Oscillatory drive is increased and steadiness is impaired when torque but not EMG is matched during a fatiguing contraction.

The increasing descending drive needed to sustain submaximal isometric torque makes it difficult to isolate fatigue-related changes to neural excitability because evoked electromyography (EMG) responses are influenced by the relative activation of the motoneuron pool. Hence, it is becoming increasingly common to investigate fatigue using a sustained contraction with maintained output from the motoneuron pool; i.e.

Acute normobaric hypoxia causes a rightward shift in the torque-frequency relationship but has no effect on postactivation potentiation.

Low fractions of inspired oxygen ([Formula: see text]; i.e., hypoxia) affect aspects of skeletal muscle contractility in humans, but it remains unclear if postactivation potentiation (PAP) and the torque-frequency (T-F) relationship are altered.

Four hours of normobaric hypoxia reduces Achilles tendon reflex inhibition.

Acute exposure to hypoxia increases postural sway, but the underlying neurophysiological factors are unclear. Golgi tendon organs (GTOs), located within the musculotendinous junction (MTJ), provide inhibitory signals to plantar flexor muscles that are important for balance control; however, it is uncertain if GTO function is influenced by hypoxia. The aim of this study was to determine how normobaric hypoxia influences lower limb tendon-evoked inhibitory reflexes during upright stance.

Creating your own line: reflections from early career scientists.

The changing landscape of academia can be difficult to navigate for anyone at any point throughout their career. One thing is certainly clear: effective mentorship is key to ensuring success, fueling scientific curiosity, and creating a sense of community. This article is a collection of personal reflections and stories, offering advice directed to aspiring and junior graduate trainees; it is written by Ph.

Normobaric hypoxia does not influence the sural nerve cutaneous reflex during standing.

Hypoxia increases postural sway compared to normoxia, but the underlying sensorimotor factors remain unclear. An important contributor to balance control is cutaneous feedback arising from the feet, which can be partially characterized by electrically evoking a reflex from a purely cutaneous nerve (i.e.

National validation of the Centers for Medicare & Medicaid Services strategy for identifying potential surgical-site infections following colon surgery and abdominal hysterectomy.

Objective: National validation of claims-based surveillance for surgical-site infections (SSIs) following colon surgery and abdominal hysterectomy.

Design: Retrospective cohort study.

Setting: US hospitals selected for data validation by Centers for Medicare & Medicaid Services (CMS).

Voluntary activation does not differ when using two different methods to determine transcranial magnetic stimulator output.

According to current guidelines, when measuring voluntary activation (VA) using transcranial magnetic stimulation (TMS), stimulator output (SO) should not exceed the intensity that, during a maximal voluntary contraction (MVC), elicits a motor evoked potential (MEP) from the antagonist muscle >15%-20% of its maximal M-wave amplitude. However, VA is based on agonist evoked-torque responses [i.e.

Steady-state chemoreflex drive captures ventilatory acclimatization during incremental ascent to high altitude: Effect of acetazolamide.

Ventilatory acclimatization (VA) is important to maintain adequate oxygenation with ascent to high altitude (HA). Transient hypoxic ventilatory response tests lack feasibility and fail to capture the integrated steady-state responses to chronic hypoxic exposure in HA fieldwork. We recently characterized a novel index of steady-state respiratory chemoreflex drive (SSCD), accounting for integrated contributions from central and peripheral respiratory chemoreceptors during steady-state breathing at prevailing chemostimuli.

Cerebrovascular and blood pressure responses during voluntary apneas are larger than rebreathing.

Both voluntary rebreathing (RB) of expired air and voluntary apneas (VA) elicit changes in arterial carbon dioxide and oxygen (CO and O) chemostimuli. These chemostimuli elicit synergistic increases in cerebral blood flow (CBF) and sympathetic nervous system activation, with the latter increasing systemic blood pressure. The extent that simultaneous and inverse changes in arterial CO and O and associated increases in blood pressure affect the CBF responses during RB versus VAs are unclear.

Maximal results with minimal stimuli: the fewest high-frequency pulses needed to measure or model prolonged low-frequency force depression in the dorsiflexors.

Quantifying prolonged low-frequency force depression (PLFFD) with the gold-standard 1-s trains presents challenges, so paired pulses have been used. Owing to greater impairment of high-frequency doublet than tetanic torque, paired pulses underestimate PLFFD. This study aimed to approximate the minimum number of high-frequency pulses needed to avoid such underestimation and assess the feasibility of modeling PLFFD from a limited number of experimental pulses.

Prior oxygenation, but not chemoreflex responsiveness, determines breath-hold duration during voluntary apnea.

Central and peripheral respiratory chemoreceptors are stimulated during voluntary breath holding due to chemostimuli (i.e., hypoxia and hypercapnia) accumulating at the metabolic rate.

Females and males do not differ for fatigability, muscle damage and magnitude of the repeated bout effect following maximal eccentric contractions.

Unaccustomed eccentric (ECC) exercise induces muscle fatigue as well as damage and initiates a protective response to minimize impairments from a subsequent bout (i.e., repeated bout effect; RBE).

Prolonged low-frequency force depression is underestimated when assessed with doublets compared with tetani in the dorsiflexors.

Prolonged low-frequency force depression (PLFFD) after damaging eccentric exercise may last for several days. Historically, PLFFD has been calculated from the tetanic force responses to trains of supramaximal stimuli. More recently, for methodological reasons, stimulation has been reduced to two pulses.

