Journal of applied physiology最新文献

The hyoid bone's inferior baseline position in obstructive sleep apnea (OSA) has led to surgical hyoid repositioning (SHR) treatment, yet outcomes vary widely. The influence of baseline hyoid position (BHP; phenotype) and SHR on upper airway (UA) function remains unclear. We aimed to investigate their impact on the UA using computational modeling.

Methods: A validated finite element model of the rabbit UA was advanced and used to simulate changes in BHP and SHR, alone and in combination. The hyoid was displaced in cranial, caudal, anterior, anterior-cranial and anterior-caudal directions from 1-4mm. Model outcomes included UA collapsibility, measured using closing pressure (Pclose), cross-sectional area (CSA) and soft tissue mechanics (displacement, stress and strain).

Results: Graded BHP increments increased Pclose for all directions, and up to 29-43% at 4mm (relative to the original BHP). Anterior-based SHR decreased Pclose (~-115% at 4mm) and increased ΔCSA (~+35% at 4mm). Cranial SHR decreased ΔPclose (-29%), minimally affecting CSA. Caudal SHR increased ΔPclose (+27%) and decreased ΔCSA (-7%). Anterior-cranial and anterior-caudal SHR produced the highest stresses and strains. SHR effects on UA outcomes were dependent on BHP, with more caudal BHPs leading to less effective surgeries.

Conclusion: BHP (phenotype) and SHR both alter UA outcomes, with effects dependent on hyoid displacement direction and magnitude. BHP influences the effectiveness of SHR in reducing UA collapsibility. These findings provide further insights into the hyoid's role in UA patency and suggest that considering the hyoid's baseline position and surgical repositioning direction/increment may help improve hyoid surgeries for OSA treatment.

The potential mechanisms involved in lactate's role in exercise-induced appetite suppression require further examination. We used sodium bicarbonate (NaHCO₃) supplementation in a double-blind, placebo-controlled, randomized crossover design to explore lactate's role on neuropeptide Y (NPY), agouti-related peptide (AgRP), and alpha-melanocyte-stimulating hormone (α-MSH) concentrations. Twelve adults (7 males; 24.2 ± 3.4 kg·m^-2; 42.18 ± 8.56 mL·kg^-1·min^-1) completed two identical high-intensity interval training sessions following ingestion of NaHCO₃ (BICARB) or sodium chloride (PLACEBO) pre-exercise. Blood lactate, acylated ghrelin, NPY, AgRP, α-MSH, and appetite perceptions were measured pre-exercise, 0-, 30-, 60-, and 90-min postexercise. Free-living energy intake (electronic food diaries) was measured the day before, of, and after each experimental session. In BICARB, blood lactate was greater postexercise (P < 0.002, d > 0.70), though acylated ghrelin was similar (P = 0.075, [Formula: see text] = 0.206) at all time points postexercise (P > 0.034, d < 0.22). NPY (P = 0.006, [Formula: see text] > 0.509) and AgRP (P < 0.001, [Formula: see text] > 0.488) had main effects of time increasing following exercise and returning to baseline, with no differences between sessions (NPY: P = 0.0.192, [Formula: see text] = 0.149; AgRP: P = 0.422, [Formula: see text] = 0.060). α-MSH had no main effect of time (P = 0.573, [Formula: see text] = 0.063) or session (P = 0.269, [Formula: see text] = 0.110). Appetite perceptions were similar during BICARB and PLACEBO (P = 0.007, d = 0.28), increasing in both sessions postexercise (P < 0.088, d > 0.57). Energy intake had a main effect of day (P = 0.025, [Formula: see text] = 0.825), where the experimental session day was greater than the day before (P = 0.010, d = 0.59) with no other differences between days (P > 0.260, d < 0.38). The lower accumulation of lactate than our previous work did not generate exercise-induced appetite suppression as there were no differences in acylated ghrelin, appetite perceptions, or peripheral concentrations of neuropeptides.NEW & NOTEWORTHY Current evidence supports lactate's role in exercise-induced appetite suppression. Here, we demonstrate a smaller degree of lactate accumulation with sodium bicarbonate ingestion and HIIT than our previous work and no subsequent suppression of acylated ghrelin concentrations, subjective appetite perceptions, or peripheral concentrations of neuropeptides. These results suggest either changes in central appetite-regulating neuropeptides are not reflected peripherally or the smaller magnitude of lactate accumulation did not generate exercise-induced appetite suppression as seen previously.

