoph Kaun.

Contribution: This author helped prepare the HACMs cell culture and in technical assistance.

Attestation: Christoph Kaun approved the final manuscript.

Name: Johann Wojta, PhD.

Contribution: This author helped design and supervise the study prepare the manuscript.

Attestation: Johann Wojta approved the final manuscript.

Name: Roman Ullrich, MD.

Contribution: This author helped design and supervise the study prepare the manuscript.

Attestation: Roman Ullrich approved the final manuscript.

Name: Verena Eva Tretter, DI, PhD.

Contribution: This author helped design and conduct the study, analyze the data, and prepare the manuscript.

Attestation: Verena Eva Tretter approved the final manuscript.

Name: Klaus Markstaller, MD.

Contribution: This author helped design and supervise the study and prepare the manuscript.

Attestation: Klaus Markstaller approved the final manuscript.

Name: Klaus Ulrich Klein, MD.

Contribution: This author helped design and conduct the study, analyze the data, prepare the manuscript, supervise the study, fund the study, and is the archival author.

Attestation: Klaus Ulrich Klein approved the final manuscript.

This manuscript was handled by: David Hillman, MD.

Back to Top | Article Outline

REFERENCES

1. Somers VK, White DP, Amin R, Abraham WT, Costa F, Culebras A, Daniels S, Floras JS, Hunt CE, Olson LJ, Pickering TG, Russell R, Woo M, Young TAmerican Heart Association Council for High Blood Pressure Research Professional Education Committee, Council on Clinical Cardiology; American Heart Association Stroke Council; American Heart Association Council on Cardiovascular Nursing; American College of Cardiology Foundation. . Sleep apnea and cardiovascular disease: an American Heart Association/American College of Cardiology Foundation Scientific Statement from the American Heart Association Council for High Blood Pressure Research Professional Education Committee, Council on Clinical Cardiology, Stroke Council, and Council on Cardiovascular Nursing. In collaboration with the National Heart, Lung, and Blood Institute National Center on Sleep Disorders Research (National Institutes of Health). Circulation. 2008;118:1080–111
2. Young T, Palta M, Dempsey J, Skatrud J, Weber S, Badr S. The occurrence of sleep-disordered breathing among middle-aged adults. N Engl J Med. 1993;328:1230–5
3. Lavie L. Obstructive sleep apnoea syndrome–an oxidative stress disorder. Sleep Med Rev. 2003;7:35–51
4. Lavie L. Oxidative stress in obstructive sleep apnea and intermittent hypoxia—revisited—the bad ugly and good: implications to the heart and brain. Sleep Med Rev. 2015;20:27–45
5. Lyons OD, Bradley TD. Heart failure and sleep apnea. Can J Cardiol. 2015;31:898–908
6. Fouladpour N, Jesudoss R, Bolden N, Shaman Z, Auckley D. Perioperative complications in obstructive sleep apnea patients undergoing surgery: a review of the legal literature. Anesth Analg. 2016:122–145–51
7. Simpson L, Hillman DR, Cooper MN, Ward KL, Hunter M, Cullen S, James A, Palmer LJ, Mukherjee S, Eastwood P. High prevalence of undiagnosed obstructive sleep apnoea in the general population and methods for screening for representative controls. Sleep Breath. 2013;17:967–73
8. Chung SA, Yuan H, Chung F. A systemic review of obstructive sleep apnea and its implications for anesthesiologists. Anesth Analg. 2008;107:1543–63
9. Hillman DR, Loadsman JA, Platt PR, Eastwood PR. Obstructive sleep apnoea and anaesthesia. Sleep Med Rev. 2004;8:459–71
10. Cadby G, McArdle N, Briffa T, Hillman DR, Simpson L, Knuiman M, Hung J. Severity of OSA is an independent predictor of incident atrial fibrillation hospitalization in a large sleep-clinic cohort. Chest. 2015;148:945–52
