Acute Exercise with Moderate Hypoxia Reduces Arterial Oxygen Saturation and Cerebral Oxygenation without Affecting Hemodynamics in Physically Active Males.

Hemodynamic changes during exercise in acute hypoxia (AH) have not been completely elucidated. The present study aimed to investigate hemodynamics during an acute bout of mild, dynamic exercise during moderate normobaric AH. Twenty-two physically active, healthy males (average age; range 23-40 years) completed a cardiopulmonary test on a cycle ergometer to determine their maximum workload (Wmax). On separate days, participants performed two randomly assigned exercise tests (three minutes pedaling at 30% of Wmax): (1) during normoxia (NORMO), and (2) during normobaric AH at 13.5% inspired oxygen (HYPO). Hemodynamics were assessed with impedance cardiography, and peripheral arterial oxygen saturation (SatO2) and cerebral oxygenation (Cox) were measured by near-infrared spectroscopy. Hemodynamic responses (heart rate, stroke volume, cardiac output, mean arterial blood pressure, ventricular emptying rate, and ventricular filling rate) were not any different between NORMO and HYPO. However, the HYPO test significantly reduced both SatO2 (96.6 ± 3.3 vs. 83.0 ± 4.5%) and Cox (71.0 ± 6.6 vs. 62.8 ± 7.4 A.U.) when compared to the NORMO test. We conclude that an acute bout of mild exercise during acute moderate normobaric hypoxia does not induce significant changes in hemodynamics, although it can cause significant reductions in SatO2 and Cox.

Systolic and diastolic function during cycling at the respiratory threshold between elderly and young healthy individuals.

The hemodynamic consequences of aging have been extensively investigated during maximal incremental exercise. However, less is known about the effects of aging on hemodynamics during submaximal steady-state exercise. The aim of the present investigation was to compare the hemodynamics of healthy elderly and young subjects during an exercise bout conducted at the gas threshold (GET) intensity. Two groups of healthy, physically active subjects were studied: the elderly group-EG (n = 11; > 60 years old) and the young group-YG (n = 13; < 35 years old). Both groups performed a 5-min rectangular exercise test at the GET intensity. Hemodynamics were measured using echocardiography. The main finding was that stroke volume responses were higher in the YG than the EG (72.5 ± 16.7 vs. 52.4 ± 8.4 ml, respectively). The increased stroke volume capacity in the YG was the consequence of a greater capacity to increase cardiac preload and contractility and, to a lesser extent, to reduce systemic vascular resistance. Importantly, the atrial contribution to ventricular diastolic filling was substantially higher in the YG when compared to the EG.

Systolic and Diastolic Functions After a Brief Acute Bout of Mild Exercise in Normobaric Hypoxia.

Acute hypoxia (AH) is a challenge to the homeostasis of the cardiovascular system, especially during exercise. Research in this area is scarce. We aimed to ascertain whether echocardiographic, Doppler, and tissue Doppler measures were able to detect changes in systolic and diastolic functions during the recovery after mild exercise in AH. Twelve healthy males (age 33.5 ± 4.8 years) completed a cardiopulmonary test on an electromagnetically braked cycle-ergometer to determine their maximum workload (Wmax). On separate days, participants performed randomly assigned two exercise sessions consisting in 3 min pedalling at 30% of Wmax: (1) one test was conducted in normoxia (NORMO) and (2) one in normobaric hypoxia with FiO2 set to 13.5% (HYPO). Hemodynamics were assessed with an echocardiographic system. The main result was that the HYPO session increased parameters related to myocardial contractility such as pre-ejection period and systolic myocardial velocity with respect to the NORMO test. Moreover, the HYPO test enhanced early transmitral filling peak velocities. No effects were detected for left ventricular volumes, as end-diastolic, end-systolic, and stroke volume were similar between the NORMO and the HYPO test. Results of the present investigation support the hypothesis that a brief, mild exercise bout in acute normobaric hypoxia does not impair systolic or diastolic functions. Rather, it appears that stroke volume is well preserved and that systolic and early diastolic functions are enhanced by exercise in hypoxia.