Skin heating helps avoid hypothermia in trauma victims but may influence the systolic (SBP) and mean arterial blood pressures (MAP) helping to guide resuscitation. We examined the effect of skin heating on tolerance and arterial blood pressure during lower body negative pressure (LBNP) across four trials. Nine participants completed 15 exercise intervals [60 s 88% peak power output (PPO) and 60 s 10% PPO] in a cold environment (0°C, 70% RH) lowering mean skin temperature (Tsk) before undergoing LBNP to pre syncope where Tsk remained low (Cold Trial: 27.6 ± 1.1°C) or was increased via a water-perfused suit 60 s into LBNP to 32.3 ± 0.7°C (Normothermic Trial), 34.8 ± 0.4°C (Warm Trial), or 36.1 ± 0.8°C (Hot Trial). Tsk was different between trials (P = 0.001). Core temperature was not different between trials, increasing with exercise (36.9 ± 0.3°C to 37.9 ± 0.4°C) and remaining elevated during LBNP (37.7 ± 0.4°C). During LBNP, MAP was greatest in the Cold Trial (88 ± 7 mmHg) and relatively lowered in the Normothermic (83 ± 5 mmHg), Warm (82 ± 5 mmHg), and Hot Trials (79 ± 7 mmHg; all P ≤ 0.017 vs. Cold). SBP was greatest in the Cold (111 ± 9 mmHg) and Normothermic Trials (110 ± 10 mmHg) and relatively lowered in the Warm (105 ± 7 mmHg) and Hot Trials (103 ± 11 mmHg; both P ≤ 0.037). LBNP tolerance was not different between trials (P = 0.746). Following exercise in a cold environment, skin heating during simulated hemorrhage lowers arterial blood pressures and has implications for prehospital care of trauma victims.NEW & NOTEWORTHY Skin heating helps avoid hypothermia in trauma victims but may influence arterial blood pressures, thus helping to guide resuscitation depending on the type of injury. Following exercise in a cold environment, arterial blood pressure was elevated during LBNP with cold skin but lowered with skin heating without changing LBNP tolerance. These findings are important for understanding the effect of skin heating on arterial blood pressure control in the prehospital and combat casualty care of trauma victims.

Breakfast skipping has been suggested to be associated with cardiovascular diseases. However, whether breakfast skipping affects vascular endothelial function (VEF), a marker of cardiovascular diseases, remains unclear. This study aimed to investigate the impact of breakfast consumption (Eating trial) and skipping (Skipping trial) on brachial artery (BA) VEF in healthy breakfast eaters. A total of nine healthy individuals (4 females and 5 males) either had breakfast between 830 and 900 or skipped it and had lunch between 1200 and 1230, followed by a 3-h rest period until 1530. For BA VEF evaluation, flow-mediated dilation (FMD) was measured by ultrasound before and after breakfast and lunch. FMD was calculated as the percent change in BA diameter normalized to the shear rate area under the curve (FMD/SR_AUC). Blood glucose, plasma insulin, and plasma free fatty acid levels in capillaries were measured before and after breakfast and lunch. At 1530, the Eating trial, but not the Skipping trial, significantly increased FMD/SR_AUC from baseline (P = 0.006). The Skipping trial showed significantly lower changes in FMD/SR_AUC from 830 than the Eating trial at 1530 (P < 0.001). We found a significant inverse correlation between changes in FMD/SR_AUC between 830 and 1530 and peak glucose levels after lunch (r = -0.882, P < 0.001) and with an incremental area under the curve for glucose between 830 and 1530 (r = -0.668, P < 0.001). These results suggest that a single bout of breakfast skipping can suppress BA VEF in the afternoon because of postlunch hyperglycemia.NEW & NOTEWORTHY Skipping breakfast does not affect vascular endothelial function (VEF) before lunch. However, after lunch on normal meals (i.e., not oral glucose tolerance test), VEF was found to be lower in those who skipped breakfast than those who ate breakfast. Such reduced postlunch VEF after skipping breakfast was associated with postprandial hyperglycemia. These results provide important insight into the impact of eating breakfast on VEF and glycemic control in healthy adults.

