Short exposure to intermittent hypoxia increases erythropoietin levels in healthy individuals

Few minutes of hypoxic exposure stabilizes hypoxia-inducible factor-1α, resulting in erythropoietin (EPO) gene transcription and production. The objective of this study was to identify the shortest intermittent hypoxia protocol necessary to increase serum EPO levels in healthy individuals. In a first experiment, spontaneous EPO changes under normoxia (NORM) and the EPO response to five 4-min cycles of intermittent hypoxia (IH5) were determined in six individuals. In a second experiment, the EPO response to eight 4-min cycles of intermittent hypoxia (IH8) and 120 min of continuous hypoxia (CONT) was determined in six individuals. All hypoxic protocols were performed at a targeted arterial oxygen saturation of 80%. There was no significant change in EPO levels in response to normoxia or in response to five cycles of intermittent hypoxia (NORM: 9.5 ± 1.8 to 10.5 ± 1.8, IH5: 11.4 ± 2.3 to 13.4 ± 2.1 mU/mL, main effect for time P = 0.35). There was an increase in EPO levels in response to eight cycles of intermittent hypoxia and 120 min of continuous hypoxia, with peak levels observed 4.5 h after the onset of hypoxia (IH8: 11.2 ± 2.0 to 16.7 ± 2.2, CONT: 11.1 ± 3.8 to 19.4 ± 3.8 mU/mL, main effect for time P < 0.01). Eight cycles of intermittent hypoxia increased EPO levels to a similar extent as 120 min of continuous hypoxia (main effect for condition P = 0.36). Eight 4-min cycles of intermittent hypoxia represent the shortest protocol to increase serum EPO levels in healthy individuals.NEW & NOTEWORTHY The objective of this study was to identify the shortest intermittent hypoxia protocol necessary to increase serum erythropoietin levels in healthy individuals. Eight 4-min bouts of intermittent hypoxia, representing a hypoxic duration of 32 min at an arterial oxygen saturation of 80%, significantly increased erythropoietin levels in healthy individuals. These findings suggest that a short session of intermittent hypoxia has the potential to increase oxygen-carrying capacity.

Hypoxic preconditioning reduces endothelial ischemia-reperfusion injury in older adults

Sudden blood flow restoration to an ischemic vessel paradoxically damages endothelial cells. Ischemic preconditioning, caused by repeated bouts of brief ischemia using local or remote cuff inflation prior to reperfusion, attenuates endothelial dysfunction following an ischemia-reperfusion injury in young adults but does not consistently protect endothelial function in older adults prone to ischemic events. Intermittent exposure to systemic hypoxemia, induced via brief bouts of breathing low levels of oxygen, attenuates endothelial dysfunction following an ischemia-reperfusion injury in young adults. The aim of this study was to determine whether systemic hypoxic preconditioning protects against ischemia-reperfusion injury in middle-aged and older adults. Twelve adults (five women, 57±9 years) participated in this randomized crossover trial. Endothelium-dependent vasodilation was assessed by brachial artery flow-mediated dilation using a semi-automated diagnostic ultrasound system before and after a 20-min blood flow occlusion that was preceded by either intermittent hypoxia, consisting of three 4-min hypoxic cycles at an arterial oxygen saturation of 80% interspersed with 4-min room air cycles, or intermittent normoxia, consisting of three 4-min normoxic cycles separated by 4-min room air cycles. When preceded by intermittent normoxia, ischemia-reperfusion injury reduced flow-mediated dilation by 4.1±2.6% (6.5±1.7 to 2.4±1.7%). In contrast, flow-mediated dilation was reduced by 2.0±1.5% when ischemia-reperfusion injury was preceded by intermittent hypoxia (5.6±1.7 to 3.6±2.3%). In conclusion, hypoxic preconditioning significantly attenuated the reduction in brachial artery flow-mediated dilation induced by an ischemia-reperfusion injury in middle-aged and older adults at greater risk for ischemic events.

