Intermittent hypoxia preconditioning can attenuate acute hypoxic injury after a sustained normobaric hypoxic exposure: A randomized clinical trial

BACKGROUND

Intermittent hypoxia (IH) is emerging as a cost-effective nonpharmacological method for vital organ protection. We aimed to assess the effects of a short-term moderate intermittent hypoxia preconditioning protocol (four cycles of 13% hypoxia lasting for 10 min with 5-min normoxia intervals) on acute hypoxic injury induced by sustained hypoxic exposure (oxygen concentration of 11.8% for 6 h).

METHODS

One hundred healthy volunteers were recruited and randomized to the IH group and the control group to receive IH or sham-IH preconditioning for 5 days, respectively, and then were sent to a hypoxic chamber for simulated acute high-altitude exposure (4500 m).

RESULTS

The overall incidence of acute mountain sickness was 27% (27/100), with 14% (7/50) in the IH group and 40% (20/50) in the control group (p = 0.003). After 6-h simulated high-altitude exposure, the mean Lake Louise Score was lower in the IH group as compared to controls (1.30 ± 1.27 vs. 2.04 ± 1.89, p = 0.024). Mean peripheral oxygen saturations (SpO2 ) and intracranial pressure (ICP) measures after acute hypoxic exposure exhibited significant differences, with the IH group showing significantly greater SpO2 values (85.47 ± 5.14 vs. 83.10 ± 5.15%, p = 0.026) and lower ICP levels than the control group (115.59 ± 32.15 vs. 130.36 ± 33.83 mmH2 O, p = 0.028). IH preconditioning also showed greater effects on serum protein gene product 9.5 (3.89 vs. 29.16 pg/mL; p = 0.048) and C-reactive protein (-0.28 vs. 0.41 mg/L; p = 0.023).

CONCLUSION

The short-term moderate IH improved the tolerance to hypoxia and exerted protection against acute hypoxic injury induced by exposure to sustained normobaric hypoxia, which provided a novel method and randomized controlled trial evidence to develop treatments for hypoxia-related disease.

Impact of Age on Cognitive Testing Practice Effects and Cardiorespiratory Responses

Objective: This study tested the hypothesis that healthy aging attenuates cognitive practice effects and, consequently, limits the familiarity-associated reductions in heart rate (HR) and breathing frequency (BF) responses during retesting. Methods: Twenty-one cognitively normal older and younger adults (65 ± 2 vs. 26 ± 1 years old) participated in the study. Mini-Mental State Examination (MMSE), Digit-Span-Test (DST), Trail Making Test (TMT-B), and California Verbal Learning Test (CVLT-II) were administered twice at 3-week intervals, while HR and BF were monitored by electrocardiography and plethysmography, respectively. Results: Cognitive performances were not affected by the age factor, and the retest factor only affected CVLT-II. HR and BF increased only in the younger adults (p < .01) during cognitive tests; retesting attenuated these responses (retest factor p < .01). Long-delay free-recall in CVLT-II was unchanged in cognitively normal older versus younger adults. Healthy aging did not diminish short-term memory assessed by DST and CVLT-II short-delay or long-delay free-recalls. Conclusions: Only CVLT-II, but not MMSE, DST or TMT-B, demonstrated cognitive retesting practice effects in the younger and older adults. Cognitive testing at 3-week intervals in cognitively normal older and younger subjects revealed divergent cardiorespiratory responses to MMSE, DST, and TMT-B cognitive testing, particularly HR, which increased only in younger adults and to a lesser extent during retesting despite the absence of practice effects.

Inter-effort recovery hypoxia: a new paradigm in sport science?

High-intensity interval training (HIIT) is a popular method for optimising sports performance and, more recently, improving health-related parameters. The inclusion of hypoxia during HIIT can promote additional gains compared with normoxia. However, reductions in the effort intensities compared with the same training performed in normoxia have been reported. Studies have reported that adding hypoxia during periods of inter-effort recovery (IEH) enables maintenance of the intensity of efforts. It also promotes additional gains from exposure to hypoxia. Our call is for researchers to consider IEH in experiments involving different models of HIIT. Additionally, we consider the need to answer the following questions: What is the clinically relevant minimum dose of exposure to hypoxia during the recovery periods between efforts so that favourable adaptations of parameters are associated with health and sports performance? How does the intensity of exertion influence the responses to hypoxia exposure during recovery periods? What are the chronic effects of different models of HIIT and hypoxia recovery on sports performance?