Case study: physical capacity and nutritional status before and after climbing two peaks with different altitude (4897-6812 m).

Vinson and Ama Dablam are summits of different altitudes (4897 and 6812 m respectively). There are no published studies comparing physiological adaptations occurring after climbing both peaks yet. This case study compares changes in certain physiological parameters and body composition of a mountaineer who ascended both peaks. The athlete was a mountaineer who already climbed the 7 Summits©. Baseline body composition, physical capacity, and cerebral oxygenation during effort were measured before and after his departure. Body composition was estimated by electrical bio-impedance, while physical capacity was measured with an incremental exercise test (treadmill) conducted in normoxia and in hypoxia corresponding to about 4000 m. Hypoxia was obtained with a hypoxic gas generator. During tests, cerebral oxygenation was estimated with near infrared spectroscopy. The ascent of mount Vinson and Ama Dablam took 4 and 15 days respectively. The ascent of mount Vinson resulted in a 2.0 kg drop in body mass and a reduction in body fat (from 15.5% to 12.1%). The ascent of Ama Dablam reduced body mass by 3.7 kg, with an increase in body fat from 11.9% to 14.7%. Physical capacity was almost unchanged after both expeditions, although there was a reduction in maximum heart rate in relation to workload after Ama Dablam. Finally, after Ama Dablam there was an increase in cerebral oxygenation during effort both in normoxia and hypoxia. It was concluded that the longer duration and the higher altitude during the Ama Dablam expedition resulted in more evident physiological changes.

A brief bout of exercise in hypoxia reduces ventricular filling rate and stroke volume response during muscle metaboreflex activation.

PURPOSE: The hemodynamic consequences of exercise in hypoxia have not been completely investigated. The present investigation aimed at studying the hemodynamic effects of contemporary normobaric hypoxia and metaboreflex activation. METHODS: Eleven physically active, healthy males (age 32.7 ± 7.2 years) completed a cardiopulmonary test on an electromagnetically braked cycle-ergometer to determine their maximum workload (Wmax). On separate days, participants performed two randomly assigned exercise sessions (3 minutes pedalling at 30% of Wmax): (1) one in normoxia (NORMO), and (2) one in normobaric hypoxia with FiO2 set to 13.5% (HYPO). After each session, the following protocol was randomly assigned: either (1) post-exercise muscle ischemia (PEMI) to study the metaboreflex, or (2) a control exercise recovery session, i.e., without metaboreflex activation. Hemodynamics were assessed with impedance cardiography. RESULTS: The main result was that the HYPO session impaired the ventricular filling rate (measured as stroke volume/diastolic time) response during PEMI versus control condition in comparison to the NORMO test (31.33 ± 68.03 vs. 81.52 ± 49.23 ml·s-1,respectively, p = 0.003). This caused a reduction in the stroke volume response (1.45 ± 9.49 vs. 10.68 ± 8.21 ml, p = 0.020). As a consequence, cardiac output response was impaired during the HYPO test. CONCLUSIONS: The present investigation suggests that a brief exercise bout in hypoxia is capable of impairing cardiac filling rate as well as stroke volume during the metaboreflex. These results are in good accordance with recent findings showing that among hemodynamic modulators, ventricular filling is the most sensible variable to hypoxic stimuli.

High-flow oxygen therapy in tracheostomized patients at high risk of weaning failure.

