Casey, Darren P.

Aging is associated with increased aortic stiffness and exaggerated stress-induced blood pressure (BP) responsiveness, both of which contribute to the risk of cardiovascular disease. Supplementation with inorganic nitrate increases nitric oxide (NO) bioavailability and is a promising potential treatment to improve vascular function. While the acute effects of dietary inorganic nitrate supplementation on various measures of vascular function and BP have been demonstrated in several studies, the effects of increasing NO bioavailability through prolonged use (i.e. weeks) is unclear. Therefore, we tested the hypothesis that 4-weeks of inorganic nitrate supplementation will effectively increase NO bioavailability (as measured by plasma nitrate and nitrite) and reduce central BP, aortic stiffness, and BP responsiveness to a cold pressor test (CPT) in older adults. Thirteen older adults (67±3 years; 7 males and 6 females) completed a randomized, double-blind, placebo-controlled, crossover trial consisting of two 4-week supplementation periods (nitrate vs. placebo) separated by a 4-week washout. Central BP and carotid-femoral pulse wave velocity (cfPWV) were measured via applanation tonometry. Peripheral BP responses were assessed using beat-by-beat BP at baseline and during CPT. Plasma [nitrate] (40±24 to 76±46 µM, P< 0.01) and [nitrite] (289±94 to 413± 28 nM, P< 0.01) increased following inorganic nitrate supplementation, but remained unchanged after placebo ([nitrate] 39±20 to 39±16 µM, P=0.97; [nitrite] 303±108 to 302±87 nM, P=0.95). Four weeks of inorganic nitrate supplementation reduced resting measures of central systolic BP (cSBP; 116±12 to 113±10 mmHg, P< 0.05) and diastolic BP (cDBP; 79±8 to 74±6 mmHg, P< 0.05), as well as cfPWV (10.2±1.3 to 9.4±1.0 m/sec, P< 0.01), whereas no changes were observed following placebo (cSBP 112±10 to 115±10 mmHg; cDBP 75±7 to 78±7 mmHg; cfPWV 10.0±1.1 to 9.8±1.0 m/sec, P >0.05 for all). Additionally, the peak change (Δ from baseline) in peripheral SBP (28±10 to 23±6 mmHg, P< 0.05) and mean arterial pressure (MAP; 17±6 to 14±3 mmHg, P< 0.05) during the CPT were reduced following nitrate with no changes observed after placebo (SBP 25±8 to 26±12 mmHg, P=0.51; MAP 14±4 to 16±8 mmHg, P=0.19). Our findings demonstrate 4-weeks of inorganic dietary nitrate supplementation has favorable effects on central BP, aortic stiffness and BP responsiveness in older adults. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Obstructive sleep apnea (OSA), a sleep disorder that is associated with exposure to repeated bouts of hypoxia overnight. Evidence suggests that the oxyhemoglobin dissociation curve (ODC) may be shifted rightward with OSA. Nitric oxide (NO) functions as an allosteric regulator of hemoglobin oxygen-binding properties, possibly shifting the ODC curve leftward. Nitrate/nitrite supplementation increases NO bioavailability and attenuates the physiological responses to hypoxia which may be due to changes in the ODC. Therefore, we explored the hypothesis that dietary nitrate supplementation improves oxygen re-saturation following inspiratory hypoxia in subjects with OSA. Fourteen subjects with untreated mild-moderate OSA (53 ± 10yr, 8M/6F; Apnea-hypopnea Index, 17.8 ± 8.1 events) completed two separate study visits. Each visit consisted of two hypoxic bouts separated by ~2 hours and the consumption of one of two beetroot juice beverages (Placebo [BR P ] containing 5-10 mg nitrate, no detectable nitrite, or Active [BR A ] containing 500mg nitrate and 40mg nitrite). For each hypoxia bout, subjects’ pulse oxygen saturation (%SpO 2 ) was titrated to ≤80% over 3-5min by blending a 10% FiO2 gas cylinder with room air. Once ≤80% SpO 2 was achieved, subjects inhaled normoxic room air (~21% FiO2) and oxygen saturation was monitored until SpO 2 returned to baseline (recovery). During recovery, SpO 2 was averaged into 5 sec bins from the end of hypoxia (nadir) up to +15 SpO 2 % above nadir. The ‘hypoxic load’ during recovery was calculated as ( i =1 ∑ n ∣Value i −nadir+15∣) and reflects a total sum of each 5 sec bin ( n ). BR A increased plasma nitrite (248 ± 155 to 738 ± 427nM, P < 0.05), whereas there was no change following BR P (266 ± 153 to 277 ± 164nM, P = 0.87). The level of desaturation (SpO 2 nadir) at the end of hypoxia did not differ within or between trials (BR A : Pre 78 ± 2 vs. 78 ± 3; BR P : Pre 78 ± 2 vs. 78 ± 2, condition x time interaction P = 0.21). Hypoxia load increased following BR P (162.7 ± 36.6 vs. 231.8 ± 65.7, P < 0.001), but was unchanged following BR A (174.3 ± 54.2 vs. 191.2 ± 52, P = 0.32). In summary, our study suggests that acute nitrate supplementation may cause a leftward shift in the ODC in patients with untreated OSA. This is supported by a reduced hypoxic load following a repeat bout of inspiratory hypoxia. These findings may have implications for the health of patients with OSA. Foundation for the National Institutes of Health, K12 AR084222 (Joshua Bock) This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Peripheral chemoreceptors located within the carotid bodies activate cardiorespiratory reflexes in response to hypoxia. Carotid body chemoreceptor activity has been shown to be enhanced in conditions such as congestive heart failure, hypertension, and possibly aging. Nitric oxide (NO) has been proposed as an inhibitory modulator of carotid body chemosensitivity in response to hypoxia. Additionally, NO bioavailability is often reduced with cardiovascular risk factors such as aging. In the present study, we tested the hypothesis that increasing NO bioavailability via dietary nitrate (NO 3 ) supplementation would reduce cardiorespiratory responses to hypoxia in older adults. A double‐blind, randomized, placebo‐controlled, cross‐over study design was used to evaluate minute ventilation (V E ) and heart rate (HR) responses to acute hypoxia in 7 older adults (66±2 years; 5M/2F) before and after 4 weeks of NO 3 supplementation (beetroot powder) and placebo (beetroot powder devoid of NO 3 ). On each study visit, subjects underwent two separate isocapnic hypoxic tests (self‐regulating, partial rebreathing system with 10% O 2 ). Subjects remained on 10% O 2 until SpO 2 reached ≤80%. The hypoxic exposures were separated by a 15‐minute washout period with the subjects breathing room air. V E , HR, and SpO 2 were continuously monitored throughout each hypoxic exposure. Data were grouped together using a 7‐breath average with the slope of the linear regression line for each dependent variable (V E and HR) versus SpO 2 serving as a measure of peripheral chemosensitivity. The slopes for the two hypoxia tests on each study visit were averaged and used for statistical comparisons. On study day one (true baseline) acute hypoxia increased both V E and HR ( P <0.05 for both). Four weeks of NO 3 supplementation reduced the hypoxic ventilatory response (−0.16 ± −0.05 vs. −0.06 ± −0.03 L/minute/%SpO 2 , P <0.05), whereas no change was observed following the placebo phase of the study (−0.14 ± −0.07 vs. −0.14 ± −0.08 L/minute/%SpO 2 , P=0.67). Additionally, the heart rate responses to acute hypoxia were also reduced following NO 3 supplementation (−0.49 ± −0.08 vs. −0.30 ± −0.05 beats/minute/%SpO 2 , P <0.05), but not with placebo (−0.54 ± −0.11 vs. −0.45 ± −0.08 beats/minute/%SpO 2 , P=0.21). Our preliminary findings suggest that supplementation of NO 3 to boost NO bioavailability in older adults blunts the cardiorespiratory responses to hypoxia. Future studies should examine the therapeutic potential of NO 3 in patient populations exhibiting exaggerated peripheral chemosensitivity. Support or Funding Information Research supported by Neogenis Inc.