Intermittent hypoxia conditioning as a potential prevention and treatment strategy for ischemic stroke: Current evidence and future directions

Ischemic stroke (IS) is the leading cause of disability and death worldwide. Owing to the aging population and unhealthy lifestyles, the incidence of cerebrovascular disease is high. Vascular risk factors include hypertension, diabetes, dyslipidemia, and obesity. Therefore, in addition to timely and effective reperfusion therapy for IS, it is crucial to actively control these risk factors to reduce the incidence and recurrence rates of IS. Evidence from human and animal studies suggests that moderate intermittent hypoxia (IH) exposure is a promising therapeutic strategy to ameliorate common vascular risk factors and comorbidities. Given the complex pathophysiological mechanisms underlying IS, effective treatment must focus on reducing injury in the acute phase and promoting repair in the recovery phase. Therefore, this review discusses the preclinical perspectives on IH conditioning as a potential treatment for neurovascular injury and highlights IH pre and postconditioning strategies for IS. Hypoxia conditioning reduces brain injury by increasing resistance to acute ischemic and hypoxic stress, exerting neuroprotective effects, and promoting post-injury repair and regeneration. However, whether IH produces beneficial effects depends not only on the hypoxic regimen but also on inter-subject differences. Therefore, we discuss the factors that may influence the effectiveness of IH treatment, including age, sex, comorbidities, and circadian rhythm, which can be used to help identify the optimal intervention population and treatment protocols for more accurate, individualized clinical translation. In conclusion, IH conditioning as a non-invasive, non-pharmacological, systemic, and multi-targeted intervention can not only reduce brain damage after stroke but can also be applied to the prevention and functional recovery of IS, providing brain protection at different stages of the disease. It represents a promising therapeutic strategy. For patients with IS and high-risk groups, IH conditioning is expected to develop as an adjunctive clinical treatment option to reduce the incidence, recurrence, disability, and mortality of IS and to reduce disease burden.

Biomechanical and structural responses of the aorta to intermittent hypobaric hypoxia in a rat model

High altitude hypoxia is a condition experienced by diverse populations worldwide. In addition, several jobs require working shifts where workers are exposed to repetitive cycles of hypobaric hypoxia and normobaric normoxia. Currently, few is known about the biomechanical cardiovascular responses of this condition. In the present study, we investigate the cycle-dependent biomechanical effects of intermittent hypobaric hypoxia (IHH) on the thoracic aorta artery, in terms of both structure and function. To determine the vascular effects of IHH, functional, mechanical and histological approaches were carried out in the thoracic aorta artery, using uniaxial, pre-stretch, ring opening, myography, and histological tests. Three groups of rats were established: control (normobaric normoxia, NN), 4-cycles of intermittent hypoxia (short-term intermittent hypobaric hypoxia, STH), and 10-cycles of intermittent hypoxia (long-term intermittent hypobaric hypoxia, LTH). The pre-stretch and ring opening tests, aimed at quantifying residual strains of the tissues in longitudinal and circumferential directions, showed that the hypoxia condition leads to an increase in the longitudinal stretch and a marked decrease of the circumferential residual strain. The uniaxial mechanical tests were used to determine the elastic properties of the tissues, showing that a general stiffening process occurs during the early stages of the IH (STH group), specially leading to a significative increase in the high strain elastic modulus ([Formula: see text]) and an increasing trend of low strain elastic modulus ([Formula: see text]). In contrast, the LTH group showed a more control-like mechanical behavior. Myography test, used to assess the vasoactive function, revealed that IH induces a high sensitivity to vasoconstrictor agents as a function of hypoxic cycles. In addition, the aorta showed an increased muscle-dependent vasorelaxation on the LTH group. Histological tests, used to quantify the elastic fiber, nuclei, and geometrical properties, showed that the STH group presents a state of vascular fibrosis, with a significant increase in elastin content, and a tendency towards an increase in collagen fibers. In addition, advanced stages of IH (LTH), showed a vascular remodeling effect with a significant increase of internal and external diameters. Considering all the multidimensional vascular effects, we propose the existence of a long-term passive adaptation mechanism and vascular dysfunction as cycle-dependent effects of intermittent exposures to hypobaric hypoxia.