11. Macfelda K, Weiss TW, Kaun C, Breuss JM, Zorn G, Oberndorfer U, Voegele-Kadletz M, Huber-Beckmann R, Ullrich R, Binder BR, Losert UM, Maurer G, Pacher R, Huber K, Wojta J. Plasminogen activator inhibitor 1 expression is regulated by the inflammatory mediators interleukin-1alpha, tumor necrosis factor-alpha, transforming growth factor-beta and oncostatin M in human cardiac myocytes. J Mol Cell Cardiol. 2002;34:1681–91
12. Baumgardner JE, Markstaller K, Pfeiffer B, Doebrich M, Otto CM. Effects of respiratory rate, plateau pressure, and positive end-expiratory pressure on PaO2 oscillations after saline lavage. Am J Respir Crit Care Med. 2002;166:1556–62
13. Bergman NA. Cyclic variations in blood oxygenation with the respiratory cycle. Anesthesiology. 1961;22:900–8
14. Folgering H, Smolders FD, Kreuzer F. Respiratory oscillations of the arterial PO2 and their effects on the ventilatory controlling system in the cat. Pflugers Arch. 1978;375:1–7
15. Purves MJ. Fluctuations of arterial oxygen tension which have the same period as respiration. Respir Physiol. 1966;1:281–96
16. Yokota H, Kreuzer F. Alveolar to arterial transmission of oxygen fluctuations due to respiration in anesthetized dogs. Pflugers Arch. 1973;340:291–306
17. Williams EM, Viale JP, Hamilton RM, McPeak H, Sutton L, Hahn CE. Within-breath arterial PO2 oscillations in an experimental model of acute respiratory distress syndrome. Br J Anaesth. 2000;85:456–9
18. Formenti F, Chen R, McPeak H, Matejovic M, Farmery AD, Hahn CE. A fibre optic oxygen sensor that detects rapid PO2 changes under simulated conditions of cyclical atelectasis in vitro. Respir Physiol Neurobiol. 2014;191:1–8
19. Markstaller K, Kauczor HU, Weiler N, Karmrodt J, Doebrich M, Ferrante M, Thelen M, Eberle B. Lung density distribution in dynamic CT correlates with oxygenation in ventilated pigs with lavage ARDS. Br J Anaesth. 2003;91:699–708
20. Klein KU, Boehme S, Hartmann EK, Szczyrba M, Heylen L, Liu T, David M, Werner C, Markstaller K, Engelhard K. Transmission of arterial oxygen partial pressure oscillations to the cerebral microcirculation in a porcine model of acute lung injury caused by cyclic recruitment and derecruitment. Br J Anaesth. 2013;110:266–73
21. Klein KU, Hartmann EK, Boehme S, Szczyrba M, Heylen L, Liu T, David M, Werner C, Markstaller K, Engelhard K. PaO2 oscillations caused by cyclic alveolar recruitment can be monitored in pig buccal mucosa microcirculation. Acta Anaesthesiol Scand. 2013;57:320–5
22. Zaugg M, Lucchinetti E, Zalunardo MP, Zumstein S, Spahn DR, Pasch T, Zollinger A. Substantial changes in arterial blood gases during thoracoscopic surgery can be missed by conventional intermittent laboratory blood gas analyses. Anesth Analg. 1998;87:647–53
23. Pfeiffer B, Syring RS, Markstaller K, Otto CM, Baumgardner JE. The implications of arterial Po2 oscillations for conventional arterial blood gas analysis. Anesth Analg. 2006;102:1758–64
24. Murry CE, Jennings RB, Reimer KA. Preconditioning with ischemia: a delay of lethal cell injury in ischemic myocardium. Circulation. 1986;74:1124–36
25. Chen L, Zhang J, Gan TX, Chen-Izu Y, Hasday JD, Karmazyn M, Balke CW, Scharf SM. Left ventricular dysfunction and associated cellular injury in rats exposed to chronic intermittent hypoxia. J Appl Physiol (1985). 2008;104:218–23
26. Gao YH, Chen L, Ma YL, He QY. Chronic intermittent hypoxia aggravates cardiomyocyte apoptosis in rat ovariectomized model. Chin Med J (Engl). 2012;125:3087–92
27. Matsushita K, Iwanaga S, Oda T, Kimura K, Shimada M, Sano M, Umezawa A, Hata J, Ogawa S. Interleukin-6/soluble interleukin-6 receptor complex reduces infarct size via inhibiting myocardial apoptosis. Lab Invest. 2005;85:1210–23
28. Chen L, Lu XY, Li J, Fu JD, Zhou ZN, Yang HT. Intermittent hypoxia protects cardiomyocytes against ischemia-reperfusion injury-induced alterations in Ca2+ homeostasis and contraction via the sarcoplasmic reticulum and Na+/Ca2+ exchange mechanisms. Am J Physiol Cell Physiol. 2006;290:C1221–9
