The hyperaemic and metaboreflex response of the diaphragm during fatiguing diaphragmatic work in humans.

During inspiratory pressure-threshold loading (ITL), the inspiratory muscle metaboreflex (IMM) increases respiratory muscle blood flow, but its effect on diaphragm blood flow (Q̇) and fatigue in humans, is unclear. Females exhibit an attenuated IMM compared to males during diaphragmatic loading, suggesting less diaphragm blood flow impedance and metaboreflex activation. We hypothesized that diaphragm hyperaemia would relate positively to metaboreflex sensitivity (i.

Acute intermittent hypercapnic hypoxia augments left ventricular contractility.

Acute intermittent hypercapnic hypoxia (IHH) evokes persistent increases in vascular sympathetic activity and blood pressure. Whether myocardial contractility is enhanced to contribute to this pressor response is unknown. We hypothesized that IHH would augment left ventricular systolic function.

Hepatic hypoxia in donation after circulatory death: Physiology, clinical relevance, and future directions.

Donation after circulatory death (DCD) has increased hepatic graft supply, but is plagued by complications that arise from hypoxic injury. There is a lack of understanding regarding donor physiology during DCD and how this contributes to hepatic dysfunction in transplantation. Herein, we outline the current DCD process and the concept of donor warm ischemic time.

Diaphragm blood flow: new avenues for human translation.

The rhythmic contraction of the diaphragm facilitates continuous pulmonary ventilation essential for life. Adequate blood flow to the diaphragm is critical to continuously support contractile function, as an imbalance in nutritive supply and demand can lead to diaphragm insufficiency, patient morbidity, and mortality. Given oxygen supply to the diaphragm is key to its function, it is no surprise that more than 200 animal studies have investigated diaphragm blood flow ([Formula: see text]) regulation over the past century.

The dynamic pathophysiology of post cardiac arrest brain injury: "time is brain".

Purpose Of Review: To review the time dependent nature of post-cardiac arrest brain injury (PCABI) while contextualizing clinical trial evidence.

Recent Findings: PCABI represents a dynamic entity with respect to its pathophysiology. Intuitively, PCABI pathophysiology has been characterized focusing on mechanisms associated with cerebral ischemia.

Quantifying Diaphragm Blood Flow With Contrast-Enhanced Ultrasound in Humans.

Background: Despite the known interplay between blood flow and function, to our knowledge, there is currently no minimally invasive method to monitor diaphragm hemodynamics. We used contrast-enhanced ultrasound to quantify relative diaphragm blood flow (Q˙) in humans and assessed the technique's efficacy and reliability during graded inspiratory pressure threshold loading. We hypothesized that: (1) Q˙ would linearly increase with pressure generation, and (2) that there would be good test-retest reliability and interanalyzer reproducibility.

Using modified Fenn diagrams to assess ventilatory acclimatization during ascent to high altitude: Effect of acetazolamide.

High altitude (HA) ascent imposes systemic hypoxia and associated risk of acute mountain sickness. Acute hypoxia elicits a hypoxic ventilatory response (HVR), which is augmented with chronic HA exposure (i.e.

Shining a light on cerebral autoregulation: Are we anywhere near the truth?

The near-infrared spectroscopy (NIRS)-derived cerebral oximetry index (COx) has become popularized for non-invasive neuromonitoring of cerebrovascular function in post-cardiac arrest patients with hypoxic-ischemic brain injury (HIBI). We provide commentary on the physiologic underpinnings and assumptions of NIRS and the COx, potential confounds in the context of HIBI, and the implications for the assessment of cerebral autoregulation.

Comparison of mild physiological effects of surgical masks and N95 respirators over 60 min at rest.

Dead-space-associated rebreathing of expired air and heat trapping with use of surgical masks and N95 respirators may underlie anecdotal reports of adverse symptoms associated with medical face barriers. Limited data exist directly comparing the physiological effects of masks and respirators at rest. We assessed the short-term physiological effects of both barrier types over 60 min at rest, including face microclimate temperature, end-tidal gases, and venous blood acid-base variables.

Functional optical coherence tomography at altitude: retinal microvascular perfusion and retinal thickness at 3,800 meters.

Cerebral hypoxia is a serious consequence of several cardiorespiratory illnesses. Measuring the retinal microvasculature at high altitude provides a surrogate for cerebral microvasculature, offering potential insight into cerebral hypoxia in critical illness. In addition, although sex-specific differences in cardiovascular diseases are strongly supported, few have focused on differences in ocular blood flow.

Acid-base balance at high altitude in lowlanders and indigenous highlanders.

High-altitude exposure results in a hyperventilatory-induced respiratory alkalosis followed by renal compensation (bicarbonaturia) to return arterial blood pH (pHa) toward sea-level values. However, acid-base balance has not been comprehensively examined in both lowlanders and indigenous populations-where the latter are thought to be fully adapted to high altitude. The purpose of this investigation was to compare acid-base balance between acclimatizing lowlanders and Andean and Sherpa highlanders at various altitudes (∼3,800, ∼4,300, and ∼5,000 m).

Acute hyperglycemia does not affect central respiratory chemoreflex responsiveness to CO in healthy humans.

The central respiratory chemoreceptor complex (CCRC) is comprised of brainstem neurons and surrounding interoceptors, which collectively increase ventilation in response to elevated brainstem tissue CO/[H] (i.e., central chemoreflex; CCR).

Severity of central sleep apnea does not affect sleeping oxygen saturation during ascent to high altitude.

Central sleep apnea (CSA) is characterized by periodic breathing (PB) during sleep, defined as intermittent periods of apnea/hypopnea and hyperventilation, with associated acute fluctuations in oxyhemoglobin saturation (SO). CSA has an incidence of ∼50% in heart failure patients but is universal at high altitude (HA; ≥2,500 m), increasing in severity with further ascent and/or time at altitude. However, whether PB is adaptive, maladaptive, or neutral with respect to sleeping SO at altitude is unclear.

Time course and magnitude of ventilatory and renal acid-base acclimatization following rapid ascent to and residence at 3,800 m over nine days.

Rapid ascent to high altitude imposes an acute hypoxic and acid-base challenge, with ventilatory and renal acclimatization countering these perturbations. Specifically, ventilatory acclimatization improves oxygenation, but with concomitant hypocapnia and respiratory alkalosis. A compensatory, renally mediated relative metabolic acidosis follows via bicarbonate elimination, normalizing arterial pH(a).

The effects of high altitude ascent on splenic contraction and the diving response during voluntary apnoea.

New Findings: What is the central question of this study? What is the relative contribution of a putative tonic splenic contraction to the haematological acclimatization process during high altitude ascent in native lowlanders? What is the main finding and its importance? Spleen volume decreased by -14.3% (-15.2 ml) per 1000 m ascent, with an attenuated apnoea-induced [Hb] increase, attesting to a tonic splenic contraction during high altitude ascent.

Cardiorespiratory hysteresis during incremental high-altitude ascent-descent quantifies the magnitude of ventilatory acclimatization.

New Findings: What is the central question of this study? We assessed the utility of a new metric for quantifying ventilatory acclimatization to high altitude, derived from differential ascent and descent steady-state cardiorespiratory variables (i.e. hysteresis).