Hypoxic breathing produces more intense hypoxemia in elderly women than in elderly men

Background: Brief hypoxic exposures are increasingly applied as interventions for aging-related conditions. To optimize the therapeutic impact of hypoxia, knowledge of the sex-related differences in physiological responses to hypoxia is essential. This study compared hypoxia-induced hypoxemic responses in elderly men and women. Methods: Seven elderly men (70.3 ± 6.0 years old) and nine women (69.4 ± 5.5 years old) breathed 10% O₂ for 5 min while arterial (SaO₂; transcutaneous photoplethysmography) and cerebral tissue O₂ saturation (ScO₂; near-infrared spectroscopy), ventilatory frequency, tidal volume, minute-ventilation, and partial pressures of end-tidal O₂ (P_ETO₂) and CO₂ (mass spectrometry) were continuously monitored. Cerebral tissue oxygen extraction fraction (OEF) equaled (SaO₂-ScO₂)/SaO₂. Results: During 5 min hypoxia SaO₂ fell from 97.0 ± 0.8% to 80.6 ± 4.6% in the men and from 96.3 ± 1.4% to 72.6 ± 4.0% in the women. The slope ΔSaO₂/min was steeper in the women than the men (-4.71 ± 0.96 vs. -3.24 ± 0.76%/min; p = 0.005). Although SaO₂ fell twice as sharply per unit decrease in P_ETO₂ in the women than the men (-1.13 ± 0.11 vs. -0.54 ± 0.06%/mmHg; p = 0.003), minute-ventilation per unit hypoxemia increased less appreciably in the women (-0.092 ± 0.014 vs. -0.160 ± 0.021 L/min/%; p = 0.023). OEF fell with hypoxia duration in the women, but remained stable in the men. Conclusion: During 5 min hypoxic breathing, elderly women experience more intense hypoxemia and reduced chemoreflex sensitivity vs. their male counterparts, which may lower OEF stability in women despite augmented O₂ dissociation from hemoglobin during hypoxia. These sex-related differences merit attention when implementing brief hypoxic exposures for therapeutic purposes.

A comprehensive review of respiratory, autonomic and cardiovascular responses to intermittent hypoxia in humans

This review explores forms of respiratory and autonomic plasticity, and associated outcome measures, that are initiated by exposure to intermittent hypoxia. The review focuses primarily on studies that have been completed in humans and primarily explores the impact of mild intermittent hypoxia on outcome measures. Studies that have explored two forms of respiratory plasticity, progressive augmentation of the hypoxic ventilatory response and long-term facilitation of ventilation and upper airway muscle activity, are initially reviewed. The role these forms of plasticity might have in sleep disordered breathing are also explored. Thereafter, the role of intermittent hypoxia in the initiation of autonomic plasticity is reviewed and the role this form of plasticity has in cardiovascular and hemodynamic responses during and following intermittent hypoxia is addressed. The role of these responses in individuals with sleep disordered breathing and spinal cord injury are subsequently addressed. Ultimately an integrated picture of the respiratory, autonomic and cardiovascular responses to intermittent hypoxia is presented. The goal of the integrated picture is to address the types of responses that one might expect in humans exposed to one-time and repeated daily exposure to mild intermittent hypoxia. This form of intermittent hypoxia is highlighted because of its potential therapeutic impact in promoting functional improvement and recovery in several physiological systems.

Intermittent hypoxia enhances shear-mediated dilation of the internal carotid artery in young adults

We explored the effects of cyclic intermittent hypoxia (IH) on shear-mediated dilation of the internal carotid artery (ICA), a potential index of cerebral endothelial function, in young adults. Cyclic IH increased blood flow and shear rate in the ICA and, as a result, increased shear-mediated dilation of the ICA. These data suggest that cyclic IH could potentially be applied as a nonpharmacological therapy to optimize cerebral vascular health.