PURPOSE: High-flow oxygen therapy delivered through nasal cannulae improves oxygenation and decreases work of breathing in critically ill patients. Little is known of the physiological effects of high-flow oxygen therapy applied to the tracheostomy cannula (T-HF). In this study, we compared the effects of T-HF or conventional low-flow oxygen therapy (conventional O2) on neuro-ventilatory drive, work of breathing, respiratory rate (RR) and gas exchange, in a mixed population of tracheostomized patients at high risk of weaning failure. METHODS: This was a single-center, unblinded, cross-over study on fourteen patients. After disconnection from the ventilator, each patient received two 1-h periods of T-HF (T-HF1 and T-HF2) alternated with 1 h of conventional O2. The inspiratory oxygen fraction was titrated to achieve an arterial O2 saturation target of 94-98% (88-92% in COPD patients). We recorded neuro-ventilatory drive (electrical diaphragmatic activity, EAdi), work of breathing (inspiratory muscular pressure-time product per breath and per minute, PTPmusc/b and PTPmusc/min, respectively) respiratory rate and arterial blood gases. RESULTS: The EAdipeak remained unchanged (mean ± SD) in the T-HF1, conventional O2 and T-HF2 study periods (8.8 ± 4.3 µV vs 8.9 ± 4.8 µV vs 9.0 ± 4.1 µV, respectively, p = 0.99). Similarly, PTPmusc/b and PTPmusc/min, RR and gas exchange remained unchanged. CONCLUSIONS: In tracheostomized patients at high risk of weaning failure from mechanical ventilation, T-HF did not improve neuro-ventilatory drive, work of breathing, respiratory rate and gas exchange compared with conventional O2 after disconnection from the ventilator. The present findings might suggest that physiological effects of high-flow therapy through tracheostomy substantially differ from nasal high flow.

Perfil dos pacientes internados por bronquiolite viral aguda em uma unidade de terapia intensiva em hospital infantil do sul do Brasil / Profile of patients admitted in an intensive care unit for acute viral bronchiolitis in a South Brazilian children’s hospital

Introdução: Bronquiolite Viral Aguda (BVA) é uma infecção respiratória que compromete vias aéreas de pequeno calibre e pode necessitar de suporte ventilatório e, nos casos mais complicados, suporte hemodinâmico. O principal agente etiológico é o Vírus Sincicial Respiratório (VSR). O objetivo deste trabalho é descrever o perfil epidemiológico de crianças com este diagnóstico em uma unidade de terapia intensiva pediátrica. Métodos: Estudo descritivo aplicado em pacientes com diagnóstico de BVA internados na Unidade de Terapia Intensiva do Hospital da Criança Conceição. Resultados: No período do estudo, ocorreram 193 casos, correspondendo a 15,8% do total de internações, com tempo aproximado de internação de 7,5 dias, acometendo crianças com uma média de idade de 3,4 meses. O VSR foi o agente etiológico mais frequente. Suporte ventilatório foi necessário em 48,2% dos pacientes e hemodinâmicos, em 28,3%. A taxa de mortalidade foi de 1,5%. Conclusão: Em uma Unidade de Terapia Intensiva Pediátrica de Porto Alegre foi estudado 193 casos de BVA, correspondendo a 15,8% do total de internações por este diagnóstico, com taxa de mortalidade de 1,5%. O principal agente etiológico causador foi o VSR e foi identificada maior prevalência de ventilação mecânica nos pacientes de menor peso e menor idade.

Introduction: Acute Viral Bronchiolitis (AVB) is a respiratory infection that affects the small-caliber airways and may require ventilatory support and, in more complicated cases, hemodynamic support. The main etiologic agent is Respiratory Syncytial Virus (RSV). The aim of this work is to describe the epidemiological profile of children with this diagnosis in a pediatric intensive care unit. Methods: A descriptive study of patients with AVB admitted to the Intensive Care Unit at Hospital da Criança Conceição. Results: In the study period there occurred 193 cases, corresponding to 15.8% of total admissions, with an approximate length of stay of 7.5 days, involving children with a mean age of 3.4 months. Respiratory syncytial virus was the most common etiologic agent. Ventilatory support was necessary in 48.2% of patients and hemodynamic support in 28.3%. The mortality rate was 1.5%. Conclusion: In a pediatric intensive care unit in Porto Alegre, 193 cases of BVA were studied, corresponding to 15.8% of total admissions for this diagnosis with a mortality rate of 1.5%. The main etiologic agent was RSV and a higher prevalence of mechanical ventilation was identified for lower weight and younger patients.