The effect of breathing hypoxic gas (15% FIO2 ) on physiological and behavioral outcomes during simulated driving in healthy subjects.

Hypoxia is mainly caused by cardiopulmonary disease or high-altitude exposure. We used a driving simulator to investigate whether breathing hypoxic gas influences driving behaviors in healthy subjects. Fifty-two healthy subjects were recruited in this study, approved by the Science and Engineering Ethical Committee. During simulated driving experiments, driving behaviors, breathing frequency, oxygen saturation (SpO2 ), and heart rate variability (HRV) were analyzed. Each subject had four driving sessions; a 10-min practice and three 20-min randomized interventions: normoxic room air (21% FIO2 ) and medical air (21% FIO2 ) and hypoxic air (equal to 15% FIO2 ), analyzed by repeated measures ANOVA. Driving behaviors and HRV frequency domains showed no significant change. Heart rate (HR; p < 0.0001), standard deviation of the RR interval (SDRR; p = 0.03), short-term HRV (SD1; p < 0.0001), breathing rate (p = 0.01), and SpO2 (p < 0.0001) were all significantly different over the three gas interventions. Pairwise comparisons showed HR increased during hypoxic gas exposure compared to both normoxic interventions, while SDRR, SD1, breathing rate, and SpO2 were lower. Breathing hypoxic gas (15% FiO2 , equivalent to 2710 m altitude) may not have a significant impact on driving behavior in healthy subjects. Furthermore, HRV was negatively affected by hypoxic gas exposure while driving suggesting further research to investigate the impact of breathing hypoxic gas on driving performance for patients with autonomic dysfunction.

Underweight and overweight men have greater exercise-induced dyspnoea than normal weight men.

INTRODUCTION: Persons with high or low body mass index (BMI), involved in clinical or mechanistic trials involving exercise testing, might estimate dyspnoea differently from persons with a normal BMI. AIMS: Our objective was to investigate the relationship between BMI and dyspnoea during exercise in normal subjects with varying BMI. MATERIAL AND METHODS: A total of 37 subjects undertook progressive exercise testing. Subjects were divided into three groups: underweight (UW), normal weight (NW), and overweight (OW). Dyspnoea was estimated using the visual analogue scale (VAS). Spirometry, maximum voluntary ventilation (MVV), and respiratory muscle strength (RMS) were measured. RESULTS AND DISCUSSION: The intercept of the VAS/ventilation relationship was significantly higher in NW subjects compared to UW (P = 0.029) and OW subjects (P = 0.040). Relative to the OW group, FVC (P = 0.020), FEV(1) (P = 0.024), MVV (P = 0.019), and RMS (P = 0.003) were significantly decreased in the UW group. The greater levels of dyspnoea in UW subjects could possibly be due to decreased RMS. Healthy persons should aim to achieve an optimum BMI range to have the lowest exercise-induced dyspnoea.

Does Ramadan fasting affect expiratory flow rates in healthy subjects?

OBJECTIVE: To assess whether Ramadan fasting affects the expiratory flow rates in healthy subjects, and to know if these effects correlate to a change in other variables. METHODS: This unmatched case-control longitudinal study includes 46 non-smoking healthy subjects who undertook lung function testing at the Aga Khan University, Pakistan. Expiratory flow rates and body mass were measured in 3 Islamic months, corresponding to November 2001 to January 2002. RESULTS: There was a significant reduction in body mass in Ramadan compared to pre and post Ramadan. No significant changes in expiratory flows were seen during Ramadan as compared to the pre Ramadan period. However, forced expiratory flow rates at 75% of vital capacity (FEF(75)) and between 75% and 85% of vital capacity (FEF(75-85)) showed a significant increase in the post Ramadan period compared to Ramadan. Changes in FEF(75) were negatively correlated to changes in body mass between Ramadan and post Ramadan. CONCLUSION: This study shows that Ramadan fasting will not affect expiratory flow rates in healthy subjects. Post Ramadan values did show an increase in FEF(75) and FEF(75-85), possibly due to changes in body water and fat content. The reductions in body mass were most probably due to lack of nutrition and not dehydration as the fasts were performed in winter. Collection of reference values or early phase clinical trials measuring expiratory flow rates should not be affected by Ramadan fasting.

The effect of Ramadan fasting on spirometry in healthy subjects.