Acute mountain sickness (AMS) represents a considerable issue for individuals sojourning to high altitudes with systemic hypoxemia known to be intimately involved in its development. Based on recent evidence that ketone ester (KE) intake attenuates hypoxemia, we investigated whether exogenous ketosis might mitigate AMS development and identified underlying physiological mechanisms. Fourteen healthy, male participants were enrolled in two 29-h protocols (simulated altitude of 4,000-4,500 m) receiving either KE or a placebo (CON) at regular timepoints throughout the protocol in a randomized, crossover manner. Physiological responses were characterized after 15 min and 4 h in hypoxia, and the protocol was terminated prematurely upon development of severe AMS (Lake Louise Score ≥ 10). KE ingestion induced a consistent diurnal ketosis (d-β-hydroxybutyrate, [βHB] of ∼3 mM), whereas blood [βHB] remained low (<0.6 mM) in CON. Each participant tolerated the protocol equally long or longer (n = 6 or n = 8, respectively) in KE. Protocol duration increased by 32% on average with KE, and doubled upon KE for severe AMS-developing participants (n = 9). Relative to CON, KE induced a mild metabolic acidosis, hyperventilation, and relative sympathetic dominance. KE also inhibited the progressive hypoxemia that was observed between 15 min and 4 h in hypoxia in CON, while concomitantly increasing cerebral oxygenation and capillary Po₂ within this timeframe despite a KE-induced reduction in cerebral oxygen supply. These data indicate that exogenous ketosis attenuates AMS development. The key underlying mechanisms include improved arterial and cerebral oxygenation, in combination with lowered cerebral blood flow and oxygen delivery, and increased sympathetic dominance.NEW & NOTEWORTHY Ketone ester intake attenuated the development of acute mountain sickness at a simulated altitude of 4,000-4,500 m. This likely resulted from a mitigation of arterial and cerebral hypoxemia, reduced cerebral blood flow, and increased sympathetic drive.

Altitude training is a cornerstone for endurance athletes for improving blood variables and performance, with optimal effects observed at ∼2,300-2,500 meters above sea level (m.a.s.l.). However, elite cyclists face challenges such as limited access to such altitudes, inadequate training facilities, and high expenses. To address these issues, a novel method involving daily exposure to carbon monoxide (CO) has been proposed to amplify altitude training adaptations at suboptimal altitudes. Thirty-one male cyclists were assigned to three groups: Live-High Train-High with CO inhalation (LHTH_CO), Live-High Train-High (LHTH), and Live-Low Train-Low (LLTL). The LHTH_CO group underwent CO inhalation twice daily in the afternoon/evening to elevate carboxyhemoglobin concentration to ∼10%. Hematological variables, in vivo muscle oxidative capacity, and physiological indicators of cycling performance were assessed before and after a 3-week altitude training camp at 2,100 m.a.s.l. LHTH_CO demonstrated a larger increase in hemoglobin mass (Hb_mass) compared to both LHTH and LLTL. Although there were no statistical differences between LHTH_CO and LHTH in submaximal and maximal performance measures, LHTH_CO displayed greater improvements in 1-min maximal power output during incremental testing (W_max), power output at lactate threshold, and maximal oxygen consumption (V̇o_2max) compared to LLTL. LHTH demonstrated a larger improvement than LLTL in W_max and V̇o_2max, with no group differences in Hb_mass or submaximal measures. Muscle oxidative capacity did not differ between groups. These findings suggest that combining moderate-altitude training with daily CO inhalation promotes hematological adaptations more effectively than moderate altitude alone and enhances cycling performance metrics in cyclists more than sea-level training.NEW & NOTEWORTHY Three weeks of training at moderate altitude with exposure to low doses of CO can significantly enhance hematological adaptations in elite cyclists compared to moderate-altitude training alone. Cycling performance determinants improved more with CO inhalation at moderate altitude compared to sea-level training, whereas there were no differences in submaximal and maximal performance measures compared to moderate-altitude training alone. This study highlights the potential of CO supplementation as an effective adjunct to altitude training regimens.

There are known sex differences in cardiorespiratory fitness (CRF). Little is known about the impact of pubertal blockade with a gonadotropin-releasing hormone agonist (GnRHa) followed by hormone therapy on CRF for transgender adolescents. We aimed to 1) determine the effect of GnRHa monotherapy on CRF and mitochondrial function and associations with metabolomic profiles and 2) evaluate changes after 1 and 12 mo of testosterone therapy among transgender adolescents. Participants assigned female at birth (n = 19, baseline age of 15.0 ± 1.0 yr) from two groups: GnRHa⁺ (n = 8) and GnRHa^- (n = 11) were examined at baseline and 1- and 12-mo post-testosterone therapy in a longitudinal observational study to assess cardiorespiratory fitness, mitochondrial respiration, and metabolic profile. Fasted morning labs included assessment of metabolomics and peripheral blood mononuclear cell mitochondrial respiration and degree of mitochondrial coupling (respiratory control ratio, RCR). A graded cycle ergometer test was performed. Baseline differences were evaluated between groups. Changes were compared with mixed linear regression models evaluating time (baseline, 1 mo, and 12 mo), group (GnRHa treatment yes/no), and their interaction. At baseline GnRHa⁺ individuals had higher relative V̇o_2peak (30.1 ± 4.83 vs. 25.24 ± 4.47 mL/kg/min, P = 0.042) than GnRHa^- individuals. In regression models, GnRHa⁺ individuals had a significant increase in peak watts (P = 0.011) and total exercise time (P = 0.005) after 12 mo of testosterone (P = 0.012) but not GnRHa^- individuals. GnRHa⁺ individuals have significantly higher RCR under carbohydrate (P = 0.0007) and lipid (P = 0.0002) conditions than GnRHa⁺ individuals. Pretreatment with GnRHa positively influences peak CRF and mitochondrial respiration in adolescent transgender males undergoing testosterone therapy.NEW & NOTEWORTHY This study demonstrates differences in exercise capacity and mitochondrial respiration at baseline based on whether or not individuals had feminizing puberty blocked. Individuals who had puberty blocked had greater improvements in cardiopulmonary exercise testing parameters after 12 mo of testosterone than those who went through feminizing puberty.