Brief exposure to intermittent hypoxia increases erythropoietin levels in older adults

Eight 4-min cycles of intermittent hypoxia represent the shortest hypoxic exposure to increase erythropoietin (EPO) levels in young adults. The impact of aging on the EPO response to a hypoxic stimulus remains equivocal. Thus, the objective of this study was to determine the effect of the same intermittent hypoxia protocol on EPO levels in older adults. Methods: Twenty-two participants (12 women, age: 53±7 years) were randomly assigned to an intermittent hypoxia group (IH, n=11) or an intermittent normoxia group (IN, n=11). Intermittent hypoxia consisted of eight 4-min cycles at a targeted oxygen saturation of 80% interspersed with normoxic cycles to resaturation. Air was made hypoxic by titrating nitrogen into a breathing circuit. Intermittent normoxia consisted of the same protocol, but nitrogen was not added to the breathing circuit. EPO levels were measured before and 4.5 hours after the beginning of each protocol. Intermittent hypoxia lowered oxygen saturation to 82±3%, which corresponded to a fraction of inspired oxygen of 10.9±1.0%. There was a greater increase in EPO levels following intermittent hypoxia than intermittent normoxia (IH: 3.2±2.2 vs. IN: 0.7±0.8 mU·ml^-1, p<0.01). A single session of eight 4-min cycles of hypoxia increased EPO levels, the glycoprotein stimulating red blood cell production, in older adults. Exposure to intermittent hypoxia has therefore the potential to increase oxygen-carrying capacity in a population with reduced red blood cell volume.

Similar endothelium-dependent vascular responses to intermittent hypoxia in young and older adults

Aging is associated with vascular endothelial dysfunction observed through a progressive loss of flow-mediated dilation caused partly by a decreased nitric oxide bioavailability. Intermittent hypoxia, consisting of alternating short bouts of breathing hypoxic and normoxic air, was reported to either maintain or improve vascular function in young adults. The aim of this study was to determine the impact of age on the vascular response to intermittent hypoxia. Twelve young adults and 11 older adults visited the laboratory on two occasions. Plasma nitrate concentrations and brachial artery flow-mediated dilation were assessed before and after exposure to either intermittent hypoxia or a sham protocol. Intermittent hypoxia consisted of eight 4-min hypoxic cycles at a targeted oxygen saturation of 80% interspersed with breathing room air to resaturation, and the sham protocol consisted of eight 4-min normoxic cycles interspersed with breathing room air. Vascular responses were assessed during intermittent hypoxia and the sham protocol. Intermittent hypoxia elicited a brachial artery vasodilation but did not change brachial artery shear rate in both young and older adults. Plasma nitrate concentrations were not significantly affected by intermittent hypoxia compared with the sham protocol in both groups. Brachial artery flow-mediated dilation was not acutely affected by intermittent hypoxia or the sham protocol in either young or older adults. In conclusion, the brachial artery vasodilatory response to intermittent hypoxia was not influenced by age. Intermittent hypoxia increased brachial artery diameter but did not acutely affect endothelium-dependent vasodilation in young or older adults.NEW & NOTEWORTHY The objective of this study was to determine the impact of age on the vascular response to intermittent hypoxia. Eight 4-min bouts of hypoxia at a targeted oxygen saturation of 80% induced a brachial artery vasodilation in both young and older adults, indicating that age does not influence the vasodilatory response to intermittent hypoxia. Intermittent hypoxia did not acutely affect brachial artery flow-mediated dilation in young or older adults.

Impaired erythropoietin response to hypoxia in type 2 diabetes

AIMS

Patients with type 2 diabetes have a 20% lower total blood volume than age- and weight-matched healthy adults, suggesting a reduced capacity to transport oxygen in this population. Intermittent hypoxia, consisting of alternating short bouts of breathing hypoxic and normoxic air, increases erythropoietin levels, the hormone regulating red blood cell production, in young and older adults. The objective of this study was to determine the effect of a single session of intermittent hypoxia on erythropoietin levels and hemoglobin mass, the absolute mass of hemoglobin contained in red blood cells, in patients with type 2 diabetes.