Mechanisms of sympathetic regulation during Apnea.

Volitional Apnea produces a robust peak sympathetic response through several interacting mechanisms. However, the specific contribution of each mechanism has not been elucidated. Muscle sympathetic activity was collected in participants (n = 10; 24 ± 3 years) that performed four maximal volitional apneas aimed at isolating lung-stretch (mechanical) and chemoreflex drive: (Ainslie and Duffin ) end-expiratory breath-hold, (Ainslie et al.

What Is the Point of the Peak? Assessing Steady-State Respiratory Chemoreflex Drive in High Altitude Field Studies.

Measurements of central and peripheral respiratory chemoreflexes are important in the context of high altitude as indices of ventilatory acclimatization. However, respiratory chemoreflex tests have many caveats in the field, including considerations of safety, portability and consistency. This overview will (a) outline commonly utilized tests of the hypoxic ventilatory response (HVR) in humans, (b) outline the caveats associated with a variety of peak response HVR tests in the laboratory and in high altitude fieldwork contexts, and (c) advance a novel index of steady-state chemoreflex drive (SS-CD) that addresses the many limitations of other chemoreflex tests.

Variable Case Detection and Many Unreported Cases of Surgical-Site Infection Following Colon Surgery and Abdominal Hysterectomy in a Statewide Validation.

OBJECTIVE To assess hospital surgical-site infection (SSI) identification and reporting following colon surgery and abdominal hysterectomy via a statewide external validation METHODS Infection preventionists (IPs) from the California Department of Public Health (CDPH) performed on-site SSI validation for surgical procedures performed in hospitals that voluntarily participated. Validation involved chart review of SSI cases previously reported by hospitals plus review of patient records flagged for review by claims codes suggestive of SSI. We assessed the sensitivity of traditional surveillance and the added benefit of claims-based surveillance.

Assessing chemoreflexes and oxygenation in the context of acute hypoxia: Implications for field studies.

Carotid chemoreceptors detect changes in PO and elicit a peripheral respiratory chemoreflex (PCR). The PCR can be tested through a transient hypoxic ventilatory response test (TT-HVR), which may not be safe nor feasible at altitude. We characterized a transient hyperoxic ventilatory withdrawal test in the setting of steady-state normobaric hypoxia (13.

Quantifying cerebrovascular reactivity in anterior and posterior cerebral circulations during voluntary breath holding.

What is the central question of this study? We developed and validated a 'stimulus index' (SI; ratio of end-tidal partial pressures of CO and O ) method to quantify cerebrovascular reactivity (CVR) in anterior and posterior cerebral circulations during breath holding. We aimed to determine whether the magnitude of CVR is correlated with breath-hold duration. What is the main finding and its importance? Using the SI method and transcranial Doppler ultrasound, we found that the magnitude of CVR of the anterior and posterior cerebral circulations is not positively correlated with physiological or psychological break-point during end-inspiratory breath holding.

Comparing and characterizing transient and steady-state tests of the peripheral chemoreflex in humans.

What is the central question of this study? We aimed to characterize the cardiorespiratory and cerebrovascular responses to transient and steady-state tests of the peripheral chemoreflex and to compare the hypoxic ventilatory responses (HVRs) between these tests. What is the main finding and its importance? The cardiovascular and cerebrovascular responses to transient tests were small in magnitude and short in duration. The steady-state isocapnic hypoxia test elicited a larger HVR than the transient 100% N(2) test, but the response magnitudes were correlated within individuals.

The ins and outs of breath holding: simple demonstrations of complex respiratory physiology.

The physiology of breath holding is complex, and voluntary breath-hold duration is affected by many factors, including practice, psychology, respiratory chemoreflexes, and lung stretch. In this activity, we outline a number of simple laboratory activities or classroom demonstrations that illustrate the complexity of the integrative physiology behind breath-hold duration. These activities require minimal equipment and are easily adapted to small-group demonstrations or a larger-group inquiry format where students can design a protocol and collect and analyze data from their classmates.

Surgical site infection surveillance following ambulatory surgery.

We assessed 4045 ambulatory surgery patients for surgical site infection (SSI) using claims-based triggers for medical chart review. Of 98 patients flagged by codes suggestive of SSI, 35 had confirmed SSIs. SSI rates ranged from 0 to 3.

The preventability of ventilator-associated events. The CDC Prevention Epicenters Wake Up and Breathe Collaborative.

Rationale: The CDC introduced ventilator-associated event (VAE) definitions in January 2013. Little is known about VAE prevention. We hypothesized that daily, coordinated spontaneous awakening trials (SATs) and spontaneous breathing trials (SBTs) might prevent VAEs.

Medicare claims can be used to identify US hospitals with higher rates of surgical site infection following vascular surgery.

Background: Surgical site infections (SSIs) following vascular surgery have high morbidity and costs, and are increasingly tracked as hospital quality measures.

Objective: To assess the ability of Medicare claims to identify US hospitals with high SSI rates after vascular surgery.

Research Design: Using claims from fee-for-service Medicare enrollees of age 65 years and older who underwent vascular surgery from 2005 to 2008, we derived hospital rankings using previously validated codes suggestive of SSI, with individual-level adjustment for age, sex, and comorbidities.