We previously reported that augmented skeletal muscle vasodilation during mild hypoxic forearm exercise includes beta‐adrenergic mechanisms. Furthermore, hypoxic vasodilation at rest is known to include beta‐adrenergic mediated nitric oxide (NO) production. Therefore, we tested the hypothesis that NO contributes to augmented vasodilation with hypoxic exercise. Twelve subjects (6M/6F; 26 ± 2 years) breathed hypoxic gas to titrate arterial O 2 saturation to 80% while remaining normocapnic via a rebreath system. Subjects performed incremental forearm exercise (10% and 20% of maximum) during saline infusion (control) and NO synthase inhibition ( N G ‐monomethyl‐L‐arginine; L‐NMMA) under normoxic and hypoxic conditions. Forearm vascular conductance (FVC; ml/min/100mmHg) was calculated from blood flow (ml/min) and blood pressure (mmHg). During the control condition, the rise in FVC (Δfrom normoxic baseline) due to hypoxic exercise was 211 ± 23 and 367 ± 34 (10% and 20% respectively). Infusion of L‐NMMA during hypoxic exercise attenuated ΔFVC at 10% (174 ± 20; P < 0.001) and 20% (317 ± 32; P < 0.01) compared to control condition. Our data indicate that NO contributes to the augmented vasodilation observed during hypoxic exercise. Supported by NIH HL‐46493 (MJJ) and AR‐55819 (DPC) and by CTSA RR‐024150.

