Progressively heterogeneous mismatch of regional oxygen delivery to consumption during graded coronary stenosis in pig left ventricle

The coronary capillary bed and its role in blood flow and oxygen delivery: A review

The assumption that the coronary capillary blood flow is exclusively regulated by precapillary vessels is not supported by recent data. Rather, the complex coronary capillary bed has unique structural and geometric characteristics that invalidate many assumptions regarding red blood cell (RBC) transport, for example, data based on a single capillary or that increases in flow are the result of capillary recruitment. It is now recognized that all coronary capillaries are open and that their variations in flow are due to structural differences, local O₂ demand and delivery, and variations in hematocrit. Recent data reveal that local mechanisms within the capillary bed regulate flow via signaling mechanisms involving RBC signaling and endothelial-associated pericytes that contract and relax in response to humoral and neural signaling. The discovery that pericytes respond to vasoactive signals (e.g., nitric oxide, phenylephrine, and adenosine) underscores the role of these cells in regulating capillary diameter and consequently RBC flux and oxygen delivery. RBCs also affect blood flow by sensing <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>P</mml:mi> <mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:msub> </mml:math> and releasing nitric oxide to facilitate relaxation of pericytes and a consequential capillary dilation. New data indicate that these signaling mechanisms allow control of blood flow in specific coronary capillaries according to their oxygen requirements. In conclusion, mechanisms in the coronary capillary bed facilitate RBC density and transit time, hematocrit, blood flow and O₂ delivery, factors that decrease capillary heterogeneity. These findings have important clinical implications for myocardial ischemia and infarction, as well as other vascular diseases.

Effect of Oxygen Therapy on Cardiovascular Outcomes in Relation to Baseline Oxygen Saturation

OBJECTIVES

The aim of this study was to determine the effect of supplemental oxygen in patients with myocardial infarction (MI) on the composite of all-cause death, rehospitalization with MI, or heart failure related to baseline oxygen saturation. A secondary objective was to investigate outcomes in patients developing hypoxemia.

BACKGROUND

In the DETO2X-AMI (Determination of the Role of Oxygen in Suspected Acute Myocardial Infarction) trial, 6,629 normoxemic patients with suspected MI were randomized to oxygen at 6 l/min for 6 to 12 h or ambient air.

METHODS

The study population of 5,010 patients with confirmed MI was divided by baseline oxygen saturation into a low-normal (90% to 94%) and a high-normal (95% to 100%) cohort. Outcomes are reported within 1 year. To increase power, all follow-up time (between 1 and 4 years) was included post hoc, and interaction analyses were performed with oxygen saturation as a continuous covariate.

RESULTS

The composite endpoint of all-cause death, rehospitalization with MI, or heart failure occurred significantly more often in patients in the low-normal cohort (17.3%) compared with those in the high-normal cohort (9.5%) (p < 0.001), and most often in patients developing hypoxemia (23.6%). Oxygen therapy compared with ambient air was not associated with improved outcomes regardless of baseline oxygen saturation (interaction p values: composite endpoint, p = 0.79; all-cause death, p = 0.33; rehospitalization with MI, p = 0.86; hospitalization for heart failure, p = 0.35).

CONCLUSIONS

Irrespective of oxygen saturation at baseline, we found no clinically relevant beneficial effect of routine oxygen therapy in normoxemic patients with MI regarding cardiovascular outcomes. Low-normal baseline oxygen saturation or development of hypoxemia was identified as an independent marker of poor prognosis. (An Efficacy and Outcome Study of Supplemental Oxygen Treatment in Patients With Suspected Myocardial Infarction; NCT01787110).

Understanding the physiology of the ageing individual: computational modelling of changes in metabolism and endurance

Ageing and lifespan are strongly affected by metabolism. The maximal possible uptake of oxygen is not only a good predictor of performance in endurance sports, but also of life expectancy. Figuratively speaking, healthy ageing is a competitive sport. Although the root cause of ageing is damage to macromolecules, it is the balance with repair processes that is decisive. Reduced or intermittent nutrition, hormones and intracellular signalling pathways that regulate metabolism have strong effects on ageing. Homeostatic regulatory processes tend to keep the environment of the cells within relatively narrow bounds. On the other hand, the body is constantly adapting to physical activity and food consumption. Spontaneous fluctuations in heart rate and other processes indicate youth and health. A (homeo)dynamic aspect of homeostasis deteriorates with age. We are now in a position to develop computational models of human metabolism and the dynamics of heart rhythm and oxygen transport that will advance our understanding of ageing. Computational modelling of the connections between dietary restriction, metabolism and protein turnover may increase insight into homeostasis of the proteins in our body. In this way, the computational reconstruction of human physiological processes, the Physiome, can help prevent frailty and age-related disease.