OBJECTIVES: Lung function tests are an important investigative tool in diagnosing respiratory diseases, judging their severity and assessing prognosis. The primary aim of the present study was to assess whether Ramadan fasting affected normal lung function values. METHODOLOGY: Forty-six non-smoking healthy males, with a mean age of 24.2 years (SD 6.4 years) were investigated. Spirometry was performed according to the recommendations of the American Thoracic Society. Days between the 15th and 25th of three Islamic months (pre-Ramadan, Ramadan and post-Ramadan) were selected for spirometry. On all three occasions, FVC, FEV(1), FEV(1)/FVC%, maximum voluntary ventilation (MVV(indirect)), PEF, FEF(25--75%) and body mass were measured. Pre- and post-Ramadan readings were compared with the readings during Ramadan fasting. The results were analysed by repeated measures analysis of variance. RESULTS: No significant change was seen in lung function during Ramadan as compared to the pre-Ramadan period. FVC was decreased significantly in the post-Ramadan period compared to Ramadan and this period was associated with a significant increase in body mass. CONCLUSION: Relative to pre-Ramadan baseline values, there was no change in spirometry during Ramadan fasting in these subjects.

Effect of repetitive exercise testing on breathlessness in humans.

There are conflicting reports on the reproducibility of the visual analogue scale (VAS) and the modified Borg scale for the estimation of breathlessness during exercise. In an attempt to clarify the situation, two groups of healthy subjects undertook a progressive exercise test either daily (Group A) or weekly (Group B) on 10 separate occasions. Breathlessness was estimated every 1 min using the VAS. After 10 occasions, both Group A (P <0.05) and Group B ( P <0.01) showed a significant increase in the mean intercept of the breathlessness/ventilation (VAS/ V (I)) relationship. The increase was not progressive; using change point regression, reproducible values were found to occur after approximately the fifth occasion in both subject groups. As the slope of the VAS/ V (I) relationship was highly reproducible and did not change with repeat testing, it would appear that at least two mechanisms are involved in the generation of the sensation of breathlessness. A decrease in the exercise heart rate over the same time period was significantly correlated with changes in the VAS/ V (I) intercept in both groups (P <0.01 and P <0.005 respectively). The relationship is unlikely to be causal, but may be indicative of a common underlying mechanism. It is suggested that breathlessness scores are likely to decrease as a direct result of repetitive testing over, on average, the first five periods of assessment. On the basis of this study, it may be inferred that a physiological mechanism contributes to the modulation of breathlessness during repetitive exercise testing.

Lung function and surface electromyography of intercostal muscles in cement mill workers.

Impairment of pulmonary function in cement mill workers has been previously reported without considering a variety of parameters that can help evaluate more thoroughly the effect of cement dust on the respiratory system. In addition, an integrated approach has not been considered to assert the involvement of respiratory muscles. Therefore, in the present study spirometry and surface electromyography (SEMG) of intercostal muscles were used for indicating pulmonary impairment. In this study, a group of 50, apparently healthy volunteers, male cement mill workers aged 20-60 years with exposure of 13 years on average, were randomly selected. They were matched with another group of 50 control healthy male subjects in terms of age, height, weight and socioeconomic status. Both groups met the standard exclusion criteria. Spirometry was performed on an electronic spirometer, while SEMG of intercostal muscles was performed by using a chart recorder. The results demonstrated statistically significant reduction in lung function parameters i.e., force vital capacity (FVC) (p < 0.0005); force expiratory volume in first second (FEV1) (p < 0.0005); peak expiratory flow (PEF) (p < 0.005); and maximum voluntary ventilation (MVV) (p < 0.0005) in cement mill workers, when compared with controls. However, the FEV1/FVC ratio was significantly higher (p < 0.025) in cement mill workers. Similarly, the parameters obtained from SEMG of intercostal muscles, i.e. number of peaks (NOP) (p < 0.0005); maximum peak amplitude (MPA) (p < 0.0005); peak to peak amplitude (PPA) (p < 0.0005); duration of response (DOR) (p < 0.0005) and maximum peak duration (MPD) (p < 0.0005), were significantly lower in cement mill workers than in controls. It is concluded that exposure to cement dust not only impairs lung function but also affects costal muscle performance, thus possibly indicating the decreased lung and thoracic compliance.