METHODS

Ten patients with type 2 diabetes were exposed to an intermittent hypoxia protocol consisting of eight 4-min cycles at a targeted oxygen saturation of 80% interspersed with normoxic cycles to resaturation. Erythropoietin and hemoglobin mass responses to intermittent hypoxia in patients with type 2 diabetes were compared to previously published data from an identical intermittent hypoxia protocol performed in age-matched older adults.

RESULTS

Intermittent hypoxia increased erythropoietin levels in older adults but did not induce any change in erythropoietin levels in patients with type 2 diabetes (3.2 ± 2.2 vs. 0.2 ± 2.7 mU/ml, p = 0.01). Hemoglobin mass indexed to body weight was 21% lower in patients with type 2 diabetes than in older adults (8.1 ± 1.7 vs. 10.2 ± 2.1 g/kg, p < 0.01).

CONCLUSIONS

These findings suggest an impaired erythropoietin response to decreased oxygen levels in patients with type 2 diabetes, which may contribute to the reduced oxygen transport capacity observed in this population.

Short bouts of hypoxia improve insulin sensitivity in adults with type 2 diabetes

Hypoxia stimulates glucose uptake independently from the action of insulin. The purpose of this study was to determine the effect of intermittent hypoxia, consisting of alternating short bouts of breathing hypoxic and room air, on glucose concentration, insulin concentration, and insulin sensitivity during an oral glucose tolerance test in adults with type 2 diabetes and adults with normal glycemic control. Nine adults with type 2 diabetes (2 women, HbA1c: 7.3 ± 1.5%, age: 52 ± 13 yr) and nine adults with normal glycemic control (4 women, HbA1c: 5.4 ± 0.1%, age: 24 ± 4 yr) performed a 2-h oral glucose tolerance test on two separate visits to the laboratory. Following ingestion of the glucose drink, participants were exposed to either an intermittent hypoxia protocol, consisting of eight 4-min hypoxic cycles at a targeted oxygen saturation of 80% interspersed with breathing room air to resaturation, or a sham protocol consisting of eight 4-min normoxic cycles interspersed with breathing room air. Intermittent hypoxia did not attenuate the increase in glucose concentration but attenuated the increase in insulin concentration in response to an oral glucose tolerance test in comparison with the sham protocol in adults with type 2 diabetes. Insulin sensitivity was greater during intermittent hypoxia in comparison with the sham protocol in adults with type 2 diabetes (0.043 ± 0.036 vs. 0.032 ± 0.046 μmol/kg/min/pmol, P = 0.01), but did not change in the control group (0.122 ± 0.015 vs. 0.128 ± 0.008 μmol/kg/min/pmol, P = 0.12). In conclusion, intermittent hypoxia improved insulin sensitivity in adults with type 2 diabetes.NEW & NOTEWORTHY The aim of this study was to determine the effect of short bouts of hypoxia, which stimulates glucose uptake, on glucose concentration, insulin concentration, and insulin sensitivity during an oral glucose tolerance test in adults with type 2 diabetes and adults with normal glycemic control. Intermittent hypoxia acutely improved insulin sensitivity in adults with type 2 diabetes.

Impact of Intermittent Hypoxia Exposure on Erythropoietin Levels in Older Individuals

