Influence of exercise modality on agreement between gas exchange and heart rate variability thresholds

The main purpose of this study was to investigate the level of agreement between the gas exchange threshold (GET) and heart rate variability threshold (HRVT) during maximal cardiopulmonary exercise testing (CPET) using three different exercise modalities. A further aim was to establish whether there was a 1:1 relationship between the percentage heart rate reserve (%HRR) and percentage oxygen uptake reserve (%V˙O2R) at intensities corresponding to GET and HRVT. Sixteen apparently healthy men 17 to 28 years of age performed three maximal CPETs (cycling, walking, and running). Mean heart rate and V˙O2 at GET and HRVT were 16 bpm (P<0.001) and 5.2 mL·kg-1·min-1 (P=0.001) higher in running than cycling, but no significant differences were observed between running and walking, or cycling and walking (P>0.05). There was a strong relationship between GET and HRVT, with R2 ranging from 0.69 to 0.90. A 1:1 relationship between %HRR and %V˙O2R was not observed at GET and HRVT. The %HRR was higher during cycling (GET mean difference=7%; HRVT mean difference=11%; both P<0.001), walking (GET mean difference=13%; HRVT mean difference=13%; both P<0.001), or running (GET mean difference=11%; HRVT mean difference=10%; both P<0.001). Therefore, using HRVT to prescribe aerobic exercise intensity appears to be valid. However, to assume a 1:1 relationship between %HRR and %V˙O2R at HRVT would probably result in overestimation of the energy expenditure during the bout of exercise.

Analysis of heart rate control to assess thermal sensitivity responses in Brazilian toads

In anurans, changes in ambient temperature influence body temperature and, therefore, energy consumption. These changes ultimately affect energy supply and, consequently, heart rate (HR). Typically, anurans living in different thermal environments have different thermal sensitivities, and these cannot be distinguished by changes in HR. We hypothesized that Rhinella jimi (a toad from a xeric environment that lives in a wide range of temperatures) would have a lower thermal sensitivity regarding cardiac control than R. icterica (originally from a tropical forest environment with a more restricted range of ambient temperatures). Thermal sensitivity was assessed by comparing animals housed at 15° and 25°C. Cardiac control was estimated by heart rate variability (HRV) and heart rate complexity (HRC). Differences in HRV between the two temperatures were not significant (P=0.214 for R. icterica and P=0.328 for R. jimi), whereas HRC differences were. All specimens but one R. jimi had a lower HRC at 15°C (all P<0.01). These results indicate that R. jimi has a lower thermal sensitivity and that cardiac control is not completely dependent on the thermal environment because HRC was not consistently different between temperatures in all R. jimi specimens. This result indicates a lack of evolutive trade-offs among temperatures given that heart rate control at 25°C is potentially not a constraint to heart rate control at 15°C.

Correlation between heart rate variability and pulmonary function adjusted by confounding factors in healthy adults

The autonomic nervous system maintains homeostasis, which is the state of balance in the body. That balance can be determined simply and noninvasively by evaluating heart rate variability (HRV). However, independently of autonomic control of the heart, HRV can be influenced by other factors, such as respiratory parameters. Little is known about the relationship between HRV and spirometric indices. In this study, our objective was to determine whether HRV correlates with spirometric indices in adults without cardiopulmonary disease, considering the main confounders (e.g., smoking and physical inactivity). In a sample of 119 asymptomatic adults (age 20-80 years), we evaluated forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1). We evaluated resting HRV indices within a 5-min window in the middle of a 10-min recording period, thereafter analyzing time and frequency domains. To evaluate daily physical activity, we instructed participants to use a triaxial accelerometer for 7 days. Physical inactivity was defined as <150 min/week of moderate to intense physical activity. We found that FVC and FEV1, respectively, correlated significantly with the following aspects of the RR interval: standard deviation of the RR intervals (r =0.31 and 0.35), low-frequency component (r =0.38 and 0.40), and Poincaré plot SD2 (r =0.34 and 0.36). Multivariate regression analysis, adjusted for age, sex, smoking, physical inactivity, and cardiovascular risk, identified the SD2 and dyslipidemia as independent predictors of FVC and FEV1 (R2=0.125 and 0.180, respectively, for both). We conclude that pulmonary function is influenced by autonomic control of cardiovascular function, independently of the main confounders.