The augmented skeletal muscle vasodilation during hypoxic exercise is due, in part, to an intensity dependent contribution of beta‐receptor activation. We tested the hypothesis that an adenosine mediated vasodilation increases with hypoxic exercise intensity. Subjects (N=10) breathed hypoxic gas to titrate arterial O 2 saturation to 80% while remaining normocapnic (re‐breath system). Consecutive bouts of forearm exercise (10% and 20% of maximum) were performed under normoxia and hypoxia during phentolamine (alpha‐receptor antagonist) alone and the combination of phentolamine / aminophyline (adenosine receptor antagonist). Exogenous adenosine administered before and after aminophyline established effective receptor blockade. Forearm vascular conductance (FVC; ml/100mmHg/min) was calculated from blood flow (ml/min) and blood pressure (mmHg). During hypoxic exercise, the rise in FVC (Δ from baseline) during phentolamine was 314±30 and 470±37 (10% and 20% respectively). ΔFVC was similar at both 10% (349±45; P=0.3) and 20% (536±47; P=0.2) exercise during hypoxia with combined phentolamine / aminophyline. This occurred despite significant reduction in ΔFVC to exogenous adenosine following phentolamine / aminophyline (P<0.03). Our data suggests that in the absence of overlying vasoconstriction, adenosine does not contribute to the augmented hypoxic exercise hyperemia in humans.

Evidence suggests that increased sympathetic tone but no change of blood pressure (BP) via lower body negative pressure (LBNP) reduces indices of aortic wave reflection in young adults. The aim of this study was to examine whether aging affects central artery hemodynamics and indices of wave reflection during LBNP. In 12 young (27 ± 2 years, 5F/7M) and 10 older (70 ± 2 years 5F/5M) subjects, noninvasive aortic pressure waveforms were synthesized from high‐fidelity radial pressure waveforms via applanation tonometry before and during 10 minutes of LBNP (‐20mmHg). Aortic BP and indices of aortic wave reflection (i.e. Augmentation index; AIx) were calculated from the generated aortic pressure waveform. Aortic systolic BP decreased during LBNP in the young (110 ± 3 vs. 106 ± 3 mmHg, P<0.05), but not the older adults (139 ± 3 vs. 136 ± 3 mmHg, P=0.15). Aortic diastolic BP did not change in either group (P=0.56). Since heart rate (HR) changed in the young (P<0.05) but not in the older adults (P=0.33) during LBNP, we used the AIx normalized to a HR of 75bpm as an index of wave reflection. AIx@75bpm decreased in young adults (‐6 ± 3 vs. ‐13 ± 3%, P<0.001), whereas no change was observed in older adults (26 ± 3 vs. 25 ± 3%, P=0.39). Our data suggest that reductions in aortic systolic blood pressure and wave reflection during lower body negative pressure are attenuated in older compared to young adults. Funded by NIH HL‐105467

Hypoxia during exercise augments vasodilation and blood flow to ensure adequate delivery of O 2 to active muscles. However, the impact of hyperoxia on skeletal muscle blood flow during exercise is poorly understood. Therefore, we tested the hypothesis that the hyperemic response to exercise with hyperbaric hyperoxia would be blunted compared to exercise during normoxia. Seven subjects (6M/1F; 26 ± 2 years) performed forearm exercise (20% of maximum) under normoxic and hyperoxic conditions. Forearm blood flow (FBF; ml/min) was measured using Doppler ultrasound. Forearm vascular conductance (FVC; ml/min/100mmHg) was calculated from FBF and blood pressure (mmHg; brachial arterial catheter). Studies were performed in a hyperbaric chamber with the subjects supine at 1 ATA (sea level) and 2.8 ATA while breathing normoxic (21% O 2 , 1 ATA; F I O 2 ≈ 150 mmHg), hyperbaric normoxic (7% O 2 , 2.8 ATA, F I O 2 ≈ 150 mmHg) and hyperoxic (7% O 2 , 2.8 ATA, F I O 2 ≈ 2100 mmHg) gas. The change in FBF and FVC (Δ from rest) during exercise under normoxia and hyperbaric normoxia did not differ (P > 0.05). However, the ΔFBF and ΔFVC during exercise under hyperoxia were attenuated by ~18–29% compared to both normoxic conditions (P ≤ 0.01). Our data suggest that exercise hyperemia in skeletal muscle is highly dependent on oxygen availability during hyperoxia as well as hypoxia. NIH HL46493 (MJJ), AR55819 (DPC) and RR‐024150.