Intermittent Hypoxia Training for Treating Mild Cognitive Impairment: A Pilot Study

Although intermittent hypoxia training (IHT) has proven effective against various clinical disorders, its impact on mild cognitive impairment (MCI) is unknown. This pilot study examined IHT's safety and therapeutic efficacy in elderly patients with amnestic MCI (aMCI). Seven patients with aMCI (age 69 ± 3 years) alternately breathed 10% O2 and room-air, each 5 minutes, for 8 cycles/session, 3 sessions/wk for 8 weeks. The patients' resting arterial pressures fell by 5 to 7 mm Hg (P < .05) and cerebral tissue oxygenation increased (P < .05) following IHT. Intermittent hypoxia training enhanced hypoxemia-induced cerebral vasodilation (P < .05) and improved mini-mental state examination and digit span scores from 25.7 ± 0.4 to 27.7 ± 0.6 (P = .038) and from 24.7 ± 1.2 to 26.1 ± 1.3 (P = .047), respectively. California verbal learning test score tended to increase (P = .102), but trail making test-B and controlled oral word association test scores were unchanged. Adaptation to moderate IHT may enhance cerebral oxygenation and hypoxia-induced cerebrovasodilation while improving short-term memory and attention in elderly patients with aMCI.

Enhanced cerebral perfusion during brief exposures to cyclic intermittent hypoxemia

Cerebral vasodilation and increased cerebral oxygen extraction help maintain cerebral oxygen uptake in the face of hypoxemia. This study examined cerebrovascular responses to intermittent hypoxemia in eight healthy men breathing 10% O2 for 5 cycles, each 6 min, interspersed with 4 min of room air breathing. Hypoxia exposures raised heart rate ( P < 0.01) without altering arterial pressure, and increased ventilation ( P < 0.01) by expanding tidal volume. Arterial oxygen saturation ([Formula: see text]) and cerebral tissue oxygenation ([Formula: see text]) fell ( P < 0.01) less appreciably in the first bout (from 97.0 ± 0.3% and 72.8 ± 1.6% to 75.5 ± 0.9% and 54.5 ± 0.9%, respectively) than the fifth bout (from 94.9 ± 0.4% and 70.8 ± 1.0% to 66.7 ± 2.3% and 49.2 ± 1.5%, respectively). Flow velocity in the middle cerebral artery ( VMCA) and cerebrovascular conductance increased in a sigmoid fashion with decreases in [Formula: see text] and [Formula: see text]. These stimulus-response curves shifted leftward and upward from the first to the fifth hypoxia bouts; thus, the centering points fell from 79.2 ± 1.4 to 74.6 ± 1.1% ( P = 0.01) and from 59.8 ± 1.0 to 56.6 ± 0.3% ( P = 0.002), and the minimum VMCA increased from 54.0 ± 0.5 to 57.2 ± 0.5 cm/s ( P = 0.0001) and from 53.9 ± 0.5 to 57.1 ± 0.3 cm/s ( P = 0.0001) for the [Formula: see text]- VMCA and [Formula: see text]- VMCA curves, respectively. Cerebral oxygen extraction increased from prehypoxia 0.22 ± 0.01 to 0.25 ± 0.02 in minute 6 of the first hypoxia bout, and remained elevated between 0.25 ± 0.01 and 0.27 ± 0.01 throughout the fifth hypoxia bout. These results demonstrate that cerebral vasodilation combined with enhanced cerebral oxygen extraction fully compensated for decreased oxygen content during acute, cyclic hypoxemia.

NEW & NOTEWORTHY Five bouts of 6-min intermittent hypoxia (IH) exposures to 10% O2 progressively reduce arterial oxygen saturation ([Formula: see text]) to 67% without causing discomfort or distress. Cerebrovascular responses to hypoxemia are dynamically reset over the course of a single IH session, such that threshold and saturation for cerebral vasodilations occurred at lower [Formula: see text] and cerebral tissue oxygenation ([Formula: see text]) during the fifth vs. first hypoxia bouts. Cerebral oxygen extraction is augmented during acute hypoxemia, which compensates for decreased arterial O2 content.

Intermittent hypoxia training protects cerebrovascular function in Alzheimer's disease