Few minutes of hypoxia exposure stabilizes hypoxia-inducible factors, resulting in erythropoietin (EPO) gene transcription and production. A brief intermittent hypoxia exposure increased EPO levels in young healthy individuals, suggesting that a single session of intermittent hypoxia has the potential to increase oxygen-carrying capacity. Thus, the objective of this study was to determine the effect of a single session of intermittent hypoxia on serum EPO levels and hemoglobin mass among older individuals. We hypothesized that a single session of intermittent hypoxia would raise serum EPO levels and lead to an increase in hemoglobin mass in older individuals. Seventeen participants (8 women, age: 54 ± 8 years, height: 177 ± 10 cm, weight: 76 ± 14 kg, BMI: 24 ± 4 kg/m² ) were randomly assigned to an intermittent hypoxia group (IH, n=11) or an intermittent normoxia group (IN, n=6). Intermittent hypoxia consisted of eight 4-minute cycles at a targeted arterial oxygen saturation of 80% interspersed with normoxic cycles to resaturation. Air was made hypoxic by titrating nitrogen into the breathing circuit. Intermittent normoxia consisted of the same protocol, but nitrogen was not added to the breathing circuit. Pulmonary gas exchange, arterial oxygen saturation, and hemodynamics were continuously measured throughout both protocols. EPO levels were measured before and 4.5 hours after the beginning of each protocol. Hemoglobin mass was assessed via carbon monoxide rebreathing the day before and seven following intermittent hypoxia or normoxia. Intermittent hypoxia lowered arterial oxygen saturation (--98 ±- 1 to 82 ± 3 %, p<0.01), which resulted in a lower fraction of inspired oxygen (20.8 ±- 0.1 to 10.9 ± 1.0 %, p<0.01). There was no significant change in EPO levels in either condition (IH:10.4 ±- 2.9 to 13.3 ± 4.2; IN: 5.6 ±- 2.4 to 6.5 ± 2.9 mU/ml, main effect for time p=0.12). Similarly, there was no change in hemoglobin mass in response to both conditions (IH: 752 ±- 189 to 754 ± 189; IN: 858 ± 177 to 879 ± 157 g, main effect for time p=0.87). Intermittent hypoxia did not affect mean arterial pressure (87 ± 15 to 88 ± 14 mmHg, p=0.18) or cardiac output (5.5 ± 1.5 to 5.7 ± 1.5 L/min, p=0.22), but increased heart rate (62 ± 9 to 68 ± 9 bpm, p<0.01). In conclusion, a single session of eight 4-minute cycles of intermittent hypoxia did not increase serum EPO levels in older individuals.

Nitric oxide enhancement supplement containing beet nitrite and nitrate benefits high intensity cycle interval training

This study investigated the effects of a beet nitric oxide enhancing (NOE) supplement comprised of nitrite and nitrate on cycling performance indices in trained cyclists.

METHODS

Subjects completed a lactate threshold test and a high-intensity interval (HIIT) protocol at 50% above functional threshold power with or without oral NOE supplement.

RESULTS

NOE supplementation enhanced lactate threshold by 7.2% (Placebo = 191.6 ± 37.3 W, NOE = 205.3 ± 39.9; p = 0.01; Effect Size (ES) = 0.40). During the HIIT protocol, NOE supplementation improved time to exhaustion 18% (Placebo = 1251 ± 562s, NOE = 1474 ± 504s; p = 0.02; ES = 0.42) and total energy expended 22.3% (Placebo = 251 ± 48.6 kJ, NOE = 306.6 ± 55.2 kJ; p = 0.01; ES = 1.079). NOE supplementation increased the intervals completed (Placebo = 7.00 ± 2.5, NOE = 8.14 ± 2.4; p = 0.03; ES = 0.42) and distance cycled (Placebo = 10.9 ± 4.0 km, NOE = 13.5 ± 3.9 km; p = 0.01; ES = 0.65). Also, target power was achieved at a higher cadence during the HIIT work and rest periods (p = 0.02), which enhanced muscle oxygen saturation (SmO₂) recovery. Time-to-fatigue was negatively correlated with the degree of SmO₂, desaturation during the HIIT work interval segment (r = -0.67; p 0.008), while both SmO₂ desaturation and the SmO₂ starting work segment saturation level correlated with a cyclist's kJ expended (SmO₂ desaturation: r = -0.51, p = 0.06; SmO₂ starting saturation: r = 0.59, p = 0.03).

CONCLUSION

NOE supplementation containing beet nitrite and nitrate enhanced submaximal (lactate threshold) and HIIT maximal effort work. The NOE supplementation resulted in a cyclist riding at higher cadence rates with lower absolute torque values at the same power during both the work and rest periods, which in-turn delayed over-all fatigue and improved total work output.