Influence of temperature on the respiration rate of minimally processed organic carrots (Daucus Carota L. cv. Brasília)

The objective of this work was to study the influence of temperature on the respiration rate of minimally processed organic carrots (Daucus Carota L. cv. Brasília) with and without the application of a gelatin film. The samples were packed in flexible bags and stored at 1, 5 and 10 °C. During the five days of storage, the CO2 and O2 concentrations in the headspace of the package were monitored by gas chromatography, and the mathematical model based on enzymatic kinetics was used to estimate the respiration rate of minimally processed organic carrots. The effect of temperature on the respiration rate was evaluated by the Arrhenius equation. The results showed that the O2 concentration decreased during the storage period and the CO2 concentration increased. The lowest O2 concentrations of 2.59 and 2.66% were found for the samples stored at 10 °C with and without the film, respectively. For the CO2 concentration, the highest concentrations of 16.25 and 16.32% were again found for the temperature of 10 °C with and without the application of the film, respectively. At the temperature of 1 °C, the maximum respiratory rates for the samples without and with the film were 10.82 and 10.44 mL CO2.kg-1/hour, respectively, after 72 hours of storage. The greatest respiratory rate was obtained at 10 °C, the maximum peak being reached after 50 hours. Activation energy values were of 50.59 kJ.mol-1, for the samples with the film, and 51.88 kJ.mol-1 for the samples without the film.

Estimate of respiration rate and physicochemical changes of fresh-cut apples stored under different temperatures

In this study, the influence of storage temperature and passive modified packaging (PMP) on the respiration rate and physicochemical properties of fresh-cut Gala apples (Malus domestica B.) was investigated. The samples were packed in flexible multilayer bags and stored at 2 °C, 5 °C, and 7 °C for eleven days. Respiration rate as a function of CO2 and O2 concentrations was determined using gas chromatography. The inhibition parameters were estimated using a mathematical model based on Michaelis-Menten equation. The following physicochemical properties were evaluated: total soluble solids, pH, titratable acidity, and reducing sugars. At 2 °C, the maximum respiration rate was observed after 150 hours. At 5 °C and 7 °C the maximum respiration rates were observed after 100 and 50 hours of storage, respectively. The inhibition model results obtained showed a clear effect of CO2 on O2 consumption. The soluble solids decreased, although not significantly, during storage at the three temperatures studied. Reducing sugars and titratable acidity decreased during storage and the pH increased. These results indicate that the respiration rate influenced the physicochemical properties.

Management of freezing rate and trehalose concentration to improve frozen dough properties and bread quality

Abstract Bread is one of the most consumed foods in the world, and alternatives have been sought to extend its shell life, and freezing is one of the most popular methods. The purpose of this study was to evaluate the effect of freezing rate and trehalose concentration on the fermentative and viscoelastic properties of dough and bread quality. Dough was prepared and trehalose was added at three concentrations (0, 400, 800 ppm); dough was pre fermented and frozen at two freezing rates then stored for 42 days. Frozen dough samples were thawed every two weeks. CO2 production and elastic and viscous modulus were determined. In addition, bread was elaborated and specific volume and firmness were evaluated. High trehalose concentrations (400 and 800 ppm) produced dough with the best viscoelastic and fermentative properties. Greater bread volume and less firmness were observed when a slow freezing rate (-.14 °C/min) was employed.

Inflation bias: an appraisal

This short paper offers a brief appraisal of the conventional inflation bias and Cukierman's new inflation bias. It may also be seen that a lack of equilibrium in the balance of payments represents another reason for the emergence of the inflationary bias in an economy.

Uma contribuição ao debate em torno da eficácia da política monetária e algumas implicações para o caso do Brasil

A contribution to the debate on the efficacy of monetary policy and some implications in the case of Brazil. The main opposition between Keynesian and Classic monetary theories is defined by the former's proposition of money non-neutrality in the long period. According to Keynes, it is not possible to describe a monetary economy's long period position without first specifying the monetary policy it is adopting. The policy is described by the choice of the short-term interest rate which exerts an important determining influence on the long term rate and, therefore, on real investment decisions. Based on this reasoning, inflation target monetary policy regimes are criticized, in particular the one adopted in post-1999 balance of payments crisis Brazil because of its deleterious impact on investment and growth.