Alzheimer's disease (AD) is a leading cause of death and disability among older adults. Modifiable vascular risk factors for AD (VRF) include obesity, hypertension, type 2 diabetes mellitus, sleep apnea, and metabolic syndrome. Here, interactions between cerebrovascular function and development of AD are reviewed, as are interventions to improve cerebral blood flow and reduce VRF. Atherosclerosis and small vessel cerebral disease impair metabolic regulation of cerebral blood flow and, along with microvascular rarefaction and altered trans-capillary exchange, create conditions favoring AD development. Although currently there are no definitive therapies for treatment or prevention of AD, reduction of VRFs lowers the risk for cognitive decline. There is increasing evidence that brief repeated exposures to moderate hypoxia, i.e. intermittent hypoxic training (IHT), improve cerebral vascular function and reduce VRFs including systemic hypertension, cardiac arrhythmias, and mental stress. In experimental AD, IHT nearly prevented endothelial dysfunction of both cerebral and extra-cerebral blood vessels, rarefaction of the brain vascular network, and the loss of neurons in the brain cortex. Associated with these vasoprotective effects, IHT improved memory and lessened AD pathology. IHT increases endothelial production of nitric oxide (NO), thereby increasing regional cerebral blood flow and augmenting the vaso- and neuroprotective effects of endothelial NO. On the other hand, in AD excessive production of NO in microglia, astrocytes, and cortical neurons generates neurotoxic peroxynitrite. IHT enhances storage of excessive NO in the form of S-nitrosothiols and dinitrosyl iron complexes. Oxidative stress plays a pivotal role in the pathogenesis of AD, and IHT reduces oxidative stress in a number of experimental pathologies. Beneficial effects of IHT in experimental neuropathologies other than AD, including dyscirculatory encephalopathy, ischemic stroke injury, audiogenic epilepsy, spinal cord injury, and alcohol withdrawal stress have also been reported. Further research on the potential benefits of IHT in AD and other brain pathologies is warranted.

Noninvasive estimation of oxygen consumption in human calf muscle through combined NMR measurements of ASL perfusion and T₂ oxymetry

The objective of this work was to demonstrate the feasibility of measuring muscle O2 consumption (V˙O2) noninvasively with a combination of functional nuclear magnetic resonance (NMR) imaging methods, and to verify that changes in muscle V˙O2 can be detected with a temporal resolution compatible with physiological investigation and patient ease. T2-based oxymetry of arterial and venous blood was combined with the arterial-spin labeling (ASL)-based determination of muscle perfusion. These measurements were performed on 8 healthy volunteers under normoxic and hypoxic conditions in order to assess the sensitivity of measurements over a range of saturation values. Blood samples were drawn simultaneously and used to titrate blood T2 measurements versus hemoglobin O2 saturation (%HbO2) in vitro. The in vitro calibration curve of blood T2 fitted very well with the %HbO2 (r(2): 0.95). The in vivo venous T2 measurements agreed well with the in vitro measurements (intraclass correlation coefficient 0.82, 95% confidence interval 0.61-0.91). Oxygen extraction at rest decreased in the calf muscles subjected to hypoxia (p = 0.031). The combination of unaltered muscle perfusion and pinched arteriovenous O2 difference (p = 0.038) pointed towards a reduced calf muscle V˙O2 during transient hypoxia (p = 0.018). The results of this pilot study confirmed that muscle O2 extraction and V˙O2 can be estimated noninvasively using a combination of functional NMR techniques. Further studies are needed to confirm the usefulness in a larger sample of volunteers and patients.

Two-week normobaric intermittent-hypoxic exposures stabilize cerebral perfusion during hypocapnia and hypercapnia

The effect of moderately extended, intermittent-hypoxia (IH) on cerebral perfusion during changes in CO2 was unknown. Thus, we assessed the changes in cerebral vascular conductance (CVC) and cerebral tissue oxygenation (ScO2) during experimental hypocapnia and hypercapnia following 14-day normobaric exposures to IH (10% O2). CVC was estimated from the ratio of mean middle cerebral arterial blood flow velocity (transcranial Doppler sonography) to mean arterial pressure (tonometry), and ScO2 in the prefrontal cortex was monitored by near-infrared spectroscopy. Changes in CVC and ScO2 during changes in partial pressure of end-tidal CO2 (PETCO2, mass spectrometry) induced by 30-s paced-hyperventilation (hypocapnia) and during 6-min CO2 rebreathing (hypercapnia) were compared before and after 14-day IH exposures in eight young nonsmokers. Repetitive IH exposures reduced the ratio of %ΔCVC/ΔPETCO2 during hypocapnia (1.00 ± 0.13 vs 1.94 ± 0.35 vs %/mmHg, P = 0.026) and the slope of ΔCVC/ΔPETCO2 during hypercapnia (1.79 ± 0.37 vs 2.97 ± 0.64 %/mmHg, P = 0.021), but had no significant effect on ΔScO2/ΔPETCO2. The ventilatory response to hypercapnia during CO2 rebreathing was significantly diminished following 14-day IH exposures (0.83 ± 0.07 vs 1.14 ± 0.09 L/min/mmHg, P = 0.009). We conclude that repetitive normobaric IH exposures significantly diminish variations of cerebral perfusion in response to hypercapnia and hypocapnia without compromising cerebral tissue oxygenation. This IH-induced blunting of cerebral vasoreactivity during CO2 variations helps buffer excessive oscillations of cerebral underperfusion and overperfusion while sustaining cerebral O2 homeostasis.