29. Ryan S, Taylor CT, McNicholas WT. Selective activation of inflammatory pathways by intermittent hypoxia in obstructive sleep apnea syndrome. Circulation. 2005;112:2660–7
30. Silverman HS, Wei S, Haigney MC, Ocampo CJ, Stern MD. Myocyte adaptation to chronic hypoxia and development of tolerance to subsequent acute severe hypoxia. Circ Res. 1997;80:699–707
31. Park AM, Nagase H, Kumar SV, Suzuki YJ. Effects of intermittent hypoxia on the heart. Antioxid Redox Signal. 2007;9:723–9
32. Toldo S, Mezzaroma E, Van Tassell BW, Farkas D, Marchetti C, Voelkel NF, Abbate A. Interleukin-1β blockade improves cardiac remodelling after myocardial infarction without interrupting the inflammasome in the mouse. Exp Physiol. 2013;98:734–45
33. Hayashi S, Kurdowska A, Miller EJ, Albright ME, Girten BE, Cohen AB. Synthetic hexa- and heptapeptides that inhibit IL-8 from binding to and activating human blood neutrophils. J Immunol. 1995;154:814–24
34. Schraufstatter IU, Trieu K, Zhao M, Rose DM, Terkeltaub RA, Burger M. IL-8-mediated cell migration in endothelial cells depends on cathepsin B activity and transactivation of the epidermal growth factor receptor. J Immunol. 2003;171:6714–22
35. Tsujimoto Y. Cell death regulation by the Bcl-2 protein family in the mitochondria. J Cell Physiol. 2003;195:158–67
36. Dayawansa NH, Gao XM, White DA, Dart AM, Du XJ. Role of MIF in myocardial ischaemia and infarction: insight from recent clinical and experimental findings. Clin Sci (Lond). 2014;127:149–61
37. Takahashi M, Nishihira J, Shimpo M, Mizue Y, Ueno S, Mano H, Kobayashi E, Ikeda U, Shimada K. Macrophage migration inhibitory factor as a redox-sensitive cytokine in cardiac myocytes. Cardiovasc Res. 2001;52:438–45
38. Colston JT, de la Rosa SD, Koehler M, Gonzales K, Mestril R, Freeman GL, Bailey SR, Chandrasekar B. Wnt-induced secreted protein-1 is a prohypertrophic and profibrotic growth factor. Am J Physiol Heart Circ Physiol. 2007;293:H1839–46
39. Venkatachalam K, Venkatesan B, Valente AJ, Melby PC, Nandish S, Reusch JE, Clark RA, Chandrasekar B. WISP1, a pro-mitogenic, pro-survival factor, mediates tumor necrosis factor-alpha (TNF-alpha)-stimulated cardiac fibroblast proliferation but inhibits TNF-alpha-induced cardiomyocyte death. J Biol Chem. 2009;284:14414–27
40. Shimizu S, Narita M, Tsujimoto Y. Bcl-2 family proteins regulate the release of apoptogenic cytochrome c by the mitochondrial channel VDAC. Nature. 1999;399:483–7
41. Nakamura S, Kugiyama K, Sugiyama S, Miyamoto S, Koide S, Fukushima H, Honda O, Yoshimura M, Ogawa H. Polymorphism in the 5’-flanking region of human glutamate-cysteine ligase modifier subunit gene is associated with myocardial infarction. Circulation. 2002;105:2968–73
42. Makarenko VV, Usatyuk PV, Yuan G, Lee MM, Nanduri J, Natarajan V, Kumar GK, Prabhakar NR. Intermittent hypoxia-induced endothelial barrier dysfunction requires ROS-dependent MAP kinase activation. Am J Physiol Cell Physiol. 2014;306:C745–52
43. Yuan G, Adhikary G, McCormick AA, Holcroft JJ, Kumar GK, Prabhakar NR. Role of oxidative stress in intermittent hypoxia-induced immediate early gene activation in rat PC12 cells. J Physiol. 2004;557:773–83
44. Baumgardner JE, Otto CM. In vitro intermittent hypoxia: challenges for creating hypoxia in cell culture. Respir Physiol Neurobiol. 2003;136:131–9
45. Tsapikouni T, Garreta E, Melo E, Navajas D, Farré R. A bioreactor for subjecting cultured cells to fast-rate intermittent hypoxia. Respir Physiol Neurobiol. 2012;182:47–52
46. Allen CB, Schneider BK, White CW. Limitations to oxygen diffusion and equilibration in in vitro cell exposure systems in hyperoxia and hypoxia. Am J Physiol Lung Cell Mol Physiol. 2001;281:L1021–7
© 2016 International Anesthesia Research Society