An empirical model for world record running speeds with distance, age, and sex: anaerobic and aerobic contributions to performance.

The objective of this study is to derive mathematical equations that closely describe published data on world record running speed as a function of distance, age, and sex. Running speed declines with increasing distance and age. Over long distances, where aerobic metabolism is dominant, speed declines in proportion to the logarithm of distance.

Designing an implementation strategy to increase health-related social needs screening: Applying the PRISM framework in a resource-limited clinical setting.

Despite growing acceptability of health-related social needs (HRSN) screening and increasing policy incentives for adoption, clinical implementation of HRSN screening remains low. HRSN screening has been particularly difficult for Community Health Centers (CHCs), which have limited resources to implement and sustain new workflows. While CHCs provide care to patients with disproportionately high levels of unmet social needs, identifying HRSN screening implementation strategies that take CHC-specific contexts into account remains elusive.

The dependence of maximum oxygen uptake and utilization (V̇O max) on hemoglobin-oxygen affinity and altitude.

Oxygen transport from the lungs to peripheral tissue is dependent on the affinity of hemoglobin for oxygen. Recent experimental data have suggested that the maximum human capacity for oxygen uptake and utilization (V̇O max) at sea level and altitude (~3000 m) is sensitive to alterations in hemoglobin-oxygen affinity. However, the effect of such alterations on V̇O max at extreme altitudes remains largely unknown due to the rarity of mutations affecting hemoglobin-oxygen affinity.

Attenuated cardiac autonomic function in humans with high-affinity hemoglobin and compensatory polycythemia.

During hypoxic exposure, humans with high-affinity hemoglobin (and compensatory polycythemia) have blunted increases in heart rate compared with healthy humans with typical oxyhemoglobin dissociation curves. This response may be associated with altered autonomic control of heart rate. Our hypothesis-generating study aimed to investigate cardiac baroreflex sensitivity and heart rate variability among nine humans with high-affinity hemoglobin [6 females, O partial pressure at 50% [Formula: see text] (P) = 16 ± 1 mmHg] compared with 12 humans with typical affinity hemoglobin (6 F, P = 26 ± 1 mmHg).

Muscle oxygenation during normoxic and hypoxic cycling exercise in humans with high-affinity haemoglobin.

New Findings: What is the central question of this study? Do humans with high-affinity haemoglobin (HAH) demonstrate attenuated skeletal muscle deoxygenation during normoxic and hypoxic exercise? What is the main finding and its importance? Examination of near-infrared spectroscopy-derived muscle oxygenation profiles suggests that fractional oxygen extraction is blunted during hypoxic exercise in humans with HAH compared with control subjects. However, muscle tissue oxygen saturation levels were higher in humans with HAH during exercise in normoxia compared with control subjects. These alterations in fractional oxygen extraction in humans with HAH might influence blood flow regulation and exercise capacity during hypoxia.

Functional implications of microvascular heterogeneity for oxygen uptake and utilization.

In the vascular system, an extensive network structure provides convective and diffusive transport of oxygen to tissue. In the microcirculation, parameters describing network structure, blood flow, and oxygen transport are highly heterogeneous. This heterogeneity can strongly affect oxygen supply and organ function, including reduced oxygen uptake in the lung and decreased oxygen delivery to tissue.

Analysis of flow resistance in the pulmonary arterial circulation: implications for hypoxic pulmonary vasoconstriction.

Hypoxic pulmonary vasoconstriction (HPV) plays an essential role in distributing blood in the lung to enhance ventilation-perfusion matching and blood oxygenation. In this study, a theoretical model of the pulmonary vasculature is used to predict the effects of vasoconstriction over specified ranges of vessel diameters on pulmonary vascular resistance (PVR). The model is used to evaluate the ability of hypothesized mechanisms of HPV to account for observed levels of PVR elevation during hypoxia.

The Oxygen Cascade During Exercise in Health and Disease.

The oxygen transport cascade describes the physiological steps that bring atmospheric oxygen into the body where it is delivered and consumed by metabolically active tissue. As such, the oxygen cascade is fundamental to our understanding of exercise in health and disease. Our narrative review will highlight each step of the oxygen transport cascade from inspiration of atmospheric oxygen down to mitochondrial consumption in both healthy active males and females along with clinical conditions.

Effects of impaired microvascular flow regulation on metabolism-perfusion matching and organ function.

Impaired tissue oxygen delivery is a major cause of organ damage and failure in critically ill patients, which can occur even when systemic parameters, including cardiac output and arterial hemoglobin saturation, are close to normal. This review addresses oxygen transport mechanisms at the microcirculatory scale, and how hypoxia may occur in spite of adequate convective oxygen supply. The structure of the microcirculation is intrinsically heterogeneous, with wide variations in vessel diameters and flow pathway lengths, and consequently also in blood flow rates and oxygen levels.

Influence of high affinity haemoglobin on the response to normoxic and hypoxic exercise.

Key Points: Theoretical models suggest there is no benefit of high affinity haemoglobin to preserve maximal oxygen uptake in acute hypoxia but the comparative biology literature has many examples of species that are evolutionarily adapted to hypoxia and have high affinity haemoglobin. We studied humans with high affinity haemoglobin and compensatory polycythaemia. These subjects performed maximal exercise tests in normoxia and hypoxia to determine how their altered haemoglobin affinity impacts hypoxic exercise tolerance.

Dissociating the effects of oxygen pressure and content on the control of breathing and acute hypoxic response.

