High-sugar feeding and increasing cholesterol levels in infants.

Hypercholesterolaemia is an important risk factor for cardiovascular disease. Both total and LDL cholesterol levels are three-fold higher at the end of the first year of life and about four-fold higher in adulthood compared with the neonatal period. In the USA, only 25% of infants are exclusively breastfed and simple carbohydrate-rich formulas are preferentially consumed. Spikes in fasting glucose and insulin have been reported in formula-fed infants and are associated with higher levels of proprotein convertase subtilisin/kexin type 9, suggesting a potential link between high simple sugar intake and consequent increase in LDL cholesterol in early childhood.

Personalized exercise dose prescription.

Physical activity (PA) is associated with increased longevity and decreased risk of cardiovascular disease, however, the majority of the general population is still sedentary. In order to maximize the health benefits of PA, health care practitioners should be familiarized with the appropriate dose of exercise for each healthy individual, depending on their habitual PA and relative fitness. The aim of this review is to quantitatively describe the lowest and the highest level of exercise that has health benefits, and what should hypothetically be considered 'the sweet spot'. Analysis of the current literature allows us to develop personalized 'exercise prescription' for healthy individuals.

Dynamic diaphragmatic MRI during apnea struggle phase in breath-hold divers.

The purpose of the study was to provide insight in diaphragmatic involuntary breathing movements (IBM) during struggle phase of apnea at total lung capacity (TLC) and functional residual capacity (FRC) using magnetic resonance imaging along with measurements of hemodynamics and arterial oxygenation. The study was performed in eight elite breath-hold divers. There was a similar increase in diaphragmatic cranio-caudal excursions towards the end of TLC and FRC apnea. The greatest diaphragmatic excursion in both apneas and during tidal breathing was in the middle and posterior part of the diaphragm. Diaphragm thickness in elite BHD was within the reference range of normal values suggesting no diaphragmatic hypertrophy in this population. We found that the range of diaphragmatic excursions increases toward the end of apneas. Additionally, our data suggest that the diaphragm participates in IBM occurrence and that various segments of the diaphragm behave nonhomogenously both in tidal breathing and IBMs.

Firing patterns of muscle sympathetic neurons during apnea in chronic heart failure patients and healthy controls.

In the present study we investigated the influence of end-expiratory breathing cessation on firing activity of muscle sympathetic fibers in 6 stable chronic heart failure (CHF) patients and in 6 healthy age and gender matched controls. Integrated multi-unit bursts, as well as action potentials (APs), were identified from multi-unit muscle sympathetic nerve activity (MSNA) recordings during baseline and during functional residual capacity (FRC) apnea. Compared with controls, CHF patients had higher burst frequency and AP firing frequency (P<0.05) at baseline. FRC apnea caused an increase in the number of APs per multi-unit sympathetic burst, in the AP frequency (P<0.05) and in the number of active clusters per multi-unit sympathetic burst in both groups (controls P<0.06, CHF group P=0.1). The data suggest a comparable pattern of sympathetic activation associated with breath hold in healthy middle-aged individuals and in stable CHF patients. Thus, recruitment patterns for this stress are not affected by CHF despite their elevated sympathetic state.

The Effects of Involuntary Respiratory Contractions on Cerebral Blood Flow during Maximal Apnoea in Trained Divers.

The effects of involuntary respiratory contractions on the cerebral blood flow response to maximal apnoea is presently unclear. We hypothesised that while respiratory contractions may augment left ventricular stroke volume, cardiac output and ultimately cerebral blood flow during the struggle phase, these contractions would simultaneously cause marked 'respiratory' variability in blood flow to the brain. Respiratory, cardiovascular and cerebrovascular parameters were measured in ten trained, male apnoea divers during maximal 'dry' breath holding. Intrathoracic pressure was estimated via oesophageal pressure. Left ventricular stroke volume, cardiac output and mean arterial pressure were monitored using finger photoplethysmography, and cerebral blood flow velocity was obtained using transcranial ultrasound. The increasingly negative inspiratory intrathoracic pressure swings of the struggle phase significantly influenced the rise in left ventricular stroke volume (R (2) = 0.63, P<0.05), thereby contributing to the increase in cerebral blood flow velocity throughout this phase of apnoea. However, these contractions also caused marked respiratory variability in left ventricular stroke volume, cardiac output, mean arterial pressure and cerebral blood flow velocity during the struggle phase (R (2) = 0.99, P<0.05). Interestingly, the magnitude of respiratory variability in cerebral blood flow velocity was inversely correlated with struggle phase duration (R (2) = 0.71, P<0.05). This study confirms the hypothesis that, on the one hand, involuntary respiratory contractions facilitate cerebral haemodynamics during the struggle phase while, on the other, these contractions produce marked respiratory variability in blood flow to the brain. In addition, our findings indicate that such variability in cerebral blood flow negatively impacts on struggle phase duration, and thus impairs breath holding performance.

Firing patterns of muscle sympathetic neurons during short-term use of continuous positive airway pressure in healthy subjects and in chronic heart failure patients.

The current study tested the hypothesis that modification in central hemodynamics during short-term continuous positive airway pressure (CPAP) application was accompanied by altered firing patterns of sympathetic nerve activity in CHF patients and healthy subjects. Muscle sympathetic nerve activity (MSNA), hemodynamic and ventilatory parameters were obtained from 8 healthy middle aged subjects and 7 CHF patients. Action potentials (APs) were extracted from MSNA neurograms, quantified as AP frequency and classified into different sized clusters. While on CPAP at 10cm H2O, multi-unit MSNA, AP frequency and mean burst area/min increased in healthy middle aged subjects (p<0.05) whereas CPAP had no effect on these variables in CHF patients. In conclusion, the impact of CPAP on central hemodynamics in healthy individuals elicited a moderate activation of sympathetic neurons through increased AP firing frequency, whereas in CHF patients both hemodynamics and MSNA remained unaltered.

Respiratory muscle pressure development during breath holding in apnea divers.

INTRODUCTION: We sought to characterize the patterns of active pressure development of the inspiratory and expiratory rib cage muscles (P(rcm,i) and P(rcm,e)), the diaphragm (P(di,i)), and the expiratory abdominal muscles (P(abm,e)) during maximal "dry" breath holding in trained apnea divers (n = 8). METHODS: Respiratory contractions were assessed via esophageal and gastric manometry. It was expected that inspiratory/expiratory pressures would progressively increase in both magnitude and frequency during the struggle phase, and that inspiratory rib cage muscle pressures would rise at a rate exceeding that of the diaphragm by the break point. RESULTS: P(rcm,i), P(di,i), P(rcm,e), and P(abm,e) significantly increased from the beginning until the end of the struggle phase (P < 0.05). Moreover, P(di,i)/P(rcm,i) and P(abm,e)/P(rcm,e) ratios had declined by the break point (P < 0.05), indicating that rib cage muscles increased their contribution to net inspiratory/expiratory pressure development by the end of the breath hold, relative to that contributed by the diaphragm and abdominal muscles. The pressure-time indices of the diaphragm and inspiratory rib cage muscles continuously increased over the struggle phase (P < 0.05). CONCLUSIONS: The "extradiaphragmatic" shift in inspiratory muscle recruitment, commensurate with increasing P(rcm,e) and P(abm,e), may reflect an extreme loading response to breathing against a heavy elastance (i.e., closed glottis). In addition, the relative intensity of diaphragmatic and inspiratory rib cage muscle contractions approaches potentially "fatiguing" levels by the break point of maximal breath holding.