Two-week normobaric intermittent hypoxia exposures enhance oxyhemoglobin equilibrium and cardiac responses during hypoxemia

Intermittent hypoxia (IH) is extensively applied to challenge cardiovascular and respiratory function, and to induce physiological acclimatization. The purpose of this study was to test the hypothesis that oxyhemoglobin equilibrium and tachycardiac responses during hypoxemia were enhanced after 14-day IH exposures. Normobaric-poikilocapnic hypoxia was induced with inhalation of 10% O2 for 5-6 min interspersed with 4 min recovery on eight nonsmokers. Heart rate (HR), arterial O2 saturation (SaO 2), and end-tidal O2 (PetO 2) were continuously monitored during cyclic normoxia and hypoxia. These variables were compared during the first and fifth hypoxic bouts between day 1 and day 14. There was a rightward shift in the oxyhemoglobin equilibrium response following 14-day IH exposures, as indicated by the greater PetO 2 (an index of arterial Po2) at 50% of SaO 2 on day 14 compared with day 1 [33.9 ± 1.5 vs. 28.2 ± 1.3 mmHg (P = 0.005) during the first hypoxic bout and 39.4 ± 2.4 vs. 31.4 ± 1.5 mmHg (P = 0.006) during the fifth hypoxic bout] and by the augmented gains of ΔSaO 2/ΔPetO 2 (i.e., deoxygenation) during PetO 2 from 65 to 40 mmHg in the first (1.12 ± 0.08 vs. 0.80 ± 0.02%/mmHg, P = 0.001) and the fifth (1.76 ± 0.31 vs. 1.05 ± 0.06%/mmHg, P = 0.024) hypoxic bouts. Repetitive IH exposures attenuated (P = 0.049) the tachycardiac response to hypoxia while significantly enhancing normoxic R-R interval variability in low-frequency and high-frequency spectra without changes in arterial blood pressure at rest or during hypoxia. We conclude that 14-day IH exposures enhance arterial O2 delivery and improve vagal control of HR during hypoxic hypoxemia.

Normobaric, intermittent hypoxia conditioning is cardio- and vasoprotective in rats

Favorable versus detrimental cardiovascular responses to intermittent hypoxia conditioning (IHC) are heavily dependent on experimental or pathological conditions, including the duration, frequency and intensity of the hypoxia exposures. Recently, we demonstrated that a program of moderate, normobaric IHC (FIO2 9.5-10% for 5-10 min/cycle, with intervening 4 min normoxia, 5-8 cycles/day for 20 days) in dogs afforded robust cardioprotection against infarction and arrhythmias induced by coronary artery occlusion-reperfusion, but this protection has not been verified in other species. Accordingly, in this investigation cardio- as well as vasoprotection were examined in male Wistar rats completing the normobaric IHC program or a sham program in which the rats continuously breathed atmospheric air. Myocardial ischemia and reperfusion (IR) was imposed by occlusion and reperfusion of the left anterior descending coronary artery in in situ experiments and by subjecting isolated, perfused hearts to global ischemia-reperfusion. Cardiac arrhythmias and myocardial infarct size were quantified in in situ experiments. Endothelial function was evaluated from the relaxation to acetylcholine of norepinephrine-precontracted aortic rings taken from in situ IR experiments, and from the increase in coronary flow produced by acetylcholine in isolated hearts. IHC sharply reduced cardiac arrhythmias during ischemia and decreased infarct size by 43% following IR. Endothelial dysfunction in aorta was marked after IR in sham rats, but not significant in IHC rats. Similar findings were found for the coronary circulations of isolated hearts. These findings support the hypothesis that moderate, normobaric IHC is cardio- and vasoprotective in a rat model of IR.