Arterial oxygen tension and oxyhemoglobin saturation () decrease in parallel during hypoxia. Distinguishing between changes in oxygen tension and oxygen content as the relevant physiological stimulus for cardiorespiratory alterations remains challenging. To overcome this, we recruited nine individuals with hemoglobinopathy manifesting as high-affinity hemoglobin [HAH; partial pressure at 50% (P) = 16 ± 0.

Modelling the relationships between haemoglobin oxygen affinity and the oxygen cascade in humans.

Key Points: Haemoglobin affinity is an integral concept in exercise physiology that impacts oxygen uptake, delivery and consumption. How chronic alterations in haemoglobin affinity impact physiology is unknown. Using human haemoglobin variants, we demonstrate that the affinity of haemoglobin for oxygen is highly correlated with haemoglobin concentration.

Effects of pulmonary flow heterogeneity on oxygen transport parameters in exercise.

Under resting normoxic conditions, the healthy lung has ample oxygen uptake capacity relative to oxygen demand, but during exercise, increased oxygen demand and utilization become increasingly dependent on ventilation-perfusion matching. A mathematical model is used to investigate the effect of pulmonary flow heterogeneity, as characterized by the coefficient of variation (CV) of capillary blood flow, on pulmonary oxygen uptake in exercise. The model reveals that any level of heterogeneity up to a CV of 3 is consistent with the observed level of arterial oxygen tension under resting conditions, but that such high levels of heterogeneity are incompatible with the levels of oxygen uptake observed during exercise.

Hemorrhagic Shock After Epicardial Pacing Wire Removal: A Case Report.

Epicardial pacing wires are routinely used to avoid hemodynamic instability due to perioperative arrhythmias after cardiac surgery. In rare cases, pacing wires themselves can be associated with potentially life-threatening complications. Herein, we present a novel case of hemorrhagic shock and hemoperitoneum after temporary epicardial pacing wire removal.

Functional sympatholysis and sympathetic escape in a theoretical model for blood flow regulation.

A mathematical simulation of flow regulation in vascular networks is used to investigate the interaction between arteriolar vasoconstriction due to sympathetic nerve activity (SNA) and vasodilation due to increased oxygen demand. A network with 13 vessel segments in series is used, each segment representing a different size range of arterioles or venules. The network includes five actively regulating arteriolar segments with time-dependent diameters influenced by shear stress, wall tension, metabolic regulation, and SNA.

Theoretical analysis of the determinants of lung oxygen diffusing capacity.

The process of pulmonary oxygen uptake is analyzed to obtain an explicit equation for lung oxygen diffusing capacity in terms of hematocrit and pulmonary capillary diameter. An axisymmetric model with discrete cylindrical erythrocytes is used to represent radial diffusion of oxygen from alveoli through the alveolar-capillary membrane into pulmonary capillaries, through the plasma, and into erythrocytes. Analysis of unsteady diffusion due to the passage of the erythrocytes shows that transport of oxygen through the alveolar-capillary membrane occurs mainly in the regions adjacent to erythrocytes, and that oxygen transport through regions adjacent to plasma gaps can be neglected.

Capillary recruitment in a theoretical model for blood flow regulation in heterogeneous microvessel networks.

In striated muscle, the number of capillaries containing moving red blood cells increases with increasing metabolic demand. This phenomenon, termed capillary recruitment, has long been recognized but its mechanism has been unclear. Here, a theoretical model for metabolic blood flow regulation in a heterogeneous network is used to test the hypothesis that capillary recruitment occurs as a result of active control of arteriolar diameters, combined with unequal partition of hematocrit at diverging microvascular bifurcations.

Theoretical comparison of wall-derived and erythrocyte-derived mechanisms for metabolic flow regulation in heterogeneous microvascular networks.

The objective of this study is to compare the effectiveness of metabolic signals derived from erythrocytes and derived from the vessel wall for regulating blood flow in heterogeneous microvascular networks. A theoretical model is used to simulate blood flow, mass transport, and vascular responses. The model accounts for myogenic, shear-dependent, and metabolic flow regulation.

A prospective trial of elective extubation in brain injured patients meeting extubation criteria for ventilatory support: a feasibility study.

Introduction: To assess the safety and feasibility of recruiting mechanically ventilated patients with brain injury who are solely intubated for airway protection and randomising them into early or delayed extubation, and to obtain estimates to refine sample-size calculations for a larger study. The design is a single-blinded block randomised controlled trial. A single large academic medical centre is the setting.

Acute Physiology and Chronic Health Evaluation (APACHE) III outcome prediction after major vascular surgery.

Objective: To investigate the performance of the Acute Physiology and Chronic Health Evaluation (APACHE) III scoring system in patients admitted to the intensive care unit (ICU) after major vascular surgery.

Design: Retrospective cohort study.

Setting: A tertiary referral center.

Perioperative statin therapy and renal outcomes after major vascular surgery: a propensity-based analysis.

Objective: To evaluate how the presence and timing of statin therapy affect perioperative renal outcomes after major vascular surgery.

Design: Retrospective cohort study.

Setting: Surgical intensive care unit at a single academic medical center.

Bayesian tracking of a nonlinear model of the capnogram.

Capnography, the monitoring of expired carbon dioxide (CO2) has been employed clinically as a non-invasive measure for the adequacy of ventilation of the alveoli of the lung. In combination with air flow measurements, the capnogram can be used to estimate the partial pressure of CO2 in the alveolar sacs. In addition, physiologically relevant parameters, such as the extent of CO2 rebreathing, the airway dead space, and the metabolic CO2 production can be predicted.

Cluster breathing associated with bihemispheric infarction and sparing of the brainstem.

Objective: To report cluster breathing pattern associated with a nonbrainstem lesion.

Design: Case report.

Setting: Neurointensive care unit, St Mary's Hospital, Rochester, Minn.