Governos autoritários e câmbio nos países latino-americanos

Authoritarian governments and exchange rate policy in Latin American countries. Our aim on this paper is to identify the exchange rate policies used by Authoritarian governments in Latin America during the 170’s and 180’s. The literature shows that the focus of the exchange rate policy was on inflation control, which was not consistent with the evidence. We show on this paper that these governments aimed at a undervalued currency because of the behavior of the external balance of the countries.

Efeitos da independência do banco central e da taxa de rotatividade sobre a inflação brasileira

Nowadays, the belief is strong in the Brazilian federal government that operational central bank independence is a basic condition to assure price stability. The literature concerning this subject highlights that a high degree of independence and a low turnover of central bank governor are associated with low inflation. This paper analyzes the relation between central bank independence and inflation in Brazil during 1980-2002. The findings denote that there is no effect on inflation due to an increase in degree of independence and a fall in turnover rate.

National exchange rate policies and international debt crises: how Brazil did not follow Argentina into a default in 2001-2002

This paper examines how exchange rate policies and IMF Stand-By Arrangements affect debt crises using econometrics and a comparison between Argentina and Brazil. It refines an existing diagram outlining crisis development to propose crisis prevention strategies. Flexible exchange rate policies reduce a country's probability of default by over 4%, but Stand-By Arrangements increase it by an inconsequential percentage. Unlike Argentina, Brazil avoided a default via a freely-floating exchange rate system, fiscal deficit reduction, and a cooperative and coordinated relationship with the IMF. The results provide policymakers from developing countries with lessons to manage their countries' default risks more effectively.

Metas para inflação e taxa de juros no Brasil: uma análise do efeito dos preços livres e administrados

After surpassed more than half a decade since the adoption of inflation targeting in Brazil, it can be seen that maintaining a high interest rate is inherent to the strategy for the conduction of the monetary policy. The objective of this paper is to show that the present policy for defining the basic interest rate of the economy, based on the response to inflation considering both market and administered prices, is onerous for the Brazilian society. Based on findings from empirical evidence in the period 1999-2004, the adoption of a core inflation, a change in the time horizon for definition of targets, and, in common agreement between Banco Central do Brasil and National Treasury, a definition of these inflation targets, as a framework to increase efficiency of the monetary regime, creates possibilities for proposing a reduction on the Selic rate.

Metas inflacionárias: a análise convencional e um modelo alternativo

Inflation targeting: the conventional analysis and an alternative model. This article has two aims: the first one is to present a formal model of the monetary policy identified generally as "inflation targeting policy", an instrument of intervention of the central bank, through the short run nominal interest rate. The second aim is to discuss and criticize the theoretical assumptions of the model specially the concepts of "natural rate of interest" and of potential product presented by the "augmented Philips curve"; and to present a more realistic control of inflation targeting which does not assume the hypotheses above, and in which inflation targeting is based on the control of real rate of interest.

Matemática agradável

This paper suggests a reconsideration of the principle that public deficits should be financed by public debt. Two main reasons are offered. First, it is admitted that public debt is an economic variable whose time behaviour is better described by a first difference equation instead of an accounting identity. The convergence condition thus obtained requires either a nominal negative interest rate or that government bonds are used to raise tax income, hypotheses not theoretically granted. As a consequence, if primary surplus is not sufficient to match interests' payment, it will be observed an explosive trend in the public debt, the due interests and the money issuing. Therefore, it lacks support to the idea that public debt prevents inflation. Second, it is shown that financing public deficit through money issuing leads to a stable equilibrium money stock. The general conclusion is that, in order to simultaneously promote economic growth and inflation control, money issuing is preferable to public debt.

Juros, câmbio e o sistema de metas de inflação no Brasil

Interest rate, exchange rate and the system of inflation target in Brazil. In the consensus view of the Brazilian system of inflation targeting, the core of inflation is due to demand shocks; the rate of interest is set to control demand; and some variation in the exchange rate happens as "collateral damage". In this note we argue that in reality core inflation comes from cost push; the interest rate affects the exchange rate; changes in the exchange rate affect costs and prices; it is the effect of interest rates on demand that is the "collateral damage" and that the long run anchor of the system is low average real wage rigidity.