We explored whether ankle torque variability or plantar perceptual threshold explains human balance control more effectively. We hypothesized that ankle torque variance is a better indicator of center of pressure (COP) velocity variance than plantar perceptual sensitivity. Two conditions were tested: loaded (23-kg vest added) and unloaded, as loading should diminish plantar sensitivity and increase COP velocity variability. We created a linear feedback model to assess the noise change in the sensorimotor loop induced by loading. Plantar sensitivity was quantified using a psychophysical approach while participants stood barefoot. A linear motor applied a force impulse on the participant's heel. A "yes-no" method of limits was selected to identify plantar sole sensory thresholds in both conditions. We observed reduced plantar sensitivity in loaded compared with unloaded conditions. In the loaded condition, participants exhibited greater COP velocity variance, with significant positive Pearson's correlations confirming a substantial association between ankle torque and COP velocity variances for both loaded [variance accounted for (VAF): r² = 44.56%, P = 0.018] and unloaded conditions (VAF: r² = 58.83%, P = 0.004). No significant correlation existed between COP velocity variance and plantar sensitivity threshold for both loaded (VAF: r² = 0.002%, P = 0.99) and unloaded conditions (VAF: r² = 21.81%, P = 0.35). The model confirmed an ∼88% rise in sensorimotor loop noise in the loaded condition. Ankle torque variance assesses the precision of nonperceptual and perceptual detection mechanisms in evaluating whole body motions and the accuracy in converting sensory cues into ankle torque.NEW & NOTEWORTHY Plantar cutaneous information contributes to balance control by modulating motor commands, but plantar perceptual sensitivity is a suboptimal indicator of balance performance. Multiple sensory cues encode whole body dynamics, guiding sensorimotor mechanisms to minimize body sway variability. Ankle torque variance is proposed as a superior measure for explaining balance control performance and evaluating the sensorimotor loop's functioning in balance control.

Human skeletal muscle fiber type composition varies greatly along the muscle, so one biopsy may not accurately represent the whole muscle. Recommendations on the number of biopsies and fiber counts using immunohistochemistry and whether these findings can be extrapolated to other muscles are lacking. We assessed fiber type composition in the vastus lateralis and gastrocnemius medialis muscles of 40 individuals. Per muscle, we took four biopsy samples from one incision, collecting two samples each from a proximally and distally directed needle. Based on another dataset involving 10 vastus lateralis biopsies per participant (n = 7), we calculated 95% limits of agreement for subsets of biopsies and fiber counts compared with the 10-biopsy average. Average absolute differences in type I fiber proportions between proximal and distal, and between within-needle samples were 6.9 and 4.5 percentage points in the vastus lateralis, and 5.5 and 4.4 percentage points in the gastrocnemius medialis, respectively. The 95% limits of agreement narrowed to ±10 percentage points when 200 fibers from at least three biopsies were analyzed, with minimal improvements with greater fiber counts. Type I fiber proportions in the vastus lateralis and gastrocnemius medialis showed a moderate positive association (r² = 0.22; P = 0.006; at least 200 fibers in each of three to four samples per muscle). In conclusion, three biopsies with a minimum of 200 counted fibers are required to estimate the vastus lateralis fiber type composition within ±10 percentage points. Even when using these standards, researchers should be cautious when extrapolating muscle fiber type proportions from one muscle to another.NEW & NOTEWORTHY Fiber type composition is equally variable in muscle biopsy samples taken from one incision as from multiple incisions. Hence, we propose two biopsies from a single incision-needles directed proximally and distally, and each rotated 180° for cutting a second sample-as a more feasible, less invasive alternative to three biopsies from as many incisions. In addition, we identified the gastrocnemius medialis as a slow-twitch muscle with an average of 64.7% slow fibers.