We tested the hypothesis that local inhibition of NOS would 1) alter the kinetics of vasodilation during dynamic forearm (FA) exercise and 2) prolong the time to reach steady state (SS). Subjects (n=22) performed rhythmic FA exercise (20% of maximum) during saline infusion (control) and NOS inhibition (L‐NMMA). Additionally, a subset of subjects performed a third trial of FA exercise during combined inhibition of either 1) NOS and adenosine (aminophylline; n=9), or 2) NOS and prostaglandins (Ketorolac; n=8). Forearm vascular conductance (FVC; ml/min/100mmHg) was calculated from blood flow (ml/min) and blood pressure (mmHg). Vasodilator kinetics were assessed by calculating the slope of the FVC response for every duty cycle between baseline and SS exercise as well as the number of duty cycles (1s contraction/2s relaxation) to reach SS. NOS inhibition reduced the kinetics of vasodilation during dynamic FA exercise (8.5 ± 0.6 vs. 11.1 ± 0.8 FVC/duty cycle; P < 0.001 vs. control) and increased the time to reach SS (25.1 ± 1 vs. 32 ± 1 duty cycles; P < 0.001 vs. control). The kinetics of vasodilation were reduced further with combined inhibition of NOS and adenosine (6.2 ± 0.8 vs. 7.5 ± 0.6 FVC/duty cycle; P < 0.05 vs. L‐NMMA alone), but not with combined inhibition of NOS and prostaglandins. Our data indicate that NOS inhibition blunts the kinetics of vasodilation during dynamic FA exercise and prolongs the time to reach SS.

Pulse wave velocity (PWV) and sympathetic nerve activity increase with age. However, it is unknown if the age‐related increase in sympathetic activity influences PWV. We determined the effect of autonomic blockade on peripheral and central arterial stiffness in young (23 ± 4 yr) and older, postmenopausal (57 ± 3 yr) women before and during administration of trimethaphan camsylate. Arterial tonometry was used to measure carotid‐radial (peripheral) and carotid‐femoral (central) PWV. The groups did not differ in height, weight, BMI, or mean arterial pressure (MAP). At baseline, peripheral PWV did not differ between the groups. However, central PWV was significantly greater in older women compared with young women (8.2 vs. 6.1 m/s, respectively; p<0.05). Trimethaphan infusion caused a substantial drop in MAP; therefore, we corrected PWV for the change in MAP. Peripheral PWV was greater in older women compared with young women (0.12 vs. 0.08 m/s·mmHg −1 ; p<0.05). In addition, central PWV remained higher in older women during trimethaphan infusion (0.11 vs. 0.08 m/s·mmHg −1 in young; p<0.05). In conclusion, central PWV was greater in older women before and during autonomic blockade, whereas peripheral PWV was only higher in the older women after autonomic blockade. This suggests that peripheral PWV is influenced by sympathetic activity to a greater extent in young vs. older women. Funded by NIH

Acute ß‐adrenergic blockade (BB) increases aortic wave reflection in young women, however, it is unknown if this effect extends to post‐menopausal women. Thus, we examined systemic BB on aortic wave reflection in 14 post‐menopausal women (58 ± 2 yr). Non‐invasive aortic pressure waveforms were synthesized from high‐fidelity radial pressure waveforms obtained from applanation tonometry before and during systemic BB (0.25mg/kg bolus, with 0.004 mg/kg/min continuous infusion of propranolol). Aortic blood pressure, augmentation index (AIx), AIx adjusted for heart rate (AIx@75), aortic augmented pressure (AP), and wasted left ventricular energy (Ew) were calculated from the aortic pressure waveform. Heart rate (60 ± 2 vs. 51 ± 2 bpm) and mean arterial pressure (95 ± 3 vs. 91 ± 3 mmHg) were reduced with BB (P < 0.05 for both). AIx increased during BB (32 ± 2 vs. 35 ± 2%, P < 0.01), however, AIx@75 was unchanged (25 ± 2 vs. 24 ± 2%, ns). Additionally, AP (20 ± 2 vs. 20 ± 2 mmHg, ns) and Ew (4313 ± 538 vs. 4277 ± 537 dyne*cm2/sec, ns) remained unchanged during BB. When compared to our previously published study in young women, indices of aortic wave reflection were significantly less affected in post‐menopausal women in response to acute systemic BB. Taken together, our data suggest that the negative effects (i.e. increased aortic wave reflection) of non‐selective BB are less pronounced in post‐menopausal women.